Multi-level active filter

• US 20070109823A1
• Filed: 05/16/2006
• Published: 05/17/2007
• Est. Priority Date: 05/17/2005
• Status: Active Grant

• Current Assignee: Siemens Energy & Automation Incorporated (Siemens AG)
• Original Assignee: Siemens Energy & Automation Incorporated (Siemens AG)
• Inventors: Rastogi, Mukul, Hammond, Peter, Simms, Stan
• Granted Patent: US 7,405,498 B2
• Time in Patent Office: Days
• US Class Current: 363/40
• CPC Class Codes: H02J 3/1857 wherein such bridge converter is a multilevel converter
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]

Abstract

A multi-phase active filter includes a group of power cells electrically connected in a three-phase configuration, a precharging circuit, and a controller that controls the voltage delivered to the plurality of power cells. Each power cell includes an inverter having a pair of direct current (DC) terminals, at least one capacitor electrically connected in parallel with the inverter, and an energy dissipating circuit that is electrically connected in parallel with the inverter. The energy dissipating circuit of each power cell self-regulates DC voltage within the cell.

Claims

1. A multi-phase active filter, comprising:

a plurality of phases, each phase comprising a plurality of power cells electrically connected in series;

wherein each phase has a first end and a second end, the first ends of each phase are electrically coupled to each other, and the second ends of each phase are positioned to be electrically connected between a power source and a load at a point of common coupling;

wherein each power cell comprises an inverter having a pair of direct current (DC) terminals and an energy dissipating circuit that is electrically connected across the DC terminals of the inverter.

2. The filter of claim 1, wherein the power cells filter harmonic current generated by the load.

3. The filter of claim 1, wherein each inverter comprises either an H-bridge inverter or a neutral point clamped single-phase inverter.

4. The filter of claim 1, wherein each cell also comprises at least one capacitor electrically connected in parallel with the inverter.

5. The filter of claim 1, further comprising a central controller that ensures DC voltage sharing in each inverter by regulating power flow, wherein each power cell self-regulates its DC voltage using its energy dissipating circuit.

6. The filter of claim 1, further comprising a precharging circuit.

7. The filter of claim 6, wherein each precharging circuit comprises:

a first contactor, a first inductor, and a second inductor electrically connected in series such that the first inductor is between the first inductor and the second inductor; and

a second contactor electrically connected in parallel across the first contactor and first inductor;

wherein the first contactor closes to energize the power cells, the second contactor closes when the power cells have charged to a nominal DC voltage, and the first contactor opens after the second contactor has closed.

8. The filter of claim 6, further comprising a controller that monitors the voltage of each power cell and activates or deactivates the first contactor and second contactor based on data that it received from monitoring.

9. The filter of claim 1, wherein energy dissipating circuit comprises a transistor and a resistor, and wherein the transistor shorts the inverter through the resistor to cause dissipation of energy through the resistor.

10. The filter of claim 9, further comprising a control circuit for each cell that activates the cell transistor and self-regulates voltage in the cell.

11. A multi-phase active filter, comprising:

a plurality of phases, each phase comprising a plurality of power cells electrically connected in series;

wherein each phase has a first end and a second end, the first ends of each phase are electrically coupled to each other, and the second ends of each phase are positioned to be electrically connected between a power source and a load at a point of common coupling;

wherein each power cell comprises an inverter having a pair of DC terminals, a rectifier electrically connected across the DC terminals, and a capacitor that is electrically connected across the DC terminals;

wherein each rectifier receives power from a set of dedicated three-phase secondary windings of a transformer.

12. The filter of claim 11, wherein the transformer is external to the filter and has a volt-ampere rating that is less than a volt-ampere rating of the filter.

13. The filter of claim 12, wherein the transformer rating is about 5 percent or less than the volt-ampere rating of the filter.

14. The filter of claim 11, further comprising a central controller that commands power flow out of the active filter.

15. A multi-phase active filter, comprising:

a plurality of power cells electrically connected in a three-phase configuration;

a precharging circuit; and

a controller that controls the voltage delivered to the plurality of power cells;

wherein each power cell comprises an inverter having a pair of direct current (DC) terminals, at least one capacitor electrically connected in parallel with the inverter, and an energy dissipating circuit that is electrically connected in parallel with the inverter;

wherein the energy dissipating circuit of each power cell self-regulates DC voltage within the cell.

16. The filter of claim 15, wherein the power cells filter harmonic current generated by a load.

17. The filter of claim 15, wherein each inverter comprises either an H-bridge inverter or a neutral point clamped single-phase inverter.

18. The filter of claim 15, further comprising a point of common coupling that electrically connects an output of the precharging circuit, a power source, and a load.

19. The filter of claim 15, wherein the precharging circuit comprises:

a first contactor, a first inductor, and a second inductor electrically connected in series such that the first inductor is between the first inductor and the second inductor; and

a second contactor electrically connected in parallel across the first contactor and first inductor;

wherein the first contactor closes to energize the power cells, the second contactor closes when the power cells have charged to a nominal DC voltage, and the first contactor opens after the second contactor has closed.

20. The filter of claim 19, further comprising a controller that monitors the voltage of each power cell and activates or deactivates the first contactor and second contactor based on data that it received from monitoring.