Phase Mutual Inductance Characteristics Of SR Motor And Research On Indirect Position Detection

SR motor has the advantages of solid structure, simple processing, reliable, lowmaintenance, simple control etc. It can be used in high temperature, even strong vibration andother harsh environments. When design the power converter, each power device series with thestator winding, to avoid the short-circuit phenomenon which appeared in ordinary inverter circuit.This further improves the reliability of SR motor control system. However, the rotor’s position isthe basis for synchronous operation of SR motor. It is the main different of open-loop steppermotor. The detection of the rotor’s position is very important to approach the performanceindications. It makes the motor processing complex, increases the cost and reduces the overallsystem reliability, due to the existence of position sensor in conventional SR motor motioncontrol system. In this paper, the relationship between the mutual inductance and rotor’s positionin SR motor has been researched, and we get a new indirect detection method to know the rotor’sposition by taking advantage of this relationship.Fistly, established the2D model of8/6SR motor using finite element analysis method.Based on this model we analyses the relationship between mutual inductance and rotor’s positionin non-excitation phase, when single-phase and two-phase excitation. We measured therelationship of mutual inductance and rotor’s position of a2.2Kw prototype, and proved thecorrectness of the finite element analysis method. We proposed an initial rotor’s positiondetection method by using a low-voltage high frequency signal injection method.The inductance of non-excitation phase is equivalent to RLC circuit which is RL series,then parallel with C. We analysis the mutual inductance electromotive force wave when the SRmotor in the two-phase excitation, chopped voltage control, and H-bridge chopper type powerstructure. We proposed two rotor position detection methods when SR motor is in two-phaseexcitation. One method is to detection the rotor’s position by detecting the EMF peak innon-excitation phase. Another method is to calculate the natural oscillation frequency of RLC toget the rotor’s position.Secondly this paper proposed a fuzzy inference method which with each phase current andthe angle controller needed as input, the estimated value of mutual inductance EMF of testedphase as output. The inference rules and the membership function of each variable are optimizedby genetic algorithm. The controller measures the two phase’s current in real-time, when the motor is running, and looks-up the table to get the estimated value of mutual inductance EMF.The controller compared the value of the estimated and the measured to get the rotor’s position,to achieve the angular position control, when SR motor is in high speed.Finally we build a nonlinear model of SR motor used the nonlinear finite element analysisresults in the Matlab/Simulink environment. The correctness of the model was proved andprovided simulation basis for optimize the design of the fuzzy rules which used for indirectposition detection. This paper uses a modular design approach to achieve the hardware design ofspeed control system and indirect position detection of SR motor, and achieved positionsensorless control of SR motor motion control system. We proposed two methods to ensure thecorrect commutation when the system is working with indirect position detection, this isimproved the reliability of indirect position detection.