Power control method during input line voltage fluctuation

A resonant power converter, comprising:

• first and second switching elements coupled across a direct current (DC) power source;
• a resonant circuit coupled between an isolation transformer primary winding and an output node between the first and second switching elements;
• a current sensing circuit coupled in series with a load across a secondary winding of the isolation transformer and configured to provide a sensor output signal representative of an output current across the load;
• a feedback circuit configured to generate an error signal corresponding to a difference between the sensor output signal and a reference signal;
• a controller comprising a frequency control input terminal, and configured to generate drive signals to the first and second switching elements at a determined operating frequency;
• a frequency control circuit coupled between the feedback circuit and the frequency control input terminal of the controller, and configured, responsive to the error signal, to determine the operating frequency of the controller with respect to defined minimum and maximum frequencies;
• and
• a reference control circuit coupled between an output terminal of the feedback circuit and a reference signal input of the feedback circuit, the reference control circuit configured to sense when the error signal exceeds a threshold value, and in response to control the reference signal wherein the error signal is reset to a value below the threshold value.