JPH05300674A - Superconducting energy storage device and control method for superconducting energy storage device - Google Patents

Abstract

PURPOSE:To ensure the storage energy within specified range while controlling the requested effective and reactive power by the improvement of the stability of a power system and the control of it, in a superconducting energy storage device. CONSTITUTION:For an A/D converter 3, DC current control circuits are provided for the signal bridge by GTO, the reactive power control circuit 11-1, and the effective power control circuit 11-2, and it adds a DC current control command value to an effective power control command. A circuit 12 operates the circulation ratio D of the A/D converter 3 and the angle alpha of lag in control, based on the command value from each control circuit, and outputs it to a gate pulse generator 9. Hereby, the system control stabilized by the superconducting energy storage device becomes feasible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting energy storage device, and more particularly to power system stabilization control, that is, active power control for stabilizing system frequency and power fluctuation and reactive power control for stabilizing system voltage. The present invention relates to a superconducting energy storage device and a control method thereof, which simultaneously control the DC current of a superconducting coil to be constant during the execution period of.

[0002]

2. Description of the Related Art A superconducting energy storage device (hereinafter referred to as SM
Known as a technique for stabilizing an electric power system by means of (called ES) is one that simultaneously performs active power control and reactive power control. For example, Japanese Examined Patent Publication (Kokoku) No. 63-18425 (Reference Example 1) employs a double bridge system in which two stages of thyristor AC / DC converters are connected in cascade, and the control delay angle of each converter is changed independently to obtain an effective power. And to control the reactive power non-interfering. In addition, the PESC1988 paper “INSTANTANEOUS
CONTROL METHODWITH A GTO CONVERTER FORACTIVE AND R
EACTIVE POWERS IN SUPERCONDUCTING MAGNETIC ENERGY
"STORAGE" (reference example 2) describes a single bridge of a self-extinguishing thyristor that controls the control delay angle and the conduction ratio to control active power and reactive power independently and simultaneously. There is.

On the other hand, as a technique for preventing a decrease in stored energy of a superconducting coil, that is, a direct current, against AC loss due to a change in a coil current of SMES, energy loss of a cryostat due to an eddy current, etc. There is one described in Japanese Patent No. 294229 (Reference Example 3).
According to this, the control delay angle of the two thyristor converters is changed when the active power control of the power system is not executed, that is, while the system is healthy and only stores electric energy. Simultaneously and non-interferingly perform reactive power control and DC current constant control.

[0004]

The magnitude of the direct current of SMES indicates the controllable range of active power and reactive power, and its securing is indispensable for actual operation of grid stabilization by SMES. is there. However, the above-mentioned conventional technique has not been effectively proposed to reduce the direct current during the simultaneous control period of active power and reactive power. Further, the simultaneous control of the reactive power and the direct current shown in Reference Example 3 above is performed during the energy storage period when the power system is stable. If an accident occurs in the power system during this time, the active power and the reactive power are disabled. It is necessary to switch to simultaneous power control. However, it is actually difficult to obtain the timing of this switching from complicated power system conditions.

An object of the present invention is to overcome the above problems of the prior art, and to perform power system stabilization control (one of active power control and reactive power control or simultaneous control) while always performing superconducting coils. Another object of the present invention is to provide a control method for ensuring the DC current of the above in a predetermined range.

Another object of the present invention is to provide an SMES and a control method therefor capable of executing a combination of active power, reactive power and DC current control without switching.

Still another object is to provide a control method for limiting the range of DC current control to a value equal to or less than a steady DC attenuation amount and giving priority to active power control over DC current control.

Other objects of the present invention will be clarified through the following description.

[0009]

The present invention has been made paying attention to the fact that active power control and DC current control are equivalent, and that the former can be controlled by using an AC component and the latter can be controlled by using a DC component as a command.

According to the present invention, in a method of controlling a superconducting energy storage device for controlling active power of a power system, a command value for active power control is corrected according to a direct current flowing through the superconducting energy storage device to perform active power control. It is characterized in that direct current constant control is also performed. That is, the DC current control system controls the DC component Id of the DC current Id flowing through the superconducting coil. Appearance and outputs a DC current control command value I _R, based on the difference between the predetermined control command value Idr, while correcting active power control instruction value P _R by the command value I _R, a DC current control and active power control Independently and simultaneously.

According to the present invention, in a superconducting energy storage device comprising a superconducting coil and an AC / DC converter for controlling electric power between the superconducting coil and the electric power system, an active power control command value is set in accordance with a request command for stabilizing the electric power system. Active power control means for determining and reactive power control means for determining reactive power control command value, and direct current control means for correcting the active power control command value according to a deviation between a direct current flowing through the superconducting coil and a predetermined command value. And a control means for controlling the AC / DC converter based on the reactive power control command value and the corrected active power control command value.

Furthermore, the present invention is characterized in that a limiter for limiting the range of the control command value of the direct current control means is provided.

[0013]

According to the SMES of the present invention, the direct current flowing through the superconducting coil, the active power and the reactive power flowing into (storing) or flowing out (discharging) the SMES are taken in, and the command value given from the host controller or the like Necessary for controlling active power and reactive power required by the power system by controlling active power and reactive power required for power system stabilization control and controlling the DC current of the superconducting coil within a predetermined range. It is possible to secure a sufficient amount of stored energy.

The control command value I _R of the DC current control system is usually set in a range that compensates for a steady decrease in DC current due to SMES characteristics and the like, but this range is for stabilizing the system. It is possible to narrow the upper and lower limits to preferentially control the active power, or conversely, to widen the upper and lower limits to accelerate the charging of the SMES, and to change according to the operating mode of the SMES.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a superconducting energy storage device (SME
S) shows the overall configuration, and the main circuit is composed of a superconducting coil 1 for storing electric power from the electric power system 2, a G / O single bridge AC / DC exchanger 3 and a converter transformer 4;
It comprises a gate pulse generator 9 for generating a gate pulse to be applied to each GTO of the AC / DC converter 3, and a controller 10 for simultaneously controlling active power, reactive power and DC current.

The control unit 10 controls the reactive power (hereinafter referred to as Q
Control), active power control (hereinafter, P control) DC current control
(Hereinafter, Id control) control command value generation circuits 11-1 to 11
-3, and a PQI control circuit 12 for calculating the flow ratio D and the control delay angle α for simultaneously executing these three controls. The Q control command value generation circuit 11-1 takes in a reactive power command value Qr given from a higher-order control device such as a power system stabilizing device (not shown) and a reactive power detection value Q from the reactive power detector 6, and outputs the command value. And the detected value are matched with each other via the error correction function G1 (s), the Q control command value (Q _R )
Is output. P control command value (P _R ) generation circuit 11-2
Is the active power command value Pr from the upper level and the active power detector 7
Input the detected value P of P, and input P through the error correction function G2 (s).
The control command value (P _R ) is output. Id control command value (I _R)
The generation circuit 11-3 is a direct current value calculating means 1 for extracting a direct current component (average value of Id) from the direct current Id taken from the direct current detector 5 including the pulsating current component according to the active power command.
6 and its output value Id. And higher DC current command value I
A predetermined calculation G3 (s) is applied to the difference of d _r to output the Id control command value (I _R ). The limiter 17 will be described later. G4 (s) is the detection value V _ac of the AC voltage detector 8.
_Is a circuit for proportionally calculating the unloaded DC voltage E _d0 of the AC / DC exchanger 3.

Here, the Id relating to the basic principle of the present invention.
The DC value calculation means 16 of the control command value generation circuit 11-3 will be described in detail. The direct current value calculating means 16 includes the coil 1
DC component (Id.) From the current Id including the pulsating current flowing in
Has the function of extracting.

If the P control command value for power system stability improvement control is given by a sine wave containing a DC component, the superconducting coil can be regarded as an ideal inductance, so that the DC current Id has an initial value of I. Then, it is represented by Formula (1).

[0019]

[Equation 1]

Here, the second term of the above equation represents the change of Id due to the AC component of the active power control command value, and the third term represents the attenuation of Id due to the DC component. It should be noted that the direct current attenuation of item 3 is SM
A steady change due to the characteristics of ES is also included.

By the way, the Id control command value generation circuit 11-
3 is for compensating for the steady DC attenuation due to the SMES characteristic shown in the third term of the DC current Id and the attenuation due to the DC of the P control command value, but the AC variation of the second term. If it is compensated by including, the active power control command value is canceled and P control becomes impossible. Therefore, it is necessary to remove the change in Id due to the AC component in the second term.

The DC value calculating means 16 is provided for this purpose, has a filter function for removing the AC component of the second term, and has a first-order lag circuit having a time constant sufficiently long with respect to the fluctuation period T of the AC component. Composed by. Output Id of the DC value calculating means 16. Is a DC average value of the first term, the third term and the second term of the equation (1) (the second term component is small and can be ignored). The means 16 can be replaced by means having an equivalent function such as a secondary delay circuit or an integrating circuit. In addition, this DC value calculating means 16 is
Even if it is provided after the difference between the command value Id _r and the measured value Id is obtained, the same function can be exhibited.

FIG. 2 shows a detailed configuration of the PQId control circuit 12. The reactive power unit conversion circuit 13, the active power unit conversion circuit 14, and the DC current conversion circuit 15 which input and normalize each control command value. And an addition circuit 18 for adding the direct current command value to the active power command value, and an α-D calculation circuit 19 for calculating the flow ratio D and the control delay angle α using these converted values as inputs. The switches 22, 23, and 24 provided on the output side of each conversion circuit are used for a functional test by an arbitrary combination.

Next, the present embodiment S constructed as described above.
The operation of the MES will be described. Assuming that the control signal of the AC / DC converter 3 configured by the GTO thyristor / single bridge is the conduction ratio D and the control delay angle α, the active power P and the reactive power Q flowing into the SMES are expressed by equations (2) and (3). )
Can be represented by.

[0025]

[Equation 2]

[0026]

[Equation 3]

Here, Ed. Is a no-load DC voltage of the AC / DC converter 3. From the above equation, it can be seen that the active power P and the reactive power Q can be simultaneously controlled by controlling the flow ratio D and the control delay angle α. Note that this is described in detail in Reference Example 2 above.

FIG. 3 shows active power P, reactive power Q and GTO.
It is a conceptual diagram which shows the flow ratio D of the thyristor converter 3, and the relationship of control delay angle (alpha). The x-axis is the active power P and the y-axis is the reactive power Q. The area of this circle shows the maximum controllable range of active power and reactive power of the grid, and its radius is proportional to the direct current. In the figure, the diameter representing the instantaneous electric power flowing into (flowing out from) the SMES is represented by the conduction ratio D, and the control delay angle with respect to the x axis is represented by α. The right half of the y-axis is the energy storage (inflow) mode of the coil, and the left half is the energy release (outflow) mode.

Now, assuming that the conduction ratio is D ₁ and the control delay angle is α ₁ , the electric power flowing into the SMES becomes the point A, that is, the active power P ₁ and the reactive power Q ₁ . Here, if the control delay angle is controlled to 180 ° -α ₁ while the flow ratio is fixed at D ₁ , the power flowing into the SMES is point B, that is, the active power −
P ₁ and reactive power Q _{1 are set} , and energy is released. This is a control for stabilizing the frequency and power fluctuation of the system by changing only the active power without changing the reactive power value. Further, if the conduction ratio is D ₂ and the control delay angle is α ₂ , the power flowing into the SMES becomes point C, that is, active power P ₁ and reactive power Q ₂ , and the active power value remains unchanged. Only the reactive power can be changed by the new demand for grid voltage stabilization. By controlling the flow ratio D and the control delay angle α as described above, it is possible to simultaneously control the active power P and the reactive power Q by SMES for the system stability improvement control.

Next, the operation of the PQId control circuit 12 will be described. The active power P and the reactive power Q shown in the equations (2) and (3) are represented by the equations (4) and (5) when represented by the normalized unit conversion values P ₀ and Q ₀ , respectively.

[0031]

[Equation 4]

[0032]

[Equation 5]

Here, the reactive power control command value QR and the active power control command value PR are set to P = PR and Q = QR in FIG.
The normalized reactive power control command value Q ₀ and active power control command value P ₀ are calculated by the unit conversion circuits 13 and 14 of FIG.

From equations (2) to (5), the flow ratio D and the control delay angle α are expressed by the following equations.

[0035]

[Equation 6]

[0036]

[Equation 7]

The present invention is characterized in that the direct current control command value is added to the active power control command value. The relationship between the active power P and the current Id ₀ due to the direct current component is expressed by a mathematical expression.
It can be represented by (8).

[0038]

[Equation 8]

Here, Vd is the terminal voltage of the superconducting coil, and L is the inductance of the superconducting coil. (8)
Applying the equation to equation (4),

[0040]

[Equation 9]

It becomes Id ₀ ′ in the above equation is a DC current change rate, and a value corresponding to this is a control command based on the difference between the command values I _{d r} and I _{d 0} as shown in the DC current control command value generation circuit 11-3 in FIG. Given as the value I _R. When the command value Id _r is given as the rate of change, the output of the arithmetic circuit for Id ₀ is also obtained as the rate of change. The necessary conversion when both are given by the current value is G3 (s) of the circuit 11-3.
By. The direct current control command value I _R is converted by the conversion circuit 15 into PI ₀ equivalent to active power.

By the way, since this PI ₀ is added to the active power control system, the equations (6) and (7) can be rewritten as follows.

[0043]

[Equation 10]

[0044]

[Equation 11]

As described above, the DC current control command value I _R ,
Active power control instruction value P _R and reactive power control instruction value Q _R
Is given to the PQId control circuit 12, the conversion circuit 13
The conversion command values Q ₀ , P ₀ , and PI ₀ are obtained from ˜15. Using the Q ₀ and the output (P ₀ + PI ₀ ) of the adder circuit 18 as inputs, the equations (10) and (11) are calculated by the conduction ratio calculator 20 and the control delay angle calculator 21 of the α-D calculator 19. Then, the flow ratio D and the control delay angle α are obtained. Therefore, using the command values Q ₀ , P ₀ , and PI ₀ of the equations (10) and (11) as independent variables, the flow ratio D of the AC / DC converter 3 and the control delay angle are
It can be controlled arbitrarily in all operating modes of SMES.

In the above example, the DC current command value Id _r is used as the SMES command value, but the stored energy amount E and the DC current Id have the following relationship.

[0047]

[Equation 12]

Therefore, the command value based on the stored energy amount E may be used instead of Id _r .

FIG. 4 illustrates the relationship between the active power and the direct current controlled as described above, and shows the operation when a sinusoidal command value is given as the active power control command value. When the direct current control command value is not added to the active power control system, the direct current Id (that is, the energy accumulated in the coil) is reduced due to the loss of the AC / DC converter, and the active power control capability is reduced. The range of change in active power P decreases as indicated by the broken line.

On the other hand, when the DC current control command value PI ₀ is added to the active power control command value P ₀ as in this embodiment, the DC current Id can be kept constant as shown by the solid line. As shown by the solid line, the range of change in active power is constant.
However, since the DC current control command value is added to the active power control system, the DC current and active power cannot be controlled internally independently. Therefore, in order to keep the direct current constant, active power is supplied to the SMES from the power grid. PL _{0 in} FIG. 4 corresponds to the addition to the active power control system by the DC current control command value. However, this PL ₀ usually corresponds to the loss due to the superconducting coil, the AC / DC converter, etc., and is very small compared to the active power control command value, so that it does not hinder active power control in actual operation.

As described above, according to this embodiment, the active power control, the reactive power control, and the direct current control are performed according to the above (1
By controlling the command values Q ₀ , P ₀ , PI ₀ in the equations (0) and (11), all operating modes of the SMES, that is, individual control of each control, two combinations of each control and three combinations of each control are performed. Can be performed without switching. In particular, by simultaneously controlling active power and reactive power and correcting the active power control command value by the DC current control system, it is possible to further improve the stabilization control of the system and maintain its controllable range. ..

Next, the function of the limiter 17 shown in FIG. 1 will be described. The limiter 17 is constituted by a well-known means for limiting the input signal within the set upper and lower limit values and outputting it. The range of the upper and lower limit values can be changed in advance or according to an instruction from another person during operation. As a result, the input DC current control command value I _R is automatically adjusted below the set upper and lower limit values.

By the way, if the DC current control command value I _R is changed significantly during active power control for system stabilization,
This reduces the function of active power control. Normally, the active power command value required for stabilization control of the power system is any sine wave signal with a period of 1 second, and the steady DC current attenuation of the SMES during this period is small, and the active power command value is small. The effect on control is only a few percent at best. Therefore, by setting the upper and lower limit values of the limiter to the maximum value such as the steady attenuation of SMES, priority control of active power control is secured, and the demand for system stabilization can be promptly addressed.

On the other hand, when controlling the superconducting coil irrespective of system stabilization such as during initial charging, the upper and lower limit values of the limiter 17 are widened to set the direct current control command value PI. By increasing, the speed of DC current accumulation can be increased. Also,
Even when energy is frequently released due to system stabilization, I _R can be increased in a required range to accelerate accumulation and energy in a control range required for system stabilization can be secured.

The SMES AC / DC converter 3 in the above embodiment is a single bridge using a GTO thyristor. However, the present invention is not limited to this configuration. That is, even in the case of the bridge of the SI thyristor, it can be realized by adding the direct current control means according to the present invention for correcting the command value of the active power control system. Note that the non-interference simultaneous control of the corrected active power control and the reactive power control can be performed by the SI thyristor as in Reference Example 1 described above.

Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, the control device 10 shown in FIGS. 1 and 2 is realized by a computer device for digital arithmetic processing.

FIG. 5 shows the configuration of the control device 10 including a central processing unit (CPU) 28, pulse generating means 25, storage means 26, input means 27, and output means 29. CPU
The processing of 28 is started by the pulse signal a which is periodically generated by the pulse generating means 25, and the arithmetic processing is performed according to the program stored in the storage means 26 in advance. First, the active power P, the reactive power Q, the AC voltage V _ac , and the DC current Id are input from the respective detectors via the input means 27, and the active power command value Pr, the reactive power command value Qr, and the DC current command value I are also included.
Incorporating d _r from the upper controller of the power system stabilization control,
A calculation process is performed while indexing a table stored in advance in the storage means 26, and the flow ratio D and the control delay angle α obtained as the calculation result are output to the gate pulse generator 9 via the output circuit 29.

As shown in FIG. 6, the repetition period T of the pulse signal a of the pulse generating means 25 is sufficiently larger than the arithmetic processing time τ of the CPU 28 and is a value capable of compensating for the above-mentioned steady attenuation of SMES. Be taken. In addition, CPU
The arithmetic processing of 28 may be activated by an event from the host controller, and may be calculated as needed for power system stabilization control.

FIG. 7 shows a series of processing flows performed by the CPU 28 in each cycle T. After the data is fetched in step 30, in steps 31 to 33, the reactive power control command value Q ₀ and the active power control command value are set. P ₀ and the direct current control command value PI ₀ are calculated, and in step 34 the flow ratio D and the control delay angle α are calculated.

Also in this embodiment, while simultaneously controlling active power and reactive power, active power control is corrected by a direct current control command value, and direct current is controlled within a predetermined range. Can be achieved.

[0061]

According to the energy storage device of the present invention,
A GTO single bridge AC / DC converter, active power control means, reactive power control means, and DC current control means are provided, and it is possible to provide an SMES capable of operating these respective controls independently or in combination. According to this, it is possible to combine arbitrary controls according to the operation mode of the SMES and the demands of the system without having a switching means which is difficult to realize in the past, and the device configuration becomes simple.

According to the control system of the energy storage device of the present invention, the direct current control for maintaining the current of the superconducting coil within the predetermined range is performed even during the control period of the active power and the reactive power required by the power system stability improvement control. It can be executed at the same time, the stored energy required for active power and reactive power control can be secured, and the actual operation of system stabilization improvement control using SMES becomes possible.

According to the control system of the energy storage device of the present invention, since the limiter is provided at the output of the DC current control system, the influence of the DC current control on the active power control is reduced, and the power system stability improvement control is performed. It is possible to give priority to active power control required by the. Furthermore, the limit value of the limiter can be varied to adjust the speed of increase or decrease of DC current, and to provide optimum control at the initial startup of SMES or when energy is frequently released due to grid stabilization. You can

[Brief description of drawings]

FIG. 1 shows a first embodiment of the present invention, in which the AC / DC converter is
The whole block diagram of the superconducting energy storage device when adopting a TO thyristor single bridge.

FIG. 2 is a functional block diagram showing the configuration of a PQId control circuit in the control device of FIG.

FIG. 3 is a conceptual diagram illustrating an operation of PQ control of the superconducting energy storage device.

FIG. 4 is an operation explanatory view for explaining the operation of DC control according to the present invention.

FIG. 5 is a functional block diagram showing a configuration of a control device of the superconducting energy storage device according to the second embodiment of the present invention.

FIG. 6 is a time chart explaining the operation of the control device of FIG.

FIG. 7 is a flowchart illustrating processing steps of the control device in FIG.

[Explanation of symbols]

1 ... Superconducting coil, 2 ... Power system, 3 ... AC / DC converter, 4
... Transformer for transformer, 5 ... DC current detector, 6 ... Reactive power detector, 7 ... Active power detector, 8 ... AC voltage detector, 9
... Gate pulse generator, 10 ... Control device, 11-1 ... Reactive power control circuit, 11-2 Active power control circuit, 11-
3 DC current control circuit, 12 ... PQId control circuit, 13-
15 ... Conversion value circuit, 16 ... DC value computing means, 17 ... Limiter, 18 ... Addition circuit, 19 ... α-D computing circuit, 20 ...
Commutation ratio calculation means, 21 ... α calculation means, 25 ... Pulse generation means, 26 ... Storage means, 27 ... Input means, 28 ... Digital calculation processing means (CPU), 29 ... Output means.

Claims (15)

[Claims] 1. A superconducting energy storage device comprising a superconducting coil and an AC / DC converter for controlling electric power between the superconducting coil and the electric power system, wherein an active power control command value is determined according to a request command for stabilizing the electric power system. Active power control means, having a direct current control means for correcting the active power control command value according to the deviation of the direct current flowing through the superconducting coil and a predetermined command value, based on the corrected active power control command value A superconducting energy storage device comprising a control means for controlling the AC / DC converter. 2. A superconducting energy storage device comprising a superconducting coil and an AC / DC converter for controlling electric power between the superconducting coil and the electric power system, wherein an active power control command value is determined in accordance with a request command for stabilizing the electric power system. There are active power control means and reactive power control means for determining a reactive power control command value, and direct current control means for correcting the active power control command value according to a deviation between a direct current flowing through the superconducting coil and a predetermined command value. However, the superconducting energy storage device is provided with control means for controlling the AC-DC converter based on the reactive power control command value and the corrected active power control command value. 3. The superconducting energy storage device according to claim 1, wherein the AC / DC converter is configured by a double bridge using a thyristor. 4. A superconducting energy storage device comprising a superconducting coil, an AC / DC converter for controlling electric power between the superconducting coil and the power system, and a controller for controlling a flow ratio and a control delay angle of the AC / DC converter, The control device, active power control means for determining an active power control command value according to a power system stabilization request command, and the active power control command according to a deviation between a direct current flowing through the superconducting coil and a predetermined command value. A superconducting energy storage device comprising: a direct current control means for determining a correction value for correcting the value; and a calculation means for calculating the flow ratio and the control delay angle based on the corrected active power control command value. 5. A superconducting energy storage device comprising a superconducting coil, an AC / DC converter for controlling electric power between the superconducting coil and the power system, and a controller for controlling the flow ratio and the control delay angle of the AC / DC converter. The control device includes an active power control unit that determines an active power control command value and a reactive power control unit that determines a reactive power control command value according to a power system stabilization request command, a DC current flowing through a superconducting coil, and a predetermined value. DC current control means for determining a correction value for correcting the active power control command value according to the deviation of the command value, and the flow ratio and control by the reactive power control command value and the corrected active power control command value. A superconducting energy storage device, characterized in that a calculation means for calculating a delay angle is provided. 6. The superconducting energy storage device according to claim 4, wherein the AC / DC converter is configured by a single bridge using a self-extinguishing thyristor. 7. The superconducting energy storage device according to claim 1, wherein the DC control means has a limiter for limiting an upper limit and / or a lower limit of the correction value. 8. The superconducting energy storage device according to claim 7, wherein the limiter limits the steady-state DC attenuation of the superconducting energy storage device so as to compensate for the steady DC attenuation. 9. A method of controlling a superconducting energy storage device for controlling active power of a power system, comprising: correcting a command value of the active power control in accordance with a direct current flowing through the superconducting energy storage device; A method for controlling a superconducting energy storage device, which is characterized in that current constant control is also performed. 10. A control method of a superconducting energy storage device for simultaneously processing active power control and reactive power control to perform power system stabilization control, wherein a command value for the active power control is a direct current flowing through the superconducting energy storage device. A method for controlling a superconducting energy storage device, characterized in that the power system stabilization control and the direct current constant control are performed together by making a correction according to the above. 11. The constant DC current control is performed by controlling a conduction ratio and a control delay angle of an AC / DC converter that controls electric power between the superconducting coil and the electric power system. The method for controlling a superconducting energy storage device according to claim 10. 12. The active power control command value is corrected based on a deviation between a DC component of a DC current flowing through the superconducting coil and a predetermined DC current command value. The method for controlling the superconducting energy storage device according to claim 11. 13. The method of controlling a superconducting energy storage device according to claim 12, wherein the predetermined DC current command value is set according to a steady DC attenuation of the superconducting energy storage device. 14. The predetermined DC current command value is set to a value larger than the steady DC attenuation amount, and the superconducting energy storage device is controlled so as to increase the charging speed. Method for controlling superconducting energy storage device of the above. 15. The superconducting energy according to claim 12, wherein the predetermined direct current command value is limited to a predetermined value or less, and the active power control is controlled prior to the direct current constant control. Storage device control method.