Research on transient behavior of SRM as its phase windings are broken

2010 2nd IEEE International Symposium on Power Electronics for Distributed Generation Systems

Research on Transient Behavior of SRM as Its

Phase Windings are Broken

Yang Yugang, Li Linhong, Fu Cai, Hu Peng

College of Electrical & Control Engineering, Liaoning Technical University, Huludao City 125105, Liaoning Province, China Abstract--This paper studies the transient behavior of

switched reluctance motor (SRM) as its phase windings are

broken. At first, this paper established a nonlinear dynamic

model of SRM and simulated SRM’s dynamic performance.

The dynamic model and the simulation results were tested

and verified by comparing the simulated results with the

experiment results. On the basis of these, this paper

analyzed the transient behavior of SRM as its one phase

windings or two phase windings are broken. By these

analyses, it can be concluded that SRM’S torque pulsation

and speed fluctuation will enhance evidently as the phase

windings are broken, and the speed of SRM will bring down

rapidly which may spoil the windings and the switching

devices if the load torque is larger than the electric-magnetic

torque. as follows: Fig.1. The mail circuit of SRM (1) When one phase is turning on, a switch in this phase is spoiled. For example, in phase A, the switch T1 is spoiled, then the current in phase-A will flow through T2, RA and D2. When T2 is turned off, the current in phase-A will flow through D1, power, RL and D2 until Index Terms--Switched reluctance motor (SRM), Phase the current damps to zero. Afterwards, this phase will not windings broken, Transient behavior turn on.

If T2 is spoiled, then the current in phase-A will flow I. INTRODUCTION through D1 and T1. When T1 is turned off, the current in

The switching devices and diodes of the inverter of phase-A will flow through D1, power, RL and D2 until switched reluctance motor (SRM) may be spoiled to lead the current damps to zero. Afterwards, this phase will not to broken faults because of the aging of the devices and turn on.

If T1 and T2 are spoiled simultaneously, then the diodes or the fluctuation of line voltage as SRM’s driving

system operate for a long time. The broken faults will current in phase-A will flow through D1, power, RL and cause transient behavior of SRM’s driving system which D2 until the current damps to zero. Afterwards, this phase causes fluctuations of the normal phase’s current, SRM’s will not turn on also. However, the situation emerges torque and the speed. These fluctuations may exceed the seldom which T1 and T2 are spoiled at the same time.

(2) When one phase such as phase-A is freewheeling, it permitted confine and lead to the spoiling of the devices

of other phases and the whole system. Therefore, it is freewheeling diode such D1 is spoiled, then there is a important to analyze the transient behavior of SRM as its large counter-electromotive force yielded by phase phase windings are broken. However, because of SRM’s winding A to let the buffering circuit of T2 flowing double convex pole structure, nonlinear of magnetic continuously. The buffering circuit of T2 is shown in circuit and complexity of the transient behavior, the Fig.2. Since the capacitance of the buffering circuit is research on the transient behavior is difficult. On the small, it may be breakdown.

(3) When the winding of phase-A is spoiled suddenly, basis of references [1] to [7], this paper studies SRM’s

transient behavior and gets relative conclusions as SRM’s then the current in this phase will become to zero at once. one phase of winding and two phases of windings are It can be seen from above analysis that one switch broken. The purpose is to find whether winding breaking device is most probably spoiled in situation (1). Therefore, affects (SRD)’s safe operation. The relative conclusions this paper studies the transient behavior of this situation. provide a theoretical basis for improving SRM’s The device T1 of phase-A is supposed to be spoiled when

SRM operates, the equivalent circuit of phase-A is shown reliability. in Fig.3 (a). When T2 is turned off, phase-A comes to the

period of freewheeling, its equivalent circuit is shown in II. TRANSIENT BEHAVIOR ANALYSIS OF SRM AS ITS ONE Fig.3 (b). PHASE WINDING IS BROKEN In Fig.3 (a): The mail circuit of SRM is shown in Fig.1. There are

three situations of one phase winding’s breaking in Fig.1

978-1-4244-5670-3/10/$26.00 ©2010 IEEE325

uA=?(ΔUD+ΔUG+iARA) (1)

In Fig.3 (b):

inductance of phase j; J is rotation inertia; D is coefficient of viscosity; ω is angular speed.

uA=?(Ud+2ΔUD+iARL)

(2)

Lj(θ,ij)=L0+{(L1+L3)[1?cos(Nrθ??0j)]

+L2[cos2(Nrθ??0j)?1]+L3[cos3(Nrθ??oj)?1]}

a

a+ij

(4)

Fig.2.

Absorb circuit of T2

Where: L0, L1, L2, L3 and aare coefficients; φ0 j is position angular of phase j.

B. Simulation and Experiment of (SRM)’s Dynamic Performance

According to the dynamic model described by formula (3) and (4), this paper compiled simulation software and simulated (SRM)’s dynamic performance. Fig.4 shows the simulated rotate speed waves of no load and load with the given rotate speed of 1200r/min and the load torque of 4.23Nm. Fig.5 shows the simulated and experimented current waves of no load and load with the given rotate speed of 1200r/min and the load torque of 4.23Nm. where the full line expresses experiment waveform, and the dotted line expresses simulated waveform. By comparing the simulated current waves with the experimented current waves, we can see that they are contiguous, the error is 10% of no load and 5% of load. This tests and verifies the validity of nonlinear dynamic model and simulation software. On the basis of this, this paper studied (SRM)’s transient behavior as its one and two phases of windings are broken.

(a) Equivalent circuit of phase-A as T1 is spoiled

(b) Equivalent circuit of phase-A as T1 comes into freewheeling

Fig.3 Equivalent circuit as Phase A is broken

III. SIMULATION AND EXPERIMENT

In order to verify the validity of the analysis above, this paper simulates (SRM)’s transient behavior as its one phase winding and two phase windings are broken. A. Nonlinear Dynamic Model of SRM

This paper suppose DC voltage U of main circuit power supply is constant, neglect the effect of magnetic hysteresis and eddy current in SRM, neglect the mutual inductance among the phases, and suppose the parameters of each phase are equal and the two windings of each phase are symmetrical. Then (SRM)’s nonlinear dynamic model is as follows:

?dij?L(θ,ij)??1

???Rij?ωijj+Uj?=?j??dtijj+Lj(θ,ij)?

??ij (3) ?

dθ=ωdt?

dω=1[T?Dω?T]

L

dtJe?

?Te=∑Tej

j=A,B,C?ij

Fig.4. Simulated wave of rotate speed (Full line expresses no load,

dotted line expresses load)

(a) no load (b) load Fig. 5. Comparison of simulated results with experiment results

Where: T=

ej

?∫Lj(θ,ij)ijdij

C. Simulation of (SRM)’s transient behavior as its one phase winding is broken

The transient behavior of a 3-phase 12/10 poles SRM of 1.1kW, 310V, 1200rpm is simulated with formulas (1) to (4) as its one phase winding is broken. The simulated results are shown in Fig.6. It can be seen from Fig. 6(e)

or C; Te is electric magnetic torque; Uj is voltage of phase j; ij is current of phase j；Rj is resistance of phase j; Lj is

?; j expresses phase A,B

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that the current in phase-A comes into freewheeling and damps to zero quickly before increasing to the maxim value because of T1’s breaking as phase-A is turning on, afterwards, phase-A will not turn on again. In order to make SRM’s torque balance with the load torque, the turn angles of the two remained phases will enlarge to increase the current magnitude. The increased current may exceed the up limit of 6.5A and comes into the state of chopping. Because there are only the remained two phases’ turning on, the torque fluctuation augments obviously and has a period of zero and negative, which causes an obvious speed ripple. If the load torque is large, the speed will fall off and the devices of the remained two phases may be spoiled because currents increase too quick and large. Therefore, proper protection measure should be adopted that turn off the remained two phases

once one phase is broken.

(e) Waveforms of 3 phase currents as the time axis is enlarged to 20

times

(f) Waveforms of 3 phase currents following (e)

Fig.6 Transient behavior of SRM as its one phase winding is broken

D. Simulation of (SRM)’s transient behavior as its two phase windings are broken

(a) Speed waveform

(b) Torque waveform

Same as one phase winding’s breaking, there are several situations of two phase windings’ breaking, but the most typical situation is that T1 and T3 (or T2 and T2) are spoiled at the same time. The equivalent circuits of two phase windings’ breaking are shown in Fig.3 also, the transient behaviors are show in Fig.7. It can be seen from Fig.7 that SRM’s speed falls off rapidly because the torque brought by the remained one phase winding can not balance with the load torque. Because there is only one phase is turning on, the torque fluctuation is much severe, this is not allowed by most load. Therefore, a protective measure should be adopted to turn off remain

phase once two phases are broken.

(c) Torque waveform as the time axis is enlarged to 20 times

(a) Speed waveform

(d) Waveforms of 3 phase currents

(b) Torque waveform

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make people select correct switch devices of SRM, and provide necessary basis for adopting various protective measures.

REFERENCES

(c) Torque Waveform as the time axis is enlarged to 20 times

(d) Torque waveform following

(c)

(e) Waveforms of 3 phase currents

[1] Gao Jingde, Wang Xiangheng, Li Fahai. Analysis of AC

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[2] Pulle D W J. New date base for switched reluctance drive

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[3] Arkadan A A, Kielgas B W. Switched reluctance motor

drive system dynamic performance prediction under internal and external fault conditions[J]. IEEE Trans on Energy Conversion, 1994, 9(1): 36~44.

[4] Yang Yugang, Yao Ruoping. Research of (SRD)’s dynamic

performance[J]. Tsinghua University Journal, 1997, 37(9): pp.82~85.

[5] Yang Yugang, Xing Kefeng, Yu Qingguang. Research of

(SRD)’s transient behavior as its one phase winding is short circuit[J]. Journal of China Coal Society, 2002,27(6): pp.665~668.

[6] Yang Yugang, Guo Fengyi, et al. Research of SRD ’s

Transient Behavior As Its Two Phases of Windings Are Short-circuit[C].IEEE/IPEMC[C] 2004.

[7] Yugang Yang, Hongzhu Li Jiaju Wu Research on Optimal

Starting Condition of Switched Reluctance Motor[C]. CES/IEEE 6h IPEMC, 2009.5, Wuhan, China.

(f) Current waveforms of phase-A

(g) Current waveforms of phase-C

Fig.7 Transient behavior of SRM as its two phase windings are broken

IV. CONCLUSION

It can be seen from above analysis that SRM’s torque fluctuation and speed ripple augment obviously when breaking fault happens. If the load torque is larger than the electromagnetic torque after breaking fault happens, SRM’s speed falls off rapidly, the remained phase windings and their devices may be spoiled. Some protective measures should be adopted to turn off the remained phases’ devices once a breaking fault happens. Therefore, the research on SRM’s breaking faults can

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