Elimination of Cogging Torque for Axial Flux Permanent Magnet Motors Based on Current Harmonic Injection

Abstract

Axial-flux permanent magnet (AFPM) disc machines are widely used for many industrial applications such as electrical vehicles, pumps, valve control and robotics due to their high power density and torque capability. One of the key issues of axial-flux permanent magnet machines for such applications is the torque quality and cogging component. Cogging torque causes torque and speed ripples, as well as acoustic noise and vibration, especially in low speed and direct drive applications. Therefore, the machine performance is affected and special precautions need to be taken. This paper focuses on harmonic injection and its effects for cogging torque minimization of axial-flux permanent magnet disc machines. Firstly, dominant harmonic order of cogging is investigated and then harmonic currents are added to the q-axis reference current. The proposed scheme is carried out on a microcontroller based servo driver and the test results confirm the effectiveness of the proposed method. It should be emphasized that this method is feasible to all permanent magnet motors having relatively large cogging torque components.