SYSTEM, METHOD, AND APPARATUS FOR AC GRID CONNECTION OF SERIES-CONNECTED INVERTERS

• US 20120091817A1
• Filed: 10/17/2011
• Published: 04/19/2012
• Est. Priority Date: 10/18/2010
• Status: Abandoned Application

• Current Assignee: Advanced Energy Industries Incorporated
• Original Assignee: Advanced Energy Industries Incorporated
• Inventors: Seymour, Eric, Gilmore, Jack Arthur, Armstrong, Mike
• Application Number:
  US13/275,259
• Publication Number:
  US 20120091817A1
• Time in Patent Office: Days
• US Class Current: 307/82
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/44 with means for ensuring correct phase sequence
• CPC Class Codes: H02M 1/0074 Plural converter units whose inputs are connected in series
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A system, method and apparatus are disclosed for converting DC power to AC power. The system includes a master controller that couples to a phase of a power distribution system and provides a synchronization signal, the phase of the power distribution system having a phase voltage. The system also includes a plurality of DC-to-AC series-connectable power converters, that receive and use the synchronization signal to convert a variable DC voltage from a corresponding one a plurality of photovoltaic panels to a variable AC voltage so that a plurality of corresponding variable AC voltages are generated by the plurality series-connectable power converters, and collectively the plurality of corresponding variable AC voltages add up the phase voltage, and each of the series-connectable power converters controls, responsive to the synchronization signal, the variable AC voltage so that the plurality of corresponding variable AC voltages are in phase.

Claims

1. A system for converting DC power to AC power, the system comprising a master controller that couples to a phase leg of a power distribution system and provides a synchronization signal and a power control signal, the phase leg of the power distribution system having a phase voltage;

a plurality of DC-to-AC series-connectable power converters arranged in series in a string, each of the DC-to-AC series-connectable power converters receives and uses the synchronization signal and the power signal to convert a variable DC voltage from a corresponding one of a plurality of photovoltaic modules to an AC voltage so that a plurality of corresponding AC voltages are generated by the plurality of series-connectable power converters, and collectively the plurality of corresponding AC voltages add up the phase voltage, and each of the series-connectable power converters controls, responsive to the synchronization signal, the AC voltage so that the plurality of corresponding variable AC voltages are all in phase.

2. The system of claim 1, wherein each of the series-connectable power converters includes:

a DC-input side including terminals to couple to a DC voltage applied by a corresponding one of the plurality of photovoltaic modules;

an AC-output side including terminals to apply an AC voltage that is based upon a level of the DC voltage;

a receiver to receive the synchronization signal and the power signal;

a power conversion component to convert the DC potential applied by the corresponding one of the plurality of photovoltaic modules to the AC voltage and control voltage; and

a controller that controls the power conversion component responsive to the received synchronization signal and the power signal

3. The system of claim 1, wherein a length of the string is determined by a ratio of a nominal, individual voltage of the AC voltage and an overall phase voltage.

4. The system of claim 1 wherein multiple strings of the series-connectable power converters are combined.

5. The system of claim 4, wherein the combined strings are connected to the phase leg.

6. The system of claim 5, wherein the combined strings are connected across a single-phase to neutral applied voltage.

7. The system of claim 5, wherein the combined strings are connected across a split-single-phase applied voltage.

8. The system of claim 4, wherein multiple sets of combined strings are connected to respective phases in a polyphase system.

10. The system of claim 8, wherein the combined strings are connected across the line-to-line phase voltages of the polyphase system.

9. The system of 8, wherein the combined strings are connected across the line-to-neutral phase voltages of the polyphase system.

11. A DC-to-AC series-connectable power converter comprising:

a DC-input side including terminals to couple to a DC potential applied by a corresponding one of a plurality of photovoltaic modules;

an AC-output side including terminals to apply an AC voltage;

a receiver to receive a synchronization signal and a power signal;

a power conversion component to convert the DC potential applied by the corresponding one of a plurality of photovoltaic modules to the AC voltage; and

a controller that controls the power conversion component, responsive to the received synchronization signal and the power signal, so that a phase of the AC voltage is synchronized with the synchronization signal and a power level output from the DC-to-AC series-connectable power converter is consistent with the power signal.

12. The DC-to-AC series-connectable power converter of claim 11, wherein the power conversion component is configured to provide reactive power flow responsive to the controller when the controller receives a reactive power flow signal that is received at the receiver.

13. The DC-to-AC series-connectable power converter of claim 11, wherein the synchronization information is provided by a common-mode signal that is transmitted by a supervisory controller and received by the receiver.

14. The DC-to-AC series-connectable power converter of claim 13, including a line output ac-bypass capacitor enabling transmission of the synchronization signal through the DC-to-AC series-connectable power converter.

15. The DC-to-AC series-connectable power converter of claim 13, wherein the receiver receives the synchronization information via the common-mode signal with respect to a provided signal ground.

16. The DC-to-AC series-connectable power converter of claim 11, wherein the receiver receives phase information and the controller controls the power conversion component based upon the phase information to provide active and reactive power control.

17. The DC-to-AC series-connectable power converter of claim 11, wherein the power conversion component is a current source conversion component that may be placed in series with other DC-to-AC series-connectable power converters using a real-time power regulation loop using hysteretic modulation of a sine-squared power function that is the product of synchronized synthetic voltage reference sine, a phased current reference sine and a power scaling coefficient based upon real time maximum power point tracking conditions.

18. The DC-to-AC series-connectable power converter of claim 11, wherein the power conversion component is a voltage source converter.

19. The DC-to-AC series-connectable power converter of claim 18, wherein the voltage source converter includes a control portion that operates in a stationary frame of reference.

20. The DC-to-AC series-connectable power converter of claim 18, wherein the voltage source converter includes a control portion that operates in a synchronous reference frame.

21. The DC-to-AC series-connectable power converter of claim 20, wherein the control portion utilizes pulse-width modulation to control the voltage source converter.

22. A method for converting DC power to AC power comprising:

arranging AC outputs of each of a plurality of DC-to-AC power converters in series with others of the DC-to-AC power converters;

receiving, at each of the DC-to-AC power converters, a synchronization signal;

converting, with each of the DC-to-AC power converters, DC power to AC power using the synchronization signal so that AC voltages output by the DC-to-AC power converters are in phase; and

applying the AC power to a phase leg of a power distribution system, a total voltage applied to the phase leg of the distribution system equals a sum of the AC voltages output by the DC-to-AC power converters.

23. The method of claim 22 including:

generating the synchronization signal responsive to sensed zero crossings of voltage on the phase of the power distribution system; and

transmitting the synchronization signal to the DC-to-AC power converters.

24. The method of claim 22, wherein the applied voltage to ground seen by each of the DC-to-AC power converters is solely a function of its position in the series connected string and applied phase voltage.

25. The method of claim 22 including arranging the AC outputs of each of a plurality of DC-to-AC power converters in series with others of the DC-to-AC power converters without the use of galvanically isolating transformers.