Parallel-connected inverters with separate controllers having impedance current regulators

• US 7,145,266 B2
• Filed: 01/20/2004
• Issued: 12/05/2006
• Est. Priority Date: 07/23/2001
• Status: Expired due to Term

• Current Assignee: WEG Electric Corporation (Wpa Participações e Serviços SA)
• Original Assignee: Northern Power Systems, Inc. (Northern Power Systems Corp.)
• Inventors: Petter, Jeffrey K, Lynch, Jonathan A.
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US10/760,868
• Publication Number:
  US 20040145357A1
• Time in Patent Office: 1,050 Days
• Field of Search: 307/64, 307/65, 307/84, 307/82
• US Class Current: 307/65
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/30 The power source being a fuel cell
• CPC Class Codes: H02J 3/18 Arrangements for adjusting, eliminating or compensating reactive power in networks for adjustment of voltage H02J3/16
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 7/40 by combination of static with dynamic converters; by combination of dynamo-electric with other dynamic or static converters
• CPC Class Codes: Y02B 10/70 Hybrid systems, e.g. uninterruptible or back-up power supplies integrating renewable energies
• CPC Class Codes: Y02B 90/10 Applications of fuel cells in buildings
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 10/76 Power conversion electric or electronic aspects
• CPC Class Codes: Y02E 40/30 Reactive power compensation
• CPC Class Codes: Y02P 90/40 Fuel cell technologies in production processes

Abstract

A control system (20) for a power converter (22) designed to convert DC power from a source (30) such as a battery, flywheel or fuel cell into AC power. The control system includes an impedance current regulator (106) for providing an impedance current signal to a summing unit (110) where it may be combined with real and reactive current command signals provided from respective sources (62, 64). The resultant current signal provided by the summing unit is provided to a voltage correction unit (112) that uses the resultant current signal in developing a correction voltage signal provided to the power converter. The correction voltage signal contains information used by the power converter in adjusting the real and reactive currents in its output AC power based on the ability of the AC power network to accept changes in current. Multiple power converters having the control system of the present invention may be connected in parallel to a single AC load or multiple AC loads, without the need for a separate control system interconnecting the power converters. The control system may be advantageously incorporated into a distributed generation network and in uninterruptible power systems, whether or not such systems are included in a distributed generation network.

Claims

1. A distributed generation network, comprising:

a) a plurality of power sources connected together in a distributed generation AC power network that is primarily inductive;

b) a plurality of power converters, at least some of which are connected in parallel, each connected to one or more of said plurality of power sources;

c) a plurality of control systems, each connected to at least one of said plurality of power converters and each including an impedance current regulator for generating an impedance current signal as a function of characteristics of AC power in the AC power network; and

d) wherein each of said plurality of control systems controls said at least one of said plurality of power converters without the need for a separate control system connected to said each control system.

2. A network according to claim 1, wherein said plurality of power sources includes AC power sources and DC power sources.

3. A network according to claim 1, wherein said plurality of power sources includes DC power sources.

4. A network according to claim 1, wherein said plurality of power sources includes AC power sources.

5. A network according to claim 1, wherein each of said plurality of control systems is connected to a corresponding respective one of said plurality of power converters.

6. A network according to claim 1, wherein at least one of said plurality of power sources is not connected to any one of said plurality of power converters.

7. A network according to claim 1, wherein said impedance current signal is used by said each control system in controlling operation of said at least one power converter.

26. A system according to claim 1, wherein said impedance current regulator generates said impedance current signal to remove non-linear components in AC power in the AC power network that is primarily inductive.

8. A distributed generation network, comprising:

a) a plurality of power sources connected together in a distributed generation AC power network that is primarily inductive;

b) a plurality of power converters, at least some of which are connected in parallel, each connected to one or more of said plurality of power sources;

c) a plurality of control systems, each connected to at least one of said plurality of power converters and each including an impedance current regulator for generating an effective output resistance as a function of characteristics of AC power in the AC power network; and

d) wherein each of said plurality of control systems controls said at least one of said plurality of power converters without the need for a centralized control system connected to said each control system.

27. A system according to claim 8, wherein said impedance current regulator generates said effective output resistance to remove non-linear components in AC power in the AC power network that is primarily inductive.

9. An uninterruptible power supply (UPS), comprising:

a) a distributed generation AC power network having a plurality of controlled current sources for providing power, wherein said plurality of controlled current sources are connected together in parallel;

b) a plurality of control systems for controlling operation of said controlled current sources, wherein each of said plurality of control systems (i) is capable of controlling at least one of said controlled current sources without the need for a separate control system connected to said each control system and (ii) includes an impedance current regulator for generating an impedance current signal as a function of characteristics of AC power in the AC power network; and

c) a switch for selectively connecting said distributed generation AC power network to a load.

10. A UPS according to claim 9, wherein at least some of said plurality of controlled current sources do not directly use fuel in developing said power.

11. A UPS according to claim 9, further including a controller connected to said switch for controlling operation of said switch.

12. A UPS according to claim 9, further including at least one device for storing energy.

13. A UPS according to claim 9, wherein said at least one of said plurality of controlled current sources includes a power source and a power converter connected to said power source.

28. A system according to claim 9, wherein said network is primarily inductive and said plurality of control systems each removes at least first and second non-liner components in said network, said first non-linear component having a frequency that is different than said second non-linear component.

14. An uninterruptible power supply (UPS), comprising:

a) a distributed generation AC power network having a plurality of controlled current sources for providing power, wherein said plurality of controlled current sources are connected together in parallel;

b) a plurality of control systems for controlling operation of said controlled current sources, wherein each of said plurality of control systems (i) is capable of controlling at least one of said controlled current sources without the need for a centralized control system connected to said each control system and (ii) includes an impedance current regulator for generating an impedance current signal as a function of characteristics of AC power in the AC power network; and

c) a switch for selectively connecting said distributed generation AC power network to a load.

29. A system according to claim 14, wherein said network is primarily inductive and said plurality of control systems each removes at least first and second non-linear components in said network, said first non-linear component having a frequency that is different than said second non-linear component.

15. An AC power network, comprising:

a) a utility AC power grid;

b) a distributed generation AC power network connected to said AC power grid, wherein said network includes;

i) a plurality of controlled current sources for providing power, wherein said plurality of controlled current sources are connected together in parallel;

ii) a plurality of control systems for controlling operation of said controlled current sources, wherein each of said plurality of control systems controls operation of at least one of said controlled current sources without the need for a separate control system connected thereto and (ii) includes an impedance current regulator for generating an impedance current signal as a function of characteristics of AC power in the AC power network.

16. A network according to claim 15, wherein said at least one of said plurality of controlled current sources includes a power source and a power converter connected to said power source.

30. A system according to claim 15, wherein said AC power grid and distributed generation AC power network, when connected, form a primarily inductive network with a first non-linear component with a first frequency and a second non-linear component with a second frequency that is different than said first frequency, further wherein said plurality of control systems each removes said first and second non-linear components.

17. An AC power network, comprising:

a) an AC power grid;

b) a distributed generation AC power network connected to said AC power grid, wherein said network includes;

i) a plurality of controlled current sources for providing power, wherein said plurality of controlled current sources are connected together in parallel;

ii) a plurality of control systems for controlling operation of said controlled current sources, wherein each of said plurality of control systems controls operation of at least one of said controlled current sources without the need for a centralized control system connected thereto and (ii) includes an impedance current regulator for generating an impedance current signal as a function of characteristics of AC power in the AC power network.

31. A system according to claim 17, wherein said AC power grid and distributed generation AC power network, when connected, form a primarily inductive network with a first non-linear component with a first frequency and a second non-linear component with a second frequency that is different than said first frequency, further wherein said plurality of control systems removes said first and second non-linear components.

18. An energy storage system, comprising:

a) a plurality of energy storage devices, each for providing power;

b) a plurality of power converters connected in parallel, wherein each of said plurality of power converters is connected to at least one of said plurality of energy storage devices; and

c) a plurality of control systems connected to said plurality of power converters for controlling operation of said plurality of power converters, wherein said plurality of control systems including an impedance current regulator for generating an impedance current signal as a function of characteristics of power provided by said plurality of energy storage devices, wherein said plurality of control systems controls operation of said plurality of power converters without the need for a separate control system connected thereto.

19. An energy storage system, comprising:

a) a plurality of energy storage devices, each for providing power;

b) a plurality of power converters connected in parallel, wherein each of said plurality of power converters is connected to at least one of said plurality of energy storage devices; and

c) a plurality of control systems connected to said plurality of power converters for controlling operation of said plurality of power converters, each of said plurality of control systems including an impedance current regulator for generating an impedance current signal as a function of characteristics of power provided by said plurality of energy storage devices, wherein said plurality of control systems controls operation of said plurality of power converters without the need for a centralized control system connected thereto.

20. An AC power network connected to an AC power grid for providing power to a load on an uninterrupted basis when said load is disconnected from the grid, the AC power network comprising:

a) a plurality of power converters connected in parallel;

b) a plurality of control systems connected to said plurality of power converters for controlling operation of said plurality of power converters, each of said plurality of control systems including an impedance current regulator for generating an impedance current signal as a function of characteristics of AC power in the AC power network, wherein said plurality of control systems are not connected to a high-speed communication system that controls operation of said plurality of control systems; and

c) a switch for selectively connecting the AC power network to the grid.

21. A system for correcting non-linear components in an AC power generation network, the system comprising:

a) a plurality of power sources, each providing output power with non-linear components; and

b) a plurality of control systems for handling power provided by said plurality of power sources, wherein said plurality of control systems use time domain control to cooperatively remove at least some of said non-linear components.

22. A system according to claim 21, wherein said non-linear components include a plurality of harmonics with different frequencies, and said plurality of control systems cooperatively remove at least some of said harmonics that have different frequencies.

23. A system according to claim 21, further wherein each of said plurality of control systems includes an impedance current regulator for generating an impedance current signal as a function of characteristics of AC power in the AC power network.

24. A system according to claim 21, wherein said plurality of control systems cooperatively remove said non-linear components without the need for a separate control system connected thereto.

25. A system according to claim 21, wherein each of said plurality of control systems is connected to one of said plurality of power sources, and non-linear components created by one of said plurality of power sources are removed in large part by said one of said plurality of control systems connected thereto, but are also removed to some extent by other ones of said plurality of control systems.

32. A system according to claim 21, wherein said non-linear components include a first non-linear component with a first frequency and a second non-linear component with a second frequency that is different than said first frequency, further wherein said plurality of control systems removes said first and second non-linear components.