JP2022038061A - Uninterruptible power supply system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost electric power system which performs a compensation operation at a high speed when an abnormality of an electric power system is performed.
SOLUTION: There are 100 non-disruptive power supply systems of a continuous commercial power supply system that supply power to a load from a distributed power supply in the event of an abnormality in the power system, and when a voltage abnormality in the power system 10 is detected, the distributed power supply 2 is used. It includes a mechanical switch 3 that starts supplying electric power to the load 30 and opens the power system, and a capacitor 41 connected in parallel to the mechanical switch. The capacitance C of the capacitor satisfies the following equation (1). C × (V / T)> i _SW (1), V is the rated voltage of the power system, T is the time from the start of opening of the mechanical switch to the stabilization of the amount of change in the voltage across the mechanical switch. The transient time, _iSW , is the breaking current that flows through the mechanical switch when the mechanical switch is opened.
[Selection diagram] Fig. 1

Description

The present invention relates to an uninterruptible power supply system of a constant commercial power supply system.

As shown in Patent Document 1, the uninterruptible power supply system of the continuous commercial power supply system includes a circuit breaker that cuts off the power supply from the power system to the load, and a distributed power supply such as a storage battery connected to the load side of the circuit breaker. It is equipped with.

In this uninterruptible power supply system, when the power system is normal, the power system supplies power to the load via a circuit breaker and the distributed power supply is operated in a grid-connected manner. On the other hand, when the power system is abnormal, the circuit breaker is opened to cut off the power supply from the power system to the load, and at the same time, the operation mode of the distributed power source is switched from current control to voltage control for independent operation. As a result, even when an abnormality occurs in the power system, power can be reliably supplied to the load without a power failure.

Japanese Patent No. 3402886

However, since the above-mentioned uninterruptible power supply system uses a semiconductor switch such as an IGBT as a circuit breaker, high-speed open / close switching operation is possible, but the energization loss due to the on-resistance of the element is not small. Further, in a high voltage environment such as high voltage or extra high voltage, it is necessary to connect a plurality of expensive semiconductor switches in series, which increases the cost and complicates the control circuit.

Therefore, the present invention has been made to solve the above-mentioned problems, and its main object is to provide a power system capable of performing compensation operation at high speed in the event of an abnormality in the power system at low cost.

That is, the non-disruptive power supply system according to the present invention supplies power to the load from the power system when the power system is normal, cuts off the power supply from the power system to the load when the power system is abnormal, and from the power system to the load. It is a constant commercial power supply system that supplies power to the load from a distributed power supply connected to a power line for supplying power to the load. The power line is provided on the power system side of the distributed power supply and the power line is provided. A mechanical switch that opens and closes, a capacitor connected in parallel to the mechanical switch in the power line, a system-side voltage detection unit that detects the voltage on the power system side of the mechanical switch, and the system-side voltage detection unit. A system abnormality detection unit that detects a voltage abnormality in the power system from the detected voltage of the above and a control unit that controls power supply by the distributed power supply are provided, and when a voltage abnormality is detected by the system abnormality detection unit, the voltage abnormality is detected. The mechanical switch is opened and the supply of power from the distributed power supply to the load is started, and the capacitor is characterized in that its capacitance C satisfies the following equation (1). And.
C × (V / T)> i _SW (1)
Here, V is the rated voltage of the power system, T is the transient time that is the time from the start of opening of the mechanical switch to the stabilization of the amount of change in the voltage across the mechanical switch, and _iSW is. This is the breaking current that flows through the mechanical switch when the mechanical switch is opened.

In such an uninterruptible power supply system, when an abnormality in the power system is detected, the mechanical switch is opened and the power supply from the distributed power supply to the load is started, so compensation is provided even in the event of a system abnormality. Power can be supplied to the target load. Here, since the impedance of the capacitor connected in parallel to the mechanical switch is set to be smaller than the arc resistance of the mechanical switch, when the mechanical switch is opened, it is commutated to the capacitor without causing an arc. And can be limited. Therefore, when an abnormality in the power system is detected, the mechanical switch can be shut off at high speed regardless of the zero point, and even in a high voltage environment such as high voltage or extra high voltage, it can be used instead of an expensive semiconductor switch. , An inexpensive mechanical switch can be used as a circuit breaker. As a result, it is possible to provide an uninterruptible power supply system that performs compensation operation at high speed in the event of an abnormality in the power system at low cost.

The non-power failure power supply system further includes a disconnection switch provided on the power system side of the distributed power supply in the power line, and the control unit starts supplying power from the distributed power supply to the load. After that, it is preferable that the disconnection switch is opened to disconnect the distributed power source and the load from the power system.

According to the present invention configured as described above, it is possible to provide a power system capable of performing compensation operation at high speed in the event of an abnormality in the power system at low cost.

It is a schematic diagram which shows the structure of the uninterruptible power supply system of this embodiment. The graph which shows an example of the operation waveform at the time of a current cutoff when there is no commutation circuit. It is a schematic diagram which shows the structure of the uninterruptible power supply system of another embodiment.

Hereinafter, the uninterruptible power supply system 100 according to the embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the uninterruptible power supply system 100 of the present embodiment is a constant commercial power supply system provided between the power system 10 and the load 30. The non-disruptive power supply system 100 supplies power to the load 30 from the power system 10 when the power system 10 is normal, and cuts off the power supply from the power system 10 to the load 30 when a voltage abnormality occurs due to a short circuit accident of the power system 10. Power is supplied from the distributed power supply 2 to the load 30.

Specifically, the non-disruptive power supply system 100 includes a distributed power supply 2, an open / close switch 3 for connecting the power system 10, the distributed power supply 2, and a load 30, a commutation circuit 4 connected in parallel to the open / close switch 3. The disconnection switch 6 provided on the power system 10 side of the on-off switch 3, the system side voltage detection unit 7 for detecting the voltage on the power system 10 side of the on-off switch 3, and the detection voltage of the system side voltage detection unit 7. A system abnormality detecting unit 8 for detecting a voltage abnormality in the power system 10 and a control unit 9 for controlling power supply by the distributed power supply 2 are provided.

The distributed power source 2 is connected to a power line L1 for supplying power from the power system 10 to the load 30. The distributed power source 2 is connected to the power system 10, for example, a DC power generation facility 21 such as solar power generation or a fuel cell, a power storage device (storage device) 22 such as a secondary battery (storage battery), and the like. Power generation equipment (not shown) that is connected to the grid using a power converter after rectifying the electrical energy output from AC such as wind power generation and micro gas turbine to DC, or synchronous power generator or induced power generation. It is an AC power generation facility 23 such as a machine. The DC power generation facility 21 and the power storage device (storage device) 22 include a power conversion device (not shown). The uninterruptible power supply system 100 may include at least a power storage device 22, and may also have any of the above-mentioned distributed power supplies 2.

The open / close switch 3 is provided on the power line L1 on the power system 10 side of the connection point of the distributed power source 2 to open / close the power line L1. Specifically, the open / close switch 3 is also referred to as a mechanical switch (hereinafter, also referred to as a mechanical switch 3). ). The mechanical switch 3 is configured to be driven to open / close in a predetermined opening time according to a signal transmitted from the control unit 9.

The commutation circuit 4 is configured so that a current flows (commutation) when the mechanical switch 3 is opened, and the current is limited. Specifically, the commutation circuit 4 includes a capacitor 41 and a resistance element 42 that are connected in parallel to the mechanical switch 3 and connected in series with each other. Specifically, the capacitor 41 is, for example, a film capacitor or the like.

When the mechanical switch 3 is opened, the capacitor 41 instantly commutates the current flowing through the mechanical switch 3 to the commutation circuit 4 without causing an arc, and causes the mechanical switch 3 to operate at high speed regardless of the zero point. The capacitance C is defined so that it can be cut off.

Here, FIG. 2 shows an example of the operation waveform when the uninterruptible power supply system 100 does not include the commutation circuit 4 and the mechanical switch 3 is opened to generate an arc. In the non-disruptive power supply system 100 of the present embodiment, in order to transfer a current to the commutation circuit 4 without generating an arc when the mechanical switch 3 is opened, the resistance of the commutation circuit 4 is the arc resistance shown in FIG. It is necessary to determine the resistance 42 so as to be smaller than the minimum value of R _ark (when the breaking current _isw is maximum).

More specifically, the capacitor 41 of the present embodiment will be described by setting the rated voltage of the power system 10 to V and changing the voltage across the mechanical switch 3 after the opening (or opening) of the mechanical switch 3 is started. The capacitor 41 is configured so as to satisfy the following equation (1), where T is the time until the amount stabilizes (also referred to as transient time) and _iSW is the breaking current (maximum) flowing when the mechanical switch 3 is opened. ing. Further, considering the error of each parameter, it is preferable to configure the capacitor 41 so as to satisfy the equation (1)'with a margin.
C × (V / T)> i _SW (1)
C × (V / T)> 1.3 × i _SW (1)'

The meaning of the above equation (1) will be described. Assuming that the current flowing through the capacitor 41 is _{ic and the potential difference applied to the} capacitor 41 is dv / dt, the current _ic can be expressed by the following equation (2).
i _c = C × (dv / dt) (2)
When the mechanical switch 3 is closed, most of the current flows through the switch having low impedance, so that _ic ≈ 0, that is, the potential difference dv / dt ≈ 0 applied to the capacitor 41. .. At the moment when the mechanical switch 3 is opened, the current _ic flowing through the capacitor 41 increases due to the voltage change between the terminals of the mechanical switch 3. At this time, assuming that the commutation to the commutation circuit 4 can be completed without causing an arc, it can be said that the voltage between the terminals of the switch rises to the rated voltage of the circuit at the moment when the mechanical switch 3 is opened. Therefore, in this case, the dv / dt of the equation (2) becomes the “rated voltage V / the transient time T of the switch”, and the current _ic flowing through the capacitor 41 becomes the equation (3).
i _c = C × (V / T) (3)

From the equation (3), it can be seen that a larger C (proportional to the length of the transient time T) is required to maintain the current _ic flowing through the capacitor 41 even when the transient time T is longer. In equation (3), this is the relationship between "the current i _c flowing through the capacitor 41 on the left side calculated by calculating without changing the value of the transient time T on the right side" and the breaking current i _SW of the mechanical switch 3. In the following, it is as follows. In order to transfer the breaking current to the commutation circuit 4 without generating an arc when the mechanical switch 3 is opened, the current i _c flowing through the capacitor 41 and the breaking current i _SW of the mechanical switch 3 are as follows. It is necessary to satisfy the equation (4) of.
i _c > i _SW (4)
By applying the above equation (2) to the equation (4), the above equation (1) is derived.

The disconnection switch 6 is provided on the power system 10 side of the distributed power source 2 (here, rather than the mechanical switch 3) in the power line L1, and is, for example, a mechanical switch. The disengagement switch 6 is controlled to open and close by the control unit 9.

The system side voltage detection unit 7 constantly detects the voltage on the power system 10 side of the mechanical switch 3 on the power line L1 via the instrument transformer. Specifically, the system side voltage detection unit 7 is connected to the power system 10 side of the parallel circuit including the mechanical switch 3 and the commutation circuit 4 via an instrument transformer. The system side voltage detection unit 7 inputs the detected voltage to the system abnormality detection unit 8.

The system abnormality detection unit 8 compares the detection voltage detected by the system side voltage detection unit 7 with a predetermined set value, and detects an instantaneous voltage drop when the detected voltage is equal to or less than the set value. do. Further, the system abnormality detection unit 8 detects frequency fluctuations (frequency increase (OF), frequency decrease (UF)) from the detection voltage detected by the system side voltage detection unit 7. It should be noted that this frequency fluctuation is, for example, a step rise or a ramp rise / fall. In addition, the system abnormality detection unit 8 may detect at least one of voltage rise, phase fluctuation, voltage imbalance, harmonic abnormality or flicker in addition to instantaneous voltage drop, frequency fluctuation and power failure.

The control unit 9 controls the operation / stop, opening / closing, and the like of each device included in the uninterruptible power supply system 100. The control unit 9 is configured to take a plurality of control modes (1) normal mode and (2) abnormal mode according to the signal from the system abnormality detection unit 8. Each control mode will be described below.

(1) Normal mode When a system abnormality is not detected by the system abnormality detection unit 8 (that is, when the power system 10 is normal), the control unit 9 closes the mechanical switch 3 and the disconnection switch 6. In this case, the power system 10 supplies AC power to the load 30 via the mechanical switch 3. Although the commutation circuit 4 is connected in parallel to the mechanical switch 3, the impedance of the mechanical switch 3 is smaller than the impedance of the commutation circuit 4, so that the power system 10 and the load 30 are on the mechanical switch 3 side. Exchange power. In this normal mode, the distributed power source 2 only charges the power storage device 22, and does not supply power to the load 30.

(2) Abnormality mode When a system abnormality such as an instantaneous voltage drop is detected by the system abnormality detection unit 8, the control unit 9 opens the mechanical switch 3 and supplies power from the distributed power source 2 to the load 30. To start. At this time, the power system 10 and the distributed power source 2 are connected to each other via the commutation circuit 4, but the current flowing from the power system 10 to the distributed power source 2 is limited by the capacitor 41 of the commutation circuit 4. Therefore, almost no tidal current is generated. In this state, the control unit 9 opens the disconnection switch 6 and completely shuts off the power system 10 and the load 30.

<Effect of this embodiment>
According to the uninterruptible power supply system 100 of the present embodiment configured in this way, when an abnormality in the power system 10 is detected, the mechanical switch 3 is opened and the power from the distributed power supply 2 to the load 30 is transferred. Since the supply is started, power can be supplied to the compensation target load 30 even when a system abnormality occurs. Here, since the capacitor 41 connected in parallel to the mechanical switch 3 makes the impedance of the commutation circuit 4 smaller than the arc resistance of the mechanical switch 3, the arc is generated when the mechanical switch 3 is opened. The current can be commutated and limited in the commutation circuit 4 without causing it. Therefore, when an abnormality in the power system 10 is detected, the mechanical switch 3 can be shut off at high speed regardless of the zero point, making it an expensive semiconductor switch even in a high voltage environment such as high voltage or extra high voltage. Alternatively, an inexpensive mechanical switch 3 can be used as a circuit breaker. As a result, it is possible to provide an uninterruptible power supply system 100 that performs compensation operation at high speed in the event of an abnormality in the power system 10 at low cost.

<Other modified embodiments>
The present invention is not limited to the above embodiment.

For example, the commutation circuit 4 may not include both the capacitor 41 and the resistance element 42 connected in series, and may include only the capacitor 41.

As shown in FIG. 3, the uninterruptible power supply system 100 of another embodiment may include a self-discharge circuit 5 connected in parallel to the mechanical switch 3 and the commutation circuit 4. In this way, after the current limiting is cut off by the mechanical switch 3 and the commutation circuit 4, the electric charge remaining in the capacitor 41 of the commutation circuit 4 can be discharged by the self-discharge circuit 5. Examples of the self-discharge circuit 5 include a resistance element 51 and an open / close switch 52 which are connected in parallel to the mechanical switch 3 and the commutation circuit 4 and connected in series to each other. In this case, the open / close switch 52 included in the self-discharge circuit 5 is turned on only when the mechanical switch 3 is open. The self-discharge circuit 5 does not have to include the open / close switch 52, but in that case, the resistance value of the self-discharge circuit 5 is configured to be at least larger than the energization resistance of the mechanical switch 3.

The disconnection switch 6 is provided on the power system 10 side of the mechanical switch 3 on the power line L1, but is not limited to this, and may be provided on the distributed power source 2 side of the mechanical switch 3 as well. It may be provided in both.

In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

100 ・ ・ ・ Power supply system 10 ・ ・ ・ Power system 30 ・ ・ ・ Load L1 ・ ・ ・ Power line 2 ・ ・ ・ Distributed power supply 3 ・ ・ ・ Mechanical switch 41 ・ ・ ・ Capacitor 7 ・ ・ ・ System side voltage detector 8 ・ ・ ・ System abnormality detection unit 9 ・ ・ ・ Control unit

Claims (2)

When the power system is normal, the power system supplies power to the load, and when the power system is abnormal, the power supply from the power system to the load is cut off, and the power system is connected to a power line for supplying power to the load. It is a continuous commercial power supply type non-disruptive power supply system that supplies power to the load from a distributed power supply.
A mechanical switch provided on the power system side of the distributed power source on the power line to open and close the power line,
A capacitor connected in parallel to the mechanical switch in the power line,
A system-side voltage detector that detects the voltage on the power system side of the mechanical switch, and
A system abnormality detection unit that detects a voltage abnormality in the power system from the detection voltage of the system side voltage detection unit,
A control unit that controls power supply by the distributed power source is provided.
When a voltage abnormality is detected by the system abnormality detection unit, the mechanical switch is opened and the power supply from the distributed power source to the load is started.
The capacitor is an uninterruptible power supply system in which the capacitance C satisfies the following equation (1).
C × (V / T)> i _SW (1)
Here, V is the rated voltage of the power system, T is the transient time that is the time from the start of opening of the mechanical switch to the stabilization of the amount of change in the voltage across the mechanical switch, and _iSW is. This is the breaking current that flows through the mechanical switch when the mechanical switch is opened. The power line is further provided with a disconnection switch provided on the power system side of the distributed power source.
The uninterruptible power supply according to claim 1, wherein the control unit opens the disconnection switch after starting the supply of electric power from the distributed power source to the load, and disconnects the distributed power source and the load from the power system. Power system.

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