POWER CONVERTING DEVICE AND METHOD FOR CONTROLLING THE SAME

• US 20090168474A1
• Filed: 12/26/2007
• Published: 07/02/2009
• Est. Priority Date: 12/26/2007
• Status: Active Grant

• Current Assignee: Hitachi Industrial Products, Ltd. (Hitachi, Ltd.)
• Original Assignee: Hitachi, Ltd.
• Inventors: Futami, Motoo, Katoh, Shuji, Kiyofuji, Yasuhiro, Ito, Tomomichi, Koseki, Shoichiro
• Granted Patent: US 7,643,317 B2
• Time in Patent Office: Days
• US Class Current: 363/78
• CPC Class Codes: H02J 3/01 Arrangements for reducing harmonics or ripples
• CPC Class Codes: Y02E 40/40 Arrangements for reducing harmonics

Abstract

In a system to which a fluctuating load is connected, compensating for fluctuation in voltage harmonics at the load connecting point and fluctuation in system current harmonics has been difficult for a power converting device connected in parallel with the load. To resolve the problem, a power converting device connected in parallel with a fluctuating load includes: a Fourier series expansion unit which executes Fourier series expansion to load current by use of a reference sine wave in sync with a system and thereby outputs Fourier coefficients; and a fundamental component calculating unit which calculates a positive phase active fundamental component of the load current from the Fourier coefficients. A current instruction of the power converting device is generated by subtracting the fundamental current from the load current. With the current instruction, the fluctuations in system current harmonics and in voltage harmonics at the connecting point can be compensated for.

Claims

1. A power converting device which is connected in parallel with a fluctuating load, comprising:

a current detecting unit which detects load current;

a Fourier series expansion unit which executes Fourier series expansion to the detected load current;

a positive phase active fundamental current calculating unit which calculates a positive phase active fundamental current based on the output of the Fourier series expansion unit; and

a current instruction value calculating unit (100) which calculates a current instruction value of the power converting device by calculating a current compensation instruction value by subtracting current obtained using at least the positive phase active fundamental current from the load current and setting the current instruction value at the current compensation instruction value or at the sum of the current compensation instruction value and a current instruction value obtained by one or more other control units.

2. The power converting device according to claim 1, further comprising a positive phase reactive fundamental current calculating unit which calculates a positive phase reactive fundamental current based on the output of the Fourier series expansion unit, wherein:

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current and low-frequency fluctuation components of the positive phase reactive fundamental current from the load current.

3. The power converting device according to claim 1, further comprising:

a positive phase reactive fundamental current calculating unit which calculates a positive phase reactive fundamental current based on the output of the Fourier series expansion unit;

a negative phase Fourier series expansion unit which executes Fourier series expansion to a negative phase component of the detected load current;

a negative phase real axis fundamental current calculating unit which calculates a negative phase real axis fundamental current based on the output of the negative phase Fourier series expansion unit; and

a negative phase imaginary axis fundamental current calculating unit which calculates a negative phase imaginary axis fundamental current based on the output of the negative phase Fourier series expansion unit, wherein;

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current and low-frequency fluctuation components of the positive phase reactive fundamental current, the negative phase real axis fundamental current and the negative phase imaginary axis fundamental current from the load current.

4. The power converting device according to claim 1, further comprising a multiple frequency component removing unit which removes frequency components around a multiple of a system frequency from the positive phase active fundamental current, wherein:

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the multiple frequency component removing unit from the load current.

5. The power converting device according to claim 1, further comprising a positive phase reactive fundamental current calculating unit which calculates a positive phase reactive fundamental current based on the output of the Fourier series expansion unit;

and

a multiple frequency component removing unit which removes frequency components around a multiple of a system frequency from the positive phase active fundamental current, wherein;

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the multiple frequency component removing unit and low-frequency fluctuation components of the positive phase reactive fundamental current from the load current.

6. The power converting device according to claim 1, further comprising:

a positive phase reactive fundamental current calculating unit which calculates a positive phase reactive fundamental current based on the output of the Fourier series expansion unit;

a negative phase Fourier series expansion unit which executes Fourier series expansion to a negative phase component of the detected load current;

a negative phase real axis fundamental current calculating unit which calculates a negative phase real axis fundamental current based on the output of the negative phase Fourier series expansion unit;

a negative phase imaginary axis fundamental current calculating unit which calculates a negative phase imaginary axis fundamental current based on the output of the negative phase Fourier series expansion unit; and

a multiple frequency component removing unit which removes frequency components around a multiple of a system frequency from the positive phase active fundamental current, wherein;

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the multiple frequency component removing unit and low-frequency fluctuation components of the positive phase reactive fundamental current, the negative phase real axis fundamental current and the negative phase imaginary axis fundamental current from the load current.

7. The power converting device according to claim 1, further comprising a high-frequency fluctuation component removing unit which removes high-frequency fluctuation components from the positive phase active fundamental current, wherein:

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the high-frequency fluctuation component removing unit from the load current.

8. The power converting device according to claim 1, further comprising:

a positive phase reactive fundamental current calculating unit which calculates a positive phase reactive fundamental current based on the output of the Fourier series expansion unit; and

a high-frequency fluctuation component removing unit which removes high-frequency fluctuation components from the positive phase active fundamental current, wherein;

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the high-frequency fluctuation component removing unit and low-frequency fluctuation components of the positive phase reactive fundamental current from the load current.

9. The power converting device according to claim 1, further comprising:

a positive phase reactive fundamental current calculating unit which calculates a positive phase reactive fundamental current based on the output of the Fourier series expansion unit;

a negative phase Fourier series expansion unit which executes Fourier series expansion to a negative phase component of the detected load current;

a negative phase real axis fundamental current calculating unit which calculates a negative phase real axis fundamental current based on the output of the negative phase Fourier series expansion unit;

a negative phase imaginary axis fundamental current calculating unit which calculates a negative phase imaginary axis fundamental current based on the output of the negative phase Fourier series expansion unit; and

a high-frequency fluctuation component removing unit which removes high-frequency fluctuation components from the positive phase active fundamental current, wherein;

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the high-frequency fluctuation component removing unit and low-frequency fluctuation components of the positive phase reactive fundamental current, the negative phase real axis fundamental current and the negative phase imaginary axis fundamental current from the load current.

10. The power converting device according to claim 1, further comprising a voltage compensation instruction value calculating unit which calculates a voltage compensation instruction value by executing Fourier series expansion to voltage detected at a connecting point, calculating a positive phase active fundamental voltage based on the result of the Fourier series expansion, subtracting the positive phase active fundamental voltage from system voltage, converting the difference into current by dividing the difference by impedance from a converter of the power converting device to the connecting point, and multiplying the obtained current by a real number, wherein:

the current instruction value calculating unit sets the current instruction value of the power converting device at the sum of the current compensation instruction value and the voltage compensation instruction value or at the sum of the current compensation instruction value, the voltage compensation instruction value and a current instruction value obtained by one or more other control units.

20. The power converting device according to claim 1, wherein:

the current instruction value calculating unit calculates the current compensation instruction value by subtracting the positive phase active fundamental current from the load current.

11. A power converting device which is connected in parallel with a fluctuating load, comprising:

a current detecting unit which detects system current;

a Fourier series expansion unit which executes Fourier series expansion to the detected system current;

a positive phase active fundamental current calculating unit (108) which calculates a positive phase active fundamental current based on the output of the Fourier series expansion unit; and

a current instruction value calculating unit which calculates a current instruction value of the power converting device by calculating a current compensation instruction value by subtracting current obtained using at least the positive phase active fundamental current from the system current and setting the current instruction value at the current compensation instruction value or at the sum of the current compensation instruction value and a current instruction value obtained by one or more other control units.

12. A current control method for a power converting device which is connected in parallel with a fluctuating load, comprising:

a current detecting step of detecting load current;

a Fourier expansion step of executing Fourier series expansion to the detected load current;

a positive phase active fundamental current calculating step of calculating a positive phase active fundamental current based on the result of the Fourier expansion step; and

a current instruction value calculating step of calculating a current instruction value of the power converting device by calculating a current compensation instruction value by subtracting current obtained using at least the positive phase active fundamental current from the load current and setting the current instruction value at the current compensation instruction value or at the sum of the current compensation instruction value and a current instruction value obtained by one or more other control steps.

13. The current control method according to claim 12, further comprising a positive phase reactive fundamental current calculating step of calculating a positive phase reactive fundamental current based on the result of the Fourier expansion step, wherein:

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current and low-frequency fluctuation components of the positive phase reactive fundamental current from the load current.

14. The current control method according to claim 12, further comprising:

a positive phase reactive fundamental current calculating step of calculating a positive phase reactive fundamental current based on the result of the Fourier expansion step;

a negative phase Fourier expansion step of executing Fourier series expansion to a negative phase component of the detected load current;

a negative phase real axis fundamental current calculating step of calculating a negative phase real axis fundamental current based on the result of the negative phase Fourier expansion step; and

a negative phase imaginary axis fundamental current calculating step of calculates a negative phase imaginary axis fundamental current based on the result of the negative phase Fourier expansion step, wherein;

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current and low-frequency fluctuation components of the positive phase reactive fundamental current, the negative phase real axis fundamental current and the negative phase imaginary axis fundamental current from the load current.

15. The current control method according to claim 12, further comprising a multiple frequency component removing step of removing frequency components around a multiple of a system frequency from the positive phase active fundamental current, wherein:

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the multiple frequency component removing step from the load current.

16. The current control method according to claim 12, further comprising a positive phase reactive fundamental current calculating step of calculating a positive phase reactive fundamental current based on the result of the Fourier expansion step;

and

a multiple frequency component removing step of removing frequency components around a multiple of a system frequency from the positive phase active fundamental current, wherein;

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the multiple frequency component removing step and low-frequency fluctuation components of the positive phase reactive fundamental current from the load current.

17. The current control method according to claim 12, further comprising:

a positive phase reactive fundamental current calculating step of calculating a positive phase reactive fundamental current based on the result of the Fourier expansion step;

a negative phase Fourier expansion step of executing Fourier series expansion to a negative phase component of the detected load current;

a negative phase real axis fundamental current calculating step of calculating a negative phase real axis fundamental current based on the result of the negative phase Fourier expansion step;

a negative phase imaginary axis fundamental current calculating step of calculating a negative phase imaginary axis fundamental current based on the result of the negative phase Fourier expansion step; and

a multiple frequency component removing step of removing frequency components around a multiple of a system frequency from the positive phase active fundamental current, wherein;

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the multiple frequency component removing step and low-frequency fluctuation components of the positive phase reactive fundamental current, the negative phase real axis fundamental current and the negative phase imaginary axis fundamental current from the load current.

18. The current control method according to claim 12, further comprising a high-frequency fluctuation component removing step of removing high-frequency fluctuation components from the positive phase active fundamental current, wherein:

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the high-frequency fluctuation component removing step from the load current.

19. The current control method according to claim 12, further comprising:

a positive phase reactive fundamental current calculating step of calculating a positive phase reactive fundamental current based on the result of the Fourier expansion step; and

a high-frequency fluctuation component removing step of removing high-frequency fluctuation components from the positive phase active fundamental current, wherein;

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current after the removal by the high-frequency fluctuation component removing step and low-frequency fluctuation components of the positive phase reactive fundamental current from the load current.

21. The current control method according to claim 12, wherein:

the current instruction value calculating step calculates the current compensation instruction value by subtracting the positive phase active fundamental current from the load current.