WO1999009631A1

WO1999009631A1 - System interconnecting device and decentralized power supply equipped with the same and having instantaneous voltage drop preventing function

Info

Publication number: WO1999009631A1
Application number: PCT/JP1997/003758
Authority: WO
Inventors: Jun Nishidai; Masakuni Asano; Noriaki Tokuda; Masaya Kikkawa
Original assignee: Nissin Electric Co., Ltd.
Priority date: 1997-08-19
Filing date: 1997-10-17
Publication date: 1999-02-25
Also published as: CA2267304A1; JP2998711B2; JPH1169664A

Abstract

A system interconnecting device (21) is interposed between two power systems, such as a power receiving bus (22) for receiving electric power through a commercial power line (25) and a cogeneration bus (23) for receiving electric power from a private power generator (27). The device (21) is provided with thyristors (TH1 and TH2), diodes (D1 and D2), and a DC reactor (L). The thyristors (TH1 and TH2) are connected to the AC terminal (AC1), the diodes (D1 and D2) are connected to the AC terminals (AC2), the thyristor (TH1) and diode (D1) are connected to the DC terminal (DC1), and the thyristor (TH2) and the diode (D2) are connected to the DC terminal (DC2). The reactor (L) is connected between the DC terminals (DC1 and DC2). Therefore, when a fault occurs in a distribution line (26), the commercial power line (25), etc., power failure due to the overload of the power generator (27) can be prevented and instantaneous voltage drop in a distribution line (28) connected with an important load can be suppressed by the current limiting action of the reactor (L).

Description

Description Grid-connected device and distributed power supply with instantaneous voltage drop prevention function

Technical field

The present invention relates to a system interconnection device used for interconnecting two electric power systems, such as a commercial power supply system and a private power generation system, for example, a system in which measures against instantaneous voltage drop due to a short circuit or the like are taken. The present invention relates to an interconnection device, and to a distributed power supply device having an instantaneous voltage drop countermeasure function that is operated by being connected to a commercial power supply system by the interconnection device. Background art

FIG. 9 is a diagram for explaining a basic interconnection configuration between the commercial power supply system and the private power generation system as described above. The commercial power line〗 drawn into the customer is connected to the power receiving bus 2, and a number of distribution lines 3 connected to a general load are connected to the power receiving bus 2.

On the other hand, a private power generator 6 via a power supply line 9 and a distribution line 4 to an important load, which accounts for 60 to 70% of the private power generation capacity, are connected to the Koziene bus 5, for example. The power receiving bus 2 and the connection bus 5 are connected to each other by a bus connecting line 8 having a circuit breaker 7 interposed therebetween. When a fault such as a short circuit, a ground fault, or an open power receiving system occurs on the commercial power supply line 1 side, the breaker 7 is driven to be cut off by a relay (not shown).

However, in such an interconnected structure, for example, receiving bus 2 or It takes, for example, about 5 to 10 cycles (100 to 200 msec at 50 Hz) from the occurrence of the failure in the distribution line 3 until the circuit breaker 7 actually operates, There is a problem that a long-term voltage drop occurs in the important load connected to the distribution line 4. In addition, since it takes a long time for the circuit breaker 7 to operate, when the circuit breaker (not shown) of the transmission line that supplies power to the commercial power line 1 is opened, the private power generator 6 In this case, the operation is performed with the load of the customer who is a few times larger than the own capacity connected, and the private power generator 6 is overloaded and stopped, and eventually all loads are cut off State.

In order to solve the problems described above, a typical prior art system interconnection device 11 as shown in FIG. 10 has been put to practical use. In FIG. 10, the same parts as those in FIG. 9 described above are denoted by the same reference numerals, and description thereof will be omitted.

The system interconnection device 11 is composed of two thyristors 12 and 13 connected in parallel with opposite polarities. During interconnection between buses 2 and 5, the gates of these thyristors 12 and 13 are driven by the output from the relay, and the thyristors 12 and 13 are conducting. At the time of the failure, the gates of the thyristors 12 and 13 are blocked, and the thyristors 12 and 13 are shut off.

The detection of the failure in driving the thyristors 12 and 13 is performed, for example, in a half cycle, and the breaking drive can be performed at the zero cross point in the subsequent half cycle. Therefore, when the DC offset current is considered, the bus 2 and the bus 5 can be cut off within one cycle (20 msec at 50 Hz) from the occurrence of the failure. However, during this time, a complete short-circuit current flows, It is inevitable that a large voltage drop will occur in the energy bus 5.

As described above, according to the above-described system interconnection device 11, the time required for interruption between the buses 2 and 5 is shorter than that of the interconnection by the circuit breaker 7, and the in-house power generation device 6 is stopped. Can be avoided. However, an instantaneous voltage drop still occurs, which affects important loads connected to the kogine bus 5 such as a computer.

On the other hand, a conventional distributed power supply device that is connected to a system using the circuit breaker 7 is configured as shown in FIG. In FIG. 11, the portions corresponding to FIG. 9 described above are denoted by the same reference numerals. This distributed power supply device is configured to include a diesel generator or a gas generator that constitutes a cogeneration system, which is an example of a so-called new energy power supply, as a private power generator 6. It is operated in parallel with the power supply system and AC. For example, an important load that occupies 60% to 70% of the private power generation capacity is connected to the distribution line 4 connected to the Koziene bus 5 of the distributed power system.

The private power generator 6 also includes an uninterruptible power supply called a secondary battery, a fuel cell, a photovoltaic power generation system, a flywheel, a wind power generation system, and a UPS, in addition to the diesel generator and the gas generator. Many types of power supplies, such as power supplies, can be considered.

As described above, when the distributed power supply system and the commercial power supply system are operated in an interconnected manner, the circuit breaker 7 is installed in the distributed power supply system. Also, countermeasures against short-circuit current such as rear turtle may be taken as necessary according to the guidelines of the interconnection. However, if a failure such as ground fault or short circuit between phases occurs as shown in reference numeral 15 in the commercial power system, Flows, and a voltage drop occurs in the distributed power supply system.

As a countermeasure against such a failure, the voltage of the commercial power supply line 1 is detected by a voltage transformer, and based on the detection result, the possibility of voltage drop is determined by an undervoltage relay, and a voltage drop below a predetermined set value is determined. Then, the circuit breaker 7 is configured to perform a breaking drive. Also, the interconnection current is detected by a current transformer, and from the detection result, whether or not the current can be increased is determined by an overcurrent relay.When an overcurrent of a predetermined set value or more is detected, the breaker 7 is shut off. In some cases, it is configured to drive.

However, until the circuit breaker 7 opens (three types of 2, 3 or 5 cycles in the JEC 230 standard), the voltage of the distributed power supply system remains low. FIG. 12 shows a voltage drop compensation range when a vacuum circuit breaker is used as the circuit breaker 7 and a range where there is no influence due to the instantaneous voltage drop of the load. FIG. 12 shows a threshold value at which an influence is exerted for each load with respect to a voltage drop rate and a voltage drop duration, and reference numeral M 1 denotes a voltage drop compensation range by the vacuum circuit breaker. It is.

As shown in FIG. 12, most of the loads connected to the distribution line 4 are out of the compensation range, and the effect of the voltage drop occurs. In other words, the distributed power supply unit shown in Fig. 11 has a power outage countermeasure for the important load by connecting the distributed power supply to the grid, but it is expected to have no effect on the instantaneous voltage drop. Can not do it. For this reason, some of the most important loads are conventionally provided with an uninterruptible power supply (UPS) as indicated by reference numeral 16.

In this uninterruptible power supply, the electric power from the cogeneration bus 5 is AC / DC converted, rectified and smoothed by a charger, stored in a battery, and stored in the battery. DC / AC conversion of the electric power stored in the unit and output to the load. Therefore, there is a problem that a semiconductor switching element or the like is required, and it is expensive, and there is a problem that a large conversion loss always occurs. Therefore, it is used for some of the most important loads. Therefore, most loads with widely used electromagnetic switches remain vulnerable to the instantaneous voltage drop.

For this reason, in order to connect the distributed power supply device to the commercial power supply system, as shown in FIG. 13, the system interconnection device 11 shown in FIG. 10 has been used. In FIG. 13, portions corresponding to the configurations in FIGS. 10 and 11 are denoted by the same reference numerals, and description thereof is omitted. However, this interconnection device 11 also requires a total of one cycle from the detection of the voltage drop to the zero crossing that can extinguish the thyristors 12 and 13. There is also.

For this reason, the compensation range of the voltage drop in the grid interconnection device 11 using the thyristors 12 and 13 is as shown by the reference numeral M2 in FIG. Therefore, although it is possible to compensate for many operations such as OA equipment and medical electrical equipment, it is still possible to compensate for electromagnetic switches interposed in distribution lines to important loads and included in important loads. There is a problem that the effect on the variable speed mode is inevitable.

Therefore, among the loads that cannot be compensated for by the grid interconnection device 11 using the thyristors 12 and 13 (outside the range indicated by the reference sign M2 in FIG. 12), For such devices, the uninterruptible power supply 16 is required.

In addition, connecting the distributed power system to the commercial power system increases the short-circuit capacity, It will be necessary to replace each circuit breaker on the load side with one having a large breaking capacity for a short time, or replace the cable connected to the circuit breaker with one having a large current capacity. Furthermore, if it takes time to shut down the system in the event of a failure,

However, there is also a problem that the in-house power generator 6 is stopped and the distributed power system is completely stopped.

An object of the present invention is to provide a system interconnection device that can suppress instantaneous voltage drop in the event of a failure when interconnecting two electric power systems, such as a commercial power supply system and an in-house power generation system, and a power supply system for the same. An object of the present invention is to provide a distributed power supply device with a function to prevent instantaneous voltage drop. Disclosure of the invention

The system interconnection device according to the invention of claim 1 is a system interconnection device that is interposed between two electric power systems and interconnects the two systems to exchange power, and Of the two AC terminals connected between the phase connection terminals, one is connected to a pair of rectifying switching elements, and the other is connected to a pair of rectifying elements. It is characterized by including a single-phase rectifier circuit and a DC reactor connected between two DC terminals, which are connection points between the rectifying switching element and the rectifying element.

According to the above configuration, when connecting between two power systems, two rectifying switching elements realized by a thyristor and the like and two rectifying elements realized by a diode or a thyristor are used. A DC reactor is connected between the DC terminals of the single-phase rectification circuit consisting of, and the AC terminals are connected to the two power systems, respectively.

Functions that can be demonstrated with this circuit include: i. During normal operation, the impedance seen from the AC side is almost zero. ϋ. When a short circuit occurs, it should instantaneously exhibit high impedance and suppress the short circuit current.

ϋί. High-speed disconnection between both systems by rectifying switching elements.

It is.

A description will be given according to i, ii, and iii above.

i. The DC reactor, when viewed from the AC terminal, can have a substantially constant impedance of substantially zero, and exhibits a large impedance only when a failure occurs.

ϋ. Even if the failure occurs, the voltage between the terminals of the DC reactor increases due to the current preserving action of the DC reactor, and the instantaneous load to the important load on the power system to be disconnected It is also possible to suppress a drop in power supply voltage. Furthermore, the current conserving action of the DC reactor can realize a current limiting action for suppressing a fault current flowing in the faulty distribution line, and also suppress a short-circuit capacity of both power systems. it can.

iii. When a failure occurs, the rectifying switching element shuts off at a high speed, and the two power systems are disconnected, causing the power generator installed in the disconnected power system to stop due to overload. There is no such thing as a power outage can be prevented.

Further, in the grid interconnection device according to the second aspect of the present invention, the DC reactor has a reactance component and a resistance component, and a current decay time constant composed of a rectifying circuit including a rectifying switching element and a rectifying element. The system of the power system By making it more than 2.5 times the power frequency cycle, no special power supply is required to define the current value at which the DC reactor starts current limiting.

That is, FIG. 2 shows the relationship between the current decay time constant and the equivalent impedance generated between the AC terminals of the grid interconnection device. Generally, DC reactance is selected so that the fault current during a system short-circuit fault is suppressed to about three times the rated current. In other words, the interconnection device has 33% impedance based on the rated current.

On the other hand, in a normal operating state, it is preferable to minimize the equivalent impedance as much as possible.In practice, the equivalent impedance shown in FIG. 2 is 3% based on the rated current, that is, the equivalent impedance shown in FIG. Since the requirement can be satisfied with the impedance of 0.09 pu (= 3% / 33%) or less, the current decay time constant can be determined from FIG. If it is 5 times or more, there is no loss at all times, and a current limiting action can be performed when a current equal to or larger than the threshold current flows due to a system failure.

Also, the distributed power supply device with instantaneous voltage drop countermeasure function according to the invention of claim 3 includes one or more power supplies, and is connected to an important load that should avoid instantaneous voltage drop and power failure. A distributed power supply unit with an instantaneous voltage drop countermeasure function that is operated in parallel with the commercial power supply system in parallel with the AC by the system interconnection device of the above, wherein the inductance of the DC reactor is connected to the commercial power supply. When the voltage drop rate that can be tolerated in the distributed power system when a system failure occurs is A, a value larger than (1 — A) / A times the equivalent inductance corresponding to the internal impedance of the distributed power system It is characterized in that it is formed to have the following reactance. CT / JP97 / 03758

θ

According to the above configuration, the grid interconnection device according to claim 1 or 2 that is interposed between the buses of the two systems, the DC reactor presents a large impedance when a failure occurs in the commercial power supply system. Suppress voltage drop in distributed power supply system and short circuit current. Thus, while the voltage drop is suppressed, the semiconductor switching element is extinguished by the protective relay, and the distributed power supply system is cut off from the commercial power supply system.

In the distributed power supply configured as described above, when a failure occurs in the commercial power supply system, the bus voltage of the distributed power supply system becomes equivalent to the equivalent inductance of the distributed S source system and the inductance of the DC reactor. As a result, the system voltage becomes a divided value. Therefore, assuming that the inductance of the DC reactor is L dc and the equivalent inductance of the distributed power system is L s, the voltage drop rate A that can be tolerated,

L d c / L s> (l-A) / A

Choose to satisfy. That is, for example, when the voltage drop rate A is 50%, the voltage drop rate is set by setting the inductance Ldc of the DC reactor to one time the equivalent inductance Ls of the distributed power supply system. It can be suppressed within the range of A. For example, if the voltage drop rate A is 25%, the inductance L dc of the DC reactor is calculated from (1 — 0.25) Z 0. It may be set to three times the inductance Ls.

In this way, the inductance L dc of the DC reactor is set in accordance with the voltage drop rate A allowed for the distributed power supply system when a failure occurs and the equivalent inductance L s of the distributed power supply system. Even without using an uninterruptible power supply, the instantaneous voltage drop of electromagnetic switches and variable motors to critical loads can be reduced. The operation of a device which is easily affected by the above can be compensated. As a result, the reliability of the interconnection operation can be improved, and the stress on the distributed power source can be reduced. In addition, since the short-circuit current is suppressed by the current limiting action of the DC reactor, it is not necessary to replace the circuit breaker or cable on the load side with an undesirably large capacity for interconnection.

Still further, the distributed power supply device with a function of preventing instantaneous voltage drop according to the invention of claim 4 is characterized in that a power supply in the distributed power supply system is a rotating machine.

According to the above configuration, if the power source in the distributed power system is a rotating machine, the circuit voltage, that is, the output voltage of the generator, becomes zero during a short-circuit accident despite the large short-circuit current flowing. When the stress between the generator and the prime mover is released, mechanical vibrations occur in the shaft, and when the short-circuit fault is cleared, the generator may carry a load exceeding its capacity. Then, a sudden braking torque is generated in the generator, and an excessive vibration torque is generated in the shaft. As described above, when a short-circuit fault occurs, stress (such as a shear pin break in the case of a turbine generator) occurs due to transient overcurrent flowing out of the generator. By suppressing the stress, the stress can be avoided.

Further, the distributed power supply device with an instantaneous voltage drop countermeasure function according to the invention of claim 5 is characterized in that the power supply in the distributed power supply system is a stationary power supply using an inverter.

According to the above configuration, the stationary power supply has no inertia like a rotating machine, and is stopped immediately to cause a power outage, so that it can be particularly suitably implemented. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram for explaining a grid interconnection device according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the current decay time constant and the equivalent impedance for an AC power supply cycle.

FIGS. 3 (a) to 3 (c) are diagrams showing a current limiting device and an example of a configuration that can be considered when the current limiting device is used for a system interconnection device.

FIGS. 4 (a) to 4 (h) are waveform diagrams for explaining the operation of the interconnection apparatus shown in FIG.

5 (a) to 5 (h) are waveform diagrams for explaining the operation of the interconnection device shown in FIG.

FIG. 6 is a single-phase connection diagram of an electric power system for explaining a distributed power supply device according to another embodiment of the present invention configured to include the system interconnection device shown in FIG.

FIGS. 7A and 7B are simulation waveform diagrams for explaining the operation of the distributed power supply device shown in FIG.

FIGS. 8A and 8B are simulation waveform diagrams illustrating the operation of the conventional distributed power supply device shown in FIG.

Fig. 9 is a diagram for explaining the basic configuration of grid interconnection.

FIG. 10 is a diagram for explaining a typical prior art interconnection system o

FIG. 11 is a single-phase power system diagram for explaining a typical prior art distributed power supply device. FIG. 12 is a graph for explaining an example of the influence of the instantaneous voltage drop of the load device and the compensation range of each device according to the present invention and the conventional technology.

FIG. 13 is a single-phase connection diagram of a power system for explaining another conventional distributed power supply device. BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a diagram for explaining a grid interconnection device 21 according to an embodiment of the present invention. The grid interconnection device 21 is interposed in the customer via a bus connection line 24 that connects the power receiving bus 22 and the kojene bus 23. A commercial power line 25 is connected to the power receiving bus 22, and a distribution line 26 for a large number of general loads is connected to the power receiving bus 22. In addition, an in-house power generator 27 is connected to the Koziene bus 23, and a distribution line 28 to which an important load such as a computer is connected is connected.

The system interconnection device 21 includes a pair of thyristors TH2, which are rectifying switching elements, a pair of diodes D1, D2, which are rectifying elements, and a DC reactor L. Is realized. It should be noted that, in the present invention, the pair of thyristors TH 1 and TH 2 are connected to either one of a pair of AC terminals AC 1 and AC 2 connected to the bus connecting line 2. A pair of diodes D 1 and D 2 are connected to the other. (In the example of Fig. 1, thyristors TH1 and TH2 are connected to AC terminal AC1, and diodes D1 and D2 are connected to AC terminal AC2.) A DC reactor L is connected between terminals DC 1 and DC 2. In the system interconnection device 21, the current decay time constant determined by the reactance component and the resistance component of the DC reactor L, and the rectifier circuit composed of the thyristor TH2 and the diodes D1, D2. As shown in Fig. 2, there is a relation between the equivalent impedance seen from the power system side and the equivalent impedance decreases as the current decay time constant increases. On the other hand, it is desirable that the device impedance during steady operation be as small as possible. Therefore, in the present invention, from FIG. 2, the current decay time constant is selected to be at least 2.5 times the system frequency cycle of the power system.

In the grid interconnection device 21 configured as described above, the gates of the thyristors TH 1 and TH 2 are driven in a normal state, and the thyristors TH 1 and TH 2 conduct, and the reference is made. The current is flowing through the path indicated by the symbol i 1 or i 2. Therefore, the direction and amplitude of the current flowing through DC reactor L are constant, and impedance Z (= ωL) of DC reactor L becomes zero, so that no loss occurs.

On the other hand, if a fault such as a short circuit in the distribution line 26, a ground fault, or the opening of the power receiving system occurs, and an overcurrent flows from the conogene energy bus 23 to the power receiving bus 22, the DC Reactor L attempts to maintain a constant current flowing between its terminals, and as the impedance の of DC reactor L increases, the voltage between the terminals increases.

As a result, the impedance as viewed from the AC terminals AC 1 and AC 2 increases, and the current flowing from the koziene bus 23 to the power receiving bus 22 via the bus connecting line 24 is suppressed. In the meantime, the gate of thyristor TH and TH2 is blocked by a short circuit or the output of a ground fault relay, and the power bus 23 is connected to the power bus 23. From Since the power is shut off at high speed within one cycle and reliably, it is possible to prevent the private power generator 27 from being overloaded.

In this way, it is possible to prevent the private power generator 27 from stopping due to a failure on the power receiving bus 22 side, and to prevent a power failure. In addition, an increase in the voltage between the terminals of the DC reactor L can also suppress the instantaneous voltage drop of the kojene bus 23. In this way, the reliability of operation of the power grid can be improved. Further, by achieving the current limiting function, it is possible to suppress the short-circuit capacity of both the kozine bus 23 and the power receiving bus 12.

Here, an example in which a single-phase mixed bridge rectifier circuit is used for a current limiting device (JP-A-49-50448) is shown in FIG. 3 (a). The current limiting device 31 includes a mixed-bridge rectifier circuit 32 and a current-limiting reactor L2 connected in parallel with each other in series with an AC line 33.

The mixed bridge rectifier circuit 32 is connected in series to a pair of thyristors th1, th2, a pair of diodes dl, d2, a DC reactor L1, and the DC reactor L1. And a DC power source B to be connected. It should be noted that one AC terminal AC1 is connected to thyristor th1 and diode d1, while the other AC terminal AC2 is connected to thyristor th2 and diode d2. Is to be done. Therefore, the thyristors th1 and th2 are connected to the DC terminal DC1, the diodes d1 and d2 are connected to the DC terminal DC2, and the DC terminals DC1 and DC2 are connected between the DC terminals DC1 and DC2. A series circuit of the DC reactor 1 and the DC power supply B is connected.

In the current limiting device 31 configured as described above, in a steady state, the thyristors thi and th 2 are conducting, bypassing the current limiting reactor L 2 and mixing the current. Line current is flowing through the combined bridge rectifier circuit 32. On the other hand, at the time of failure, the current exceeding the current value set by the DC power supply B is suppressed by the DC reactor L1, and the current limiting effect is exhibited. Then, cut off the thyristor thl and th2. When the thyristors th1 and th2 are cut off, an undesired overvoltage is generated between the AC terminals AC2 and AC2, and the current limiting reactor L2 for suppressing the overvoltage causes the AC terminals ACI, Form a bypass circuit between AC2. Due to the existence of this current limiting end vector L2, it cannot be applied to a grid interconnection device for the purpose of disconnecting the interconnection.

In the mixed bridge rectifier circuit 32 configured as described above, the current limiting reactor 2 is intentionally deleted, and the DC power source B that determines the threshold current at which the DC reactor L1 operates is deleted. Let us suppose that it is used for a grid interconnection device as in the invention. Fig. 3 (b) shows the configuration of the grid interconnection device 41 in such a configuration. In the system interconnection device 41, the parts that are similar to and correspond to the system interconnection device 21 of the present invention are given the same reference numerals, and description thereof is omitted.

It should be noted that in this grid interconnection device 41, one AC terminal AC1 is connected to the thyristor TH1a and diode D1a, and the other AC terminal AC2 is connected to the thyristor TH1. 2a and diode D2a are connected. Therefore, a pair of thyristors TH la and TH 2a are connected to the DC terminal DC1, and a pair of diodes D 1a and D 2a are connected to the DC terminal DC 2. become. Further, a DC reactor L is interposed between the DC terminals DC1 and DC2.

That is, the grid interconnection device 21 of the present invention is a single-phase prism rectifier circuit. The connection between the thyristor and the diode is different.

Figures 4 and 5 show the simulation waveforms of each part during the disconnection operation of these grid interconnection devices 21 and 41, respectively. The simulation conditions are as follows: the% impedance on the commercial power supply side is 100, the reactance of the power supply is 1.0 Opu, the power supply frequency is 50 Hz, and the DC reactor L Is 4. O pu. As shown in Fig. 4 (a) and Fig. 5 (a), the current flowing through the thyristor TH1 and TH1a, respectively, passes through a half cycle after the AC terminal AC1 is at the high level, The arc is extinguished once the zero crossing is reached, and thereafter, the current stops flowing.

As a result, the current flowing through the diode D2 is the current corresponding to the current flowing through the thyristor TH1 indicated by reference numeral 1 in FIG. 4 (c), and the current due to the energy released from the DC reactor L. 2, the current flowing through the diode D 2a is represented by the current corresponding to the current flowing through the thyristor TH 1a indicated by reference numeral S 1 in FIG. , β 3, β 4,…, the current is added by the energy released from the DC reactor L. This phenomenon is, as indicated by reference numeral i3 in FIG. 3 (b), that the thyristor TH1a is extinguished by the current flowing back due to the interruption of the thyristor TH1a. This is not possible, and occurs because the current increases.

Therefore, as shown in Fig. 4 (b), the current flowing through the thyristor TH2 is extinguished in only a half cycle when the AC terminal AC2 is at the high level, whereas the current flowing through the thyristor TH2a is higher. As shown in Fig. 5 (b), the flowing current increases every cycle. In addition, As shown in FIG. 4 (d), the current flowing through the diode D 1 is different from the current flowing through the thyristor TH 2 shown in FIG. 4 (b) and the DC current indicated by reference numeral 2 in FIG. 4 (c). The current flowing through the diode D1a is the sum of the current due to the discharge of the reactor L and the current flowing through the diode D1a, as shown in FIG. 5 (d), and the diode D2a shown in FIG. 5 (c). It increases with each cycle, as does the current flowing through the circuit.

As a result, in each of the grid interconnection device 21 and the grid interconnection device 41, the current flowing through the DC reactor L is shown in Fig. 4 (e) and Fig. 5 (e). The voltage of bus 23 is shown in Fig. 4 (f) and Fig. 5 (f), the voltage of receiving bus 22 is shown in Fig. 4 (g) and Fig. 5 (g), and the receiving bus is 22 The fault current flowing to the side 2 is shown in Fig. 4 (h) and Fig. 5 (h).

In the grid interconnection device 21 according to the present invention, the current flowing through the DC reactor L converges at a substantially constant value as shown in FIG. Then, as shown in FIG. 5 (e), the value is increased every one cycle. Correspondingly, the fault current is also rapidly and reliably shut off in one cycle in the grid interconnection device 21 of the present invention as shown in FIG. In the interconnection device 41, as shown in FIG. 5 (h), the number increases every cycle.

Therefore, although this grid interconnection device 41 functions as a current limiting device, it cannot extinguish either thyristor TH la or TH 2a, and It cannot be used as a grid connection device.

In this regard, the grid interconnection device 21 according to the present invention has a DC reactor when a failure occurs. The fault current can be reliably shut off by performing current limiting operation with the torque L and shutting off the thyristor TH1 and TH2. As a result, the instantaneous voltage drop can be greatly improved, and the uninterruptible power supply that has been provided separately for conventional computers and other important loads can be omitted. In addition, it is possible to shut down at a high speed, thereby preventing the private power generator 27 from being overloaded, causing a power outage due to the stoppage of the private power generator 27, and a generator shuffling due to a sudden overload. Thus, it is possible to reliably prevent undesired situations such as occurrence of excessive torque load on the vehicle. Furthermore, it is also possible to reduce the short-circuit capacity on both the side of the power bus 23 and the side of the power receiving bus 22.

Also, in the above-mentioned Japanese Patent Application Laid-Open No. 49-50448, there is disclosed an example in which a thyristor-pure pure-bridge rectifier circuit is used for a current limiting device. This example is shown in Fig. 3 (c). The pure bridge rectifier circuit 32a of the current limiting device 31a always has a thyristor th1 to th4 by the action of the DC power supply B, similarly to the configuration of FIG. 3 (a) described above. If the current in the AC circuit is less than the current value, the impedance seen from the AC side becomes zero, and if the current value is more than the current value, the circuit performs current limiting operation. .

The addition of the DC power source B for such a purpose makes it technically and economically difficult to realize the invention. The grid interconnection device 21 according to the present invention does not include such a DC power supply B, and as described above, the reactance and resistance components of the DC reactor L and the thyristor TH 1, By selecting the current decay time constant determined by TH2 and the rectifier circuit composed of diodes D1 and D2 to be at least 2.5 times the system frequency cycle of the power system, Unnecessary and disclosed in JP-A-49-504-48 The information technology is completely different in composition.

Another embodiment of the present invention will be described below with reference to FIGS. 6 to 8 and FIG. 12 described above.

FIG. 6 is a single-phase connection diagram of a power system for describing a distributed power supply device according to another embodiment of the present invention. The grid interconnection device 51 provided in this distributed power supply has the same configuration as the above-described grid interconnection device 21, and connects the receiving bus 54 and the Koziene bus 56 to each other. It enables the grid-connected operation between the commercial power system and the distributed power system.

The commercial power line 53 drawn from the power source 52 of the commercial power system into the customer is connected to the receiving bus 54. Many distribution lines 55 connected to a general load are connected to the receiving bus 54. In addition, the power bus 56 of the distributed power system is connected to a power source 58 such as a cogeneration system via a power line 57. The Kozine bus 56 is also connected to a number of distribution lines 60 to critical loads.

The system interconnection device 51 includes a circuit breaker 61, a single-phase rectifier circuit 62, and a DC reactor 63. The single-phase rectifier circuit 62 connects a pair of thyristors TH2 and TH2 to at least one of the two AC terminals (the circuit breaker 61 side in the example of FIG. 6). It is composed of a bridge circuit of semiconductor rectifiers consisting of thyristors TH1 and TH2 and a pair of diodes D1 and D2. As a result, in the event of a failure, shutoff drive within 1Z2 cycles (10 msec at 50 Hz) becomes possible, and then the breaker 61 shuts off. One of the two AC terminals of the single-phase rectifier circuit 62 is connected to the connector bus 56, and the other is connected to the power receiving bus 54 via the circuit breaker 61. In addition, this single-phase rectifier circuit 6 A DC reactor 63 is connected between the two DC terminals 2 as described above.

The voltages of the power supply lines 53 and 57 are detected by the undervoltage relays 67 and 68 via the voltage transformers 65 and 66, respectively, and the undervoltage relays 67 and 68 are When the voltage of the power supply lines 53 and 57 becomes a predetermined set value with respect to the rated voltage, for example, 85% or less, it is determined that a failure has occurred, and the thyristors TH 1 and TH 2 Is extinguished, and the circuit breaker 61 is turned off.

In the distributed power supply configured as described above, the system impedance on the power supply 58 side looks almost L, and assuming that the equivalent inductance corresponding to the internal impedance of the power supply 58 is Ls, In the present invention, when the allowable voltage drop rate of the distributed power system is A, the inductance L dc of the DC reactor 63 is represented by L dc with respect to the equivalent inductance L s of the distributed power system. / L s> (1 -A) / A… Select to satisfy the relationship of (1).

Here, as shown by reference numeral 69, when a ground fault occurs in the commercial power supply system, the voltage of the power supply bus 56 is obtained by changing the voltage V of the power supply 58 to the equivalent inductance L s And the inductance L dc of the DC rear reactor 63 are the divided values. Therefore, the system voltage V 'after the fault is

V = Ldc / (Ldc + Ls) xV- (2).

Therefore, for example, when the allowable voltage drop rate A is 50%, the above equation (1) is used to make the inductance Ldc equal to the inductance of the power supply 58 substantially equal to the equivalent inductance Ls. And by When a failure occurs in the commercial power supply system as indicated by the reference numeral 69, the decrease in the BE of the power supply bus 56 in the distributed power supply system can be suppressed to 50% of the voltage V of the power supply 58. it can. Also, for example, when the allowable voltage drop rate A is 25%, the multiple L dc ZL s becomes larger than 3 according to the above equation 1, and the DC reactance 6 3 By setting the inductance Ldc of the power generator to 3 times, the voltage drop of the cogeneration bus 56 can be suppressed to 75% of the voltage V of the power supply 58.o

As is clear from the above equation, the voltage drop can be reduced as the inductance Ldc of the DC reactor 63 is set to be larger, but the voltage obtained at the time of failure is insufficient. It is desirable that the voltage be equal to or less than the set value of the voltage relay 68.

7 and 8 show the results of breaking the operation of the distributed power supply of the present invention and the operation of the distributed power supply shown in FIG. 13 at the time of occurrence of a failure, respectively. Fig. 7 (a) shows the bus voltage of the Kozi energy bus 56, Fig. 7 (b) shows the interconnection current flowing through the grid interconnection device 51, and Fig. 8 (a) shows the This is the bus voltage, and Fig. 8 (b) is the interconnection current flowing through the interconnection device 11. The ground fault occurrence timing is set to the zero crossing point, and the inductance L dc of the DC reactor 63 in the grid interconnection device 51 of the present invention is the equivalent inductance of the power supply 58. L is set to 1 time. As is clear from comparison between FIG. 7 (a) and FIG. 8 (a), in the present invention, the voltage drop is suppressed to 50% or less, and FIGS. 7 (b) and 8 (b) As is clear from the comparison of and, the interconnection current is also suppressed to less than 1/2. As described above, in the distributed power supply device according to the present invention, the DC By setting the inductance L dc of the reactor 63 based on the permissible voltage drop rate A and the equivalent inductance L s, the level at which the voltage drop in the event of a failure in the commercial power supply system is desired. Can be suppressed. For example, if the allowable voltage drop rate A is set to 50%, the compensation range of the voltage drop in FIG. 12 is indicated by reference numeral M3, and a variable speed motor for power electronics applications and The stable operation of the electromagnetic switch 59 (see Fig. 6) to which the load is connected can be compensated.

This makes it possible to compensate for the operation of the variable speed motor and the electromagnetic switch with low loss and low cost without using an uninterruptible power supply. As a result, the reliability of the interconnection operation can be improved, and the stress on the distributed power source can be reduced. In addition, due to the current limiting action of the DC reactor 63 and the high-speed current cutoff action of the thyristor, the short-circuit capacity of the electromagnetic switch 59 on the load side does not need to be unnecessarily increased. In connecting the system to the commercial power system, it is not necessary to replace the distribution line 60 or the electromagnetic switch 59.

The grid interconnection devices 21 and 51 are not limited to the above-described mixed bridge of thyristor and diode, but may be configured of a thyristor pure bridge. Good. In the grid interconnection device 51, the circuit breaker 61 may be omitted. Industrial applicability

As described above, in the system interconnection device according to the present invention, when a failure occurs, the rectifying switching element can be shut off at high speed to disconnect the two power systems, and the failure can be prevented. Even if it occurs, current is stored by DC reactor This function can also suppress the instantaneous drop in the power supply voltage to the important load on the power system side to be disconnected, so that the two power systems can be interconnected with each other to exchange power. It can be suitably applied to system equipment.

Further, as described above, the distributed power supply device with the instantaneous voltage drop countermeasure function according to the present invention is connected to the commercial power supply system by using the above-described system interconnection device, and In the event of a failure, the distributed power system bus voltage, in which the system voltage is divided by the equivalent inductance L s and the DC termination inductor L dc, is applied to the distributed power system. Since it is within the allowable value, the operation of important loads can be compensated with low loss and low cost without using an uninterruptible power supply, and it is suitable for a distributed power supply. be able to.

Claims

The scope of the claims

1. A system interconnection device that is interposed between two power systems and interconnects both systems to exchange power

A pair of rectifying switching elements is connected to one of the two AC terminals connected between the phase connection terminals of both systems, and a pair of rectifying elements is connected to the other. A single-phase rectifier circuit,

A system interconnection device characterized by including a DC reactor connected between two DC terminals which are connection points between the rectifying switching element and the rectifying element.

2. When the reactance component and the resistance component of the DC reactor and the current decay time constant composed of the rectifying circuit of the rectifying switching element and the rectifying element are at least 2.5 times the system frequency cycle of the power system. The grid interconnection device according to claim 1, wherein:

3.1 An important load that is provided with one or more power supplies and should avoid instantaneous voltage drop and power failure is connected, and is connected in parallel with the commercial power supply system by the grid interconnection device according to claim 1 or 2. A distributed power supply with an instantaneous voltage drop countermeasure function

Assuming that the inductance of the DC reactor is A, the voltage drop rate that can be tolerated in the distributed power supply system when a failure occurs in the commercial power supply system, an equivalent inductance equivalent to the internal impedance of the distributed power supply system A distributed power supply with instantaneous voltage drop countermeasures, characterized in that it has a reactance that is greater than (1-A) no A times the impedance.

4. The power supply in the distributed power supply system is a rotating machine. A distributed power supply unit with a function to prevent instantaneous voltage drop according to claim 3.

5. The distributed power supply with instantaneous voltage drop prevention function according to claim 3, wherein the power supply in the distributed power supply system is a stationary power supply using an inverter.