JPH01177839A - Superconducting energy storage system - Google Patents

Abstract

PURPOSE:To obtain a system in which power loss is suppressed to a remarkably small value by providing a switch in series with a superconductor for forming a DC closing circuit at the time of storing energy, and operating to open or close the switch at the time of switching normal conduction/superconduction. CONSTITUTION:A system for forming a DC closing circuit by connecting superconducting coil 5 and a superconducting conductor 3 in series with the DC side of an AC/DC converter 1, and switching the conductor 3 to a superconducting state at the time of storing energy, a switch 2 is provided in series with the conductor 3. The switch 2 is closed immediately before the conductor 3 is switched to the superconducting state, and the switch 2 is opened immediately after the conductor 3 is switched to a normal conducting state. Thus, a large current circuit can be opened or closed even by the switch 2 having a small rated value, and power loss at the conductor 3 can be suppressed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention is a superconducting energy storage system that stores energy using superconducting coils and supplies the stored energy to an AC system when necessary. It is related to.

(Conventional technology) In recent years, the amount of power generated by nuclear power generation has been increasing, and as a result, aging thermal power generation facilities are being forced to start up and shut down in order to cope with fluctuations in power demand on -day. The reality is that

A superconducting energy storage system that uses superconducting coils to store and release electrical energy to adjust power demand has been proposed as a new technology to keep the number of startups and shutdowns of aging thermal power facilities low. There is.

FIG. 3 is a circuit diagram showing the configuration of this type of conventional energy storage system. In the figure, a power conversion device 1 is configured by a transformer 1a and an AC/DC converter 1b using a thyristor element or the like. The AC side terminal of this power converter 1 is connected to an AC system (not shown), and a resistor 4° superconducting coil 5 and a thyrisk switch 7 are connected in parallel to the DC side terminal.

Here, if the demand power is too small compared to the generated power of the AC system, the superconducting coil 5
to store energy. During energy storage, the thyrisk switch 7 is fired, and a current in the reflux mode is applied to it. is washed away. - On the other hand, when the demanded power is excessive compared to the generated power, the energy stored in the superconducting coil 5 is supplied to the commercial grid via the power conversion device 1. At this time,
The thyrisk switch 7 is turned off.

Through the above operations, it is possible to respond to daily fluctuations in power demand.

Note that when there is an abnormality in the superconducting coil 5 and it is necessary to rapidly release the stored energy to the outside, the resistor 4 can be consumes stored energy.

Currently, some superconducting energy storage systems being planned have superconducting coils 5 with a rated current of several hundred kiloamperes (KA). In this case, the minimum firing voltage of the thyrisk switch 7 is as small as 1 to 2 [V] at most, but when the current of the superconducting coil reaches several hundreds (KA),
The steady state power loss is on the order of megawatts (MW), and the power loss in the thyrisk switch becomes very large.

On the other hand, some thyristor elements currently in practical use have a rated current of 4 (KA), but the superconducting current I is several hundred [KA]. In order to use this thyristor element in a circuit that flows current, approximately 4,000 elements had to be connected in parallel, and in that case, a new technology had to be established to ensure current balance.

Furthermore, the economics of a system that requires approximately 4,000 thyrisk switches has been questioned.

Therefore, a system shown in FIG. 4 has been proposed as an alternative system. The energy storage system shown in FIG. 4 uses a superconducting conductor 3 in place of the cyrisk switch 7 in the system shown in FIG.

With this configuration, for example, when energy is not transferred to or from a commercial grid, the superconducting conductor 3 is brought into a superconducting state and the current I in the reflux mode is generated as shown in the figure. flow.

Further, when transmitting and receiving energy with a commercial grid, for example, heat is applied to the superconducting conductor 3 to raise the temperature, thereby breaking the superconducting state and bringing it into the normal conducting state. In a normally conductive state, it normally acts as a resistance element with a diameter of several tens of ohms (Ω).

On the other hand, also in the mode of protecting the superconducting coil 5, by breaking the superconducting state of the superconducting conductor 3, the current 11 is caused to flow through the resistor 4, and the stored energy is consumed here. The resistance 4 is approximately 1 to 2 [Ω], although it varies depending on the rated current I and rated inductance of the superconducting coil 5.
A diameter of about 100 ml is used.

Comparing this energy storage system shown in Fig. 4 with the system shown in Fig. 3, it is found that since the resistance value of the superconducting conductor is theoretically zero, there is no steady state loss in the reflux mode, and furthermore, the energy storage system shown in Fig. Since only one superconducting conductor is required instead of individual cyrisk elements, there is no need to consider current imbalance, and superconducting coil 5
It was also economical because the superconducting conductor could be cooled using the same cooling system.

(Problems to be Solved by the Invention) However, even in the conventional energy storage system shown in Fig. 4, there is a large power loss when transferring energy to and from the commercial grid, and there is also a cost associated with the deterioration of the characteristics of the superconducting conductor. The problem was that it was a heavy burden.

In other words, the resistance value of the superconducting conductor 3 in the normal conduction state is at the upper limit of several tens of ohms (Ω) in terms of economy and feasibility, and the rated DC voltage of the power converter is kilovolt (KV).
), the power loss of the superconducting conductor 3 when transmitting and receiving power to and from an AC system using this power conversion device will be on the order of megawatts (MW).

In addition, if the superconducting conductor 3 is used for a long period of time in a normal conducting state,
Even if this is used while being cooled, the temperature will be higher than in the superconducting state, and the heat generation will cause significant deterioration and property deterioration. Therefore, the cost burden associated with its replacement increases.

This invention has been made to solve the above-mentioned problems, and aims to provide a superconducting energy storage system that significantly reduces power loss and is highly economical.

[Structure of the invention]

(Means for Solving the Problems) The present invention is characterized in that a superconducting coil and a superconducting conductor are connected in parallel between DC terminals of an AC/DC power converter, and when transmitting and receiving power to and from an AC system, the superconducting conductor is turned into a normal conductor. A superconducting energy storage system that sets the superconducting conductor to a superconducting state and puts the superconducting conductor in a superconducting state during energy storage, the superconducting energy storage system including a switch inserted in series with the superconducting conductor, immediately before transitioning the superconducting conductor from a normal to a superconducting state. The method is characterized in that the switch is turned on, and immediately after the superconducting conductor is transferred from a superconducting state to a normal conducting state, the switch is turned off.

(Function) Generally, if there is a switch capable of opening and closing a DC circuit of several hundred KA, this switch may be used in place of the above-mentioned superconducting conductor. However, since the feasibility of such a switch is low, conventionally superconducting conductors have been used. However, if the current value during on/off operations can be kept low, even a switch with a low rating can open and close a high current circuit.

This invention skillfully utilizes this principle by inserting a switch such as a switch in series with a superconducting conductor, and attempting to turn off the switch while maintaining the superconducting conductor in a normal conducting state. However, at this time, the OFF operation is performed immediately after the superconducting conductor is transferred from the superconducting state to the normal conducting state, and the ON operation is performed immediately before transferring the superconducting conductor from the normal conducting state to the superconducting state.

Therefore, the current when turning on the switch and the current when turning it off are suppressed by the resistance value of the superconducting conductor in the normal conducting state, so the switch can open or close a large current circuit. At the same time, this switch can cut off most of the current in the normal conductor state of the superconducting conductor, and the power consumption in the superconducting conductor can be suppressed to substantially zero. Further, by reducing the power consumption to zero, it is possible to prevent deterioration of the superconducting conductor, and there is almost no need to replace it, resulting in an economically superior product.

(Embodiment) FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and in the figure, the same reference numerals as in FIG. 4 indicate the same elements. Then, a switch 2 such as a mechanical switch is inserted in series with the superconducting conductor 3, and the switch 2 is turned on and off according to whether the superconducting conductor 3 is in a superconducting state or in a normal conducting state. A switch control means 8 is provided.

The operation of this embodiment configured as described above will be explained below.

First, when no power is stored in the superconducting coil 5, the superconducting conductor 3 is kept in a normal conducting state, and the switch control means 8 keeps the switch 2 open.

When storing AC power in this state, the AC/DC converter 1 converts the AC power into DC power and causes the DC current to flow through the superconducting coil 5. When the current reaches a desired level, the switch control means 8 closes the switch 2, and then transitions the superconducting conductor 3 from the superconducting state to the normal conducting state, and also switches the superconducting conductor 3, such as a thyristor, constituting the converter 1a. All gate signals are cut off. At this time, no current flows through the switch 2 and the superconducting conductor 3 until the switch 2 is closed. A current suppressed by the resistance value flows, and when the superconducting conductor 3 enters the superconducting state and the elements constituting the converter 1a are placed in the gate blocking state, the direct current flowing there flows through the switch 2 and the superconducting conductor 3. The current Io in the freewheeling mode having a large value flows through the circuit. Therefore, the power Ii in the superconducting conductor 3 during power storage
Loss can be reduced to virtually zero. Also, switch 2
The current at the time of opening is suppressed to a low level by the resistance of the superconducting conductor 3, so it does not cause contact abnormalities.Next, when it becomes necessary to transfer the stored power to the AC system, By operating the DC converter 1 and transitioning the superconducting conductor 3 from a superconducting state to a normal conducting state, a current I in a reflux mode flows through the switch 2 and the superconducting conductor 3.

If the switch control means 8 opens the switch 2 at this point, the current I in the freewheel mode will flow through the AC/DC converter 1. all of which flows to the AC/DC converter 1. At this time, some current flows through the superconducting conductor 3 in the normal conductive state until the switch 2 is opened, but by opening the switch 2 immediately after that, the power loss in the superconducting conductor 3 during power transfer can be substantially reduced. It can be made zero. Also,
Since the switch 2 is opened when the current flowing through the superconducting conductor 3 becomes small, contact abnormality does not occur when the switch 2 is opened.

Next, the case where an abnormality occurs in the superconducting coil 5 and the stored energy needs to be rapidly released will be explained separately in the case of energy storage and transfer, and the reflux mode in which energy is stored.

a) When it becomes necessary to protect the superconducting coil 5 during energy storage and transfer, all of the thyristors constituting the converter 1a are placed in a gate-blocked state. At this time, switch 2 is in the open state, so
The current flowing through the superconducting coil 5 flows into the resistor 4, and the energy that has been stored up until now is consumed by this resistor 4.

b) During reflux mode In this state, the switch control means 8 closes the switch 2, and when it becomes necessary to protect the superconducting coil 5, the superconducting conductor 3 is brought into a normal conduction state, and the switch control means 8 closes the switch 2. Means 8 then open switch 2.

In this way, since the AC/DC converter 1 is in an inactive state, the current I in the reflux mode. flows into resistor 4, where energy is consumed.

Through the above operations, the superconducting coil 5 can be protected. Furthermore, although a direct current of several hundred [KA] flows through the switch 2, it is turned on and off when the superconducting conductor 3 is in a normal conduction state, so a switch with a rated capacity of only about 100 [A] is sufficient. , is fully achievable given the current technology.

In the above embodiment, since the resistor 4 was directly connected to the DC terminal of the AC/DC converter 1, energy storage and
There is power loss during transfer. FIG. 2 shows an embodiment for eliminating this power loss, in which a thyrisk switch 6 is inserted in series with the resistor 4, and the switch 2 is turned on and off by the switch control means 9 in the same manner as described above. In addition, the cyrisk switch 6 is used only when protecting the superconducting coil 5.
Turn on. Furthermore, even if current flows through this thyrisk switch 6, it only flows for a very short time, so
Even if a configuration in which many thyristors are connected in parallel is adopted, there is no need to worry about current imbalance.

Furthermore, in all of the above embodiments, the switch 2 is turned on and off by a switch control means in conjunction with a superconducting cooling system (not shown), but if energy storage and transfer are not frequent, this may be manually operated. You may.

Furthermore, although a mechanical switch is used as the switch 2 in the above embodiment, a non-contact switch may be used instead.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a switch is provided that is connected in series with the superconducting conductor, and the switch is turned on immediately before the superconducting conductor is transferred from the normal conducting state to the superconducting state. Since this switch is turned off immediately after transitioning from the superconducting state to the normal conducting state, it is possible to significantly reduce power loss compared to conventional devices, and to obtain a superconducting energy storage system that is highly economical. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a circuit diagram showing the configuration of another embodiment, and FIGS. 3 and 4 are circuit diagrams each showing the configuration of a conventional superconducting energy storage system. 1...AC/DC converter, 2...switch, 3...
...Superconducting conductor, 4...Resistor, 5...Superconducting coil, 6.7...Sirisk switch, 8,9...Switch control means. Applicant's agent Mr. Sato

Claims (1)

[Claims] A superconducting coil and a superconducting conductor are connected in parallel between the DC terminals of an AC/DC power converter, and the superconducting conductor is placed in a normal conducting state when transmitting and receiving power to and from an AC system, and the superconducting conductor is placed in a superconducting state while storing energy. A superconducting energy storage system comprising a switch inserted in series with the superconducting conductor, and immediately before transitioning the superconducting conductor from a normal conductive state to a superconducting state, the switch is turned on, and the superconducting conductor is brought into a superconducting state. A superconducting energy storage system characterized in that the switch is turned off immediately after transitioning from a state to a normal conducting state.