INVERTER SYNCHRONIZATION

• US 20160105093A1
• Filed: 06/10/2014
• Published: 04/14/2016
• Est. Priority Date: 06/19/2013
• Status: Active Grant

• Current Assignee: Danfoss Power Electronics A/S (Danfoss A/S)
• Original Assignee: Danfoss Power Electronics A/S (Danfoss A/S)
• Inventors: Della Flora, Leandro
• Granted Patent: US 9,742,260 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• 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: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 7/44 by static converters
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A method of initiating a grid-tied inverter is described, in which in-rush currents and DC overvoltage conditions are reduced or avoided. The method uses a pulse width modulator to drive the inverter under the control of a voltage feedforward signal such that the inverter output is dependent on the measured grid voltage. Then, an AC current feedback controller is enabled and the pulse width modulator is used to drive the inverter under the control of both the voltage feedforward control signal and the feedback control signal.

Claims

1. A method comprising:

enabling an AC voltage feedforward controller of a grid-tied inverter;

setting a voltage feedforward gain of the AC voltage feedforward controller to unity and using the AC feedforward controller to generate a feedforward control signal that is a product of a measured voltage of the grid and the voltage feedforward gain;

using a pulse width modulator to drive the inverter under the control of the feedforward control signal, such that the inverter output is dependent on the measured grid voltage;

enabling an AC current feedback controller;

using the AC current feedback controller to generate a feedback control signal based on a measured output current of the inverter; and

using the pulse width modulator to drive the inverter under the control of both the feedforward control signal and the feedback control signal.

2. The method as claimed in claim 1, wherein an AC relay is used to connect the inverter to the grid.

3. The method as claimed in claim 2, wherein, in the event that the AC relay is initially in an open position, the AC relay is closed when the pulse width modulator is driving the inverter under the control of the feedforward control signal and the AC current feedback controller is enabled after the AC relay is closed.

4. The method as claimed in claim 2, wherein, in the event that the AC relay is initially closed, the pulse width modulator is enabled after the AC voltage feedforward controller has been enabled with unity voltage feedforward gain.

5. The method as claimed in claim 1, further comprising reducing the voltage feedforward gain of the AC voltage feedforward controller from unity to a normal operating value after the AC current feedback controller is enabled.

6. The method as claimed in claim 1, further comprising a DC-bus voltage controller configured to regulate the inverter DC bus voltage.

7. The method as claimed in claim 6, wherein the DC-bus voltage controller is enabled after or at the same time as the AC current feedback controller has been enabled.

8. The method as claimed in claim 6, wherein the DC-bus voltage controller has a first, faster, mode of operation and a second, slower, mode of operation, wherein, when the DC-bus voltage controller is enabled, the first mode of operation is used and, after a period of time, the second mode of operation is used.

16. The method as claimed in claim 3, wherein, in the event that the AC relay is initially closed, the pulse width modulator is enabled after the AC voltage feedforward controller has been enabled with unity voltage feedforward gain.

17. The method as claimed in claim 2, further comprising reducing the voltage feedforward gain of the AC voltage feedforward controller from unity to a normal operating value after the AC current feedback controller is enabled.

18. The method as claimed in claim 3, further comprising reducing the voltage feedforward gain of the AC voltage feedforward controller from unity to a normal operating value after the AC current feedback controller is enabled.

19. The method as claimed in claim 4, further comprising reducing the voltage feedforward gain of the AC voltage feedforward controller from unity to a normal operating value after the AC current feedback controller is enabled.

20. The method as claimed in claim 2, further comprising a DC-bus voltage controller configured to regulate the inverter DC bus voltage.

9. An inverter comprising:

an AC voltage feedforward controller having a voltage feedforward gain, wherein the AC feedforward controller is used to generate a feedforward control signal that is a product of a measured voltage of the grid and the voltage feedforward gain;

an AC current feedback controller that is configured to generate a feedback control signal based on a measured output current of the inverter; and

a pulse width modulator that drives the inverter,

wherein;

with the AC current feedback controller disabled and the voltage feedforward gain of the AC voltage feedforward controller set to unity, the pulse width modulator drives the inverter under the control of the feedforward control signal, such that the inverter output is dependent on the measured grid voltage; and

with the AC current feedback controller enabled, the pulse width modulator drives the inverter under the control of both the feedforward control signal and the feedback control signal.

10. The inverter as claimed in claim 9, further comprising an AC relay used to connect the inverter to the grid.

11. The inverter as claimed in claim 10, wherein, in the event that the AC relay is initially in an open position, the AC relay is closed when the pulse width modulator is driving the inverter under the control of the feedforward control signal and the AC current feedback controller is enabled after the AC relay is closed.

12. The inverter as claimed in claim 10, wherein, in the event that the AC relay is initially closed, the pulse width modulator is enabled after the AC voltage feedforward controller has been enabled with unity voltage feedforward gain.

13. The inverter as claimed in claim 9, further comprising a DC-bus voltage controller configured to regulate the inverter DC bus voltage.

14. The inverter as claimed in claim 13, wherein the DC-bus voltage controller is enabled after or at the same time as the AC current feedback controller has been enabled.

15. The inverter as claimed in claim 9, wherein the inverter is a multi-phase inverter.