Ground fault detectors for power facilities, power facilities, energy storage facilities, and charging / discharging equipment.
The integrated ground fault detector for power equipment uses a resistance grounding circuit and detection unit to detect both DC and AC faults, reducing complexity and cost by combining detection methods, while ensuring high accuracy and early fault detection.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- GS YUASA CORP
- Filing Date
- 2024-12-27
- Publication Date
- 2026-07-09
AI Technical Summary
Existing power equipment requires separate DC and AC ground fault detectors, leading to increased complexity and cost due to the need for multiple detectors or circuits.
A ground fault detector that integrates a resistance grounding circuit and a detection unit to detect both DC and AC ground faults using the P-phase and N-phase voltages of the DC power supply, allowing for the detection of AC ground faults with a DC ground fault detector.
Reduces the number of ground fault detectors and circuits, simplifies detection, and achieves cost savings while maintaining high accuracy and early detection of AC ground faults.
Smart Images
Figure 2026115147000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a ground fault detector for power equipment.
Background Art
[0002] From the perspective of energy conservation, the introduction of power equipment such as energy storage systems and distributed power systems is being promoted. One of the protection devices for power equipment is a ground fault detector. One of the documents disclosing techniques related to ground fault detectors is Patent Document 1.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In power equipment, ground fault accidents include DC ground faults and AC ground faults. If a DC ground fault detector and an AC ground fault detector are provided separately, there is a problem that the number of ground fault detectors or circuits increases or becomes complicated, resulting in cost increase.
[0005] The present invention aims to reduce the number of ground fault detectors or circuits.
Means for Solving the Problems
[0006] The ground fault detector for power equipment includes a resistance grounding circuit that grounds the P-phase power line and the N-phase power line connecting the DC power supply and the power converter to the neutral point via a resistor, and a detection unit that detects a ground fault based on at least one of the P-phase voltage and the N-phase voltage of the DC power supply. When a periodically fluctuating voltage component is superimposed on at least one of the P-phase voltage or the N-phase voltage of the DC power supply, the detection unit determines an abnormality or an AC ground fault.
Effects of the Invention
[0007] This technology can reduce the number of ground fault detectors or circuits required. [Brief explanation of the drawing]
[0008] [Figure 1] Circuit diagram of power equipment [Figure 2] Schematic diagram of a resistance-grounded circuit [Figure 3] Diagram showing the normal size of V1 and V2. [Figure 4] Diagram showing the magnitudes of V1 and V2 during a DC ground fault. [Figure 5] Schematic diagram of a resistance-grounded circuit [Figure 6] Voltage waveforms superimposed on the P-phase and N-phase during an AC ground fault. [Figure 7] Diagram showing detection timeouts T1 and T2. [Figure 8] Block diagram of the energy storage system [Figure 9] Block diagram of the charging and discharging equipment [Modes for carrying out the invention]
[0009] This section provides an overview of ground fault detectors. (1) A ground fault detector for a power facility according to one embodiment of the present invention includes a resistance grounding circuit that grounds the P-phase power line and the N-phase power line connecting the DC power supply and the power converter to the neutral point via a resistor, and a detection unit that detects a ground fault based on at least one of the P-phase voltage and the N-phase voltage of the DC power supply. The detection unit determines that there is an abnormality or an AC ground fault if a periodically fluctuating voltage component is superimposed on at least one of the P-phase voltage or the N-phase voltage of the DC power supply. In the ground fault detector described in (1), any configuration other than the above is arbitrary and may be used. Superposition means that one signal or voltage is superimposed on another signal or voltage.
[0010] According to the configuration in (1), AC ground faults can be detected using a DC ground fault detector, eliminating the need to install two ground fault detectors, one for DC and one for AC. This reduces the number of ground fault detectors or circuits, resulting in cost savings. Furthermore, it simplifies detection and avoids circuit complexity.
[0011] (2) A ground fault detector as described in (1), wherein the detection unit may determine the periodicity of the superimposed voltage component by determining whether the voltage component superimposed on at least one of the P-phase voltage and N-phase voltage of the DC power supply repeatedly moves up and down a threshold. According to (2), the periodicity of the voltage superimposed on the P-phase and N-phase can be determined by program processing.
[0012] (3) A ground fault detector according to (1) or (2), wherein the detection unit may use a voltage component superimposed on at least one of the P-phase voltage and N-phase voltage of the DC power supply as a signal with twice the amplitude based on the voltage difference between the P-phase voltage and the N-phase voltage of the DC power supply. According to (3), a periodically fluctuating voltage component can be used as a signal with twice the amplitude based on the voltage difference between the P-phase and N-phase. Therefore, the magnitude relative to the threshold can be accurately determined, and the accuracy of AC ground fault detection is high.
[0013] (4) The ground fault detector described in (3), wherein the detection unit may compare the signal of the full-wave rectified waveform of the voltage difference between the P phase and N phase of the DC power supply with a threshold and determine the periodicity of the superimposed voltage component. According to (4), the number of times the threshold is switched between large and small is greater than that of an unrectified normal waveform (twice as many times per period). Therefore, AC ground faults can be detected in a short time (about half the time).
[0014] <Embodiment 1> 1. Explanation of Power Equipment 10 As shown in Figure 1, the power equipment 10 includes a DC power supply 20, a power converter 30, and a ground fault detector 50. The DC power supply 20 is connected to the power converter 30 via a P-phase (+) power line 60P and an N-phase (-) power line 60N.
[0015] The power converter 30 is, for example, a semiconductor power converter, and includes a power unit 31 such as an inverter and relays 32 and 33. The power unit 31 is connected to the DC power supply 20 via the relay 32, and is connected to the AC system 100 via the relay 33. In the following description, for the power converter 30, the connection terminal to the DC power supply 20 is taken as the input side, and the connection terminal to the AC system 100 is taken as the output side.
[0016] The ground fault detector 50 is located on the input side of the semiconductor power converter 30, and includes a resistance grounding circuit 51 and a detection unit 53.
[0017] As shown in FIG. 2, the resistance grounding circuit 51 includes a first resistor R1 that grounds the power line 60P of the P phase of the DC power supply 20 and a second resistor R2 that grounds the power line 60N of the N phase. In this embodiment, the first resistor R1 and the second resistor R2 have the same resistance value (R1 = R2). The first resistor R1 and the second resistor R2 may be composed of a plurality of resistors R. E is the neutral point.
[0018] The detection unit 53 is, for example, a microcomputer, and takes in the levels of the first voltage V1 and the second voltage V2 after reducing them by a voltage dividing circuit. As shown in FIG. 1, the detection unit 53 includes a first detection unit 53A and a second detection unit 53B. In this embodiment, the first detection unit 53A and the second detection unit 53B are shown separately due to the difference in functions, but the first detection unit 53A and the second detection unit 53B may be the same circuit or the same device, or may be different circuits or different devices.
[0019] The first detection unit 53A detects a DC ground fault based on V1 and V2. The second detection unit 53B detects an AC ground fault based on V1 and V2. The detection unit 53 can detect DC ground faults and AC ground faults in parallel by the first detection unit 53A and the second detection unit 53B.
[0020] As shown in FIG. 2, V1 is the voltage between P and E (the voltage of the P phase with respect to the neutral point E), and V2 is the voltage between N and E (the voltage of the N phase with respect to the neutral point E).
[0021] The P-phase and N-phase power lines 60P and 60N are grounded to the neutral point E by resistors R1 and R2, and the two resistors R1 and R2 have the same resistance value (R1=R2). Therefore, under normal conditions, V1 and V2 have different polarities and are half the magnitude of the line voltage V0 between P and N. That is, V1=V0 / 2 and V2=-V0 / 2.
[0022] 2. Ground fault detection operation In Figure 1, R3 is the DC ground fault resistance, and R4 is the AC ground fault resistance. When a DC ground fault occurs, a ground fault current I1 flows to the neutral point E through the path of the DC ground fault resistance R3. When an AC ground fault occurs, a ground fault current I2 flows to the neutral point E through the path of the AC ground fault resistance R4. (1) DC ground fault Figure 3 shows the magnitudes (absolute values) of V1 and V2 under normal conditions, and Figure 4 shows the magnitudes (absolute values) of V1 and V2 during a DC ground fault. Under normal conditions, V1 and V2 are balanced and their magnitudes (absolute values) are the same. During a DC ground fault, V1 and V2 change from their normal state and become unbalanced. Therefore, a DC ground fault can be detected from the voltage change of V1 or V2.
[0023] In this embodiment, the difference ΔV between the magnitudes (absolute values) of V1 and V2 is detected, and if the difference ΔV exceeds a threshold for a predetermined period of time, it is determined to be a DC ground fault.
[0024] (2)AC ground fault As shown in Figure 5, when an AC ground fault occurs, periodically fluctuating voltage components S1 and S2 are superimposed on the P-phase and N-phase power lines 60P and 60N. Therefore, an AC ground fault can be detected by detecting the periodically fluctuating voltage components S1 and S2 from the first voltage V1 or the second voltage V2. Superposition means that one signal or voltage is superimposed on another signal or voltage. In this example, it means that the periodically fluctuating voltage component S1 is superimposed on the first voltage V1 (DC voltage), or that the periodically fluctuating voltage component S2 is superimposed on the second voltage V2 (DC voltage).
[0025] As shown in Figure 6, the voltage component S1 superimposed on the P phase and the voltage component S2 superimposed on the N phase have waveforms with inverted polarity (out of phase). Therefore, by taking the voltage difference V1-V2 between the first voltage V1 and the second voltage V2, a signal S3 is obtained in which the amplitudes of voltage components S1 and S2 are doubled.
[0026] In this embodiment, as shown in Figure 6, a signal S3 with double the amplitude is full-wave rectified and compared with a threshold. If the full-wave rectified signal S4 repeatedly fluctuates above and below the threshold, it is determined to be an AC ground fault. The threshold should be set near the peak values of signals S3 and S4. In this way, DC ground faults and AC ground faults can be distinguished using the same circuit.
[0027] 3. Detection time limit AC ground faults have the potential to spread to interconnected power systems, so early detection is desirable. Therefore, a difference can be set between the first time period T1 for detecting DC ground faults and the second time period T2 for detecting AC ground faults, and as shown in Figure 7, the second time period T2 may be shorter than the first time period T1.
[0028] The first period T1 can be adjusted according to the DC ground fault detection condition (a set value for the time during which the difference ΔV continuously exceeds the threshold), and the second period T2 can be adjusted according to the AC ground fault detection condition (a set value for the number of times the signal S4 moves up or down the threshold).
[0029] By creating a difference between the time delays T1 and T2 for detecting ground faults, it is expected that AC ground faults can be detected early, thereby suppressing fault propagation. For DC ground faults, careful judgment is possible, which is expected to reduce misjudgments.
[0030] 4. Examples of applications of this technology The power equipment 10 may also be an energy storage system or other energy storage equipment 10A. Figure 8 is a block diagram of the energy storage equipment 10A. The energy storage equipment 10A includes an energy storage device 110, a power unit 120 such as an inverter, and a ground fault detector 50. The energy storage equipment 10A is connected to the AC grid 140 and adjusts the supply and demand of power. The energy storage device 110 is an example of a DC power source, and the power unit 120 is an example of a power converter.
[0031] The power equipment 10 may also be an EV charging and discharging equipment 10B such as a V2X system. Figure 9 is a block diagram of the charging and discharging equipment 10B. The charging and discharging equipment 10B includes a vehicle battery 150, a charger / discharger 160, and a ground fault detector 50. The charging and discharging equipment 10B is a system that is connected to an AC grid 180 and charges and discharges the vehicle battery 150. The vehicle battery 150 is an example of a DC power source, and the charger / discharger 160 is an example of a power converter.
[0032] 5. Explanation of Effects (1) The ground fault detector 50 is installed on the input side (DC power supply side) of the power converter 30 and is therefore for detecting DC ground faults. Since the ground fault detector 50 for detecting DC ground faults can also detect AC ground faults, there is no need to install two ground fault detectors, one for detecting DC ground faults and one for detecting AC ground faults. Therefore, it is possible to reduce the number of ground fault detectors or circuits, resulting in cost advantages. In addition, it is possible to avoid increasing the complexity of the circuit.
[0033] (2) This configuration determines the periodicity of the voltage components S1 and S2 superimposed on the P-phase and N-phase of the DC power supply 20 by determining whether the voltage components S1 and S2 superimposed on the P-phase and N-phase repeatedly move up and down a threshold. In this way, the periodicity of the voltage components S1 and S2 superimposed on the P-phase and N-phase can be determined by program processing, making it possible to simplify the hardware circuit.
[0034] (3) The periodically fluctuating voltage components S1 and S2 can be converted into signals with twice the amplitude using the voltage difference V1-V2 between the P-phase and N-phase. Therefore, the magnitude of the signals relative to the threshold can be accurately determined, resulting in high accuracy in detecting AC ground faults. In particular, in this example, when V1 and V2 are input to the detection unit 53, the voltage level is reduced by a voltage divider circuit. Therefore, the voltage change of the signals superimposed on V1 and V2 is small, which is effective because it can be difficult to determine the magnitude of the signals relative to the threshold.
[0035] (4) By comparing the full-wave rectified signal S4 with the threshold, the number of times the signal switches between being greater than or less than the threshold is increased compared to the unrectified normal waveform (twice as many times per period TW). Therefore, AC ground faults can be detected in a short time (about half the time). TW is the period of the voltage components S1 and S2 superimposed on the P-phase voltage V1 and N-phase voltage V2.
[0036] <Other Embodiments> The present invention is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included in the technical scope of the present invention.
[0037] (1) In the above embodiment, an example of applying this technology to the energy storage equipment 10A and the charging / discharging equipment 10B was shown, but it may also be applied to other power equipment such as an uninterruptible power supply.
[0038] (2) In the above embodiment, an energy storage device 110 and a vehicle battery 150 were shown as examples of a DC power source. Any DC power source capable of DC output is acceptable, and may also be a solar power generation panel (PV).
[0039] (3) In the above embodiment, a power unit 120 and a charger / discharger 160 were shown as examples of power converters. The power converter is not limited to the configuration of the embodiment, but can be any AC / DC converter. Furthermore, it is not necessarily limited to those using semiconductor elements.
[0040] (4) In the above embodiment, a first detection unit 53A for DC ground faults and a second detection unit 53B for AC ground faults are provided. A single detection unit 53 may detect both DC ground faults and AC ground faults. In this case, if there is a voltage abnormality (for example, a voltage change) in the P phase or N phase, one may be detected first, and then the other may be detected. An AC ground fault may be detected first, followed by a DC ground fault, or a DC ground fault may be detected first, followed by an AC ground fault.
[0041] (5) In the above embodiment, a DC ground fault was determined based on the difference ΔV between the magnitudes of V1 and V2. A DC ground fault may also be determined based on changes in the magnitudes of V1 and V2, as long as it detects an imbalance in the voltages V1 and V2 associated with the ground fault.
[0042] (6) In the above embodiment, an AC ground fault was determined based on signal S4. An AC ground fault may also be determined based on signal S3, or based on V1 or V2, as long as it detects periodic voltage components S1 and S2 superimposed on the P and N phases of the DC power supply 20 in conjunction with the ground fault.
[0043] (7) In the above embodiment, a DC ground fault was determined when the difference ΔV between the first voltage V1 and the second voltage V2 exceeded a threshold for a predetermined period of time, but it may also be determined to be an abnormality. Also, in the above embodiment, an AC ground fault was determined when voltage components S1 and S2 that fluctuate periodically from the first voltage V1 or the second voltage V2 were detected, but it may also be determined to be an abnormality. [Explanation of Symbols]
[0044] 10 Power equipment 10A Energy Storage Equipment 10B Charging and discharging equipment 20 DC power supply 30 Power Converters 50 Ground fault detector 51 Resistance grounding circuit 53 Detection unit 100 AC system
Claims
1. A ground fault detector for power equipment, A resistive grounding circuit connects the P-phase power line and the N-phase power line that connect the DC power supply and the power converter to the neutral point via a resistor. The system includes a detection unit that detects a ground fault based on at least one of the voltages of the P-phase and N-phase of the DC power supply, The detection unit is a ground fault detector that determines an abnormality or AC ground fault when a periodically fluctuating voltage component is superimposed on at least one of the P-phase voltage or N-phase voltage of the DC power supply.
2. A ground fault detector according to claim 1, The detection unit is a ground fault detector that determines the periodicity of the superimposed voltage component by determining whether the voltage component superimposed on at least one of the P-phase voltage and N-phase voltage of the DC power supply repeatedly fluctuates above and below a threshold.
3. A ground fault detector according to claim 1 or claim 2, The detection unit is a ground fault detector that takes a voltage component superimposed on at least one of the voltages of the P-phase and N-phase of the DC power supply and converts it into a signal with twice the amplitude based on the voltage difference between the P-phase and N-phase of the DC power supply.
4. A ground fault detector according to claim 3, The detection unit is a ground fault detector that compares the signal of the full-wave rectified waveform of the voltage difference between the P phase and N phase of the DC power supply with a threshold value and determines the periodicity of the superimposed voltage components.
5. DC power supply and Power converter and A power installation comprising a ground fault detector according to any one of claims 1 to 4.
6. The energy storage equipment according to claim 5.
7. The charging and discharging equipment according to claim 5.