Power conversion device and control method thereof

A control method applied in a power conversion device, wherein the power conversion device converts a direct-current (DC) voltage to an alternating current corresponding to an alternating-current (AC) voltage according to a pulse width modulation (PWM) control signal and an output control signal, the method is for providing the PWM control signal and the output control signal, and the method comprises:

• obtaining an alternating current command according to the product of the absolute value of the phasor of the AC voltage and a DC current command, the alternating current command corresponding to the instantaneous value of the AC current;
• obtaining a feed-forward signal according to the product of the alternating current command and a gain value, the feed-forward signal representing an angle, and the gain value corresponding to the ratio between the effective values of the AC voltage and the alternating current;
• providing the PWM control signal according to an angular frequency and the angle represented by the feed-forward signal, the angular frequency corresponding to the resonance frequency of the power conversion device;
• and
• providing the output control signal according to the instantaneous value of the AC voltage.

A power conversion device, for converting a direct-current (DC) voltage to an alternating current corresponding to an alternating-current (AC) voltage according to the AC voltage, comprising:

• a control unit, for providing a pulse width modulation (PWM) control signal and an output control signal according to the instantaneous value of the AC voltage;
• a power conversion unit, for converting the DC voltage to a high-frequency current having two envelops corresponding to the waveform of the AC voltage, comprising;
• a DC to AC conversion circuit, comprising a full-bridge inverter having four active switch elements, wherein the four active switch elements are turned on correspondingly under control of the PWM control signal, the four active switch elements being turned on accordingly are for converting the DC voltage to a converted voltage, the amplitude of the converted voltage is substantially equal to the level of the DC voltage, and the duty cycle of the converted voltage corresponds to the absolute value of the instantaneous value of the AC voltage;
• and
• an immitance conversion circuit, for converting the converted current to the high-frequency current by way of resonance;
• and
• an output unit, comprising:
• an inductive circuit, for providing two induced currents according to the high-frequency current, wherein one induced current and the high-frequency current are in phase, and the other induced current and the high-frequency current are in antiphase;
• a full-wave rectifying circuit, for full-wave rectifying the two induced currents;
• an inverter circuit, comprising another two active switch elements which are turned on alternatively under control of the output control signal, wherein the another two active switch elements being turned on alternatively are for transferring the two full-wave rectified induced currents, respectively, so as to output an output current;
• and
• a filter circuit, for filtering the output current to provide the alternating current.