KR20070072295A - Method for compensating reactive power and apparatus thereof - Google Patents

Abstract

A method and an apparatus for compensating for a reactive power are provided to reduce an electrical shock to an HVDC(High Voltage Direct Current) converter by minimizing the switching number of a switch by adjusting a capacitance of a capacitor bank. A candidate capacitance calculator(230) calculates a reactive power by a system, a maximum supply power of an additional system, and capacitances of capacitor banks within a main operation range of the system. A minimum switching amount selector selects a minimum switching amount minimizing the switching number of the capacitor bank. A sensitivity calculator(250) calculates sensitivities for respective load lines, which are connected to the system. A reactive power calculator(260) calculates maximum and minimum values of the capacitor bank by using the line sensitivity and an allowable voltage variation range. A capacitance adjusting unit(270) increases the capacitance of the capacitor bank according to the maximum and minimum values of the reactive power variation range.

Description

Reactive power compensation method and device {Method for compensating reactive power and Apparatus

1A illustrates a switching on / off state according to a conventional reactive power compensation method.

1B is a graph illustrating supply and demand states of reactive power according to a conventional reactive power compensation method.

2 is a block diagram of a reactive power compensation device according to the present invention.

3 is a flowchart according to an embodiment of the present invention.

4 is a flowchart according to another embodiment of the present invention.

5 is a flowchart according to another embodiment of the present invention.

6 illustrates a switching on / off state according to the embodiment of FIG. 3.

7 is a graph illustrating a probable state of reactive power according to the embodiment of FIG. 3.

8 is a graph illustrating a result of calculating an overvoltage value within an allowable range of 5% according to the embodiment of FIG. 5.

9 illustrates a switching on / off state according to the embodiment of FIG. 5.

10 is a graph illustrating a probable state of reactive power according to the embodiment of FIG. 5.

The present invention relates to a high voltage direct current (HVDC) system, and more particularly, to a method and apparatus for compensating reactive power in consideration of a main operating range.

High voltage direct current (HVDC) systems consume reactive power depending on the amount of active power received. Therefore, they have phase modifying equipment to supply reactive power or they are supplied from AC systems. In case of receiving from AC system, there is no problem when the reactive power reserve of AC system is sufficient and the reactive power source exists near HVDC system, so that reactive power can be supplied to HVDC system stably. If the voltage coupling occurs faster than the corresponding action of the load tap changer (LTC), the HVDC converter adjusts the firing angle to keep the DC voltage constant.

If the AC voltage drop is very fast and instantaneously, and the control of the firing angle α and the arc angle γ of the converter does not correspond to this, a current failure occurs. If a current failure occurs, active power transfer is interrupted until DC control is restored. During the recovery of active power transmission, the reactive power requirement of the converter increases in proportion to the increased active power, so that a dynamically controlled reactive power supply system is an important factor in the dynamic characteristics of the HVDC system.

The most common of these reactive power compensation devices is the capacitor bank, which is inexpensive and easy to control. However, switches, especially capacitor banks using mechanical switches, cannot be dynamic reactive power compensators, and supply reactive power is proportional to the bus voltage, preventing the supply of scheduled reactive power at low voltages.

However, the HVDC system is equipped with a harmonic filter, which acts as a capacitor bank that supplies reactive power at a power frequency of 60 kHz, so that reactor banks to prevent reactive power from flowing through these filter banks and filter switching flow into the AC system. Supplies reactive power according to the change of active power.

1A illustrates a switching on / off state according to a conventional reactive power compensation method.

In FIG. 1A, a dual tuned filter (DTF) and a high pass filter (HPF) are filters for removing harmonics. In FIG. 1A, SHNT.R means a switch shunt bank including a capacitor bank.

As shown in FIG. 1A, as the main operation section Pdc changes, all the filters and the switch shunt banks operate. In other words, it can be seen that the switch installed in the filter is excessively switched.

1B is a graph illustrating supply and demand states of reactive power according to a conventional reactive power compensation method.

In FIG. 1B, it can be seen that the reactive power supply amount changes every time the active power changes by 20 megawatts. That is, as in FIG. 1A, it can be seen that the switch installed in the filter is excessively switched.

Therefore, in the conventional reactive power compensation method, when the HVDC system is operated near the switching point of the filter, the switch that connects the filter to the grid is excessively operated due to frequent fluctuations in the generator output, and the switch is subjected to excessive stress to give a lifetime. There is a problem of shortening.

In order to solve the above technical problem, the present invention is to provide a free power compensation method for determining the capacity of the capacitor bank to minimize the number of switching of the switch connected to the filter, and applied to the system.

In order to solve the above other technical problem, the present invention is to provide a reactive power compensation device to which the reactive power compensation method is applied.

In order to solve the above technical problem, the present invention includes the steps of calculating the amount of reactive power required by the system, the maximum supply capacity of the additional invalid supply device existing in the system and the capacitor bank capacities satisfying the range of the main operating section of the system, Selecting a minimum switching capacity that minimizes the number of switching of the capacitor bank among the calculated capacitor bank capacities, and adjusting the capacitor bank capacity connected to the system to the minimum switching capacity.

In addition, the present invention to solve the above technical problem, the step of calculating the sensitivity of each bus bar of the load bus connected to the grid, the reactive power of the capacitor bank connected to the grid using the sensitivity of each bus and a predetermined allowable voltage fluctuation range Calculating a maximum value and a minimum value of the change amount and increasing the capacitor bank capacity according to the maximum value and the minimum value of the reactive power change amount.

In addition, in order to solve the above technical problem, the present invention calculates the amount of reactive power required by the system, the maximum supply capacity of the additional invalid supply device existing in the system and the capacitor bank capacities that satisfy the range of the main operation section of the system. Selecting a minimum switching capacity that minimizes the number of switching of the capacitor bank among the calculated capacitor bank capacities, adjusting a capacitor bank capacity connected to the grid to the minimum switching capacity, a load bus connected to the grid Calculating a sensitivity of each bus bar of the circuit, calculating a maximum value and a minimum value of reactive power variation of the capacitor bank connected to the grid using the sensitivity of each bus and a predetermined allowable voltage variation range, and the maximum value of the reactive power variation And increase the capacitor bank capacity according to the minimum value. It comprises the step of.

In order to solve the above other technical problem, the present invention provides a candidate for calculating the amount of reactive power required by a system, a maximum supply capacity of an additional invalid supply device existing in the system, and capacitor bank capacities satisfying a range of the main operation section of the system. A capacitance calculating unit, a minimum switching capacity selecting unit selecting a minimum switching capacity that minimizes the switching frequency of the capacitor bank among the calculated capacitor bank capacities, a sensitivity calculating unit calculating a sensitivity of each bus bar of a load bus connected to the grid, A reactive power calculator for calculating a maximum and minimum value of the reactive power change amount of the capacitor bank connected to the grid using the selection sensitivity and a predetermined allowable voltage variation range, and adjusting the capacitor bank capacity connected to the grid to the minimum switching capacity, The maximum value of the reactive power change amount and Depending on the minimum value and includes a capacity control that increases the capacity of the capacitor bank.

Hereinafter, with reference to the drawings will be described a preferred embodiment of the present invention.

2 is a block diagram of a reactive power compensation device according to the present invention.

The alternating current power of the generator 200 is converted to direct current in the HVDC system, and again to alternating current in the load 220.

Capacitor bank 210 represents a reactive power supply that includes a filter (not shown).

The candidate capacity calculator 230 calculates capacitor bank capacities satisfying a reactive power amount required by the system, a maximum supply capacity of an additional invalid supply device existing in the system, and a range of a main operation section of the system.

The minimum switching capacitance selector 240 selects the minimum switching capacitance that minimizes the number of switching of the capacitor bank 210 among the calculated capacitor bank capacities.

The sensitivity calculator 250 calculates the sensitivity of each bus bar of the load bus bar connected to the grid.

The reactive power calculator 260 calculates the maximum value and the minimum value of the reactive power change amount of the capacitor bank 210 connected to the grid by using the bus line sensitivity and a predetermined allowable voltage variation range.

The capacity controller 270 is connected to the capacitor bank 210, and adjusts the capacity of the capacitor bank 210 connected to the grid to the minimum switching capacity calculated above. In addition, the capacitance adjusting unit 270 increases the capacitance of the capacitor bank 210 according to the maximum value and the minimum value of the reactive power change amount calculated above.

3 is a flowchart according to an embodiment of the present invention.

First, the capacitor bank capacity that satisfies the amount of reactive power required by the system, the maximum supply capacity of the additional reactive supply device existing in the system, and the main operating section of the system is calculated (step 300).

Preferably, the process 300 includes setting a first equation for the capacitor bank capacity such that the reactive power supplied by the capacitor bank in the system is less than the reactive power required by the system.

Preferably, this process (process 300) includes setting a second equation for the capacitor bank capacity such that the reactive power of the additional reactive supply present in the system is less than or equal to the maximum supply capacity of the reactive power supply. .

Preferably, this step 300 includes setting a third equation for the capacitor bank capacity such that the operating section of the system is within a predetermined main operating range.

Preferably, this process (process 300) includes calculating a capacitor bank capacity by applying a branch and bound method to the first equation, the second equation, and the third equation.

In this case, the branch limit method is a kind of enumeration that calculates all possible solutions of the equation, but the branching solution is used to quickly determine the validity of the solution using the upper bound and the lower bound and enumerate as few possible solutions as possible. That's how. In other words, this technique is not a full enumeration, but a partial enumeration.

Next, among the capacitor bank capacities calculated above, a minimum switching capacitance that minimizes the switching frequency of the capacitor bank is selected (operation 310).

Finally, the capacitor bank capacity connected to the grid is adjusted to the minimum switching capacity (step 320).

Referring to the process of Figure 3 as an equation.

First, the reactive power supply state of the HVDC system inverter stage may be written as Equation 1 below.

From this, the output of the additional reactive power compensation device is defined as in Equation 2 below.

The reactive power Q ₁ consumed by the HVDC system is generally about 50-65% of the active power of the faucet, and the Q ₄ supplied or supplied from the AC system is obtained through electric power flow calculation.

Thus, the control variable is the amount of reactive power supplied by the filter and the reactor and the amount of additional reactive power compensation device supplied.

The reactive power compensation described above is optimized using the Branch and Bound method of integer programming.

An example of such a process is as follows.

The reactive power Q1 consumed by the HVDC system is about 50-65% of the active power of the faucet, and the Q4 supplied or supplied from the AC system is obtained through tide calculation.

Thus, the control variable is the amount of reactive power supplied by the filter and the reactor and the amount of additional reactive power compensation device supplied.

Although there are many objective functions for optimization, it is assumed here that the objective function is selected to minimize switching of the capacitor bank (Equation (3)).

There are constraints that must be satisfied while minimizing this objective function. As shown in Eq. (4), the reactive power supplied by the capacitor bank should not supply more than the reactive power required by the HVDC system. The filter should always be turned on

If there is an additional reactive power supply as shown in Eq. (5), the amount supplied from it should also be limited to the supply capacity of the device.

Finally, as shown in Eq. (6), the main operating section must satisfy the desired range.

These can be summarized as Equations (3), (4), (5), and (6) below.

The optimization problem is optimized by using the branch and bound method of integer programming to optimize the reactive power compensation described above, and the results of FIGS. 6 and 7 are obtained.

Determination of the unit capacity of the filter for reactive power compensation is used to about 5% of the system short-circuit capacity as shown in Equation 3 to limit the magnitude of the overvoltage generated when the unit capacitor / reactor is added to or removed from the system.

Capacitor / Reactor Unit Capacity = (Unit System Short Circuit Capacity) × 0.05

In the case of a low short-circuit ratio system, when the system has a large impedance and a filter is used as a reactive power compensator, the effective short-circuit ratio (ESCR) decreases and the dV / dQ sensitivity increases as the amount of power received increases. Is more likely to occur. Therefore, when estimating the capacity of a unit capacitor, dV / dQ sensitivity of each low bus ratio system should be calculated and considered in determining the unit capacity.

Embodiments to consider the sensitivity of each line of the system when determining the unit capacity is as follows.

4 is a flowchart according to another embodiment of the present invention.

First, the sensitivity of each bus bar of a load bus connected to the grid is calculated (step 430). Preferably, this process (step 430) includes a step of calculating the sensitivity for each mother line using a Jacobian matrix for the line.

Next, the maximum value and the minimum value of the reactive power change amount of the capacitor bank connected to the grid are calculated using the sensitivity of each bus and a predetermined allowable voltage variation range (step 440). Preferably, this process (step 440) is a process in which a predetermined allowable voltage variation range is within a voltage change rate of 0.05 within the system.

Finally, the capacitor bank capacity is increased according to the maximum value and the minimum value of the reactive power change amount (step 450).

The process of calculating the above-described sensitivity for each bus bar is explained as follows.

The sensitivity matrix of each busbar is calculated from Equation 4 and Equation 5 below from the Jacobian matrix of the system.

In the above Equation 5, if all state variables are shifted to the right side and the dependent variable is shifted to the left side, the equation can be written as Equation 6 below.

Equation 6 may be divided into two parts as in Equation 7 and Equation 8 below.

Where t _pq = transformer tap position between p and q busbars, S * = sensitivity matrix, generator busbars 1,2, ..., m, and load busbars = m + 1, ..., n.

Since the dependent variables ΔP and ΔV of Equations 7 and 8 must satisfy Equations 1 and 2, Equations 9 and 10 can be written as follows.

Where ΔQmini = Qmini-Qi, ΔQMaxi = QMaxi-Qi, Qmini, = minimum reactive power output at generator bus i, QMaxi = maximum reactive power output at generator bus I, Qi = actual reactive power output at generator bus i , i = generator bus (1,2, ..., m), and m + x = bus with switched shunt bank (m ≤ m + x ≤ n).

As a result, dV / dQ of the load bus line i can be obtained from Equation (10).

In addition, it is possible to determine the maximum / minimum amount of reactive power variation of the switched shunt bank under a 5% allowable voltage variation.

5 is a flowchart according to another embodiment of the present invention.

First, the capacitor bank capacity that satisfies the amount of reactive power required by the system, the maximum supply capacity of the additional reactive supply device existing in the system, and the main operating range of the system is calculated (step 500).

Next, a minimum switching capacity is selected among the calculated capacitor bank capacities to minimize the number of switching of the capacitor bank (operation 510).

If the minimum switching capacity is selected, the capacitor bank capacity connected to the grid is adjusted to the minimum switching capacity (step 520).

Next, the bus sensitivity of each load bus connected to the grid is calculated (step 530).

When the bus sensitivity is calculated, the maximum and minimum values of the reactive power variation of the capacitor bank connected to the grid are calculated using the bus sensitivity and the predetermined allowable voltage variation range (operation 540). Preferably, the predetermined allowable voltage fluctuation range is a range in which the voltage change rate of the system is within 0.05.

Finally, the capacitor bank capacity is increased according to the maximum and minimum values of the reactive power variation calculated above (step 550).

6 illustrates a switching on / off state according to the embodiment of FIG. 3.

In FIG. 6, DTF (Dual Tuned Filter) and HPF (High Pass Filter) are filters for removing harmonics. In FIG. 6, SHNT.R means a switch shunt bank including a capacitor bank.

In FIG. 6, it can be seen that switching does not occur in the second DTF, which is a filter for removing harmonics, and that the number of switching is reduced as compared with FIG. 1A.

7 is a graph illustrating a probable state of reactive power according to the embodiment of FIG. 3.

In FIG. 7, it can be seen that the reactive power change according to the active power change is smaller than that in FIG. 1B.

8 is a graph illustrating a result of calculating an overvoltage value within an allowable range of 5% according to the embodiment of FIG. 5.

By calculating dV / dQ of the load bus line i from Equation 10, it is possible to determine the maximum / minimum amount of reactive power variation of the switched shunt bank under a 5% allowable voltage variation. For example, it can be concluded that the maximum overvoltage value when the capacitor bank capacity is 13.75 MVAr, 27.5 MVAr, and 37.5 MVAr is calculated as shown in FIG. 8 and can be increased to 37.5 MVAr when 5% is the allowable variation.

9 illustrates a switching on / off state according to the embodiment of FIG. 5.

In FIG. 9, DTF (Dual Tuned Filter) and HPF (High Pass Filter) are filters for removing harmonics. In FIG. 9, SHNT.R means a switch shunt bank including a capacitor bank.

10 is a graph illustrating a probable state of reactive power according to the embodiment of FIG. 5.

9 and 10, it can be seen that the results of FIGS. 6 and 7 can be further optimized by simultaneously applying the methods of FIGS. 3 and 4 described above. In other words, it can be seen that by increasing the size of the capacitor bank can be further optimized.

In FIGS. 9 and 10, the number of switching is twice, which is less than that of the conventional reactive power compensation method, and since two of the four filters (DTF # 2 and HPF # 2) are not used, the filter is already installed. It can be seen that the reliability of the system can be increased. In addition, it can be seen that there is an advantage that the number of switching times when the amount of power reception changes when the amount of power reception is large, compared to the existing HVDC main operation section of 110 ~ 150㎿.

Preferably, the reactive power compensation method of the present invention may be provided in the form of a computer-readable recording medium for executing on a computer.

The invention can be implemented via software. When implemented in software, the constituent means of the present invention are code segments that perform the necessary work. The program or code segments may be stored on a processor readable medium or transmitted by a computer data signal coupled with a carrier on a transmission medium or network.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and will be understood by those of ordinary skill in the art that various modifications and variations can be made therefrom. However, such modifications should be considered to be within the technical protection scope of the present invention. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described above, according to the present invention, the filter by determining the capacity of the capacitor bank to minimize the number of switching of the switch connecting the system and the filter while taking into account the strength of the system and all reactive power sources, When the HVDC system is operating near the switching point of the generator, the generator output will fluctuate frequently to prevent excessive operation of the switch connecting the filter to the grid, to prolong the life of the switch, and to protect the electrical shock from the HVDC converter. There is an effect that can be reduced.

Claims (11)

Calculating capacitor bank capacities that satisfy the amount of reactive power required by the system, the maximum supply capacity of additional reactive supplies present in the system, and a range of the main operating section of the system; Selecting a minimum switching capacity of the calculated capacitor bank capacities to minimize the number of switching of the capacitor bank; And And adjusting the capacitor bank capacity connected to the grid to the minimum switching capacity. The method of claim 1, Computing the capacitor bank capacity Setting a first equation for said capacitor bank capacity such that the reactive power supplied by said capacitor bank in said system is equal to or less than the reactive power required by said system;  Setting a second equation for the capacitor bank capacity such that the reactive power amount of the additional reactive supply device present in the system is less than or equal to the maximum supply capacity of the reactive power supply device; Setting a third equation for the capacitor bank capacity such that the operating period of the system is within a predetermined main operating range; And And calculating the capacitor bank capacity by applying a branching method to the first equation, the second equation, and the third equation. Calculating sensitivity of each bus bar of the load bus bar connected to the grid; Calculating a maximum value and a minimum value of a reactive power change amount of a capacitor bank connected to the grid using the bus line sensitivity and a predetermined allowable voltage variation range; And And increasing the capacitor bank capacity according to the maximum and minimum values of the reactive power change amount. The method of claim 3, wherein The step of calculating the sensitivity for each bus line Computing the reactive power for each bus line using a Jacobian matrix for the system characterized in that the reactive power compensation method. The method of claim 3, wherein Computing the maximum value and the minimum value of the reactive power change amount And the predetermined allowable voltage fluctuation range is within 0.05 of the voltage change rate of the system. Calculating capacitor bank capacities that satisfy the amount of reactive power required by the system, the maximum supply capacity of additional reactive supplies present in the system, and the main operating range of the system; Selecting a minimum switching capacity of the calculated capacitor bank capacities to minimize the number of switching of the capacitor bank; Adjusting a capacitor bank capacity connected to the system to the minimum switching capacity; Calculating the sensitivity of each bus bar of the load bus bar connected to the system; Calculating a maximum value and a minimum value of a reactive power change amount of a capacitor bank connected to the grid using the bus line sensitivity and a predetermined allowable voltage variation range; And And increasing the capacitor bank capacity according to the maximum and minimum values of the reactive power change amount. The method of claim 6, Computing the capacitor bank capacity Setting a first equation for said capacitor bank capacity such that the reactive power supplied by said capacitor bank in said system is equal to or less than the reactive power required by said system;  Setting a second equation for the capacitor bank capacity such that the reactive power amount of the additional reactive supply device present in the system is less than or equal to the maximum supply capacity of the reactive power supply device; Setting a third equation for the capacitor bank capacity such that the operating period of the system is within a predetermined main operating range; And And calculating the capacitor bank capacity by applying a branching method to the first equation, the second equation, and the third equation. The method of claim 6, The step of calculating the sensitivity for each bus line Computing the reactive power for each bus line using a Jacobian matrix for the system characterized in that the reactive power compensation method. The method of claim 6, Computing the maximum value and the minimum value of the reactive power change amount And the predetermined allowable voltage fluctuation range is within 0.05 of the voltage change rate of the system. A computer-readable recording medium having recorded thereon a program for executing the method of claim 1 on a computer. A candidate capacity calculating unit for calculating a capacitor power required to satisfy a reactive power amount required by a system, a maximum supply capacity of an additional reactive supply device existing in the system, and a main operating range of the system; A minimum switching capacity selection unit for selecting a minimum switching capacity of the calculated capacitor bank capacities to minimize the number of switching of the capacitor bank; A sensitivity calculation unit for calculating the sensitivity of each bus bar of the load bus bar connected to the system; A reactive power calculator configured to calculate a maximum value and a minimum value of a reactive power change amount of a capacitor bank connected to the grid by using the bus line sensitivity and a predetermined allowable voltage variation range; And And a capacity adjusting unit which adjusts the capacitor bank capacity connected to the system to the minimum switching capacity and increases the capacitor bank capacity according to the maximum value and the minimum value of the reactive power change amount.

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