Abstract : Based on the theory of PWM frequency conversion control, this paper analyzes the harmonics of the output waveform of the widely used modulation methods, discusses various factors contributing to harmonic generation, and proposes an effective suppression method to reduce the harm of harmonics to the motor. Keywords : SPWM method, Special Harmonic Eliminate (SHE) method, LC filter 1 Introduction With the widespread application of PWM technology in frequency conversion control, frequency converters have become important devices for AC motor speed regulation, offering not only a wide modulation range but also significant energy-saving effects. However, harmonics generated during the inverter process increase motor losses, reduce efficiency and power factor, and generate electromagnetic noise. The most significant impact is the torque pulsation caused by low-frequency harmonics, ultimately leading to speed pulsation. Currently, the most effective modulation methods for suppressing harmonics are Sinusoidal Pulse Width Modulation (SPWM) or Special Harmonic Eliminate (SHE), but these methods still struggle to prevent high-frequency harmonics from causing insulation failure in motor windings and bearing damage. This paper conducts a detailed harmonic analysis of these two methods and, based on the distribution of harmonics in the frequency spectrum, proposes a method to reduce the harm of harmonics to motor performance. [b]2 Harmonic Analysis of Common Modulation Methods[/b] For PWM-type frequency converter control, the U/f control method is generally adopted from the perspective of constant torque driven by the motor. This method controls the output voltage of the frequency converter while changing the frequency to ensure constant magnetic flux and achieve constant torque. Therefore, the PWM control principle achieves U/f control by changing the modulation depth and commutation frequency. Currently, modulation methods with high-quality waveform output include: SPWM and SHE. 2.1 Harmonic Analysis of SPWM Sinusoidal pulse width modulation (SPWM) uses the intersection of a triangular wave and a sine wave as the switching control signal for the frequency converter power supply. Its basic principle is shown in Figure 1. [b][align=center]For details, please click: Comprehensive Method for Harmonic Suppression in PWM-type Frequency Converter Control[/align][/b]