Active Power Filter

• US 20080219035A1
• Filed: 08/28/2007
• Published: 09/11/2008
• Est. Priority Date: 03/05/2007
• Status: Active Grant

• Current Assignee: Ablerex Electronics Company Limited (Ablerex Overseas Corporation Limited)
• Original Assignee: Ablerex Electronics Company Limited (Ablerex Overseas Corporation Limited)
• Inventors: Hsu, Wen-Pin, Kuo, Yu-Ting, Chou, Hung-Liang, Wu, Chin-Chang, Yang, Jiunn-Jye
• Granted Patent: US 7,787,267 B2
• Time in Patent Office: Days
• US Class Current: 363/41
• CPC Class Codes: H02J 3/1842 wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]

Abstract

An active power filter comprises an energy storage capacitor, an inverter, a filtering circuit and a controller. The inverter is controlled to act as a virtual resister at a fundamental frequency for compensating for the power loss of the active power filter, act as a virtual capacitor at a fundamental frequency for compensating for a fundamental reactive power of the load, and/or generate a harmonic current for suppressing the harmonic currents of specific orders of the load.

Claims

1. An active power filter, comprising:

an energy storage capacitor providing a regulated DC voltage;

an inverter including a plurality of power electronic switches, with the inverter electrically connecting with two terminals of the energy storage capacitor for switching the regulated DC voltage;

a filtering circuit providing two sets of terminals with one of the sets electrically connecting to the inverter and the other electrically connecting to power lines between a power source and a load; and

a controller outputting control signals transmitted to the inverter for driving the power electronic switches;

wherein the controller detects a source current, a source voltage and an energy storage capacitor voltage for calculating a reference signal and detects an output current of the active power filter, the output current tracking the reference signal through a feedback control of the controller, so as to control the power electronic switches of the inverter generating a compensating current.

2. The active power filter as defined in claim 1, wherein the compensating current comprises a component being proportional to a fundamental voltage of the power source for controlling the active power filter acting as a virtual resistor at fundamental frequency and connecting with the power source in parallel to compensate for the power loss of the active power filter.

3. The active power filter as defined in claim 1, wherein the compensating current comprises a component being proportional to a differential value of a fundamental voltage of the power source for controlling the active power filter acting as a virtual capacitor at fundamental frequency and connecting with the power source in parallel to compensate for the fundament reactive power of the load and the power loss of the active power filter 3.

4. The active power filter as defined in claim 1, wherein the compensating current comprises harmonic components of specific orders for operating the active power filter to attenuate a compound of the harmonic currents of specific orders with a predetermined attenuating ratio.

5. The active power filter as defined in claim 1, wherein the controller further comprises a harmonic current loop, a fundamental reactive current loop and a fundamental real current loop.

6. The active power filter as defined in claim 5, wherein the harmonic current loop comprises a first current sensor, a band-rejection filter and a harmonic calculating and amplifying circuit, with the first current sensor detecting the source current and transmitting a signal through the band-rejection filter to filter out the signal of a fundamental component, the output of the band-rejection filter transmits to the harmonic calculating and amplifying circuit to calculate the harmonic component of each specified order and then amplifies them by different gains in accordance with the predetermined attenuation thereof.

7. The active power filter as defined in claim 6 further comprises a current sensor for detecting a current of the load and calculating the source current by the current of the load and the output current of the active power filter.

8. The active power filter as defined in claim 5, wherein the reactive power circuit comprises a fundamental reactive power calculating circuit, a first voltage sensor, a band-pass filter, a differentiating circuit and a first multiplier, with the first voltage sensor sensing the source voltage, and the output signals of the first voltage sensor and a first current sensor are transmitted to the fundamental reactive power calculating circuit for calculating a value of the virtual capacitor of the inverter, with the signal generated by the first voltage sensor being transmitted to the band-pass filter to obtain a fundamental voltage of the power source, with the output signals of the fundamental reactive power calculating circuit and the differentiating circuit are transmitted to the first multiplier to generate a signal being proportional to a differential value of the fundamental voltage of the power source.

9. The active power filter as defined in claim 5, wherein the real power circuit comprises a second voltage sensor, a first subtracter, a first controller and a second multiplier, with the second voltage sensor detecting the energy storage capacitor voltage and sending a signal to the first subtracter together with a predetermined signal, with the output of the first subtracter being transmitted to the first controller for setting a value of the virtual resistor of the inverter, with the outputs of the first controller and a band-pass filter are transmitted to the second multiplier to obtain a fundamental voltage of the power source to generate a signal being proportional to the fundamental voltage of the power source.

10. The active power filter as defined in claim 5, wherein the controller further comprises a selecting circuit selecting the reference signal from a combination from the outputs of the harmonic current loop, the fundamental reactive current loop and the fundamental real current loop.

11. The active power filter as defined in claim 10, wherein the selecting circuit selects a combination by adding the outputs of the fundamental reactive current loop and the fundamental real current loop together to compensate for the fundamental reactive power of the load.

12. The active power filter as defined in claim 10, wherein the selecting circuit selects a combination by adding the outputs of the fundamental real current loop and the harmonic current loop together to suppress the harmonic currents of specific orders of the load.

13. The active power filter as defined in claim 10, wherein the selecting circuit selects a combination by adding the outputs of the harmonic current loop, the fundamental reactive current loop and the fundamental real current loop together to compensate the fundamental reactive power and suppress the harmonic currents of specific orders of the load.

14. The active power filter as defined in claim 5, wherein the controller further comprises a second current sensor, a second subtracter, a second controller and a pulse width modulation (PWM) circuit, with the second current sensor detecting an output current of the active power filter, the outputs of the second current sensor and the reference signal are transmitted to the second subtracter, and the output of the second subtracter are transmitted to the second controller, then the output of the second controller are sent to the PWM circuit, so as to generate control signals for the power electronic switches within the inverter.

15. The active power filter as defined in claim 1, wherein applying the active power filter to a three-phase four-wire power system the inverter is configured by a three arms bridge structure, each arm is consisted of two series connected two power electronic switches, with the energy storage capacitor being formed by two serially connecting DC capacitors.

16. The active power filter as defined in claim 1, wherein applying the active power filter to a three-phase four-wire power system the inverter is configured by a four arms bridge structure, and each arm is consisted of two series connected power electronic switches, with the energy storage capacitor being formed by single DC capacitor.

17. The active power filter as defined in claim 1, wherein applying the active power filter to a three-phase three-wire power system the inverter is configured by a three arms bridge structure, and each arm is consisted of two series connected power electronic switches, with the energy storage capacitor being formed by single DC capacitor.

18. The active power filter as defined in claim 1, further comprising an AC power capacitor employed to connect with the filtering circuit in series and link with the power lines for applying to a power source with higher voltage level.