Method and circuit arrangement with means for a leakage current compensation in a photovoltaic system with multiple differential current sensors

Patent metadata

Field	Value
Publication number	US-9768610-B2
Application number	US-201614997740-A
Country	US
Kind code	B2
Filing date	Jan 18, 2016
Priority date	Jul 18, 2013
Publication date	Sep 19, 2017
Grant date	Sep 19, 2017

Abstract

A method for leakage current compensation in a photovoltaic system includes determining a reference current flowing from at least one current-carrying line under voltage via a capacitor to earth, and generating a compensation current, having a phase and a frequency of the reference current, and having an amplitude adjusted by a negative scaling factor based on the reference current. The method further includes determining a current sum using a differential current sensor for at least a portion thereof, wherein the addends of the current sum are the currents through a complete set of current-carrying lines and the compensation current, minimizing the determined current sum by adjusting the scaling factor, and routing the compensation current through at least one other differential current sensor, such that the compensation current compensates a leakage current component of a differential current monitored by the other differential current sensor. A related device and system is also disclosed.

First claim

The invention claimed is:

1. A method for leakage current compensation in a photovoltaic system, comprising:
determining a reference current flowing from at least one current-carrying line under voltage via a capacitor to earth;
generating a compensation current, having a phase and a frequency of the reference current, and having an amplitude adjusted by a negative scaling factor based on the reference current;
determining a current sum using a differential current sensor for at least a portion thereof, wherein addends of the current sum are currents through a complete set of current-carrying lines and the compensation current;
minimizing the determined current sum by adjusting the negative scaling factor;
routing the compensation current through at least one other differential current sensor, such that the compensation current compensates a leakage current component of a differential current monitored by the at least one other differential current sensor.

2. The method as claimed in claim 1 , wherein the compensation current is routed on a neutral conductor through the at least one other differential current sensor.

3. The method as claimed in claim 1 , wherein the compensation current is carried through a conductor loop that extends through all differential current sensors at which the leakage current component of the monitored differential current is compensated.

4. The method as claimed in claim 1 , wherein the compensation current is also carried through the differential current sensor, in order to determine the current sum in the form of the differential current determined by the differential current sensor.

5. A circuit arrangement for leakage current compensation in a photovoltaic system, the circuit arrangement comprising:
at least one capacitor connected between a current-carrying line under voltage and earth;
a current determining element for determining a reference current flowing, via the at least one capacitor, to earth;
a current source configured to generate a compensation current having a phase and a frequency of the reference current, and having an amplitude adjusted by a negative scaling factor based on the reference current;
a differential current sensor for determining at least a portion of a current sum, wherein addends of the current sum determined are currents through a complete set of current-carrying lines and the compensation current; and
a logic circuit configured to minimize the determined current sum by adjusting the negative scaling factor;
a conductor loop configured to route the compensation current through at least one other differential current sensor such that the compensation current compensates a leakage current component of a differential current monitored by the at least one other differential current sensor.

6. The circuit arrangement as claimed in claim 5 , wherein the conductor loop comprises a portion of a neutral conductor through the at least one other differential current sensor.

7. The circuit arrangement as claimed in claim 5 , wherein the conductor loop extends through a plurality of differential current sensors.

8. The circuit arrangement as claimed in claim 5 , wherein the conductor loop extends through the differential current sensor, the differential current sensor determining the current sum in the form of the differential current.

9. A photovoltaic inverter, comprising:
an input to which a photovoltaic generator can be connected;
an output configured to output an alternating current;
an earth connection for connecting to earth;
a differential current sensor configured to determine a differential current;
at least one capacitor connected between a current-carrying line under voltage and the earth connection;
a current determining element for determining a reference current flowing, via the at least one capacitor, to the earth connection;
a current source configured to generate a compensation current, having a phase and a frequency of the reference current, and having an amplitude adjusted by a negative scaling factor based on the reference current;
wherein the differential current sensor is configured for determining a current sum, wherein addends of the current sum are currents through a complete set of current-carrying lines and the compensation current, and wherein the differential current sensor determines at least the currents through the complete set of current-carrying lines; and
a logic circuit configured to minimize the determined current sum by adjusting the negative scaling factor;
two connections between which the compensation current generated by the current source flows when they have been electrically connected to each other.

10. The photovoltaic inverter as claimed in claim 9 , wherein the two connections comprise a connection for a neutral conductor of the output alternating current.

11. The photovoltaic inverter as claimed in claim 9 , wherein the two connections comprise, at the output, the earth connection or a connection additional thereto for a functional earth.

12. The photovoltaic inverter as claimed in claim 9 , further comprising a line that extends from the current source to one of the two connections through the differential current sensor such that the current sum in the form of the differential current is determined by the differential current sensor.

Assignees

• Sma Solar Technology Ag

Inventors

• Bieniek Sebastian
• Hopf Markus

Classifications

• H02H3/17

  by means of an auxiliary voltage injected into the installation to be protected {(using summation current transformers H02H3/33)} · CPC title

• G01R19/10 Primary

  Measuring sum, difference or ratio · CPC title

• H02M7/42

  Conversion of DC power input into AC power output without possibility of reversal · CPC title

• H01L31/02021

  Electricity · mapped topic

• Y02E10/50

  Photovoltaic [PV] energy · CPC title