Ground-fault detecting device and related method

A ground-fault detecting device, comprising:

• a first detecting module, having a first input terminal, a second input terminal, and a third input terminal coupled to a first-phase electric power, a second-phase electric power, and a third-phase electric power on an AC (Alternating Current) side of a photovoltaic power generating system respectively, for sampling voltages of the first-phase electric power, the second-phase electric power, and the third-phase electric power to generate a first sampled voltage, a second sampled voltage, and a third sampled voltage respectively;
• and
• a controller, coupled to the first detecting module, for determining if a ground-fault occurs in the AC side before the photovoltaic power generating system is connected to a grid according to the first sampled voltage, the second sampled voltage, and the third sampled voltage;
• wherein the controller generates an alarm signal when the ground-fault occurs in the AC side, wherein the first detecting module comprises:
• a first matching impedance device, having a first terminal coupled to the first-phase electric power;
• a first grounding resistor, having a first terminal coupled to a second terminal of the first matching impedance device, and a second terminal coupled to a ground;
• a second matching impedance device, having a first terminal coupled to the second-phase electric power;
• a second grounding resistor, having a first terminal coupled to a second terminal of the second matching impedance device, and a second terminal coupled to the ground;
• a third matching impedance device, having a first terminal coupled to the third-phase electric power;
• a third grounding resistor, having a first terminal coupled to a second terminal of the third matching impedance device, and a second terminal coupled to the ground;
• wherein the first sampled voltage is a voltage difference between the first terminal and the second terminal of the first grounding resistor;
• the second sampled voltage is the voltage difference between the first terminal and the second terminal of the second grounding resistor;
• the third sampled voltage is the voltage difference between the first terminal and the second terminal of the third grounding resistor.