A Control Strategy for Four-Switch Three-Phase

Brushless DC Motor Using Single Current Sensor

Abstract

A control strategy based on single current sensor is proposed for a four-switch three-

phase brushless dc (BLDC) motor system to lower cost and improve performance. The

system’s whole working process is divided into two groups. In modes 2, 3, 5, and 6, where

phase c works, phase-c current is sensed to control phases a and b, and phase-c current is

consequently regulated. In modes 1 and 4, the combination of four sub operating modes for

controlling phase-c current is proposed based on detailed analysis on the different rules that

these operating modes have on phase-c current. Phase-c current is maintained at nearly zero

level first, and phase-a and phase-b currents are regulated by speed circle. To improve control

performance, a single-neuron adaptive proportional–integral (PI) algorithm is adopted to

realizethe speed regulator. Simulation and experimental systems are set up to verify the

proposed strategy. According to simulation and experimental results, the proposed strategy

shows good self-adapted track ability with low current ripple and strong robustness to the

given speed reference model. Also, the structure of the drive is simplified.

INTRODUCTION For the past two decades several Asian countries such as Japan, which have been under

pressure from high energy prices, have implemented variable speed PM motor drives for

energy saving applications such as air conditioners and refrigerators. On the other hand, the

U.S.A. has kept on using cheap induction motor drives, which have around 10% lower

efficiency than adjustable PM motor drives for energy saving applications. Therefore

recently, the increase in energy prices spurs higher demands of variable speed PM motor

drives. Also, recent rapid proliferation of motor drives into the automobile industry, based on

hybrid drives, generates a serious demand for high efficient PM motor drives, and this was

the beginning of interest in BLDC motors.

BLDC motors, also called Permanent Magnet DC Synchronous motors, are one of the motor

types that have more rapidly gained popularity, mainly because of their better characteristics

and performance. These motors are used in a great amount of industrial sectors because their

architecture is suitable for any safety critical applications.

The brushless DC motor is a synchronous electric motor that, from a modelling perspective,

looks exactly like a DC motor, having a linear relationship between current and torque,

voltage and rpm. It is an electronically controlled commutation system, instead of having a

mechanical commutation, which is typical of brushed motors. Additionally, the

electromagnets do not move, the permanent magnets rotate and the armature remains static.

This gets around the problem of how to transfer current to a moving armature. In order to do

this, the brush-system/commutator assembly is replaced by an intelligent electronic

controller, which performs the same power distribution as a brushed DC motor. BLDC

motors have many advantages over brushed DC motors and induction motors, such as a better

speed versus torque characteristics, high dynamic response, high efficiency and reliability,

long operating life (no brush erosion), noiseless operation, higher speed ranges, and reduction

of electromagnetic interference (EMI). In addition, the ratio of delivered torque to the size of

the motor is higher, making it useful in applications where space and weight are critical

factors, especially in aerospace applications.

The control of BLDC motors can be done in sensor or sensorless mode, but to reduce overall

cost of actuating devices, sensorless control techniques are normally used. The advantage of

sensorless BLDC motor control is that the sensing part can be omitted, and thus overall costs

can be considerably reduced. The disadvantages of sensorless control are higher requirements

for control algorithms and more complicated electronics [3]. All of the electrical motors that

do not require an electrical connection (made with brushes) between stationary and rotating

parts can be considered as brushless permanent magnet (PM) machines, which can be

categorised based on the PMs mounting and the back-EMF shape. The PMs can be surface

mounted on the rotor (SMPM) or installed inside of the rotor (IPM), and the back-EMF shape

can either be sinusoidal or trapezoidal. According to the back-EMF shape, PM AC

synchronous motors (PMAC or PMSM) have sinusoidal back-EMF and Brushless DC motors

(BLDC or BPM) have trapezoidal back-EMF. A PMAC motor is typically excited by a three-

phase sinusoidal current, and a BLDC motor is usually powered by a set of currents having a

quasi-square waveform.

Because of their high power density, reliability, efficiency, maintenance free nature and silent

operation, permanent magnet (PM) motors have been widely used in a variety of applications

inindustrial automation, computers, aerospace, military (gun turrets drives for combat

vehicles), automotive (hybrid vehicles) and household products. However, the PM BLDC

motors are inherently electronically controlled and require rotor position information for

proper commutation of currents in its stator windings. It is not desirable to use the position

sensors for applications where reliability is of utmost importance because a sensor failure

may cause instability in the control system. These limitations of using position sensors

combined with the availability of powerful and economical microprocessors have spurred the

development of sensorless control technology. Solving this problem effectively will open the

way for full penetration of this motor drive into all low cost, high reliability, and large

volume applications.

The remainder of the paper is arranged as follows. Section 2 describes the position and speed

control fundamentals of BLDC motors using sensors. Next, Section 3 explains the control

improvements applying sensorless techniques, describing the motor controller model and the

most important techniques based on back-EMF sensing. Section 4 also briefly analyses the

sensorless techniques using estimators and model-based schemes. In addition, Section 5

compares the feasibility of the control methods, and describes some relevant implementation

issues, such as open-loop starting. Finally, Section 6 provides an overview for the

applications of BLDC motor controllers, as well as conclusions are drawn in Section 7.

2. Position and Speed Control of BLDC Motors Using Sensors

PM motor drives require a rotor position sensor to properly perform phase

commutation and/or current control. For PMAC motors, a constant supply of position

information is necessary; thus a position sensor with high resolution, such as a shaft encoder

or a resolver, is typically used. For BLDC motors, only the knowledge of six phase-

commutation instants per electrical cycle is needed; therefore, low-cost Hall-effect sensors

are usually used. Also, electromagnetic variable reluctance (VR) sensors or accelerometers

have been extensively applied to measure motor position and speed. The reality is that

angular motion sensors based on magnetic field sensing principles stand out because of their

many inherent advantages and sensing benefits.

2.1. Position and Speed Sensors

As explained before, some of the most frequently used devices in position and speed

applications are Hall-effect sensors, variable reluctance sensors and accelerometers. Each of

these types of devices is discussed further below.

2.1.1. Hall-effect sensors

These kinds of devices are based on Hall-effect theory, which states that if an electric current-

carrying conductor is kept in a magnetic field, the magnetic field exerts a transverse force on

the moving charge carriers that tends to push them to one side of the conductor. A build-up of

charge at the sides of the conductors will balance this magnetic influence producing a

measurable voltage between the two sides of the conductor. The presence of this measurable

transverse voltage is called the Hall-effect because it was discovered by Edwin Hall in 1879.

Unlike a brushed DC motor, the commutation of a BLDC motor is controlled electronically.

To rotate the BLDC motor the stator windings should be energized in a sequence. It is

important to know the rotor position in order to understand which winding will be energized

following the energizing sequence. Rotor position is sensed using Hall-effect sensors

embedded into the stator.

Most BLDC motors have three Hall sensors inside the stator on the non-driving end of

the motor. Whenever the rotor magnetic poles pass near the Hall sensors they give a high or

low signal indicating the N or S pole is passing near the sensors. Based on the combination of

these three Hall sensor signals, the exact sequence of commutation can be determined. Figure

1 shows a transverse section of a BLDC motor with a rotor that has alternate N and S

permanent magnets. Hall sensors are embedded into the stationary part of the motor.

Embedding the Hall sensors into the stator is a complex process because any misalignment in

these Hall sensors with respect to the rotor magnets will generate an error in determination of

the rotor position. To simplify the process of mounting the Hall sensors onto the stator some

motors may have the Hall sensor magnets on the rotor, in addition to the main rotor magnets.

Therefore, whenever the rotor rotates the Hall sensor magnets give the same effect as the

main magnets. The Hall sensors are normally mounted on a printed circuit board and fixed to

the enclosure cap on the non-driving end. This enables users to adjust the complete assembly

of Hall sensors to align with the rotor magnets in order to achieve the best performance.

Figure 1. BLDC motor transverse section

Nowadays, because miniaturized brushless motors are introduced in many applications,

new position sensors are being developed, such as a three branches vertical Hall sensor

depicted in Figure 2a. The connecting principle between the brushless motor and this sensor

is reminiscent of the miniaturized magnetic angular encoder based on 3-D Hall sensors. A

permanent magnet is fixed at the end of a rotary shaft and the magnetic sensor is placed

below, and the magnet creates a magnetic field parallel to the sensor surface. This surface

corresponds to the sensitive directions of the magnetic sensor. Three-phase brushless motors

need three signals with a phase shift of 120° for control, so a closed-loop regulation may be

used to improve the motor performance. Each branch could be interpreted as a half of a

vertical Hall sensor and are rotated by 120° in comparison to the other. Only a half of a

vertical Hall sensor is used since little space is available for the five electrical contacts (two

for the supply voltage and three to extract the Hall voltages). This sensor automatically

creates three signals with a phase shift of 120°, which directly correspond to the motor

driving signals, to simplify the motor control in a closed-loop configuration. A drawing of

this device’s use as angular position sensor for brushless motor control is given in Figure 2b.

A first alignment is between the rotor orientation and the permanent magnet, and a second

alignment is between the stator and the sensor. This alignment will allow the motion

information for the motor and the information about its shaft angular position.

Figure 2. (a) Schematic representation of a three branches Hall sensor. (b) Three branches

vertical Hall device mounted as angular position sensor for brushless motor control

2.1.2. Variable reluctance (VR) wheel speed sensors

This kind of sensor is used to measure position and speed of moving metal components,

and is often referred as a passive magnetic sensor because it does not need to be powered. It

consist of a permanent magnet, a ferromagnetic pole piece, a pickup coil, and a rotating

toothed wheel, as Figure 3 illustrates. This device is basically a permanent magnet with wire

wrapped around it. It is usually a simple circuit of only two wires where in most cases

polarity is not important, and the physics behind its operation include magnetic induction.

Figure 3. Variable Reluctance sensor that senses movement of the toothed wheel

2.1.3. Accelerometers

An accelerometer is a electromechanical device that measures acceleration forces, which

are related to the freefall effect. Several types are available to detect magnitude and direction

of the acceleration as a vector quantity, and can be used to sense position, vibration and

shock. The most common design is based on a combination of Newton’s law of mass

acceleration and Hooke’s law of spring action. Then, conceptually, an accelerometer behaves

as a damped mass on a spring, which is depicted in Figure 4. When the accelerometer

experiences acceleration, the mass is displaced to the point that the spring is able to accelerate

the mass at the same rate as the casing. The displacement is then measured to give the

acceleration.

Figure 4. Basic spring-mass system accelerometer

Conventional Control Method Using Sensors

A BLDC motor is driven by voltage strokes coupled with the rotor position. These

strokes must be properly applied to the active phases of the three-phase winding system so

that the angle between the stator flux and the rotor flux is kept close to 90° to get the

maximum generated torque. Therefore, the controller needs some means of determining the

rotor's orientation/position (relative to the stator coils), such as Hall-effect sensors, which are

mounted in or near the machine’s air gap to detect the magnetic field of the passing rotor

magnets. Each sensor outputs a high level for 180° of an electrical rotation, and a low level

for the other 180°. The three sensors have a 60° relative offset from each other. This divides a

rotation into six phases (3-bit code)

Figure 5. Electronically commutated BLDC motor drive

The process of switching the current to flow through only two phases for every 60 electrical

degree rotation of the rotor is called electronic commutation. The motor is supplied from a

three-phase inverter, and the switching actions can be simply triggered by the use of signals

from position sensors that are mounted at appropriate points around the stator. When

mounted at 60 electrical degree intervals and aligned properly with the stator phase windings

these Hall switches deliver digital pulses that can be decoded into the desired three-phase

switching sequence [15]. A BLDC motor drive with a six-step inverter and Hall position

sensors is shown in Figure

Figure 6. Hall sensor signal, back-EMF, output torque and phase current

Techniques and Advances in Sensorless Control

Position sensors can be completely eliminated, thus reducing further cost and size of motor

assembly, in those applications in which only variable speed control (i.e., no positioning) is

required and system dynamics is not particularly demanding (i.e., slowly or, at least,

predictably varying load). In fact, some control methods, such as back-EMF and current

sensing, provide, in most cases, enough information to estimate with sufficient precision the

rotor position and, therefore, to operate the motor with synchronous phase currents. A PM

brushless drive that does not require position sensors but only electrical measurements is

called a sensorless drive [4].

The BLDC motor provides an attractive candidate for sensorless operation because the nature

of its excitation inherently offers a low-cost way to extract rotor position information from

motor-terminal voltages. In the excitation of a three-phase BLDC motor, except for the

phase-commutation periods, only two of the three phase windings are conducting at a time

and the no conducting phase carries the back-EMF. There are many categories of sensorless

control strategies [6]; however, the most popular category is based on back electromotive

forces or back-EMFs [17]. Sensing back-EMF of unused phase is the most cost efficient

method to obtain the commutation sequence in star wound motors. Since back-EMF is zero at

standstill and proportional to speed, the measured terminal voltage that has large signal-to-

noise ratio cannot detect zero crossing at low speeds. That is the reason why in all back-

EMF-based sensorless methods the low-speed performance is limited, and an open-loop

starting strategy is required.

Generally, a brushless DC motor consists of a permanent magnet synchronous motor that

converts electrical energy to mechanical energy, an inverter corresponding to brushes and

commutators, and a shaft position sensor [19], as Figure 7 shows. In this figure, each of the

three inverter phases are highlighted in a different colour, including the neutral point: red

phase A, green phase B, blue phase C, and pink neutral point N. The stator iron of the BLDC

motor has a non-linear magnetic saturation characteristic, which is the basis from which it is

possible to determine the initial position of the rotor. When the stator winding is energized,

applying a DC voltage for a certain time, a magnetic field with a fixed direction will be

established. Then, the current responses are different due to the inductance difference, and

this variation of the current responses contains the information of the rotor position.

Therefore, the inductance of stator winding is a function of the rotor position.

Figure 7. Typical sensorless BLDC motor drive

The analysis of the circuit depicted in Figure 7 is based on the motor model for phase A

(highlighted in red colour), illustrated in Figure 8, and the following assumptions are

considered:

• The motor is not saturated.

• Stator resistances of all the windings are equal (RS), self inductances are constant (LS) and

mutual inductances (M) are zero.

• Iron losses are negligible.

Figure 8. Equivalent circuit of the BLDC motor for phase A

In this paper, conventional and recent advancement of back-EMF sensing methods for the

PM BLDC motors and generators are presented, which are split in two categories; direct and

indirect back-EMF detection [22]:

• Direct back-EMF detection methods: the back-EMF of floating phase is sensed and its zero

crossing is detected by comparing it with neutral point voltage. This scheme suffers from

high common mode voltage and high frequency noise due to the PWM drive, so it requires

low pass filters, and voltage dividers. The methods can be classified as:

o Back-EMF Zero Crossing Detection (ZCD) or Terminal Voltage Sensing.

o PWM strategies.

• Indirect back-EMF detection methods: because filtering introduces commutation delay at

high speeds and attenuation causes reduction in signal sensitivity at low speeds, the speed

range is narrowed in direct back-EMF detection methods. In order to reduce switching noise,

the indirect back-EMF detection methods are used. These methods are the following:

o Back-EMF Integration.

o Third Harmonic Voltage Integration.

o Free-wheeling Diode Conduction or Terminal Current Sensing.

Applications

The terminal voltage sensing method is widely used for low cost industrial applications

such as fans, pumps and compressor drives where frequent speed variation is not required.

Nevertheless, BLDC motors need a rotor position sensor, and this reduces the system

ruggedness, complicates the motor configuration and its mass production. This sensor can be

has been eliminated through this sensing technique. In spite of the back-EMF being zero at

standstill, this technique permits the starting of a separately controlled synchronous motor

without a sensor, because the PWM signal generated in the control computer chops the motor

voltage by the commutation transistors to control the motor speed. An example is a motor

pump unit, developed for commercial vehicle applications, in which control strategy can be

based on the back-EMF zero-crossing method, and speed control loop is closed by means of

the virtual feedback provided by the commutation point prediction.

Another important field is the super high speed motors, which are receiving increasing

attentions in various applications such as machine tools, because of the advantages of their

small size and light weight at the same power level

Methods based on PWM strategies

There are many methods based on PWM control schemes, but the most relevant are

conventional 120º, elimination of virtual neutral point, techniques for low speed, high speed

and small power applications, and direct current controlled, which are explained below.

Technique for low speed or low voltage applications

For low voltage applications, the voltage drop across the BJT’s or MOSFET’s will

affect the performance. When the motor speed goes low, zero crossing is not evenly

distributed. Besides, if the speed goes further low, the back-EMF amplitude becomes too low

to detect.

There are basically two methods to correct the offset voltage of back-EMF signal . One of

them is to use complementary PWM as shown in Figure 15, which also reduces the

conduction loss. Another method is to eliminate the effect of diode voltage drop in order to

add a constant voltage to compensate the effect of diode, and threshold voltage for avoiding

the asymmetry in the distribution of zero crossing [24]. Then, in order to eliminate the non-

zero voltage drop effect, a complementary PWM can be used, which will also reduce the

power dissipation in the devices

Figure. Complementary PWM algorithm

Direct current controlled PWM technique (hysteresis current control):

With the advantages of BLDC motor drives , it is possible to use a reduced converter

configuration with advanced control techniques. Then one switch leg in the conventional six-

switch converter, showed in Figure 7, is redundant to drive the three-phase BLDC motor,

which results in the possibility of the four-switch configuration instead of six switches [21],

as shown in Figure 17. This new drive consists of two switch legs and split capacitor bank, so

two phases are connected to the switch legs and the other phase to the midpoint of DC-Link

capacitors. But with this configuration, the limited voltages make very difficult to obtain 120°

conducting profiles. This is the well-known problem asymmetric voltage PWM , which

results in the 60° phase-shifted PWM strategy to generate three-phase balanced current

profiles. Also, the conventional PWM schemes cannot be directly applied for the new drive

configuration.

Fig: Four-switch converter for driving a three-phase BLDC motor

The direct current PWM control technique is based on the current controlled PWM

method, instead of the voltage controlled PWM, which generates robust speed and torque

responses and is simple to be implemented from the hardware and software points of view.

Therefore, the four-switch three-phase BLDC motor drive, mainly applied to AC induction

motor drives until now, could be a good alternative to the conventional configuration with

respect to low-cost and high performance. In a PWM control strategy for the four-switch

three-phase BLDC motor drive, the three-phase currents always meet the condition of

Equation It means that control of the two-phase currents can guarantee the generation of the

120º conducting three-phase currents profiles. For completing this task, the two-phase

currents are directly controlled using the hysteresis current control method by four switches.

SEMICONDUCTOR DEVICES

Power electronics and converters utilizing them made a head start when the first

device the Silicon Controlled Rectifier was proposed by Bell Labs and commercially

produced by General Electric in the earlier fifties. The Mercury Arc Rectifiers were well in

use by that time and the robust and compact SCR first started replacing it in the rectifiers and

cycloconverters. The necessity arose of extending the application of the SCR beyond the line-

commutated mode of action, which called for external measures to circumvent its turn-off

incapability via its control terminals. Various turn-off schemes were proposed and their

classification was suggested but it became increasingly obvious that a device with turn-off

capability was desirable, which would permit it a wider application. The turn-off networks

and aids were impractical at higher powers.

The Bipolar transistor, which had by the sixties been developed to handle a few tens

of amperes and block a few hundred volts, arrived as the first competitor to the SCR. It is

superior to the SCR in its turn-off capability, which could be exercised via its control

terminals. This permitted the replacement of the SCR in all forced-commutated inverters and

choppers. However, the gain (power) of the SCR is a few decades superior to that of the

Bipolar transistorand the high base currents required to switch the Bipolar spawned the

Darlington. Three or more stage Darlingtons are available as a single chip complete with

accessories for its convenient drive. Higher operating frequencies were obtainable with a

discrete Bipolars compared to the 'fast' inverter-grade SCRs permitting reduction of filter

components. But the Darlington's operating frequency had to be reduced to permit a

sequential turn-off of the drivers and the main transistor. Further, the incapability of the

Bipolar to block reverse voltages restricted its use.

The Power MOSFET burst into the scene commercially near the end seventies.

This device also represents the first successful marriage between modern integrated circuit

and discrete power semiconductor manufacturing technologies. Its voltage drive capability –

giving it again a higher gain, the ease of its paralleling and most importantly the much higher

operating frequencies reaching upto a few MHz saw it replacing the Bipolar also at the sub-

10 KW range mainly for SMPS type of applications. Extension of VLSI manufacturing

facilities for the MOSFET reduced its price vis-à-vis the Bipolar also. However, being a

majority carrier device its on-state voltage is dictated by the RDS(ON) of the device, which

in turn is proportional to about VDSS 2.3rating of the MOSFET. Consequently, high-voltage

MOSFETS are not commercially viable.

Improvements were being tried out on the SCR regarding its turn-off capability

mostly by reducing the turn-on gain. Different versions of the Gate-turn-off device, the Gate

turn-off Thyristor (GTO), were proposed by various manufacturers - each advocating their

own symbol for the device. The requirement for an extremely high turn-off control current

via the gate and the comparatively higher cost of the device restricted its application only to

inverters rated above a few hundred KVA.

The lookout for a more efficient, cheap, fast and robust turn-off-able device

proceeded in different directions with MOS drives for both the basic thysistor and the

Bipolar. The Insulated Gate Bipolar Transistor (IGBT) – basically a MOSFET driven Bipolar

from its terminal characteristics has been a successful proposition with devices being made

available at about 4 KV and 4 KA. Its switching frequency of about 25 KHz and ease of

connection and drive saw it totally removing the Bipolar from practically all applications.

Industrially, only the MOSFET has been able to continue in the sub – 10 KVA range

primarily because of its high switching frequency. The IGBT has also pushed up the GTO to

applications above 2-5 MVA.

Subsequent developments in converter topologies – especially the three-level

inverter permitted use of the IGBT in converters of 5 MVA range. However at ratings above

that the GTO (6KV/6KA device of Mitsubishi) based converters had some space. Only SCR

based converters are possible at the highest range where line-commutated or load-

commutated converters were the only solution. The surge current, the peak repetition voltage

and I2t ratings are applicable only to the thyristors making them more robust, specially

thermally, than the transistors of all varieties.Silicon carbide is a wide band gap

semiconductor with an energy band gap wider than about 2 eV that possesses extremely high

thermal, chemical, and mechanical stability. Silicon carbide is the only wide band gap

semiconductor among gallium nitride (GaN, EG = 3.4 eV), aluminum nitride (AlN, EG = 6.2

eV), and silicon carbide that possesses a high-quality native oxide suitable for use as an MOS

insulator in electronic devices The breakdown field in SiC is about 8 times higher than in

silicon. This is important for high-voltage power switching transistors. For example, a device

of a given size in SiC will have a blocking voltage 8 times higher than the same device in

silicon. More importantly, the on-resistance of the SiC device will be about two decades

lower than the silicon device. Consequently, the efficiency of the power converter is higher.

In addition, SiC-based semiconductor switches can operate at high temperatures (~600_C)

without much change in their electrical properties. Thus the converter has a higher reliability.

Reduced losses and allowable higher operating temperatures result in smaller heatsink size.

Moreover, the high frequency operating capability of SiC converters lowers the filtering

requirement and the filter size. As a result, they are compact, light, reliable, and efficient and

have a high power density. These qualities satisfy the requirements of power converters for

most applications and they are expected to be the devices of the future.

Ratings have been progressively increasing for all devices while the newer devices

offer substantially better performance. With the SCR and the pin-diodes, so called because of

the sandwiched intrinsic ‘i’-layer between the ‘p’ and ‘n’ layers, having mostly line-

commutated converter applications, emphasis was mostly on their static characteristics -

forward and reverse voltage blocking, current carrying and over-current ratings, on-state

forward voltage etc and also on issues like paralleling and series operation of the devices. As

the operating speeds of the devices increased, the dynamic (switching) characteristics of the

devices assumed greater importance as most of the dissipation was during these transients.

Attention turned to the development of efficient drive networks and protection techniques

which were found to enhance the performance of the devices and their peak power handling

capacities. Issues related to paralleling were resolved by the system designer within the

device itself like in MOSFETS, while the converter topology was required to take care of

their series operation as in multi-level converters.

The range of power devices thus developed over the last few decades can be represented as a

tree, on the basis of their controllability and other dominant features.

Tree diagram of power semiconducting devices

Power MOSFET:

Power MOSFET is a device that evolved from MOS integrated circuit technology.

The first attempts to develop high voltage MOSFETs were by redesigning lateral MOSFET

to increase their voltage blocking capacity. The resulting technology was called lateral double

diffused MOS (DMOS). However it was soon realized that much larger breakdown voltage

and current ratings could be achieved by resorting to a vertically oriented structure. Since

then, vertical DMOS (VDMOS) structure has been adapted by virtually all manufacturers of

Power MOSFET. A power MOSFET using VDMOS technology has vertically oriented three

layer structure of alternating p type and n type semiconductors as shown

Fig: schematic construction of POWER MOSFET

Operating principle of a MOSFET:

At first glance it would appear that there is no path for any current to flow between

the source and the drain terminals since at least one of the p n junctions (source – body and

body-Drain) will be reverse biased for either polarity of the applied voltage between the

source and the drain. There is no possibility of current injection from the gate terminal either

since the gate oxide is a very good insulator. However, application of a positive voltage at the

gate terminal with respect to the source will covert the silicon surface beneath the gate oxide

into an n type layer or “channel”, thus connecting the Source to the Drain as explained next.

The gate region of a MOSFET which is composed of the gate metallization, the gate (silicon)

oxide layer and the p-body silicon forms a high quality capacitor. When a small voltage is

application to this capacitor structure with gate terminal positive with respect to the source

(note that body and source are shorted) a depletion region forms at the interface between the

SiO2 and the silicon as shown in Fig

Fig: Gate control of MOSFET conduction. (a) Depletion layer formation; (b) Free electron accumulation; (c) Formation of inversion layer.

The positive charge induced on the gate metallization repels the majority hole carriers

from the interface region between the gate oxide and the p type body. This exposes the

negatively charged acceptors and a depletion region is created.

Further increase in VGS causes the depletion layer to grow in thickness. At the same time the

electric field at the oxide-silicon interface gets larger and begins to attract free electrons as

shown in Fig(b). The immediate source of electron is electron-hole generation by thermal

ionization. The holes are repelled into the semiconductor bulk ahead of the depletion region.

The extra holes are neutralized by electrons from the source.

As VGS increases further the density of free electrons at the interface becomes equal to

the free hole density in the bulk of the body region beyond the depletion layer. The layer of

free electrons at the interface is called the inversion layer and is shown in Fig 6.4 (c). The

inversion layer has all the properties of an n type semiconductor and is a conductive path or

“channel” between the drain and the source which permits flow of current between the drain

and the source. Since current conduction in this device takes place through an n- type

“channel” created by the electric field due to gate source voltage it is called “Enhancement

type n-channel MOSFET”.

The value of VGS at which the inversion layer is considered to have formed is called

the “Gate – Source threshold voltage VGS (th)”. As VGS is increased beyond VGS(th) the

inversion layer gets some what thicker and more conductive, since the density of free

electrons increases further with increase in VGS. The inversion layer screens the depletion

layer adjacent to it from increasing VGS. The depletion layer thickness now remains

constant.

Steady state output i-v characteristics of a MOSFET The MOSFET, like the BJT is a three terminal device where the voltage on the gate

terminal controls the flow of current between the output terminals, Source and Drain. The

source terminal is common between the input and the output of a MOSFET. The output

characteristics of a MOSFET is then a plot of drain current (iD) as a function of the Drain –

Source voltage (VDS) with gate source voltage (VGS) as a parameter. Fig 6.5 (a) shows such

a characteristics.

Fig : Output i-v characteristics of a Power MOSFET (a) i-v characteristics; (b) Components of ON-state resistance; (c) Electron drift velocity vs Electric field; (d) Transfer

Differences between BJT and MOSFET:

A MOSFET like a BJT has alternating layers of p and n type semiconductors.

However, unlike BJT the p type body region of a MOSFET does not have an external

electrical connection. The gate terminal is insulated for the semiconductor by a thin layer of

SiO2. The body itself is shorted with n+ type source by the source metallization. Thus

minority carrier injection across the source-body interface is prevented. Conduction in a

MOSFET occurs due to formation of a high density n type channel in the p type body region

due to the electric field produced by the gate-source voltage. This n type channel connects n+

type source and drain regions. Current conduction takes place between the drain and the

source through this channel due to flow of electrons only (majority carriers). Where as in a

BJT, current conduction occurs due to minority carrier injection across the Base-Emitter

junction. Thus a MOSFET is a voltage controlled majority carrier device while a BJT is a

minority carrier bipolar device.

Introduction of inverter:

Inverter:

Inverter is power electronic circuit that converts a direct current into an

alternative current power of desired magnitude and frequency. The inverters find their

application in modern ac motor and uninterruptible power supplies.

1.2 classicification of inverter:

Based on the source used

Voltage source inverter

Current source inverter

Based on switching methods

Pulse width modulation inverters

Square wave inverters

Based on switching devices used

Transistorized inverter

Thyristorised inverter

Based on the inversion principle

Resonant inverter

Non- Resonant inverter

TRADITIONAL SOURCE INVERTERS

Traditional source inverters are Voltage Source Inverter and Current Source

Inverter. The input of Voltage Source Inverter is a stiff dc voltage supply, which can be a

battery or a controlled rectifier both single phase and three phase voltage source inverter are

used in industry. The switching device can be a conventional MOSFET, Thyristor, or a power

transistor.

Voltage source inverter is one which the dc source has small or negligible impedance.

In other words a voltage source inverter has stiff dc source voltage at its input terminals. A

current-fed inverter or current source inverter is fed with adjustable dc current source. In

current source inverter output current waves are not affected by the load.

VOLTAGE SOURCE INVERTER

When the power requirement is high, three phase inverters are used. When three

single phase inverters are connected in parallel, we can get the three phase inverter. The

gating signals for the three phase inverters have a phase difference of 120o. These inverters

take their dc supply from a battery or from a rectifier and can be called as six-step bridge

inverter. Fig.1.1 shows the three phase inverter using six MOSFET’s and with diodes.

A large capacitor is connected at the input terminals tends to make the input dc

voltage constant. This capacitor also suppresses the harmonics fed back to the source.

The Voltage Source Inverter is widely used. However, it has the some conceptual and

theoretical barriers and limitations. The AC output voltage is limited and cannot exceed the AC input

voltage. Therefore the Voltage Source Inverter is only buck (step down) inverter operation for DC to

AC power conversion or boost (step-up) operation for AC to DC power conversion.

Fig.1.2 Current Source Inverter

The traditional three phase Current Source Inverter structure is shown in Fig.1.2.

A dc current source feeds the three phase main inverter circuit. The dc current source can be a

relatively large dc inductor fed by a Voltage Source such as a battery or a rectifier. It consists

of six switches and with anti parallel diodes. This diode provides the bidirectional current

flow and unidirectional voltage blocking capability.

Current Source Inverter has the following conceptual and theoretical barriers

and limitations. The ac output voltage has to be greater than the original dc voltage that feeds

the dc inductor or the dc voltage produced is always smaller than the ac input voltage.

Therefore this inverter is a boost inverter for dc to ac power conversion. For applications

where a wide voltage range is desirable, an additional dc to dc buck converter is needed. The

additional power conversion stage increases system cost and lowest efficiency.

At least one of the upper devices and one of the lower devices have to be gated on and

maintained on at any time. Other wise, an open circuit of the DC inductor would occur and

destroy the devices. The open circuit problem by EMI noise’s misgatting-off is a major

concern of the converters reliability. A current source inverter is fed from a constant current

source. Therefore load current remains constant irrespective of the load on the Inverter. The

load voltage changes as per the magnitude of load impedance. When a voltage source has a

large inductance in series with it, it behaves as a current source .The large inductance

maintains the current constant.

MODE OF INVERTERS OPERATION

The mode of inverter operation is mainly classified based on the thyristor

conduction period as

180ºconduction

120ºconduction

Three phase inverters are normally used for high power applications. Three single

phase half or full bridge inverters can be connected in parallel to form the configuration of a

three phase inverter. The gating signals of single phase inverters should be advanced or

delayed by 120º with respect to each other in order to obtain three phase balanced voltages.

The three phase output can be obtained from a configuration of six switches and

six diodes. Two types of control signals can be applied to the switches: 180ºconduction or

120ºconduction [7,8].

180° CONDUCTION

Each switch conducts for 180°. Three switches remain on at any instant of time.

When switch 1 is switched on, terminal ‘a’ is connected to the positive terminal of the dc

input voltage. When switch 4 is switched on, terminal ‘a’ is connected to the negative

terminal of the dc source. There are six modes of operation in a cycle and the duration of

each mode is 60°. The switches are numbered in the sequence of gating the switches 123,

234, 345, 456, 561, 612. The gating signals are shifted from each other by 60° to obtain three

phase balanced voltages [7,8].

During mode 1 for 0 ≤ ωt ≤ π/3, switches 1 and 6 conducts.

van = Vs/2 vbn = -Vs/2 vcn =

During mode 2 for π/3 ≤ ωt ≤ 2π/3, switches 1 and 2 conduct.

van = Vs/2 vbn = 0 vcn = -Vs/2

During mode 3 for 2π/3 ≤ ωt ≤ 3π/3, switches 2 and 3 conduct.

van = 0 vbn = Vs/2 vcn = -Vs/2

During mode 1 for 0 ≤ ωt ≤ π/3, switches 1 and 6 conducts.

van = Vs/2 vbn = -Vs/2 vcn = 0

During mode 2 for π/3 ≤ ωt ≤ 2π/3, switches 1 and 2 conduct.

van = Vs/2 vbn = 0 vcn = -Vs/2

During mode 3 for 2π/3 ≤ ωt ≤ 3π/3, switches 2 and 3 conduct.

van = 0 vbn = Vs/2 vcn = -Vs/2

120° CONDUCTION

Each switch conducts for 120°. Only two switches remain on at any instant of

time. The conduction sequence of switches is 61, 12, 23, 34, 45, 56, and 61. There are three

modes of operation in a half cycle and the equivalent circuits for wye connected load are

shown in Fig. 3.3.

During mode 1 for 0 ≤ ωt ≤ π/3, switches 1 and 6 conducts.

van = Vs/2 vbn = -Vs/2 vcn = 0

During mode 2 for π/3 ≤ ωt ≤ 2π/3, switches 1 and 2 conduct.

van = Vs/2 vbn = 0 vcn = -Vs/2

During mode 3 for 2π/3 ≤ ωt ≤ 3π/3, switches 2 and 3 conduct.

van = 0 vbn = Vs/2 vcn = -Vs/2

The a to b line voltage is vab =√3 van with a phase advance of 30°. There

is a delay of π/6 between the turning off switch 1 and turning on of switch 4. Thus there

should be no short circuit of the dc supply through one upper and lower switch. At any time,

two load terminals are connected to the dc supply and the third one remains open. The

potential of this open terminal will depend on the load characteristics and would be

unpredictable. Since one switch conducts for 120°, the switches are less utilized as compared

to that of 180° conduction for the load condition.

COMPARISON OF CSI , VSI AND ZSN

Current Source InverterVoltage Source Inverter

Impedance Source

Network

1. As inductor is used in the

dc link, the source

impedance is high. It acts as

a constant current source.

2. A CSI can capable of

withstanding short circuit

across any two

of its output terminals.

Hence momentary short

circuit on load and mis-firing

of switches are acceptable.

3. CSI is used in only buck

or boost operation of

inverter.

4. The main circuit cannot be

interchangeable.

5. It is affected by the EMI

noise.

As capacitor is used in the dc

link, it acts as a low

impedance voltage source.

A VSI cannot accept the

mis-firing of switches.

VSI is used in only a buck or

boost operation of inverter.

The main circuit cannot be

interchanged here also.

It is also affected by the EMI

noise.

FOUR-SWITCH THREE-PHASE BLDC MOTOR CONTROL BASED ON PHASE C CURRENT:Fig. 1 shows the configuration of a four-switch inverter for the three-phase BLDC motor.

Four-switch three-phase inverter.

Two common capacitors, instead of a pair of bridges, are used, and phase c is out of

control because it is connected to the midpoint of the series capacitors. A conventional PWM

scheme for the six-switch inverter is used for the four-switch inverter topology of the BLDC

motor drive, and its phase current waveforms are shown in Fig. 2. From Fig. 2, it is noted that

ic cannot hold at zero, and it causes an additional and unexpected current, resulting in current

distortion in phases a and b, and even in the breakdown of the system. The same problem is

inherited by the four-switch mode, and it causes the produced voltage vectors to be limited

and asymmetric, which were well known as “asymmetric voltage vectors.” The BLDC motor

needs quasi-square current waveforms, which are synchronized with the back-EMF to

generate constant output torque and have 120◦ conducting and 60◦ nonconducting regions.

Also, at every instant, only two phases are conductive, and the other phase is inactive.

Compared with the conventional six-switch three-phase inverter for the BLDC motor, the

whole working process of the BLDC motor is divided into six modes, as shown in Table I.

Phase c involves four modes, including modes 2, 3, 5, and 6. Only one switch should work in

the four modes. Taking mode 2 for instance, switch VS1 and diode D2 work to conduct

current in this mode. Mode 2 is divided into modes 21 and 22, as shown in Fig. 3. Switch

VS1 turns on, while −ic is less than current threshold I∗. As ic = −(ia + ib) and the current

flows through only two phases, ia increases and ib = 0. Then, ic is controlled.

Fig : Suboperating modes of mode 2. (a) Mode 21. (b) Mode 22.

Fig : Suboperating modes of mode 1. (a) Mode 11. (b) Mode 12. (c) Mode 13. (d) Mode 14.

Considering three balanced phase windings, assuming that the performance of power devices

of the inverter is ideal, and ignoring armature reaction, slot effect, and iron losses, the voltage

equations for a three-phase BLDC motor can be described as

where ux represents the terminal phase voltage with respect to power ground, ix is the

rectangular-shaped phase current, ex is the trapezoidal-shaped back-EMF, uN is the neutral-

point voltage with respect to power ground, and R and L are the resistance and equivalent

inductance of the phase windings, respectively.

where C represents the value of capacitors of C1 and C2 and U is the dc-link voltage.

Equation (3) can be rewritten as follows, in which uc is the only argument:

ua = 0 and ub = 0. The values of dic/dt(t = 0) in different suboperating modes are shown in

Table II.

According to Table II, the four suboperating modes have different rules to phase current. In

mode 11, ia and –ib rise quickly, and ic varies proportionally with the back-EMF of phase c.

In mode 12, ia and −ib drop quickly, and ic changes proportionally with the back-EMF of

phase c. Compared with modes 11 and 12, ic falls much quicker in mode 13 and rises much

quicker in mode 14. Identical conclusion can be drawn in the cases of Δ = 0 and Δ < 0. Thus,

mode 1 could be optimized by reasonable combination of four suboperating modes. First of

all, the equation ic = 0 must be satisfied to keep the system stable as follows. When ic

deviates seriously from zero, modes 13 and 14 work. When ic remains at zero, modes 11 and

12 work. Because ia and ib cannot be detected, a speed loop is used here to decide the duty of

PWM signals.

Pulse width modulation: Traditional solenoid driver electronics rely on linear control, which is the application of a

constant voltage across a resistance to produce an output current that is directly proportional

to the voltage. Feedback can be used to achieve an output that matches exactly the control

signal. However, this scheme dissipates a lot of power as heat, and it is therefore very

inefficient. A more efficient technique employs pulse width modulation (PWM) to produce

the constant current through the coil.

A PWM signal is not constant. Rather, the signal is on for part of its period, and off for the

rest. The duty cycle, D, refers to the percentage of the period for which the signal is on. The

duty cycle can be anywhere from 0, the signal is always off, to 1, where the signal is

constantly on. A 50% D.

A simple method to generate the PWM pulse train corresponding to a given signal is the

intersective PWM: the signal (here the red sinewave) is compared with a sawtooth waveform

(blue). When the latter is less than the former, the PWM signal (magenta) is in high state (1).

Otherwise it is in the low state (0).

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is

a modulation technique that controls the width of the pulse, formally the pulse duration,

based on modulator signal information. Although this modulation technique can be used to

encode information for transmission, its main use is to allow the control of the power

supplied to electrical devices, especially to inertial loads such as motors. In addition, PWM is

one of the two principal algorithms used in photovoltaic solar battery chargers,[1] the other

being MPPT.

The average value of voltage (and current) fed to the load is controlled by turning the switch

between supply and load on and off at a fast pace. The longer the switch is on compared to

the off periods, the higher the power supplied to the load.

The PWM switching frequency has to be much faster than what would affect the load, which

is to say the device that uses the power. Typically switching has to be done several times a

minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of

kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and

computer power supplies.

The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of

time; a low duty cycle corresponds to low power, because the power is off for most of the

time. Duty cycle is expressed in percent, 100% being fully on.

The main advantage of PWM is that power loss in the switching devices is very low. When a

switch is off there is practically no current, and when it is on, there is almost no voltage drop

across the switch. Power loss, being the product of voltage and current, is thus in both cases

close to zero. PWM also works well with digital controls, which, because of their on/off

nature, can easily set the needed duty cycle.

PWM has also been used in certain communication systems where its duty cycle has been

used to convey information over a communications channel.

MATLAB\SIMULINK

INTRODUCTION TO MATLAB:

MATLAB is a software package for computation in engineering, science, and applied

mathematics.

The harmonic content in the generator current decreases its lifespan and increases the power

loss due to heating .In this project, an alternative multi-input rectifier structure is proposed for

hybrid wind/solar energy systems. The proposed design is a fusion of the Cuk and SEPIC

converters.

It offers a powerful programming language, excellent graphics, and a wide range of expert

knowledge. MATLAB is published by and a trademark of The MathWorks, Inc.

The focus in MATLAB is on computation, not mathematics: Symbolic expressions

and manipulations are not possible (except through the optional Symbolic Toolbox, a clever

interface to maple). All results are not only numerical but inexact, thanks to the rounding

errors inherent in computer arithmetic. The limitation to numerical computation can be seen

as a drawback, but it’s a source of strength too: MATLAB is much preferred to Maple,

Mathematical, and the like when it comes to numerics.

On the other hand, compared to other numerically oriented languages like C++ and

FORTRAN, MATLAB is much easier to use and comes with a huge standard library.1 the

unfavorable comparison here is a gap in execution speed. This gap is not always as dramatic

as popular lore has it, and it can often be narrowed or closed with good MATLAB

programming (see section 6). Moreover, one can link other codes into MATLAB, or vice

versa, and MATLAB now optionally supports parallel computing. Still, MATLAB is usually

not the tool of choice for maximum-performance Computing.

The MATLAB niche is numerical computation on workstations for non-experts in

computation. This is a huge niche—one way to tell is to look at the number of MATLAB-

related books on mathworks.com. Even for supercomputer users, MATLAB can be a

valuable environment in which to explore and fine-tune algorithms before more laborious

coding in another language. Most successful computing languages and environments acquire

a distinctive character or culture.

In MATLAB, that culture contains several elements: an experimental and graphical bias,

resulting from the interactive environment and compression of the write-compile-link-

execute analyze cycle; an emphasis on syntax that is compact and friendly to the interactive

mode, rather than tightly constrained and verbose; a kitchen-sink mentality for providing

functionality; and a high degree of openness and transparency (though not to the extent of

being open source software).

The fifty-cent tour:

When you start MATLAB, you get a multipaneled desktop. The layout and behavior

of the desktop and its components are highly customizable (and may in fact already be

customized for your site).

The component that is the heart of MATLAB is called the Command Window,

located on the 1Here and elsewhere I am thinking of the “old FORTRAN,” FORTRAN 77.

This is not a commentary on the usefulness of FORTRAN 90 but on my ignorance of it.

INTRODUCTION

Right by default. Here you can give MATLAB commands typed at the prompt, >>.

Unlike FORTRAN and other compiled computer languages, MATLAB is an interpreted

environment—you give a command, and MATLAB tries to execute it right away before

asking for another.

At the top left you can see the Current Directory. In general MATLAB is aware

only of files in the current directory (folder) and on its path, which can be customized.

Commands for working with the directory and path include cd, what, addpath, and editpath

(or you can choose “File/Set path. . . ” from the menus). You can add files to a directory on

the path and thereby add commands to MATLAB; we will return to this subject in section 3.

Next to the Current Directory tab is the Workspace tab. The workspace shows you what

variable names are currently defined and some information about their contents. (At start-up

it is, naturally, empty.) This represents another break from compiled environments: variables

created in the workspace persist for you to examine and modify, even after code execution

stops. Below the CommandWindow/Workspace window is the Command History window.

As you enter commands, they are recorded here. This record persists across different

MATLAB sessions, and commands or blocks of commands can be copied from here or saved

to files.

As you explore MATLAB, you will soon encounter some toolboxes. These are

individually packaged sets of capabilities that provide in-depth expertise on particular subject

areas. There is no need to load them explicitly—once installed, they are always available

transparently. You may also encounter Simulink, which is a semi-independent graphical

control-engineering package not covered in this document.

Graphical versus command-line usage:-

MATLAB was originally entirely a command-line environment, and it retains that

orientation. But it is now possible to access a great deal of the functionality from graphical

interfaces—menus, buttons, and so on. These interfaces are especially useful to beginners,

because they lay out the available choices clearly.2 As a rule, graphical interfaces can be

more natural for certain types of interactive work, such as annotating a graph or debugging a

program, whereas typed commands remain better for complex, precise, repeated, or

reproducible tasks. One does not always need to make a choice, though; for instance, it is

possible to save a figure’s styles as a template that can be used with different data by pointing

and clicking. Moreover, you can package code you want to distribute with your own

graphical interface, one that itself may be designed with a combination of graphical and

command-oriented tools. In the end, an advanced MATLAB user should be able to exploit

both modes of work to be productive.

That said, the focus of this document is on typed commands. In many (most?) cases

these have graphical interface equivalents, even if I don’t explicitly point them out.

In particular, feel free to right-click (on Control-click on a Mac) on various objects to see

what you might be able to do to them.

WHAT IS SIMULINK

Simulink (Simulation and Link) is an extension of MATLAB by Math works Inc. It

works with MATLAB to offer modeling, simulating, and analyzing of dynamical systems

under a graphical user interface (GUI) environment. The construction of a model is simplified

with click-and-drag mouse operations. Simulink includes a comprehensive block library of

toolboxes for both linear and nonlinear analyses. Models are hierarchical, which allow using

both top-down and bottom-up approaches. As Simulink is an integral part of MATLAB, it is

easy to switch back and forth during the analysis process and thus, the user may take full

advantage of features offered in both environments. This tutorial presents the basic features

of Simulink and is focused on control systems as it has been written for students in my

control systems.

Getting Started:

To start a Simulink session, you'd need to bring up Mat lab program first. From Mat lab

command window, enter:

>> simulink

Alternately, you may click on the Simulink icon located on the toolbar as shown

To see the content of the block set, click on the "+" sign at the beginning of each toolbox.

To start a model click on the NEW FILE ICON as shown in the screenshot above.

Alternately, you may use keystrokes CTRL+N.

A new window will appear on the screen. You will be constructing your model in this

window. Also in this window the constructed model is simulated. A screenshot of a typical

working (model) window that looks like one shown below:

To become familiarized with the structure and the environment of Simulink, you are

encouraged to explore the toolboxes and scan their contents.

You may not know what they are all about but perhaps you could catch on the

organization of these toolboxes according to the category. For instant, you may see Control

System Toolbox to consist of the Linear Time Invariant (LTI) system library and the

MATLAB functions can be found under Function and Tables of the Simulink main toolbox.

A good way to learn Simulink (or any computer program in general) is to practice and

explore. Making mistakes is a part of the learning curve. So, fear not, you should be.

A simple model is used here to introduce some basic features of Simulink. Please

follow the steps below to construct a simple model.

STEP 1: CREATING BLOCKS.:

From BLOCK SET CATEGORIES section of the SIMULINK LIBRARY BROWSER

window, click on the "+" sign next to the Simulink group to expand the tree and select (click

on) Sources.

A set of blocks will appear in the BLOCKSET group. Click on the Sine Wave

blockand drag it to the workspace window (also known as model window)

I am going to save this model under the filename: "simexample1". To save a model,

you may click on the floppy diskette icon. Or from FILE menu, select Save or CTRL+S. All

Simulink model file will have an extension ".mdl". Simulink recognizes file with .mdl

extension as a simulation model (similar to how MATLAB recognizes files with the

extension .m as an MFile).

Continue to build your model by adding more components (or blocks) to your model

window. We'll continue to add a Scope from Sinks library, an Integrator block from

Continuous library, and a Mux block from Signal Routing library.

NOTE: If you wish to locate a block knowing its name, you may enter the name in the

SEARCH WINDOW (at Find prompt) and Simulink will bring up the specified block.

To move the blocks around, simply click on it and drag it to a desired location. Once

all the blocks are dragged over to the work space should consist of the following components:

You may remove (delete) a block by simply clicking on it once to turn on the "select

mode" (with four corner boxes) and use the DEL key or keys combination CTRL-X.

STEP 2: MAKING CONNECTIONS:

To establish connections between the blocks, move the cursor to the output port represented

by ">" sign on the block. Once placed at a port, the cursor will turn into a cross "+" enabling

you to make connection between blocks.

To make a connection: left-click while holding down the control key (on your keyboard) and

drag from source port to a destination port.

The connected model is shown below.

A sine signal is generated by the Sine Wave block (a source) and is displayed by the

scope. The integrated sine signal is sent to scope for display along with the original signal

from the source via the Mux, whose function is to multiplex signals in form of scalar, vector,

or matrix into a bus.

STEP 3: RUNNING SIMULATION:

You now can run the simulation of the simple system above by clicking on the play

button (alternatively, you may use key sequence CTRL+T, or choose Start submenu under

Simulation menu).

Double click on the Scope block to display of the scope.

INTRODUCTION:

SimPowerSystems and other products of the Physical Modelling product family work

together with Simulink® to model electrical, mechanical, and control systems.

SimPowerSystems operates in the Simulink environment. Therefore, before starting

this user’s guide, you should be familiar with Simulink. For help with Simulink, see the

Simulink documentation. Or, if you apply Simulink to signal processing and communications

tasks (as opposed to control system design tasks), see the Signal Processing Block set

documentation.

The Role of Simulation in Design:

Electrical power systems are combinations of electrical circuits and electromechanical

devices like motors and generators. Engineers working in this discipline are constantly

improving the performance of the systems. Requirements for drastically increased efficiency

have forced power system designers to use power electronic devices and sophisticated control

system concepts that tax traditional analysis tools and techniques. Further complicating the

analyst’s role is the fact that the system is often so nonlinear that the only way to understand

it is through simulation.

Land-based power generation from hydroelectric, steam, or other devices is not the

only use of power systems. A common attribute of these systems is their use of power

electronics and control systems to achieve their performance objectives.

WHAT IS SIMPOWERSYSTEMS?

Sim Power Systems is a modern design tool that allows scientists and engineers to

rapidly and easily build models that simulate power systems.

SimPowerSystems uses the Simulink environment, allowing you to build a model using

simple click and drag procedures. Not only can you draw the circuit topology rapidly, but

your analysis of the circuit can include its interactions with mechanical, thermal, control, and

other disciplines. This is possible because all the electrical parts of the simulation interact

with the extensive Simulink modelling library. Since Simulink uses MATLAB® as its

computational engine, designers can also use MATLAB toolboxes and Simulink block sets.

SimPowerSystems and Sim Mechanics share a special

Physical Modelling block and connection line interface.

SimPowerSystems Libraries

You can rapidly put SimPowerSystems to work. The libraries contain models of

typical power equipment such as transformers, lines, machines, and power electronics. These

models are proven ones coming from textbooks, and their validity is based on the experience

of the Power Systems Testing and Simulation Laboratory of Hydro-Québec, a large North

American utility located in Canada, and also on the experience of École de Technologies

Superior and University Laval.

The capabilities of SimPowerSystems for modelling a typical electrical system are

illustrated in demonstration files. And for users who want to refresh their knowledge of

power system theory, there are also self-learning case studies.

The SimPowerSystems main library, power lib, organizes its blocks into libraries

according to their behaviour. The power lib library window displays the block library icons

and names. Double-click a library icon to open the library and access the blocks. The main

SimPowerSystems power lib library window also contains the Powergui block that opens a

graphical user interface for the steady-state analysis of electrical circuits.

Nonlinear Simulink Blocks for SimPowerSystems Models:

The nonlinear Simulink blocks of the power lib library are stored in a special\block

library named powerlib_models. These masked Simulink models are used by

SimPowerSystems to build the equivalent Simulink model of your circuit. See Chapter 3,

“Improving Simulation Performance” for a description of the powerlib_models library

You must have the following products installed to use SimPowerSystems:

• MATLAB

• Simulink

CONCLUSION

An advanced double-loop control strategy based on the fourswitch topology for the

BLDC motor drive has been proposed. A single-neuron adaptive PI controller is used by the

outer loop to develop the performance of speed control. The algorithm is easy to implement

on the microcontroller, and the cost of the whole system is lowered because only one current

sensor is required. Finally, qualified performance was verified by simulation and

experimental results under different work conditions, at different speeds, and under different

loads. It should be noted that reducing the quantity of current sensor surely brings some

negative impacts to the control system, such as maximum current limitation in certain modes.

Additionally, the program tends to be complicated because a special algorithm is necessary as

compensation on the reduction of current sensor. Consequently, the software overhead is

increased. For further research, how to improve system reliability and optimize software

design should be the key point to implement the proposed strategy in industrial application.

REFERENCES

[1] K.-W. Lee, D.-K. Kim, B.-T. Kim, and B.-I. Kwon, “A novel starting method of the

surface permanent-magnet BLDC motors without position sensor for reciprocating

compressor,” IEEE Trans. Ind. Appl., vol. 44, no. 1, pp. 85–92, Jan./Feb. 2008.

[2] D.-K. Kim, K.-W. Lee, and B.-I. Kwon, “Commutation torque ripple reduction in a

position sensorless brushless DC motor drive,” IEEE Trans. Power Electron., vol. 21, no. 6,

pp. 1762–1768, Nov. 2006.

[3] F. Rodriguez and A. Emadi, “A novel digital control technique for brushless DC motor

drives,” IEEE Trans. Ind. Electron., vol. 54, no. 5, pp. 2365–2373, Oct. 2007.

[4] C.-W. Hung, C.-T. Lin, C.-W. Liu, and J.-Y. Yen, “A variable-sampling controller for

brushless DC motor drives with low-resolution position sensors,” IEEE Trans. Ind. Electron.,

vol. 54, no. 5, pp. 2846–2852, Oct. 2007.

[5] S. Rajagopalan, J. M. Aller, J. A. Restrepo, T. G. Habetler, and R. G. Harley, “Analytic-

wavelet-ridge-based detection of dynamic eccentricity in brushless direct current (BLDC)

motors functioning under operating conditions,” IEEE Trans. Ind. Electron., vol. 54, no. 3,

pp. 1410–1419, Jun. 2007.

[6] G. J. Su and J. W. Mckeever, “Low-cost sensorless control of brushless DC motors with

improved speed range,” IEEE Trans. Power Electron., vol. 19, no. 2, pp. 296–302, Mar.

2004.

[7] C. T. Pan and E. Fang, “A phase-locked-loop-assisted internal model adjustable-speed

controller for BLDC motors,” IEEE Trans. Ind. Electron., vol. 55, no. 9, pp. 3415–3425, Sep.

2008.

[8] L. Parsa and H. Lei, “Interior permanent magnet motors with reduced torque pulsation,”

IEEE Trans. Ind. Electron., vol. 55, no. 2, pp. 602–609, Feb. 2008.

[9] D.-H. Jung and I.-J. Ha, “Low-cost sensorless control of brushless DC motors using a

frequency-independent phase shifter,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 744–

752, Jul. 2000.

[10] J.-H. Lee, S.-C. Ahn, and D.-S. Hyun, “A BLDCM drive with trapezoidal back EMF

using four-switch three phase inverter,” in Conf. Rec. IEEE IAS Annu. Meeting, 2000, vol. 3,

pp. 1705–1709