Closed Loop Speed Control of 6/4 Pole Switched Reluctance

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105
Dr. RAMA RAO P.V.V, Ms. D. SAILAJA, Mr. P. DEVIKIRAN and Mr. A. PHANI KUMAR
Closed Loop Speed Control of 6/4 Pole Switched
Reluctance Motor
Dr. RAMA RAO
P.V.V.
Professor & Head,
EEE Dept.
Shri Vishnu
Engineering College
for Women,
Bhimavaram, India
[email protected]
.com
Ms. D. SAILAJA
M. Tech (Power
Electronics) Student,
EEE Dept.
Shri Vishnu
Engineering College
for Women,
Bhimavaram, India
[email protected]
l.com
Abstract: The Switched reluctance Motor (SRM) is a member
of the Electric Machines Family. It’s simple structure and
ruggedness and capability make it more attractive for
Industrial applications. These machines have inherent high
torque ripple, acoustic noise and difficulty to control. In this
work, modeling, simulation and analysis of Switched
Reluctance motor has been done. This Switched reluctance
motor controlling is simulated in MATLAB/SIMULINK. PI
Control and voltage control have been implemented. The result
obtained from simulation have been presented in the paper.
Keywords: Switched Reluctance Motor (SRM), Torque,
Magnetic field, Segmented SRM, PI Control, Hysteresis
Control and Voltage Control.
I. INTRODUCTION
The electrical drives play an important role on the
productivity to any industry. The requirement of drives
depends upon the available mains and load characteristics.
Brushless variable speed drive using SRM has become
popular relative to other drives and represents an economical
alternative to PM brushless motors in many applications. In
last few years the SRM have gained increasing attention
since they offer the possibility of electric drives which are
mechanically and electrically more rugged than those built
up around the conventional AC and DC motors. In case of
SRM drive, the technical superiority of the AC drive is
obtained or even enhanced at a very low cost. This is possible
due to the simple motor construction and the requirement of a
simple unipolar power modulator for controlling the speed.
In order to get performance oriented Drive, the accurate
modelling of a Motor is to be done [1]. The performance of
machine can be checked with the help of Mat lab / Simulink.
This helps to design the Controller for the motor. Modelling
can be done with the help of mathematical equations.
In Switched Reluctance Motor the torque is developed
because of the tendency of the magnetic circuit to adopt the
configuration of minimum reluctance i.e. the rotor moves in
line with the stator pole thus maximizing the inductance of
the excited coil. The magnetic behaviour of SRM is highly
Mr. P. DEVIKIRAN
Asst. Professor, EEE
Dept.
Shri Vishnu
Engineering College
for Women,
Bhimavaram, India
[email protected]
in
Mr. A. PHANI
KUMAR
Asst. Professor, EEE
Dept.
Shri Vishnu
Engineering College
for Women,
Bhimavaram, India
[email protected]
.in
nonlinear [2] [5]. But by assuming an idealistic linear
magnetic model, the behaviour pattern of the SRM can be
adjusted with ease without serious loss of integrity from the
actual behaviour pattern.
The physical appearance of a Switched Reluctance motor is
similar to that of other rotating motors (AC and DC)
Induction Motor, DC motor etc. The construction of 6/4 (6
stator poles, 4 rotor poles) poles SRM has doubly salient
construction. Usually the number of stator and rotor poles is
even [3]. The windings of Switched Reluctance Motor are
simpler than those of other types of motor. There is winding
only on stator poles, simply wound on it and no winding on
rotor poles. The winding of opposite poles is connected in
series or in parallel forming no of phases exactly half of the
number of stator poles. Therefore excitation of single phase
excites two stator poles. The rotor has simple laminated
salient pole structure without winding [4]. This is the
advantage of this motor as it reduces copper loss in rotor
winding. The stampings are made preferably of silicon steel,
especially in higher efficiency applications. For aerospace
application the rotor is operating at very high speed, for that
cobalt, iron and variants are used. The air gap is kept as
minimum as possible, especially 0.1 to 0.3 mm. The rotor
and stator pole arcs should be approximately the same. If the
rotor pole arc is larger than the stator pole arc it is more
advantageous.
II. SRM CHARACTERISTICS
In the Switched Reluctance Motor, only the stator carriers
windings, while the rotor is made of steel laminations
without conductors or permanent magnets. This very simple
structure greatly reduces its cost. Motivated by this
mechanical simplicity together with the recent advances in
the power electronics components, much research has taken
place in the last decade.
The SRM, when compared with the ac and dc machines,
shows two main advantages.
1) It is a very reliable machine since each phase is largely
independent physically, magnetically, and electrically from
International Journal of Emerging Trends in Electrical and Electronics (IJETEE – ISSN: 2320-9569)
Vol. 10, Issue. 10, Oct. 2014
106
Dr. RAMA RAO P.V.V, Ms. D. SAILAJA, Mr. P. DEVIKIRAN and Mr. A. PHANI KUMAR
the other machine phases.
2) It can achieve very high speeds (20000—50000 rev/m)
because of the lack of conductors or magnets on the rotor.
However, the SRM has some limitations.
1) It must always be electronically commutated and thus
cannot run directly from a dc bus or an ac line.
2) Its salient structure causes strong nonlinear magnetic
characteristics, complicating its analysis and control.
3) The SRM shows strong torque ripple and noisy effects.
A. Normal SRM
1) Stator side design
a. Stator Pole Arc
(2)
b. Stator Pole Width
(3)
c. Stator Yoke Width
(4)
d. Stator Pole Height
-
Fig.1. Aligned position
(5)
2) Rotor side design
a. Rotor Pole Arc
(6)
b. Rotor Pole Width
(7)
Fig.2. Unaligned position
The SRM motion is produced because of the variable
reluctance in the air gap between the rotor and the stator.
When a stator winding is energized, producing a single
magnetic field, reluctance torque is produced by the tendency
of the rotor to move to its minimum reluctance position.
When a rotor pole is aligned with a stator pole, as shown in
Fig. 1, there is no torque because field lines are orthogonal to
the surfaces (considering a small gap). In this position, the
inductance is maximal since reluctance is minimum (one
neglects the reluctance of the magnetic circuit). If one
displaces the rotor of its position, there will be torque
production that will tend to bring back the rotor toward the
aligned position. If current is injected in the phase when in
the unaligned position, as shown in Fig. 2, there will not be
torque production (or very little). If one displaces the rotor of
the unaligned position, then a torque tends to displace the
rotor toward the next aligned position.
c. Rotor Yoke Width
(8)
d. Rotor Pole Height
(9)
B. SEGMENTED SRM (SSRM)
1) Stator side design
a. Stator Pole Arc
(10)
b. Stator Pole Width
(11)
III. SRM MATHEMATICAL MODEL
Voltage equation is as follows.
c. Stator Yoke Width
(12)
+
(1)
d. Stator Pole Height
International Journal of Emerging Trends in Electrical and Electronics (IJETEE – ISSN: 2320-9569)
Vol. 10, Issue. 10, Oct. 2014
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Dr. RAMA RAO P.V.V, Ms. D. SAILAJA, Mr. P. DEVIKIRAN and Mr. A. PHANI KUMAR
-
(13)
2) Rotor side design
a. Rotor Pole Arc
(14)
b. Rotor Pole Width
(15)
c. Rotor Pole Height
(16)
d. Total number of turns
(17)
Where As is electrical load Size of the conductor
(18)
The instantaneous voltage across the terminals of a
phase of an SR motor winding is related to the flux linked in
the winding by Faraday’s law as
(19)
Where V is the terminal voltage, I am the phase current, R is
the phase winding resistance, and Ψ is the flux linked by the
winding. Because of the double salience construction of the
SR motor and the magnetic saturation effects, the flux linked
in an SRM phase varies as a function of rotor position and
the phase current. Above equation can be expanded as
(20)
Where
is defined as L( , I), the instantaneous
inductance, and term
is the instantaneous
back electromotive force (EMF).
Fig.3. H-bridge asymmetric converter
The maximum control and flexibility is obtained, however,
with the H-bridge asymmetric type converter shown in Fig.3.
Each phase has two insulated gate bipolar transistors
(IGBTs) and two diodes. The number of semiconductors is
the same as for an inverter. However, the structure is
completely different. One can also notice that it is not
possible to short-circuit the source because the resistance of
the coils limits the current.
As linearity is assumed, the flux relation is given by
= ( )
(21)
The co-energy is given by
= (1/2) ( ) 2
(22)
Resulting in a torque given by
2
T=
(23)
The above expression shows that this converter is
unidirectional in current because torque production does not
depend on the current sign but only of dL/dsign.
The simulation curves shown in figures (4) to (11) are
those obtained by assuming ideal inductance shape when
excited by voltage source. The control takes place applying
the voltage source to a phase coil at turn-on angle on until a
turn-off angle off. After that, the applied voltage is reversed
until a certain demagnetizing angle d, which allows the
return of the magnetic flux toward zero. To apply voltage V
in one phase, the two IGBTs Q1 and Q2 in Fig.3 must be ON.
On the contrary, to apply the –V voltage and assure the
current continuity, the two diodes D1 and D2 are used.
V. SIMULATION RESULTS
Based on the SRM drive speed control simulation is
presented. In this PI control is used for speed control and
compared with open loop speed control the Fig.4 to Fig.6
show different drive models of switched reluctance motor.
Fig.5 shows the A phase torque of SRM motor. Fig.8 and Fig.
9 show the total torque of the SRM motor in open loop and
closed loop control strategies. Speed curves of the SRM
motor with and without PI controller are presented in Fig.11
and Fig.10 respectively.
IV. ENERGIZING STRATEGIES
There are several possible configurations to energize an SRM
from a converter. The different energizing structures
distinguish themselves by their number of semiconductors
and passive components. They also depend on the number of
phases and the way the stator coils are connected.
Fig.4. Simulink model of the open loop SRM without
modelling
International Journal of Emerging Trends in Electrical and Electronics (IJETEE – ISSN: 2320-9569)
Vol. 10, Issue. 10, Oct. 2014
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Dr. RAMA RAO P.V.V, Ms. D. SAILAJA, Mr. P. DEVIKIRAN and Mr. A. PHANI KUMAR
Fig.5. Simulink model of the closed loop SRM without
modelling
Fig.11. Speed curve of the open loop SRM
Fig.6. Simulink model of the SRM with modelling
Fig.4 shows the Simulink model of the open loop Switched
reluctance motor without modelling. Fig.5 shows the
Simulink model of the closed loop Switched reluctance motor
with modelling. Fig.6 shows the Simulink model of the
closed loop Switched reluctance motor without modelling.
Fig.12. Speed curve of the closed loop SRM
Fig.11 shows the speed curve of the SRM with open loop at
required speed compared to the PI controller based circuit in
Fig.12.
Fig.7 Phase currents of SRM
Fig.7 shows the Phase Currents of SRM motor with PI
control.
VI. CONCLUSION
In this paper a closed loop PI control of the SRM motor is
modelled and simulated assuming constant Inductance.
Steady state operation of the SRM was obtained with PI
control of speed. The system is modeled by using the
MATLAB/SIMULINK and results are obtained.
REFERENCES
Fig.8 Total torque of the open loop SRM
Fig.8 shows the total torque of the open loop SRM.
[1] Nascimento, J., Rolim, L., Heidrich, P., et al. (1996) Design and simulation
aspects of a switched reluctance drive. In Proceedings of the 4± Brazilian
Power Electronics Conference (COBEP96), S˜ao Paulo, 1996, 79—83.
[2] Miller, T. J. E. (1993) Switched Reluctance Motors and Their Control.
Oxford, UK: Magma Physics Publishing and Clarendon Press-Oxford, 1993.
[3] Lawrenson, P. J., Stephenson, J. M., Blenkinsop, P. T., Corda, J., and
Fulton, N. N. (1980) Variable-speed switched reluctance motor. IEE
Proceedings Inst. Elect. Eng., 127, 4 (June 1980), 253—265.
[4] Henao, H., Capolino, G. A., Bassily, E., and Poloujadoff, M. (1997) A new
control angle strategy for switched reluctance motor. In Proceedings of EPE
’97, 3 (1997), 613—618.
Fig.9 Total torque
Fig.9 shows the total torque of the SRM compared with
closed loop PI control.
[5] Stephenson, J. M., and Corda, J. (1979) Computation torque and current in
doubly salient reluctance motors from nonlinear magnetization data. IEE
Proceedings, 126, 5 (May 1979), 393—396.
[6] Elliot, C. R., Stephenson, J. M., and McClelland, M. L. (1995) Advances in
switched reluctance drive system dynamic simulation. In Proceedings of EPE
’95, 3 (1995), 622—626.
[7] Rodrigues, M., Suemitsu, W. I., Costa Branco, P. J., Dente, J. A., and
Rolim, L. G. (1997) Fuzzy logic control for a switched reluctance motor. IJEE
INTERNATIONAL JOURNAL OF ELECTRICAL, ELECTRONICS AND
TELECOMMUNICATION ENGINEERING ©IJEET ISSN 2249-3085
IEEE International Symposium on Industrial Electronics (ISIE ’97), 2 (June
1997), 527—531.
Fig.10. Inductance of SRM
Fig.10. shows the inductance of SRM in both closed loop and
open loop strategies.
[8] Rodrigues, M., Costa Branco, P. J., and Suemitsu, W. Fuzzy logic torque
ripple reduction by turn-off angle compensation for switched reluctance motors.
IEEE Transactions on Industrial Electronics, 48, 3 (June 2001), 711—715.
(Available as a technical report at http://pbranco.ist.utl.pt).
International Journal of Emerging Trends in Electrical and Electronics (IJETEE – ISSN: 2320-9569)
Vol. 10, Issue. 10, Oct. 2014
Dr. RAMA RAO P.V.V, Ms. D. SAILAJA, Mr. P. DEVIKIRAN and Mr. A. PHANI KUMAR
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[9] Henriques, L., Rolim, L., Suemitsu, W., Costa Branco, P. J., and Dente, J.
A. Torque ripple minimization in a switched reluctance drive by neuro-fuzzy
compensation. IEEE Transactions on Magnetics, 36, 5 (Sept.2000),
3592—3594. (Available as technical report at http://pbranco.ist.utl.pt).
[10] Costa Branco, P. J. (2000) Influence of magnetic nonlinearities on
simulation accuracy of switched reluctance motor models. In Systems and
Control: Theory and Applications, World Scientific and Engineering Society
Press, 403—408. (Available as technical report at http://pbranco.ist.utl.pt)
[11] Bose, B. K., Miller, T. J. E., and Szczesny, P. M. (1986) Microcomputer
control of switched reluctance motor. IEEE Transactions on Industry
Applications, IA-22, 4 (June 1986), 708—715.
International Journal of Emerging Trends in Electrical and Electronics (IJETEE – ISSN: 2320-9569)
Vol. 10, Issue. 10, Oct. 2014
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