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General-Purpose Inverter Technologies

Sushi-serving rotary conveyor system

Mini-conveyor system

It doesn’t matter how much fish Iload on the conveyor, it alwayscarries them smoothly.

Rotary press for printing machine

Inverter user’s success storiesNowadays, Fuji Electric Inverters are indispensable to your systems.

FRENIC5000G9Sseries

FVR-C9Sseries

FRENIC5000P9Sseries

FVR-E9Sseries

Fuji Electric can provide you with the products best suited to meet your requirements.The torque-vector-control type FRENIC5000G9S series isideal for use in washing machines for commercial use andautomated parking garages.The FRENIC5000P9S series is best suited for variable-speedapplications such as fans, and pumps.The FVR-E9S series featuring high environmental protectionperformance is suitable for wood-working machines etc.

For mini-conveyors and ventilation fans, use the FVR-C9Sseries which offers you simplified operation and low cost.Fuji Electric can supply you with inverters conforming with theEN Standards, UL Standards and/or the cUL Standards.

Fuji Electric Inverters

Our powerful inverters enable vehicles to be lifted very smoothly.

Our compact and easy-to-operateinverters are also at work here.

The inverter assures stable, high-speed operation of the machine.

Commercial-use washing machines

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Research laboratory equipment

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Automated parking garage

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CONTENTS

Present Status and Future Prospects 70for General-Purpose Inverter Technologies

Novel Technologies for Power Conversion Circuits 74

Noise Reduction Methods for Power Electronic Equipment 78

Recent Variable-Speed Drive Technology 82

Downsizing Technology for General-Purpose Inverters 85

Large-Capacity Variable-Speed AC Drive 90

Cover Photo:Variable-speed drive systems

such as general-purpose invertersare used in mechanical equipmentin various industrial fields and con-tribute to automation, reduction inlabor, and advance in performancefor the equipment.

Since having marketed general-purpose inverters first in the indus-try in 1977, Fuji Electric has takenthe lead in promoting their totaldigitization, downsizing, advancesin performance and functions.

The cover photo, which picturesa motor for machine tool spindledrive and general-purpose invertersconforming to the internationalstandard, is aimed at imaging quickacce lerat ion /dece lerat ion andsmooth speed control performances.

Head Office : No.12-1, 1-chome, Yurakucho, Chiyoda-ku, Tokyo, Japan

General-Purpose Inverter Technologies

FRENIC5000MS5 for Machine Tool Spindle Drives 95

Vol. 44 No. 3 FUJI ELECTRIC REVIEW70

Takao YanaseShinobu Kawabata

Present Status and Future Prospectsfor General-Purpose Inverter Technologies

1. Introduction

Variable-speed drive systems, typically represent-ed by general-purpose inverters and servo systems, areused in many industrial fields. They contribute to theenergy savings, automation, labor savings, and high-efficiency operation of machines and equipment. Bothinverters and servo systems have improved economi-cally since the advent of power transistors. They havemade rapid progress with the spread of energy-savingmeasures due to the oil crisis.

This paper outlines the basic technologies thathave driven these developments, modern technologiesfor future development, and Fuji Electric’s perspective.Our abundant product line is also introduced.

2. Modern Technologies of General-PurposeInverter

2.1 Power conversion circuit technologiesVariable-speed drive systems typically represented

by general-purpose standard inverters have realizedsmall size and high efficiency through the use of low-loss power devices such as insulated-gate bipolartransistors (IGBTs), a high-efficiency cooling technolo-gy, and a large-scale integration technology usingmetal-based printed circuit boards. These develop-ments will be pursued and should prove successful inthe future.

From the viewpoint of main circuit systems, mostdrive systems are composed of a diode rectifier circuitand a PWM inverter circuit, as shown in Fig. 1. Thiscombination has been used since its inception andseems to be well established technically and economi-cally. However, it requires a dynamic braking circuitto dissipate the regenerated energy during brakingand harmonic current generated in the input powersource. One general method of reducing harmoniccurrent is to connect a DC or AC reactor, as shown inFig. 1.

To efficiently return regenerated energy to thepower source during braking and to greatly reduceinput harmonic current, the PWM converters shown inFig. 2 have come into use. However, this method

requires an AC reactor on the power supply side. Inaddition, according to the condition of the powersource, an LC filter must be added. Therefore, thismethod requires further amplification and cost reduc-tion.

To meet these requirements, Fuji Electric studieda direct AC-AC converter system as a new main circuitsystem. We proposed a system to greatly reduce inputharmonic current without an additional reactor byregarding the motor winding and converter circuit as aunified system. This currently being studied for futureproduction. (For further details, please see “NovelTechnologies for Power Conversion Circuits” in thisspecial issue.)

Fig.2 Inverter circuit with PWM converter

Fig.1 Typical main circuit of general-purpose inverter

AC reactor

Diode rectifier circuit

DC reactor

Dynamic braking circuit

PWM inverter circuit

Motor

Powersupply

Sm

ooth

ing

capa

cito

r

M

AC reactor

PWM converter circuit

Inverter circuit

Motor

Powersupply

Sm

ooth

ing

capa

cito

r

M

Present Status and Future Prospects for General-Purpose Inverter Technologies 71

2.2 Noise reduction methodsElectronic equipment such as inverters and servo

systems performs high-efficiency power conversion byhigh-speed switching with IGBTs. But this high-speedswitching causes high frequency noise.

In other countries and regions around the world,this noise has come under regulation based on therecommendation of the IEC (International Electrotech-nical Commission).

Figure 3 shows an example of noise terminalvoltage measured in an inverter and the limit values.The curve with a note of CISPR class B ③ shownbetween the data without the noise filter ① and withthe noise filter ② is the limit value (recommendedvalue) for connections to power sources in residential

and commercial districts. The present method ofsatisfying these limits in inverters and servo systemsis to connect a filter in the power supply circuit anduses shielded wires on the main circuit to the motor.

Fuji Electric is actively researching the noisegeneration mechanism and transmission process,IGBT soft switching methods to suppress noise, andnoise reduction methods for DC-DC converters for thecontrol power supply. (Please refer to “Noise Reduc-tion Methods for Power Electronics Equipment” in thisspecial issue.)

2.3 Control technologiesDue to progress in microprocessor and gate array

LSI technologies and technical development in motorcontrol techniques, the control technologies of invertersand servo systems have been advancing every year.

In addition to technologies that improve motortorque controllability such as sensorless vector controland torque vector control, technical developments thatimprove application performance such as the tuning ofmotor control parameters and adaptability controlincluding matching the mechanical system are inprogress. In the future technologies for furtherimproving handling ease and for high-efficiency vectorcontrol using a general-purpose standard inverter anda general-purpose motor will be developed.

To obtain a smooth rotation at a low speed with V/f(voltage/frequency) controlled inverters, many controlsystems that reduce output voltage distortion andoffset have been devised. For example, Fuji Electricdeveloped a special LSI-based digital AVR technologywhich realized smooth rotation characteristics.

In addition, a variable-speed drive with general-purpose inverters has up to now been mainly intendedfor induction motors. But to improve operationefficiency, the latest trend is toward driving perma-nent magnet type synchronous motors (PM motors).However, as demonstrated by conventional servo sys-tems, magnetic pole position or speed sensors aregenerally used for the PM motor drive. As introducedin the article “Recent Variable-Speed Drive Technolo-gy” in this issue, Fuji Electric is researching PM motordrive systems that do not require magnetic poleposition or speed sensors.

2.4 Harmonic current reduction methods for large-capacity invertersHarmonic current reduction methods for convert-

ers are as described in 2.1, above. However, atransformer is supplied for use by the large capacityconverter. The 12-pulse connection system shown inFig. 4 is the most economical harmonic current reduc-tion method.

Fuji Electric produces a large-capacity inverterseries that can meet 12-pulse connection by the sixinput terminals of its input rectifier that is divided intotwo parts. (For details, see “Large-Capacity Variable-

Fig.4 A 12-pulse connection for a large-capacity inverter

Fig.3 Example of noise terminal voltage (measured and limitvalues)

0.120

40

60

80

100

1 10 100

① Measured values (without filter)② Measured values (with filter) ③ Limit values (CISPR class B)

Frequency (MHz)

③

②

①

Noi

se t

erm

inal

vol

tage

(dB

µV)

Transformer

Motor

Inverter

M3　


Speed AC Drive” in this issue.)

3. Fuji Electric’s Variable-Speed Drive SystemSeries

Fuji Electric’s abundant product series of inverterfor simple variable-speed drive to servo systems forhigh-precision, quick response control allows the mosteconomical selection for any variable-speed drive use.

An outline of the product series is described below.Fuji Electric’s typical inverter series are shown in

Table1.The general-purpose standard inverters, based on

Fuji Electric’s original torque vector-controlled, high-performance, multi-function FRENIC5000G9S series,cover the entire range of small to large capacities. TheFRENIC5000P9S series, its sister series, is economicalfor fan and pump loads.

A distinctive feature is that many series preparedfor small capacity ranges allow selection from a broadcost performance to meet diversified needs. The FVR-E9S series, equipped with torque vector control likethe FRENIC5000G9S, is capable of quick responsecontrol and suitable for frequent acceleration anddeceleration. The FVR-C11S series is very small andexceedingly economical for simple variable-speed driveuse.

General-purpose vector control inverters, equipped

with high-performance vector control and utilized likegeneral-purpose standard inverters, are widely used inelevators and multistory parking lots. When thedriven motor is not equipped with a pulse encoder, it isalso possible to convey the function to sensorless vectorcontrol.

The series for the machine tool drive is describedin detail in “FRENIC5000MS5 for Machine Tool Spin-dle Drive” in this special issue. It is a new series,greatly improved in both structure and performance.From the viewpoint of control performance, there aretwo series; the FRENIC5000M5 used for NC lathesand the FRENIC5000V5 used for machining centers.Both have the advantage that the adoption of aseparate structure for the converter and invertersections enables the free selection of a high-efficiencypower regeneration converter and an economical dy-namic braking system.

A power regenerating PWM converter connected tothe main circuit DC-bus terminals of the inverterperforms high-efficiency power regeneration and main-tains input current to a sinusoidal current. It isgenerally used for elevator loads with frequent dynam-ic braking. Further more, demands for it is rapidlyincreasing because its use greatly reduces input har-monic current. The principle that “the transfercoefficient for a 6-pulse converter equals zero” isapplied according to the “Guidelines for the control of

Table 1 Fuji Electric’s typical inverter series

Category Series Supplyvoltage

Main featuresCapacity range (kW) Frequency control range (Hz)

General-purpose standard inverters

General-purposevector controlinverters

Regeneration PWM converters

Machine tool spindle drive inverters

FVR-C11S

FVR-E9S

FRENIC5000G9S

FRENIC5000P9S

FRENIC5000VG5

RHC

FRENIC5000M5

FRENIC5000V5

Single phase 200V3-phase 200V

3-phase 200V3-phase 400V



3-phase 200V

3-phase 400V


Single phase 100VSingle phase 200V3-phase 200V3-phase 400V

10,0001,0001000.1

0.10.1

0.10.10.1

1 10 100 1,000

For variable torque load™Provided with automatic energy-saving

operation mode most suitable for fan and pump loads (factory setting)

High-performance, multi-function inverters™Standard enclosure IP40 (for 22kW or

less)™Enclosure IP56 available (for 22kW or

less)

General industrial high-performance vector control inverters™For speed control with quick response™Capable of torque control with external

analog signals

Regeneration converters™High-efficiency power regeneration™Reduction in input harmonic current

Machine tool spindle drive inverters™M5 (torque vector control without PG)™V5 (vector control with PG)™Selection between dynamic or

regeneration braking for the converter possible

High-performance, general-purpose inverters ™Standard enclosure IP40™Enclosure IP65 available

Miniature type for simple variable-speed drive

0.4

0.75

3.7

3.73.7

2.2

2.2

0.2 90

120

400400400400

400400

270

270

120

120120

120120

90

5050

6060

22

110

0.4

0.75

7.57.5

0.75

1.5

400

400

400

500

45

55

5.5

3.7

5.5

Present Status and Future Prospects for General-Purpose Inverter Technologies 73

harmonics by consumers of high or very high voltagepower supplies” in Japan.

4. Conclusion

Demands for variable-speed drive, including ener-gy-saving operation and utilization aiming at automa-tion and saving labor have increased. Sophisticatedand diversified systems have more often includedvariable-speed drive.

Up to now, developments have attached impor-tance to improvements in performance and multiplefunctions. However, factors such as “user-friendly”,“environment-friendly” and “high reliability” are likelyto have priority with regard to drive systems in thefuture.

From the viewpoint of user friendliness, the simpli-fication or automation of setting work during equip-

ment setup and matching work of control parameterswith the mechanical system are key points.

From the viewpoint of environmental friendliness,in addition to the problem of materials used forpackaging and parts, technical developments to reduceelectric noise and harmonic current more economicallyare the next issues.

From the viewpoint of reliability, the fundamentaltopics are to complete the protective functions and adesign that extends the lifetime for each part. Ofcourse, there are difficulties in balancing lifetime witheconomical efficiency. Functions such as a forecastingfunction for life expectancy before equipment failureare desired.

Fuji Electric will continually tackle these subjectsto offer perfect variable-speed drive systems. Wewould appreciate your views as an actual user or aplanner on our products.


Kouetsu FujitaYasuhiro OkumaJun’ichi Itoh

Novel Technologiesfor Power Conversion Circuits

Fig.1 Circuit of the matrix converter

1. Introduction

Variable speed controllers for general-purpose in-verters have progressively been of higher quality,smaller size, lighter weight and lower cost. Thesedevelopments have been accomplished by such progres-sive technologies as power devices. A control methodand the control devices necessary to realize thismethod, and other technologies including cooling andmounting. However, the main circuit of the inverter isstill widely used without any remarkable changessince it was first introduced.

On the other hand, in order to solve the problem ofsource harmonics, the main circuit for the wholevariable speed controller has tended to become morecomplicate due to the requirements of adding animproving power factor reactor to the diode rectifierand the use of a high power factor converter.

Fuji Electric has been developing a new maincircuit for the future variable speed controller. Thispaper introduces new power conversion circuits andthe novel technologies for analyzing them.

2. Analysis and Application of the Direct Con-verter

2.1 Features of the direct converterThe purposes of applying the three-phase to three-

phase direct converter are as follows:(1) higher power factor of input current for the power

supply

(2) reduction of conduction loss by decreasing thenumber of conduction devices in the main circuit

(3) compactness and lighter weight by removing partsof the DC link

Figure 1 shows a fundamental circuit of a typicalmatrix converter in the direct converter. The circuitconnects to a total of 9 bi-directional switches, with 3switches forming a phase. For the direct converter, adirectly split up waveform of the input supply voltageas output is used. Therefore, the matrix converter hasthe maximum controllability of the input supply cur-rent and output voltage in the three-phase to three-phase direct converter, because each phase of theoutput terminal can be selected all phases of the inputterminal independently other phases of the outputterminal.

2.2 Analyzing method of the direct converterAs the circuit of the matrix converter shown in

Fig. 1 needs a bi-directional switch, many varieties ofcircuits are under consideration. A circuit with a fewernumber of devices has also been proposed by restrict-ing the function of the matrix converter.

As a result, it is difficult to compare the controlcharacteristics of the many proposed circuits with thesame specifications, and a standard analyzing methodhas not yet been completely established. Fuji Electrichas therefore established an analyzing method toevaluate the control characteristics of various circuitsto study the direct converter circuit. In this analyzingmethod, the relationship of input and output voltages

Fig.2 System configuration of the direct converter

R S

VU W

T

s1 s2 s3 s4 s5 s6 s7 s8 s9

Power supply

vRSv

ST

vTS

vUVv

VW

v WU

Load

MAC-AC direct converter


Fig.3 Instantaneous space vectors of the matrix converter

of the direct converter shown in Fig.2 has been definedby using the switching matrix S (n, m). In the case ofthe three-phase to three-phase direct converter, S isdefined as a matrix of 3, 3-type as equation (1).

...................................... (1)

Each element of S is defined as a switchingfunction for each switch. The switching function isdefined by the total number of path currents which isbased on both input and output voltage.

Subsequently the relationship between input andoutput supply voltage of the direct converter has beencleared by expressing the instantaneous space vectoras an output voltage. Equation (2) shows an operationfor the instantaneous space vector of the outputvoltage.

......... (2)

Equation (3) shows the switch matrix of Fig. 1, andFig. 3 shows the instantaneous space vectors of theoutput voltage at a supply voltage phase.

.......... (3)

There are 27 types of vectors, shown with asterisksin Fig. 3, and selection of 3 kinds of switches is possibleat one output phase. The circle in Fig. 3 also shows alocus of the supply voltage vector. The dotted lineconnects to each outer points of the output voltagevectors, and voltage in the region can be output as anaverage by the PWM. A circle inscribed within thedotted line shows a locus of maximum voltage as far aspossible without generation of low order harmonics.

2.3 Application examplesFigure 4 shows a circuit with three parts of

switches removed from the matrix converter in Fig. 1.The circuit is called a delta converter due to the use ofa delta connection for input, as 2 series of bi-directional switches are connected between each line.Analytic examples of the operation by applying theproposed analysis to the delta converter follow.

Equation (4) and Fig. 5 show a switch matrix of thedelta converter and a possible output voltage rangedependent on both the instantaneous space vector foroutput voltage at a source phase and the PWM,respectively.

................................. (4)

Because 2 switches are connected to each three-phase of output, the circuit has 8 kinds of outputvoltage vectors and can control the amplitude ofvibration but cannot output an arbitrary frequency.Furthermore, it is able to analyze the possible controlrange of input current phase with the same analyzingmethod. From these results, the delta converter isexpected to apply equipment for power factor improve-ment and reduce the starting current in the inductionmotor. This is because the delta converter is a VVCF(variable voltage constant frequency) circuit which cancontrol the amplitude of vibration in the output voltagewhile controlling the power factor at 1 for the inductive

Fig.4 Circuit of the delta converter

= =v uv

v vw

vwu

v RS

v ST

v TS

S3×3

v = =vαv β

v RS

v ST

v TS3 3/22

01 －1/2

－ 3/2－1/2 S

3×3

S =s 1 s 5－s 2 s 4 s 2 s 6－s 3 s 5 s 3 s 4－s 1 s 6

s 4 s 8－s 5 s 7 s 5 s 9－s 6 s 8 s 6 s 7－s 4 s 9

s 2 s 7－s 1 s 8 s 3 s 8－s 2 s 9 s 1 s 9－s 3 s 7

Fig.5 Instantaneous space vectors of the delta converter

S =s 1 s 3

－s 6 s 3

s 2 s 6

s 2 s 4

s 3 s 5

－s 2 s 5

－s 1 s 4

s 4 s 6

s 1 s 5

ω

β

α

Power supplying voltage vector

R S

VU W

T

s1 s2 s3 s4 s5 s6

ω

β

α

Power supply voltage vector


and capacitive load of up to 120°.

3. Direct Linked Type Frequency Changer

3.1 Circuit configurationThe matrix converter of the circuit as shown in Fig.

1 requires a bi-directional switch. The switch with thesnabber circuit is an AC snabber. Fuji Electric hasdeveloped a direct linked type frequency changerwhich has a basically configured DC clamped type ofbilateral switching circuit using a DC snabber (RCDand C snabber). The DC snabber is widely used forinverters and general-purpose IGBT modules.

Figure 6 shows the main circuit configuration. Thecircuit has the same function as the matrix converterand is capable of both input current and output voltage

control. This is because the instantaneous space vectorof output voltage is equal to the matrix converter inFig. 3.

3.2 ResultsFigure 7 shows the output voltage and current

waveforms of a general-purpose motor with 3 phase200V input and 4 poles 2.2kW output and is driven bya main carrier frequency of 16kHz. An applied voltagewaveform to the motor has a path swept out by peakvalue and described as three-phase all-wave. Theinput voltage waveform is directly split up and distrib-uted. On the other hand, the output current is asinewave that has performed without problem.

4. New Single-Phase High Power Factor Con-verter

In the case of a single-phase input small-capacityinverter, harmonics generated in the equipment arealso regulated by the “Guidelines for the reduction ofharmonic emission due to electrical and electronicequipment for household and general use.” A single-phase input circuit uses a large reactor inductance forpower factor improvement. It requires a large DC linkcapacitor to absorb double the power ripples as com-pared with the input frequency. Therefore, theapplication of a PWM converter has been expected forthe circuit to achieve smaller sized equipment and amore perfect sinewave input current. A full-bridgetype PWM converter is used when a regenerationfunction to the power supply is required. Fuji Electrichas developed a new single-phase high power factorconverter to realize a smaller size and more economicalPWM converter. An outline of the circuit will bepresented below.

4.1 Circuit configuration and operating principleFigure 8 shows a circuit configuration of the

developed full-bridge type new single-phase high pow-er factor converter. The circuit has the same functionsas the former full-bridge type PWM converter and itrealizes a sinewave curved waveform of supplying

Fig.8 The newest single-phase to three-phase high powerfactor converter

Fig.7 Voltage and current waveform of the direct linked typefrequency changer

A6757-17-168

vuv200V/div

iu5A/div

5ms/div

Fig.6 Direct linked type frequency changer

Sn

ubb

erci

rcu

itS

nu

bber

circ

uit

Sn

ubb

erci

rcu

itT

S

R

W

V

U

DC clamped type bilateral switching circuit

Motor

Powersupply


Fig.9 Voltage and current waveform of the newest single-phase to three-phase high power factor converter

current and recovery of power supply. Features of thecircuit include a terminal of single-phase power supplyconnected to the center of the upper and lower arm inthe converter and another terminal connected to aneutral point of the stator coil in the motor driven bythe converter. Therefore, a single-phase power supplycurrent supplies the power to the DC link as a zero-sequence current of the motor.

The operating principle of the circuit will now beexplained. First, load control of the three-phaseinduction motor is controlled by voltage control of thethree-phase induction motor is controlled by voltagecontrol of the three-phase PWM inverter lines, identi-cal to the former method. The circuit is controlled byselection of the inverter’s 2 types of zero-voltagevectors, as the supplying current is realized by thecontrol of the inverter’s zero-sequence component.This fact allows the possible elimination of a couple ofupper and lower arms from the converter whilerealizing the same functions as the former full-bridgetype PWM converter. The circuit can be reduced insize and cost, as it is able to use leakage inductance ofthe load motor for the reactance during switching.

4.2 ResultsExperimental results are shown in Fig. 9 for the

variable speed driving general-purpose motor of the 3phase 200V input and 4 poles 750W output combinednew single-phase high power factor converter with asingle-phase 100V output. The experiment gives anincreased DC link voltage up to 380V and an operatedIGBT with 600V blocking capability at 10kHz ofcarrier frequency and 33Hz output frequency. Outputcurrent waveform iu of the inverter is an added straincurrent of 50Hz supplying current and 33Hz drivingcurrent of the motor. On the other hand, the waveformof the supplying current i s at the neutral point of themotor is a sinewave waveform. The motor drivingcurrent, which is derived from 1/3 of the inverter’ssupply current, has approximately a sinewave shapedwaveform current. This allows for smooth control of

the motor’s operation.

5. Conclusion

This paper presented the newest technologies forpower conversion circuits for the variable sped control-ler. These technologies include the analyzing methodof the three-phase to three-phase direct converter, thedelta converter and the direct linked type frequencychanger as the concrete circuit and the new single-phase high power factor converter. Fuji Electric willcontinue to develop new technologies for the circuitand will offer in a timely manner new products inresponse to market needs.

References(1) M. Venturini et al. : A New Sinewave In, Sinewave Out

Conversion Technique Eliminates Reactive Elements,Proceeding of Power Conversion Vol.4, No. 1 (1980)

(2) K.Mino et al. : Direct Liked Type Frequency ChangerBased on DC-Clamped Bilateral Switching CircuitTopology, IEEE Industry Applications Society AnnualMeeting, New Orleans, Louisiana, October, (1977)

Motor current

Power supply current

Positive-(and negative-) sequence current

Motor phase voltage 200V/div

10ms/div

10A/div

10A/div

10A/div0

0

0

0

iu

iu

vu

i s

i s /3－


Shin’ichi IshiiSeiki IgarashiJiro Toyosaki

Noise Reduction Methodsfor Power Electronic Equipment

1. Introduction

Power electronic equipment represented by suchequipment as inverters and servos are used in a widerange of applications from industrial factories toordinary homes for improving productivity and/orsaving energy.

Wider use of these equipment is expected in thefuture, however there is concern that noise generatedby these equipment may adversely influence otherequipment.

The noise generated by these equipment can beroughly classified in the following three categories:① harmonic current emissions flowing into the pow-

er source (abbreviated as “source harmonic cur-rents” below),

② disturbance voltages generated from the mainsource terminals (abbreviated as “main terminaldisturbance voltage” below), and

Fig.2 Circuit configuration of single-phase PWM converterwith line current sensor

Fig.1 Configuration of capacitor input type diode rectifiercircuit and its operating waveforms

Current i s

ReactorCapacitor

(a) Single-phase rectifier circuit

(b) Operating waveforms

Load

0

0

Power source

v s

Power source voltage (v s)100 V/div

Current (i s)5 A/div

Time axis scale : 5ms/div

Gate signal

Capacitor

Load

Reference value for DC voltage

Control circuit

Current i sPower source

Reactor

v s

③ electromagnetic interference radiated out of theequipment itself (abbreviated as “electromagneticdisturbance emission” below)

These noise levels are regulated by several guide-lines(1).

Several noise reduction methods will be introducedin this paper.

2. Noise Reduction Methods

2.1 Reduction of source harmonic currentsIn the main circuits of many power electronic

equipment, capacitor-input type diode rectifying cir-cuits are generally used as rectifiers for converting ACvoltage to DC voltage. Figure 1 (a) shows a single-phase rectifier circuit. The current from the powersource shown in this figure flows through a reactor anda single-phase full-wave rectifier bridge and charges asmoothing capacitor. The current flow and the lineterminal voltage are shown in Fig. 1 (b). As the figureillustrates, the waveform of the current flowing in thepower source becomes distorted. There are concernsthat this distorted current may influence other equip-ment connected to the same power source resulting inoverheating, audio noise, vibration and other distur-bances. Therefore, it is necessary to reduce this


distorted wave current, the so-called source harmoniccurrent. Connection of a reactor and use of a PWM(pulse width modulation) converter are methods toreduce noise.

Figure 2 shows an example of source harmoniccurrents reduction methods. In this method, becausethe line current is directly controlled, a line currentsensor must be provided and the converter controlcircuit must be insulated from the current sensor.This increases complexity of the circuit structure andreduces reliability.

A reduction method that suppresses source har-monic currents below a regulated level without usingany line current sensor will now be introduced.

The circuit diagram of a line current sensor-lesssingle-phase PWM converter and its operating wave-forms are shown in Figs. 3 (a) and (b) respectively.These waveforms illustrate the source harmonic cur-rents clearing the regulated level. An advantage ofthis method is that insulation from the main circuit isnot necessary because the line current sensor isreplaced with a DC current sensor.

The operating principle of this line current sensor-less single-phase PWM converter is briefly explainedbelow.

To reduce the source harmonic currents it isappropriate to make a sinusoidal wave current flow in

phase with the source line voltage. In other words, theconverter must generate a sinusoidal wave voltage,equal to the line voltage plus the reactor voltage drop,at its input terminal. Specifically, a sinusoidal wavevoltage for making the source power factor equal to 1must be calculated from the converter output powerand the reactor’s reactance. If the converter generatesthe calculated voltage at its input terminal, thewaveform of the line current becomes sinusoidal insteady state.

2.2 Reduction of main terminal disturbance voltagesMain terminal disturbance voltages generated by

power electronic equipment are caused by harmoniccurrent flowing from the equipment into the powersource due to semiconductor switching devices turningon and off in the main circuit. Details of themechanism that generates this phenomenon is de-scribed in technical reports and other documents. Themechanism will be briefly explained below.

Harmonic currents flow when voltage transitions(abbreviated as “dv /dt” below), generated by the on-offof semiconductor switching devices, are added to thestray inductance and stray capacitance of electricalcomponents that comprise the equipment. In otherwords, these harmonic currents depend on the dv /dt ofsemiconductor switching devices. Therefore if thisdv /dt is made smaller, the harmonic currents decrease

Fig.3 Circuit configuration of line current sensor-less single-phase PWM converter and its operating waveforms Fig.4 Gate driving circuit

Input voltage (v in)100 V/div

Current (i s)5 A/div

Current i s

Power source

Reactor

Gate signal

Control circuitReference value for DC voltage

Inputvoltage

(a) Line current sensor-less single-phase PWM converter circuit

(b) Operating waveformsTime axis scale : 5ms/div

Load

Capacitor

0

0

vCE

R1

R3

R4

R2

SW1

SW3SW4

SW1

SW2

On-off decision circuit

Comparator

R1 R3 R4

R2

D

C

LE

R5

On

(a) Using passive devices only

(b) Using some active devices

SW2

SW3

On


main circuits, specifically IGBT devices, must be madesmaller. A gate driving circuit for smaller dv /dt will beintroduced below.

Figure 4 (a) shows a gate driving circuit composedof passive devices only and Fig. 4 (b) shows anotherdriving circuit that uses several active devices. Figures5 and 6 show the operating waveforms at the time ofturn-off for the IGBT devices driven by these gatedriving circuits. Figure 5 illustrates the difference ofdv /dt when the gate current value is changed by aswitch (SW3) in the circuit configuration of Fig. 4 (a).Figure 6 illustrates the difference of dv /dt whenswitches (SW3, SW4) in the circuit configuration ofFig. 4 (b) are kept open and operated according to theon-off decision circuit. As these operating waveformsshow, dv /dt can be suppressed by the gate drivingconditions. The operation of these driving methods isexplained below.

It is known that the dv /dt of IGBT depends on thevalue of gate resistance. When the resistance value isincreased, the dv /dt generally tends to decrease. Thischaracteristic can be utilized to suppress the dv /dt .The circuit in Fig. 4 (a) is configured to drive the gateafter the gate resistance value has been changedexternally by switch SW3. An advantage of thismethod is that the gate current level can be changedby switching switch SW3 and thus the gate drivingcircuit consists of fewer parts. On the other hand,although the dv /dt itself can be made smaller, thismethod has a disadvantage in that a smaller dv /dtmakes the switching power loss larger. This methodmay be utilized in applications that allow a reducednumber of switching times (frequency) for suppressingnoise generation.

The configuration of the circuit in Fig. 4 (b) is afurther development of the above-mentioned method.This method reduces both the dv /dt and the switchingpower loss by detecting current transitions, makinggood use of wiring stray inductance between IGBTchips in the IGBT module and the module terminalblock, and by suppressing the values of gate resistanceand voltage at on-off time points.

2.3 Reduction of electromagnetic disturbance emissionIn the same manner as main terminal disturbance

voltages, electromagnetic disturbance emission gener-ated by power electronic equipment is caused byharmonic currents flowing from an equipment into thepower source. However, the electromagnetic distur-bance emission has a higher frequency range thanmain terminal disturbance voltages and is emittedfrom the equipment in the form of electromagneticwaves. Details of this mechanism are described intechnical reports and other documents.

The main source of electromagnetic disturbanceemission from inverters or servo-amplifiers is semicon-ductor switching devices that are used in the maincircuits and switching regulator type power supplies in

Fig.6 Operating waveforms (device used : 2MBI 150N-060)

Fig.5 Operating waveforms (device used : 2MBI 75-060N)

(a) SW3 : Open

(b) SW3 : Closed

100 ns/div

0

100 ns/div

0

25 A/divi c

100 V/divvCE

25 A/divi c

100 V/divvCE

(a) SW4 : Open

100 ns/div

0

0

0.4 A/divig

50 A/divi c

(b) SW4 :When on-off decision circuit is operating

100 ns/div

0

0

SW4 On

100 V/divvCE

0.4 A/divig

50 A/divi c

100 V/divvCE

and then the main terminal disturbance voltages canbe reduced.

Therefore, dv /dt of semiconductor devices used in


control circuitry for power electronic equipment. Theelectromagnetic disturbance emission is generatedwhen such devices switch on and off. The method ofreducing noise from the former main circuit hasalready been described in section 2.2. The method forreducing noise from the latter switching regulator willbe described below. For cost-performance consider-ations, a fly-back type DC-DC converter (abbreviatedas “DC-DC converter” below) is generally utilized asthe switching regulator. To lower the emission ofelectromagnetic disturbance emission from the DC-DCconverter, it is sufficient to reduce the dv /dt of themain switch. The main switch is most commonly adevice such as an IGBT or MOSFET. To reduce dv /dtof the device, as described in the previous section, it iseffective to increase the value of gate resistance.However, it is anticipated that this would increase theswitching power loss and thus lower efficiency andrequire larger cooling fins for the devices. Further, thelonger switching time makes high frequency switchingdifficult. As a result, the size of a pulse transformerused in the DC-DC converter will become larger.

Here a new DC-DC converter system utilizingresonance phenomena will be introduced. Figure 7 (a)shows the circuit structure of the new DC-DC convert-er system and Fig. 7 (b) shows measured levels of theelectromagnetic disturbance emission from a certainconventional system and the new system. As Fig. 7 (b)illustrates, the new system radiates less electromag-netic waves by approximately 15 dB (at nearby 35MHz). The operating principle of the new DC-DCconverter system will be briefly explained below.

Figure 8 shows a timing-chart of operation of thenew system. In this figure, after resetting the pulsetransformer (mode III), a resonance phenomenon occursbetween the primary inductance of the pulse trans-former and the resonant capacitor (mode IV). Thedevice voltage drops according to a certain dv /dtdetermined by the resonance phenomena. If the deviceis turned on at the lowest point of the phenomena, thedv /dt of the device at its turn-on time point can bemade smaller than the case where resonance phenome-na is not utilized. In theory, no switching power loss isproduced due to zero voltage switching. Because theresonant capacitor acts as a snubber, the dv /dt of thedevice at the turn-off time point can be reduced.Further, the switching power loss becomes theoretical-ly zero because the device current commutes to thesnubber at that time. Therefore, it is possible toreduce the dv /dt without increasing switching powerdissipation.

3. Conclusion

Several noise reduction methods for power elec-tronic equipment represented by power convertershave been introduced above. In the future, suchequipment may come into wider use throughout theworld and accordingly various regulations regardingnoise will be enforced further.

Fuji Electric will continue to promote the timelyresearch and development of noise reduction tech-niques to meet market requirements.

Reference(1) CISPR Pub.11 (CISPR : Comité International Social

des Perturbations Radio-electriques) (1990)

Fig.7 Configuration of DC-DC converter circuit and measuredresults of electromagnetic disturbance emission level

Fig.8 Operation timing-chart (new system)

DiodeCurrent

Diode

Controlcircuit

Resonant capacitor Device voltage

Frequency (MHz)

DC powersupply

Zener diode

Pulse transformer

CapacitorLoad

(a) Circuit configuration of new DC-DC converter system

(b) Measured results of electromagnetic disturbance emission level

Lev

el (

dBµV

/m)

Lev

el (

dBµV

/m)

Frequency (MHz)30 50 70 100 200

30 50 70 100 200

0

20

40

60

0

20

40

60(Conventional

system)

(New system)

Gate voltageOn

Current

Mode I Mode III Mode IV

Mode II

Device voltage

Off


Fig.2 Current waveform at 0.06Hz (12.5 A/div, 5 s/div)

Takashi AiharaHidetoshi UmidaHirokazu Tajima

Recent Variable-Speed Drive Technology

1. Introduction

Recent trends in variable-speed drive technologyfor induction-motor drives include the development ofhigh-torque control at low speed(1), highly responsivesensor-less vector control, low rotational fluctuation,and minimum time acceleration/deceleration technolo-gy.

In addition, adaptive drive technology that in-cludes the mechanical system and high-efficiency sen-sor-less synchronous motor drives are also beingdeveloped.

In this paper, we introduce the following threetechnologies that are concerned with low rotationalfluctuation control, minimum time acceleration/decel-eration technology for induction-motor drives, and thesensor-less synchronous motor drive.(1) High-accuracy output voltage control technology(2) Minimum time acceleration/deceleration technology(3) Sensor-less synchronous motor drive technology

2. High-Accuracy Output Voltage Control Tech-nology

High-accuracy output voltage control is very im-portant in obtaining low rotational fluctuation of theV /f control and sensor-less vector control.

Three main factors cause rotational fluctuation.(1) Offset of the output voltage(2) Unbalance between 3 phases of the output voltage(3) Distortion of the output voltage caused by PWM

dead-time to avoid a short-circuit of the maincircuit.

Especially at very low speeds, item (3) is thedominant factor. Since even slight voltage distortionwill affect the torque ripple, quick and high-accuracyoutput voltage control is necessary.

These error factors are caused by timing errors ofthe PWM control, quantizing errors of the digitalprocessing, and the delay and on-voltage drop ofswitching devices.

Previously, measures such as software compensa-tion and PWM timing compensation were implementedto counteract these error factors. However, it is very

difficult to completely compensate for all the variouserror factors.

For this reason, Fuji Electric has developed digitalvoltage control technology, and has achieved lowrotational fluctuation with quick and high-accuracyoutput voltage control.

Figure 1 shows an example of the system configura-tion. The sensor-less vector control algorithm createsthe voltage reference, and voltage feedback is appliedso that the output voltage will equal the voltagereference.

The voltage feedback almost completely compen-sates for the various error factors.

The digital control realizes high-speed samplingand high-accuracy control. LSI technology results in acompact circuit size.

Figure 2 shows the current waveform of an induc-tion motor drive with V /f control (no load, 0.06Hz).

Fig.1 System configuration

Frequency setting

Voltage reference

Con-troller PWM

Voltage feedback

Motor

Inve

rter

＜LSI＞

Sensor-less vector control calcula-tion

Recent Variable-Speed Drive Technology 83

Even when the current is not controlled, the voltagefeedback control results in a very smooth waveform atlow speed.

Figure 3 shows a comparison of the rotationalfluctuation. With the digital voltage control, weobtained the same low rotational fluctuation as in thecase of vector control with PG (pulse generator).

3. Minimum Time Acceleration/DecelerationTechnology

Torque control is made possible by the sensor-lessvector control. By controlling the torque to be themaximum of the system, we can realize minimumacceleration/deceleration times.

Figure 4 shows the speed-torque characteristic ofthe sensor-less vector control. Solid lines indicateactual values, and dotted lines represent ideal values.It can be seen that the system can control the torquealmost entirely along the ideal lines. Minimumacceleration/deceleration time can be realized by apply-ing this torque control function.

Figure 5 shows the acceleration/deceleration wave-form with applied sensor-less vector control. Thecurrent is almost constant for acceleration/decelerationbetween 0 r/min to 5,400 r/min. Especially in theconstant power region (above 1,500 r/min), the torquedecrease is inversely proportional to the output fre-quency. Increasing rate of the output frequencyautomatically decreases in the high-speed region.

With this function, minimum acceleration/deceler-ation time can be realized by setting shorter accelera-tion/deceleration times. Therefore, the setting is verysimple, and it is not necessary to tune the acceleration/deceleration time nor the acceleration/decelerationpattern as in conventional systems.

4. Sensor-less Synchronous Motor DriveThe permanent magnet synchronous motor

(PMSM) has advantages of low loss and small size,

because no secondary loss occurs in the rotor as in thecase of induction motors. Due to the merits of smallsize and high efficiency, the range of applications forPMSM is spreading.

PMSM drive systems such as servomotors utilizeposition and velocity sensors. However, in high-efficiency applications such as fans and pumps, be-cause these systems are usually used only with apower line, a sensor-less drive is necessary. Thesensor-less PMSM drive method utilizing emf of thePMSM has already been established. However, amethod of starting from either the stand-still orrotating states and a drive method for low-speeds (lessthan several tens of r/min) are still in the research anddevelopment stages.

Fuji Electric is working to develop these advancedtechnologies and has proposed a method that utilizeselectrical saliency for the method of starting fromstand-still and for the low speed(2) drive method. Ourmethod utilizes a special motor in which inductancevaries corresponding to the position of the rotor. Thesystem monitors changes in inductance via the powerline and calculates the rotor position to realize asensor-less PMSM drive method. System characteris-tics are introduced below.

Figure 6 shows the speed waveform at the static

Fig.3 Comparison of rotational fluctuations

20

18

16

14

12

10

8

6

4

2

0

Rot

atio

nal

flu

ctu

atio

n (

r/m

in)

1 3 5Output frequency (Hz)

V /f control with voltage control and without PG

The vector control with PG

10 15 50 75 100

Fig.4 Speed-torque characteristics

Fig.5 Acceleration/deceleration waveform with torque limiting

120

80

40

0

0 1,000 2,000 3,000 4,000 5,000 6,000

Ou

tpu

t to

rqu

e (%

)

- 120

- 80

- 40

Rotational speed (r/min)

1 s

5,400 r/min

100 A

Speed

0

0

Current


speed reference of 10 r/min. This system can drivePMSM smoothly even at such low speeds.

Figure 7 shows the response when an impact loadis applied at the velocity reference of 0 r/min. Even at0 r/min, this system can maintain the rated torque.

In an application such as a fan, the system must beable to start when wind is causing the motor to rotate.If a system does not have an output voltage sensor,since it usually cannot know the position and velocityof the rotor, it may not be able to start.

Under these conditions, Fuji Electric proposed astarting method that estimates the position and veloci-ty of the rotor instantaneously from the emf of thePMSM. In this method, when starting, the systemtemporarily short-circuits the motor output using themain circuit of the inverter. The system monitors themotor current, and calculates the position and velocity

Fig.6 Steady-state operation (10 r/min, no load)

Fig.7 Performance with applied load (rated load)

0

0

360°

50 r/min

0.8 s

Speed

Angle estimation

0

0

100%

4 s

Speed

Load torque

200 r/min

Fig.8 Starting from rotating state

0

0

0

01,000 r/min

2 Aiu

iw2 A

Angle estimation

Speed

160 ms

360°

of the rotor. After the output voltage is made to equalthe motor terminal voltage, a soft start of the system ispossible.

Figure 8 shows the velocity and current waveformswhen this system starts under free-rotation at- 1,000 r/min and accelerates to +1,000 r/min. It canbe seen that the system achieves a good start and thatthere is no current shock.

5. Conclusion

This paper has introduced low rotational fluctua-tion control, minimum time acceleration/decelerationtechnology for induction-motor drives, and the sensor-less synchronous motor drive as recent variable-speeddrive technologies. These technologies will contributeto the high-performance of drive systems in response tomarket needs.

Fuji Electric will continue to challenge itself todevelop new technology to realize market needs.

Reference(1) M.Yamazoe: General-Purpose Inverter, FRENIC5000

G9S/P9S, Fuji Electric Review, Vol.41, No.1, p.7-12(1995)

(2) T.Aihara: Sensor-less Torque Control of Salient-PoleSynchronous Motor at Zero Speed Operation, APEC’97,Vol.2, p715-720 (1997)


Takao IchiharaKenji OkamotoOsamu Shiokawa

Downsizing Technologyfor General-Purpose Inverters

Fig.1 Downsizing trend of general-purpose inverters (0.75kW)

1. Introduction

General-purpose inverters are products suited forfunction advancement, energy savings and labor sav-ings in field of general-purpose industrial equipment.The market for general-purpose inverters is expandingyear after year.

This trend is the result of downsizing, pricereduction, function advancement, and improved reli-ability. In particular, the progress in downsizing hasbeen amazing. For example, as shown in Fig. 1, thevolume of general-purpose inverters has decreased toless than 1/10 the volume of the first general-purposeinverters that came onto the market. This fact hasgreatly contributed to the increased range of applica-tions for general-purpose inverters.

A summary of typical downsizing technology thathas been cultivated by Fuji Electric is described in thispaper.

2. Downsizing Technology for Control Circuit

2.1. Development of one-chip MPUWhen general-purpose inverters were first intro-

duced, the exclusive area for control circuitry was

rather large because all functions were realized byhardware. Thereafter, with the introduction of micro-processors (MPUs), most processing of general-purposeinverters was performed by software, and sectionswhere processing by software was too slow, such as thePWM generating unit, were realized by hardware.Thus, general-purpose inverters with advanced func-tions were realized through a simple hardware con-struction. Furthermore, in contrast to priorMPU+ASIC (application specific integrated circuit)control circuit construction, development of LSI pro-cess technology and integration technology from mi-

Vol

um

e (×

100c

m3 )

19810

20

40

60

80

100

120

1984 1987

(Year)

1991 1996

108

66

37

21

9.6

Fig.3 External view of control circuit for small inverter

Fig.2 Voltage/current detection (non-isolated)

Pow

er s

upp

ly

Motor

Voltagedetection

MPU

IM

Inverter

N line

Currentdetection

Shunt resister


Fig.4 Conventional control power supply and gate drive circuit

cron-order to sub-micron-order has enabled general-purpose inverters to be controlled by one chip. Withthis technology, the actual mounting area has becomeless than half that of the MPU+ASIC configuration.

2.2 Downsizing of detection circuitAll detection of main circuit current and DC link

circuit voltage was performed via an isolation device.As shown in Fig. 2, a non-insulated method in whichthe MPU itself is connected to the N line of a DC linkcircuit has been utilized in small-size general-purposeinverters. This method enables direct input of thecurrent and voltage to be detected to the A-D converterof the MPU. Through this method, not only has theisolation device and accompanying isolated powersupply become unnecessary, but since the interface forvoltage and current detection can be constructed froma simple circuit such as a voltage divider or a shuntresistor, remarkable downsizing has become possible.

2.3 Mount technology for control circuitHigh density mounting in the periphery of the

MPU and analog ICs is realized through the introduc-tion of COB (chip on board) technology in which bareIC chips are mounted directly onto a printed circuitboard. COB enables not only a reduction of mountingarea, but also a lowering of mounting height. There-fore, further downsizing is possible by stacking thecontrol printed circuit boards. Figure 3 shows anexternal view of a control circuit board for a small-sizeinverter that utilizes COB technology. All controlcircuits for the small-size general-purpose inverter are

constructed with dimensions of 74.5× 65× 13 (mm)and two printed circuit boards are stacked.

3. Miniaturization of Control Power Supply andGate Drive Circuit

As shown in Fig. 4, in the case of conventionalcontrol power supplies, a 5V power supply that drivesdigital circuits such as the MPU, and other variouspower supplies that drive the high-side IGBTs andlow-side IGBTs were constructed by a DC-DC convert-er from a DC power supply which is an output of therectifier. Power supplies were isolated from eachother. A gate drive circuit controls six IGBTs bytransmission of PWM signals from the MPU throughphoto-couplers. To downsize these circuits, miniatur-ization of each part is an obvious solution, but it is alsoimportant to standardize and clarify the role of eachcircuit.

3.1 Reduction of the number of control power supplies,introduction of gate drive ICBy replacing transistors used in the switching

element of DC-DC converter with MOSFET, theswitching frequency was increased from several tens ofkHz to one hundred and several tens of kHz. Thisenabled miniaturization of the transformer core sizeand reduction of the smoothing capacitor capacity.However, since many types of control power suppliesare required for general-purpose inverters, this mea-sure alone did not result in miniaturization of thetransformer bobbin that correspond to increases of the

High-side IGBT drive power supply (U-phase)

High-side IGBT drive power supply (V-phase)

High-side IGBT drive power supply (W-phase)

Low-side power supply

5V

MPU

Transformer

R

S

T

+

Tran-sistor

U

V

WLow-side power supply

Rectifier

Rectifier

Rectifier

Rectifier

Rectifier

Rectifier


Fig.5 Simplified control power supply and gate drive circuit

switching frequency. Therefore, as shown in Fig. 5, inorder to miniaturize the transformers, the number ofbobbin pins was reduced by making the groundpotential common for the primary side of the trans-formers, the 5V power supply, and the power suppliesfor high and low-side IGBT. Previously these groundshad been isolated from one another. Furthermore, sixphoto-couplers are eliminated by utilizing a gate driveIC in which three kinds of high-side potentials and onelow-side potential are isolated from one another insideeach chip.

3.2 Introduction of solid capacitorsAlthough aluminum electrolytic capacitors are pop-

ular as smoothing capacitors in control power supplies,they result in an inefficient use of space since theirarea and volume are larger than that of other parts onthe printed circuit board. The efficient utilization ofspace inside general-purpose inverters is important torealize miniaturization, hence a small size capacitor isrequired. Under the worst conditions for general-purpose inverters, the temperature surrounding thecapacitors is 80 to 85°C. Even under such hightemperatures, the life span of the capacitors must be

made to approximately equal that of the aluminumelectrolytic capacitors. To satisfy this requirement, asolid capacitor was introduced which is small in sizeand in equivalent series resistance, and high inallowable ripple current. Table 1 shows a comparisonof capacitance and volume between a solid capacitorand a aluminum electrolytic capacitor having equiva-lent performance characteristics.

As described above, through miniaturization of theparts themselves and reduction of the number of parts(particularly large parts for isolation such as the photo-coupler), the printed circuit board area of both thecontrol power supply circuit and the gate drive circuitwas reduced to approximately half of its conventionalsize.

4. Downsizing Technology for Main Circuits

A metal based circuit board, originally developedby Fuji Electric as an essential element of general-purpose inverters, is described below with respect toits background, structure, performance and merits.

4.1 Development of multi-zone metal based circuit boardsThe efficiency of general-purpose inverters is ap-

proximately 95%, with the remaining 5% loss requiredto finally dissipate heat into the atmosphere. Reduc-tion of this loss or improved cooling performance is akey to the realization of downsizing. In spite of theadvent of low loss power devices in the current trend ofpower semi-conductors, a reduction of generated losscannot be expected easily because of market demandsfor the suppression of noise emitted by general-purposeinverters or for the achievement of low motor noise

Table 1 Comparison between solid capacitor and aluminumelectrolytic capacitor

Level shift

Level shift

Level shift

High-side gate signal (U-phase)

High-side gate signal (V-phase)

High-side gate signal (W-phase)

Gate drive IC

Low-side gate signal

Rectifier

Isolator

Rectifier

Rectifier

R

S

T

U

V

W

High-side power supplyTransformer

Low-side power supply

5V

MPU

＋

MOSFET

Classification

Item

Capacitance ratio 331

Volume ratio 61

Solid capacitorAluminumelectrolyticcapacitor

Note) Switching frequency: 100kHz


through high speed switching. These market demandsare inversely related to the reduction of loss. Further-more, if the mounting density of parts is increased torealize downsizing, problems may result because thegenerated loss per unit area will increase and someparts will exceed their maximum allowable tempera-ture. To solve this problem, the development of a novelcircuit board with low thermal resistance, enablingefficient dissipation of generated loss in general-purpose inverters and allowing high density mounting,is necessary.

It is desirable that high loss parts such as IGBTsor rectifier diodes are mounted on an insulated circuitboard with low thermal resistance, and relatively lowloss parts such as control power supply circuit parts orcontrol circuit parts are mounted on an insulatedcircuit board with low dielectric constant to minimizethe effect of stray capacitance. The multi-zone metalbased circuit board is a metal based circuit board thatcombines different insulation properties to realizedownsizing and reduce costs.

4.2 Structure and characteristics of multi-zone metalbased circuit boardsAs shown in Fig. 6, in the multi-zone metal based

circuit board two types of insulating materials withdifferent characteristics are placed on a metal baseplane, copper foil is laid on top, and then the board ismanufactured by a vacuum heat press process. Insula-tion materials consist of insulation-A with gives priori-ty to low thermal resistance by increasing the amountof filler to exceed 75% and insulation-B which givespriority to a low dielectric constant by reducing the

amount of filler to 0%. Typical characteristics of themulti-zone metal based circuit board are shown inTable 2. Usually the base of the multi-zone metalbased circuit board is set to earth potential, and thedielectric break down voltage between the base and thecopper foil pattern is prescribed as 10kV or more, amargin of approximately 10 times the actual appliedvoltage.

4.3 Merits of multi-zone metal based circuit boardsSince the thermal resistance of multi-zone metal

based circuit boards is remarkably low compared withglass epoxy circuit boards, the following merits are canbe listed.(1) Volume reduction of mounted parts

Since the thermal resistance of metal based circuitboards (in the case of insulation B) is approximately1/4 compared to glass epoxy circuit boards, resistanceof 1/4W is sufficient where a resistance of 1W was usedpreviously. Therefore, high-density mounting can berealized.(2) Narrowing of conductor width

In addition to the mounting parts, temperaturerise of the conductor on the circuit board surface due toheat generation can also be reduced by low thermalresistance. Higher current is allowed for a conductorwith identical width and in thickness. On the otherhand, the conductor can be made narrower for anidentical current.

5. Downsizing of Heat Sink

In addition to the metal based circuit board, thereare heat sinks used to effectively radiate the heatgenerated in general-purpose inverters. The heatradiation capacity of the heat sink has a large affect onthe external dimensions of small-size general-purposeinverters.

Until now, aluminum die-cast heat sinks weregenerally used. However, the manufacture of compactheat sinks with high radiation efficiency is difficult bythe die casting method and is restricted by following

Fig.6 Structure of multi-zone metal based circuit board

Table 2 Typical characteristics of multi-zone metal basedcircuit boards

Fig.7 Cross section of heat sink with riveted cooling ribs

Copper foil

Metal base

Insulation A Insulation B

Heat sink base

Rivet

Cooling rib

Classification

Item

Dielectric breakdown voltage 10kV or more

Thermal resistance* 10014

Dielectric constant* 65100

Insulation A(power zone)

Insulation B(control power

supply)

* Thermal resistance and dielectric constant values are indicated as ratios with each insulation material.


items.(1) The die strength determines the upper limit of

cooling rib height.(2) The fluidity of melted metal determines the lower

limit of cooling rib thickness.To solve these problems, a cooling rib that utilizes

press technology has been developed. Figure 7 showsthe construction of a pressed heat sink with rivetedcooling ribs. The heat sink with riveted cooling ribsincreases the heat radiation surface area of the entireheat sink by riveting thin aluminum plates to the base.

By utilizing riveted cooling ribs, downsizing of 41%

in volume and weight reduction of 57% are attainedcompared with the conventional die-cast heat sink.

6. Conclusion

A summary of downsizing technology for general-purpose inverters has been presented. To expand thescope of the market even more, further downsizing andthe price reductions will be necessary. Fuji Electricwill continue to develop this technology to satisfy userexpectations.


Masakazu YoshidaMasato MochizukiNaoki Kanazawa

Large-Capacity Variable-Speed AC Drive

1. Introduction

With the increasing range of applications for motordriver inverters and customer satisfaction with theirhigh performance, multi-functionality, small size, lowprice, etc., the demand for inverters that can drivelarger capacity motors has increased.

Fuji Electric has developed large capacity powerconverters corresponding to the FRENIC5000G9S/P9Sand VG5S inverter series and the PWM converter RHCseries, which were widely utilized as inverters forgeneral industries. In this paper, we will present anoverview of these large capacity power converters.

2. Main Circuit Configuration and Structure

2.1 Basic concept and featuresBesides offering enlarged capacity, since these

converters are installed in important equipment, thesepower converters should exhibit improved maintain-ability and have the following features.(1) Functionality and performance that is standard-

ized with the smaller capacity seriesUsing these converters, we attempted to enlarge

the capacities of the FRENIC5000G9S/P9S and VG5Sinverter series and the PWM converter RHC series.Because we provided large capacity inverters with thesame control system and functions as those of the midand small capacity inverters currently available on themarket, a consistent system configuration can beestablished throughout from small to large capacityinverters.(2) Improved maintainability

In the main circuit of the inverter, rectifier diodesand IGBT parts for each phase are separated ontoindividual trays, and stored on a rack inside the panel.With this configuration, if a failure should occur in aninverter, the inverter can be restored within a shorttime simply by pulling out the failed tray and replac-ing it with the spare tray.

Figure 1 shows the panel structure applied to aninverter. The uppermost stage contains a rectifierdiode tray; the second stage, an IGBT tray of U phase;the third stage, a control printed circuit board; and the

fourth and fifth stages, IGBT trays of V and W phases.These trays can be easily pulled out toward the frontside by detaching the connections to the main circuitconductors and the connector to the control wires.

Improved cooling efficiency has enabled the invert-er size to be decreased. The depth dimension for allmodels has been standardized at 600mm, saving spaceand allowing maintenance to be performed at the frontside. These measures remarkably facilitate inspectionand maintenance.(3) Enriched protection function

In addition to inheriting the protection functions of

Fig.1 Inverter panel

Fig.2 IGBT tray


Table 1 Large capacity inverter/converter specifications

Fig.3 Schematic diagrams of large capacity IGBT inverters

the mid and small capacity series, these power con-verters are provided with semiconductor protectionfuses in each phase of the main circuit and in eachphase of the IGBT to limit the propagation of a failure.

Further, each tray is provided with a fault indica-tion function to facilitate the identification of faultytrays.

2.2 Main circuit configurationEach arm of the three-phase bridge in this large

capacity power converter has a maximum of eightIGBT modules (300A, 1,200V) connected in parallel toachieve large capacity. This configuration might havea problem with distributing current among the IGBTmodules. However, the current balance between themodules is maintained at 0.8 or more by reducing theinductance of the wiring bars between the modules,controlling the module characteristics, etc.

The IGBT tray is shown in Fig. 2. The tray, whichcontains the IGBTs of one phase, also contains thepower supply circuit and driving circuits necessary fordriving the IGBTs, and a fault indication function.

The cooling fan for IGBTs is configured such thatit can be easily replaced by opening the front coverwithout pulling out the tray.

3. Application of the Large Capacity PowerConverter to Various Inverter/ConverterSeries

3.1 Application to invertersThe main specifications of inverter/converter that

use this large capacity converter are shown in Table 1.Since all of these products have the same controlsystem and functions as those of the mid and small

capacity inverters that currently are on the market, aconsistent system configuration can be establishedfrom small to large capacity inverters. Figure 3 showsschematic diagrams of the main circuit for single-unitand multi-unit systems.3.1.1 Single-unit system

Maximum capacities of the standard motors, whichcan be driven by the single-unit system, were in-creased to 400kW for a constant torque load (G9S),500kW for a variable torque load (P9S), and 400kW fora high-performance vector-control inverter (VG5S).

Previously, these capacity ranges were achieved byoperating two inverters in parallel. With the increasedcapacity, dimensions of the panel can be dramaticallyreduced.3.1.2 Multi-unit system

In order to drive motors having a capacity of

DC reactor

Rectifier

Magnetic contactor

Fuse

Fuse

Frequencysetter

Power supply

MCCB

IGBT

CT

Controlcircuit

Control signal

M Motor(a) Single-unit system

Electrolytic capacitor

< Inverter panel >

< Power supply panel >

Magnetic contactor

Frequencysetter


Controlcircuit

Controlcircuit

Control signal

Motor(b) Multi-unit system

Power supply

MCCB

DC reactor

Fuse

Fuse

IGBT

CTCT

Rectifier

< Inverter panel > Slave

M

< Inverter panel >Master



Inverter FRENIC5000

G9S P9S VG5S

to 400kW to 500kW to 400kW to 400kW

150% 120% 150% 150%

Sinusoidal PWM controlConstant DC voltage controlPower factor control

™

™

™

Sinusoidal PWM control (with torque vector control)

Vector controlASR control with ACR minor loop

™

™

380 to 420V/50Hz380 to 480V/60Hz

380 to 420V/50Hz380 to 480V/60H

380 to 420V/50Hz380 to 440V/60Hz

Seriesname

Item

PWMconverter

RHC

Range of capacity

Overload capacity

Control system

Power supply voltage


greater than 400kW, we developed a multi-unit systemin the VG5S series. In a multi-unit system (up to amaximum of six units), the motor is provided withmultiple windings and an inverter is provided for eachwinding.

A block diagram of the control circuit for driving atwo-winding motor is shown in Fig. 4. The master unitperforms speed control, vector calculation and currentcontrol in the same manner as in a single-unit system.The slave unit performs only current control in re-sponse to each reference value sent from the masterunit.

Because of requirements for reduced wiring, immu-nity to noise and high-speed, a serial communicationsystem with optical fiber is utilized for the exchange ofcontrol information between the master and slaveunits.

In the slave unit, the phase angle data of thevector converter (VD), which determines the phase ofcurrent, is corrected based on the phase angle refer-ence (θ*), stator frequency reference (ω1*), transmis-sion delay time and transmission period. Then, theshift of phase angles between both units is cancelled.As a result, the current balance between the windingscan be achieved.

In conventional systems, there was a problem thatthe carrier signals of the master and slave units cannotbe synchronized. Therefore, an AC reactor is insertedbetween the inverter and motor as a means to preventan increase of the current ripple. However, in this

system, the information of the time difference betweenthe communication reference signal and carrier signalof the master unit is sent from the master unit to theslave unit, and the slave unit corrects the period of thecarrier based on this information. This synchronizesthe carrier signals between both units.

3.2 Harmonic suppression technologyAs is well known, a typical input circuit consists of

a three-phase rectifying bridge network constructedfrom diodes. After smoothing with a capacitor in thelink circuit, an AC voltage of variable voltage andvariable frequency is obtained via the PWM inverteron the output side.

Since low harmonic currents are generated by therectifying and smoothing processes of this input ACpower supply circuit, these harmonics are suppressedin accordance with the Japanese guidelines.

We will introduce means to suppress harmoniccurrents in the converter itself or in the power supplytransformer.3.2.1 Twelve-pulse rectifier

The three-phase bridge method (with a smoothingcapacitor) generates harmonic current having theorders of 6n± 1(n=1, 2, 3,...). The lower the order, thegreater the values become. This system is also called a6-pulse rectifier since the ripple frequency in therectified output is six times of the power supplyfrequency.

When the rectifier circuit is divided into two

Fig.4 Control circuit block diagram of multi-unit system

Two-winding motor

ASR

Master unit

Slave unit

ACR VD PWM÷

Φ*

IT* VM*VT*

IT

IM*

IM

r*ω *τ

Magnetic fluxcalculation

Phase anglecorrection

Carrier signalcorrection

AΦR VD

ACRIT*IM*

Vu*

Vw*Vv*

*θ

∫IM

PG

VD PWMVM*VT*

IT IMVD

Vu*

Vw*Vv*

AΦR: Magnetic flux regulatorACR: Current regulator VD: Vector converter PG: Pulse generator

1*ωs*ωcalculation

s*ω

rω

*θ1*ω

IT* : Torque current referenceIM*: Magnetizing current reference 1*: Stator frequency reference *: Phase angle referenceθω

IM: Magnetizing current detected value Φ*: Magnetic flux reference r*: Speed reference ASR: Speed regulatorω

s*: Phase angle reference after the correction r: Speed detected value s*: Slip frequency reference IT: Torque current detected value

ωω

θ

IT*, IM*,Transmission of carrier synchronizing information etc.

1*ω*,θ

s*θ

Opt

ical

tran

smis

sion


Table 2 Example of harmonic current

Fig.7 Input current waveform of PWM converter

circuits as shown in Fig. 5 and AC voltages having aphase difference of 30° are supplied through a 3-winding transformer where the 2 secondary windingshave separate connection systems, a so-called 12-pulserectifier circuit is constructed. In this circuit, ifharmonic current components in the right and leftcircuits are ideally balanced, only the currents of thefundamental component and 12n± 1(n=1, 2, 3,...) ordercomponents will flow through the primary winding ofthe transformer. This completely eliminates compo-nents of the orders of 5, 7, 17, 19, etc.

In practice, however, some components remain dueto differences in the impedance and voltages of bothwindings. For a 400 V class transformer where

™ the voltage error is 2V or less,™ the impedance is 2.7% or more, and™ the amount of impedance scattering is 10% or less,residual amounts can be calculated using the

values in Table 2.Further, when a transformer similar to that de-

scribed above is applied to the circuit shown in Fig. 3(b) and the secondary windings of the transformer areseparately connected to the master and slave circuits,

Fig.6 Schematic diagram of inverter with PWM converter

the inverter side is controlled such that the dividedwindings are always supplied with the same amount ofpower. Since both secondary windings of the trans-former consume the same power, the difference in thetransformation ratios of both windings is cancelled.

Residual components are determined by the volt-age differences and the impedance in the transformerin Fig. 5. However, when a 12-pulse rectifier is utilizedin the circuit of Fig. 3 (b), the amount of residualcomponents is determined by the precision of thecontrol on the inverter side.3.2.2 PWM converter

Fuji Electric has supplied PWM converters of 5.5 to220kW for inverter to the market. The range of

1.2

(Unit: %)

1.40.40.44.07.01.63.4

25231917131175ObjectOrder

12-pulse rectifier circuit

Fig.5 Schematic diagram of inverter with 12-pulse rectifier

DC reactor

Magnetic contactor

Fuse

Frequency setter

MCCB

Controlcircuit

Control signal

< Inverter panel >



IGBT

CT

M Motor

Reactor

ReactorCapacitor

Resistor

Magnetic contactor

Fuse

Frequencysetter

Power supply

MCCB

IGBT

CT

Fuse

Controlcircuit

Controlcircuit

Control signal

IGBT

CT

M Motor


< Converter panel >

< Inverter panel >


Current

Voltage


application for these converters is increasing. Inaddition to enlarged inverter capacities, these PWMconverters are also designed to be compatible with theenlarged inverter capacities.

A schematic diagram of an inverter with PWMconverter is shown in Fig. 6. Since the three-phasebridge with IGBTs performs PWM control instead ofthe diode rectifier, the input current waveform is madesinusoidal and the power factor can be controlled toapproximately 1. Figure 7 shows the waveforms of theinput current and phase voltage when this PWMconverter is utilized.

Since this PWM converter not only reduces har-monic current, but can also return regenerative energy

to the power supply side, it has been favorably receivedin applications to lifting devices such as cranes andelevators.

4. Conclusion

In this paper we have introduced the large capacitypower converter.

Fuji Electric will continue to respond to marketneeds by supplying highly reliable inverters andoptimal systems, including higher capacities for anexpanding range of applications and countermeasuresagainst harmonics which have recently been problem-atic.


Yoshikazu TanakaHiroaki HayashiHiroshi Takahashi

FRENIC5000MS5 for Machine ToolSpindle Drives

1. Introduction

In AC spindle drive systems for machine tools,operation such as frequent acceleration and decelera-tion, operation with low rotation ripple and lowvibration, as well as various control functions includ-ing spindle positioning control, are generally required.Fuji Electric has responded to market requirements forspindle drive systems through the introduction of thetorque vector control type FRENIC5000M3 series,suitable for driving the main spindle of lathe typemachine tools, and the high performance vector controltype FRENIC5000V3 series, suitable for machiningcenters.

In recent years, however, along with requirementsfor space-saving in the installation of the machine toolitself, there have been demands for further downsizingof the spindle drive system. Synchronized operationcontrol are also required to handle combined machin-ing that utilizes multiple spindles. Further, it is alsobecoming necessary to comply with various regulationsrepresented by the EC machinery directive. To meetthese requirements Fuji Electric has developed thenew FRENIC5000MS5 series. A summary of which ispresented below.

2. Features of the New Series

The FRENIC5000MS5 series has the followingfeatures as a spindle drive system for machine tools.

2.1 Separated construction for the converter and inverterAn external view of the FRENIC5000MS5 series is

shown in Fig. 1. The drive unit (inverter circuit part)is on the left, and on its front panel can be seen thedisplay and connectors for input/output signals. Onthe right is the converter unit (rectifier circuit andsmoothing ripple-free circuit). Both units are mountedside-by-side and connected by bar wiring to the DC busof the main circuits.

There are two drive units in this series, the“FRENIC5000M5 series” mainly for the spindle driveof lathes and the “FRENIC5000V5 series” having ahigh performance vector control that is suitable for

machining centers. There are also two series ofconverter units, the “dynamic braking type converterunit” and the “regenerative braking converter unit”,which make various combined applications possible.

Because a single converter unit can drive severaldrive units, it is easy to construct multi-drive systemsconsisting of a main spindle, sub-spindles and toolspindles. With this method, because braking energy isused for driving other spindles via the DC bus, thesystem operates with higher efficiency than a systemhaving an inverter and converter for every spindle.

2.2 Standard specification complies with EC directiveThe EC directive (low voltage directive) is adopted

as the standard specification for all types of driveunits, converter units and motors including options,making the products suitable for the internationalmachine tool market.

The control input/output signals to/from the driveunit can be switched for compatibility with either asink input or source input, allowing interchangeabilityamong conventional model types.

2.3 Improvement of basic functionsFigure 2 shows a block diagram of the control

Fig.1 External view of FRENIC5000MS5


Fig.2 Block diagram of control circuit of FRENIC5000M5

circuit of the FRENIC5000M5 series. For PWM controland digital AVR control which require high speedcalculations, control circuits are constructed fromnewly developed ASIC. Torque vector control is pro-cessed by the software, together with other sequentialoperations and calculating operations.

Through utilization of this new control method, theaccuracy of torque limiting characteristics has in-creased, response to impact loads and acceleration/deceleration performance have also improved, androtation ripple has been suppressed to a large extent.

2.4 DownsizingBy applying a newly developed ASIC and by

reconstructing the cooling elements with heat pipetype cooling fins, the control circuit has been down-sized and the installation space reduced by 60%compared with conventional products.

In addition, by standardizing the height and thelength of mounting surfaces for all model types, allunits can be mounted side-by-side and thus the spaceoccupied by the spindle drive unit can be greatlyreduced.

2.5 Integrating and reducing the option cardsSome of the control functions of several options

(synchronized operation, pulse-encoder type orienta-tion, switching of the motor windings, etc.) have beenmoved to the main control P.C.B. This has reduced theload of additional boards and integrated the more than10 conventional options into 4 types of options. Theseoptions are applicable and common to both theFRENIC5000M5 and FRENIC5000V5 series.

3. Operating Characteristics

A typical example of operating characteristics ofthe torque control type FRENIC5000M5, a member ofthe FRENIC5000MS5 series, is introduced below.

3.1 Torque limiting characteristicsFigure 3 shows a typical example of the torque

limiting characteristics measured at 11/7.5kW. It canbe seen that the maximum torque of 120% is securedover the entire range.

3.2 Acceleration and deceleration characteristicsFigure 4 shows an oscillogram of acceleration and

deceleration operation. This operating characteristic isfor a motor having a capacity of 11/7.5kW combinedwith an inertia load of 0.4 kg-m2.

Compared with the conventional FRENIC5000M3series, a time reduction of about 10% has beenachieved, resulting in acceleration and decelerationcharacteristics comparable with those of the conven-tional vector controlled FRENIC5000V3 series. Boththe acceleration time and deceleration time satisfy thetheoretical values calculated at the maximum torque of120%.

3.3 Rotation ripple characteristicsFigure 5 shows a measurement of the rotation

ripple for operation of a single 7.5/5.5kW motor. As areference, operation data for drive units of the conven-tional FRENIC5000M3 and FRENIC5000V3 series areshown on the same graph. A large improvement has

Speed setting Software

Ramp generator

f *

id*

iq*

id

iq i1

V1

V*

Vd*, Vq*

θ

Asic

Frequencygenerator(torque current limit)

Motor

Σ

f /V

ACR

AVR

IMPWM inver-ter

Carrier

Σ-∆converter

Sin

e w

ave

gen

erat

or

Torquevector controller

Vectorconverter

Slip compen-sation


been realized compared with the FRENIC5000M3series.

3.4 Orientation control characteristicsFigure 6 shows an example of the operating

characteristic of high-precision multi-point orientationcontrol. The oscillogram shows operation of onerevolution of positioning control from a stopped condi-tion at 0° to 360°. The time required until output ofthe completion signal is reduced by approximately 20%compared with that of the conventional FRENIC5000M3 series.

To improve performance of the FRENIC5000MS5series, the creeping speed has been increased, and analgorithm has been implemented to generate a speedpattern for deceleration within a minimal time fromthe creeping speed to approximately the final stopposition.

3.5 Easy setup and simple displayTo realize user-friendly operation of the FRENIC

5000MS5, software for the loader that runs on Win-dows 95(*) on a personal computer has been developed

for the loader.To make setup and adjustment at the installation

site easier, this software for the loader is equipped

Fig.3 Torque limiting characteristics

0

Mot

or t

orqu

e (%

)

160

120

80

40

-120

- 80

- 40

0 1,000 2,000 3,000 4,000 5,000 6,000Rotational speed (r/min)

Fig.5 Comparison of rotation ripple (7.5/5.5kW single motoroperation)

4

∆N

(r/

min

) (O

vera

ll) 3

2

1

00

Output frequency (Hz)

20 40 60 80

M3

M5

V3

100 120 140 160

Fig.4 Acceleration and deceleration characteristics (11/7.5kW,Inertia load 0.4kg-m2)

100 A

2 s

Load meter

Motor current

Motor speed

6,000r/min

10 V

Fig.6 Orientation control characteristics

Orientation command

Orientation completion signal

Position deviation

11.25°

0.5 s

Fig.7 Example of the monitoring display screen

* Windows 95 : A trademark of Microsoft Corp., USA


with a function to collectively set standard settingvalues prepared in accordance with machine types, afunction to read and copy the set values of othermachines, a function for monitoring various operatingconditions, and an operation function by which thedrive unit can be test-operated by settings on theloader side.

Figure 7 shows a display of the monitoring opera-tion as an example display screen during operation ofthe personal computer. In this example, the leftcolumn (Operation monitor) indicates such items asthe rotation speed of the motors and spindles, theupper middle section (Input signal status) indicatesthe existence of digital input signals, the lower middlesection (Output signal status) indicates the existenceof digital output signals, the upper right section(Output meter) shows the scale of the analog output

and the lower right section (Alarm record) shows thehistory of the past four trips.

4. Conclusion

A summary of the FRENIC5000MS5 series includ-ing its options has been presented above. By separat-ing the drive unit and converter unit, this series hasbeen made compatible with a wide range of machinetools. To extend its application range further, FujiElectric will continue to improve the product seriesand to develop products having enriched systems.Furthermore, we will increase efforts to equip ourproduct series of spindle drive units with sufficientfunctions and performance to meet the needs of thestill evolving and developing machine tool market.

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