Insulation impedance detection circuit and insulation impedance detection method of photovoltaic inverter system

An insulation impedance detection circuit of a photovoltaic inverter system, the photovoltaic inverter system comprises one or more input circuits and an inverter circuit, each of the input circuits electrically coupled to the inverter circuit through a positive bus and a negative bus, with a first equivalent impedance Rp between the positive bus and a protective earth point, and a second equivalent impedance Rn between the negative bus and the protective earth point, wherein the insulation impedance detection circuit comprising:

• a bus voltage sampling circuit coupled to the positive bus and the negative bus for sampling the bus voltage and generating a first bus voltage and a second bus voltage;
• a protective earth voltage sampling circuit coupled to the protective earth point for sampling the protective earth voltage and generating a first protective earth voltage and a second protective earth voltage corresponding to the first bus voltage and the second bus voltage, respectively;
• and
• a controller coupled to the bus voltage sampling circuit and the protective earth voltage sampling circuit for calculating an equivalent insulation impedance of the photovoltaic inverter system according to the first bus voltage, the second bus voltage, the first protective earth voltage and the second protective earth voltage, and controlling interconnection between the inverter circuit and a power grid when the equivalent insulation impedance is larger than or equal to a threshold value.