The Research On Mitigation Strategy Of Low-speed Torque Pulsation For A LCI-fed Synchronous Motor

In recent years, LCI-fed(Load Commutated Inverter) electrically excited synchronous motor control system with high power factor, large unit capacity and high control accuracy becomes a hot issue both at home and abroad. At present, obvious low-speed torque pulsation phenomenon exists in domestic high-power synchronous motor at the beginning of the start. In order to solve this problem, mechanical sensors are used in most control systems for detecting of rotor position in real time. However, traditional mechanical sensors bring many adverse effects to the AC drive system. So the research on sensorless rotor position detection method has important practical significance.This paper analyzes the reason for low-speed torque pulsation phenomenon in electric excitation synchronous motor control system at first. To tackle this problem, realizing zero speed and low speed rotor position detection to s mitigate low-speed torque pulsation phenomenon is proposed. Rotor position detection method below 4Hz is introduced, which includes theoretical analysis and formula derivation. And then a mitigation strategy of low-speed torque pulsation phenomenon is given.Rotor position detection method based on high frequency signal injection in motor excitation part is selected in the LCI-fed electrically excited synchronous motor system. What’s more, reasonable injection signal frequency is given at the same time. On this basis, this paper presents the scheme about extracting rotor position information from the synchronous motor three-phase induction voltage, and explains the scheme of three-phase motor induction voltage signal processing. The hardware design of signal processing is completed, and the design details of band-pass filter for high frequency signal extraction is given. In view of the high frequency signal envelope extraction, three feasible solutions are put forward, by the comparison and analysis of experimental results, the envelope extraction scheme based on ADL5511 are adopted. Based on TMS320F2812 and MAX1308, the AD sampling system and rotor position detection system are realized. In addition, this paper introduces the algorithms of rotor position detection under zero speed, rotor position detection under low speed and low-speed torque pulsation mitigation strategy in detail. Finally, both the high frequency signal envelope correction scheme and rotor position correction scheme are given and verified through experiment.Based on MATLAB software platform, simulation verification of rotor position detection algorithm is carried on, and this method is proved to be effective. On the experimental platform of 15 k W electrically excited synchronous motor, the experiments that three-phase voltage signal processing and rotor position detection under low speed are completed. Experimental results achieve the expected effect, and the rotor position detection below 4 Hz can be realized. With the low speed torque pulsation mitigation strategy, synchronous motor starts smoothly and low-speed torque pulsation phenomenon is improved significantly.