Improved nonlinear sliding mode control based on load disturbance observer for permanent magnet synchronous motor servo system

Introduction

The permanent magnet synchronous motor (PMSM) has been widely used in many fields, such as high-performance computer numerical control (CNC) system, aerospace industry, and robot, owing to its advantages including compact structure, high power density, high inertia torque ratio, and high efficiency.¹ In order to acquire fast four-quadrant operation and smooth start and acceleration, the field-oriented control or space vector control is employed in the design of PMSM drive.^2–4 However, PMSM is a time-varying nonlinear system with multivariable and strong coupling and easily influenced by the external interference. Furthermore, the model parameter mismatch and perturbation existed in the PMSM mathematical model of field-oriented control system since the model is built in the hypothesis of neglecting the influence of magnetic circuit saturation, hysteresis, and eddy current. Therefore, the traditional proportional–integral (PI) controller is unable to satisfy the dynamic response performance of PMSM due to its fixed proportional gain and integral time constant.^5–7 In recent years, many nonlinear control strategies have been developed for PMSM servo system to improve the dynamic response such as neural-based robust control algorithms,^7–9 adaptive control,^10–13 H_∞ control,¹⁴ and sliding mode control (SMC).^3,4

The SMC is employed frequently in the AC servo control system due to its good performance of fast response and insensitivity to the matched parameter perturbation and disturbance. The principle for designing SMC is to construct the sliding surface based on the system state variables. Zhang and Panda¹⁵ presented the conventional linear sliding surface (LSS) used in PMSM speed control to make the system convergent within finite settling time. The non-singular terminal sliding mode manifold is proposed in PMSM speed regulation system to obtain a faster convergent speed and a better tracking precision.¹⁶ Recently, SMC has been combined with intelligent control method to achieve better performance of PMSM control.^17,18 However, according to the control law design of traditional SMC system with mismatched uncertainties, the states can only be driven to the sliding surface in finite time rather than the desired equilibrium. This leads to many researches on the SMC design for uncertain systems with mismatched uncertainties. The linear matrix inequality (LMI)-based sliding surface design for SMC has been proposed to guarantee the asymptotic stability of full order...