Power conversion device and control method thereof

• US 8,059,434 B2
• Filed: 07/21/2009
• Issued: 11/15/2011
• Est. Priority Date: 12/08/2008
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Huang, Yung-Fu, Konishi, Yoshihiro
• Primary Examiner(s): Berhane; Adolf
• Assistant Examiner(s): Finch, III; Fred E
• Application Number:
  US12/506,398
• Publication Number:
  US 20100142233A1
• Time in Patent Office: 847 Days
• Field of Search: 363/17, 363/21.02, 363/37, 363/97, 363/98, 363/131, 363/132
• US Class Current: 363/98
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage

Abstract

A power conversion device is provided for converting a DC voltage to an alternating current corresponding to an AC voltage according to the AC voltage, which includes a power conversion unit and an output unit. The power conversion unit converts the DC voltage to a high-frequency current having two envelops corresponding to the waveform of the AC voltage. The output unit includes an inductive circuit, a full-wave rectifying circuit, an inverter circuit and a filter circuit. The inductive circuit provides 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. The full-wave rectifying circuit full-wave rectifies the two induced currents. The inverter circuit alternatively transfers the two full-wave rectified induced currents, and thus output an output current. The filter circuit filters the output current to provide the alternating current.

Claims

1. 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 power conversion unit, for converting the DC voltage to a high-frequency current having two envelops corresponding to the waveform of the AC voltage, the power conversion unit comprising;

a DC to AC conversion circuit, for converting the DC voltage to a converted voltage, wherein 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, wherein the DC to AC conversion circuit comprises a full-bridge inverter having four active switch elements, the four active switch elements are turned on correspondingly under control of a pulse width modulation (PWM) control signal, and the four active switch elements being turned on correspondingly are for converting the DC voltage to the converted voltage; and

an immitance conversion circuit, for converting the converted voltage to the high-frequency current by way of resonance;

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, for alternatively transferring the two full-wave rectified induced currents so as to output an output current; and

a filter circuit, for filtering the output current to provide the alternating current; and

a control unit, for providing the PWM control signal according to an instantaneous value of the AC voltage;

wherein, the control unit obtains an alternating current command according to a product of the absolute value of the phasor of the AC voltage and a DC current command, and the alternating current command corresponds to an instantaneous value of the alternating current;

wherein, the control unit further obtains a feed-forward signal according to a product of the alternating current command and a gain value, the feed-forward signal represents an angle, and the gain value corresponds to a ratio between effective values of the AC voltage and the alternating current; and

wherein, the control unit further provides the PWM control signal according to an angular frequency and the angle represented by the feed-forward signal, and the angular frequency corresponds to a resonance frequency of the immitance conversion circuit.

2. The power conversion device according to claim 1, wherein the fundamental frequency and the phase of the output current are substantially equal to the frequency and the phase of the AC voltage, respectively.

3. The power conversion device according to claim 1, wherein the duty cycle of the converted voltage is in direct proportion to the absolute value of the instantaneous value of the AC voltage.

4. The power conversion device according to claim 1, wherein the DC to AC conversion circuit is further for adjusting the duty cycle of the converted voltage according to the level of the DC voltage.

5. The power conversion device according to claim 1, wherein the control unit further adjusts the angle represented by the feed-forward signal according to the level of the DC voltage.

6. The power conversion device according to claim 1, wherein the control unit further obtains a current difference according to the difference between the absolute value of the instantaneous value of the AC current and the value represented by the alternating current command;

wherein, the control unit further converts the current difference to a feed-back signal by way of proportional-Integral (PI) control, and the feed-back signal represents another angle; and

wherein, the control unit provides the PWM control signal according to the angular frequency and a sum of the two angles represented by the feed-forward signal and the feed-back signal.

7. The power conversion device according to claim 1, wherein the immitance conversion circuit comprises:

two inductors, connected in series; and

a capacitor, coupled with one end to the series-connected end of the two inductors;

wherein, one end of the two series-connected inductors and the other end of the capacitor are for receiving the converted voltage, and the other end of the two series-connected inductors and the other end of the capacitor are coupled to the inductive circuit and serve as two ends for providing the high-frequency current.

8. The power conversion device according to claim 1, wherein the inductive circuit comprises a transformer which comprises:

a primary winding, for receiving the high-frequency current; and

two secondary windings, for providing the two induced currents, respectively.

9. The power conversion device according to claim 8, wherein a turns ratio between the primary winding and one of the two secondary windings is substantially equal to a turns ration between the primary winding and the other one of the two secondary windings.

10. The power conversion device according to claim 1, wherein the full-wave rectifying circuit comprises four passive switch elements, two of the four passive switch elements are connected in series and the other two of the four passive switch elements are connected in series, two series-connected ends of the two passive switch elements and the other two passive switch elements are coupled to the inductive circuit for receiving the two induced currents, the two passive switch elements are connected in parallel to the other two passive switch elements, two parallel-connected ends of the two passive switch elements and the other two passive switch elements are coupled to the inverter circuit, and the two parallel-connected ends serve as two ends for providing the two full-wave rectified induced currents.

11. The power conversion device according to claim 1, wherein the inverter circuit comprises:

two active switch elements, being alternately turned on under control of an output control signal;

wherein, the active switch elements being alternately turned on are for transferring the two full-wave rectified induced current, so as to make the inverter circuit output the output current.

12. The power conversion device according to claim 11, further comprising:

a control unit, for providing the output control signal according to the instantaneous value of the AC voltage.

13. The power conversion device according to claim 12, wherein the control unit provides the output control signal according to the polarity of the instantaneous value of the AC voltage;

wherein, when the polarity of the instantaneous value of the AC voltage is positive, the output control signal has a first level and is for turning on one of the two active switch elements; and

when the polarity of the instantaneous value of the AC voltage is negative, the output control signal has a second level and is for turning on the other one of the two active switch elements.

14. The power conversion device according to claim 11, wherein the two active switch elements are connected in series, two ends of the two series-connected active switch elements are coupled to the full-wave rectifying circuit and serve as two ends for providing the two full-wave rectified induced currents, and the series-connected end of the two active switch elements is coupled to the filter circuit and serves as one end for providing the output current.

15. The power conversion device according to claim 1, wherein the filter circuit comprises a capacitor, and the operation frequency of the capacitor is substantially equal to the frequency of the AC voltage.

16. 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 a product of the absolute value of the phasor of the AC voltage and a DC current command, the alternating current command corresponding to an instantaneous value of an alternating current;

obtaining a feed-forward signal according to a product of the alternating current command and a gain value, the feed-forward signal representing an angle, and the gain value corresponding to a ratio between 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 a resonance frequency of the power conversion device; and

providing the output control signal according to an instantaneous value of the AC voltage.

17. The control method according to claim 16, wherein the fundamental frequency and the phase of the alternating current are substantially equal to the frequency and the phase of the AC voltage, respectively.

18. The control method according to claim 16, further comprising:

adjusting the angle represented by the feed-forward signal according to the level of the DC voltage, so as to adjust the PWM control signal.

19. The control method according to claim 16, further comprising:

obtaining a current difference according to a difference between the value represented by the alternating current command and the absolute value of the instantaneous value of the alternating current;

converting the current difference to a feed-back signal by way of proportional-Integral (PI) control, the feed-back signal representing another angle; and

wherein, the step of providing the PWM control signal comprises;

providing the PWM control signal according to the angular frequency and the sum of the two angles represented by the feed-forward signal and the feed-back signal.

20. The control method according to claim 16, wherein the step of providing the output control signal comprises:

providing the output control signal according to the polarity of the instantaneous value of the AC voltage;

wherein, when the polarity of the instantaneous value of the AC voltage is positive, the output control signal has a first level and is for turning on one of two active switch elements; and

when the polarity of the instantaneous value of the AC voltage is negative, the output control signal has a second level and is for turning on the other one of the two active switch elements.