Sliding Mode Speed Control of PMLSM with Load Force Observer

Siding mode control is a kind of nonlinear variable structure control. The chattering problem is the main problem that influence the smooth running of system. To reduce the chattering problem and keep the stability of sliding mode control at the same time, an improved boundary layer control is proposed in this paper. The error of reference velocity and real velocity is selected to make up the sliding plane. And the gain of the saturation function is variable to speed up the tracking speed of velocity and reduce the chattering problem when speed error is small. And a load thrust observer is proposed in this paper to observe the thrust ripple for feedforward compensation. Experiment results show that the improved boundary layer control can realize faster velocity tracking speed and also suppress the intrinsic chattering of sliding mode control.

I. Introduction

Permanent magnet linear synchronous motor(PMLSM) has the advantage of simple structure, high efficiency, high power density, and high reliability. Over the years, PMLSM has been widely used in space field, medical field, semiconductor manufacturing field and so on. And these fields are very demanding on the accuracy and the response speed of PMLSM. So, increasing the speed accuracy and the response speed are of great importance. PI controller is a commonly used method because it has strong robustness and is easy to design, but PMLSM is a nonlinear and strong coupling system, so sometimes it cannot meet the requirements of high performance control [1].