Abstract: This paper proposes a detection circuit and method of insulation impedance for photovoltaic array, which contains a voltage sampling circuit of photovoltaic negative electrode to the earth, two electronic switches and three balance resistors. In order to balance the sampling resistance, a balance resistor equivalent to the resistance of the voltage sampling branch is always connected in parallel between the positive electrode of the photovoltaic panel and the earth, so that the voltage of the sampling point between the negative electrode of the photovoltaic panel and the earth will not be extremely small when the insulation performance is normal, which reduces the requirements for voltage sampling accuracy. The branch consisting of an electronic switch and a resistor in series is connected between the positive/negative electrodes of the photovoltaic panel and the earth, and the resistor in series is equivalent to the critical insulation impedance that meets the leakage current standard. When the impedance of one electrode of the photovoltaic panel decreases, the other pole electronic switch is closed connected in parallel with the other electrode, and the corresponding balance resistor is connected to improve the sensitivity of the sampling voltage to the impedance change of the circuit, so as to calculate the actual impedance of the circuit. The proposed method can obtain accurate insulation impedance with low-precision voltage sampling, which improves the reliability of detection.

Key words: insulation resistance, balancing resistance, leakage current, PV arrays