GB2030389A

GB2030389A - Superconduction energy storage and transfer

Info

Publication number: GB2030389A
Application number: GB7931191A
Authority: GB
Original assignee: National Laboratory for High Energy Physics
Current assignee: National Laboratory for High Energy Physics
Priority date: 1978-09-14
Filing date: 1979-09-07
Publication date: 1980-04-02
Also published as: DE2936943A1; FR2436524A1; DE2936943C2; GB2030389B; JPS569867B2; FR2436524B1; JPS5541149A

Abstract

For storing and transferring superconduction energy, a DC-AC-DC thyristor transducer 6 is provided between a superconduction energy storage coil 1 and a load 2 which may also be a superconduction coil. Gate control circuits 7, 8 control the frequency of an intermediate AC output of the transducer. Safe and efficient storage and transfer of energy are realized by controlling the frequency in order to provide stable operation of the thyristors and adjustment of the DC output level. <IMAGE>

Description

SPECIFICATION Su perco nduction energy storage and transfer This invention relates to a thyristor transducing device used to store and transfer superconduction energy and to a method of using such a transducing device. More particularly, the invention concerns a thyristor transducing device suitable for transferring superconduction energy stored in the DC state to a load coil in the superconduction state or a like load consuming energy in the DC state.

A coil in the superconduction state (hereinafter referred to as a superconduction coil) usually has a resistance R nearly equal to zero, so that the time constant L/R of this superconduction coil is very large, and current circulated through this superconduction coil can be maintained without substantial attenuation.

Besides, since the superconduction coil is able the store the maximum superconduction energy of (1/2) Ll2 (I being current), it is industrially promising as a coil capable of storing surplus power in place of pumping power generation and storing pulse power of large-size accelerators.

To take out the stored superconduction energy and transfer it to a DC load, a superconduction energy transfer means is required between the superconduction energy storing means and the DC load.

The DC load may, for instance, be a superconduction coil in the case where a magnet or coil of an accelerator or of a TOKAMAK nuclear fusion reactor is manufactured as such a coil. To transfer superconduction energy to the load coil in the superconduction state, such as the aforementioned magnet or coil, a specific transducer is required.

Such specific transducer may, for instance, be a self-exciting DC-AC-DC thyristor transducer, in which the input and output are DC and an intermediate output is AC.

However, such DC-AC-DC thyristor transducers are liable to present such problems as commutation or firing failure.

More particularly, in a DC-AC-DC thyristor transducer the intermediate AC output voltage level varies in dependence upon the input DC current value. Therefore, if the operation frequency of the inverter (i.e., DC-AC thyristor transducer) constituting the first stage of the DC-AC-DC thyristor transducer is constant, the AC voltage value is reduced with a reduction of the input DC current, this making it impossible to cause commutation and firing of the thyristors of the second stage converter (i.e. AC-DC thyristor transducer).

In such a case, operational failure of the converter results.

The invention aims to solve the above problems and to provide a superconduction energy storage and transfer device, which is capable of making full use of superconduction energy.

Accordingly, the invention provides a superconduction energy storage and transfer transducing device, in which a DC-AC-DC thyristor transducer is provided between a superconduction energy storage coil and a load, said DC--AC---DC thyristor transducer having a frequency control circuit capable of controlling the frequency of an intermediate AC output of said DC-AC-DC thyristortransducer.

The invention also provides a method of using a superconduction energy storage and transfer transducing device, in which the frequency of an intermediate AC voltage output of a DC-AC-DC thyristortransducer provided between a superconduction energy storage coil and a load is controlled to regulate said AC voltage output to be within a range capable of maintaining the stable operation of the thyristors in said DC-AC-DC thyristor transducer.

The invention further provides a method of using a superconduction storage and transportation transducing device, in which the frequency of an intermediate AC voltage output of a DC-AC-DC thyristor transducer provided between a superconduction energy storage coil and a load is controlled to control the final DC output of said DC-AC-DC thyristor transducer.

In order that the invention may be readily understood, an embodiment of an energy storage and transfer device according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a circuit diagram of the device; and FIGURE 2 is a graph showing the intermediate AC voltage output of the device.

As shown in Figure 1, a superconduction coil 1 capable of storing superconduction energy is coupled to a DC load coil 2 in the superconduction state via a self-exciting DC-AC-DC thyristor transducer 6 comprising two thyristor bridges 3 and 4 and commutation capacitors 5 connected in a delta confuguration.

The input and final output of the DC-AC-DC thyristor transducer 6 are DC, and an intermediate output of the transducer is AC, as implied by the name of the transducer.

The intermediate output is a three-phase AC output, the respective phases of which are produced between the opposite terminals of the respective commutation capacitors 5. The waveform of one of the three phases of this AC output is shown in Figure 2.

Gate control circuits 7 and 8 acting as frequency control circuits are connected to the gate terminals of the thyristors constituting the respective thyristor bridges 3 and 4 of the DC-AC-DC thyristor transducer 6. These gate control circuits 7 and 8 can fire the individual thyristors of the respective bridges by supplying successive trigger signals to the gate terminals of the individual thyristors at a suitable period when the input to the thyristor bridges 3 and 4 are DC.

Thus, it is possible to transduce an DC input to each bridge to an AC output, and also the frequency of the AC output can be controlled by varying the trigger signal period.

Such gate control circuits 7 and 8 may be constituted for instance, by a circuit using a ring counter and capable of producing successive trigger signals at a desired period.

The gate control circuits 7 and 8 also function as phase angle control circuits, that is, they permit the thyristor firing timing to be freely varied by varying the phase angle a when the inputs to the thyristor bridges 3 and 4 are AC. Thus, it is possible to transduce an AC input to each bridge to a DC output and also obtain continuous control of the DC output value.

Such a phase angle control circuit may be formed, for instance, by a circuit using uni-junction transistors for suitably controlling the phase angle .

It will be understood that, when the thyristor bridges 3 and 4 are used as an inverter, the gate control cicuits 7 and 8 are used as a frequency control circuit. When the thyristor bridges 3 and 4 are used as a converter the gate control circuits 7 and 8 are operated as a phase angle control circuit.

The peak voltage Vcp across the commutation capacitors 5 is given as lo Vcp = 4fc (1) where f is the operating frequency of the inverter, C is the capacitance of the capacitors 5 and 1o is the input current.

Now, stored energy in an accelerator or TOKAMAK nuclear fusion reactor will be discussed by using specific numerical values. It is assumed that the stored energy is set to 1 09 to 1010 J and that the input current 10 is set to 10 KA.

At this time, with the optimum thyristor voltage set to 1.5 kV and the inverter operation frequency f to 50 Hz, the capacitance C of the capacitors 5 is calculated from equation (1) to be about 3.3 x 104us.

While it is necessary to use capacitors of very high capacitance as the commutation capacitors 5 underthe above conditions, increasing the operating frequency ften-fold to 500 Hz means that the capacitance of the capacitors 5 used can be reduced to one-tenth of the above calculated capacitance value.

In the case of operation with the stored energy substantially discharged and the input current 10 reduced to about 1 OOA, the voltage Vcp is reduced to 1 5 V. With such voltage it is difficult to obtain reliable commutation and firing of large-size hightension-bearing thyristors. However, by reducing the operation frequency f down to 50 Hz again the voltage Vcp is increased to 1 50 V so that it becomes possible to obtain safe commutation and firing of the thyristors.

By suitably controlling the operation frequency f in the above way it is possible to adjust the voltage value Vcp of the intermediate AC voltage output to be in a range, within which the steady and stable operation of the thyristors in the DC-AC-DC thyristortransducer 6 can be maintained (in the instant case 1,500 to 1 50 V).

The above numerical example is given to show the upper and lower limits of the thyristor rating.

In practice, the inverter operating frequency f is controlled to regulate the aforementioned AC voltage output so that it has a substantially constant value of 500 to 700 V.

When discharging stored energy from the superconduction coil 1 using the aforementioned device embodying the invention, the first stage thyristor bridge 3 is operated as an inverter by operating the gate control circuit 7 as a frequency control circuit. Further, by controlling the period of the trigger signals supplied to the gate terminals of the thyristors the peak voltage Vcp across the commutation capacitors 5 can be controlled to be within a suitable range as mentioned earlier, this permitting stable operation of the second stage thyristor bridge 4 which is operated as a converter. As a result, with the control circuit 8 operated as phase angle control circuit, a desired DC output is supplied from the output terminals of the thyristor bridge 4 to the load coil 2 to cause excitation of the load coil 2 for charging.

When storing energy in the superconduction coil 1 , the above operation is reversed. More particularly, the thyristor bridge 4 is operated as an inverter by operating the gate control circuit 8 as a frequency control circuit, and the thyristor bridge 3 is operated as converter by operating the gate control circuit 7 as a phase angle control circuit.

It will be appreciated that the invention enables the stable operation of the second stage converter to be maintained, without any need to increase the size of the commutation capacitors 5, through control of the frequency of the intermediate AC voltage output of the DC-AC-DC thyristor transducer 6.

When the thyristor bridge 3 or 4 are used as a converter it is in practice to obtain the desired DC output through phase angle control as mentioned earlier.

However, it is also possible continuously to vary the DC output of the DC-AC-DC thyristor transducer 6 through adjustment of the peak capacitor terminal voltage Vcp in equation (1).

Accordingly, to charge the load coil 2 through adjustment of the DC output of the DC-AC-DC thyristor transducer 6 by another method of using the device of the invention, the first stage thyristor bridge 3 is operated as inverter, and the peak voltage Vcp across the capacitors 5 is suitably adjusted within a range, within which the stable operation of the thyristors constituting the second stage converter can be maintained, by varying the period of the trigger signals from the gate control circuit 7. In this way. the desired DC output is supplied from the output terminals of the second state thyristor bridge 4 operated as a converter to the load coil 2, thus permitting charging of the load coil 2 with a desired quantity of energy by excitation.

Further, when storing energy in the superconduction coil 1, the above operation may be reversed so as suitably to adjust the charge of energy. More particularly, the thyristor bridge 4 may be operated as an inverter, while the thyristor bridge 3 is operated as a converter.

It will be appreciated that, with the aforementioned other method according to the invention, the DC output of the DC-AC-DC thyristor transducer 6 can be controlled to a desired value through control of the frequency of the intermediate AC voltage output of the DC-AC-DC thyristortransducer 6, thus permitting free control of the extent of charging of the load coil 2 orsuperconduction coil 1.

The said other method according to the invention may also be carried out together with phase angle control, and in this case the reliability of the system can be widely improved.

Exemplary ratings of individual component elements in the case where a transducer embodying the invention is applied to a 100 KJ energy storage system are as follows: the coil size of the storage coil 1 and load coil 2 is 200 mm in diameter by 200 mm; the coil current is 1,000 A; the coil wire material is Nb-Ti; the coil inductance is 0.22 H and the coil energy capacity is 1 00 kJ; the voltage and current values of the thyristor elements are respectively 1,000 V and 500 A; and the voltage and capacitance of the commutation capacitors 5 are respectively 300 V and 600 ,uF.

It will be seen from this example that the capacitance of the commutation capacitors 5 can be considerably reduced compared to known devices.

In the embodiment illustrated in Figure 1, the commutation capacitors 5 are connected in a delta configuration. They could however equally be connected in a star configuration.

Furthermore, the intermediate AC output is not limited to a three phase output.

As has been described in the foregoing, since a superconduction energy storage and transfer device embodying the invention is constructed so as to permit control of the frequency of the intermediate AC output of the DC-AC-DC thyristor transducer, the DC input DC output system can be smoothly operated, and also it is possible to obtain very efficient and safe energy transfer between the superconduction energy storage coil and superconduction load coil.

In addition, since by the method of using the transducing device embodying the invention the intermediate AC output voltage of the DC-AC-DC thyristor transducer is controlled to be in a range, within which the stable operation of the thyristors of the DC-AC-DC thyristor transducer can be maintained, through control of the frequency of the AC output voltage, it is possible to obtain stable operation of the converter constituting the second stage of the DC-AC-DC thyristor transducer.

Further, since by the other described method of using the transducing device embodying the invention the DC output as the final output of the DC-AC-DC thyristor transducer is controlled through control of the frequency of the intermediate AC voltage output of the DC-AC-DC thyristor transducer, it is possible to control the DC output without phase angle control and thus obtain the output control in the first state inverter. Also, this other method can be carried out together with the phase angle control, and in this case it is possible to obtain wide improvement of the reliability of the system.

Claims

1. A superconduction energy storage and transfer transducing device in which a DC-AC-DC thyristor transducer is provided between the superconduction energy storage coil and a load, said DC-AC-DC thyristortransducer having a frequency control circuit capable of controlling the frequency of an intermediate AC output of said DC-AC-DC thyristor transducer.

2. A method of using a superconduction energy storage and transfer transducing device in which the frequency of an intermediate AC voltage output of a DC-AC-DC thyristor transducer provided between a superconduction energy storage coil and a load is controlled to regulate said AC voltage output to be within a range capable of maintaining the stable operation of the thyristors in said DC-AC-DC thyristor transducer.

3. A method of using a superconduction storage and transportation transducing device, in which the frequency of an intermediate AC voltage output of a DC-AC-DC thyristor transducer provided between a superconduction energy storage coil and a load is controlled to control the final DC output of said DC-AC-DC thyristor transducer.

4. A superconduction energy storage and transfer transducer device according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.

5. A method of using a superconduction energy storage and transfer transducing device according to claim 2 and substantially as hereinbefore described with reference to the accompanying drawing.

6. A method of using a superconduction energy storage and transfer transducing device according to claim 3 and substantially as hereinbefore described with reference to the accompanying drawing.

7. Any novel feature or combination of features herein described.