Research On Tolerant Control Of Switched Reluctance Motor System

Switched reluctance motor(SRM)has certain competitiveness in industrial application area relying on its simple structure,controllable multi-parameters,solid rotor without windings and good fault tolerance capability.But due to the factors,including over-voltage,over-current and over-heat,some faults may occur in SRM drive,and the faults are mainly concentrated on phase windings,current sensors,power converter and position sensors.If the fault can not be treated timely,the stable operation of SRM will be destroyed.Hence,it is necessary to study the diagnostic and tolerant control methods for the faults in SRM drive.Due to the insulation aging of the stator winding,the phase-to-phase fault may happen.Firstly,the phase-to-phase fault modes are discussed for different connections of phase windings,and the fault mechanisms are analysed in different fault modes.Then the equivalent circuit of SRM with phase-to-phase fault is established.The incoming line current and outgoing line current are calculated with the optimized phase current detection method.The phase-to-phase fault will be detected by monitoring the error between the incoming line current and outgoing line current of each phase.In order to decrease the adverse effect on SRM drive,a triple closed-loop control strategy is proposed by adjusting the switching states of power transistors.The three closed-loops include the speed loop,phase current regulation loop and the short current restriction loop.Simulations and experiments show that the proposed method can restrict the short-circuit current effectively.The control and protection of SRM drive rely on the accuracy phase current.Flexible,economical and convenient phase current detection method is essential.A novel phase current reconstruction method is proposed by optimizing the locations of two current sensors.According to the operation principle of SRM,at most two phases will conduct at the same time.Each electrical period will be divided into three sub-regions,and each phase current can be calculated by solving the linear equations associated with the currents of two sensors.The fault sensor with offset current will be identified by judging the errors at the rising edge of each drive signal.The offset current will be compensated with the two proposed methods including the direct compensation scheme and the proportional integral compensation scheme.The fault power transistor,which is used for regulating the phase current,will be detected by recognizing the synchronous relationship between the chopping signal and the phase current slope.The fault power transistor,which is controlled based on the rotor position,will be detected by comparing the freewheeling time of two adjacent phases.The tolerant reconstruction method is realized with a virtual current sensor.The proposed method is independent of the open-circuit fault of power transistor.Simulations and experiments show that the proposed phase current reconstruction method is flexible and accuracy,and can be easily extended to SRMs with higher number of phases.In order to further improve the reliability of SRM drive,a tolerant power converter is proposed with bidirectional power units based on the conventional topology.The tolerant structure is suitable for winding fault,power transistor faults and the compound fault conditions.In normal case,the bidirectional power units are idle.After the occurrence of open-circuit fault in power transistor,the topology will be reconstructed to realize tolerant operation.After the occurrence of short-circuit fault in power transistor,the torque ripple of SRM will be minimized with the optimized turn-off angle adjustment strategy,and the operation performance of SRM drive will be improved.When the phase winding is in open-circuit fault case,the reduced torque of SRM will be compensated with the tolerant topology.Simulations and experiments show that the SRM drive is capble of operating even in fault conditions.Accuracy rotor position is necessary for the operation of SRM.In the low cost applications,the photoelectric sensors are appreciated.For three-phase SRMs,three photoelectric sensors should be strictly installed with 120 electrical degrees apart.But due to the factors,such as the mechanical process,the misaligned case may occur.The effect of the single and double misaligned photoelectric sensors on the SRM drive are analysed,and two strategies are proposed to avoid the misaligned cases.One method is realized based on the dynamic time warping algorithm,and the other method is implemented with single photoelectric sensor by optimizing the structure of the adopted slotted-disk.The proposed methods are easy for online implementation and can be integrated into the conventional control strategy.Experimental results validate that the two methods can avoid the misaligned case effectively.