JP3403928B2 - Power storage system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-grounded DC power storage device, an AC power supply in which one wire is grounded, and a non-insulated bidirectional connected between the DC power storage device and the AC power supply. The present invention relates to a power storage system capable of safely disconnecting a DC power storage device in a power storage system including a power converter even when the DC power storage device has a ground fault.

[0002]

2. Description of the Related Art FIG. 5 is a ground fault of a direct current power storage device in a direct current power storage system including a commercial alternating current power supply with one wire grounded, a direct current power storage device and an insulating bidirectional power converter. It is a conventional example of a state where a failure has occurred and a method of detecting the failure. Here, 1 is a commercial AC power supply, 20 is an insulation type bidirectional power converter, 3a and 3b are connection points between the bidirectional power converter and a DC power storage device, 4 is a DC power storage device,
5 is a ground fault resistance when a part of the DC power storage device has a ground fault, 6a and 6b are ground fault detection resistors, and 7a and 7b
Is a switch for detecting resistance, 8 is a circuit breaker, and 9 is an insulating transformer. The bidirectional power conversion device 20 functions as a rectifying device for the commercial AC power supply 1 when the DC power storage device 4 is charged, and as a connection inverter to the commercial AC power supply 1 when the DC power storage device 4 is discharged. Take action. When a ground fault occurs in a part of the DC power storage device 4, a ground fault resistance 5 is generated between the ground fault location and the ground. When the value of this ground fault resistance 5 is detected and becomes less than the reference value, the circuit breaker 8
Take measures such as operating. As a method of detecting the value of the ground fault resistance 5, since the DC power storage device 4 is insulated from the ground by the insulation transformer 9, the resistance 6 for ground fault detection is used.
The voltage detection method by a and 6b is possible. The voltage across the ground fault detection resistor 6a is measured with the detection resistance changeover switch 7a turned on and the detection resistance changeover switch 7b turned off, and conversely the detection resistance changeover switch 7a is turned off and the detection resistance changeover switch is turned off. The voltage across the resistor 6b for ground fault detection is measured with 7b turned on. The value of the ground fault resistance 5 can be calculated from these voltage values, the resistance values of the ground fault detection resistors 6a and 6b, and the voltage across the DC power storage device 4. When the value of the ground fault resistance 5 becomes equal to or less than the reference value, the circuit breaker 8 is operated.

[0003]

The conventional method can be applied only when the DC power storage device and the ground are insulated from each other by the insulating transformer, and when the DC power storage device and the ground are not insulated from each other. There was a problem that it could not be applied.

The present invention has been made in view of the above circumstances, and it is easy to detect a ground fault in a DC power storage device in a non-insulated power storage system, and to safely disconnect the power storage device during a ground fault. The purpose is to provide a storage system.

[0005]

In order to achieve the above object, the power storage system of the present invention comprises a non-insulated bidirectional power converter connected between a commercial AC power supply and a DC power storage device. In the power storage system, detecting means for detecting an AC component of the unbalanced current in the charging / discharging current of the DC power storage device as a detection value, and DC power storage when the detection value detected by the detection means exceeds a reference value. It is characterized by comprising a separating means for separating the device.

Further, the power storage system of the present invention includes a non-grounded DC power storage device, a commercial AC power supply whose one line is grounded, and a non-connected DC power storage device and the commercial AC power supply. In a power storage system including an insulating bidirectional power conversion device, a current sensor for detecting an unbalanced current of a charging / discharging current of the bidirectional power conversion device charging / discharging the DC power storage device, and the current sensor. A band-pass filter that passes the AC power supply frequency component of the unbalanced current detected by the above, and the output value of the band-pass filter exceeds the value obtained by dividing the voltage across the DC power storage device by the allowable ground fault resistance value. And a means for disconnecting the DC power storage device according to the output signal of the comparator.

The power storage system of the present invention is also characterized in that the output value of the band-pass filter is a value obtained by dividing the voltage across the DC power storage device by twice the ground fault resistance value. Since the present invention takes the above-mentioned means,
It is possible to detect the ground fault of the DC power storage device in the non-insulated power storage system.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention. Here, 1 is a commercial alternating-current power supply consisting of u-phase, v-phase, and w-phase with one wire grounded, and 2 is a non-insulated bidirectional power conversion device that does not use an insulating transformer for charging and discharging the direct-current power storage device. 3a and 3b are connection points between the bidirectional power converter and the DC power storage device, 4 is a non-grounded DC power storage device, and 5 is a ground fault when a part of the DC power storage device has a ground fault. A resistor, 8 is a circuit breaker, 10 is a high-frequency switch which is turned on to the H side or the L side corresponding to each phase, 11 is a current sensor for detecting an unbalanced current of charging / discharging current of the bidirectional power converter, and 12 is A divider, 13 is a band pass filter for passing the AC power source frequency component of the unbalanced current detected by the current sensor, 14 is a comparator, 15
1, 152, 153, 154 are capacitors, 161, 1
Reference numerals 62 and 163 represent inductors. The bidirectional power conversion device 2 uses the commercial AC power supply 1 when charging the DC power storage device 4.
The high-frequency switching operation is performed as a rectifier of the above, and as an interconnection inverter to the commercial AC power supply 1 when discharging from the DC power storage device 4. When the DC power storage device 4 has a ground fault, a ground fault current flows through the ground fault resistor 5, and the current passes through the connection point 3a or 3b and flows into the w-phase ground point of the commercial AC power supply 1. The currents in 3a and 3b are unbalanced. Therefore, the ground fault can be detected by detecting the unbalanced current, that is, the ground fault current. The ground fault current has an AC component and a DC component. However, since the DC component depends on the voltage difference between the ground fault location and the ground, it is necessary to detect only the AC component. The reason will be described below. The ground fault current is determined by the voltage difference between the ground fault location and the ground and the resistance value of the ground fault resistor 5. Since the voltage waveform between the ground fault and the ground differs depending on the control method of the high frequency switch 10, an example will be described here. As shown in FIG. 2, each phase voltage is compared with a reference triangular wave, and the high frequency switch 10 corresponding to each phase is turned on to the H side or the L side due to the voltage relationship. FIG. 3 shows voltage waveforms with respect to the ground of the connection points 3a and 3b in this case. Although it fluctuates at a high frequency due to switching, the average value becomes a sine wave having a commercial AC cycle with an amplitude of V / 2 as shown by the broken line. From this, the DC component of the ground fault current, which is a value obtained by dividing the voltage difference between the ground fault location and the ground by the resistance value of the ground fault resistor 5, depends on the ground fault location, but the AC component does not depend on the ground fault location. I understand. As described above, in order to detect the ground fault, first, only the AC component of the ground fault current is detected by the current sensor 11. Since the switching frequency component of the AC component detected by the current sensor 11 is easily affected by noise such as lightning surge, the bandpass filter 13 is used to extract only the commercial AC frequency component. As shown in FIG. 4, the output of the band pass filter 13 has a waveform whose amplitude is a value obtained by dividing the voltage V across the DC power storage device 4 by twice the value Rg of the ground fault resistor 5. The output of the band pass filter 13 is compared with a reference value in a comparator 14 as a detected value. When the detected value exceeds the reference value, a signal is output from the comparator 14, the operation of the circuit breaker 8 is taken, and the DC power storage device 4 is disconnected.
Assuming that the value of the ground fault resistance 5 determined to be the ground fault failure is Rs, the reference value input to the comparator 14 is the ground fault resistance value Rs that allows the voltage V across the DC power storage device 4 in the divider 12 to be allowed. Use the value divided by. That is, according to the present embodiment example, it is possible to detect the ground fault of the DC power storage device 4 in the non-insulated power storage system, which is impossible in the conventional example.

[0009]

As described above, according to the present invention, it is possible to detect the ground fault of the DC power storage device in the non-insulated power storage system. Therefore, by removing the insulating transformer as compared with the insulated power storage system, it is possible to secure the safety of the non-insulated power storage system that can be downsized, improved in efficiency, and reduced in cost. Examples of the DC power storage device include a storage battery, a capacitor, and Na.
An S battery or the like can be considered.

[Brief description of drawings]

FIG. 1 is a circuit configuration explanatory diagram showing an embodiment of the present invention.

FIG. 2 is a signal waveform explanatory diagram showing a method of controlling a high frequency switch according to an embodiment of the present invention.

FIG. 3 is a waveform diagram showing a voltage fluctuation waveform with respect to the ground at the connection point between the bidirectional power conversion device and the DC power storage device according to the embodiment of the present invention.

FIG. 4 is a waveform diagram showing an output waveform of the bandpass filter according to the embodiment of the present invention.

FIG. 5 is a circuit configuration diagram showing a conventional power storage system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Commercial AC power supply, 2 ... Non-isolated bidirectional power converter, 3a, 3b ... Connection point of bidirectional power converter and DC power storage device, 4 ... Ungrounded DC power storage device, 5 ... DC Ground fault resistance when part of the power storage device has a ground fault, 8 ... Circuit breaker, 10 ... High frequency switch for turning on to H side or L side corresponding to each phase, 11 ... Current sensor, 12 ... divider, 13 ... bandpass filter, 14 ...
Comparator.

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Claims (3)

(57) [Claims] 1. A power storage system comprising a non-insulated bidirectional power conversion device connected between a commercial AC power supply and a DC power storage device, wherein an unbalanced current among charge / discharge currents of the DC power storage device. An electric power storage system comprising: a detection unit that detects the AC component as a detection value; and a disconnection unit that disconnects the DC power storage device when the detection value detected by the detection unit exceeds a reference value. 2. A non-grounded DC power storage device, a commercial AC power supply in which one line is grounded, and a non-insulated bidirectional power conversion connected between the DC power storage device and the commercial AC power supply. In a power storage system including a device, a current sensor that detects an unbalanced current of a charging / discharging current of a bidirectional power conversion device that charges / discharges the DC power storage device, and an unbalanced current detected by the current sensor. A band pass filter that passes the frequency component of the AC power source, and a signal that outputs a signal when the output value of the band pass filter exceeds the value obtained by dividing the voltage across the DC power storage device by the allowable ground fault resistance value And a means for disconnecting the DC power storage device according to an output signal of the comparator. 3. The power storage system according to claim 2, wherein the output value of the band-pass filter is a value obtained by dividing the voltage across the DC power storage device by twice the ground fault resistance value.