Reactive power compensation system

Abstract

To provide a low-loss reactive power compensation system.SOLUTION: A reactive power compensation system includes phase modifying equipment 1 that outputs one of the (N+1) reactive powers Q0 to QN that change stepwise to a distribution line 10, a reactive power compensator 4 that outputs a desired reactive power to the distribution line 10, and a control device 9 that causes the phase modifying equipment 1 to output the reactive power Qn that has the smallest deviation from a target reactive power QT among the (N+1) reactive powers Q0 to QN, and causes the reactive power compensator 4 to output a reactive power ΔQ that is the deviation between the target reactive power QT and the reactive power Qn. Therefore, the output of the reactive power compensator 4 can be suppressed to a low level, thereby reducing losses.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a reactive power compensation system, and more particularly to a reactive power compensation system that supplies reactive power to a distribution line.

Background Art

[0002] For example, Japanese Patent Application Laid-Open No. 2018-7299 discloses a phase-modulating facility that outputs a predetermined value of reactive power to a distribution line, a reactive power compensation device that outputs a desired value of reactive power to the distribution line, and when the target reactive power is less than or equal to the predetermined value, the output of the phase-modulating facility is stopped and the target reactive power is output from the reactive power compensation device, and when the target reactive power is greater than the predetermined value, a control unit that outputs reactive power from the phase-modulating facility and stops the operation of the reactive power compensation device is provided.

[0003] The phase-modulating facility includes a shunt reactor or a leading power capacitor that supplies a predetermined value of reactive power. The reactive power compensation device includes a self-excited reactive power compensation device that supplies a desired value of reactive power by turning on and off switching elements.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In such a reactive power compensation system, a larger loss occurs in the reactive power compensation device than in the phase-modulating facility. However, in the conventional reactive power compensation system, when the target reactive power is less than or equal to the predetermined value, the target reactive power is generated only by the reactive power compensation device, so there is a problem that the loss is large.

[0006] Therefore, the primary purpose of this disclosure is to provide a low-loss reactive power compensation system. [Means for solving the problem]

[0007] The reactive power compensation system according to this disclosure comprises a phase adjustment device that outputs one of a plurality of reactive powers that change in a step-like manner to a distribution line, a reactive power compensation device that outputs a desired reactive power to a distribution line, a first control unit that determines the first reactive power among the plurality of reactive powers which has the smallest deviation from a target reactive power and causes the phase adjustment device to output the first reactive power, and a second control unit that determines a second reactive power which is the deviation between the target reactive power and the first reactive power and causes the reactive power compensation device to output the second reactive power. [Effects of the Invention]

[0008] In the reactive power compensation system described herein, the first reactive power with the smallest deviation from the target reactive power among multiple reactive powers is output from the phase adjustment equipment, and the second reactive power, which is the deviation between the target reactive power and the first reactive power, is output from the reactive power compensation device. Therefore, the output of the reactive power compensation device can be suppressed to reduce losses. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit block diagram showing the configuration of a reactive power compensation system according to Embodiment 1 of the present disclosure. [Figure 2] This block diagram shows the portion of the control device shown in Figure 1 that is related to the control of the phase adjustment equipment. [Figure 3] This block diagram shows the portion of the control device shown in Figure 1 that is related to the control of the reactive power compensation device. [Figure 4] Figure 1 is a circuit block diagram illustrating the configuration of a self-oscillating SVC. [Figure 5] This is a circuit block diagram showing the configuration of a reactive power compensation system according to Embodiment 2 of the present disclosure. [Modes for carrying out the invention]

[0010] [Embodiment 1] Figure 1 is a circuit block diagram showing the configuration of a reactive power compensation system according to Embodiment 1 of the present disclosure. In Figure 1, the reactive power compensation system comprises a phase adjustment device 1, a reactive power compensation device 4, a voltage detector 7, a current detector 8, and a control device 9.

[0011] Both the phase-shifting equipment 1 and the reactive power compensation device 4 are connected to the distribution line 10. Each of the phase-shifting equipment 1 and the reactive power compensation device 4 is controlled by a control device 9 and supplies reactive power to the distribution line 10. The distribution line 10 is connected to the transmission line 12 via an interconnection transformer 11. The transmission line 12 receives AC power from the commercial AC power source 13.

[0012] Furthermore, multiple power generators 14 and multiple loads 15 are connected to the power distribution line 10. The power generators 14 generate alternating current (AC) power and output it to the power distribution line 10. The power generators 14 may generate AC power using natural energy such as wind or solar power, or they may be private power generation equipment that does not use natural energy. The loads 15 are driven by the AC power received from the power distribution line 10.

[0013] The voltage detector 7 detects the instantaneous value of the AC voltage VS at a predetermined location on the power distribution line 10 and outputs a signal indicating the detected value to the control device 9. The current detector 8 detects the instantaneous value of the AC current I flowing through a predetermined location on the power distribution line 10 and outputs a signal indicating the detected value to the control device 9.

[0014] The control device 9 determines the target reactive power QT to be supplied to the distribution line 10 based on the output signals of the voltage detector 7 and the current detector 8, and causes the phase adjustment equipment 1 and the reactive power compensation device 4 to supply the target reactive power QT to the distribution line 10.

[0015] More specifically, the phase-shifting equipment 1 includes N shunt reactors 2 and N switches 3, each connected between the distribution line 10 and the N shunt reactors 2. N is a natural number greater than or equal to 2. Each of the N shunt reactors 2 supplies a predetermined value of leading reactive power Q1. The on and off states of each of the N switches 3 are controlled by the control device 9.

[0016] When one switch 3 is turned on, a predetermined value of leading reactive power Q1 is supplied to the distribution line 10 from one shunt reactor 2 corresponding to that switch 3. When N switches 3 are turned on, leading reactive power QN = N × Q1 is supplied to the distribution line 10 from N shunt reactors 2.

[0017] When n of the N switches 3 are turned on, leading reactive power Qn = n × Q1 is supplied to the distribution line 10 from the n shunt reactors 2. n is an integer between 0 and N. If n = 0, the leading reactive power Q0 output from the phase regulating equipment 1 to the distribution line 10 is 0 (var). Therefore, the phase regulating equipment 1 outputs one of the (N+1) leading reactive powers Q0 to QN, which increase in a step-like manner from 0 to QN, to the distribution line 10.

[0018] In this embodiment 1, preliminary investigations have shown that it is mainly necessary to supply leading reactive power to the distribution line 10, so a phase adjustment system 1 including N shunt reactors 2 is provided.

[0019] The reactive power compensation device 4 includes M self-excited SVCs (Static Var Compensators) 5 and M switches 6 connected between the distribution line 10 and the M self-excited SVCs 5 respectively. M is a natural number greater than or equal to 2. The self-excited SVC 5 is also called a STATCOM (Static Synchronous Compensator) and includes power electronics elements capable of high-frequency switching operations such as IEGT (Injection Enhanced Gate Transistor), GCT (Gate Commutated Turn-off thyristor), and IGBT (Insulated Gate Bipolar Transistor).

[0020] Assuming that leading phase is positive (+) and lagging phase is negative (-), each self-excited SVC 5 is controlled by the control device 9 and outputs reactive power QY with a desired value between -QX and +QX to the distribution line 10. QX is the rated reactive power of the self-excited SVC 5.

[0021] The on and off of each of the M switches 6 are controlled by the control device 9. When one switch 6 is turned on, reactive power QY is supplied from one self-excited SVC 5 corresponding to that switch 6 to the distribution line 10. When the M switches 6 are turned on, reactive power QZ = M × QY is supplied from the M self-excited SVCs 5 to the distribution line 10.

[0022] When m out of the M switches 6 are turned on, reactive power QZ = m × QY with a desired value between -m × QX and +m × QX is supplied from the m self-excited SVCs 5 to the distribution line 10. In this case, the supply of reactive power QZ = m × QY is evenly shared by the m self-excited SVCs 5, and each self-excited SVC 5 outputs reactive power QY = QZ / m to the distribution line 10. m is a natural number greater than or equal to 1 and less than or equal to M.

[0023] Figure 2 is a block diagram showing the portion of the control device 9 related to the control of the phase shifting equipment 1. In Figure 2, the control device 9 includes a reactive power calculation unit 20, a reactive power command unit 21, a storage unit 22, a calculation unit 23, a signal generation unit 24, a timer 25, and a latch circuit 26.

[0024] The reactive power calculation unit 20 determines the reactive power QS supplied to the distribution line 10 from the power generator 14 and the load 15 based on the AC voltage VS of the distribution line 10 detected by the voltage detector 7 (Figure 1) and the AC current I flowing through the distribution line 10 detected by the current detector 8.

[0025] The reactive power command unit 21 determines a target reactive power QT = -QS, which is the opposite polarity of the reactive power QS obtained by the reactive power calculation unit 20, and outputs a signal indicating that target reactive power QT. The storage unit 22 stores (N+1) values ​​of leading reactive powers Q0 to QN that can be output by the phase adjustment equipment 1.

[0026] The calculation unit 23 finds the reactive power Qn (first reactive power) among the leading reactive powers Q0 to QN stored in the memory unit 22 that has the smallest deviation ΔQ from the target reactive power QT, and then finds the number n of switches 3 that should be turned on in order to output that reactive power Qn from the phase adjustment equipment 1.

[0027] The signal generation unit 24 generates signals A1 to AN based on the number n switches 3 determined by the calculation unit 23. Signals A1 to AN each correspond to N switches 3. The signal generation unit 24 sets the signals A1 to AN corresponding to the number n switches 3 to the "H" level.

[0028] For example, the signal generator 24 sets all signals A1 to AN to "L" level when n=0, and sets all signals A1 to AN to "H" level when n=N. Also, when n=1, the signal generator 24 sets signal A1 to "H" level and the other signals A2 to AN to "L" level.

[0029] Timer 25 outputs a pulse signal P1 at predetermined intervals (for example, every 2 hours). Latch circuit 26 receives signals A1 to AN in response to pulse signal P1, and holds and outputs the received signals A1 to AN as signals B1 to BN.

[0030] Each of the N switches 3 turns on or off according to the logic level of signals B1 to BN. For example, if signals B1 to BN are all at the "H" level, all N switches 3 turn on. If signals B1 to BN are all at the "L" level, all N switches 3 turn off. If signal B1 is at the "H" level and signals B2 to BN are all at the "L" level, only the first switch 3 out of the N switches 3 turns on, and the remaining (N-1) switches 3 turn off.

[0031] When switch 3 is turned on, an inrush current flows for a short time, damaging switch 3. Therefore, frequently turning switch 3 on and off shortens its lifespan. To extend the lifespan of switch 3, a timer 25 and a latch circuit 26 limit the on and off cycles of switch 3 to once within a predetermined time. Circuit sections 20-26 shown in Figure 2 constitute one embodiment of the "first control unit".

[0032] Figure 3 is a block diagram showing the portion of the control device 9 related to the control of the reactive power compensation device 4. In Figure 3, the control device 9 includes a reactive power calculation unit 30, a subtractor 31, a storage unit 32, a calculation unit 33, a signal generation unit 34, a timer 35, a latch circuit 36, and a reactive power command unit 37.

[0033] The reactive power calculation unit 30 determines the number n of switches 3 that are turned on based on the output signals B1 to BN of the latch circuit 26 (Figure 2), multiplies this number n by the leading reactive power Q1 supplied by the shunt reactor 2 to determine the leading reactive power Qn supplied from the phase adjustment equipment 1 to the distribution line 10.

[0034] The subtracter 31 calculates the reactive power deviation ΔQ = QT - Qn, which is the difference between the target reactive power QT obtained by the reactive power command unit 21 (Fig. 2) and the reactive power Qn obtained by the reactive power calculation unit 30.

[0035] The memory unit 32 stores the number of self-excited SVCs 5, denoted as M, and the rated reactive power QX of the self-excited SVCs 5. The calculation unit 33 determines the minimum number of self-excited SVCs 5, denoted as m, required to supply the reactive power deviation ΔQ based on the reactive power deviation ΔQ (the second reactive power) obtained by the subtracter 31, the number M stored in the memory unit 32, and the rated reactive power QX. m is a natural number greater than or equal to 1 and less than or equal to M.

[0036] For example, when (m - 1)×QX < ΔQ < m×QX, (m - 1) self-excited SVCs 5 cannot supply the leading reactive power ΔQ, while m self-excited SVCs 5 can supply the leading reactive power ΔQ. Therefore, m is the minimum number of units.

[0037] Also, when -m×QX < ΔQ < -(m - 1)×QX, (m - 1) self-excited SVCs 5 cannot supply the lagging reactive power ΔQ, while m self-excited SVCs 5 can supply the lagging reactive power ΔQ. Therefore, m is the minimum number of units.

[0038] The signal generation unit 34 generates signals E1 to EM based on the number of units m obtained by the calculation unit 33. The signals E1 to EM correspond to M sets of self-excited SVCs 5 and switches 6, respectively. The signal generation unit 34 sets the signals of the number m of self-excited SVCs among the signals E1 to EM to the "H" level.

[0039] For example, when m = M, the signal generation unit 34 sets all the signals E1 to EM to the "H" level. Also, when m = 1, the signal generation unit 34 sets the signal E1 to the "H" level and the other signals E2 to EM to the "L" level.

[0040] Timer 35 outputs a pulse signal P2 at predetermined intervals (for example, every hour). Latch circuit 36 ​​receives signals E1 to EM in response to the pulse signal P2, and holds and outputs the received signals E1 to EM as signals F1 to FM.

[0041] Each of the M-unit self-excited SVC5s is activated or deactivated according to the logic levels of signals F1 to FM. For example, if signals F1 to FM are all at the "H" level, all M-unit self-excited SVC5s are activated. If signal F1 is at the "H" level and signals F2 to FM are all at the "L" level, only the first of the M-unit self-excited SVC5s is activated, and the remaining (M-1) units of self-excited SVC5s are deactivated.

[0042] Furthermore, each of the M switches 6 turns on or off according to the logic level of signals F1 to FM. For example, if signals F1 to FM are all at the "H" level, all M switches 6 turn on. If signals F1 to FM are all at the "L" level, all M switches 6 turn off. If signal F1 is at the "H" level and signals F2 to FM are all at the "L" level, only the first of the M switches 6 turns on, and the remaining (M-1) switches 6 turn off.

[0043] Frequent operation and deactivation of the self-excited SVC5 shortens its lifespan. Additionally, a short inrush current flows when the switch 6 is turned on, damaging it. Therefore, frequent on and off of the switch 6 shortens its lifespan. To extend the lifespan of both the self-excited SVC5 and the switch 6, the timer 35 and latch circuit 36 ​​limit the activation and deactivation of the self-excited SVC5 and the on and off of the switch 6 to once within a predetermined time frame.

[0044] The reactive power command unit 37 determines the number of activated self-excited SVC5 units m based on signals F1 to FM. The reactive power command unit 37 also divides the reactive power ΔQ of the deviation obtained by the subtractor 31 by the number of activated self-excited SVC5 units m to determine the reactive power QY = ΔQ / m that each of the m self-excited SVC5 units should output. The reactive power command unit 37 then generates a reactive power command value QC representing the determined reactive power QY and assigns this reactive power command value QC to each of the m self-excited SVC5 units.

[0045] Each of the m activated self-excited SVC5 units out of the M units outputs a reactive power QY = ΔQ / m to the distribution line 10, corresponding to the reactive power command value QC. The operation of the other deactivated self-excited SVC5 units is stopped. Circuit sections 30-37 shown in Figure 3 constitute one embodiment of the "second control unit".

[0046] Figure 4 is a circuit block diagram illustrating the configuration of a self-excited SVC5. In Figure 4, the self-excited SVC5 includes an inverter 40, a capacitor 41, a transformer 42, voltage detectors 43 and 44, a current detector 45, and a control device 46. Figure 4 shows the Mth self-excited SVC5 out of M units.

[0047] The inverter 40 is a well-known type containing multiple sets of IGBTs and diodes. Each set of IGBTs and diodes is connected in antiparallel to the others. A capacitor 41 is connected between the DC terminals 40a and 40b of the inverter 40. The inverter 40 converts the DC voltage VD across the terminals of the capacitor 41 into a commercial frequency AC voltage and outputs it to the AC terminal 40c.

[0048] The primary winding 42a of transformer 42 is connected to the AC terminal 40c of inverter 40, and the secondary winding 42b of transformer 42 is connected to the distribution line 10 via switch 6. Transformer 42 is the dominant inductance component between inverter 40 and distribution line 10. A reactor may also be connected between the secondary winding 42b of transformer 42 and switch 6. Switch 6 turns on when signal FM is at a "H" level and turns off when signal FM is at a "L" level.

[0049] The voltage detector 43 detects the DC voltage VD between the terminals of the capacitor 41 and outputs a signal indicating the detected value to the control device 46. The voltage detector 44 detects the instantaneous value of the AC output voltage VO of the inverter 40 and outputs a signal indicating the detected value to the control device 46. The current detector 45 detects the instantaneous value of the AC output current IO of the inverter 40 and outputs a signal indicating the detected value to the control device 46.

[0050] The control device 46 controls the inverter 40 based on the output signals of the voltage detectors 43, 44 and the current detector 45, the signal FM from the latch circuit 36 ​​(Figure 3), and the reactive power command value QC from the reactive power command unit 37 (Figure 3).

[0051] In other words, when the signal FM is at the "H" level, the control device 46 controls the inverter 40 based on the AC output voltage VO indicated by the output signal of the voltage detector 44 and the AC output current IO indicated by the output signal of the current detector 45, so that the reactive power QY supplied by the inverter 40 matches the reactive power indicated by the reactive power command value QC.

[0052] At this time, the control device 46 reduces the amplitude of the AC output voltage VO of the inverter 40 to less than the amplitude of the AC voltage VS of the distribution line 10, thereby operating the self-excited SVC5 as a shunt reactor and outputting leading reactive power.

[0053] Furthermore, the control device 46 makes the amplitude of the AC output voltage VO of the inverter 40 larger than the amplitude of the AC voltage VS of the distribution line 10, thereby causing the self-excited SVC5 to operate as a phase-advancing capacitor and output lagging reactive power.

[0054] Furthermore, if the signal FM is at the "L" level, the control device 46 stops the operation of the inverter 40. In this case, all IGBTs included in the inverter 40 are kept in the off state. The first to (M-1) self-excited SVC5 have the same configuration as the Mth self-excited SVC5, so their explanation will not be repeated.

[0055] Next, the operation of the reactive power compensation system shown in Figures 1 to 4 will be explained. The voltage detector 7 and current detector 8 (Figure 1) detect the AC voltage VS and AC current I of the power distribution line 10, and based on these detected values, the reactive power calculation unit 20 (Figure 2) calculates the reactive power QS. Based on this reactive power QS, the reactive power command unit 21 calculates the target reactive power QT = -QS, and a signal indicating this target reactive power QT is provided to the calculation unit 23.

[0056] The calculation unit 23 determines the reactive power Qn among the (N+1) reactive powers Q0 to QN stored in the memory unit 22 that has the smallest deviation ΔQ from the target reactive power QT. The calculation unit 23 also determines the number n of switches 3 (Figure 1) that should be turned on in order to output that reactive power Qn from the phase adjustment equipment 1 (Figure 1).

[0057] The signal generation unit 24 (Figure 2) generates signals A1 to AN based on the number n switches 3. Each of signals A1 to AN corresponds to one of the N switches 3. The signals corresponding to n switches 3 among signals A1 to AN are set to the "H" level.

[0058] Timer 25 outputs a pulse signal P1 at predetermined intervals (for example, every 2 hours). In response to this pulse signal P1, signals A1 to AN are taken into the latch circuit 26, held and output as signals B1 to BN.

[0059] As a result, n of the N switches 3 are turned on, while the remaining switches 3 are turned off, n shunt reactors 2 are connected to the distribution line 10, and leading reactive power Qn is supplied from the n shunt reactors 2 to the distribution line 10.

[0060] Furthermore, the reactive power calculation unit 30 (Figure 3) determines the number n of switches 3 that are turned on based on the output signals B1 to BN of the latch circuit 26, and based on that number n, the leading reactive power Qn supplied from the phase adjustment equipment 1 to the distribution line 10 is determined.

[0061] The subtractor 31 calculates the reactive power ΔQ = QT - Qn, which is the difference between the target reactive power QT (Figure 2) determined by the reactive power command unit 21 and the reactive power Qn determined by the reactive power calculation unit 30.

[0062] The calculation unit 33 (Figure 3) determines the minimum number of self-excited SVC5 units m required to supply the reactive power ΔQ due to the deviation, based on the number of self-excited SVC5 units M and the rated reactive power QX stored in the storage unit 32.

[0063] The signal generation unit 34 generates signals E1 to EM based on the number m determined by the calculation unit 33. Signals E1 to EM correspond to M sets of self-excited SVC5 and switches 6, respectively. A number of signals E1 to EM corresponding to the number m of self-excited SVC5s are set to the "H" level.

[0064] A pulse signal P2 is output from the timer 35 at predetermined intervals (for example, every hour). In response to the pulse signal P2, signals E1 to EM are taken into the latch circuit 36 ​​and held and output as signals F1 to FM. As a result, m of the M switches 6 are turned on, while the remaining switches 6 are turned off, and m self-excited SVCs 5 are connected to the distribution line 10. Also, only m of the M self-excited SVCs 5 are activated, while the remaining self-excited SVCs 5 are deactivated.

[0065] The calculation unit 33 determines the number of activated self-excited SVC5 units m based on signals F1 to FM, and the reactive power ΔQ of the deviation obtained by the subtractor 31 is divided by the number of self-excited SVC5 units m to determine the reactive power QY = ΔQ / m that each of the m self-excited SVC5 units should output. In addition, the reactive power command unit 37 generates a reactive power command value QC representing the reactive power QY, and this reactive power command value QC is assigned to each of the m self-excited SVC5 units.

[0066] As a result, reactive power QY = ΔQ / m, corresponding to the reactive power command value QC, is supplied to the distribution line 10 from each of the m activated self-excited SVC5 units out of the M units of self-excited SVC5. The operation of the other deactivated self-excited SVC5 units is stopped. In this way, the reactive power Qn of the target reactive power QT is supplied from the n shunt reactors 2, and the reactive power ΔQ, which is the deviation between the target reactive power QT and the reactive power Qn, is supplied from the m units of self-excited SVC5.

[0067] Next, a specific example will be explained. Assume N=6 and M=5, each shunt reactor 2 outputs a leading reactive power Q1 of 1000kvar, and each self-excited SVC 5 can output a desired reactive power QY between -1000kvar and +1000kvar. The phase-shifting equipment 1 outputs one of seven leading reactive powers Q0 to Q6, which increase stepwise from 0 to 6000kvar in 1000kvar increments, and outputs a leading reactive power Qn.

[0068] When the target reactive power QT is 4600 kvar, the calculation unit 23 (Figure 2) determines that the sixth leading reactive power Q6 = 5000 (kvar) is the sixth leading reactive power Q0 to Q6, which has the smallest deviation from the target reactive power QT, and the number of switches 3 to be turned on, n = 5, is determined. As a result, five of the six switches 3 are turned on, and 5000 kvar of leading reactive power Q6 is output from the five shunt reactors 2.

[0069] Furthermore, the subtractor 31 (Figure 3) calculates the deviation ΔQ = QT - Q6 = 4600 - 5000 = -400 (kvar) between the target reactive power QT and the reactive power Q6. The calculation unit 33 also calculates the minimum number of self-excited SVC5 units m = 1 required to supply the reactive power ΔQ = -400 (kvar) of the deviation. As a result, one switch 6 is turned on, lagging reactive power QY of -400 kvar is supplied from one self-excited SVC5, and reactive power of 5000 - 400 = 4600 (kvar) is supplied from the phase-shifting equipment 1 and the reactive power compensation device 4.

[0070] Furthermore, if the target reactive power QT is 7500kvar, the calculation unit 23 (Figure 2) determines the seventh leading reactive power Q6 = 6000 (kvar), which has the smallest deviation from the target reactive power QT among the seven leading reactive powers Q0 to Q6, and the number of switches 3 to be turned on, n = 6, is determined. As a result, all six switches 3 are turned on, and 6000kvar of leading reactive power Q6 is output from the six shunt reactors 2.

[0071] Furthermore, the subtractor 31 (Figure 3) calculates the deviation ΔQ = QT - Q6 = 7500 - 6000 = 1500 (kvar) between the target reactive power QT and the reactive power Q6. The calculation unit 33 then calculates the minimum number of units m = 2 required to supply the leading reactive power ΔQ = 1500 (kvar) for the deviation. As a result, the two switches 6 are turned on, and 750 kvar each of the two self-excited SVCs 5 supply a total of 1500 kvar of leading reactive power QZ, and the phase adjustment equipment 1 and the reactive power compensation device 4 supply 6000 + 1500 = 7500 (kvar) of leading reactive power.

[0072] As described above, in this embodiment 1, a phase-shifting equipment 1 including N shunt reactors 2 and a reactive power compensation device 4 including M self-excited SVCs 5 are provided. The reactive power Qn with the smallest deviation from the target reactive power QT among the (N+1) reactive powers Q0 to Q1 is output from the phase-shifting equipment 1, and the reactive power ΔQ, which is the deviation between the target reactive power QT and the reactive power Qn, is output from the reactive power compensation device 4. Therefore, the output of the reactive power compensation device 4 can be minimized, and losses can be reduced.

[0073] [Embodiment 2] In Embodiment 1 described above, preliminary investigations revealed that it is necessary to supply mainly leading reactive power to the distribution line 10, so a phase adjustment equipment 1 including N shunt reactors 2 was provided. Embodiment 2 describes a case where preliminary investigations revealed that it is necessary to supply mainly lagging reactive power to the distribution line 10.

[0074] Figure 5 is a circuit block diagram showing the configuration of a reactive power compensation system according to Embodiment 2 of this disclosure, and is shown in comparison with Figure 1. Referring to Figure 5, the difference between this reactive power compensation system and the reactive power compensation system of Embodiment 1 is that the phase regulating equipment 1 is replaced by phase regulating equipment 51. Phase regulating equipment 51 is obtained by replacing the shunt reactor 2 of phase regulating equipment 1 with a phase-advancing capacitor 52.

[0075] In other words, the phase-shifting equipment 51 includes N phase-advancing capacitors 52 and N switches 3, each connected between the distribution line 10 and the N phase-advancing capacitors 52. Each of the N phase-advancing capacitors 52 supplies a predetermined value of lagging reactive power Q1. The on and off states of each of the N switches 3 are controlled by the control device 9.

[0076] When one switch 3 is turned on, a predetermined value of lagging reactive power Q1 is supplied to the distribution line 10 from one phase-advancing capacitor 52 corresponding to that switch 3. When N switches 3 are turned on, lagging reactive power QN = N × Q1 is supplied to the distribution line 10 from N phase-advancing capacitors 52.

[0077] When n of the N switches 3 are turned on, lagging reactive power Qn = n × Q1 is supplied to the distribution line 10 from the n phase-advancing capacitors 52. When n = 0, the lagging reactive power Q0 output from the phase-adjusting equipment 51 to the distribution line 10 is 0 (var). Therefore, the phase-adjusting equipment 51 outputs one of the (N+1) lagging reactive powers Q0 to QN, which increase in a step-like manner from 0 to QN, to the distribution line 10.

[0078] However, in Embodiment 1, the leading phase was positive (+) and the lagging phase was negative (-), but in Embodiment 2, the lagging phase is positive (+) and the leading phase is negative (-). The other configurations and operations are the same as in Embodiment 1, so their explanation will not be repeated.

[0079] In this second embodiment, the same effects as in the first embodiment can be obtained. The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The present invention is indicated by the claims rather than by the foregoing description, and all modifications are intended to be in the sense and scope equivalent to the claims. [Explanation of Symbols]

[0080] 1.51 Phase adjustment equipment, 2 Shunt reactor, 3.6 Switches, 4 Reactive power compensation device, 5 Self-excited SVC, 7.43.44 Voltage detector, 8.45 Current detector, 9.46 Control device, 10 Distribution line, 11 Interconnection transformer, 12 Transmission line, 13 Commercial AC power supply, 14 Generator, 15 Load, 20.30 Reactive power calculation unit, 21.37 Reactive power command unit, 22.32 Memory unit, 23.33 Calculation unit, 24.34 Signal generation unit, 25.35 Timer, 26.36 Latch circuit, 31 Subtractor, 40 Inverter, 41 Capacitor, 42 Transformer, 52 Phase-advancing capacitor.

Claims

1. A phase-shifting device that outputs one of several reactive powers that change in a step-like manner to a distribution line, A reactive power compensation device that outputs the desired reactive power to the distribution line, A first control unit that determines the first reactive power among the plurality of reactive powers that has the smallest deviation from the target reactive power, and causes the phase adjustment equipment to output the first reactive power, A reactive power compensation system comprising: a second control unit that determines a second reactive power as the difference between the target reactive power and the first reactive power, and causes the reactive power compensation device to output the second reactive power.

2. The aforementioned phase adjustment equipment is Multiple shunt reactors, Each includes a plurality of switches connected between the distribution line and the plurality of shunt reactors, The reactive power compensation system according to claim 1, wherein the first control unit determines the number of switches to be turned on in order to output the first reactive power from the phase adjustment equipment, turns on that number of switches, and turns off the remaining switches.

3. The reactive power compensation system according to claim 2, wherein the first control unit turns each of the multiple switches on or off only once per predetermined time interval.

4. The aforementioned phase adjustment equipment is Multiple phase-shifting capacitors, Each includes a plurality of switches connected between the distribution line and the plurality of phase-shifting capacitors, The reactive power compensation system according to claim 1, wherein the first control unit determines the number of switches to be turned on in order to output the first reactive power from the phase adjustment equipment, turns on that number of switches, and turns off the remaining switches.

5. The reactive power compensation system according to claim 4, wherein the first control unit turns each of the plurality of switches on or off only once per predetermined time interval.

6. The reactive power compensation device is Multiple self-excited reactive power compensators, Each includes a plurality of switches connected between the distribution line and the plurality of self-excited reactive power compensators, The reactive power compensation system according to claim 1, wherein the second control unit determines the minimum number of self-excited reactive power compensation devices required to output the second reactive power from the reactive power compensation device, turns on that number of switches and turns off the remaining switches, and outputs the second reactive power from that number of self-excited reactive power compensation devices.

7. The reactive power compensation system according to claim 6, wherein the second control unit turns each of the plurality of switches on or off only once per predetermined time interval.

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