Power conversion apparatus and control method thereof

1. A power conversion apparatus cooperated with an aerogenerator being controlled to operate at a maximum power approximation line, said power conversion apparatus outputting an AC signal including an AC voltage signal and an AC current signal, comprising:

an AC/DC conversion circuit receiving the AC signal and outputting a voltage signal and including a switching element; and

a control module including:

a voltage sensing circuit generating a voltage reference signal according to the AC voltage signal;

a harmonic generation circuit generating a harmonic injection signal according to the voltage reference signal; and

a maximum power tracking circuit including:

a subtraction circuit outputting a first DC signal and a second DC signal according to the voltage reference signal;

an arithmetic circuit outputting a reference signal according to the first DC signal, the second DC signal and a voltage error signal;

a current sensing circuit outputting a feedforward signal according to one phase of the AC current signal;

a current control circuit outputting an error signal according to the reference signal and the feedforward signal; and

a pulse width modulation circuit outputting a control signal to control the switching element according to the error signal and the harmonic injection signal, so that the aerogenerator operates at the maximum power approximation line.

2. The power conversion apparatus as recited in claim 1 , wherein the AC/DC conversion circuit is a three-phase single-switch boost converter.

3. The power conversion apparatus as recited in claim 1 , wherein the maximum power tracking circuit further includes a voltage feedback compensation circuit, which outputs the voltage error signal according to the output voltage and a reference voltage.

4. The power conversion apparatus as recited in claim 3 , wherein the voltage feedback compensation circuit includes a voltage division unit and an error amplifier unit, the voltage division unit executes a voltage division to the output voltage to output a voltage division signal, the voltage division signal is inputted to the negative end of the error amplifier unit, and the reference voltage is inputted to the positive end of the error amplifier unit.

5. The power conversion apparatus as recited in claim 4 , wherein the error amplifier unit makes the voltage value of the voltage division signal and the waveform thereof substantially the same as the reference voltage.

6. The power conversion apparatus as recited in claim 1 , wherein the subtraction circuit includes a low-pass filter unit and a differential amplifier unit, the low-pass filter unit outputs the first DC signal according to the voltage reference signal, and the differential amplifier unit generates the second DC signal according to the first DC signal and a reference voltage.

7. The power conversion apparatus as recited in claim 1 , wherein the arithmetic circuit multiplies the first DC signal by the voltage error signal and then divide the product by the square of the second DC signal to obtain the reference signal.

8. The power conversion apparatus as recited in claim 7 , wherein the maximum power tracking circuit further includes a control resistor, which generates a control voltage according to the reference signal, and the control voltage is directly proportional to the reference signal.

9. The power conversion apparatus as recited in claim 8 , wherein the current control circuit makes the voltage value of the feedforward signal and the waveform thereof substantially the same as the control voltage.

10. The power conversion apparatus as recited in claim 1 , wherein the voltage sensing circuit reduce the voltage of the AC voltage signal and rectifies the AC voltage signal to output the voltage reference signal.

11. The power conversion apparatus as recited in claim 10 , wherein the harmonic generation circuit includes a high-pass filter unit and an inverting amplifier unit, the high-pass filter unit filters out the low-frequency portion of the voltage reference signal to generate a filter signal, and the inverting amplifier unit inverts the phase of the filter signal to output the harmonic injection signal.

12. The power conversion apparatus as recited in claim 11 , wherein the error signal and the harmonic injection signal are added together and then inputted to the pulse width modulation circuit.

13. The power conversion apparatus as recited in claim 11 , wherein the frequency of any of the voltage reference signal and the harmonic injection signal is six times that of the AC voltage signal.

14. A control method of a power conversion apparatus cooperated with an aerogenerator being controlled to operate at a maximum power approximation line, said power conversion apparatus outputting an AC signal including an AC voltage signal and an AC current signal, wherein the power conversion apparatus includes an AC/DC conversion circuit and a control module, the AC/DC conversion circuit receives the AC signal and outputs a voltage signal and includes a switching element, the control module includes a voltage sensing circuit, a harmonic generation circuit and a maximum power tracking circuit including a subtraction circuit, an arithmetic circuit, a current sensing circuit, a current control circuit and a pulse width modulation circuit, the control method comprising steps of:

generating a voltage reference signal according to the AC voltage signal by the voltage sensing circuit;

generating a harmonic injection signal according to the voltage reference signal by the harmonic generation circuit;

outputting a first DC signal and a second DC signal according to the voltage reference signal by the subtraction circuit;

outputting a reference signal according to the first DC signal, the second DC signal and a voltage error signal by the arithmetic circuit;

outputting a feedforward signal according to one phase of the AC current signal by the current sensing circuit;

outputting an error signal according to the reference signal and the feedforward signal by the current control circuit; and

outputting a control signal to control the switching element according to the error signal and the harmonic injection signal by the pulse width modulation circuit, so that the aerogenerator operates at the maximum power approximation line.

15. The control method as recited in claim 14 , before the subtraction circuit outputs the second DC signal, further comprising steps of:

outputting the first DC signal according to the voltage reference signal by a low-pass filter unit of the subtraction circuit; and

generating the second DC signal according to the first DC signal and a reference voltage by a differential amplifier unit of the subtraction circuit.

16. The control method as recited in claim 15 , before the arithmetic circuit outputs the reference signal, further comprising a step of:

multiplying the first DC signal by the voltage error signal and then dividing the product by the square of the second DC signal to obtain the reference signal by the arithmetic circuit.

17. The control method as recited in claim 16 , before the current control circuit outputs the error signal, further comprising a step of:

generating a control voltage according to the reference signal by a control resistor, and the control voltage being directly proportional to the reference signal.

18. The control method as recited in claim 14 , in the step of generating the harmonic injection signal by the harmonic generation circuit, further comprising steps of:

generating a filter signal by a high-pass filter unit of the harmonic generation circuit filtering out the low-frequency portion of the voltage reference signal; and

inverting the phase of the filter signal by an inverting amplifier unit of the harmonic generation circuit to output the harmonic injection signal.

19. The control method as recited in claim 18 , wherein the error signal and the harmonic injection signal are added together and then inputted to the pulse width modulation circuit.

20. The control method as recited in claim 18 , wherein the frequency of each of the voltage reference signal and the harmonic injection signal is six times that of the AC voltage signal.