Method of controllable rectification to shorten voltage recovery time of consequent-pole permanent magnet generator

Abstract: To realize the function of automotive engine stop-start, it is promising that traditional independent starter and generator in automobile are replaced by the integrated starter/generator (ISG), which contributes to energy conservation and emission reduction. Hybrid excitation starter/generator is a potential selection for the ISG, which has high efficiency over extensive working range, high power density, low maintenance, and high reliability without brushes. The consequent-pole permanent magnet (CPPM) brushless direct-current generator (BLDCG) electromotive force (EMF) is designed to the trapezoidal wave. The trapezoidal wave electromotive force CPPM motor is different from the existing sine wave electromotive force CPPM motor. It has the advantages of high power density, small direct-current (DC) voltage harmonic ripple, only requiring low cost and low resolution Holzer position sensor, simple control and other advantages. The CPPM motor can output stable voltage in the wide speed range. However, the normal brushless DC generator needs to match the complex power converter. Therefore, The CPPM motor is a new type of motor used for electric vehicle. This kind of motor has a good prospect in the application of the ISG of automobile. Generally, the excitation current regulation combined with diode rectification is adopted to meet the requirement of alternator technical specification. However, the large time constant of about 100 ms in excitation winding will cause DC-link voltage drop and lead to abnormal operation of automotive sensitive device, such as engine control unit, and radio. In generating mode, the CPPM BLDCG can be seen as hybrid excitation brushless DC generator. In view of relatively low time constant in armature winding of CPPM BLDCG, it is possible to improve DC-link voltage dynamic performance by regulating armature winding current. This paper takes CPPM BLDCG of 14 V as the research object and aims to shorten the time of voltage recovery. With the method of controlled rectification without increasing hardware cost, the dynamic adjustment process of voltage is analyzed, and the theoretical calculation and experiment of voltage recovery time under 2 different modes of controlled rectifier and diode rectifier are completed. BLDCG CPPM is controlled by the combination of the traditional diode rectifier and the electric field regulation. Its DC voltage recovery time is influenced by the time constant of the excitation winding, which is at the 100 ms level. The dynamic response speed of BLDCG CPPM is maintained at a lower level. A controlled rectification method is proposed to improve DC-link voltage recovery time of CPPM BLDCG. In view of the fast energy storage and release in armature winding, the voltage recovery speed is increased by improving the total EMF of armature winding. The method needs no additional hardware cost. In addition, the method can be extended to hybrid excitation motor with other structures. Dynamic process of CPPM BLDCG with controlled rectification and ultra-capacitor is analyzed by the state-space average method. Theory calculation and experiment on the controlled and diode rectification are separately completed. The results show that the voltage recovery time with the controlled rectification is almost the half of that with the diode rectification. The reason is that the controlled rectifier using BLDCG CPPM armature windings to achieve rapid energy storage and release, can effectively improve the armature winding EMF, and thus can shorten the voltage regulation time. It is of great significance to improve the reliability of the on-board sensitive electronic equipment. Therefore, this kind of controllable rectification method has a good prospect in the automobile ISG application aspect.