Power conversion having energy storage with dynamic reference

• US 8,624,561 B1
• Filed: 11/05/2010
• Issued: 01/07/2014
• Est. Priority Date: 12/29/2009
• Status: Active Grant

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Solarbridge Technologies Incorporated (Totalenergies Se)
• Inventors: Slavin, Keith
• Primary Examiner(s): Fantu, Yalkew
• Application Number:
  US12/940,068
• Time in Patent Office: 1,159 Days
• Field of Search: 320/166
• US Class Current: 320/166
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A power conversion system may include a controller to cause a power stage to control the flow of power to or from an energy storage device in response to a dynamic reference. The flow of power to or from the energy storage device may be controlled at a substantially higher speed than power fluctuations in a power source or load. In a power conversion system, a model including an energy storage device may be generated in real-time, and a condition of the energy storage device may be determined in response to the model.

Claims

1. An inverter to convert a direct current (DC) power from a DC source to an alternating current (AC) power, the inverter comprising:

a DC link capacitor;

an input stage electrically coupled to the DC link capacitor, the input stage configured to be electrically coupled to the DC source to receive a DC input power therefrom and generate a DC output waveform;

an output stage electrically coupled to the DC link capacitor and configured to convert the DC output waveform to an AC output waveform; and

a controller electrically coupled to the input stage and the DC link capacitor, the controller configured to;

(i) generate a dynamic reference signal as a function of a model of the DC link capacitor,

(ii) generate a control signal as a function of the dynamic reference signal and a measurement signal indicative of an operational parameter of the DC link capacitor, and

(iii) control the input stage using the control signal to control a flow of power to the DC link capacitor.

2. The inverter of claim 1, wherein the model of the DC link capacitor is a function of a reference capacitance value of the DC link capacitor.

3. The inverter of claim 2, wherein the controller is further configured to determine the present capacitance value of the DC link capacitor based on the operational parameter of the DC link capacitor and the dynamic reference signal.

4. The inverter of claim 3, wherein the controller is further configured to:

determine a difference between the reference capacitance value of the DC link capacitor and the present capacitance value of the DC link capacitor, and

generate an alert in response to the difference being greater than a threshold amount.

5. The inverter of claim 4, wherein to generate the alert comprises to transmit a report indicating a condition of the DC link capacitor.

6. The inverter of claim 5, wherein the report includes the present capacitance value of the DC link capacitor.

7. The inverter of claim 5, wherein to transmit the report comprises to transmit the report using power-line communications.

8. The inverter of claim 4, wherein to generate the alert comprises to generate an alert in response to the difference being greater than a first threshold, and wherein the controller is further to:

control operation of the input stage in response to the difference being greater than a second threshold that is greater than the first threshold.

9. The inverter of claim 8, wherein the control is further to disable at least one of the input stage and the output stage in response to the difference being greater than the second threshold.

10. The inverter of claim 1, wherein to generate the dynamic reference signal comprises to generate a dynamic reference signal as a function of the model of the DC link capacitor, the DC input power of the input stage, and a DC input power of the output stage.

11. The inverter of claim 1, wherein to generate the control signal comprises to generate a control signal based on a difference between the dynamic reference signal and the measurement signal.

12. The inverter of claim 1, wherein the dynamic reference signal is a voltage signal and the operational parameter is a voltage of the DC link capacitor.

13. The inverter of claim 1, wherein to control the input stage comprises to control the operational parameter of the DC link capacitor toward the dynamic reference signal.

14. A method for controlling a direct current-to-alternating current (DC-to-AC) inverter, the DC-to-AC inverter including a DC link capacitor, an input stage electrically connected to the DC link capacitor, and an output stage electrically connected to the DC link capacitor, the method comprising:

generating, by a controller of the DC-to-AC inverter, a dynamic reference signal as a function of a model of the DC link capacitor;

generating, by the controller, a control signal as a function of the dynamic reference signal and a measurement signal indicative of an operational parameter of the DC link capacitor, and

controlling, by the controller and using the control signal, the input stage of the inverter to control a flow of power to the DC link capacitor.

15. The method of claim 14, wherein generating the dynamic reference signal comprises generating a dynamic reference signal as a function of a model of the DC link capacitor based on a reference capacitance value of the DC link capacitor.

16. The method of claim 15, further comprising determining the present capacitance value of the DC link capacitor based on the operational parameter of the DC link capacitor and the dynamic reference signal.

17. The method of claim 16, further comprising:

determining a difference between the reference capacitance value of the DC link capacitor and the present capacitance value of the DC link capacitor, and

generating an alert in response to the difference being greater than a threshold amount.

18. The method of claim 17, wherein generating the alert comprises transmitting a report indicating a condition of the DC link capacitor.

19. The method of claim 18, wherein transmitting the report comprises transmitting the report using power-line communications.

20. The method of claim 17, wherein generating the alert comprises generating an alert in response to the difference being greater than a first threshold, and wherein the method further comprises:

disabling at least one of the input stage and the output stage in response to the difference being greater than a second threshold that is greater than the first threshold.

21. The method of claim 14, wherein:

generating the dynamic reference signal comprises generating a dynamic reference voltage signal, and

generating the control signal comprises generating the control signal as a function of the dynamic reference voltage signal and a measurement signal indicative of a voltage of the DC link capacitor.

22. A system comprising:

a photovoltaic panel configured to generate a DC power output

a DC-to-AC inverter comprising;

a DC link capacitor;

an input stage having an input electrically coupled to the photovoltaic panel to receive the DC power output therefrom and an output electrically coupled to the DC link capacitor;

an output stage having an input electrically coupled to the DC link capacitor;

a first voltage sensor configured to generate a first voltage signal indicative of an input voltage of the input stage;

a first current sensor configured to generate a second current signal indicative of an input current of the input stage;

a second voltage sensor configured to generate a second voltage signal indicative of a voltage of the DC link capacitor;

a second current sensor configured to generate a second current signal indicative of an output current; and

a controller electrically coupled to the input stage and configured to;

(i) generate a dynamic reference voltage signal as a function of a model of the DC link capacitor, the first voltage signal, the first current signal, the second voltage signal, and the second current signal,

(ii) generate a control signal as a function of the dynamic reference voltage signal and a measurement signal indicative of the voltage of the DC link capacitor, and

(iii) control the input stage using the control signal to control a flow of power to the DC link capacitor.