Circuit and method for detecting direct-current power ground insulation resistor

Abstract

The invention relates to a circuit and a method for detecting a direct-current power ground insulation resistor. The circuit comprises resistors R1 to R5 and switches S1 to S2, wherein the resistors R1 and R3 have the same resistance value; the resistors R2 and R4 have the same resistance value; one end of the resistor R2 is connected to an anode of a direct-current power supply through the resistor R1, and the other end of the resistor R2 is grounded through the switch S1; the resistors R1 and R2 and the switch S1 form a first detection branch circuit; one end of the resistor R4 is connected to a cathode of the direct-current power supply through the resistor R3, and the other end of the resistor R4 is grounded through the switch S2; the resistors R3 and R4 and the switch S2 form a second detection branch circuit; and the resistor R5 is connected with the first detection branch circuit or the second detection branch circuit in parallel. The circuit has the advantages as follows: when resistance values of positive and negative ground insulation resistors R+ and R- of the direct-current power supply are reduced in a uniform amplitude way or close to each other, the resistance values of the resistors R+ and R- can be still detected, and detection precision of the resistors R+ and R- can be also guaranteed.

Description

technical field [0001] The invention is applied in the field of photovoltaic power generation, and can also be applied in the field of electric vehicles, and in particular relates to a detection circuit and a detection method for a DC power supply to ground insulation resistance used in a photovoltaic inverter. Background technique [0002] According to the requirements of safety regulations, it is necessary to test the insulation resistance of the photovoltaic inverter to the ground. If the insulation resistance is less than the specified value, the photovoltaic inverter is not allowed to be connected to the grid. [0003] At present, the insulation resistance of photovoltaic inverters to the ground usually adopts a detection method based on the principle of bridge balance. Such as figure 1 As shown, two known resistors R are connected in parallel between the positive and negative ground of the photovoltaic cell PV a , R b , through the sense resistor R a The voltage ac...

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Problems solved by technology

However, since the resistor R 5 The resistance and resistance R 1 with resistor R 2 The sum of is relatively small, so that in the switch S 1 When closed, the photovoltaic cell PV + The resistance to ground is much smaller than that of photovoltaic cells PV - resistance to ground, switch S 1 Resistance R when closed 4 The voltage Vo at both ends is relatively large, so the sampling voltage range is relatively large, so when the voltage is small, the error of Vo will be relatively large, which will affect the positive insulation resistance R + and negative insulation resistance to ground R - detection accuracy

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