Non-patent document 1, non-patent document 2 and non-patent document 3 are known as background art in the technical field. In these non-patent documents, the following matters are generally disclosed.
There are mainly individual control method and central control method (central VQC method) as methods of voltage/reactive power control. It is to be noted that the voltage/reactive power control also includes automatic voltage control (AVC), which is referred to as voltage/reactive power control here.
The individual control method is a method of controlling based only on the information within the own site of each electric power station, and is divided into a time schedule control method and an individual voltage/reactive power Q control (voltage/reactive power control, VQC) method. Since information is distributed and determined by each control device, it is also referred to as a distributed control method.
In the time schedule control method, controlling are performed individually between: controlling by way of inputting and opening operation of the phase adjustment facility such as power capacitor (SC: static condenser (capacitor), static capacitor, shunt capacitor) and shunt reactors (ShR: shunt reactor, shunt reactor) according to time schedule; and controlling of mainly voltage regulating relays (voltage regulating relay, 90 Ry) of the transformer, on-load tap changer (LTC: tap changer/device under load) by automatic voltage regulator and load ratio control transformer (LRT, tap changeover transformer/device under load).
The individual VQC method cooperatively controls the phase adjustment facility and the LRT and the LTC of the transformer, and includes, as main control methods, the V1-V2 control method, the V2-Q1 control method, and the V2 control method. The V2 control method does not cooperatively control the phase adjustment facility, the LRT and the LTC of the transformer, but it is included as the individual VQC method.
The V1-V2 control method is a method in which the deviation of the measured value from the reference value, the target value, or the setting value of the primary bus voltage V1 and the secondary bus voltage V2 is integrated, and when the integration value of the deviation exceeds a specified value, a control signal is sent to one of the phase adjustment facility, the LRT and the LTC of the transformer to control the voltage.
The V1-Q1 control method is a method in which the deviation of the measured value from the reference value, the target value, or the setting value of the secondary bus voltage V2 and the transformer first pass reactive power Q1 are integrated, and when the integration value of the deviation exceeds a specified value, a control signal is sent to one of the phase adjustment facility, the LRT and the LTC of the transformer to control the voltage.
The V2 control method is a method in which the deviation of the measured value from the reference value, the target value, or the setting value of the secondary bus voltage V2 is integrated, and when the integration value of the deviation exceeds a specified value, a control signal is sent to the LRT and the LTC of the transformer to control the voltage.
The individual VQC method requires that each substation device independently determine and operate, the timepiece of each device be precisely matched and the pattern of the reference value, the target value, or the setting value be switched, and that the coordination of the entire system be set up, but since the method is highly compliant with changes in system condition such as accident and so on and is capable of high speed control, it is possible to maintain a balance between the voltage and the reactive power in voltage stability patterns of various systems.
The central VQC method collects system measurement data (active power P, reactive power Q, voltage V, and the like) of a plurality of measurement devices installed in the power system and performs computation (determination) with a central control unit, a central processing unit, a system stabilization unit, and the like installed in a central power supply command station, and the like, using the system measurement data and system facility data, and controls the main voltage control device and voltage/reactive power control device of the power system cooperatively with a control method that can be divided into indirect control method (target value command method, target value control method) and direct control method. In the indirect control method, a reference value, a target value, or a setting value is transmitted, and in the direct control method, an operation command is transmitted. This method is also referred to as a centralized control method, since information is concentrated and determined by the central control unit. Like the target value control method, the method can be a combination of the centralized control method and the individual VQC method (distributed control method) in some cases. From the viewpoint of voltage/reactive power control, the power supply operation system has a hierarchical structure mainly hierarchically classified by voltage class and is also referred to as hierarchical voltage control (HVC).
Here, the voltage control device includes an Automatic Voltage Regulator (AVR), Automatic Reactive Power (Q) Regulator (AQR), Power System Voltage Regulator (PSVR), Synchronous Condenser (RC, rotary capacitor), Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM), and the like, in addition to the phase adjustment facility, the LRT and the LTC of the transformer, which is the voltage/reactive power control device.
As a general method of the computation of the central VQC method, there is a method of combining one or more deviations from reference value, target value, or setting value (such as reference voltage, target voltage, or setting voltage) at a plurality of voltage monitoring points of the system into one evaluation function and obtaining an operation amount of the device to minimizing the same. For the evaluation function, the minimization of the voltage deviation at the monitoring point and the transmission loss of the monitoring transmission line are often adopted, and the sensitivity coefficient by the AC method or the sensitivity coefficient by the DC method is often used for the evaluation of the effect. The security of the system may be considered. Since the central VQC method requires determination of the voltage in the system and the active and reactive power distribution, sensitivity analysis of the effect by each control device and selective computation of the optimum control pattern, the controlling takes about several minutes depending on the computation processing capability of the central processing unit. For this reason, especially the direct control method may not be able to provide high-speed controlling at the time of an accident, and it is thus used in combination with the individual control method that is capable of high-speed controlling in some cases. For the computation of the central VQC method, since it is necessary to minimize or maximize the evaluation function in order to obtain the optimum system state, various minimization calculations and optimal power flow calculations (OPF) are often used.
In the indirect control method (target value command method, target value control method), the reference value, the target value, or the setting value calculated by the central VQC device is sent from the central control device (central VQC device) to an individual control device (individual VQC device), for example, and when the reference value, the target value, or the setting value is the target value of the voltage and the reactive power, for example, a deviation between the voltage and the reactive power at the monitoring point (control target point) of the individual VQC device and target values of the voltage and the reactive power is detected according to the individual VQC method, and the voltage control device is operated so that the voltage and the reactive power at the monitoring point is maintained at the target value of the voltage or the reactive power.
There are cases of controlling collectively the individual VQC devices installed at respective sites of the system, or indirectly controlling the individual VQC devices installed at the sites of the system grouped in several blocks, or controlling only specific individual VQC device, and the like. Examples of the technical background of the indirect control method include Tanimoto, Morita, Takahashi, Sakamoto, Kurokawa, Fukui: “Central VQC method based on target voltage command to individual VQC device”, Journal of the Institute of Electrical Engineers of Japan, Vol. 126, N. 8, pp. 783-788 (2006).
The computation at the individual VQC device calculates an amount of integration of the deviation between the voltage and the voltage target value at the monitoring point (strictly, the deviation amount from the dead zone), and when the calculated result exceeds a preset value, sends a control output to the voltage control device. Therefore, when the target voltage is changed, a time delay occurs before the voltage is controlled close to the target voltage. Therefore, in order to control the system voltage close to the desired target voltage upon sudden change in the load as in the daytime, the target voltage is set in advance in consideration of this time delay. Specifically, the optimal power flow calculation (OPF) of the central VQC device is performed in the prediction system one point ahead (for example, a few minutes ahead) and command is issued accordingly. As a result, it may be expected that the last voltage distribution that is obtained after several minutes of the calculation would approach the optimum distribution. In the event that a large voltage violation is detected due to a system accident or the like, a function may also be provided, which executes the optimal power flow calculation (OPF) of the system section at that point in time and commands the individual VQC device with a temporary target voltage.
In the central VQC device, the direct control method causes the voltage control device to operate so that the state of the voltage and the reactive power of the monitoring point are optimized by calculating and transmitting the operation command of the voltage control device calculated by the central VQC device. The computation method of the central VQC device is the method described above. In the direct control method, as described above, control is performed at about several minute-interval, and the central VQC device performs optimal power flow calculation (O) of a prediction system one point ahead and controls based thereon, as in the indirect control method.
For the background technology in this technical field, reference can be made to JP-A-2003-259555 (PTL 1). This publication describes: “The monitoring point deviation amount integration means 15 integrates deviation amounts from the upper limit value and the lower limit value of the bus the voltage and the reactive power flow to be monitored from the system state obtained by the voltage system information grasping means 11, and the departure determination means 13 activates the control amount calculation means 12 when the deviation amount integration value exceeds a preset departure threshold value. The control amount calculation means 12 calculates the control amount of the voltage/reactive power adjustment device 3 so that the bus voltage and the reactive power flow to be monitored are within an allowable value, and outputs a command to the voltage/reactive power adjustment device 3 through the command output means 14 and the information transmission devices 4c and 4d. As a result, it is possible to suppress a response to a micro disturbance, and to perform control even when the deviation occurs for a short time when a large departure occurs”.
For the background technology in this technical field, reference can be made to JP-A-2002-165367 (PTL 2). This publication describes: “The voltage/reactive power control system includes a central VQC device 101 and a plurality of individual VQC devices 202. The central VQC device 101 receives the active power flow P from the plurality of individual VQC devices 202, calculates a reference voltage which is the optimal target voltage of the individual VQC device 202 in each block based thereon, and transmits the reference voltage to the individual VQC device 202. In the individual control unit 200, the reactive power amount Q from a predetermined position in the block 201 is gathered in the individual VQC device 202 and controls the balance of the reactive power Q in an autonomous distributed manner to maintain the reference voltage transmitted from the central VQC device 101”.
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