JP2001095156A - Power distribution system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new power distribution system which can introduce dispersed power or DC power of a power storage means or the like easily and at low cost. SOLUTION: In a power distribution system which supplies a consumer with power through a distribution line 3 from a substation for distribution, an AC-DC- AC converter 5 which has the first inverter/converter, the second inverter/ converter, and a circuit on DC side installed between the first inverter/converter and the second inverter/converter, is arranged in each distribution cable 3, and a DC power source 6 can be connected to the circuit on DC side of this AC-DC-AC converter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The invention of this application relates to a power distribution system. More specifically, the invention of this application makes it possible to easily and inexpensively introduce a DC power supply such as a distributed power supply or a power storage means, and to respond to recent power supply and distribution forms with a high degree of freedom. A possible new power distribution system.

[0002]

2. Description of the Related Art The power generated by thermal, hydro, nuclear, and various other power plants is first boosted by a transformer and then transmitted through a transmission line to form a primary substation, a secondary substation, and the like.
The power is sent to distribution substations, and the voltage is reduced to a voltage required for various customers (demand facilities and customers) from each substation through distribution lines. Such a series of flows is called an electric power system, and is a consistent electric power system from power generation to final use of electric power. In this power system, generally, from the power station to the distribution substation (including the primary and secondary consumers from the primary and secondary substations), the transmission system (also called the transmission system) and the distribution substation to the final Up to the consumer, the distribution system (also referred to as the distribution system) is distinguished, and the distribution system is the part closest to the general consumer.

In this power distribution system, for example, as shown in FIGS. 4 and 5, power from a power distribution substation (1) is supplied to each customer through a power distribution line (3). I have. 4 and 5, the distribution substation (1) is provided with a transformer (2) and a circuit breaker (A) provided on the distribution line (3) from the transformer (2). ,
Between each branch point of the distribution line (3) (referred to as a distribution line section), a switch (4) and a communication switch (a) are provided at necessary places.

In this case, during normal operation, as shown in FIG. 4, for example, the communication switch (a) is open (disconnected).
This is a radial distribution system (also referred to as a resin distribution system) operated for each distribution line (2). From this normal operation state, if an accident occurs in the distribution line (3) at the accident point as exemplified in FIG. 5, for example, the following operation is performed.

<A> First, the circuit breaker (A) of the distribution substation (1) to which the distribution line (3) at the fault point is connected is switched from the closed state [ON] to the open state [OFF]. <B> At this time, in a healthy distribution line section where no accident has occurred, the power supply from the distribution substation (1) is temporarily stopped, and the power is cut off.

<C> Next, the switch (4) between the distribution line (3) at the fault point and the sound distribution line section is switched from the closed state [ON] to the open state [OFF]. <D> Further, the communication switch (b) between the healthy distribution line section and another distribution line section adjacent thereto is switched from the open state [off] to the closed state [on].

As a result, a healthy distribution line section can be relieved from an accidental distribution line section. However, it is difficult for such a conventional power distribution system to flexibly respond to recent changes in the power supply / distribution mode.

[0008] That is, conventionally, the AC power from the distribution substation (1) was only unilaterally distributed to consumers, but in recent years, significant persons and the like have been using DC power sources such as distributed power sources and power storage means. It is often used to connect the DC power from the DC power supply to the distribution line (3). In a power distribution system, various problems occur when interconnecting a DC power supply. For example, if an attempt is made to connect a distributed power supply such as a solar cell or a power storage means such as a battery to the distribution line (3), it is necessary to separately install an inverter for the distribution line (3) through which AC power flows. However, when a large number of DC power sources are connected to the AC distribution line (3), voltage management of the distribution line (3) and load / power management of the distribution line section become complicated. I will.

Therefore, the invention of this application has been made in view of the circumstances described above, and solves the problems of the prior art, so that a DC power supply such as a distributed power supply or a power storage means can be easily and easily provided. It is an object to provide a new power distribution system that can be introduced at low cost.

[0010]

Means for Solving the Problems The present invention solves the above-mentioned problems by providing a power distribution system for supplying power from a distribution substation to consumers through distribution lines.
An AC-DC-AC converter having a first inverter converter, a second inverter converter, and a DC side circuit provided between the first inverter converter and the second inverter converter is distributed to each distribution line. And a DC power supply is connectable to a DC side circuit of the AC-DC-AC converter.
It is provided as an aspect that the DC power supply is a distributed power supply and / or power storage means (claim 2).

[0011]

Embodiments of the present invention will be described below in more detail with reference to the accompanying drawings.

[0012]

1 and 2 conceptually illustrate a main part of a power distribution system according to an embodiment of the present invention. FIG. 3 shows an AC-DC-AC used in the power distribution system. 3 is a diagram conceptually illustrating a main configuration of a converter.

For example, as shown in FIGS. 1 to 3, the power distribution system of the present invention is a power distribution system for supplying power from a power distribution substation (1) to a consumer (not shown) through a power distribution line (3). A system comprising a first inverter converter (51) and a second inverter converter (5).
2) and an AC-DC-AC converter (5) having a DC side circuit (53) provided between the first inverter converter (51) and the second inverter converter (52). (3), this exchange-
A DC power supply (6) can be connected to the DC side circuit (53) of the DC-AC converter (5).

To further explain the case, in the example shown in FIGS. 1 and 2, the transformer (2) of the distribution substation (1)
An AC-DC-AC converter (5) is arranged on the distribution line (3) extending from the power distribution line (3) and on each distribution line (3) branched from the distribution line (3). Compared with the conventional power distribution system illustrated in FIGS. 4 and 5, an AC-DC-AC converter (5) is provided instead of each of the circuit breaker (A) and the communication switch (A). Each AC-DC-
A DC power supply (6) can be connected to the AC converter (5). More specifically, as illustrated in FIG. 3, for example, in each AC-DC-AC converter (5), the power from the distribution line (3) at one end is supplied to the first inverter converter (51) or Second inverter / converter (5
After being converted to DC by 2), the DC power passes through the DC side circuit (53), and is returned from the second inverter converter (52) or the first inverter converter (51) on the opposite side as AC again to the distribution line (3) at the other end. ) Is output. In the example of FIG. 3, the DC power supply (6) is a DC output means (6) such as a distributed power supply or a power storage device that outputs DC power by itself.
1) and the DC provided on the output side of the DC output means (61)
/ DC converter (62), and the output side of the DC / DC converter (62) is connected to the input side of the DC side circuit (53) to connect to the DC side circuit (53) through which DC power flows. They are being interconnected.

In such a power distribution system of the present invention, during normal operation, for example, as illustrated in FIG. 1, the AC-DC-AC converter (5) and the switch (4) are all in the closed state [ON]. As a result, a network-like power distribution system that is always closed and linked to a plurality of adjacent distribution lines (3) as much as possible, that is, power always flows through all the distribution lines (3). When an accident such as a ground fault or short circuit occurs in the distribution line (3) at the accident point as illustrated in FIG. 2 from the normal operation, for example, the following operation is performed.

<A> First, the switch (4) to which the distribution line (3) at the accident point is connected is switched from the closed state [ON] to the open state [OFF]. <B> Next, the AC-DC-AC converter (5) to which the distribution line (3) at the fault point is connected is closed [ON].
To open circuit state [OFF].

<C> At this time, in a healthy distribution line section where no accident has occurred, the other AC-DC-AC converter (5) is always in the closed state [ON] and another distribution substation is used. Since power is supplied from the place (1), there is no power outage.

Therefore, unlike the conventional power distribution system described above, a network-type power distribution system using an AC-DC-AC converter (5) is employed. Even if an accident occurs,
The adjacent other distribution line (3) can continue to supply power, and can realize uninterrupted power distribution.

The "closed state" of the AC-DC-AC converter (5) is defined as the "closed state".
When both 1) and the second inverter / converter (52) are operating, power flow control of active power and reactive power is performed between the distribution line (3) on the input side and the distribution line (3) on the output side. The “open circuit state” refers to a state in which one or both of the first inverter converter (51) and the second inverter converter (52) is in a stopped state, and
A state in which power flow control of active power and reactive power is not performed between the distribution lines (3) at both ends of the DC-AC converter (5).

The AC-DC-AC converter (5), in particular, the first inverter converter (51) and the second inverter converter (52) are provided with AC power or DC power from the distribution substation (1). In order to achieve effective distribution of DC power from the DC power supply (6) when the power supply (6) is connected, for example, the following functions and control / operation must be possible. Is preferred.

A. Switching can be performed by, for example, a PWM method (the switching frequency is, for example, several tens of kHz or more). b. It has an operation function of a voltage source mode (also referred to as a self-sustaining operation mode) in which the voltage and frequency of the AC side (that is, the same applies to the distribution line (3) on the input side and / or the output side hereinafter) are operated by external command values.

C. It has an operation function of a current source mode (also referred to as an interconnection operation mode) that operates with reference to the AC side voltage and frequency. d. In order to be able to cooperate with an adjacent AC-DC-AC converter (5), it has an operation function in which the voltage and frequency have drooping characteristics like a synchronous generator.

E. Each of the above-described operation functions can be switched by an external command. f. In order to be able to control the active power and the reactive power passing through the AC-DC-AC converter (5), a voltage value inside the interconnection reactor and a voltage phase difference between the interconnection reactors are commanded from outside. Can be controlled.

G. The current can be controlled within the specified value when a short circuit occurs on the AC side. h. If an accident such as a short circuit or ground fault occurs on the AC side, the accident is detected and the first inverter / converter (51) and / or
Alternatively, the operation of the second inverter / converter (52) is stopped. As a result, as described above, the AC-DC-AC converter (5) is in the open circuit state, and the adjacent healthy other distribution line (3) can be protected.

I. The DC side (that is, the first inverter converter (51) and the second inverter converter (5)
2) and between the DC side circuit (53) and the DC power supply (6). If an accident such as a short circuit or a ground fault occurs in the following, the accident is detected and the operation of the AC-DC-AC converter (5) is stopped. Thereby, the distribution line (3) and the DC power supply (6) linked to the AC-DC-AC converter (5) can be protected.

J. When harmonic distortion equal to or more than the reference value occurs in the voltage waveform on the AC side, control is possible to cancel the harmonic distortion. Thereby, an active filter function is realized.

K. The grounding system between the distribution lines (3) at both ends of the AC-DC-AC converter (5) can be separated. Furthermore, it is preferable that the DC side circuit (53) be capable of performing the following functions, control and operation. <A> When the DC power supply (6) is a capacitor a. Three-phase unbalanced power within the reference value can be supplied to the AC side.

B. Reactive power within the reference value can be supplied to the AC side. <B> When the DC power supply (6) is a storage battery: a. It is possible to charge and discharge the active power within the reference value for the AC side.

B. Three-phase unbalanced power within the reference value can be supplied to the AC side. c. Reactive power within the reference value can be supplied to the AC side. Needless to say, the above-described functions, control / operation, and each reference value can be arbitrarily adjusted by various factors such as the amount of power distribution and the specifications of the power distribution equipment.

Of course, the present invention is not limited to the above examples, and various embodiments are possible in detail. For example, in the embodiment shown in FIG. 3, the AC distribution line (3) is of a three-phase three-wire type, but for example, a three-phase four-wire type, a single-phase two-wire type, a single-phase three-wire type, and the like. It is needless to say that the present invention can also be applied to the power distribution system. In the embodiment shown in FIGS. 1 and 2, the AC-DC-AC converter (5) is provided instead of the transformer (A) and the communication switch (A). (4) may also be replaced by an AC-DC-AC converter (5), and in this case as well as above, as close as possible via all AC-DC-AC converters (5) A network-like power distribution system that is normally closed and linked to a plurality of distribution lines (3) is formed, and the DC power supply (6) can be arbitrarily interconnected, and for example, the above-described various controls and operations can be performed. It is preferred that it is.

[0031]

The power distribution system of the present invention described in detail above has the following remarkable effects by the AC-DC-AC converter (5) disposed on each distribution line (3) as described above. Have.

<A> Effects of the DC-side circuit (53) of the AC-DC-AC converter (5) The DC-side power supply (6) such as a distributed power supply such as a solar cell or a power storage means such as a battery is a DC-side circuit. Since it is only necessary to connect to (53), there is no need to separately install an inverter as in the past, and power distribution is performed regardless of voltage management of the distribution line (3) and load / power management of the distribution line section. It is possible to easily and inexpensively introduce the DC power supply (6) into the system, and it is possible to respond to recent power supply and distribution modes with a high degree of freedom.

<B> Effect on AC side of AC-DC-AC converter (5) a. Conventionally, power flow control between the distribution lines (3) could not be performed. However, according to the present invention, power flow control between the distribution lines (3) can be performed using the AC-DC-AC converter (5). Therefore, the power supply between the distribution lines (3) can be smoothed,
It is possible to improve the utilization rate of the distribution line (3) and suppress investment in distribution facilities.

B. Conventionally, the voltage of the distribution line (3) is controlled discontinuously and with a tap that is slow in time, so fine voltage control cannot be performed. In order to suppress the voltage rise due to the reverse power flow by the power source, the delayed reactive power flows through the distribution line (3), and the loss of the distribution line (3) increases. Also,
Since it is not possible to control the power flow between the distribution lines (3), it is necessary to concentrate the active power on the distribution line (3) having a large load, and the distribution line loss has increased. On the other hand, in the present invention, fine voltage control of the distribution line (3) becomes possible by performing voltage control on the AC side of the AC-DC-AC converter (5). Since there is no need to supply unnecessary reactive power, loss of the distribution line (3) can be reduced. In addition, the power flow between the distribution lines (3) can be controlled by using the AC-DC-AC converter (5), and the active power flowing through the distribution line (3) can be controlled to a minimum. The loss of 3) can be further reduced.

C. Conventionally, when a short circuit accident occurs in the distribution line (3), a large current is supplied from a power system (that is, the above-described transmission system) higher than the distribution substation (1). However, in the present invention, the distribution line (3) in each section is surrounded by the AC-DC-AC converter (5). Even if a short circuit accident occurs, excessive current is not supplied as in the past,
Short-circuit capacity of distribution line equipment and customer's power receiving equipment can be reduced,
Cost reduction of various facilities can be achieved.

D. Conventionally, since the voltage of the distribution line (3) is controlled discontinuously and with a tap that is slow in time, fine voltage control cannot be performed. The harmonics on the 1) side flowed into the distribution line (3) and had a bad influence on the consumer, and the harmonic source in the distribution line (3) was also a factor of an adverse effect on the consumer. On the other hand, in the present invention,
Not only can the voltage of the distribution line (3) be finely controlled using the DC-AC converter (5), but also the AC-DC-AC converter even if there is a harmonic source on the distribution substation (1) side. Since the distribution line (3) is connected via (5), there is no adverse effect on consumers. Further, even if a harmonic source is present in the distribution line (3), if the active-filter function is given to the AC-DC-AC converter (5) as described above, it is connected to the distribution line (3). Adverse impact on existing consumers can be suppressed. Therefore, power quality such as voltage, harmonics, and frequency can be improved.

E. Conventionally, when a ground fault or short circuit accident occurs in the distribution line (3) as described above, the other healthy distribution line (3) also temporarily loses power. In addition, a DC power supply (6) such as a distributed power supply linked to the distribution line (3) needs an isolated operation prevention function other than a voltage or frequency relay,
Further, a direct voltage rise suppression function is required, and it is difficult to introduce a DC power supply (6). Furthermore, distribution line (3)
The magnitude of the ground fault current due to the ground fault occurring in the above is an amount proportional to the ground capacity of all distribution lines (3) supplied from the transformer (2) of the distribution substation (1). It was a large ground fault current. On the other hand, in the present invention, as described above, the power failure due to the ground fault / short circuit accident is caused by AC-DC-
Since it is limited to the distribution line section surrounded by the AC converter (5), the power supply reliability can be significantly improved. In addition,
Since the voltage of the distribution line (3) can be monitored by the DC-AC converter (5), the isolated operation phenomenon caused by the DC power supply (6) such as the distributed power supply is prevented by the AC-DC-AC converter (5). Detection and response (ie, changing the voltage or frequency of the AC system by causing the AC system to fluctuate in active power or reactive power) is possible, and the DC power supply (6) has a single unit other than the voltage or frequency relay. Driving prevention function is not required. Furthermore, since the AC-DC-AC converter (5) can finely control the voltage on the high voltage side, the function of suppressing the voltage rise of the DC power supply (6) becomes unnecessary. Therefore,
The introduction of the DC power supply (6) can be realized extremely easily and at low cost. Further, since each distribution line section can be separated from the grounding system by the AC-DC-AC converter (5), the ground fault current is small, and the class B grounding of the transformer (2) for reducing the distribution voltage is easy. And the class B grounding resistance value may be large, so that the cost of the class B grounding work can be reduced.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram conceptually illustrating an operation mode during normal operation of a power distribution system according to an embodiment of the present invention.

FIG. 2 is a main part configuration diagram conceptually illustrating an operation mode of a power distribution system according to an embodiment of the present invention at the time of a distribution line accident.

FIG. 3 is a diagram conceptually illustrating a configuration of a main part of an AC-DC-AC converter.

FIG. 4 is a main part configuration diagram conceptually illustrating an operation mode during normal operation of a conventional power distribution system.

FIG. 5 is a main part configuration diagram conceptually illustrating an operation mode of the power distribution system of FIG. 4 at the time of a distribution line accident.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Distribution substation 2 Transformer 3 Distribution line 4 Switch 5 AC-DC-AC converter 51 First inverter / converter 52 Second inverter / converter 53 DC side circuit 6 DC power supply 61 DC output means 62 DC / DC conversion vessel

Claims (2)

[Claims] 1. A power distribution system for supplying power from a distribution substation to a consumer through a distribution line, wherein a first inverter converter, a second inverter converter, and a first inverter converter and a second inverter converter are provided. An AC-DC-AC converter having a DC-side circuit provided in each of the distribution lines is provided.
A power distribution system, wherein a DC power supply is connectable to a DC side circuit of a DC-AC converter. 2. The power distribution system according to claim 1, wherein the DC power supply is a distributed power supply and / or power storage means.