Traditional variable-frequency power supplies adopt a two-stage structure consisting of uncontrolled rectification and variable-voltage variable-frequency (VVVF) inverter. These power supplies focus solely on the quality of the output sine waveform, voltage and frequency accuracy, and reliability, without considering whether the current at the system input end may cause harmonic pollution to the grid or whether the variable-frequency power supply injects a large amount of high-frequency harmonic current into the grid. Today, in addition to the above requirements for variable-frequency power supplies, environmental friendliness and pollution-free operation are also demanded. The development of active power factor correction (APFC) technology and its mature application in switching power supplies can effectively address this issue, improving the power factor. The combination of an active power corrector and an inverter also forms a two-stage structure, combining the advantages of uncontrolled rectification and inverter control. Furthermore, it not only enhances the system's power factor, effectively reduces harmonic pollution, but also increases the voltage level of the intermediate DC link, expanding the system's voltage output range.