Design of an Improved Sliding Mode Observer for Sensorless Switched Reluctance Motors

Aiming at the problems of large torque pulsation of switched reluctance motor and the jitter vibration and slow error convergence rate of conventional sliding mode observer, an improved sliding mode observer that suppresses the torque pulsation, reduces the jitter vibration, and improves the convergence rate is introduced in order to realize the precise control of switched reluctance motor without position sensor. The improved sliding mode observer adopts an novel exponential function as the switching function, and introduces an improved power exponential convergence law as the convergence law for speed observation. The stability and finite time convergence of the system are proved by means of the Lyapunov function. By comparing the simulation data and results of the sliding mode observer before and after the improvement, it is concluded that either the switching function or the convergence law control alone can reduce the jitter and increase the convergence rate, and the improved sliding mode observer combining the two can further reduce the error, inhibit the jitter with more obvious effect, make the system run more stably, and the estimation value can be close to the actual value quickly.

I. Introduction

Switched Reluctance Motor (SRM) has many advantages such as simple structure, low manufacturing cost, wide speed range, high fault tolerance, flexible control parameters, etc. It has been used in many fields such as aerospace, electric vehicles, industrial automation and household appliances[1]. However, the special biconvex structure and nonlinearity of SRMs lead to large system output torque pulsations, limiting their application range[2]. In addition, conventional control methods rely on position sensors to obtain rotor position information for SRM speed regulation and phase change. Yet, installing mechanical position sensors increases system cost and complexity, and reduces operational reliability. Therefore, the research on sensorless control of SRM and reduction of torque pulsation is of great importance[3].