Photovoltaic energy system and method for detecting ground insulation impedance

Patent metadata

Field	Value
Publication number	US-11852671-B2
Application number	US-202217707436-A
Country	US
Kind code	B2
Filing date	Mar 29, 2022
Priority date	Mar 31, 2021
Publication date	Dec 26, 2023
Grant date	Dec 26, 2023

Abstract

A photovoltaic energy system and a method for detecting a ground insulation impedance, improve accuracy of detecting a ground insulation impedance after one or more conversion circuits are connected in parallel. The photovoltaic energy system includes one or more conversion circuits and a detection circuit. The detection circuit includes an alternating current signal source and a sampling resistor that are connected in series, a first sampling circuit, and a control circuit. The control circuit is configured to control the alternating current signal source to output harmonic signals of a first frequency and a second frequency. The first sampling circuit is configured to: when the alternating current signal source outputs the harmonic signal of the first frequency, collect a voltage at both terminals of the sampling resistor to obtain a first voltage.

First claim

What is claimed is:

1. A photovoltaic energy system comprising:
one or more conversion circuits; and
a detection circuit, wherein the one or more conversion circuits are connected in parallel between a positive bus and a negative bus;
wherein, the detection circuit comprises a signal source excitation branch, a first sampling circuit, and a control circuit; one terminal of the signal source excitation branch is connected to a ground wire, and the other terminal of the signal source excitation branch is connected to the positive bus or the negative bus; the signal source excitation branch comprises an alternating current signal source and a sampling resistor that are connected in series; and the first sampling circuit is connected in parallel to the sampling resistor, and the control circuit is connected to both an input terminal of the alternating current signal source and an output terminal of the first sampling circuit;
the control circuit is configured to control the alternating current signal source to output harmonic signals of a first frequency and a second frequency, wherein the first frequency is different from the second frequency;
the first sampling circuit is configured to: when the alternating current signal source outputs the harmonic signal of the first frequency, collect a voltage at both terminals of the sampling resistor to obtain a first voltage; when the alternating current signal source outputs the harmonic signal of the second frequency, collect a voltage at both terminals of the sampling resistor to obtain a second voltage; and send the first voltage and the second voltage to the control circuit; and
the control circuit is further configured to obtain, based on the harmonic signals of the first frequency and the second frequency, the first voltage, and the second voltage, a ground insulation impedance obtained after the one or more conversion circuits are connected in parallel.

2. The photovoltaic energy system according to claim 1 , wherein, the detection circuit further comprises a direct current blocking capacitor, the other terminal of the signal source excitation branch is connected to the positive bus or the negative bus through the direct current blocking capacitor, and the direct current blocking capacitor is configured to isolate a direct current signal in the one or more conversion circuits for the detection circuit.

3. The photovoltaic energy system according to claim 1 , wherein, the first sampling circuit is further configured to: collect a first phase corresponding to the first voltage when the first voltage is collected, collect a second phase corresponding to the second voltage when the second voltage is collected, and send the first phase and the second phase to the control circuit; and
the control circuit is configured to detect, based on the harmonic signals of the first frequency and the second frequency, the first voltage, the second voltage, the first phase, and the second phase, the ground insulation impedance obtained after the one or more conversion circuits are connected in parallel.

4. The photovoltaic energy system according to claim 1 , wherein, the control circuit is further configured to: when the ground insulation impedance is greater than or equal to a first impedance threshold, detect that an insulation status of the one or more conversion circuits is normal.

5. The photovoltaic energy system according to claim 4 , wherein, the detection circuit further comprises a leakage current sampling circuit one-to-one connected to the one or more conversion circuits, an input terminal of each leakage current sampling circuit is connected to both an input terminal and an output terminal of a conversion circuit connected to the leakage current sampling circuit, and an output terminal of each leakage current sampling circuit is connected to the control circuit;
wherein, each leakage current sampling circuit is configured to: sample a first leakage current between the connected conversion circuit and the positive bus and a second leakage current between the connected conversion circuit and the negative bus to obtain a total leakage current of the connected conversion circuit; and send the total leakage current to the control circuit.

6. The photovoltaic energy system according to claim 5 , wherein, the control circuit is further configured to: when the ground insulation impedance is less than a second impedance threshold, detect that an insulation status of a conversion circuit corresponding to a total leakage current whose value is the largest in the total leakage currents sent by all the leakage current sampling circuits is abnormal, wherein the second impedance threshold is half of the first impedance threshold.

7. The photovoltaic energy system according to claim 6 , wherein, the detection circuit further comprises a second sampling circuit and a third sampling circuit, wherein,
one terminal of the second sampling circuit is connected to the positive bus and the other terminal of the second sampling circuit is connected to the ground wire, and the second sampling circuit is connected to the control circuit and is configured to: sample a voltage between the positive bus and the ground wire to obtain a first bus voltage, and send the first bus voltage to the control circuit;
wherein, one terminal of the third sampling circuit is connected to the negative bus and the other terminal of the third sampling circuit is connected to the ground wire, and the third sampling circuit is connected to the control circuit and is configured to: sample a voltage between the negative bus and the ground wire to obtain a second bus voltage, and send the second bus voltage to the control circuit.

8. The photovoltaic energy system according to claim 7 , wherein, the control circuit is further configured to:
when the ground insulation impedance is less than the first impedance threshold and greater than or equal to the second impedance threshold, detect, based on the first leakage current and the second leakage current of each conversion circuit, the first bus voltage, the second bus voltage, and the ground insulation impedance, a positive ground insulation impedance obtained after the one or more conversion circuits are connected in parallel between the positive bus and the ground wire and a negative ground insulation impedance obtained after the one or more conversion circuits are connected in parallel between the negative bus and the ground wire.

9. The photovoltaic energy system according to claim 8 , wherein, when the positive ground insulation impedance is greater than or equal to the first impedance threshold, the control circuit is further configured to:
detect that an insulation status of the one or more conversion circuits between the positive bus and the ground wire is normal, otherwise,
detect that an insulation status of the one or more conversion circuits between the positive bus and the ground wire is abnormal.

10. The photovoltaic energy system according to claim 8 , wherein, when the negative ground insulation impedance is greater than or equal to the first impedance threshold, the control circuit is further configured to:
detect that an insulation status of the one or more conversion circuits between the negative bus and the ground wire is normal, else, and
detect that an insulation status of the one or more conversion circuits between the negative bus and the ground wire is abnormal.

11. The photovoltaic energy system according to claim 7 , wherein, the detection circuit further comprises an alternating current signal filter one-to-one connected to each leakage current sampling circuit, an input terminal of each alternating current signal filter is con

Assignees

• Huawei Digital Power Tech Co Ltd

Inventors

• Wang Zhong
• Zhang Shengjie
• Li Jianshan
• Peng Yu
• Yu Shijiang
• Zhou He
• Yu Bo

Classifications

• H02J2101/24

  Photovoltaics · CPC title

• G01R31/14 Primary

  Circuits therefor {, e.g. for generating test voltages, sensing circuits (G01R31/1209 - G01R31/1227 take precedence; for testing switches G01R31/327)} · CPC title

• G01R31/52

  Testing for short-circuits, leakage current or ground faults · CPC title

• H02J3/381

  Dispersed generators · CPC title

• H02J2300/24

  Electricity · mapped topic