JP2012125019A - Stabilizer for power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stabilizer for a power system capable of supplying active power and absorbing reactive power at low loss, allowing easy maintenance.SOLUTION: A stabilizer 10 for a power system to be connected to a power system for suppressing and stabilizing a fluctuation of the power system comprises: an electric double-layer capacitor 13 to be used as a power storage device; a power converter 14 to be connected to the electric double-layer capacitor for converting a DC to an AC and an AC to a DC: and a control means 12 for controlling the power converter. The control means comprises: a calculation part 12a to calculate a target value for controlling active/reactive power, which calculates a target value for controlling active power and a target value for controlling reactive power according to a state quantity of the power system; and a calculation part 12b to calculate a command value for amplitude/phase difference, which calculates a command value of amplitude of an output voltage being output from the electric power converter and a command value of phase difference between the power system voltage and an output voltage being output from the power converter, according to the target value for controlling active power and the target value for controlling reactive power both of which are calculated by the calculation part to calculate a target value for controlling active/reactive power.

Description

  The present invention relates to a power system stabilization device, and more particularly to a power system stabilization device that stabilizes a power system by suppressing fluctuations in the power system caused by an accident or the like.

  In recent power systems, long-distance heavy tidal power transmission lines tend to increase as power sources become remote and unevenly distributed due to difficulties in power location and demand is concentrated in urban areas. The longer the distance of the transmission line and the heavy tidal current, the more difficult it is to stabilize the power system, and the need for countermeasures is increasing.

  In order to stabilize the electric power system, it is effective to reinforce the electric power system such as a new transmission line, but a huge investment is required for the construction of the transmission line. The installation of a power system stabilization device that is relatively inexpensive and can be installed in a relatively short period of time is considered as the next best measure compared to the construction of transmission lines.

  When the energy balance of the power system is lost due to various factors such as a power system accident, the power system generator is accelerated or decelerated and the power system is shaken. In order to suppress this fluctuation and stabilize the power system, it is effective to reduce the energy imbalance of the power system. Energy imbalance in the power system can be reduced by performing effective power compensation through appropriate supply and absorption of active power according to fluctuations in the power system. In addition, reactive power compensation by appropriately supplying and absorbing reactive power is performed to maintain the voltage of the power system, thereby controlling the flow of energy in the power system and improving the energy balance of the power system.

  As shown above, there are active power compensation and reactive power compensation as methods for stabilizing the power system, but the effect of active power compensation that directly eliminates the energy imbalance that causes the power system oscillation is generally effective. It is said to be expensive.

  As devices capable of compensating active power and reactive power, superconducting power storage devices (SMES), flywheel generators, and the like have been proposed. As a device capable of only reactive power compensation, there is a reactive power compensation device such as a self-excited reactive power compensation device (STATCOM) or a static reactive power compensation device (SVC) as disclosed in Patent Document 1. Of these, SMES, flywheel generator, and STATCOM each convert energy stored in superconducting coils, flywheels, and electrolytic capacitors, which are power storage devices, into arbitrary AC power using a power converter, etc. Power compensation or reactive power compensation is performed.

  Although the purpose of the power system stabilizer is different from that of the power system stabilization device, when the power system voltage drops in the event of a power system failure, the load is immediately connected to the power system after the accident is detected in order to avoid the impact on the load due to the voltage drop. In the voltage sag compensator intended to supply power at an appropriate voltage, as disclosed in Patent Document 2, an electric double layer capacitor is applied to the power storage device, which is effective for several seconds. Electric power can be supplied. However, in this instantaneous voltage drop countermeasure device, it is difficult to supply a large amount of active power necessary for stabilizing the power system.

JP 2003-61249 A JP 2009-27844 A

  The SMES / flywheel generator capable of active power compensation has a problem that the loss of the power storage device is large and the maintenance burden is large. In other words, SMES maintains a cryogenic state of the superconducting coil that is the power storage device, and cooling loss occurs. Since the flyhole generator is a rotating machine, bearing loss occurs, and the overall efficiency of each device is about 80 to 90%. In addition, SMES is an auxiliary machine that maintains its cryogenic state, and a flywheel generator has a heavy maintenance burden, such as periodic maintenance of the rotating parts that wear out. Because of these problems, the SMES / flywheel generator has no practical application as a power system stabilizing device.

  Furthermore, STATCOM as disclosed in Patent Document 1 uses an electrolytic capacitor as a power storage device, maintains a cryogenic state like SMES, maintenance of a cooling device for that purpose, and a movable part such as a flywheel generator Therefore, it is easier to maintain than the above active power compensator, and in the capacitor, which is a power storage device, there is almost no loss during standby after charging. Since loss can be kept low, it is widely applied to power systems. However, STATCOM, on the other hand, has a high stabilization effect because it cannot supply and absorb active power in the same 1-2 second period as the power system oscillation period because the energy density of the electrolytic capacitor, which is a power storage device, is low. There was a problem that active power compensation was not possible.

  In view of the above problems, an object of the present invention is to provide a power system stabilizing device capable of supplying and absorbing active power and reactive power. That is, the power system stabilizing device of the present invention detects a system fault from information that suddenly changes at the time of an accident such as a bus voltage and a line power flow by the system fault detection unit immediately after the accident detection, and forcibly sets the control target value to the maximum absorption amount. By compulsorily controlling so that the active power becomes effective, the active power having a high power system stabilizing effect can be compensated.

The power system stabilizing device according to the present invention is configured as follows to achieve the above object.
A first power system stabilizing device (corresponding to claim 1) is a power system stabilizing device that is connected to the power system and suppresses fluctuations of the power system to stabilize the power system. A multi-layer capacitor; a power converter connected to the electric double layer capacitor and converting direct current to alternating current; alternating current to direct current; and control means for controlling the power conversion apparatus, the control means comprising the power system An active / reactive power control target value calculation unit that calculates an active power control target value and a reactive power control target value based on a state quantity of the active power control, and the active power control calculated by the active / reactive power control target value calculation unit Based on the target value and the reactive power control target value, an amplitude / phase difference command value calculation unit that calculates a command value of the phase difference between the amplitude of the output voltage output from the power converter and the power system voltage is provided. It is characterized in.
In the above configuration, the second power system stabilizing device (corresponding to claim 2) is preferably configured such that the state quantity of the power system is a bus frequency or a generator speed as the active power control input signal. A bus voltage as the reactive power control input signal.
In the above configuration, the third power system stabilizing device (corresponding to claim 3) is preferably configured such that the active / reactive power control target value calculation unit includes a system fault detection unit that detects a system fault, and the bus A frequency fluctuation detecting unit that detects a frequency fluctuation based on a frequency or a generator speed; an active power control target value calculating unit that calculates an active power control target value based on the frequency fluctuation detected from the frequency fluctuation detecting unit; An accident / normal control switching unit that switches between an accident control and a normal control is provided, and the accident / normal control switching unit compulsorily absorbs the active power control target value at the time of the accident. The control is switched so as to calculate the quantity.
In the above configuration, the fourth power system stabilizing device (corresponding to claim 4) is preferably configured such that the accident / normal-time control switching unit starts the deceleration by the generator during the accident control. It is characterized in that it is terminated before and switched to normal control.

  According to the present invention, by using an electric double layer capacitor as a power storage device, it is possible to supply and absorb active power and reactive power, and there is less loss than existing active / reactive power compensation devices, and maintenance is easy. Thus, a practical power system stabilizing device can be provided.

It is a block diagram which shows the structure of the electric power system stabilization apparatus which concerns on embodiment of this invention. It is a block diagram which shows the active / reactive power control target value calculating part shown in FIG. It is a figure which shows the principle of control with the control apparatus shown in FIG. FIG. 2 is an equivalent circuit diagram of the power system stabilizing device shown in FIG. 1. It is a figure explaining the forced control at the time of an accident in the electric power system stabilization apparatus shown in FIG.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
First, the configuration of the power system to which the power system stabilizing device according to the present embodiment is connected will be described. FIG. 1 shows a part of a power system, and is schematically configured from a bus 1 and a partial power system 2 to which the bus 1 is connected and including a generator. The power system stabilizing device according to the present invention is connected to this power system. The power system stabilization device 10 includes a power system information detection unit 11, a control device 12, an electric double layer capacitor 13, a self-excited conversion device 14, and a transformer 15. The power system stabilizing device 10 is connected to the bus 1 connected to the partial power system 2 via a transformer 15. In addition, a power system information detection unit 11 that detects power system information is connected to lines such as a transmission line and a transformer in the bus 1 and the partial power system 2, and a signal from the power system information detection unit 11 is Are input to the control device 12.

  The power system information detection unit 11 detects information on the bus 1 and the peripheral system, that is, the bus frequency or the generator speed, the bus voltage, the line current, and the like, which are the state quantities of the bus 1 and the peripheral system, as state quantities of the power system. Device. In the present embodiment, the bus frequency or generator speed is used as an active power control input signal, the bus voltage is used as a reactive power control input signal, and the line power and bus voltage are used as accident detection input signals. It is assumed that the data is input from the unit 11 to the control device 12.

Next, the active power control input signal and the reactive power control input signal input to the control device 12 will be described.
The active power control input signal and the reactive power control input signal for calculating the active power control target value P and the reactive power control target value Q can directly capture the fluctuation of the generator and the movement of the voltage by system analysis. It is necessary to select the amount of system state change that can be made. The bus frequency and the bus voltage, which are information obtained from the power system stabilizing device installation bus, can be considered as the simplest signal because it is versatile (there are few restrictions on the installation location). In accordance with the power system information, active power and reactive power are supplied / absorbed from the power system stabilizing device 10 so as to compensate for changes in the active / reactive power of the power system, and the power system is stabilized.

  In general, the active power compensator needs to be installed in the vicinity of the generator in order to obtain its effect, and when it is installed in a power plant, it is easy to obtain information on the generator. The power system stabilizing device 10 according to the present embodiment having a function may use the generator speed instead of the bus frequency as the active power control signal. Moreover, since the main purpose of the power system stabilization device 10 is to control the power system at the time of an accident, it is possible to reliably detect the occurrence of the accident and to respond to the effective power absorption that is highly effective as the stabilization control immediately after the accident. In order to increase the power supply voltage, it is conceivable to use a combination of the bus voltage that suddenly decreases at the time of the accident and the effective diversion current such as the generator and transmission line that rapidly decrease as an auxiliary input signal.

The control device 12 includes an active / reactive power control target value calculation unit 12a that calculates an active power control target value P and a reactive power control target value Q based on the active power control input signal and the reactive power control input signal, Based on the active power control target value P and the reactive power control target value Q calculated by the active / reactive power control target value calculation unit 12a, the output voltage amplitude _VOUT and the system voltage Vs output from the self-excited converter 14 are shown. And an amplitude / phase difference command value calculation unit 12b for calculating a command value of the phase difference θ.

  Since the electric double layer capacitor 13 has an energy density of about 100 times that of the electrolytic capacitor used in the existing STATCOM, the electric power can be supplied for about 100 times the time with the same capacity.

  The self-excited conversion device 14 is a power conversion device that converts direct current into alternating current and converts alternating current into direct current. For example, a GTO (gate turn-off thyristor) or IGBT (IGT) having a function of turning on and off the current flowing through the element. An inverter using a switching element such as an insulated gate bipolar transistor). The self-excited conversion device 14 has a function of creating a voltage waveform having an arbitrary amplitude, phase, and frequency.

The active / reactive power control target value calculation unit 12a will be described with reference to FIG.
The active / reactive power control target value calculation unit 12a includes a system fault detection unit 20 that detects a system fault based on the line current and bus voltage of the power system, and a frequency fluctuation based on the input bus frequency or generator speed. Is included, and an active power control target value calculator 24 that calculates an active power control target value based on the frequency fluctuation detected from the frequency fluctuation detector 21 is provided. The active power control target value calculation unit 24 includes an accident / normal control switching unit 24a that switches between an accident control and a normal control.
In addition, a charge amount maintenance control target value calculation unit 26 for calculating a target value for maintaining and controlling the charge amount of the electric double layer capacitor 13 based on the DC voltage VD of the electric double layer capacitor 13 and the active power output is provided. ing.
Further, an active power control target value synthesizing unit 27 that synthesizes a control target value of active power based on an output from the active power control target value calculating unit 24 and an output from the charge amount maintenance control target value calculating unit 26 is provided. .
Further, a voltage fluctuation detecting unit 28 that detects a voltage fluctuation based on the input bus voltage, and a reactive power control target value calculation that calculates a reactive power control target value based on the voltage fluctuation output from the voltage fluctuation detecting unit 28. A portion 29 is provided.
Furthermore, based on the output from the active power control target value combining unit 27 and the output from the reactive power control target value calculating unit 29, the active power control target value and the reactive power control target value are set to be equal to or less than the capacity capable of being output. And a control target value synthesizing unit 30 that outputs the active power control target value P and the reactive power control target value Q.

  In order to continuously compensate for active power, it is also necessary to control the electric storage amount of the electric double layer capacitor 13 to be constant, and it is necessary to calculate an optimal control target by combining these conditions. For this purpose, the active / reactive power control target value calculator 12a detects the amount of electricity stored in the electric double layer capacitor 13, and calculates the control target including the amount of electricity stored.

Next, the control principle in the amplitude / phase difference command value calculation unit 12b will be described with reference to FIG. FIG. 3A is a diagram showing the waveforms of the system voltage Vs and the output voltage _VOUT . FIG. 3B is a vector diagram showing the relationship among the active power P, the reactive power Q, and the apparent power S. FIG. 3C is a diagram showing the relationship among the output voltage V _OUT , the output current I _OUT, and the system voltage Vs using vectors, with the effective component corresponding to the d-axis and the ineffective component corresponding to the q-axis. is there. In FIG. 3B and FIG. 3C, the symbol δ represents the power factor angle of I _OUT with respect to the system voltage Vs. In FIG. 3, it is assumed that the voltage difference between the system voltage Vs and the output voltage _VOUT is ΔV, and the phase difference is θ.

  Further, the self-excited conversion device 14 can be equivalently represented in a form in which two AC voltage sources E1 and E2 are connected via a reactance Xt as shown in FIG. Here, the reactance Xt is an equivalent reactance of the transformer 15.

At this time, the active power control target value P and the reactive power control target value Q to be output are expressed by the following equation (1) using the output voltage _VOUT , the system voltage Vs, the phase difference θ between them, and the reactance Xt generated by the transformer 15. , Expressed as equation (2).

Active power control target value P = Vs · I _OUT · cos δ
= (V _OUT · Vs · sin θ) / Xt (1)
Reactive power control target value Q = Vs · I _OUT · sin δ
= ( _VOUT · Vs · cos θ−Vs ² ) / Xt (2)
The command value V _OUT , θ to the self-excited conversion device 14 that satisfies the above is expressed as Equation (3) and Equation (4).
V _OUT = (Xt / Vs) × √ ((Q + (Vs ² / Xt)) ² + P ² ) (3)
θ = tan ⁻¹ (P / (Q + (Vs ² / Xt))) (4)
In addition, the capacity | capacitance of a system stabilization apparatus = maximum apparent power Smax is represented by Formula (5).
Smax ≧ (Vs / Xt) × √ (V _OUT ² + Vs ² −2VOUT · Vscos θ)
(5)

Therefore, in the control device 12, the active / reactive power control target value calculation unit 12a obtains the active power control target value P and the reactive power control target value Q from the bus frequency or generator speed and the bus voltage. Then, the command values V _OUT and θ are calculated from the active power control target value P and the reactive power control target value Q using the equations (3) and (4) in the amplitude / phase difference command value calculation unit 12b.

Next, actual control in the power system stabilizing device 10 will be described. First, normal control will be described. The self-excited conversion device 14 charges the electric double layer capacitor 13 under the control of the control device 12. Then, by using the self-excited converter 14 from the DC voltage, an AC voltage having a voltage different from that of the power system is generated based on the command value _VOUT calculated by the control device 12, and reactive power is generated by the voltage difference with the bus 1. Control to output. Moreover, in order to output active power, the power system stabilizing device 10 controls the phase difference between the output voltage and the power system voltage based on the command value θ calculated by the control device 12, and the phase difference from the bus 1 Control to output active power. The active / reactive power control target value calculation unit 12 a receives the DC voltage VD of the electric double layer capacitor 13 or the active power output, and controls the voltage of the electric double layer capacitor 13. The active / reactive power control target value calculation unit 12a receives an accident detection input signal from the power system information detection unit 11, and performs forced control to absorb active power from the power system intensively when an accident occurs. The forced control will be described in detail later.

  Next, an active power control method when an accident is detected will be described with reference to FIG. FIG. 5A is a diagram illustrating a frequency change after a system fault, and FIG. 5B is a diagram illustrating an active power output of the power system stabilizing device 10.

  In accident control (countermeasures for nearby accidents), fluctuations such as generator acceleration / deceleration appear as an increase / decrease in bus frequency or generator speed, and appear as an increase / decrease in frequency electrically. As described above, the bus frequency or the generator speed is effective as the power system information for this purpose. The generator starts accelerating immediately after the accident, but the generator speed and bus frequency are as shown by the curve C1 in FIG. 5 (a), such as the bus voltage indicated by the dotted line C2 and the line current near the generator. Compared to information that changes suddenly at times, it changes gradually after an accident due to the inertia of the generator. Therefore, when the bus frequency or the generator speed is used as the control input signal and the active power control target value P is calculated according to the change, the active power absorption amount is as shown by the dotted line C3 in FIG. Since the frequency gradually increases as the frequency increases, it is not possible to obtain a large amount of active power absorption with a high stabilizing effect immediately after an accident that requires the largest amount of active power compensation.

  In order to compensate for the fact that a large amount of active power absorption cannot be obtained as described above, in this embodiment, control for a predetermined time immediately after the detection of an accident (forced control) and normal control after the elapse of the predetermined time, Control is divided into two. That is, immediately after the accident detection, the system fault detection unit 20 detects a system fault from information such as a bus voltage and a line power flow that changes suddenly at the time of the accident, and immediately after the accident, the active power target value calculation unit 24 performs the operation shown in FIG. As shown by a curve C4, the control target value of active power compensation having a high stabilization effect is forcibly set to the maximum absorption amount, and forced control is performed.

  The power system stabilization device 10 basically performs control to cancel the acceleration and deceleration of the generator, but the forced control immediately after the accident is a control to absorb and decelerate the energy of the generator that accelerates by absorbing active power. Therefore, if forced control is continued until the generator starts to decelerate, deceleration is promoted and the reverse effect is obtained. The target value of active power calculated from the bus frequency, etc. is set so that the maximum amount is reached during acceleration before the generator starts to decelerate, although the rise is gradual. , Continue as a minimum until the target value calculated from the bus frequency etc. reaches the maximum, before the generator starts decelerating (1/4 before the oscillation cycle, if the oscillation cycle is 2 seconds, 0 immediately after the accident .5s) must be reset reliably. The reset timing is indicated by the symbol tr in FIG.

  Then, after a predetermined time has passed immediately after the accident detection, the normal / normal control is switched by the switching of the accident / normal control switching unit 24a. This normal control can be the same control as the normal control described above, and is performed as a control subsequent to the above-mentioned forced control. If the bus frequency or generator speed exceeds the threshold when the power cannot be maintained, control is performed. Note that the threshold value is set to a value that can be operated when the stability of the system becomes a problem, such as during an accident, from a simulation or the like, not operating due to the system fluctuation during normal operation.

  As described above, in the power system stabilizing device 10, the electric double layer capacitor 13 is charged by the control of the control device 12, and the AC voltage having a voltage different from that of the power system is used from the DC voltage by using the self-excited conversion device 14. And is controlled to output reactive power according to the voltage difference from the power system. Moreover, in order to output active power, the power system stabilization apparatus 10 controls the phase of the output voltage and outputs active power based on the phase difference from the power system.

  As described above, in the power system stabilizing device 10 according to the present embodiment, since the electric double layer capacitor is used, there is no problem of maintenance / inspection like the existing active / reactive power compensator, and the stabilization effect is improved. This increases the possibility of applying a high effective / reactive power compensator to the power system. In addition, it is possible to provide a power system stabilizing device that can easily supply active power and can perform power compensation at the time of an accident without delay in response.

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely schematically shown to the extent that the present invention can be understood and implemented, and numerical values and active / reactive power control target values P · The calculation method of Q and the like are merely examples. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

DESCRIPTION OF SYMBOLS 1 Bus 2 Partial electric power system 10 Electric power system stabilization apparatus 11 Electric power system information detection part 12 Control apparatus (control means)
12a Active / Reactive Power Control Target Value Calculation Unit 12b Amplitude / Phase Difference Command Value Calculation Unit 13 Electric Double Layer Capacitor (Power Storage Device)
14 Self-excited converter (power converter)
DESCRIPTION OF SYMBOLS 15 Transformer 20 System fault detection part 21 Frequency fluctuation detection part 24 Active power control target value calculation part 24a Fault / normal control switching part 26 Charge amount maintenance control target value calculation part 27 Active power control target value synthesis part 28 Voltage fluctuation Detection unit 29 Reactive power control target value calculation unit 30 Control target value synthesis unit

Claims (4)

An electric power system stabilizing device connected to an electric power system and suppressing and stabilizing the electric power system,
An electric double layer capacitor used as a power storage device;
A power converter connected to the electric double layer capacitor and converting direct current to alternating current and alternating current to direct current;
Control means for controlling the power converter,
The control means includes an active / reactive power control target value calculation unit that calculates an active power control target value and a reactive power control target value based on a state quantity of the power system, and the active / reactive power control target value calculation unit. Based on the active power control target value and the reactive power control target value calculated by the above, the amplitude / phase difference for calculating the command value of the phase difference between the amplitude of the output voltage output from the power converter and the power system voltage A power system stabilizing device having a command value calculation unit.   2. The power system stability according to claim 1, wherein the state quantity of the power system is a bus frequency or a generator speed as an input signal for active power control and a bus voltage as an input signal for reactive power control. Device. The active / reactive power control target value calculation unit includes a system fault detection unit for detecting a system fault,
A frequency fluctuation detection unit that detects a frequency fluctuation based on the bus frequency or the generator speed, and an active power control target value calculation part that calculates an active power control target value based on the frequency fluctuation detected from the frequency fluctuation detection unit And an accident / normal control switching unit that switches between an accident control and a normal control, and the accident / normal control switching unit compulsorily maximizes the active power control target value during the accident. The power system stabilizing device according to claim 1, wherein the control is switched so that the amount of absorption is calculated.   The power system stabilization according to claim 3, wherein the accident / normal-time control switching unit terminates the control at the time of the accident before the generator starts decelerating and switches to normal-time control. apparatus.

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