The frequency converter controls and stabilizes its frequency by detecting the phase of the output voltage. The phase-locked technology uses the feedback principle to continuously monitor and adjust the difference between the output signal and the reference signal to ensure the accurate generation of the required stable and qualified AC power supply. This method depends on the detection circuit and controller, by comparing the deviation or error between the actual output waveform and the expected waveform, and correcting it according to the result to keep synchronization. This can meet the requirements of equipment operation and provide reliable operation in special application scenarios.