Research On Sensorless Control Of Switched Reluctance Motor At Standstill And Low Speed

Switched reluctance motor (SRM) has received considerable attention and wide application inmany fields due to its simple structure, smaller size, high efficiency, and wide speed regulation. Theaccurate real-time rotor position is the fundamental prerequisite to the switched reluctance motordrive. Recently, photoelectric sensor, magneto-dependent sensor, and rotary transformer have beenused in SRM to obtain the real-time rotor position. But they add the cost and complication of themotor and control system, and deteriorated the reliability. Thus they can not be used in some extremeconditions, such as high temperature, oil and dust environment. Consequently, it is quite necessary toresearch the sensorless control method which based on phase current and phase voltage, with themethod, low cost, high efficiency and reliability could be ensured.In this paper, the basic theory and mathematical models of SRM is introduced, and the sensorlessstarting schemes are investigated.First, a method with injecting voltage pulse in the unexited phase based starting scheme is proposed.Before start-up, each phase is excited in sequence with a narrow voltage pulse. According to therelationship of resultant current and phase inductance, the initial conduction phase can be determined.The unexcited phases should be injected with the voltage pulse, and the phase commutation point canbe estimated by comparing the resultant current in the unexited phase. And then the three phases canbe excited in turn to complete start-up. In order to avoid the estimation error in the currentfree-wheeling regions, the improved method with a current threshold which can eliminate the signalof mis-conduction is proposed. The control method presented in this paper can realize the start-up ofSRM without position sensor, and the motor can run at a certain speed. Simulation and experimentverify the validity of the proposed methodAnd then, the sensorless control method of low speed which based on the double thresholds ofcurrent is discussed. At low speed, the current threshold can be determined from the curve of resultantcurrent amplitude. With the threshold, commutation can be realized smoothly and there is no need tocalculate accurate rotor angle. This method is easy to implement, simulation and experiment hasverified its validity.At last, a starting method for sensorless control under asymmetric inductances is presented. Due tomechanical reasons, the inductance of each phase are not always symmetric, which will cause start-uphesitation. The starting scheme based on symmetric inductance is introduced, and then the deepanalysis of asymmetric character is demonstrated and a modify algorithm is presented. A wrong initialdriving signal that caused by asymmetric inductance can be eliminated by the proposed method evento avoid start-up hesitation. Simulation verifies the validity of the proposed method.The simulation is performed under Matlab/simulation environment. And besides, the experimentsare implemented based on a12/8structure SRM drive system. According to the hardware equipment,operating characteristics and the algorithm have been validated.