Adaptive Overmodulation Strategy for PMSM Field-Weakening Control Based on Working Quadrant

Abstract

In the traditional overmodulation method, the reference of voltage loop is usually fixed to a constant value for field-weakening control of permanent magnet synchronous motors (PMSMs). Although the maximum output voltage can reach the fundamental amplitude of six-step mode, it results in the problem of overlarge voltage regardless of the actual requirement, causing serious torque harmonics. To address this problem, an adaptive overmodulation strategy is proposed based on the working quadrant to diminish the redundant voltage of overmodulation. The concept of the working quadrants is defined in this paper, which is divided into four cases according to the speed error and stator current. Then, three kinds of reference voltages are designed to satisfy the control requirements of the defined working quadrants. On this basis, the range of output torque is analyzed and expressed on the operation condition plane. Compared with the traditional overmodulation method, the studied approach can adjust the reference voltage according to the actual working quadrants dynamically, so as to ensure rapidity in transient state and reduce torque harmonics in steady state. The experimental results from a 2.2kW PMSM platform verify the effectiveness of the studied approach.