Method and apparatus for connecting a photovoltaic system to a power grid

• US 8,115,426 B2
• Filed: 08/12/2009
• Issued: 02/14/2012
• Est. Priority Date: 08/20/2008
• Status: Expired due to Fees

• Current Assignee: Adensis Gmbh
• Original Assignee: Adensis Gmbh
• Inventors: Beck, Bernhard, Neussner, Thomas, Wenzlik, Constantin
• Primary Examiner(s): Santana, Eduardo Colon
• Application Number:
  US12/540,020
• Publication Number:
  US 20100090634A1
• Time in Patent Office: 916 Days
• Field of Search: 318/139, 318/140, 318/480, 318/432, 318/434, 318/609, 307/151, 363/41, 363/101, 363/102, 310/113, 136/244, 323/906, 323/299
• US Class Current: 318/139
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/42 with automatic parallel connection when synchronisation is achieved
• CPC Class Codes: H02J 3/44 with means for ensuring correct phase sequence
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02M 7/54 by dynamic converters
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

An apparatus and a method for preparing connection of a photovoltaic system (Q1) as a first energy source to a power grid (13) by way of a motor generator set (5, 6, 7) is presented. The DC motor (5) is coupled to a three-phase generator (7) by way of a shaft (6), wherein the three-phase generator (7) can be connected to the power grid (13). It has been observed that connecting this type of apparatus to the small or varying power output of the photovoltaic system (Q1) can be difficult and time-consuming. To enable a clean and quick connection, the DC motor (5) is powered with electric DC current from a second DC current source (Q2), wherein the operation of the three-phase generator (7) is matched to the conditions in the power grid (13) with the help of the second DC current source (Q2), and wherein the photovoltaic system (Q1) is connected to the DC motor (5) and the second DC current source (Q2) is disconnected from the DC motor (5) only after a complete match has been attained. This enables a quick and precise connection of the photovoltaic system (Q1) to the power grid (13) with defined parameters using the three-phase generator (7).

Claims

1. A method for synchronizing an output from a motor-generator set with a power grid, the motor-generator set comprising a DC motor connected via a shaft with a three-phase generator and having a photovoltaic system as a primary energy source and a second DC energy source, said method comprising the steps of:

connecting the second DC energy source with the DC motor to supply electric energy;

matching a rotation speed and phase angle of the three-phase generator to conditions of the power grid with the supplied energy; and

after matching is completed, disconnecting the second DC energy source from the DC motor and connecting the photovoltaic system with the DC motor as the primary energy source.

2. The method of claim 1, wherein after matching of the rotation speed and the phase angle of the three-phase generator have been completed, connecting the three-phase generator with the power grid before disconnecting the second DC energy source from the motor generator set.

3. The method of claim 1, wherein the second DC energy source is connectable with the input terminals of the DC motor via a switch.

4. The method of claim 3, wherein the switch is a switching element, which connects the photovoltaic system with the DC motor at the same time the second DC current source is disconnected from the DC motor.

5. The method of claim 1, wherein the second DC energy source is powered from the power grid.

6. The method of claim 1, wherein the second DC energy source is an electric energy storage device.

7. The method of claim 1, further comprising the steps of providing an additional switching element between the three-phase generator and the power grid;

and actuating the additional switching element for coupling the three-phase generator to the power grid.

8. The method of claim 1, wherein power output of the second DC energy source is below 20% of a nominal power of the DC motor.

9. The method of claim 1, wherein the second DC energy source is a motor that is coupled to the shaft of the motor-generator set, with the motor when energized driving the motor-generator set.

10. Apparatus for synchronizing an output from a motor-generator set with a power grid, comprising:

a photovoltaic system having a plurality of photovoltaic modules and representing a primary DC energy source;

a second DC energy source;

a three-phase generator having an output switchably electrically connected to a power grid having for supplying a generated AC voltage;

a DC motor coupled to the three-phase generator by a shaft and switchably electrically connected to one of the photovoltaic system and the second DC energy source; and

a control unit, which controllably drives the DC motor from the second DC energy source, until a line frequency and phase angle of the power grid matches a line frequency and phase angle at the output of the three-phase generator, whereafter the control unit disconnects the second DC energy source from the DC motor and connects the photovoltaic system to the DC motor as primary DC energy source.