Tracking method and tracking device for a voltage converter for a photovoltaic system

• US 9,444,365 B2
• Filed: 04/24/2014
• Issued: 09/13/2016
• Est. Priority Date: 10/28/2011
• Status: Active Grant

• Current Assignee: SMA Solar Technology AG
• Original Assignee: SMA Solar Technology AG
• Inventors: Bock, Martin, Mueller, Tobias, Ortmann, Thomas, Unru, Alexander
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): Tiku, Sisay G
• Application Number:
  US14/260,741
• Publication Number:
  US 20140233263A1
• Time in Patent Office: 873 Days
• Field of Search: 363/44, 363/48, 363/53, 363/537
• US Class Current: 1/1
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02M 7/42 Conversion of dc power input into ac power output without possibility of reversal
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

The disclosure relates to a tracking method for a voltage transformer, in particular an inverter, of a photovoltaic system. In the method, an intermediate circuit voltage is repeatedly decreased or increased in one direction to a lower or higher voltage by voltage steps of a specified magnitude. The method is characterized in that an average rate of change of the intermediate circuit voltage in a partial time period between two voltage steps is limited by a maximum average rate of change, the maximum average rate of change being defined according to the magnitude of the intermediate circuit voltage. The disclosure further relates to a tracking device designed to perform the tracking method and to an inverter equipped with the tracking device.

Claims

1. A tracking method for a voltage converter, in particular an inverter, of a photovoltaic system, for tracking a working point of a PV generator, comprising:

changing an intermediate circuit voltage by voltage increments of a predetermined level in a direction towards a lower or a higher voltage; and

limiting a mean rate of change of the intermediate circuit voltage in a subperiod between two voltage increments by a maximum mean rate of change, wherein the maximum mean rate of change is determined depending on a level of a voltage difference between the intermediate circuit voltage and a minimum required intermediate circuit voltage.

2. The tracking method of claim 1, wherein the maximum mean rate of change decreases as the level of the voltage difference decreases.

3. The tracking method of claim 2, wherein the maximum mean rate of change is constant above a fixed intermediate circuit voltage.

4. The tracking method of claim 1, wherein the minimum required intermediate circuit voltage is determined based on a mains voltage.

5. The tracking method of claim 4, wherein the minimum required intermediate circuit voltage is further determined based on a feed-in current.

6. The tracking method of claim 1, wherein the minimum required intermediate circuit voltage is updated regularly.

7. The tracking method of claim 6, wherein the updating of the minimum required intermediate circuit voltage is performed more frequently than the voltage increments by an integer multiple.

8. The tracking method of claim 1, wherein a level of the voltage increments is determined depending on a level of the intermediate circuit voltage.

9. The tracking method of claim 1, wherein a setpoint value for the intermediate circuit voltage is provided as a continuous function with a finite rate of change.

10. The tracking method of claim 9, wherein changes in the setpoint value are provided with a ramp function.

11. The tracking method of claim 1, wherein the maximum mean rate of change is determined by means of an update rate for a control of a current fed-in by the inverter into an AC voltage grid.

12. A tracking device for an inverter for use in a photovoltaic (PV) generation system, for tracking a working point of a PV generator in the PV generation system, comprising:

first input ports configured to receive an intermediate circuit voltage associated with the inverter; and

second input ports configured to receive an electric power associated with an output power of the PV Generator,

wherein the tracking device is configured to;

determine a setpoint value of the intermediate circuit voltage based on the received intermediate circuit voltage and electric power;

change the intermediate circuit voltage by voltage increments of a predetermined level in a direction towards a lower or a higher voltage based on the determined setpoint; and

limit a mean rate of change of the intermediate circuit voltage in a subperiod between two voltage increments by a maximum mean rate of change, wherein the maximum mean rate of change is determined depending on a level of a voltage difference between the intermediate circuit voltage and a minimum required intermediate circuit voltage.

13. The inverter of claim 12, wherein the maximum mean rate of change decreases as the level of the voltage difference decreases.

14. The inverter of claim 13, wherein the maximum mean rate of change is constant above a fixed intermediate circuit voltage.

15. The inverter of claim 12, wherein the minimum required intermediate circuit voltage is determined based on a mains voltage.

16. The inverter of claim 15, wherein the minimum required intermediate circuit voltage is further determined based on a feed-in current.

17. The inverter of claim 12, wherein a level of the voltage increments is determined depending on a level of the intermediate circuit voltage.