In the field of high-current, high-power AC drives, the maximum switching frequency of the inverter is limited by switching losses, which requires the inverter to operate at lower carrier ratios. This will bring a series of problems such as high harmonic content in the output current, especially the lower harmonics, affecting system performance. Under the current mainstream asynchronous Pulse Width Modulation method, in order to improve the current output quality and driving performance of the inverter under low carrier ratios, it is necessary to analyze its modulation characteristics and modulation problems. In this way, the modulation strategy can be optimized and a better control effect can be achieved. This paper discusses the performance of asynchronous PWM strategy at low carrier ratios, specifically including the beat phenomenon, the fundamental amplitude loss, and the subharmonic problem, and accordingly proposes carrier ratio control methods, which are verified by simulation models.