Research On Current Control Strategy Of Hybrid Excitation Synchronous Machine

Hybrid excitation synchronous machine(HESM) is a novel machine which combines permanent magnet synchronous machine and field wounded synchronous machine. The goal is to combines the advanteges of both the machines above, so HESM can control excitation flux and has high efficiency. Due to the properties of low speed high torque and wide speed range operation, HESM can satisfy the demand of the electric drive system. This paper mainly revolves around a tangential/radial hybrid excitation synchronous machine(T/R-HESM).According to T/R-HESM structure and operation principle, this paper presents the mathematical models of motor in static coordinate, and then presents the decoupling mathematical model in rotary two-phase coordinate under the principle of coordinate transformation. In order to acquire inductance parameters, finite element simulation method and experimental method are used. The definition method is applied to finite element simulation method and the direct load method is applied to experimental method. The measured results are used to analyse the three relation between d-axis inductance, field current and armature current.A noval i_d=0 control strategy is proposed in this paper. Control system switches between different control strategies according to the running state: When voltage constraint is inactive and given torque is satisfied, copper minimum control strategy is adopted; When voltage constraint is active and given torque is satisfied, constant torque control strategy is adopted; When voltage constraint is inactive and given torque is unsatisfied, maximum torque control strategy is adopted. Field current compensation method and q-axis current switching point are employed to ensure the smooth switching between different control strategies. Field current compensation method can regulate the field current, which is simple, robust and well adjustable.Next, the structure of HESM drive system is introduced and the motor controller is developed. The model-based design method is applied to software development which can realize from model simulation to DSP software and software debugging. Finally simulation and experimental results show that, compared to general control strategy, the control strategy proposed can effectively use the DC bus, improve the efficiency and output torque at low speed, and broaden the speed range.