Method for Recognizing Theft of a PV Module and a Failure of a Bypass Diode of a PV Module, Corresponding PV Sub-Generator Junction Box, PV Inverter, and Corresponding PV System

A method for recognizing theft of at least one photovoltaic (PV) module of a PV system, which has at least one PV string, connected in parallel, of serially connected PV modules for supplying a field voltage, wherein each of the PV modules has a plurality of serially connected PV cells, the method comprising:

• providing bypass diodes connected in an anti-parallel manner for protecting said plural serially connected PV cells;
• connecting, during a non-feeding operation, a test voltage that is negative relative to the field voltage to said at least one PV string to set a test current through the bypass diodes;
• and
• automatically outputting a theft message when one of the test current changes at a given test voltage and the test voltage changes at a given test current.

A photovoltaic (PV) sub-generator junction box for a PV system, comprising:

• a plurality of electrical terminals for respectively connecting to a plurality of PV string lines, each of the plural PV string lines having a plurality of serially connected PV modules, each with a plurality of serially connected PV cells;
• and
• a sub-generator terminal for connecting to a PV sub-generator line of a remotely located central PV inverter;
• an electronic control unit, the PV sub-generator junction box being configured for switching a test voltage that is negative relative to a field voltage generated by said PV modules to the PV sub-generator line during a non-feeding operation such that a test current through at least one bypass diode of the PV modules can be set;
• at least one of a voltage measuring unit for acquiring the test voltage and a current measuring unit for acquiring the test current;
• wherein at least one of a theft message is output by the control unit when at least one of the test current and the test voltage changes;
• and
• wherein a failure message for the at least one bypass diode is output by the control unit when a presently acquired test voltage is reduced in comparison with a previously measured comparison voltage by approximately an integral multiple of a forward voltage of one of the at least one bypass diode or when, because of an open-circuit state of one of the at least one bypass diode instead of the test current to be set, only a residual current smaller in comparison therewith can be set.

A photovoltaic (PV) inverter for a PV system, comprising:

• at least one sub-generator terminal for connection of at least one of:
• a respective PV sub-generator line of a plurality of PV sub-generator junction boxes or a respective PV main direct current line of a PV generator junction box connected in between the PV inverter and the plurality of PV sub-generator junction boxes;
• a power connector for connection to a power supply network;
• a central control unit for controlling the PV inverter;
• an auxiliary voltage supply for providing an auxiliary voltage;
• and
• a coupling switch for feeding the auxiliary voltage into the at least one of the PV sub-generator line and PV main direct current lines.