Research On Active Disturbance Rejection Control For PMSM Servo System

At present, permanent magnet synchronous motor(PMSM), which possesses the advantages of simple structure, high power density, high efficiency, smooth operation and etc., has become the first choice in the small or medium-sized power field of high-precision servo drives. Nevertheless, there exist numerous disturbances, from both internal and external, which will deteriorate the system performance, especially in direct drives or harsh applications. Therefore, it has a great significance to effectively reject all the unknown disturbances in high-performance AC servo systems. In this paper, the application and implementation of active disturbance rejection control(ADRC) for PMSM servo system have been studied.ADRC was proposed to overcome the inherent weaknesses of classical PID controller. This novel nonlinear controller consists of three parts: tracking differentiator(TD), nonlinear state error feedback(NLSEF) and extended state observer(ESO). ADRC integrates the merits of PID and modern control theory, and achieves high performance separately by two ways, a high-effective feedback regulation and a direct compensation based on disturbance estimation. Therefore, it essentially improves the control precision and disturbance rejection property and has strong robustness and universality.The application of ADRC for speed control in the PMSM servo system is first studied and the design of a first-order ADRC in the speed-loop is elaborated. Through theoretical analysis, simulation and experimental results, the tracking performance and disturbance rejection property of the system are improved by using non-smooth feedback(NSF) and disturbance estimation compensation based on ESO. Considering the fact that the estimation error of inertia will result in a degradation of system performance, an improved inertia identification method based on disturbance observer(DOB) is adopted to adaptively adjust the corresponding coefficient in ADRC. Therefore, it achieves a better speed response in the case of inertia variations.Next, a first-order ADRC in the position-loop is also designed and thus a PMSM position servo system is constructed based on two cascaded ADRCs. Simulation and experimental results show that compared with conventional control, the proposed method achieves faster response, higher precision and stronger disturbance rejection.