Protection System

Abstract

To provide a protection system which enables the rise of a DC voltage in a DC circuit to be changed when necessary.SOLUTION: In a variable-speed withdrawal power generation system to which the protection system is applied, a secondary excitation converter 1 comprises at least one chopper 14 that suppresses the rise of a DC voltage in a DC circuit and a control device 2 that causes the chopper to operate multiple resistors. When a system failure occurs, whether to operate an excessive voltage prevention device immediately on the basis of a reactive power command value or a reactive current command value can be appropriately determined. The operation of the excessive voltage prevention device is advanced to prevent a zero cross error from occurring by reducing the number of choppers to be operated in a group 14 of N choppers when necessary.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE The present invention relates to a protection system. [Background technology]

[0002] In recent years, adjustable-speed pumped-storage power generation systems, which contribute to stabilizing power grids with their high-speed output control, have been developed and introduced worldwide.

[0003] Fig. 11 shows an example of the configuration of a typical adjustable speed pumped storage power generation system.

[0004] The adjustable speed pumped storage power generation system shown in Fig. 11 is configured to be electrically connectable via a transmission line 3 and a circuit breaker 4 that are connected to a power grid, and is equipped with a main transformer 5, a generator motor (induction machine) 6, a water turbine 7, and a secondary excitation converter 1 including an inverter 11, a converter 12, a capacitor 13, a chopper group 14, an overvoltage protection device 15 (hereinafter, "OVP 15"), an excitation transformer 16, etc. Each of the chopper group 14 includes a resistor 141 and a switching element 142 that are directly connected to each other. The OVP 15 includes a plurality of thyristors 151 that form a short circuit.

[0005] The adjustable speed pumped storage power generation system configured as above employs a secondary excitation converter method in which excitation is performed using a secondary excitation converter 1 connected to the secondary winding (rotor winding) of the generator motor 6. This adjustable speed pumped storage power generation system is a system that is operated in connection with a power grid, and requires protective operation in the event of a grid failure. Therefore, the above-mentioned chopper group 14 and OVP 15 are provided in the secondary excitation converter 1 as protective devices that perform the protective operation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3286049 [Patent Document 2] Patent No. 6640635 [Patent Document 3] Patent No. 6371021 Summary of the Invention [Problem to be solved by the invention]

[0007] Figure 12 shows a typical change in transmission line current after a grid fault occurs.

[0008] As shown in Fig. 12, for example, if a fault occurs in the transmission line 3 at time t1, a DC component is superimposed on the current (transmission line current) flowing through the transmission line 3, and the transmission line current exhibits a current waveform that has AC and DC components. In response to the occurrence of a fault, the contacts of the circuit breaker 4 open at time t2, but if the DC component is large, an arc is drawn between the contacts and the current continues to flow until the current becomes zero (zero crosses). If the time from the occurrence of a fault until the current crosses zero (hereinafter referred to as the "zero cross time") is long, the contacts of the circuit breaker 4 will be damaged, so the zero cross time must be short. The phenomenon in which the current does not cross zero within a specified time after the fault is called a zero miss.

[0009] As a method to avoid this, the OVP 15 is used. As shown in FIG. 11, the OVP 15 is a device having a plurality of thyristors 151 connected to a circuit connecting the secondary winding of the generator motor 6 and the inverter 11, and short-circuits the lines (phases) of the circuit by firing each thyristor. For example, as shown in FIG. 13, when the OVP 15 is operated at time t4, an AC component is superimposed on the transmission line current on the system side of the main transformer 5, and the AC component of the AC component and the DC component becomes large. This allows the transmission line current to zero-cross in a shorter time, for example, at time t5, and the occurrence of a zero miss can be avoided. The earlier the OVP 15 operates, the shorter the zero-cross time can be, so that early OVP operation is expected after the occurrence of a system fault.

[0010] The DC voltage V of the secondary excitation converter 1 relative to a predetermined threshold voltage is used as a trigger for operating the OVP 15. D There is a method that uses the excess of DC voltage V Dis the voltage of a DC circuit (DC link circuit) arranged between the inverter 11 and the converter 12 in the secondary excitation converter 1. For example, as shown in FIG. fault When a system fault occurs at and a transient DC component flows into the secondary excitation converter 1, the DC voltage V D increases as shown by the solid line L0. Without any countermeasures, the chopper operation threshold TH_CHOP will be exceeded immediately, causing an overvoltage, as shown by the solid line L1. D When exceeds the chopper operation threshold TH_CHOP, the chopper group 14 is turned on to cause the chopper group 14 to absorb the energy of the DC circuit. D The rise in the DC voltage V D The rise in the DC voltage V D When the voltage reaches the threshold value TH_OVP, the OVP 15 is operated to short-circuit the lines at the output terminal of the inverter 11. When the lines are short-circuited, no more DC current flows into the DC circuit.

[0011] After a system fault occurs, the DC voltage V D If increases, the OVP 15 operates earlier and the zero cross time becomes shorter. However, since the chopper operation threshold TH_CHOP is lower than the OVP operation threshold TH_OVP, when the chopper group 14 operates, the DC voltage V D The rise in is suppressed and becomes gentle as shown by the dashed line L2. Therefore, if the chopper group 14 does not operate, the time when the failure occurs T fault After that, at time T1, the DC voltage V D When the resistor 141 of the chopper group 14 is increased, the DC voltage V D However, even if a failure occurs that does not require the OVP 15 to operate, the OVP 15 will be operated.

[0012] Such problems are not limited to power generation systems that use hydraulic power, such as the above-mentioned adjustable speed pumped storage power generation system, but can also occur in power generation systems that use other energy sources, such as wind power.

[0013] The problem that the invention aims to solve is to provide a protection system which makes it possible to vary the DC voltage rise in a DC circuit as required. [Means for solving the problem]

[0014] The protection system of the embodiment includes: A first means is applied to a power generation system and shorts lines of a circuit connecting a secondary winding of a generator motor and an inverter by firing a plurality of thyristors connected to the circuit; At least one chopper and a second means for suppressing a rise in the DC voltage in the DC circuit by a power supply protection system, the power supply protection system being provided with: A control device is provided that applies a plurality of resistances to the chopper. Effect of the Invention

[0015] The DC voltage rise in the DC circuit can be varied as required. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing an example of the configuration of a variable speed pumped storage power generation system to which a protection system according to a first embodiment is applied. [Diagram 2] FIG. 1 is a block diagram showing an example of a functional configuration of a protection system according to a first embodiment. [Diagram 3] 4 is a graph showing an example of a plurality of examples of temporal changes in a DC voltage VD realized by the protection system according to the first embodiment. [Figure 4] FIG. 11 is a block diagram showing an example of a functional configuration of a protection system according to a second embodiment. [Diagram 5] 10 is a time chart for explaining an example of control of a chopper gate signal realized by a protection system according to a second embodiment. [Figure 6] 10 is a graph showing an example of a plurality of types of temporal changes in a DC voltage VD realized by a protection system according to a second embodiment. [Figure 7] 6 is a time chart showing a modification of the time chart shown in FIG. 5. [Figure 8] 7 is a graph showing a modification of the graph shown in FIG. 6. [Figure 9] FIG. 5 is a diagram showing a modification of the configuration shown in FIG. 4. [Figure 10] FIG. 13 is a diagram showing an example of the configuration of a doubly excited converter provided in a variable speed pumped storage power generation system to which a protection system according to a fourth embodiment is applied. [Figure 11] 1 is a diagram showing an example of the configuration of a typical adjustable speed pumped storage power generation system. [Figure 12] FIG. 13 is a diagram for explaining a case where the time from the occurrence of a fault to the zero crossing of a current is long. [Figure 13] FIG. 13 is a diagram for explaining a case where the time from the occurrence of a fault to the zero crossing of a current is short. [Figure 14] 4 is a graph for explaining changes over time in a DC voltage VD. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, embodiments will be described with reference to the drawings.

[0018] [First embodiment] First, a first embodiment will be described, focusing on differences from the background art described above.

[0019] Fig. 1 is a diagram showing an example of the configuration of an adjustable speed pumped storage power generation system to which a protection system according to a first embodiment is applied. In Fig. 1, elements common to Fig. 11 are given the same reference numerals. Note that, although this embodiment shows an example in which the protection system is applied to an adjustable speed pumped storage power generation system, the protection system is not limited to power generation systems using hydraulic power such as adjustable speed pumped storage power generation systems, but can also be applied to power generation systems using other energy sources such as wind power.

[0020] As described above, the variable speed pumped storage power generation system shown in FIG. 1 is configured to be electrically connectable to the power grid via the transmission line 3 and the circuit breaker 4, and is also provided with a main transformer 5, a generator motor (induction machine) 6, a water turbine 7, and a secondary excitation converter 1 including an inverter 11, a converter 12, a capacitor 13, a chopper group 14, an OVP 15, and an excitation transformer 16. The inverter 11 and the converter 12 are configured as two-level converters. Each of the chopper groups 14 includes a resistor 141 and a switching element 142 that are connected in series. The OVP 15 includes a plurality of thyristors 151 that form a short circuit. A resistor may be connected in series to each of the thyristors 151. The variable speed pumped storage power generation system is also provided with a control device 2 that controls the secondary excitation converter 1.

[0021] The generator motor 6 is, for example, a variable speed generator motor configured as a doubly-fed AC motor. The water turbine 7 is coupled to the generator motor 6 through a rotating shaft, and is also coupled to a pump (not shown).

[0022] The secondary excitation converter 1 has a function as a frequency converter that supplies, for example, a variable frequency AC to the secondary winding of the generator motor 6, and excites the generator motor 6 as a self-excited excitation device.

[0023] Although the secondary excitation converter 1 may have one chopper, this embodiment will describe an example in which a plurality of choppers 14 are provided as shown in Fig. 1. Also, not all of the individual components shown in Fig. 1 are necessarily required, and some components (such as the main transformer 5 or the excitation transformer 16) can be omitted.

[0024] The adjustable speed pumped storage power generation system shown in Fig. 1 employs a secondary excitation converter method in which excitation is performed using a secondary excitation converter 1 connected to the secondary winding (rotor winding) of a generator motor 6. This adjustable speed pumped storage power generation system is a system that is operated in connection with a power grid, and requires protective operation in the event of a grid failure. Therefore, the above-mentioned chopper group 14 and OVP 15 are provided in the secondary excitation converter 1 as protective devices that perform the protective operation.

[0025] The chopper group 14 and the OVP 15 provided in the secondary excitation converter 1 function as a protection device that performs a protective operation when a system fault occurs. The chopper group 14 and the OVP 15 operate under the control of the control device 2.

[0026] The control device 2 controls the secondary excitation converter 1, and controls the AC voltage, current, frequency, and phase to be supplied to the secondary winding (rotor winding) of the generator motor 6, as well as controls gate signals to be supplied to the gates of the switching elements 142 of each chopper 14 and gate signals to be supplied to the gates of each thyristor 151 of the OVP 15. All or part of the control by the control device 2 may be realized by a program executed by a processor, for example.

[0027] In this embodiment, a protection system including the chopper group 14 and the control device 2 is used to protect the DC voltage V in the DC circuit of the secondary excitation converter 1 when a system fault occurs. D This makes it possible to change the rise in the chopper load as necessary. In this protection system, the chopper group 14 is connected in parallel in the DC circuit of the secondary excitation converter 1, and each chopper group can operate independently under the control of the control device 2. The control device 2 can variably control the operation of the parallel-connected chopper group 14 individually (or in groups).

[0028] In particular, the control device 2 controls the operation state of the variable speed pumped storage power generation system and the DC voltage V D Monitors the DC voltage V Dexceeds a predetermined threshold, the control device 2 has a function of applying a plurality of resistances to the chopper group 14 according to the operating state. The control device 2 is configured to change the resistance applied to the chopper group 14 according to, for example, the reactive power or reactive current of the adjustable speed pumped storage power generation system, and for example, the resistance applied to the chopper group 14 is increased as the reactive power or reactive current of the adjustable speed pumped storage power generation system increases.

[0029] The multiple resistances referred to here refer to multiple resistances in a broad sense, including, for example, a case where multiple resistances of the chopper group 14 as a whole are realized by changing the number of choppers to be operated among the chopper group 14, as well as a case where multiple changes in time of the resistance of the chopper group are realized by changing the timing at which the chopper group 14 (or a part of it) is operated, or by changing the time for which the supply of a signal to the chopper group 14 (or a part of it) to operate is blocked (masked) to the chopper 14.

[0030] In this first embodiment, an example is shown in which the control device 2 changes the number of choppers to be operated among the chopper group 14 depending on the operating state of the adjustable speed pumped storage power generation system, thereby realizing multiple resistances for the chopper group 14 as a whole.

[0031] The control device 2 is configured to change the resistance acting on the chopper group 14 by changing the number of choppers to be operated among the chopper group 14 in accordance with, for example, the reactive power or reactive current of the adjustable speed pumped storage power generation system; for example, the larger the reactive power or reactive current of the adjustable speed pumped storage power generation system, the fewer the number of choppers to be operated among the chopper group 14.

[0032] For example, when the reactive power (weak excitation) output of the variable speed pumped storage power generation system is large, the transient DC component after the fault occurs becomes large and zero miss is likely to occur. Therefore, in order to operate the OVP 15 more quickly, the control device 2 adjusts the DC voltage V DReduce the number of choppers to be operated so that the rise of [] becomes steep. On the other hand, when the reactive power (weak field excitation) output of the variable-speed pumped-storage power generation system is not large, the possibility of zero miss is low and it is not necessary to operate OVP15 quickly. Therefore, in order to make use of the original function of the chopper group 14, the control device 2 controls the DC voltage V D Increase the number of choppers to be operated so that the rise of [] is suppressed and becomes gentle.

[0033] FIG. 2 is a block diagram showing an example of the functional configuration of the protection system according to the first embodiment. FIG. 3 is a graph showing an example of a plurality of temporal changes of the DC voltage V D realized by the protection system according to the first embodiment. In the present embodiment, an example in which there are two patterns of temporal changes of the DC voltage V D is shown, but the present invention is not limited to this, and the number of patterns of temporal changes of the DC voltage V D can be three or more.

[0034] Here, the chopper group 14 is composed of N chopper groups connected in parallel, and all of them are in the off state during normal operation. Further, the chopper gate signal generation unit 21 of the control device 2 supplies chopper gate signals G1, G2,..., G N to the N chopper groups 14 individually, and can turn on or off the N chopper groups 14 individually. Also, let the number of choppers 14 in the on state among the N chopper groups 14 (chopper operation number) be represented by N ON . Here, the value of N ON is a natural number, and for example, either one of the values a and b (where a < b, a < N, b <= N) is set according to the operating state of the variable-speed pumped-storage power generation system.

[0035] As shown in FIG. 2, in the first embodiment, the control device 2 is provided with a chopper gate signal generation unit 21 and an operating state determination unit 22.

[0036] The chopper gate signal generation unit 21 generates chopper gate signals G1, G2,..., G Nand outputting them to the corresponding chopper groups 14.

[0037] For example, the chopper gate signal generator 21 may be configured to monitor the DC voltage V D exceeds the chopper operation threshold TH_CHOP, the number of choppers to be operated (i.e., the number of chopper gate signals to be switched from the OFF state to the ON state) is determined according to the operating state determined by the operating state determination unit 22, and the determined number of chopper gate signals are switched from the OFF state to the ON state. Note that the number of choppers to be operated, which is determined here, may be adjusted as appropriate. By adjusting the number of choppers to be operated according to the operating state, the DC voltage V D It is possible to adjust the time it takes for the voltage to reach the chopper operation threshold TH_CHOP and the OVP operation threshold TH_OVP.

[0038] The operating state determination unit 22 determines the operating state of the variable speed pumped storage power generation system, and is configured to determine the operating state of the variable speed pumped storage power generation system based on, for example, a reactive power command value Q * (or reactive current command value) and based on this, determine the state of the reactive power (or reactive current) of the adjustable speed pumped storage power generation system.

[0039] For example, the operating state determination unit 22 determines the reactive power command value Q * When the reactive power command value Q exceeds a predetermined threshold, the variable speed pumped storage power generation system is determined to be in a state where the reactive power is large (i.e., the transient DC component after the occurrence of a fault is large and the system is prone to zero misses). * If the reactive power command value Q is below a predetermined threshold, it is determined that the reactive power output of the variable speed pumped storage power generation system is not large. * However, a similar determination may be made using a reactive current command value instead of the reactive power command value.

[0040] When the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is large, the chopper gate signal generation unit 21 increases the DC voltage V D The number of chopper operations N is set so that the rise in ON is set to a, for example, and a chopper gate signals corresponding to a choppers 14 are switched from the OFF state to the ON state.

[0041] On the other hand, when the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is not large, the chopper gate signal generation unit 21 determines that the possibility of a zero miss occurring is low and there is no need to operate the OVP 15 quickly, so the chopper operation number N ON is set to b, for example, and b chopper gate signals corresponding to the b choppers 14 are switched from the OFF state to the ON state.

[0042] In such a configuration, as shown in FIG. fault When a system fault occurs at and a transient DC component flows into the secondary excitation converter 1, the DC voltage V D As shown by the solid line L0, when it reaches the chopper operation threshold TH_CHOP, N ON This chopper group 14 is turned on and operates.

[0043] For example, when the reactive power of a variable speed pumped storage power generation system is large, the number of chopper operations N ON is set to, for example, a. In this case, the DC voltage V D is the solid line L a As shown in ON = b, and at time T a When the OVP operation threshold TH_OVP is reached, the OVP 15 operates.

[0044] On the other hand, when the reactive power of the variable speed pumped storage power generation system is not large, the number of chopper operations N ON is set to, for example, b. In this case, the DC voltage V D is dashed line L b As shown inON = a, and at time T a A time later than T b When the OVP operation threshold TH_OVP is reached, the OVP 15 operates.

[0045] According to the first embodiment, when a grid fault occurs, it is possible to appropriately determine whether or not the OVP 15 should be operated immediately based on the reactive power command value or the reactive current command value, and, if necessary, the number of choppers to be operated among the N chopper groups 14 can be reduced to hasten the operation of the OVP 15 and avoid the occurrence of a zero miss.

[0046] In the first embodiment, the method of changing the resistance of the chopper group 14 as a whole by changing how many of the choppers 14 connected in parallel are operated has been described, but the resistance can be changed equivalently by a different method. In the embodiment described later, such a different method will be introduced.

[0047] [Second embodiment] Next, a second embodiment will be described. In the following, the description of the parts that overlap with the first embodiment will be omitted, and the description will focus on the parts that are different from the first embodiment.

[0048] The configuration of an adjustable speed pumped storage power generation system to which the protection system according to the second embodiment is applied is the same as the configuration shown in FIG. 1 of the first embodiment.

[0049] In the first embodiment described above, a method was shown in which a plurality of resistances for the chopper group 14 as a whole were realized by changing the number of choppers to be operated among the chopper group 14. In this second embodiment, a method is shown in which a plurality of temporal changes in the resistance of the chopper group are realized by changing the timing at which the chopper group 14 (or a part thereof) is operated, or by changing the time for which a signal that operates the chopper group 14 (or a part thereof) is masked.

[0050] In this second embodiment, an example is shown in which the control device 2 realizes multiple resistances for the chopper group 14 as a whole by changing the timing for operating the chopper group 14 (or a part of it) or by changing the time for masking a signal for operating the chopper group 14 (or a part of it) depending on the operating state of the adjustable speed pumped storage power generation system.

[0051] The control device 2 is configured to change the resistance acting on the chopper group 14, for example, by delaying the timing of operating the chopper group 14 (or a part of it) or lengthening the time for which the signal for operating the chopper group 14 (or a part of it) is masked, depending on the reactive power or reactive current of the adjustable speed pumped storage power generation system; for example, the greater the reactive power or reactive current of the adjustable speed pumped storage power generation system, the later the timing of operating the chopper group 14 (or a part of it) is, or the longer the time for which the signal for operating the chopper group 14 (or a part of it) is masked.

[0052] For example, when the reactive power (weak excitation) output of the adjustable speed pumped storage power generation system is large, the transient DC component after the occurrence of a fault becomes large and zero miss is likely to occur, so in order to operate the OVP 15 sooner, the control device 2 delays the timing of operating the chopper group 14 or lengthens the time for masking the signal that operates the chopper group 14. On the other hand, when the reactive power (weak excitation) output of the adjustable speed pumped storage power generation system is not large, the possibility of zero miss occurring is low and there is no need to operate the OVP 15 sooner, so in order to utilize the original function of the chopper group 14, the control device 2 does not delay the timing of operating the chopper group 14 but keeps it normal, or does not mask the signal that operates the chopper group 14.

[0053] Fig. 4 is a block diagram showing an example of a functional configuration of a protection system according to a second embodiment. Fig. 5 is a time chart for explaining an example of control of a chopper gate signal realized by the protection system according to the second embodiment. Fig. 6 is a time chart for explaining an example of control of a DC voltage V D 1 is a graph showing an example of a plurality of types of temporal changes in the DC voltage V D The following shows an example in which there are two patterns of time change of DC voltage V D It is also possible to have three or more patterns of temporal change.

[0054] As shown in Fig. 4, in the second embodiment, in addition to the configuration shown in Fig. 2, a delay processing unit 23 is further provided in the control device 2. Note that, although the driving state determination unit 22 described above is not shown in Fig. 4, the driving state determination unit 22 is also provided in the control device 2 as in the case of Fig. 2.

[0055] The chopper gate signal generating unit 21 generates chopper gate signals G1, G2, . . . , G N (or a chopper gate signal GATE that is a combination of these) and supplies the signal to the delay processing unit 23.

[0056] For example, the chopper gate signal generator 21 may be configured to monitor the DC voltage V D When the chopper operation threshold TH_CHOP is exceeded, the chopper gate signals G1, G2, ..., G N (or a chopper gate signal GATE which is a combination of these) is switched from the OFF state to the ON state.

[0057] The delay processing unit 23 receives the chopper gate signals G1, G2, . . . , G1, G2, . . . , G2, supplied from the chopper gate signal generating unit 21. N to the chopper group 14, the timing at which one or more chopper gate signals are switched from an OFF state to an ON state is delayed by a predetermined time.

[0058] For example, the delay processing unit 23 determines a time width for delaying the operation of the chopper group 14 in accordance with the operating state determined by the operating state determination unit 22 (not shown), and supplies chopper gate signals G1, G2, ..., G to the chopper group 14 for the determined time width. N delays the switching from the off state to the on state.

[0059] Here, an example is shown in which the delay time width is the same for all chopper gate signals when delaying the operation of the chopper group 14 according to the operating state, but the delay time width may be different for each chopper gate signal. Also, the number of chopper gate signals to which a delay is applied may be changed according to the operating state. By adjusting the delay time width for each chopper gate signal or adjusting the number of chopper gate signals to which a delay is applied, the DC voltage V D It is possible to adjust the time it takes for the voltage to reach the chopper operation threshold TH_CHOP and the OVP operation threshold TH_OVP.

[0060] For example, when the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is in a large state, the delay processing unit 23 delays the DC voltage V D The chopper gate signals G1, G2, ..., G N 5, the delay processing unit 23 delays the switching of the chopper gate signal GATE supplied from the chopper gate signal generating unit 21 from the OFF state to the ON state by a predetermined time width T d The chopper gate signals G1, G2, . . . , G are supplied to the chopper group 14 at a timing delayed by N For example, the delay processing unit 23 switches the chopper gate signals G1, G2, ..., G from an OFF state to an ON state as the reactive power or reactive current of the variable speed pumped storage power generation system indicated by the determination result of the operation state determination unit 22 increases. N The timing at which the switch is switched from the OFF state to the ON state is delayed.

[0061] On the other hand, when the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is not large, the delay processing unit 23 delays the chopper gate signals G1, G2, . . . , G N In this case, the delay processing unit 23 delays the switching of the chopper gate signals G1, G2, ..., GATE to be supplied to the chopper group 14 at the timing when the chopper gate signal GATE changes from the off state to the on state. N from the OFF state to the ON state.

[0062] In addition, the time interval T d The value of time span T may be changed as appropriate. d By adjusting the DC voltage V D It is possible to adjust the time it takes for the voltage to reach the chopper operation threshold TH_CHOP and the OVP operation threshold TH_OVP.

[0063] In such a configuration, as shown in FIG. fault When a system fault occurs at and a transient DC component flows into the secondary excitation converter 1, the DC voltage V D rises as shown by the solid line L0, and the DC voltage V D When the chopper operation threshold TH_CHOP is reached, the chopper gate signal GATE described above changes from the OFF state to the ON state.

[0064] For example, when the reactive power of the variable speed pumped storage power generation system is large, the transient DC component after the fault occurs becomes large and zero miss is likely to occur. In order to avoid zero miss, the chopper gate signals G1, G2, ..., G N The switching from the OFF state to the ON state occurs within a certain time period T d is delayed by

[0065] In this case, the DC voltage V D After the chopper gate signal GATE reaches the chopper operation threshold TH_CHOP and goes into the on state, a predetermined delay T dUntil the N chopper groups 14 are activated, the DC voltage V D is the solid line L c As shown in FIG. 14, the voltage V rises sharply (similar to the solid line L1 in FIG. 14).

[0066] time width T d After this time, the chopper gate signals G1, G2, ..., G N changes from an off state to an on state, and the N chopper groups 14 operate, generating a DC voltage V D is the solid line L d At this time, the DC voltage V D Since the delay is increased to some extent, the OVP operation threshold TH_OVP is reached at time T3, which is earlier than when there is no delay, and the OVP 15 operates.

[0067] On the other hand, when the reactive power of the variable speed pumped storage power generation system is not large, the time span T d There is no delay, and the DC voltage V D When the DC voltage V reaches the chopper operation threshold TH_CHOP and the chopper gate signal GATE is turned on, the N chopper groups 14 are simultaneously operated. D As shown by the solid line L2, increases gradually, and reaches the OVP operation threshold TH_OVP at time T2, which is later than time T3, and the OVP 15 operates.

[0068] So far, an example has been shown in which the operations of all of the N chopper groups 14 are delayed, but instead of delaying the operations of all of the chopper groups 14, it is also possible to delay the operations of only a portion (one or more) of the choppers 14. Below, an example in which the operations of only a portion of the choppers 14 are delayed is shown.

[0069] Fig. 7 is a time chart showing a modification of the time chart shown in Fig. 5. Fig. 8 is a graph showing a modification of the graph shown in Fig. 6.

[0070] Here, chopper gate signals G1, G2, …, G N Among them, one chopper gate signal Gk 10. Here, we show an example of delaying the switching of the chopper gate signal G from its off state to its on state, but instead using two or more chopper gate signals G k , . . . may be switched from the OFF state to the ON state with a delay. k+1 ,…,G N The timing charts relating to the above are omitted.

[0071] When the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is in a large state, the delay processing unit 23 delays the chopper gate signal G k 7, the delay processing unit 23 delays the switching from the OFF state to the ON state only when the chopper gate signal GATE supplied from the chopper gate signal generating unit 21 changes from the OFF state to the ON state. k Chopper gate signals G1, G2, …, G k-1 and G k+1 ,…,G N is switched from the OFF state to the ON state, and the chopper gate signal GATE is switched from the OFF state to the ON state for a period of time T d The chopper gate signal G k For example, the delay processing unit 23 switches the chopper gate signal G from an OFF state to an ON state as the reactive power or reactive current of the variable speed pumped storage power generation system indicated by the determination result of the operation state determination unit 22 increases. k The timing at which the switch is switched from the OFF state to the ON state is delayed.

[0072] On the other hand, when the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is not large, the delay processing unit 23 delays the chopper gate signal G k All chopper gate signals G1, G2, …, G N The chopper gate signals G1, G2, ..., G are switched from the off state to the on state without any delay, and are switched at the normal timing. NIn this case, the delay processing unit 23 delays the chopper gate signals G1, G2, ..., GATE at the timing when the chopper gate signal GATE changes from the OFF state to the ON state. N from the OFF state to the ON state.

[0073] In addition, the time interval T d The value of time span T may be changed as appropriate. d By adjusting the DC voltage V D It is possible to adjust the time it takes for the voltage to reach the chopper operation threshold TH_CHOP and the OVP operation threshold TH_OVP.

[0074] In such a configuration, as shown in FIG. fault When a system fault occurs at and a transient DC component flows into the secondary excitation converter 1, the DC voltage V D rises as indicated by the solid line L0, and when it reaches the chopper operation threshold TH_CHOP, the above-mentioned chopper gate signal GATE changes from the OFF state to the ON state.

[0075] For example, when the reactive power of the variable speed pumped storage power generation system is large, the transient DC component after the fault occurs becomes large and zero miss is likely to occur. In order to avoid zero miss, the chopper gate signals G1, G2, ..., G N Of the chopper gate signals G k The switching from the OFF state to the ON state occurs within a certain time period T d is delayed by

[0076] In this case, the DC voltage V D When the chopper gate signal GATE reaches the chopper operation threshold TH_CHOP and the chopper gate signal GATE is turned on, k Chopper gate signals G1, G2, …, G k-1 and G k+1 ,…,G N are turned on and the corresponding N-1 choppers operate, but after a certain delay T d Until the chopper gate signal G kdoes not turn on and the corresponding chopper 14 does not operate, and the DC voltage V D is the solid line L e At this time, the DC voltage V D is the solid line L e As shown in FIG. 6, the solid line L c 14).

[0077] time width T d After this time, the chopper gate signal G k The chopper gate signal G k A chopper 14 corresponding to the DC voltage V D is the solid line L f At this time, the DC voltage V D Since the delay has increased to some extent, the OVP operation threshold TH_OVP is reached at time T3, which is earlier than when there is no delay, and the OVP 15 operates.

[0078] In this way, as shown in FIG. 8, a DC voltage V D It is possible to form a pattern of time-varying changes.

[0079] FIG. 9 is a diagram showing a modification of the configuration shown in FIG.

[0080] As shown in FIG. 9, in the control device 2, a mask processing unit 24 is arranged in place of the delay processing unit 23.

[0081] As described above, the chopper gate signal generating unit 21 generates chopper gate signals G1, G2, . . . , G N (or a chopper gate signal GATE that is a combination of these) and supplies the signal to the delay processing unit 23.

[0082] For example, the chopper gate signal generator 21 may be configured to monitor the DC voltage V DWhen the chopper operation threshold TH_CHOP is exceeded, the chopper gate signals G1, G2, ..., G N from the OFF state to the ON state.

[0083] The mask processing unit 24 receives the chopper gate signals G1, G2, . . . , G from the chopper gate signal generating unit 21. N to the chopper group 14, the amplifier has a function of masking one or more chopper gate signals for a predetermined period of time (blocking the supply of the chopper gate signal to the chopper 14).

[0084] For example, the mask processing unit 24 determines a time width for delaying the operation of the chopper group 14 in accordance with the operating state determined by the operating state determination unit 22 (not shown), and supplies chopper gate signals G1, G2, ..., G to the chopper group 14 (or a part of it) for the period of the determined time width. N (or part of it) is masked.

[0085] Here, an example is shown in which the masking time width is the same for all chopper gate signals when delaying the operation of the chopper group 14 according to the operating state, but the masking time width may be different for each chopper gate signal. Also, the number of chopper gate signals to which masking is applied may be changed according to the operating state. By adjusting the masking time width for each chopper gate signal or adjusting the number of chopper gate signals to which masking is applied, the DC voltage V D It is possible to adjust the time it takes for the voltage to reach the chopper operation threshold TH_CHOP and the OVP operation threshold TH_OVP.

[0086] For example, when the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is in a large state, the mask processing unit 24 adjusts the DC voltage V D The on-state chopper gate signals G1, G2, ..., G N (or a part of it) for a time span of T dFor example, the delay processing unit 23 masks only the chopper gate signals G1, G2, ..., G as the reactive power or reactive current of the variable speed pumped storage power generation system, which is indicated by the determination result of the operation state determination unit 22, is larger. N The time span T for masking d Lengthen the length.

[0087] On the other hand, when the operation state determination unit 22 determines that the reactive power of the variable speed pumped storage power generation system is not large, the mask processing unit 24 masks the chopper gate signals G1, G2, . . . , G N (or part of it) is not masked and is output as is.

[0088] In this case, the DC voltage V D The change over time is similar to that shown in FIG. 6 and FIG. 8, and therefore the description thereof will be omitted.

[0089] According to the second embodiment, when a system fault occurs, it is possible to appropriately determine whether or not to immediately operate the OVP 15 based on the reactive power command value or the reactive current command value, and, if necessary, it is possible to hasten the operation of the OVP 15 and avoid the occurrence of a zero miss by delaying the timing of operating the chopper group 14 (or a part of it) or by lengthening the time for masking the signal that operates the chopper group 14 (or a part of it).

[0090] [Third embodiment] Next, a third embodiment will be described. In the following, the description of the parts that overlap with the first and second embodiments will be omitted, and the description will focus on the parts that are different from the first and second embodiments.

[0091] In the first and second embodiments described above, an example was shown in which the control device 2 realizes multiple resistances for the chopper group 14 as a whole depending on the reactive power or reactive current of the adjustable speed pumped storage power generation system. In this third embodiment, an example is shown in which the control device 2 realizes multiple resistances for the chopper group 14 as a whole depending on the type of system fault.

[0092] The control device 2 has a function of monitoring changes in the system voltage, detecting a system fault from the change in the system voltage, and identifying the type of system fault. For example, the control device 2 can identify whether the system fault is a fault in only one of the three lines constituting the three-phase AC (such as a one-phase ground fault) or a fault in all three lines (such as a three-phase ground fault). In the case of a fault in all three lines, the control device 2 can determine, for example, that the OVP 15 should be immediately operated and can detect the DC voltage V D In the case of a fault in only one line, for example, it is determined that OVP15 should not be operated immediately, and the DC voltage V D The increase in the temperature is suppressed and controlled to be gradual.

[0093] The control device 2 may be configured to change the resistance acting on the chopper group 14 by changing the number of choppers to be operated among the chopper group 14, depending on the type of grid failure, for example.

[0094] In addition, the control device 2 may be configured to change the resistance acting on the chopper group 14, for example, by delaying the timing of operating the chopper group 14 (or a part of it) or lengthening the time for masking a signal that operates the chopper group 14 (or a part of it), depending on the type of system fault.

[0095] According to the third embodiment, when a system fault occurs, it is possible to appropriately determine whether or not OVP 15 should be operated immediately based on the type of system fault, and if necessary, it is possible to hasten the operation of OVP 15 to avoid the occurrence of a zero miss.

[0096] [Fourth embodiment] Next, a fourth embodiment will be described. In the following, the description of the parts that overlap with the first to third embodiments will be omitted, and the description will focus on the parts that are different from the first and second embodiments.

[0097] In the first to third embodiments described above, examples were shown in which a two-level converter was applied to the secondary excitation converter 1, but in this fourth embodiment, an example is shown in which a neutral-point clamped converter, i.e., an NPC (Neutral-Point-Clamped) converter is applied to the secondary excitation converter 1.

[0098] Fig. 10 is a diagram showing an example of the configuration of a secondary excitation converter provided in a variable speed pumped storage power generation system to which a protection system according to a fourth embodiment is applied. In Fig. 10, elements common to Fig. 1 are denoted by the same reference numerals.

[0099] The adjustable speed pumped storage power generation system shown in Fig. 10 is configured to be electrically connectable via a transmission line 3 and a circuit breaker 4 leading to a power grid as shown in Fig. 1, although not shown, and also includes a main transformer 5, a generator motor (induction machine) 6, and a water turbine 7. This adjustable speed pumped storage power generation system includes a secondary excitation converter 1 including an inverter 11, a converter 12, a two-stage capacitor 13, a two-stage chopper group 14, an OVP 15 (not shown), an excitation transformer 16 (not shown), etc. The inverter 11 and the converter 12 are configured as a three-phase NPC converter. This adjustable speed pumped storage power generation system also includes a control device 2 (not shown).

[0100] In the case of an NPC converter, there are two DC circuits, one on the P side and one on the N side (voltage V DP The circuit part where voltage V DN A capacitor 13 and a chopper group 14 are connected to each of the circuits.

[0101] In the example of Fig. 10, a plurality of chopper groups 14A to 14N are connected in parallel. Each chopper group includes one chopper 14 on the P side and one chopper 14 on the N side, and can operate independently on a chopper group basis. A control device 2 (not shown) can variably control the chopper groups 14 individually for each chopper group.

[0102] In the fourth embodiment, the control device 2 controls the chopper group 14 not on a chopper-by-chopper basis but on a chopper-group basis. Other specific control methods are similar to those described in the first to third embodiments.

[0103] Also, a configuration may be adopted in which a plurality of secondary excitation converters 1 shown in Fig. 10 are prepared and connected in parallel. In this case, for example, the three-phase AC side circuits of the plurality of inverters 11 may be connected in parallel to the secondary winding of the generator motor 6 shown in Fig. 1, and the three-phase AC side circuits of the plurality of converters 12 may be connected in parallel to the excitation transformer 16 or the stator winding of the generator motor 6 shown in Fig. 1. In this case, the DC circuits may be separately arranged in the plurality of secondary excitation converters, or only one DC circuit may be arranged collectively.

[0104] According to the fourth embodiment, even when an NPC converter is applied to the secondary excitation converter instead of a two-level converter, the same effects as those of the second to fourth embodiments can be obtained.

[0105] As described above in detail, according to each embodiment, the increase in DC voltage in the DC circuit can be changed as necessary.

[0106] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0107] 1...secondary excitation converter, 2...control device, 3...transmission line, 4...circuit breaker, 5...main transformer, 6...generator motor, 7...water turbine, 11...inverter, 12...converter, 13...capacitor, 14...chopper, 141...resistor, 142...switching element, 15...overvoltage protection device (OVP), 151...thyristor, 16...excitation transformer, 21...chopper gate signal generating unit, 22...operating state determination unit, 23...delay processing unit, 24...mask processing unit.

Claims

1. A protection system applied to a power generation system, comprising: a first means for short-circuiting between the lines of a circuit connecting a secondary winding of a generator motor and an inverter by ignition of a plurality of thyristors connected to the circuit; and a second means for suppressing an increase in DC voltage in the DC circuit by at least one chopper, a control device that applies a plurality of resistances to the chopper so that a rise in DC voltage in the DC circuit when a system fault occurs can be changed according to an operating state of the power generation system; Protection system.

2. The chopper is composed of a plurality of choppers that operate independently. The protection system of claim 1 .

3. The control device includes: changing the resistance applied to the chopper in response to an operating state of the power generation system; A protection system according to claim 1 or 2.

4. The control device includes: changing the number of choppers to be operated among the plurality of choppers according to an operating state of the power generation system; The protection system of claim 2.

5. The control device includes: changing a timing for operating the chopper depending on an operating state of the power generation system; A protection system according to claim 1 or 2.

6. The control device includes: changing a time for masking a signal for operating the chopper according to an operating state of the power generation system; A protection system according to claim 1 or 2.

7. The control device includes: changing a resistance applied to the chopper in response to a reactive power or a reactive current of the power generation system; A protection system according to claim 1 or 2.

8. The control device includes: The larger the reactive power or reactive current of the power generation system, the larger the resistance applied to the chopper is. The protection system of claim 7.

9. The control device includes: changing the number of choppers to be operated among the plurality of choppers according to the reactive power or reactive current of the power generation system; The protection system of claim 2.

10. The control device includes: the number of choppers to be operated among the plurality of choppers is reduced as the reactive power or reactive current of the power generation system is increased; 10. The protection system of claim 9.

11. The control device includes: changing a timing for operating the chopper in response to a reactive power or a reactive current of the power generation system; A protection system according to claim 1 or 2.

12. The control device includes: the timing of operating the chopper is delayed as the reactive power or reactive current of the power generation system is larger; 12. The protection system of claim 11.

13. The control device includes: changing a time for masking a signal for operating the chopper in accordance with a reactive power or a reactive current of the power generation system; A protection system according to claim 1 or 2.

14. The control device includes: The larger the reactive power or reactive current of the power generation system, the longer the masking time of the signal for operating the chopper is set.

14. The protection system of claim 13.

15. The control device includes: A system fault is detected from a change in the system voltage, and the resistance applied to the chopper is changed according to the type of the fault. A protection system according to claim 1 or 2.

16. The control device includes: detecting a system fault from a change in a system voltage, and changing the number of choppers to be operated among the plurality of choppers according to the type of the fault; The protection system of claim 2.

17. The control device includes: A system fault is detected from a change in the system voltage, and the timing of operating the chopper is changed according to the type of the fault. A protection system according to claim 1 or 2.

18. The control device includes: a system fault is detected from a change in a system voltage, and a time for masking a signal for operating the chopper is changed according to the type of the fault; A protection system according to claim 1 or 2.

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