Speed Control of BLDC Motor in Electro-Hydraulic Power Steering System Based on Fuzzy-PI Controller 2018-01-0698

Electro-hydraulic power steering system (EHPS) uses the motor as the power source instead of the engine to assist drivers to steer. Compared with traditional hydraulic power steering system (HPS), EHPS system has a better performance in energy saving and driving feeling. In EHPS system, the speed control of the motor determines the performance of the whole system. In this paper, a speed control system of brushless direct current (BLDC) motor based on a Fuzzy-PI controller is established. In addition to the function to adjust speed by adjusting voltage, field weakening is utilized to get a wider speed range, so that the EHPS system has a better performance. To solve the control mode switching problem introduced by the jumping of the motor speed between high-speed range, in which the field weakening is required, and low-speed range in which normal control method is applied, a switching method based on multi-parameter, including control mode, speed changing rate and other factors is proposed. In this way, the motor speed adjustment will be smoother in control mode switching period and make a better transition performance even when the motor load is variable. In addition, an optimized Fuzzy-PI controller is designed to get a faster response in the motor speed adjustment. According to the speed error and its changing rate, the proposed fuzzy controller can adjust gains of an optimized PI controller online. The proposed control method was verified on an EHPS test bench and promising results have been obtained.