Research On Speed Control Strategy Of Low Speed High Torque Permanent Magnet Synchronous Motor

Compared with electric drive systems adopting motor-reductor structure, permanent magnet synchronous motor(PMSM) direct drive system possesses advantages in operation efficiency, control precision and dynamic performance. It has become the mainstream on low speed serve occasions such as elevator, high precision numerical control machines and test turntables, and is playing an important role in the process of making motor system more energy-efficient, as well as in the localization process of high-end equipment manufacturing. This paper carries out a series of researches focusing on smooth speed control issues of low speed high torque permanent magnet synchronous motor drive system, including speed ripple reduction methods, novel speed control strategies and speed measurement algorithms.To reduce the speed ripple caused by non-ideal factors in the PMSM drive system such as flux harmonics and current measurement errors, mathematical model of speed ripple is established and the impaction of the non-ideal fators is revealed from the perspective of control system. On the basis of works above, a novel speed ripple reduction strategy for both current loop and speed loop based on proportional-integral-resonant controller is proposed. The design method of controller parameters is evaluated. Theoretic analysis and experiment results indicate that the current loop controller can suppress the speed ripple caused by harmonics of back emf and dead time effect effectively, as well as improving tracking performance. The speed loop controller can suppress the speed ripple caused by cogging torque and current measurement errors, as well as neutralizing the impaction of periodic changing flux.The traditional speed control strategy has difficulties in guaranteeing tracking performance and anti-disturbance performance at the same time, as well as totally eliminating speed overshoots. To solve the problem, this paper proposes two kinds of two-degree-of-freedom proportional integral(2-DOF PI) speed control strategies, which are reference feedforward 2-DOF PI control strategy and active damping 2-DOF PI control strategy, respectively. The controller parameter design procedure is also provided. Theoretic analysis and experiment results indicate that the two speed control strategies can both make a good compromise between tracking and anti-disturbance performance, as well as accomplish no overshoot speed control.The errors and time delay introduced by speed measurement process have serious impaction on the speed control performance of low speed high torque PMSM drive systems. However, the M/T speed measurement algorithm is not able to make a good compromise between speed measurement error and time delay. To solve this problem, this paper proposes a speed measurement algorithm based on overlapped measurement regions. The optimal design of the measurement region is also provided. Given that the above algorithm is not able to totally eliminate the time delay, an adaptive Kalman speed observer is further developed. Theoretic analysis and experiment results indicate that the two method can reduce the time delay and improve measurement precision.