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JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 772
IMPLEMENTATION OF LOW COST SWITCHED RELUCTANCE
MOTOR DRIVE USING RT-LAB
Jignesh Makwana1, Ambarisha Mishra
2, Pramod agarwal
3, S.P Srivastava
4
1Research Scholar, Electrical Department IIT Roorkee, Uttrakhand, India, [email protected]
2Research Scholar, Electrical Department IIT Roorkee, Uttrakhand, India,[email protected]
3Professor & Head, Electrical Department, IIT Roorkee, Uttrakhand, India, [email protected]
4Professor, Electrical Department, IIT Roorkee, Uttrakhand, India, [email protected]
Abstract This paper demonstrates the implementation of low cost switched reluctance motor (SRM) drive and application of RT lab as real time
hardware-in-loop (HIL) controller. Split DC converter and positioning sensing arrangement is developed for 500W 8/6 pole SRM.
Control part is implemented using Opal RT Lab technology. Application and optimistic characteristics of proposed low cost drive are
described. Experimental results of performance and efficiency for proposed SRM drive are presented which shows very low cost
versus performance ratio compare to induction motor and permanent magnet motor drive.
Index Term— Converter, reluctance motor, RT Lab, electric drives
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1. INTRODUCTION
The Switched Reluctance Motor (SRM) drive promises an
impressive set of benefits over its competition includes high
efficiency over a wide speed range and partial loads, high-
speed capability, easy cooling with heat source only in the
stator, ruggedness for high-temperature or vibration
environments, and relatively simple mechanical construction.
But sheer numbers of induction and brushless permanent
magnet (PM) motors at work in industrial and commercial
applications testify to their well-established manufacturing
infrastructure and user acceptance. This has limited wide use of
SRM - a technology that offers a practical alternative for
various demanding applications. Perhaps today‟s growing
demand for energy efficiency motivates the users and
companies to look at SRM as an alternative comes from
concern about magnet material cost in PM synchronous motors
and a desire to move away from induction motors for overall
efficiency and system cost.
Current resurgence in demand is observed for SRM drive with
a variety of platforms intended for industry, includes high
speed applications such as screw compressors, blowers, and
high-speed pumps and low-speed, high-torque areas
(conveyors, feeders).
SRMs can‟t run direct-on-line, thus require an associated power
converter (drive) to complete an SRM drive system. SRM
power converter topology differs from that of conventional ac
drives in the arrangement of power switch and fly-back diode
circuits. For smaller drives, use of power modules is a cost-
effective design route, but off-the-shelf modules are not
available for SRM as for other motor technologies. As more
applications become variable speed, the SRM option, whose
cost is competitive with an equivalent inverter-fed induction
motor, becomes viable across a growing range of applications.
This paper presents the development of low cost SRM drive
which includes development of split DC controller and open
loop controller with position sensing arrangement. Fixed
frequency PWM controller is developed and implemented using
Opal RT Lab.
A single phase induction motor achieved worldwide acceptance
for general purpose motor drive in domestics and industrial
application because its feature to run direct on AC lines without
having costly converters. Beside large number of converter and
control modules are readily available today for induction motor
and brushless DC motors. While there are no such a converter
and controller modules are available for the SRM which
discourage the usage of the SRM technology which offers a
high performance and efficiency. Low cost SRM drive
presented in this paper is to show the performance of SRM to
run directly on AC mains supply with low cost but reliable
converter and position sensing arrangement without starting
hesitation.
JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 773
2. SWITCHED RELUCTANCE MOTOR
Switched Reluctance Motor is a doubly salient and singly
excited motor. Unlike conventional AC or DC motor which
required either two winding or one winding and one permanent
magnet to produce the torque SRM have only winding in the
stator. The rotor has no windings, magnets or cage windings
but is built up from a stack of salient pole laminations. Torque
is produced due to force of attraction between magnetic field of
stator winding and magnetic material of rotor. SR machines
offer a wide variety of aspect ratios and salient pole topologies.
Each application is likely to a better suited to a specific SR
topology. Fig. 1 shows the geometry of four phase SRM having
8 stator pole and 6 rotor pole which denoted by 8/6 SRM in
general. Generally, selection of higher number of phase and
pole reduces the torque ripple, but it required more switching
devices. Some important old references of the SRM are [1]-[5].
Fig-1: Geometry of four phase 8/6 SRM
When current is passed through the phase winding the rotor tends
to align with the stator poles and it produces a torque that tends
to move the rotor to a minimum reluctance position. The
direction of torque generated is a function of rotor position with
respect to energized phase, and is independent of direction of
current flow through phase winding. Continues torque can be
produced by intelligently synchronizing each phase‟s excitation
with the rotor position. An equivalent expression of torque is,
constanti
cwT
(1)
or
constant
f
i
wT
(2)
Where cw and fw are co-energy and stored field energy
respectively. Mathematically,
diwc (3)
and diw f (4)
Fig. 2 shows the typical magnetic characteristics of the SRM
which represent the number of magnetic curves relates flux
linkage and phase current for unaligned to aligned position of
rotor. Its shows the two saturation mainly due to pole corner
saturation near unaligned position at lower current and due to
saturation of yoke near aligned position at higher current. If
magnetic saturation is neglected then the relation between flux-
linkage and current at an instantaneous position θ is a straight
line whose slope represents an instantaneous inductance L.
Thus Ψ = Li and,
2
2
1Liww fc (5)
Therefore torque d
dLiT 2
2
1 N-m (6)
Fig.-2: Typical flux linkage characteristics of SRM
Variation of idealized phase inductance is shown in Fig. 3. To
develop continuous torque in positive direction it is required to
energize the phase only during their respective rising inductance
period as shown in Fig. 3 which explains the necessity of
position sensor to command the phase current.
Different converter topology may be use to energize the phase of
the SRM but most common is two switched per phase
asymmetric converter shown in Fig. 4. There are number of
converter topology is published in the literature to reduce the
number of switches per phase and reduce the cost of converter
and firing circuit [6]-[11].
JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 774
Fig-3: Inductance profile of four phase SRM
Fig-4: Asymmetric bridge converter
There are several methods to control the torque-speed and the
position of the SRM. Hysteresis current control and PWM
control are two low cost and simplest methods for easy
implementation. In hysteresis control phase switch turned off and
on according whether the current flowing through the winding is
greater or less than the reference current, while in PWM control
fixed frequency variable duty cycle scheme can be employed to
regulate the current as shown in Fig 5.
3. POSITION SENSING ARRANGEMENT AND
PWM CONTROL STRATEGY
There are so many options for choosing position sensing
scheme for the SRM drive including absolute or incremental
encoder, Hall Effect sensors or even many sensorless methods
have been developed [12]-[16]. Low cost high speed position
sensing arrangement with control scheme is shows in Fig 6.
Toothed disk having teeth symmetrical to the rotor pole is
attached on shaft and is in perfect synchronization with the
rotor pole. Disk cuts the light emitted by the source which
generates two digital pulses to decide commutation period of
the phase. By combining high speed TTL logics individual
commutation pulse can be generated for all phases which mixed
with the PWM signal to achieve current control as shown in Fig
6. For easy and flexibility Opal RT Lab is used to implement
controller part.
Fig-5: PWM and hysteresis current control
Fig. 7 shows the commutation pulse C4 and C3 which decide the
conduction period of phase 4 and phase 3 respectively while
conduction period of phase 2 and phase 1 is decided by
commutation pulse C2 and C1 which are logically invert of C4
and C3 respectively. Fig. 8 shows that commutation pulse is
logically mixed with the fixed frequency PWM pulse and
generated gate pulse are applied to the isolated MOSFET driver
circuit shown in Fig. 9 to achieve the current and speed control of
the SRM.
Fig-6: Position sensing arrangement and control logic
JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 775
Fig-7: Commutation pulse to decide on-off instant of phase
Fig-8: Gate pulse; Commutation pulse combined with PWM pulse
4. SPLIT DC CONVERTER
Unlike conventional AC and DC motor SRM cannot run with
direct AC or DC supply. SRM require converter circuit to guide
the current in appropriate phase with rotor position sensing
arrangement. Fig. 9 shows split DC one switched per phase
converter circuit for SRM. Simple diode bride with filter is
added to AC to DC conversion. Here main aim is to obtain
performance characteristics of 0.5KW SRM with 230 V AC
mains. Assume that there is no magnetic saturation that means
inductance is unaffected by the current. Also neglecting the
mutual inductance for the simplicity voltage equation of the one
phase is,
d
diR
dt
diRV
phmphph
phphphph (7)
Where phV is the phase voltage equal to 2dcV and
rmsdc VV 2
d
dLi
dt
diLiRV
phphm
phphphphph
)()( (8)
One switched and one diode is associated with each phases. At
any instant two phase are ON to maximize the torque and
which also minimize the torque ripple. Alternative phases (1,3
and 2,4) are never going to conduct simultaneously. It also
helps in balancing the capacitor C1 and C2. Fig. 10 shows the
mode of operation of the converter. Mode 1 is phase energize
mode and mode 2 is regenerating mode. When M1 is ON
voltage across phase is Vdc/2 and current is circulating through
C1, M1 and Phase 1. At the instant of turning OFF M1; diode
D1 comes in conduction and current circulate through the D1,
Phase 1 and C2.
Fig-9: One switched per phase split DC converter with AC
mains
Mode 1 Mode 2
Fig-10: Mode of operation of split DC converter
5. OPAL RT-LAB TECHNOLOGY
Real-time simulation of SRM drives on a CPU-based real-time
simulator can produce accurate results, but can also have the
undesirable effect of causing current overshoots because of
model latency. To remedy this problem, an FPGA
implementation is desirable because it offers a very low
calculation time and I/O latency.
JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 776
RT-LAB, from Opal-RT Technologies, is a real-time
simulation platform that enables real time and HIL (hardware in
loop) simulation of controllers, electric plants or both, through
automatic code generation methods. The entire process occurs
without the need for handwritten „C‟ code, enabling very rapid
deployment of prototyped controllers or HIL-simulated plants.
The process is notably very efficient when applied to I/O code
because RT-LAB provides a set of simulink blocks that
automatically configure common I/O functions, like analog
input/outputs and time-stamping capable digital I/Os, with a 10
nanosecond resolution. Special interpolating models use this
timing information to greatly increase simulation accuracy [17].
RT-LAB simulator is equipped with a user-programmable
FPGA card. The FPGA card can be programmed with the
Xilinx system generator blockset for simulink enabling
implementation of complex sensor models like resolvers,
Resolver-To-Digital and FM resolvers or even complex motor
drives [18], [19].
RT-Lab is used as real time hardware-in-loop controller in this
implementation for easy and flexibility.
Table I summarizes the characteristics of FPGA board used in
this paper and Table II summarize the input output card used
for analog output of phase current and gate pulse.
Table-1: Reconfigurable FPGA Boards
Table-2: Input output configuration
6. HARDWARE IN LOOP CONTROLLER
As shown in Fig. 6 two rotor position signals are applied to the
analog input card of RT- Lab. Here logic operation is
performed to mix the fixed frequency PWM control signal to
control the current and speed of the motor. From analog output
card four gate pulses are taken out and supplied to the
MOSFET driver circuit as shown in Fig. 6. Duty cycle of the
PWM pulse can be controlled in real time to control the motor
speed. User interface is provided to control and record/observe
the motor speed in real time.
RT Lab allows to model a subsystem in MATLAB simulink
environment with some own rules and perform automatic code
generation and transfer of the simulink model for the FPGA
implementation. Fig. 11 shows the subsystem modelled for the
present controller. Subsystem named “SM_speed_control”
contain the model of the actual controller while subsystem
named “SC_speed_control” represent the model for user
interface for online parameter control and monitor. Fig. 12
shows the modelling of controller and Fig. 13 shows user
interface panel available for HIL speed control and monitor.
Fig-11: Controller subsystem
Fig-12: Subsystem model of controller
Fig-13: User interface available for real time control and
monitor
JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 777
7. PERFORMANCE CHARACTERISTICS OF SRM
DRIVE
Fig. 14 to Fig. 22 shows the different performance plots for the
projected SRM drive include speed-torque characteristics,
efficiency, power-factor, no-load input power, noise analysis
and vibration details. Fig.23 shows the commutation pulse with
the phase current at no-load speed of 1100 rpm. Fig. 24 shows
the phase voltage and phase current waveform for the motor
speed of 880 rpm and load torque of 4 kg-cm. Fig. 25 shows the
experimental setup for the proposed SRM drive.
Fig-14: Speed torque characteristics
Fig-15: Efficiency versus speed
Fig-16: Efficiency versus load
Fig-17: Steady state speed versus PWM duty cycle
Fig-18: No-load current versus speed
Fig-19: No load power input versus speed
Fig-20: No load power factor versus speed
JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 778
Fig-21: Noise performance versus speed
Fig-22: Vibration performance versus speed
Fig-23: Commutation pulse and phase current at no load speed
of 1100 rpm
Fig-24: Phase voltage and current at 880 rpm and load of 4 Kg-cm
Fig. 25 Experimental setup
8. CONCLUSION
Projected scheme shows impressive advantages over
conventional motor drive regard in motor, converter and control
electronics. Motor offer maintenance free robust performance
with low manufacturing cost and low material cost. Rotor
inertia is very low because of salient pole type construction
lead to low weight and small size compare to conventional AC
and DC motor. Stator is simple to wind; end turns are short and
robust and have no phase-phase crossovers support low cast
easy manufacturing steps and also easy to repair. In most
applications the bulk of the losses appear on the stator which is
relatively easier to cool. Because there is no any costly
permanent magnet on rotor permissible rotor temperature is
high compare to permanent magnet motor in cost effective way.
Motor provide higher torque compare to commutator motor and
induction motor at all speed. Furthermore starting torque can be
very high without the problem of excessive inrush currents and
extremely high speed is possible. Motor is fully resistant to
environment contras to the permanent magnet motor.
SRM Controllers add to the benefits, since they do not need a
bipolar (reversed) device because torque is independent of
direction of current. One switched per phase MOSFET
controller is cost effective compare to inverter particularly for
brushless permanent magnet machines. It offers fault tolerant
operation with one or more faulty phase or even with shorted
MOSFET. It is found experimentally that with one phase open
motor is running with 80% of its full capacity and with one
MOSFET shorted motor is running with less efficiency and
JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 779
capacity because one phase is always remains on irrelative of
rotor position which generate negative torque and required
more starting current. In addition projected converter allows
two-phase excitation at a time which reduces the ripple in the
torque.
Furthermore digital controller and MOSFET driver add to the
benefit of low cost in simplest way. MOSFET driver circuit
required only three isolated power supply while mostly used
asymmetric bridge converter of SRM requires five. Low
frequency PWM speed controller offers benefits over hysteresis
controller that it does not required a single current sensor while
hysteresis controller requires four current sensors for reference
current and four individual controllers. Low frequency PWM
control reduces the switching losses and acoustic noise thus
increases the performance and efficiency in simple and cost
effective way. Body mounted infrared positioning scheme add
the benefits of cost with compare to costly encoders with
reliable performance with CMOS and TTL logics for very high
speed performance.
Result dictates that the cost versus performance ratio of the
proposed SRM drive is quite low. It‟s observed that proposed
SRM drive gives rugged performance with 230V AC mains
supply without starting hesitation.
Use of RT-Lab is much time saving in developing a control
model for the practical electric motor drives and offer great
easy and flexibility.
Counter part of the proposed drives is the level of acoustic
noise production which prevents the use of SRM for the
domestic application like fan and other continuous duty
application.
APPENDIX
Motor Specifications:
Duty Type continuous
Motor Type 8/6 four phase SRM
Output power 0.5 KW
Phase voltage 150 V
Number of turn per phase 310 turns per phase,
Resistance per phase 4.5 ohm per phase,
Stator outer diameter 90.8mm
Rotor outer diameter 48.4mm
Electronics specifications:
Power switch: IRFP450A
Diode: MUR1560
PWM frequency 1.66 KHz
ACKNOWLEDGMENT
Author is thankful to the electric department of Indian Institute
of Technology Roorkee for providing required equipments for
experimental setup.
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JIGNESH MAKWANA* et al. ISSN: 2250–3676
[IJESAT] INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE & ADVANCED TECHNOLOGY Volume-2, Issue-4, 772 – 780
IJESAT | Jul-Aug 2012
Available online @ http://www.ijesat.org 780
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BIOGRAPHIES
Jignesh Makwana received the B.E and
M.E degrees in Electrical Engineering from
the Birla Vishvakarma Mahavidhyalaya,
v.v.nagar, gujarat, India, and L.D.
Engineering College, ahemadabad, gujarat,
India in 2004 and 2006 respectively. He was
a lecturer with the C.U. Shah College of
Engineering and Technology from 2006 to
2008 and joined the R.K College of Engineering and
Technology in 2008. Currently he is a research scholar in
Electrical Department of Indian Institute of Technology,
Roorkee, India. His fields of interest are electric machines,
drives and power electronics.
Ambarisha Mishra was born in 1986. He
received B.Tech. (Electrical) from Uttar
Pradesh.Technical University Lucknow, India,
in 2007 and M.Tech.(Power Electronics &
Drives) from National Institute of Technology
Kurukshetra, India, in 2009. Currently he is
pursuing PhD from in Electrical Engineering Department,
Indian Institute of Technology Roorkee, India. His field of
interest includes electric drives and power electronics.
Pramod Agarwal received the B.E., M.E.,
and Ph.D degrees in Electrical Engineering
from the University of Roorkee, India, in
1983, 1985 and 1995, respectively. He joined
the erstwhile University of Roorkee, India in
1985 as Lecturer. He was a Postdoctoral
Fellow with the Ecole de technologie superior, University of
Quebec, Montreal, Canada. He is currently a Professor with the
Department of Electrical Engineering, Indian Institute of
Technology, Roorkee, India. He has developed a number of
educational units for laboratory experimentation. His fields of
specialization are electrical machines, power electronics,
microprocessor and microcomputer controlled ac/dc drives,
active power filters, multi-level inverters and high power factor
converters.
S. P. Srivastava received the bachelor's
and master's degrees in Electrical
Technology from I.T. Banarus Hindu
University, Varanasi, India in 1976, 1979
respectively and the Ph. D degree in
Electrical Engineering from the University
of Roorkee, India in 1983. Currently he is
with Indian Institute of Technology (IIT) Roorkee, India, where
he is a Professor in the Department of Electrical Engineering.
His research interests include power apparatus and electric
drives.