JP2007060832A - Distributed power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provided a distributed power supply system for quickly and reliably switching an operation to a power converter when a power system is interrupted. <P>SOLUTION: The distributed power supply system comprises a semiconductor switch 2 connected between the power system 1 and a load 3, the power converter 5 connected to the load 3 in parallel and converting DC from a storage apparatus 4 into AC, a system voltage detector 7, voltage difference detecting means 8A, 8B for detecting voltage differences between a primary voltage and a secondary voltage in the semiconductor switch, a current detecting means 9 for detecting a current flowing in the semiconductor switch, and a control means 6 for controlling operations of the semiconductor switch and the power converter. The control means 6 has a means for providing an off-instruction to the semiconductor switch when an output voltage from the system voltage detector 7 is determined as an interruption level, and an open determining means 64 for determining an open of the semiconductor switch 2 based on outputs from the voltage difference detecting means 8A, 8B and the current detecting means 9, and activates the operation of the power converter 5 based on an output from the open determining means 64. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a distributed power supply system configured to perform interconnection operation with a power system.

  Conventional distributed power supply systems usually have a configuration in which power is supplied from a power system to a load via a system interconnection switch using a semiconductor element, and a power converter is connected in parallel with the load. .

  If the power system is normal, the grid connection switch is closed, power is supplied from the power system to the load, and at the same time, the power system is a power storage device such as a secondary battery connected to the DC section of the power converter. To charge.

  When a voltage fluctuation or the like occurs in the power system and the voltage drops or a power failure occurs, the system interconnection switch is instructed to open. At this time, in order to continue power supply to the load, the power converter is operated as an inverter to supply power from the power storage device such as a secondary battery to the load.

In many cases, a semiconductor element having no self-extinguishing capability such as a thyristor is used for the grid connection switch. This is because the overload resistance can be increased as compared with a semiconductor element having a self-extinguishing capability. In order to open a semiconductor device that does not have such a self-extinguishing capability, it is necessary to wait half a cycle in terms of the frequency of the power system after the command to open is issued to the grid interconnection switch and the gate pulse is lost. There is. For this reason, in order to open the grid connection switch faster, a proposal has been made to control the power converter so that the current flowing through the grid connection switch is reduced at the same time that an open command is given to the grid connection switch. (For example, refer to Patent Document 1).
JP-A-11-341686 (5th page, FIG. 1)

  According to the method disclosed in Patent Document 1, since the power converter is controlled so that the current flowing through the grid interconnection switch is reduced, it is possible to reduce the delay time for opening the grid interconnection switch. It becomes. However, in the distributed power supply system disclosed in Patent Document 1, it is not detected that the grid interconnection switch has been reliably opened when power supply from the power converter to the load is started.

  In order to operate the load stably, when a power failure or voltage fluctuation occurs in the power system, it is necessary to quickly start feeding from the power converter. However, if power supply from the power converter is started without detecting that the grid connection switch has been reliably opened, there may be a problem such as an abnormal current flowing from the power converter to the power system.

  The present invention has been made to solve the above-described problems, and provides a distributed power supply system capable of switching operation to the power converter side quickly and reliably in the event of a power failure. It is aimed.

  To achieve the above object, a distributed power supply system according to the present invention includes a semiconductor switch having one end connected to a power supply system and the other end connected to a load, and connected in parallel to the load and connected to the power system. A power converter that performs charging, a chargeable / dischargeable power storage device connected to the DC side of the power converter, a system voltage detector that detects the voltage of the power system, and a primary voltage of the semiconductor switch 2 A differential voltage detection means for detecting a differential voltage of the secondary side voltage; a current detection means for detecting a current flowing through the semiconductor switch; and a control means for controlling the operation of the semiconductor switch and the power converter, The control means includes means for giving an off command to the semiconductor switch when the output voltage of the system voltage detector is determined to be a power failure level, and outputs of the differential voltage detection means and the current detection means. The semiconductor switch has an open determining means for determining that it is now opened, is characterized in that so as to start operation of the power converter by an output of said opening determining means.

  According to the present invention, the current flowing through the grid connection switch and the potential difference between the primary side and the secondary side of the grid connection switch are detected, and it is determined by this detection signal that the grid connection switch has been opened. Since it did in this way, the distributed power supply system which can perform operation switching to the power converter side quickly and reliably at the time of a power failure of an electric power system can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram showing a distributed power supply system according to the present invention. The power system 1 supplies power to the load 3 via the grid connection switch 2. In parallel with the load 3, an AC output of a power converter 5 that converts DC of the power storage device 4, which is a DC power supply, into AC is connected. The grid interconnection switch 2 is a semiconductor switch that does not have a self-extinguishing capability, and operates according to an on / off command from the control unit 6. An operation command for the power converter 5 is also given from the control unit 6.

  The voltage of the power system 1 is detected by a voltage detector 7, and this output is given to the control unit 6. The input voltage of the grid connection switch 2 is detected by the voltage detector 8A, the output voltage of the grid connection switch 2 is detected by the voltage detector 8B, and the output is given to the control unit 6. Further, the output current of the grid connection switch 2 is detected by a current detector 9, and the output is also given to the control unit 6. The current detector 9 may be provided on the input side of the grid connection switch 2.

  Hereinafter, an internal configuration of the control unit 6 will be described. The control unit 6 has many functions related to the operation control of the grid connection switch 2 and the power converter 5, but FIG. 1 shows only the part related to the operation control of the present invention. Illustration of the function is omitted.

  The voltage signal detected by the voltage detector 7 is given to the power failure detection circuit 61 to detect whether or not the power supply system 1 has failed. When the power failure detection circuit 61 determines that the power supply system 1 has failed, the power failure detection circuit 61 outputs an off command to the system interconnection switch 2.

  Output signals of the voltage detector 8A, the voltage detector 8B, and the current detector 9 are given to the state detection circuit 62. The state detection circuit 62 detects whether the difference between the output signals of the voltage detector 8A and the voltage detector 8B is greater than or equal to a predetermined value and whether the output signal of the current detector 9 is less than or equal to a predetermined value. The output signal of this state detection circuit 62 is given to the OFF determination circuit 63. Then, the OFF determination circuit 63 determines whether or not the grid interconnection switch 2 is opened (off) by a method described later. Although details will be described later, the OFF determination circuit 63 may output a pilot voltage application command to the power converter 5 for this determination.

  When the OFF determination circuit 63 determines that the grid connection switch 2 is open (OFF), the AND circuit 64 takes the logical product of this determination output and the OFF command from the power failure detection circuit 61 described above. An ON command is given to the power converter 5 by the output of. As a result, the power converter 5 is released from the gate block and starts supplying power to the load 3.

  Next, details of the operation will be described with reference to FIGS. FIG. 2 is an operation flowchart of the control unit 6.

  In step ST1 of FIG. 2, when the power failure detection circuit 61 detects a power failure, the power failure detection circuit 61 outputs an off command for turning off the grid interconnection switch 2 (ST2). In this state, the state detection circuit 62 detects whether the current Is detected by the current detector 9 is equal to or less than a predetermined current value Ith. If the current Is is not equal to or smaller than the predetermined current value Ith, this detection operation is repeated until the current Is is equal to or smaller than the predetermined current value Ith (ST3). As a result, when the current Is becomes equal to or lower than the predetermined current value Ith, an operation for detecting whether the difference voltage ΔV between the output signals of the voltage detector 8A and the voltage detector 8B is equal to or higher than the predetermined voltage value Vth is performed (ST4). ). If the difference voltage ΔV is greater than or equal to the predetermined voltage value Vth in step ST4, the OFF determination circuit 63 determines that the grid connection switch 2 has been opened (off), and gives an on command to the power converter 5 (ST5). .

  In step ST4, when the difference voltage ΔV is not equal to or higher than the predetermined voltage value Vth, there may be a case where a power failure has occurred such that the power supply system 1 is open, or the applied AC voltage is near the zero cross. At this time, the OFF determination circuit 63 outputs a pilot voltage application command to the power converter 5 (ST6). This pilot voltage is set to a voltage sufficiently larger than the above-described voltage value Vth. Since the difference voltage ΔV instantaneously becomes equal to or higher than the predetermined voltage value Vth in the normal case by the operation of step ST6, the determination result in step ST4 of the OFF determination circuit 63 is YES, so that the power converter 5 is turned on in step ST5. The power supply from the power converter 5 to the load 3 can be started by giving a command.

  In the above, the predetermined current value Ith is a very small current that is much larger than the leakage current of the semiconductor element that does not have the self-extinguishing capability that constitutes the grid connection switch 2, and the predetermined voltage value Vth It is preferable that the voltage be much smaller than the ON voltage of the semiconductor element that does not have the self-extinguishing capability.

  FIG. 3 shows an example of a voltage and current detection circuit for each phase of the grid interconnection switch 2. As shown in FIG. 3, each phase of the grid connection switch 2 includes grid connection switches 2U, 2V, and 2W. Since the voltage detectors 8A and 8B are mainly intended to obtain the voltage difference ΔV, the voltage detectors 8UV, 8VW and 8WV capable of obtaining the line voltage difference of each phase as shown in FIG. These outputs may be given to the control unit 6.

  Further, the current detector 9 is provided for each phase if there are three phases, but it is also possible to use only two phases of the current detectors 9V and 9W as shown in FIG.

  In the configuration of the voltage / current detection circuit shown in FIG. 3, whether the current Is in step ST3 shown in FIG. 2 is equal to or smaller than a predetermined current value Ith is determined by two phases, V phase and W phase. When both the currents of the two phases are equal to or less than the predetermined current value Ith, the determination in step ST-3 is YES. Similarly, whether or not the difference voltage ΔV in step ST-4 is equal to or higher than the predetermined voltage value Vth is determined as YES in step ST-4 when the difference voltages of all three phases are equal to or higher than the predetermined voltage value Vth.

The block block diagram which shows the distributed power supply system which concerns on this invention. The operation | movement flowchart of the distributed power supply system control part which concerns on this invention. The circuit block diagram which shows an example of the voltage of each phase of a grid connection switch, and a current detection circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power system 2, 2U, 2V, 2W System connection switch 3 Load 4 Power storage device 5 Power converter 6 Control part 61 Power failure detection circuit 62 State detection circuit 63 OFF determination circuit 64 AND circuit 7 Voltage detector 8A, 8B, 8UV , 8VW, 8WU Voltage detector 9, 9V, 9W Current detector

Claims (4)

A semiconductor switch having one end connected to the power supply system and the other end connected to a load;
A power converter connected in parallel with the load and performing interconnection operation with the power system;
A chargeable / dischargeable power storage device connected to the DC side of the power converter;
A system voltage detector for detecting the voltage of the power system;
Differential voltage detection means for detecting a differential voltage between a primary side voltage and a secondary side voltage of the semiconductor switch;
Current detection means for detecting a current flowing through the semiconductor switch;
Control means for controlling the operation of the semiconductor switch and the power converter,
The control means includes
Means for giving an off command to the semiconductor switch when the output voltage of the system voltage detector is determined to be a power failure level;
An open determination means for determining that the semiconductor switch is opened by outputs of the differential voltage detection means and the current detection means;
The distributed power supply system, wherein operation of the power converter is started by an output of the open determination means. The open determination means includes
The current detected by the current detection means is below a predetermined value,
And when the differential voltage detected by the differential voltage detection means is a predetermined value or more,
2. The distributed power supply system according to claim 1, wherein it is determined that the semiconductor switch is opened. The open determination means includes
The current detected by the current detection means is below a predetermined value,
And when the differential voltage detected by the differential voltage detection means is less than a predetermined value,
The distributed power supply system according to claim 2, wherein a pilot voltage application command is given to the power converter so that the power converter is operated at a predetermined voltage. The current detection means detects a current of at least two phases;
The differential voltage detection means detects the differential voltages of all three phases,
The open determination means includes
The currents of the at least two phases are both below a predetermined value;
When the differential voltage of each of the three phases is greater than or equal to a predetermined value,
4. The distributed power supply system according to claim 2, wherein it is determined that the semiconductor switch is opened.

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