JP2002125320A - Distributed power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To fully protect a load from a voltage drop by cutting off a system in a short time using a forced arc-extinguishing signal outputted from a power converter, even if disconnection causes system troubles. SOLUTION: An energy storage part 6 is provided on DC side of the power converter 5 which is connected between a system power supply 1 and a load 2 via an interconnection transformer 4. In the event of power failure of the system power supply 1, a system interconnection switch 7, interconnected between the system power supply 1 and the power converter 5 and having no self arc-extinguishing capability is turned off by the forced arc-extinguishing signal outputted from the power converter 5, and off status of the system interconnection switch 7 is detected by a control circuit 15. In this distributed power supply system which allows the power converter 5 to carry out self-driving by converting the power converter 5 from a current control mode to a voltage control mode, the control circuit 15 is provided with a zero-phase-voltage generation preventing circuit which forcibly causes the polarity of prescribed phase system current to be reversed, if wrong determination makes the polarity of the system current the identical for all the three phases in the event of power failure in the system power supply 1 caused by disconnection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed power supply system, and more particularly, to linking a distributed power supply for load leveling to a system power supply and instantaneously switching the distributed power supply to maintain power supply to a load in the event of a system failure. The present invention relates to a distributed power supply system that is separated from a power system and supplies power to a load by independent operation of the distributed power supply.

[0002]

2. Description of the Related Art For example, in a distributed power supply system in which a distributed power supply for load leveling is connected to a system power supply, a load that always requires power supply (hereinafter referred to as an important load) is instantaneously caused by a system failure such as a power failure. In order to protect against voltage drop, in the event of a system failure, the distributed power supply is instantaneously disconnected from the system, and has a power failure compensation function for supplying power to important loads by independent operation of the distributed power supply.

FIG. 4 shows an example of a main circuit configuration of a distributed power supply system having a distributed power supply 3 between a system power supply 1 and a load 2. This distributed power supply system comprises a system power supply 1 and an important load 2
And a power converter 5 connected via an interconnecting transformer 4
And has a schematic configuration in which an energy storage unit 6 is provided on the DC side. A system interconnection switch 7 is provided between the system power supply 1 and the power converter 5 to instantaneously disconnect the distributed power supply 3 from the system in the event of a system failure.

[0004] The power converter 5 is a bidirectional AC / DC converter having an inverter function and a rectifying function. The control is switched to an inverter operation in which the DC power charged to the inverter is converted to AC and supplied to the important load 2. As the energy storage unit 6, a chargeable / dischargeable secondary battery such as a lead battery is used. Further, as the system interconnection switch 7, a thyristor switch, which is a semiconductor element having no self-extinguishing ability, is used.

[0005] When the system power supply 1 is normal, an interconnection operation for executing power transfer between the system power supply 1 and the distributed power supply 3 is performed for the purpose of load leveling, and the power converter 5 is controlled by current. Operating in mode. The transmission and reception of power between the system power supply 1 and the distributed power supply 3 is performed by charging the power of the system power supply 1 to the energy storage unit 6 by the rectifying operation of the power converter 5 as described above. This is performed by outputting the electric power charged to 6 to the system by the inverter operation of the power converter 5.

As described above, in the interconnection operation of the distributed power source 3 for load leveling, for example, charging is performed from the system power source to the distributed power source during a light load at night, and from the distributed power source during a heavy load during the day. Discharge is performed to the system power source side, thereby cutting the peak value of the contract power of the power consumer who owns the distributed power source 3, reducing the basic price of the power consumed by the power consumer, and reducing the electricity price. It is possible to use midnight power.

On the other hand, when an instantaneous voltage drop occurs due to a system fault, the distributed power source 3 is disconnected from the system by shutting off the system interconnection switch 7 connected between the system power source 1 and the important load 2. The converter 5 is operated by switching from the current control mode to the voltage control mode, and shifts to the self-sustaining operation of the distributed power supply 3.

That is, the current control mode during the interconnection operation of the distributed power source 3 is a voltage source having an infinitely small impedance,
That is, it is effective when the system power supply 1 exists,
When the system interconnection switch 7 is cut off due to a system accident, the system power supply 1 is cut off and becomes inexistent. Therefore, in this current control mode, the distributed power supply 3 cannot operate independently and the power converter 5 stops. Therefore, it is necessary to switch the power converter 5 to the voltage control mode and operate the distributed power supply 3 independently.

When the system voltage drops instantaneously due to the system fault, the instantaneous voltage drop is detected to stop the current control mode, which is the control mode during the interconnection operation of the distributed power source 3, and to switch the system interconnection switch 7 To stop the ignition signal.

Here, since the system interconnection switch 7 has no self-extinguishing ability, the polarity of the current flowing through the system interconnection switch 7 which is conducting is determined, and based on the determination result, the system interconnection switch 7 is switched on. 7, the polarity opposite to the current flowing through
The power converter 5 outputs a forced arc extinguishing signal having a polarity for reducing the current flowing in the conducting system interconnection switch 7, and forcibly sets the current flowing in the system interconnection switch 7 to zero by the forced arc extinguishing signal. As a result, the system interconnection switch 7 is turned off.

After the system interconnection switch 7 is turned off, the current control mode of the power converter 5 during the interconnection operation of the distributed power source 3 is switched to the voltage control mode, and the operation of the distributed power source 3 is shifted to the independent operation. By the self-sustained operation of the distributed power supply 3, the power supply to the important load 2 by the distributed power supply 3 is continued.

[0012]

By the way, there are two types of the above-mentioned system accidents (point A in the figure), namely, a short-circuit accident due to a lightning strike or a flying object and an open accident due to a failure of a circuit breaker. When the system fault is a short-circuit fault, when the short-circuit fault occurs, a current flows through the grid connection switch 7, so that the polarity of the current flowing through the grid connection switch 7 that is conducting as described above is determined. Then, based on the determination result, a forced arc extinguishing signal having a polarity opposite to that of the current flowing through the system interconnection switch 7 is output from the power converter 5, and the current flowing through the system interconnection switch 7 is output by the forced arc extinguishing signal. By forcibly setting it to zero, the system interconnection switch 7 can be turned off.

Therefore, the distributed power source 3 can be instantaneously disconnected from the system by the forced arc extinguishing of the system interconnection switch 7,
By switching the power converter 5 from the current control mode to the voltage control mode, it is possible to quickly shift to the independent operation of the distributed power supply 3.

However, when the system fault is an open fault, since the current flowing through the system connection switch 7 is zero, it is difficult to determine the polarity of the current flowing through the system connection switch 7. For example, in a three-phase three-wire AC power system, a current polarity pattern that does not normally occur, that is, a zero-phase pattern in which all three phases (u-phase, v-phase, and w-phase) have the same polarity occurs as an erroneous determination result. It is possible.

In this case, the power converter 5 outputs a zero-phase forced extinguishing signal based on the result of the erroneous determination of the zero-phase pattern. Here, since the interconnection transformer 4 provided on the output side of the power converter 5 cannot output the zero-phase voltage to the system side, forcibly extinguish the zero-phase output from the power converter 5. The generation of the difference voltage between both ends of the system interconnection switch 7 due to the signal cannot be confirmed.

As a result, the OFF of the system interconnection switch 7 cannot be confirmed instantaneously, the voltage drop due to the opening accident is prolonged, and it becomes difficult to protect the important load 2 from a power failure.

Therefore, the present invention has been proposed in view of the above-mentioned problems, and an object of the present invention is to provide a forced arc-extinguishing signal output from a power converter even when a system fault is an open fault. OFF the system interconnection switch in a short time
Another object of the present invention is to provide a distributed power supply system capable of reliably protecting an important load from an instantaneous voltage drop.

[0018]

As a technical means for achieving the above object, the present invention provides a power converter connected between a system power supply and a load via an interconnection transformer on the DC side. A distributed power supply is provided, and in the event of a power failure of the system power supply, a system interconnection switch interposed between the system power supply and the power converter and having no self-extinguishing capability is forcibly extinguished by the power converter. It is turned off by the signal, and the O
FF is detected by a control circuit, and based on an output command from the control circuit, the power converter is switched from a current control mode to a voltage control mode to operate independently,
In a distributed power supply system for supplying a load by converting the DC voltage of the distributed power supply with a power converter and supplying the load to the load, the control circuit includes: A zero-phase voltage generation prevention circuit for forcibly inverting the polarity of an arbitrary one-phase system current is provided (claim 1).

In the distributed power supply system according to the present invention, when a power failure of the system power supply is caused by an open accident, even if the current flowing through the system connection switch becomes zero, a differential voltage is generated at both ends of the system connection switch. Becomes easier.

In other words, even if the current flowing through the grid connection switch becomes zero due to the opening accident and a zero-phase pattern in which the polarity of the system current is the same for all three phases occurs as an erroneous determination result, the zero-phase voltage generation of the control circuit occurs. By inverting the polarity of any one-phase system current by the prevention circuit, a forced arc extinguishing signal having a predetermined voltage value can be generated. As a result,
The system interconnection switch can be instantaneously turned off by a forced arc extinguishing signal output from the power converter via the interconnection transformer.

According to a first aspect of the present invention, the control circuit further comprises a polarity determination circuit for determining the polarity of the system current by a zero cross comparison circuit at a stage preceding the zero-phase voltage generation prevention circuit. 2).

When a power failure occurs in the system power supply due to an open accident, even if a zero-phase pattern in which the polarity of the system current is the same for all three phases is generated as an erroneous determination result by the zero-cross comparison circuit of the polarity determination circuit, the zero-cross A forced arc extinguishing signal having a predetermined voltage value can be generated by inverting the polarity of an arbitrary one-phase system current by a zero-phase voltage generation prevention circuit provided at a subsequent stage of the comparison circuit.

According to a second aspect of the present invention, the polarity determination circuit of the control circuit has an automatic offset correction circuit that adjusts a zero point of the amplifier circuit when determining the polarity of the system current when the system current is small. (Claim 3).

By adjusting the zero point of the amplifier circuit by this automatic offset correction circuit, even if the system current is minute, the polarity of the system current can be three-phase after the accuracy of the polarity judgment of the system current is improved in advance. Only when the same zero-phase pattern is generated as an erroneous determination result, the polarity of an arbitrary one-phase system current can be inverted.

The control circuit according to the present invention is based on the difference voltage between the system voltages detected by two instrument transformers provided on both the system power supply side and the power converter side of the system interconnection switch. When a power failure occurs in a system power supply due to an opening accident, an OFF of a system interconnection switch is detected (claim 4).

When the power failure of the system power supply is caused by an open accident, if the system interconnection switch is in the OFF state by the forced arc extinguishing signal of the system interconnection switch output from the power converter, the power of the system interconnection switch is turned off. A voltage is generated on the power converter side by the forced arc extinguishing signal, and no voltage is generated on the system power supply side due to an open accident. Therefore, if the voltage difference between both ends of the system interconnection switch is detected, the OFF of the system switch can be confirmed, and based on this, the current control mode of the power converter is switched to the voltage control mode and the operation shifts to the self-sustaining operation. Can be done.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the distributed power supply system according to the present invention will be described in detail below. The same parts as those in FIG. 4 are denoted by the same reference numerals.

The distributed power supply system of the embodiment shown in FIG. 1 has a main circuit configuration in which a distributed power supply 11 is provided between a system power supply 1 and an important load 2. This distributed power system
An energy storage unit 6 is provided on the DC side of the power converter 5 connected between the system power supply 1 and the important load 2 via the interconnection transformer 4.
Is provided. A system interconnection switch 7 is provided between the system power supply 1 and the power converter 5 to instantaneously disconnect the distributed power supply 11 from the system in the event of a system failure. Further, detection signals Vs from the current transformer 12 provided on the system bus and the two instrument transformers 13 and 14 provided at both ends of the system interconnection switch 7, that is, on the system power supply side and the power converter side. ₁ and a control circuit 15 for controlling the operation of the power converter 5 based on Vs ₂ .

The power converter 5 is a bidirectional AC / DC converter having an inverter function and a rectifying function. The power converter 5 performs a rectification operation of converting the electric power from the system power supply 1 into a direct current and charging the energy storage unit 6. The control is switched to an inverter operation in which the DC power charged to the inverter is converted to AC and supplied to the important load 2. As the energy storage unit 6, a chargeable / dischargeable secondary battery such as a lead battery is used. Further, as the system interconnection switch 7, a thyristor switch, which is a semiconductor element having no self-extinguishing ability, is used.

When the system power supply 1 is normal, the control circuit 15
The grid connection switch 7 is in the ON state by the ignition signal Pa from the system, and the interconnection operation for executing power transfer between the system power supply 1 and the distributed power supply 11 is performed for the purpose of load leveling, The power converter 5 is operated in the current control mode based on the output command ref from the control circuit 15. The transfer of power between the system power supply 1 and the distributed power supply 11 is performed by the rectification operation of the power converter 5 as described above.
Is stored in the energy storage unit 6, and the power stored in the energy storage unit 6 is output to the system by the inverter operation of the power converter 5.

As described above, in the interconnection operation of the distributed power supply 11 for the purpose of load leveling, for example, charging is performed from the system power supply to the distributed power supply during a light load at night and from the distributed power supply during a heavy load during the day. Discharge is performed to the system power supply side, thereby cutting the peak value of the contract power of the power customer who owns the distributed power source 11, reducing the basic price of power consumed by the power customer, and lowering the power price. It is possible to use midnight power.

On the other hand, when the system voltage drops instantaneously due to a system fault (point A in the figure), the instantaneous voltage drop is detected by a voltage drop detection circuit (not shown) provided in the control circuit 15 and the distributed power The current control mode which is the control mode at the time of the interconnection operation 11 is stopped, and the firing signal Pa of the system interconnection switch 7 is stopped.

When the system fault is a short-circuit fault, when the short-circuit fault occurs, a current flows through the grid-connecting switch 7.
s is detected by the current transformer 12, and the polarity of the current Is is determined by the polarity determination circuit 16 of the control circuit 15 (see FIG. 2). 1 shows a single-phase circuit, while FIG. 2 shows a three-phase circuit (u-phase, v-phase, and w-phase).

As shown in FIG. 2, the polarity judging circuit 16 comprises an amplifying circuit 17, an automatic offset correcting circuit 18 and a zero cross comparing circuit 19, and the currents Is-u, v detected by the current transformer 12. , W are amplified by the amplifier circuit 17, and the polarity of the current is determined by the zero-cross comparison circuit 19 based on the output of the amplifier circuit 17. Here, the polarity determination accuracy can be improved by adjusting the zero point of the amplifier circuit 17 even when the system current is very small by the automatic offset correction circuit 18.

Based on the judgment results Cu, v, w output from the polarity judgment circuit 16, the system interconnection switch 7
Arc extinguishing signals Pbu, v, w having polarities opposite to the current flowing through
Is superimposed on the control command signal ref-u, v, w and sent to the power converter 5 as an output command ref (-u ', v', w ').

As described above, the current flowing through the system interconnection switch 7 is forcibly reduced to zero by the forced arc extinguishing signal Pbu-v, v, w output from the power converter 5, whereby the system interconnection switch 7 Is turned off. In the case of this short circuit accident, the forced arc extinguishing signal Pb output from the polarity determination circuit 16
-u, v, w are output as they are from a zero-phase voltage generation prevention circuit 20, which will be described later.

Accordingly, the system is cut off by forcibly extinguishing the system interconnection switch 7, whereby the distributed power source 11 is instantaneously disconnected from the system, and the power converter 5 is switched from the current control mode to the voltage control mode to switch the distributed power source 11 Shifts to independent operation. By the independent operation of the distributed power supply 11, the power supply to the important load 2 by the distributed power supply 11 is continued.

On the other hand, when the system fault is an open fault, the current flowing through the grid connection switch 7 is zero.
The polarity of the current flowing in the system interconnection switch 7 may be erroneously determined. That is, in the polarity determination circuit 16 of the control circuit 15, when the current detected from the current transformer 12 is zero, the determination result C−
For example, a current polarity pattern that does not normally occur, that is, a zero-phase pattern in which all three phases (U-phase, V-phase, and W-phase) have the same polarity may occur as u, v, and w.

In this case, the zero-phase forced extinguishing signal Pbu-u,
If v and w are output as they are, the interconnection transformer 4 cannot output the zero-phase voltage to the system side, so the zero-phase forced arc extinguishing signal Pbu, u output from the power converter 5 is output.
The difference voltage between both ends of the system interconnection switch 7 cannot be confirmed by v and w.
The FF cannot be confirmed.

Therefore, in the zero-phase voltage generation prevention circuit 20 provided at the subsequent stage of the polarity determination circuit 16, the zero-phase pattern in which the polarity of the system current is the same for all three phases is obtained from the polarity determination circuit 16 as an erroneous determination result. When the signal is output, the polarity of the arbitrary one-phase system current is inverted to generate a forced arc extinguishing signal Pbu-v, v, w having a predetermined voltage value.

This zero-phase voltage generation preventing circuit 20 is similar to that shown in FIG.
As shown in (a), the first and second AND circuits 21,
22 and first and second OR circuits 23 and 24, and based on a truth table as shown in FIG. 3B, (Cu, Cv, Cw) = (0,0,
(Pb-u, Pb-v, Pb-w) = even when the zero-phase pattern of (0) or (1, 1, 1) is input.
An output in which the polarity of an arbitrary one-phase system current is inverted, such as (0, 0, 1) or (0, 1, 1), is obtained.

The forced arc extinguishing signal P of the system interconnection switch 7
bu, v, w are superimposed on the control command signal ref-u, v, w, and the output command ref (-u ',
v ', w'). In the event of an open accident, the forced arc-extinguishing signal Pb-
Voltages due to u, v, and w are generated, and no voltage is generated on the system power supply side due to an open accident. Therefore, by detecting the voltage difference between both ends of the system interconnection switch 7 by the two instrument transformers 13 and 14 provided at both ends of the system interconnection switch 7, the OFF state of the system interconnection switch 7 is confirmed. Based on this, it is possible to reliably switch the current control mode of the power converter 5 to the voltage control mode and quickly shift to the self-sustaining operation.

[0043]

According to the present invention, when the power failure of the system power supply is caused by an open accident, even if the current flowing through the system interconnection switch becomes zero, the polarity of the current flowing through the system interconnection switch can be determined. It will be easier. In other words, even if the current flowing through the grid connection switch becomes zero due to an open accident and a zero-phase pattern in which the polarity of the system current is the same for all three phases occurs as a misjudgment result, the zero-phase voltage generation prevention circuit of the control circuit , By inverting the polarity of any one-phase system current,
A forced arc-extinguishing signal having a predetermined voltage value can be generated. As a result, the OF of the system interconnection switch is turned on by the forced arc-extinguishing signal output from the power converter via the interconnection transformer.
F can be confirmed instantaneously. In this way, even if the system accident is an open accident, the system can be shut down in a short time by the forced arc extinguishing signal output from the power converter, and the load can be reliably protected from voltage drop and reliability can be improved. , A distributed power supply system with a high power supply can be provided.

[Brief description of the drawings]

FIG. 1 is a main circuit configuration diagram showing an embodiment of a distributed power supply system according to the present invention.

FIG. 2 is a block diagram showing a polarity determination circuit and a zero-phase voltage generation prevention circuit in the control circuit of FIG. 1;

FIG. 3A is a block diagram illustrating an example of a logic circuit constituting a zero-phase voltage generation prevention circuit, and FIG. 3B is a truth table of the example of the logic circuit of FIG.

FIG. 4 is a main circuit configuration diagram showing a conventional example of a distributed power supply system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 System power supply 2 Load 4 Interconnection transformer 5 Power converter 6 Energy storage unit 7 System interconnection switch 11 Distributed power supply 15 Control circuit 16 Polarity judgment circuit 18 Automatic offset correction circuit 19 Zero cross comparison circuit 20 Zero phase voltage generation prevention circuit

Claims (4)

[Claims] 1. An energy storage unit is provided on the DC side of a power converter connected between a system power supply and a load via an interconnection transformer, so that a power supply between the system power supply and the power converter is provided during a power outage of the system power supply. Is turned off by the forced arc-extinguishing signal output from the power converter, and the control circuit detects that the system interconnection switch is OFF, The power converter is switched from the current control mode to the voltage control mode based on an output command from the control circuit and is operated independently to convert the DC voltage of the energy storage unit into a power and supply it to the load. In a distributed power supply system, the control circuit forcibly reverses the polarity of an arbitrary one-phase system current when all three phases have the same polarity at the time of a system power failure due to an open accident. Distributed power system characterized by comprising a zero-phase voltage prevention circuit cell. 2. The dispersion control method according to claim 1, wherein the control circuit includes a polarity determination circuit for determining the polarity of the system current by a zero cross comparison circuit at a stage preceding the zero-phase voltage generation prevention circuit. Power system. 3. The control circuit according to claim 2, wherein the polarity determination circuit includes an automatic offset correction circuit that adjusts a zero point of the amplifier circuit when determining the polarity of the system current when the system current is very small. A distributed power supply system according to claim 1. 4. The system according to claim 1, wherein the control circuit is configured to open an accident based on a difference voltage between system voltages detected by two instrument transformers provided on both a system power supply side and a power converter side of the system interconnection switch. 4. The system according to claim 1, wherein when a power failure of the system power supply occurs, an OFF of the system interconnection switch is detected.
A distributed power supply system according to any one of the above.