The Research On Driving System And Control Strategy Of Switched Reluctance Machines For Low-voltage Electric Vehicles

Switched reluctance motor(SRM)has many advantages,such as simple structure,large starting torque,strong fault-tolerant ability and flexible control.It will have broad application prospects in the field of low-voltage electric vehicles.In this paper,the motor drive system and control strategy of switched reluctance for low voltage electric vehicle are studied as follows:In order to solve the problems of non-isolation of heavy and weak currents in the existing SRM non-isolation driving system of electric vehicles,as well as the high cost and large volume of SRM isolation system,an isolation driving system of SRM for low-voltage electric vehicle based on the sampling current of constantan wire is proposed.The system uses a high-speed optocoupler to isolate between the PWM control signal and the MOSFET drive signal,and a linear optocoupler to isolate the phase current sample and the bus voltage sample from the controller AD sample.The experimental results verify that the proposed method can achieve the isolation of digital ground and power ground without increasing system volume and cost,thus further improving the reliability of low-voltage electric vehicle SRM drive system,which has important application prospects.Aiming at the starting and medium-high speed operation control of electric vehicle SRM,a starting control method based on dynamic chopper and a medium-high speed running integrated control strategy combining PWM control and APC control are proposed.At the moment of static starting,the current chopper line is given in segments according to the PWM duty cycle given by the accelerator,so as to ensure that the motor can start smoothly in different load modes and avoid the starting jitter of the electric vehicle;Three-stage zone chopping control is realized according to the logic of the three-phase rotor position signal during low-speed starting operation,so as to avoid the synthetic torque drop caused by the small slope of the excitation phase and the demagnetization phase in the starting commutation overlap region,effectively increasing the combined torque of the region.The torque enhances the starting ability of the motor and also reduces the torque ripple of the starting operation.For the overload operation,a three-stage chopping control strategy is proposed to increase the chopping limit of the single-phase conduction region,further increasing the starting torque;For medium-high speed operation,a comprehensive control strategy of medium-high speed operation combining PWM control and APC control is adopted to realize the comprehensive adjustment of bus voltage,opening angle and turn-off angle,and to ensure the smooth start,instantaneous speed increase and stable operation of motor under different load modes by combining with starting method.This paper verifies the effectiveness of this control strategy through experiments.In response to the most important problems that may occur in SRM drive system under the complicated operating conditions of low-voltage electric vehicles,namely over-current and start-blocking problems,The overcurrent protection control strategy based on hardware and software collaborative diagnosis and the stall protection control strategy based on rotor position signal logic which are proposed respectively improve the timeliness of overcurrent protection,avoid the interference of the rotation speed calculation error on the stall fault protection during start and low speed operation,and also solve the problem that the start delay lag can not be effectively judged.On this basis,this paper also carries out software design for other conventional faults of electric vehicle SRM drive system.Finally,the feasibility of the above method is verified by experiments.