INSULATION IMPEDANCE DETECTION CIRCUIT, AND METHOD

An insulation resistance detection circuit and method relate to the field of grid-connected inverters, and are used to detect whether a direct current input terminal of an inverter is short-circuited to protecting earthing or has low resistance to protecting earthing. The insulation resistance detection circuit includes a controller (11), an inverter circuit (12), a first direct current voltage source (DC1), a second direct current voltage source (DC2), a filter circuit (13), and a switch circuit (14). The controller (11) is configured to: open a first relay (F1), and close second relays (F2 to FM), or switch an on/off status of at least one of the second relays (F2 to FM); determine, based on a first measurement value between a positive input terminal (DC+) of the inverter circuit (12) and an earthing point, whether the positive input terminal (DC+) of the inverter circuit (12) is short-circuited to protecting earthing or has low resistance to protecting earthing; and determine, based on a second measurement value between a negative input terminal (DC-) of the inverter circuit (12) and the earthing point, whether the negative input terminal (DC-) of the inverter circuit (12) is short-circuited to protecting earthing or has low resistance to protecting earthing, where the first relay (F1) is a relay in M relays that is connected to at least one impedor in parallel, and the second relays (F2 to FM) are relays other than the first relay in the M relays.