Safety detection device and method of grid-connected inverter

Patent metadata

Field	Value
Publication number	US-10505370-B2
Application number	US-201415502396-A
Country	US
Kind code	B2
Filing date	Sep 30, 2014
Priority date	Sep 30, 2014
Publication date	Dec 10, 2019
Grant date	Dec 10, 2019

Abstract

Provided is a grid-connected inverter safety detection device applied in a photovoltaic inverter system and including voltage detection circuit, a filter circuit, a comparison circuit and a controller. The voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal for any phase of the three-phase power grid and the ground. The filter circuit is configured to filter out an alternating current component of the voltage detected by the voltage detection circuit and to retain an direct current component of the voltage. The comparison circuit is configured to compare the direct current component of the voltage with a preset voltage value and transmit a comparison result to the controller. The controller is configured to determine, according to the comparison result, whether an alternating current side at the output terminal of the inverter has normal insulation.

First claim

The invention claimed is:

1. A grid-connected inverter safety detection device applied in a photovoltaic inverter system, wherein the photovoltaic inverter system comprises a PV array, an inverter, a switch, a power grid, and resistors comprising a phase resistor and a N-wire resistor, wherein output terminals of the PV array are connected to input terminals of the inverter, an output terminal of the inverter are connected to a first terminal of the power grid via the switch, the switch is in an off state, a second terminal of the power grid functions as a point N which is connected to a negative output terminal of the PV array via the N-wire resistor, and the first terminal of the power grid are connected to the negative output terminal of the PV array via the phase resistor; and
the device comprises a voltage detection circuit, a filter circuit, a comparison circuit and a controller, wherein
the voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal of the power grid and the ground;
the filter circuit is configured to filter out an alternating current component of the voltage detected by the voltage detection circuit and to retain a direct current component of the voltage;
the comparison circuit is configured to compare the direct current component of the voltage with a preset voltage value and transmit a comparison result to the controller; and
the controller is configured to determine, according to the comparison result, whether an alternating current side at the output terminals of the inverter has normal insulation.

2. The grid-connected inverter safety detection device according to claim 1 , wherein the preset voltage value is interrelated with the voltage of the negative output terminal of the PV array relative to the ground.

3. The grid-connected inverter safety detection device according to claim 2 , further comprising a potential induced degradation PID circuit, wherein
the potential induced degradation PID circuit comprises a first switch and an equivalent element which are connected in series to each other, the equivalent element comprises at least one of a fuse, a resistor, a diode, a cell plate and a switch power supply;
the negative output terminal of the PV array is grounded via the potential induced degradation PID circuit; and
the first switch is turned off when the voltage detection circuit detects the voltage between the point N and the ground, or the voltage between the first terminal for any phase of the three-phase power grid and the ground.

4. The grid-connected inverter safety detection device according to claim 1 , wherein the filter circuit is one of a low-pass filter, an average value filter, an integrator and a band-rejection filter.

5. The grid-connected inverter safety detection device according to claim 4 , further comprising a potential induced degradation PID circuit, wherein
the potential induced degradation PID circuit comprises a first switch and an equivalent element which are connected in series to each other, the equivalent element comprises at least one of a fuse, a resistor, a diode, a cell plate and a switch power supply;
the negative output terminal of the PV array is grounded via the potential induced degradation PID circuit; and
the first switch is turned off when the voltage detection circuit detects the voltage between the point N and the ground, or the voltage between the first terminal for any phase of the three-phase power grid and the ground.

6. The grid-connected inverter safety detection device according to claim 1 , further comprising a potential induced degradation PID circuit, wherein
the potential induced degradation PID circuit comprises a first switch and an equivalent element which are connected in series to each other, the equivalent element comprises at least one of a fuse, a resistor, a diode, a cell plate and a switch power supply;
the negative output terminal of the PV array is grounded via the potential induced degradation PID circuit; and
the first switch is turned off when the voltage detection circuit detects the voltage between the point N and the ground, or the voltage between the first terminal of the power grid and the ground.

7. The grid-connected inverter safety detection device according to claim 1 , wherein
the power grid is a three-phase power grid, the switch is a three-phase switch, and the phase resistor comprises a first resistor, a second resistor and a third resistor;
the output terminal of the inverter comprises three output terminals;
the first terminal of the three-phase power grid comprises three first terminals connected respectively to the three output terminals of the inverter via the three-phase switch, and connected to the negative output terminal of the PV array via the first resistor, the second resistor and the third resistor respectively;
the second terminal of the three-phase power grid comprises three second terminals connected together as the point N; and
the voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal for any phase of the three-phase power grid and the ground.

8. A grid-connected inverter safety detection device applied in a photovoltaic inverter system, wherein the photovoltaic inverter system comprises a PV array, an inverter, a switch, a power grid, and resistors comprising a phase resistor and a N-wire resistor, wherein an output terminal of the PV array are connected to input terminals of the inverter, an output terminal of the inverter are connected to a first terminal of the power grid via the switch, the switch is in an off state, a second terminal of the power grid functions as a point N which is connected to a negative output terminal of the PV array via the N-wire resistor, and the first terminal of the power grid are connected to the negative output terminal of the PV array via phase resistor; and
the device comprises a voltage detection circuit, an AD converter and a controller, wherein
the voltage detection circuit is configured to detect a voltage between the point N and the ground, or a voltage between the first terminal of the power grid and the ground;
the AD converter is configured to convert the voltage detected by the voltage detection circuit into a digital signal; and
the controller is configured to filter out an alternating current component of the digital signal and to retain a direct current component of the digital signal; and to determine whether the direct current component of the digital signal is greater than a preset voltage value, wherein it is determined that an alternating current side at the output terminals of the inverter has normal insulation if the direct current component of the digital signal is greater than the preset voltage value, and it is determined that the alternating current side at the output terminal of the inverter has abnormal insulation if the direct current component of the digital signal is smaller than the preset voltage value.

9. The grid-connected inverter safety detection device according to claim 8 , wherein
the power grid is a three-phase power grid, the switch is a three-phase switch, and the phase resistor comprises a first resistor, a second resistor and a third resistor;
the output terminal of the inverter comprises three output terminals;
the first terminal of the three-phase power grid comprises three first terminals connected respectively to the three output terminals of the inverter via the three-phase switch, and connected to the negative output terminal of the PV array via the first resistor, the second resistor and the third resistor respectively;
the second terminal of

Assignees

• Sungrow Power Supply Co Ltd

Inventors

• Geng Houlai
• Xu Qingqing
• Xing Jun
• Li Haoyuan
• Mei Xiaodong

Classifications

• H02H3/332

  with means responsive to DC component in the fault current · CPC title

• H02H3/353

  involving comparison of phase voltages · CPC title

• H02H3/34

  of a three-phase system · CPC title

• H02S50/00

  Monitoring or testing of PV systems, e.g. load balancing or fault identification · CPC title

• H02J2101/24

  Photovoltaics · CPC title