Stability analysis of I-f startup method for PMSM drive systems

Abstract

In low-cost permanent magnet synchronous motor (PMSM) drive systems, the rotor position is usually estimated based on the back-electromotive force. However, such estimation methods have the common drawback of having large errors in low-speed regions. In order to solve that drawback in the start-up phase, the I-f start-up method is studied as its compatibility with the FOC control structure. The purpose of such a method is to make the motor accelerate and overcome the low-speed threshold. The process of implementing the I-f startup algorithm is divided into two stages, the first one is acceleration stage and the second one is smooth transition stage. During the acceleration phase, the motor speed is controlled using a constant-magnitude current vector located on a virtual rotating reference frame. Analyzes of possible oscillations and causes of system instability during the start-up phase are clarified in this study. The requirement of the parameters of the virtual rotating reference frame and the current vector for ensuring the acceleration process is under control is presented. The smooth transition stage is added so that large peak current pulses do not occur when switching from start-up mode to closed-loop control mode. The algorithm for reducing the virtual current vector magnitude by a simple linear ramp function is shown in this paper.  The analysis is verified through the simulation results.