Photovoltaic inverter comprising an upstream DC/DC converter and temperature regulation of the power semiconductors

Patent metadata

Field	Value
Publication number	US-10186966-B2
Application number	US-201615185756-A
Country	US
Kind code	B2
Filing date	Jun 17, 2016
Priority date	Dec 18, 2013
Publication date	Jan 22, 2019
Grant date	Jan 22, 2019

Abstract

A method and corresponding system for operating an inverter includes setting an input voltage (U PV ) of the inverter by an input-side DC-DC converter and/or an output-side inverter bridge, wherein the input voltage (U PV ) corresponds to an MPP voltage (U MPP ) at which a generator connectable on the input side outputs a maximum electrical power, and determining a first temperature value (T DCDC ) in the DC-DC converter and a second temperature value (T DCAC ) in the inverter bridge. The method or corresponding system further includes changing the input voltage (U PV ) of the inverter with respect to the MPP voltage (U MPP ) if at least one of the determined temperature values (T DCDC , T DCAC ) exceeds a limit value (T max,DCDC , T max,DCAC ) assigned to the respective temperature values (T DCDC , T DCAC ), increasing the input voltage (U PV ) with respect to the MPP voltage (U MPP ) if an exceedance of the limit value (T max,DCDC ) for the first temperature value (T DCDC ) in the DC-DC converter is determined and/or the MPP voltage (U MPP ) lies below a predefined limit voltage (U limit ), and otherwise reducing the input voltage (U PV ) ith respect to the MPP voltage (U MPP ).

First claim

The invention claimed is:

1. A method for operating an inverter comprising:
setting an input voltage (U PV ) of the inverter by an input-side DC-DC converter and/or an output-side inverter bridge, wherein the input voltage (U PV ) corresponds to an MPP voltage (U MPP ) at which a generator connectable on the input side outputs a maximum electrical power;
determining a first temperature value (T DCDC ) in the DC-DC converter and a second temperature value (T DCAC ) in the inverter bridge;
changing the input voltage (U PV ) of the inverter with respect to the MPP voltage (U MPP ) if at least one of the determined temperature values (T DCDC , T DCAC ) exceeds a limit value (T max,DCDC , T max,DCAC ) assigned to the respective temperature values (T DCDC , T DCAC ), wherein changing the input voltage U PV comprises:
increasing the input voltage (U PV ) with respect to the MPP voltage (U MPP ) if an exceedance of the limit value (T max,DCDC ) for the first temperature value (T DCDC ) in the DC-DC converter is determined and/or the MPP voltage (U MPP ) lies below a predefined limit voltage (U limit ); and
otherwise reducing the input voltage (U PV ) with respect to the MPP voltage (U MPP ).

2. The method as claimed in claim 1 , wherein the limit voltage (U limit ) is between 50% and 150% of a minimum voltage of a DC voltage link circuit of the inverter.

3. The method as claimed in claim 2 , wherein the minimum voltage of the DC voltage link circuit corresponds to a minimum required link circuit voltage (U ZWK,min ) for feeding an AC current into an AC voltage grid.

4. The method as claimed in claim 1 , wherein the limit voltage (U limit ) is defined depending on the temperature values (T DCDC , T DCAC ) determined during operation with maximum possible electrical power.

5. The method as claimed in claim 1 , wherein the temperature values (T DCDC , T DCAC ) are in each case determined repeatedly and compared with the limit values (T max,DCDC , T max,DCAC ) respectively assigned to them.

6. The method as claimed in claim 5 , wherein after a change of the input voltage (U PV ) with respect to the MPP voltage (U MPP ) the difference between input voltage (U PV ) and MPP voltage (U MPP ) is increased if at least one of the determined temperature values (T DCDC , T DCAC ) still exceeds the limit value (T max,DCDC , T max,DCAC ) respectively assigned to it.

7. The method as claimed in claim 1 , wherein the input voltage (U PV ) of the inverter is set by virtue of an MPP tracking method if all the determined temperature values (T DCDC , T DCAC ) fall below the limit values (T max,DCDC , T max,DCAC ) respectively assigned to them, and wherein the input voltage (U PV ) of the inverter is set depending on the first temperature value (T DCDC ) in the DC-DC converter and/or depending on the second temperature value (T DCAC ) in the inverter bridge if one of the determined temperature values (T DCDC , T DCAC ) exceeds the limit value (T max,DCDC , T max,DCAC ) assigned to it.

8. The method as claimed in claim 7 , wherein a temperature-dependent regulation is activated for setting the input voltage (U PV ) of the inverter depending on a temperature value (T DCDC , T DCAC ) if one of the determined temperature values (T DCDC , T DCAC ) exceeds the limit value (T max,DCDC , T max,DCAC ) assigned to it, wherein the temperature-dependent regulation is deactivated if all the determined temperature values (T DCDC , T DCAC ) fall below the limit values (T max,DCDC , T max,DCAC ) respectively assigned to them.

9. The method as claimed in claim 1 , wherein the input voltage (U PV ) is reduced to zero, in particular by the generator being short-circuited by means of the DC-DC converter, if the input voltage (U PV ) is increased on account of an exceedance of one of the limit values (T max,DCDC , T max,DCAC ) by one of the determined temperature values (T DCDC , T DCAC ) and exceeds a limit value (U PV,max ) for the input voltage (U PV ) of the inverter and/or a limit value (U ZWK,max ) for the link circuit voltage (U ZWK ).

10. The method as claimed in claim 1 , wherein the input voltage (U PV ) is increased to an open circuit voltage (U 0 ) of the generator if an exceedance of the limit value (T max,DCDC ) for the first temperature value (T DCDC ) in the DC-DC converter is determined, while the input voltage (U PV ) is reduced on account of an exceedance of the limit value (T max,DCAC ) for the second temperature value (T DCAC ) in the inverter bridge and lies below a minimum required link circuit voltage (U ZWK,min ).

11. The method as claimed in claim 8 , wherein the input voltage (U PV ) is reduced to zero, in particular by the generator being short-circuited by means of the DC-DC converter, if the open circuit voltage (U 0 ) of the generator lies above the limit value (U PV,max ) for the input voltage (U PV ) of the inverter and/or the limit value (U ZWK,max ) for the link circuit voltage (U ZWK ).

12. The method as claimed in claim 1 , wherein the temperature values (T DCDC , T DCAC ) in the DC-DC converter and/or in the inverter bridge are determined on the basis of temperature models, wherein the temperature models process measurement values of temperature sensors which are assigned to the DC-DC converter and/or to the inverter bridge, and wherein the temperature values (T DCDC , T DCAC ) represent temperatures at or in semiconductor switches of the DC-DC converter and/or of the inverter bridge.

13. An inverter for an energy generating installation, comprising:
an input-side DC-DC converter;
an output-side inverter bridge;
a control device configured to drive the DC-DC converter and the inverter bridge with control signals; and
temperature sensors respectively assigned to the DC-DC converter and to the inverter bridge,
wherein the control device is configured to:
set an input voltage (U PV ) of the inverter by an input-side DC-DC converter and/or an output-side inverter bridge, wherein the input voltage (U PV ) corresponds to an MPP voltage (U MPP ) at which a generator connectable on the input side outputs a maximum electrical power;
determine a first temperature value (T DCDC ) in the DC-DC converter and a second temperature value (T DCAC ) in the inverter bridge from the temperature sensors respectively assigned thereto;
change the input voltage (U PV ) of the inverter with respect to the MPP voltage (U MPP ) if at least one of the determined temperature values (T DCDC , T DCAC ) exceeds a limit value (T max,DCDC , T max,DCAC ) assigned to the respective temperature values (T DCDC , T DCAC ), wherein to change the input voltage U PV ), the control device is configured to:
increase the input voltage (U PV ) with respect to the MPP voltage (U MPP ) if an exceedance of the limit value (T max,DCDC ) for the first temperature value (T DCPC ) in the DC-DC converter is determined and/or the MPP voltage (U MPP ) lies below a predefined limit voltage (U limit ); and
otherwise reduce the input voltage (U PV ) with respect to the MPP voltage (U MPP ).

14. The inverter as claimed in claim 13 , further comprising a generator selectively connectable to the inverter on the input side.

15. The inverter as claimed in claim 13 , wherein the DC-DC converter is a boost converter.

16. The inverter as claimed in claim 13 , wherein the DC-DC converter comprises at least one semiconductor switch and the inverter bridge comprises at least two semiconductor switches.

17. The inverter as claimed in claim 13 , wherein the inverter bridge comprises a filter inductance arranged on the output side.

Assignees

• Sma Solar Technology Ag

Inventors

• Unru Alexander
• Bock Martin

Classifications

• H02M7/537

  using semiconductor devices only, e.g. single switched pulse inverters · CPC title

• H02M1/32

  Means for protecting converters other than automatic disconnection · CPC title

• H02M7/53871

  with automatic control of output voltage or current · CPC title

• H02M3/156

  with automatic control of output voltage or current, e.g. switching regulators · CPC title

• H02J2101/25

  involving maximum power point tracking control for photovoltaic sources · CPC title