Insulation resistance detection method, device and system

The invention relates to an insulation resistance detection method, device and system, which are used for reducing the cost and complexity of alternating current ground insulation resistance detection. The method comprises the following steps that: an inverter injects a first common-mode voltage to an alternating current side, and the first common-mode voltage is divided by alternating current ground insulation impedance of an alternating current cable and direct current ground insulation impedance of a photovoltaic unit; the inverter can obtain the impedance value of the alternating-current ground insulation impedance according to the first common-mode voltage, the partial voltage of the alternating-current ground insulation impedance to the first common-mode voltage (namely the second common-mode voltage on the alternating-current ground insulation impedance) and the impedance value of the direct-current ground insulation impedance. The inverter which is necessary equipment in the photovoltaic power generat