Research On Sensorless Control Of Two-Phase Switched Reluctance Motor

Switched reluctance motor(SRM)is a high performance rare-earth-free special motor with simple structure,high reliability,low cost and wide speed regulation range.The two-phase SRM,as a switched reluctance motor with small numbers of phases,can simplify the control system,and the application in unidirectional high-speed operation can highlight the advantages of low cost and high reliability.However,the presence of position sensors can weaken the advantages of the body structure,making the motor limited in extreme operating conditions such as high temperature and high speed,and most of the existing sensorless control techniques are based on the motor topology with three or more phases,while the two-phase structure is rarely involved.Therefore,in this thesis,the sensorless control technology of two-phase SRM is studied accordingly,and the corresponding theoretical analysis,simulation and experimental verification of the control strategies for motor starting,low-medium speed,high-medium speed and operation under full speed domain conditions are carried out as follows:First of all,the basic structure,operating principle and control method of twophase SRM are briefly outlined.The linear inductance model is used to analyze the lack of self-starting capability of the two-phase structure and the partitioning anomaly caused by the special phase difference,based on which the progressive step rotor structure is adopted to widen the inductance rise region to enhance the self-starting capability.At the same time,the FEM software is used to optimize the torque characteristics and simulate the dynamic operation of the prototype,and the resulting torque and inductance characteristics curves are used to build the motor body module in the subsequent control system model.After that,when the motor is at standstill or running at low-medium speeds,this thesis proposes a two-phase SRM starting method based on the high-frequency pulse injection method and divides the low-speed algorithm into two categories according to the current chopping mode in the non-conducting interval.When the motor is starting,the two phases are first switched on one after the other to put the motor in a short inertial running state,after which high-frequency pulses are injected into both phases at the same time,and when the pulse current peak of a phase is in the falling phase it is set as the initial excitation phase,thus dividing the rotor position into four regions and deriving the corresponding conduction logic.For low-medium speed operation,when the low-threshold current hysteresis loop chopping method is used in the nonconducting region,the real-time current slope difference is calculated and linear recursion is performed based on the adjacent maximum slope difference points to calculate the motor speed and rotor position,which can avoid the effect of magnetic saturation;When pulses of fixed frequency are injected in the non-conducting region,the current peak comparison method with threshold updated is proposed,which sets an initial threshold value based on the minimum inductance position and issues a position retrieval pulse when the pulse current peak is not lower than this threshold value,and finally calculates the real-time speed and rotor position by the adjacent pulse interval and updates the threshold state,which weakens the influence of motion counter potential and improves the estimation range of the original algorithm.Further,when the motor is medium-high speed,this thesis investigates the current gradient method and the inductance gradient method applied to two-phase SRM,reclassifies the two types of methods according to the phase inductance pole point,and discusses the position calculation results of different algorithms under various operating conditions.Meanwhile,aiming at the switching problem of sensorless control algorithm between different speed domains,an algorithm switching strategy based on single speed threshold is proposed,which projects the upper and lower speed thresholds by the maximum speed applicable to the low-speed algorithm and the front-end chopper state,and sets the thresholds within the upper and lower limits to achieve fast switching between the low-speed and high-speed algorithms.Finally,a experiment platform based on RT-LAB is built,including the power converter,motor body and control system,etc.The experiment platform is used to conduct relevant experiments on various control algorithms described in the thesis,and the experimental results verify the correctness of the control algorithms.