Method for DC-AC conversion

Patent metadata

Field	Value
Publication number	US-9917444-B2
Application number	US-201414770555-A
Country	US
Kind code	B2
Filing date	Feb 24, 2014
Priority date	Feb 27, 2013
Publication date	Mar 13, 2018
Grant date	Mar 13, 2018

Abstract

A method of controlling a plurality of DC/AC converters in cascade configuration, each being arranged to receive an input direct current and voltage from a respective photovoltaic panel and to deliver an electric output. The method includes receiving information representing at least one of frequency, phase, amplitude and harmonics of a required AC, and receiving information on the input direct current and voltage to each one of the plurality of DC/AC converters. Based on the received information, each one of the plurality of DC/AC converters is individually controlled in such manner that the combined output from the plurality of DC/AC converters produces an AC matching the required AC.

First claim

The invention claimed is:

1. A method of controlling a plurality of DC/AC converters in cascade configuration, each one of the plurality of DC/AC converters being arranged to receive an input direct current and voltage from a respective photovoltaic (PV) panel, and to deliver an output, the method comprising:
receiving information representing at least one of frequency, phase, amplitude and harmonics of a required AC;
receiving information representing at least one of current and voltage of the input direct current and voltage to each one of the plurality of DC/AC converters; and
based on the received information, individually controlling each one of the plurality of DC/AC converters such that the combined output of the plurality of DC/AC converters produces an AC matching the required AC, wherein one or more dummy unit is further connected to the plurality of DC/AC converters in cascade configuration, said one or more dummy unit comprising an energy storage element adapted to be charged and to output direct current and voltage, and a DC/AC converter, wherein the method further comprises:
using the one or more dummy unit for producing an output such that the combined output from the plurality of DC/AC converters produces an AC matching the required AC.

2. The method according to claim 1 , further comprising:
charging an energy storage element electrically connected to at least one of the plurality of DC/AC converters.

3. The method according to claim 2 , wherein charging the energy storage element comprises charging the energy storage element using output current from at least one of:
at least one of the plurality of DC/AC converters in the cascade configuration,
the power grid, and
the photovoltaic panel connected to the DC/AC converter.

4. The method according to claim 2 , further comprising:
in response to at least one of:
at least one of current and voltage of the input direct current and voltage to a DC/AC converter received from the photovoltaic panel, and

the combined output from the plurality of DC/AC converters,
being below a respective threshold,
inputting direct current and voltage to the DC/AC converter from the energy storage element, and
converting, at the DC/AC converter, the received input direct current and voltage to output such that the combined output of the plurality of DC/AC converters produces an AC matching the required AC.

5. The method according to claim 2 , wherein the steps of charging the energy storage element and inputting direct current and voltage to the DC/AC converter from the energy storage element are performed during a time shorter than 1 second.

6. The method according to claim 1 , wherein at least one of the plurality of DC/AC converters comprises a switch placed between the at least one DC/AC converter and a photovoltaic panel, and wherein the method further comprises the step of altering the switch to disconnect the at least one DC/AC converter from the photovoltaic panel.

7. The method according to claim 1 , wherein each one of the plurality of DC/AC converters is individually controlled such that each one of the respective photovoltaic panels is operated in their respective optimum working points.

8. The method according to claim 1 , wherein the information representing at least one of current and voltage of the input direct current and voltage to each one of the plurality of DC/AC converters is received repeatedly during operation.

9. The method according to claim 1 , further comprising receiving information on the number of DC/AC converters in cascade configuration.

10. The method according to claim 1 , further comprising receiving information on at least one of:
the number of DC/AC converters currently connected to a photovoltaic panel,
the number of DC/AC converters currently connected to a non-operating photovoltaic panel, and
the number of dummy units currently connected in the cascade configuration.

11. The method according to claim 1 , wherein each one of the plurality of DC/AC converters is arranged to be integrated with a respective PV panel.

12. The method according to claim 1 , wherein each one of the plurality of DC/AC converters is controlled by a microcontroller.

13. The method according to claim 1 , wherein each one of the plurality of DC/AC converters is an H-bridge converter.

14. The method according to claim 1 , wherein the energy storage element is a capacitor.

15. The method according to claim 1 , wherein the required AC is a grid AC.

Assignees

• Optistring Tech Ab
• Abb Schweiz Ag

Inventors

• Modeer Tomas
• Lindgren Anders
• Bergquist Gustav

Classifications

• H02J3/28 Primary

  Arrangements for balancing of the load in networks by storage of energy · CPC title

• H02J3/381

  Dispersed generators · CPC title

• H02M7/49

  Combination of the output voltage waveforms of a plurality of converters · CPC title

• H02J7/345

  using capacitors as storage or buffering devices · CPC title

• H02J7/34

  Parallel operation in networks using both storage and other DC sources, e.g. providing buffering (H02J7/14 takes precedence) · CPC title