Control method and system for photovoltaic inverters whose AC sides are connected in parallel

• US 10,027,125 B2
• Filed: 12/15/2015
• Issued: 07/17/2018
• Est. Priority Date: 12/31/2014
• Status: Active Grant

• Current Assignee: Sungrow Power Supply Co., Ltd.
• Original Assignee: Sungrow Power Supply Co., Ltd.
• Inventors: Pan, Nianan, Cheng, Lin, Tao, Lei
• Primary Examiner(s): JAGER, RYAN C
• Application Number:
  US14/969,411
• Publication Number:
  US 20160190811A1
• Time in Patent Office: 945 Days
• Field of Search: 307 82
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02M 1/123 Suppression of common mode voltage or current
• CPC Class Codes: H02M 7/44 by static converters
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel
• CPC Class Codes: H02S 40/32 comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A control method and apparatus for photovoltaic inverters connected in parallel at an AC side are provided and the method includes the following steps: detecting a first direct voltage of the first inverter and a second direct voltage of the second inverter; obtaining a difference between the first direct voltage and the second direct voltage; and adjusting the direct voltages of the inverters to control the difference to be within a predetermined range and control a common-mode voltage in the common-mode loop to be within a predetermined common-mode voltage range.

Claims

1. A control method for photovoltaic inverters whose AC sides are connected in parallel, applied to a system in which AC sides of inverters are connected in parallel and DC sides of the inverters are independent from each other, wherein the system comprises at least two inverters which are a first inverter and a second inverter, wherein an input terminal of the first inverter is connected with a first PV array, an input terminal of the second inverter is connected with a second PV array, the first PV array and the second PV array each have a parasitic capacitance to ground, and the first inverter is coupled with the second PV array through the parasitic capacitances to form a common-mode loop;

wherein the method comprises;

detecting a first direct voltage of the first inverter and a second direct voltage of the second inverter;

obtaining a difference between the first direct voltage and the second direct voltage; and

adjusting the direct voltages of the inverters to control the difference to be within a predetermined range and to control a common-mode voltage in the common-mode loop to be within a predetermined common-mode voltage range.

2. The control method for photovoltaic inverters whose AC sides are connected in parallel according to claim 1, wherein the obtaining a difference between the first direct voltage and the second direct voltage;

and adjusting the direct voltages of the inverters to control the difference to be within a predetermined range comprises;

obtaining an absolute value of the difference between the first direct voltage and the second direct voltage, and adjusting the direct voltages of the inverters to control the absolute value to be smaller than a predetermined voltage.

3. The control method for photovoltaic inverters whose AC sides are connected in parallel according to claim 2, wherein the first inverter is a host inverter, and the second inverter is a slave inverter;

and

the control the absolute value to be smaller than the predetermined voltage comprises;

adjusting the direct voltage of the slave inverter based on the direct voltage of the host inverter to control the absolute value to be smaller than the predetermined voltage.

4. The control method for photovoltaic inverters whose AC sides are connected in parallel according to claim 1, wherein before receiving the direct voltage of the host inverter transmitted from the host inverter, the method further comprises:

controlling a carrier wave of the host inverter to be synchronized with a carrier wave of the slave inverter to control a phase of the common-mode voltage to be within a predetermined phase range.

5. A control apparatus for photovoltaic inverters whose AC sides are connected in parallel, comprising:

a detection unit, a difference obtaining unit and a control unit, wherein

the detection unit is configured to detect a first direct voltage of the first inverter and a second direct voltage of the second inverter;

the difference obtaining unit is configured to obtain a difference between the first direct voltage and the second direct voltage; and

the control unit is configured to adjust the direct voltages of the inverters to control the difference to be within a predetermined range.

6. The control apparatus for photovoltaic inverters whose AC sides are connected in parallel according to claim 5, wherein the difference obtaining unit comprises an absolute value obtaining sub-unit;

wherein the absolute value obtaining sub-unit is configured to obtain an absolute value of the difference between the first direct voltage and the second direct voltage; and

the control unit comprises a control sub-unit configured to adjust the direct voltages of the inverters to control the absolute value to be smaller than a predetermined voltage.

7. The control apparatus for photovoltaic inverters whose AC sides are connected in parallel according to claim 6, wherein the control sub-unit comprises a following sub-unit configured to adjust a direct voltage of a slave inverter based on a direct voltage of a host inverter to control the absolute value to be smaller than the predetermined voltage.

8. A photovoltaic inverter system in which AC sides of inverters are connected in parallel, comprising:

at least two inverters which are a first inverter and a second inverter, wherein an input terminal of the first inverter is connected with a first PV array, an input terminal of the second inverter is connected with a second PV array, the first PV array and the second PV array each have a parasitic capacitance to ground, and the first inverter is coupled with the second inverter through the parasitic capacitances to form a common-mode loop;

wherein the AC side of the first inverter and the AC side of the second inverter are connected in parallel, and a DC side of the first inverter is independent from a DC side of the second inverter;

wherein the first inverter functions as a host inverter, and the second inverter functions as a slave inverter;

wherein the host inverter is configured to transmit a direct voltage of the host inverter to the slave inverter;

wherein the slave inverter is configured to obtain a difference between the direct voltage of the host inverter and a direct voltage of the slave inverter, and adjust the direct voltage of the slave inverter to control the difference to be within a predetermined range and to control a common-mode voltage in the common-mode loop to be within a predetermined common-mode voltage range.

9. The photovoltaic inverter system in which AC sides of inverters are connected in parallel according to claim 8, wherein a carrier wave of the host inverter is controlled to be synchronized with a carrier wave of the slave inverter to control a phase of the common-mode voltage to be within a predetermined phase range.

10. The photovoltaic inverter system in which AC sides of inverters are connected in parallel according to claim 8, wherein the slave inverter is configured to obtain an absolute value of the difference between the direct voltage of the host inverter and the direct voltage of the slave inverter, and adjust the direct voltage of the slave inverter based on the direct voltage of the host inverter to control the absolute value to be smaller than a predetermined voltage.