JP2008104262A - Islanding pevention for apparatus distributed power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an islanding prevention which apparatus modifies a protective function for interconnection with a commercial system, in a low-voltage distribution system which has a DC power source such as a solar cell, a fuel cell, etc. <P>SOLUTION: The distributed power unit 10 has the DC power source 11, an inverter 12 which converts the DC power generated from the DC power source 11, and an interconnection breaker 13 for interconnecting with a single-phase three-line type low-voltage distribution system 3. Besides, it is connected with the single-phase three-line low-voltage distribution system. It is provided with a voltage unbalance detector 16 which detects the unbalance between the two interphase voltages of the single-phase three-line low-voltage distribution system 3 connected to the distributed power unit 10. A controller 14 stops the above inverter 12 or disconnects the decentralized power unit from the single-phase three-line type low-voltage distribution system by means of the above system breaker 13 when the voltage unbalance detector 16 detects the unbalance between the two interphase voltages of the single-phase three-line type low-voltage distribution system 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an isolated operation prevention device for a distributed power supply device having a direct current power supply unit such as a solar cell or a fuel cell, and in particular, an improvement in a protection function for system interconnection to a commercial system. is there.

  In recent years, due to increased interest in energy saving and CO2 emission reduction, new energy power generation devices such as fuel cells, gas engine cogeneration systems, and the like have been put into practical use. These distributed power supply apparatuses generally use a form in which DC power is converted to AC power by an inverter. In addition, the operation method is basically based on grid connection to the commercial system, rather than operating independently from the commercial system. Therefore, when connecting to a commercial system, some protection functions related to the system connection are necessary.

  As an important protection function, it is necessary to install an isolated operation prevention device to disconnect the distributed power supply device from the system when the distributed power supply device continues to operate in the event of a system power outage, or when it is in a so-called isolated operation state. .

  That is, in this type of grid interconnection system, DC power generated by private power generators on the customer side equipment is converted into AC power by an inverter and linked to the distribution system. The output voltage of the inverter is connected to the distribution system. The same size and the same frequency are controlled. In addition, the operating voltage point of the private power generator is controlled by the inverter so that the amount of power generated by the private power generator is always maximized.

  In this grid-connected system, when the power supply of the distribution system is stopped (cut off) due to inspection, construction, accident, etc., if the power generator and inverter are operated while connected to the distribution system, the reverse power flow caused by the so-called reverse voltage May flow into the grid in a power outage and threaten the safety of the distribution system. For this reason, it is necessary to reliably detect the isolated operation state of the customer-side equipment and disconnect (disconnect) the inverter from the distribution system.

  The islanding operation detection function has two methods, passive and active. The active power P and the reactive power Q output from the distributed power supply device in the islanding system downstream from the circuit breaker disconnected at the time of a system power failure are the load requirements. If it is in an unbalanced state with either quantity, it can be detected passively.

  However, since the active power P and the reactive power Q output from the distributed power supply device are in a balanced supply and demand state where both the active power P and the reactive power Q required by the load match, it cannot be detected passively. It is necessary to prevent isolated operation by an active system that constantly applies a slight disturbance to the system and detects fluctuations such as voltage and frequency that become noticeable due to the disturbance after the transition to isolated operation.

  When distributed power sources such as solar and fuel cells are widely used as residential (household) cogeneration systems, they may be densely installed in a relatively small area, resulting in a so-called high-density interconnected state. There is. In such a high-density interconnected state, minute fluctuations generated by the active method cancel each other, and the detection sensitivity of the isolated operation state may decrease, which is a problem.

  Various methods have been proposed as active methods, and it has been verified by actual tests that the detection sensitivity does not decrease due to mutual interference if the same method is combined. Therefore, there is a case in which a decrease occurs. Therefore, development of a new active method that does not interfere with other methods is being promoted.

  To prevent this decrease in sensitivity, a drop in line voltage at the time of a short-circuit failure of a high-voltage distribution line or the occurrence of zero-phase voltage at the time of a ground fault is detected, and a load is forcibly applied to bring the supply and demand unbalanced state. The system (see Patent Document 1) or when the frequency / harmonic content of the low-voltage distribution line fluctuates at the time of shifting to single operation, and the dedicated load resistance of the distributed power supply device is turned on, and it is stopped by detecting the undervoltage A method (see Patent Document 2) has been proposed.

JP 2005-341666 A JP 2002-291158 A

  Just for the invention of Patent Document 1 and Patent Document 2 is a passive system that constantly faint disturbance without giving to the system, the voltage at the time of islanding migration, to detect specific changes in the frequency and harmonic content There is an inconvenience that unnecessary operation occurs. Conventionally, by combining this passive method with the active method that puts resistance after detection and puts it into an unbalanced state of supply and demand, it is aimed at preventing unnecessary operation that is a problem of the passive method Yes.

  However, in the conventional method as described above, it is necessary to provide a detection device for monitoring the system voltage and frequency, an arithmetic device for performing determination of isolated operation, etc., which is disadvantageous in terms of cost and installation. There was a problem that could not be denied.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and its purpose is to provide a new detection device and arithmetic device outside without reducing the detection sensitivity. It is an object of the present invention to provide an isolated operation prevention device for a distributed power supply device that can detect an isolated operation.

  In order to achieve the above object, an isolated operation prevention device for a distributed power supply apparatus according to the present invention includes a DC power supply unit, an inverter for converting DC power generated from the DC power supply unit to AC, a single-phase three-wire low voltage A distributed power supply device having a connection circuit breaker for connecting to a distribution system and connected to a single-phase three-wire low-voltage distribution system; and a single-phase three-wire low-voltage distribution connected to the distributed power supply device A voltage imbalance detection device for detecting an imbalance between two phase voltages of the system, and the inverter when the voltage imbalance detection device detects a voltage imbalance between two phases of a single-phase three-wire low-voltage distribution system. Or a control device for disconnecting from the single-phase three-wire low-voltage distribution system of the distributed power supply device by the system breaker.

  That is, the balance between the power generation facility output and the load is a continuation condition of the single operation state, but in addition to the low probability that the condition is satisfied, it is an electric system that is supplied to a general household 100V / 200V In the case of the single-phase three-wire system, it is unlikely that the condition that the R-phase load and the T-phase load are balanced and that the state continues for the time until the reclosing of the system breaker overlaps.

  Therefore, in the present invention, focusing on this point, if a power source such as a 200 V output inverter is connected at the time of a single-phase three-wire system power failure, the R-phase load and the T-phase load are unbalanced. By utilizing the fact that the phase and T phase voltages become unbalanced, that is, one phase rises according to the load ratio and the other phase falls, the voltage unbalance detection device is made passive and active alone in the prior art. This is a substitute for the operation detection device.

  According to the present invention, the passive and active isolated operation detection devices in the prior art are not required, and it is possible to reliably prevent the isolated operation of the distributed power supply device with a simple configuration.

(1) First Embodiment Hereinafter, a first embodiment of the present invention will be described in detail with reference to the block diagram of FIG.

  In FIG. 1, the distributed power supply device 10 is electrically connected to a 100V / 200V single-phase three-wire low-voltage distribution system 3. This distributed power supply apparatus 10 includes a DC power supply section 11, a 200V single-phase two-wire inverter 12 that converts DC power generated by the DC power supply section 11 into AC power, and a connection between the distributed power supply apparatus 10 and a distribution system. Alternatively, it includes a connection breaker 13 that performs disconnection, a control device 14 that stops the inverter 12 and outputs a disconnection command for the connection breaker 13, a passive single operation detection device 15, and a voltage imbalance detection device 16. Is done.

  The voltage imbalance detection device 16 detects an overvoltage generated due to an imbalance between the R-phase load 31 and the T-phase load 32 of the customer load 30 when a host circuit breaker (system breaker not shown) is opened. By outputting this to the control device 14, a stop command for the inverter 12 or an operation command for the interconnection breaker 13 for disconnecting the distributed power supply device 10 is output from the control device 14.

  As an example of the voltage imbalance detection device 16, a grid connected to an electrical system such as a power generation facility in the “Resource grid interconnection technical requirement guideline for ensuring power quality” dated October 1, 2004, as a resource energy agency. Even if the electrical system is different, a protective device defined as a technical requirement that can be connected may be used as it is.

  On the other hand, the single-phase three-wire low-voltage distribution system 3 is stepped down from the 6600V high-voltage distribution system 1 by the pole transformer 2, and the electric system is also converted into a 100V / 200V single-phase three-wire system. It is a low-voltage distribution system configuration that is supplied to most households.

Next, the operation of the first embodiment having the above-described configuration will be described according to the operation flowchart of FIG.
The distributed power supply device 10 is operated in conjunction with the low voltage distribution system 3. When the power generation output of the distributed power supply 10 is larger than the customer load 30, the surplus that covers the customer load 30 is supplied to the high-voltage distribution line 10 via another customer load or the pole transformer 2. The Conversely, when the power generation output of the distributed power supply 10 is smaller than the consumer load 30, the difference (shortage) is supplied from the high-voltage distribution line 10 to the consumer load 30.

  In such a state, when an accident occurs in any of the high-voltage distribution lines 10 (step 301 in FIG. 3), a system breaker (not shown) is disconnected (step 302), and the distributed power supply apparatus 10 is disconnected from the system. (Step 303). In order to simplify the description, it is assumed that the power generation device in the area separated from the system is only the distributed power supply device 10 and the load is only the customer load 30.

  If the active power P and reactive power Q output from the distributed power supply apparatus 10 are unbalanced in either the active power P or reactive power Q requested by the customer load 30 (YES in step 304), the system (Step 305), the isolated operation can be detected by a voltage or frequency protection device (not shown) (step 306), and in response to this, the control device 14 stops the inverter 12 and the interconnection breaker 13 Can be taken to prevent isolated operation (step 307).

  Conversely, when the active power P and the reactive power Q output from the distributed power supply device 10 are in equilibrium with both the active power P and the reactive power Q requested by the customer load 30 (NO in step 304), Since changes in voltage, frequency, phase, etc. do not occur, the isolated operation cannot be detected by a voltage or frequency protection device and a passive isolated operation detection device (not shown).

  However, when the R-phase load 31 and the T-phase load 32 of the customer load 30 are unbalanced (YES in step 308), the 100V / 200V single-phase three-wire low-voltage distribution system is selected according to the load ratio. Since either of the voltages on both sides of the neutral line (referred to as R-phase voltage and T-phase voltage) rises and voltage imbalance occurs, the voltage imbalance detection device 16 operates (step 309).

  Then, the control device 14 receives the operation signal of the voltage imbalance detection device 16 and issues a stop command for the inverter 12 and a disconnection command for the interconnection breaker 13 so that it cannot be detected only by the passive islanding detection device 15. Even in the case of an isolated operation, an isolated operation prevention measure can be taken (step 307).

  That is, the balance between the power generation facility output and the load is a continuation condition of the single operation state, but in addition to the low probability that the condition is satisfied, it is an electric system that is supplied to a general household 100V / 200V In the case of the single-phase three-wire type, the condition that the R-phase load 31 and the T-phase load 32 are balanced and the state continues for the time until reclosing of the system breaker can hardly overlap.

  Therefore, in the present invention, focusing on this point, if a power source such as a 200 V output inverter is connected at the time of a single-phase three-wire system power failure, the R-phase load and the T-phase load are unbalanced. The voltage imbalance detector 16 is detected passively and actively by using the fact that the phase and T phase voltages are unbalanced, that is, one phase rises and the other phase falls according to the load ratio. It is a substitute for the device.

  When the installation location of the distributed power supply 10 is determined, the load situation downstream of the pole transformer 2 is measured in advance, and the case where the R-phase side load and the T-phase side load coincide with each other only occurs instantaneously. If it can be confirmed, with the configuration of the present embodiment, it is considered that there is no practical problem by preventing the continuation of the single operation state.

  As described above, the isolated operation prevention device of the present embodiment does not require an active isolated operation detection device, so that the minute fluctuations generated by the active method cancel each other and the detection sensitivity of the isolated operation state decreases. Nor. As a result, distributed power sources such as sunlight and fuel cells are densely installed in a relatively narrow area of a 100V / 200V single-phase three-wire low-voltage distribution system as a residential (household) cogeneration system. Even in a so-called high-density interconnected state, unbalanced overvoltage is generated for all distributed power supplies, so the detection sensitivity is not lowered at all.

  In addition, since the distributed power supply device adopting the 200V single-phase two-wire inverter has a device for detecting voltage imbalance, it is also necessary to add a new detection device, determination device, etc. inside and outside. Absent.

(2) Second Embodiment FIG. 2 is a system configuration diagram of an isolated operation preventing apparatus according to a second embodiment of the present invention. In the second embodiment, on the system side of the voltage imbalance detection device 16 of the first embodiment, a resistance device 20 having a switch 21 is provided between the power supply phases.

  In FIG. 2, the resistance device 20 is connected in series with the switch 21 to the neutral phase and the T-phase power phase of the 100 V / 200 V single-phase three-wire low-voltage distribution system 3. Note that the series body of the resistor and the switch is similarly connected to the neutral phase and the R phase power supply phase, but is omitted in the figure. The switch 21 is composed of a mechanical switch or a semiconductor switch.

  The operation of the second embodiment having such a configuration will be described. Similar to the description of the operation of the first embodiment, the description will be made on the assumption that the power generation apparatus of the single operation system is only the distributed power supply apparatus 10 and the load is only the consumer load 30.

  When the distributed power supply device 10 is in an independent operation state, the active power P and the reactive power Q output from the distributed power supply device 10 are in balance with the active power P and the reactive power Q required by the customer load 30. In the normal voltage or frequency protection device or the voltage imbalance detection device 16, the isolated operation state is detected, and in response to this, the control device 14 stops the inverter 12 and issues a disconnection command for the interconnection breaker 13. By taking it out, it is possible to take measures to prevent isolated operation. This is the same as in the first embodiment.

  However, in the first embodiment, when the power generation facility output and the load are balanced, the unbalance rate between the R-phase load 31 and the T-phase load 32 is small, and the R-phase voltage or the overvoltage level of the T-phase voltage is small. In some cases, the voltage / frequency protection device and the voltage imbalance device 16 may make it difficult to detect the isolated operation state.

  Therefore, in the second embodiment, even in such a case, the state of the isolated operation can be reliably detected and the isolated operation can be prevented. The operation will be described below.

  First, the control device 14 constantly monitors the R-phase voltage and the T-phase voltage of the 100V / 200V single-phase three-wire low-voltage distribution system 3 to which the distributed power supply device 10 is connected. When the voltage is lower than%, the resistance device 20 is connected in parallel to the T-phase load 32 by closing the switch 21 connected to the phase in which the voltage is reduced by a signal from the control device 14. Here, the description will be made assuming that the T-phase voltage is reduced from the illustrated relationship.

  Even if the resistance device 20 is added, if the system is normal, the R-phase voltage and the T-phase voltage do not change, but if a voltage imbalance occurs due to the shift to the single operation, the T-phase voltage decreases. The addition of the resistor acts in the direction in which the unbalance rate of the load of the R-phase load 31 and the T-phase load 32 + the resistance device 20 increases, so that the T-phase voltage further decreases.

  Conversely, the R-phase voltage rises and is detected by the voltage imbalance detection device 16, and the control device 14 issues a stop command for the inverter 12 and a disconnection command for the interconnection breaker 13, thereby taking measures to prevent the continuation of the single operation. be able to.

  Here, it has been explained that either one of the phase voltages of the single-phase three-wire system has been reduced and a resistance device connected to the phase is turned on. However, when one of the phase voltages drops, Since the voltage of the other phase rises, it is clear that the same effect is obtained even if the resistance device is turned on because one of the phase voltages has risen.

  As described above, according to the second embodiment, as in the first embodiment, the active type isolated operation detecting device is not required, so that the minute fluctuations generated by the active method cancel each other, and the isolated operation state The detection sensitivity is not lowered. As a result, distributed power sources such as sunlight and fuel cells are densely installed in a relatively narrow area of a 100V / 200V single-phase three-wire low-voltage distribution system as a residential (household) cogeneration system. Even in a so-called high-density interconnected state, unbalanced overvoltage is generated for all distributed power supplies, so the detection sensitivity is not lowered at all.

  In particular, compared with the first embodiment, two sets of resistance devices and two sets of switches are added. However, since a short time is required for turning on the resistors, a large-capacity resistance device is unnecessary. Further, in the case where the distributed power supply 10 is a fuel cell or the like having an auxiliary machine such as a heater, it is possible to confirm whether or not there is a shift to the single operation by turning on the heater for a short time.

The system block diagram of the isolated operation prevention apparatus of the 1st Embodiment of this invention. The system block diagram of the isolated operation prevention apparatus of the 2nd Embodiment of this invention. The flowchart which shows operation | movement of 1st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... High voltage distribution system 2 ... Pole transformer 3 ... Low voltage distribution system (single phase 3 wire type)
DESCRIPTION OF SYMBOLS 10 ... Distributed power supply device 11 ... DC power supply part 12 ... Inverter 13 ... Interconnection circuit breaker 14 ... Control device 15 ... Voltage imbalance detection device 20 ... Resistance device 21 ... Switch 30 ... Consumer load 31 ... R phase load 32 ... T-phase load

Claims (3)

A DC power supply unit, an inverter for converting DC power generated from the DC power supply unit into AC, and a connection breaker for connecting to a single-phase three-wire low-voltage distribution system; Distributed power supply device connected to a low-voltage distribution system,
A voltage imbalance detection device for detecting an imbalance between two phase voltages of a single-phase three-wire low-voltage distribution system connected to the distributed power supply device;
When the voltage unbalance detection device detects an unbalance between two phase voltages of a single-phase three-wire low-voltage distribution system, the inverter is stopped or the single-phase three-wire low-voltage distribution of the distributed power supply by the system breaker A control device for disconnecting from the system;
An isolated operation preventing device for a distributed power supply device, comprising: The control device includes a voltage monitoring unit that monitors a voltage between each phase of a single-phase three-wire low-voltage distribution system, and a determination unit that outputs a signal when the voltage of one phase exceeds a threshold value,
A resistance device connected between each phase of the single-phase three-wire low-voltage distribution system, and an opening / closing means for turning on the resistance device by the control device when the voltage of one phase exceeds a threshold value The isolated operation prevention device for a distributed power supply device according to claim 1.   3. The isolated operation prevention apparatus for a distributed power supply according to claim 2, wherein the opening / closing means includes a mechanical switch or a semiconductor switch.

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