Current Harmonic Suppression at Low Switching Frequency of High-Speed Permanent Magnet Motor Based on Decoupling Control

Due to a variety of issues, such as high switching device losses and unstable operation induced by high inverter operating frequencies during operation, high-speed permanent magnet motors are frequently run in environments with low inverter switching frequencies. This paper investigates the problems of severe dq-axis current coupling and high harmonic current content when high-speed permanent magnet synchronous motor operates at low switching frequency. In the current loop, a feedforward decoupling control technique is used to achieve dynamic decoupling of dq-axis currents. In addition, a harmonic suppression algorithm based on harmonic voltage injection is proposed, which extracts the stator harmonic currents under the 5th and 7th harmonics synchronous rotating coordinate system and derives the harmonic voltage expression to calculate the harmonic voltages, and finally injects the harmonic voltages into the voltage feedback link of the system to achieve the effect of current harmonic suppression. Simulation proves that this control method can effectively realize dq-axis current decoupling and suppress stator current distortion, indicating that the control algorithm adopted in this paper can achieve the research purpose.

I. Introduction

High-speed permanent magnet motors have significant advantages such as small size, light weight, high efficiency, fast dynamic response, high power factor, etc., and can realise the direct-drive structure, which has a very broad application prospect in the fields of China's military equipment, aerospace, energy security, etc., and is the key research object in the field of international electrical engineering. Since high-speed permanent magnet motors frequently run at high fundamental frequencies, the switching frequency of power devices is often very high. This condition is likely to cause system operation instability and switch damage possible. As a result, high-speed permanent magnet motors are frequently operated in low switching frequency environments. However, when the high-speed permanent magnet motor is operated at a low switching frequency, the carrier ratio is relatively low, resulting in poorer sinusoidal degree of the stator current, and a significant increase in the harmonic content of the current. Furthermore, as motor speed increases, the degree of motor system connection deepens, resulting in unstable system operation.