Determining insulation resistance for photovoltaics

A device for determining an insulation resistance (RISO) of a photovoltaic system with respect to earth potential (EP), comprising

• a DC-DC converter unit which converts a first DC voltage generated by a photovoltaic generator into a second DC voltage, which is applied to an intermediate circuit that temporarily stores the electrical energy, supplied by the photovoltaic generator, for a DC-AC converter unit connected thereto, the DC-DC converter unit comprising at least one controllable booster switch operated in a clocked manner in order to charge the intermediate circuit;
• wherein the intermediate circuit contains a reference node (BK) having an adjustable reference potential (BP), and comprising
• a measuring unit, which picks up measuring voltages between the reference potential (BP) and the earth potential (EP) at different reference potentials (BP), and
• an evaluation unit which evaluates the measuring voltages that have been picked up in order to determine the insulation resistance of the photovoltaic generator of the photovoltaic system;
• and
• a discharge circuit connected to the intermediate circuit for adjusting the reference potential (BP) at the reference node (BK) of the intermediate circuit.