JP7265512B2 - reactive power compensator - Google Patents

Description

Embodiments of the present invention relate to reactive power compensators.

A self-excited reactive power compensator that is connected to an AC power system and outputs reactive power to the power system to suppress fluctuations in the voltage of the power system is known. A reactive power compensator includes a converter that converts power and a controller that controls the operation of the converter. Such reactive power compensators are used, for example, to suppress flicker in electric furnaces.

In a self-excited reactive power compensator used to suppress flicker in an electric furnace, a control mode that supplies compensation current for the detected load current fluctuation and outputs reactive power according to an arbitrarily set command value. Two control modes have been provided: a control mode for

In such a reactive power compensator, there is a possibility that the controller detects an overcurrent in the output current of the converter and unintentionally stops the converter when switching between control modes.

When switching between control modes, if there is a large difference between the command values of the control modes, the command values change abruptly according to the switching of the control modes. If the command value changes abruptly in this way, the output current of the converter cannot follow the command value, causing an overshoot, and as a result, overcurrent may occur as described above. .

For this reason, it is desirable for the reactive power compensator to be able to suppress unintended stoppage of operation due to overcurrent even when switching between two control modes.

JP-A-57-25014

An embodiment of the present invention provides a reactive power compensator that suppresses unintended stoppage of operation due to overcurrent.

According to the embodiment of the present invention, it is connected to a load system to which an electric furnace is connected, and outputs reactive power to the load system, thereby suppressing fluctuations in the voltage of the load system due to the operation of the electric furnace. A self-commutated converter and a control device for controlling the operation of the self-commutated converter in accordance with a command value related to the output current output from the self-commutated converter to the load system, the controller comprising: A first control mode for controlling the operation of the self-commutated converter to suppress voltage flicker in the load system, and a control mode for controlling the operation of the self-commutated converter to output constant reactive power to the load system. and a control device having a second control mode, wherein the control device changes from the command value for the first control mode in accordance with switching from the first control mode to the second control mode A reactive power compensator is provided for gradually changing the command value for the first control mode to the command value for the second control mode when switching to the command value for the second control mode. .

A reactive power compensator that suppresses unintended stoppage of operation due to overcurrent is provided.

1 is a block diagram schematically showing an electric furnace system and a reactive power compensator according to an embodiment; FIG. It is a block diagram which represents typically the control apparatus which concerns on embodiment. 1 is a block diagram schematically showing a switching circuit according to an embodiment; FIG. 4(a) to 4(e) are graphs schematically showing an example of the operation of the reactive power compensator according to the embodiment. FIGS. 5(a) to 5(e) are graphs schematically showing an example of reference operation of the reactive power compensator. 6(a) and 6(b) are graphs schematically showing a modification of the operation of the reactive power compensator according to the embodiment.

Each embodiment will be described below with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between portions, and the like are not necessarily the same as the actual ones. Also, even when the same parts are shown, the dimensions and ratios may be different depending on the drawing.
In addition, in the present specification and each figure, the same reference numerals are given to the same elements as those described above with respect to the already-appearing figures, and detailed description thereof will be omitted as appropriate.

FIG. 1 is a block diagram schematically showing an electric furnace system and a reactive power compensator according to an embodiment.
As shown in FIG. 1 , the electric furnace system 2 includes a reactive power compensator 10 and an electric furnace 100 . The reactive power compensator 10 and the electric furnace 100 are connected to a load system 102 . The load system 102 is connected to a power system 108 via a transformer 104, a power receiving system 106, and the like. The load system 102 is supplied with three-phase AC power supplied from a power system 108 and transformed by a transformer 104 or the like.

The electric furnace 100 melts metal materials based on three-phase AC power supplied from the load system 102 . The electric furnace 100 is, for example, an arc furnace. The electric furnace 100 melts the metal material charged into the furnace body by raising and lowering the electrode and generating arc discharge between the electrode and the metal material (for example, scrap).

By outputting reactive power to the load system 102 , the reactive power compensator 10 suppresses fluctuations in the voltage of the load system 102 caused by the operation of the electric furnace 100 .

The electric furnace system 2 further comprises voltage detectors 110, 112, current detectors 114, 116, and a harmonic filter 118, for example.

Voltage detector 110 detects AC voltage vs1 of power receiving system 106 and inputs the detection result to reactive power compensator 10 . In other words, the AC voltage vs1 of the power receiving system 106 is the AC voltage of the power system 108 . Voltage detector 110 , in other words, detects the AC voltage of power system 108 .

Voltage detector 112 detects AC voltage vs2 of load system 102 and inputs the detection result to reactive power compensator 10 . The current detector 114 detects an AC load current i _L flowing through the electric furnace 100 and inputs the detection result to the reactive power compensator 10 . Current detector 116 detects an output current I _SVC output from reactive power compensator 10 to load system 102 and inputs the detection result to reactive power compensator 10 .

Harmonic filter 118 is connected to load system 102 and suppresses harmonics with respect to the frequency of the AC voltage of load system 102 . Note that the load system 102 includes, for example, a phase-advancing capacitor for compensating for the delayed reactive power of the electric furnace 100 to improve the power factor, a thyristor controlled reactor (TCR) that is a phase-modifying facility, and the like. , may be further connected.

A reactive power compensator 10 includes a self-commutated converter 12 and a controller 14 . The self-commutated converter 12 is connected to a load system 102 to which the electric furnace 100 is connected. The self-commutated converter 12 has, for example, a plurality of self-commutated switching elements connected in a full bridge, and a charge storage element connected to the DC end of each switching element. The self-commutated converter 12 converts the AC power of the load system 102 into DC power by switching each switching element, stores the DC power in the charge storage element, and converts the DC power stored in the charge storage element into AC power. , to the load system 102 to suppress fluctuations in the voltage of the load system 102 .

Controller 14 controls the operation of self-commutated converter 12 . That is, the control device 14 controls switching of each switching element of the self-commutated converter 12 . Detection results of voltage detectors 110 and 112 and current detectors 114 and 116 are input to control device 14 .

The control device 14 suppresses fluctuations in the voltage of the load system 102 by controlling the operation of the self-commutated converter 12 based on the detection results of the voltage detectors 110 and 112 and the current detector 114 .

Also, based on the detection result of the current detector 116, the control device 14 detects an overcurrent of the output current I _SVC . The control device 14 determines whether or not the detection result of the current detector 116 is equal to or higher than a predetermined overcurrent detection level, and detects an overcurrent of the output current I _SVC when it is equal to or higher than the overcurrent detection level. The controller 14 stops the operation of the self-commutated converter 12 when it detects an overcurrent of the output current I _SVC .

The control device 14 controls the operation of the self-commutated converter 12 so as to suppress the voltage flicker of the load system 102 due to the operation of the electric furnace 100, and the constant reactive power to the load system 102 in a first control mode. and a second control mode for controlling the operation of the self-commutated converter 12 to output.

The first control mode is selected, for example, when the electric furnace 100 is in operation. The second control mode is selected, for example, when the electric furnace 100 is stopped.

For example, during operation of the electric furnace 100, voltage flicker is likely to occur because the distance between the electrode and the metal material is not stable when the metal material is melted. Therefore, when the electric furnace 100 is operated in which the voltage of the load system 102 fluctuates sharply, the occurrence of voltage flicker due to the operation of the electric furnace 100 can be suppressed by selecting the first control mode. The first control mode is, in other words, a flicker suppression control mode.

On the other hand, when the electric furnace 100 is stopped, the voltage of the load system 102 may fluctuate due to the influence of the harmonic filter 118 or the like. Therefore, when the electric furnace 100 is stopped when the voltage of the load system 102 fluctuates constantly, the voltage fluctuation of the load system 102 due to the stop of the electric furnace 100 can be suppressed by selecting the second control mode. can. The second control mode is, in other words, the constant reactive power control mode.

FIG. 2 is a block diagram schematically showing the control device according to the embodiment.
As shown in FIG. 2, the control device 14 includes a synchronization detection circuit 20, a dq conversion circuit 22, a current command value calculation circuit 24, a switching circuit 26, a current command value calculation circuit 28, and an inverse dq conversion circuit. 30 and a control circuit 32 .

The AC voltage vs1 of the power receiving system 106 (power system 108) is input to the synchronous detection circuit 20 . The synchronous detection circuit 20 detects a synchronous phase θ synchronized with the AC voltage of the electric power system 108 based on the input AC voltage vs1. The synchronization detection circuit 20 detects the synchronization phase θ synchronized with the AC voltage of the electric power system 108 by using, for example, PLL (Phase-Locked-Loop) calculation. The synchronization detection circuit 20 inputs the detected synchronization phase θ to the dq conversion circuit 22 and the inverse dq conversion circuit 30 .

The dq conversion circuit 22 receives the synchronous phase θ from the synchronous detection circuit 20 and the load current _iL detected by the current detector 114 . The dq conversion circuit 22 performs, for example, three-phase to two-phase conversion (Clark transformation) on the load current _iL , which is a three-phase current signal, and converts the current signal after the two-phase conversion based on the synchronous phase θ. By performing dq transformation (Park transformation) on the electric furnace 100, the current signal i _d of the active current (d-axis component) of the load current i _L flowing in the electric furnace 100 and the current signal i _q of the reactive current (q-axis component) , is calculated.

Based on the current signals _id and _iq , the current command value calculation circuit 24 outputs a command value (D command value) and the reactive current command value (Q command value). In other words, the current command value calculation circuit 24 calculates the command value of the active current and the command value of the reactive current for the first control mode. The current command value calculation circuit 24 calculates a command value of active current and a command value of reactive current for the first control mode by, for example, proportional integral calculation.

Note that the active current command value and the reactive current command value for the first control mode are not limited to being calculated within the control device 14. can be entered in

The switching circuit 26 receives the active current command value and the reactive current command value for the first control mode from the current command value calculation circuit 24, and outputs the reactive current command value (Q command value) and a switching signal are input.

The command value of the active current in the second control mode is set to 0 pu (Per Unit), for example. Therefore, only the reactive current command value is input to the switching circuit 26 for the second control mode. The command value of the reactive current for the second control mode may be a preset constant value, or may be input to the switching circuit 26 from a host controller or the like via a network or the like.

The switching signal is a signal that instructs the switching circuit 26 to switch between the first control mode and the second control mode. The switching circuit 26 selectively inputs either the command value for the first control mode or the command value for the second control mode to the current command value calculation circuit 28 according to the input switching signal. The switching signal may be input to the switching circuit 26 from a host controller or the like via a network or the like. Alternatively, the switching signal may be generated within the control device 14 based on the AC voltage vs2, the load current _iL, or the like.

The current command value calculation circuit 28 calculates the active current (d-axis component) current signal i _d ^* and reactive current (q-axis component) current signal i _q ^* .

The inverse dq conversion circuit 30 receives the synchronization phase θ from the synchronization detection circuit 20 and inversely converts the current signals i _d ^* and i _q ^* inputted from the current command value calculation circuit 28 (inverse Park conversion). and inverse Clarke transformation), the current signal _i ^* of ^the three-phase output current to be output from the self-commutated converter 12 to the load system 102 is calculated based on the current signals id* and _iq ^* .

Based on the current signal i ^* input from the inverse dq conversion circuit 30, the control circuit 32 is a self-commutated converter for outputting an output current corresponding to the current signal i ^* from the self-commutated converter 12 to the load system 102. 12 control signals are generated and the operation of the self-commutated converter 12 is controlled based on the generated control signals.

Thus, the controller 14 controls the operation of the self-commutated converter 12 according to the command values (the D command value and the Q command value) related to the output current I _SVC output from the self-commutated converter 12 to the load system 102. . As a result, in the first control mode, the control device 14 can suppress voltage flicker in the load system 102 based on the command values of the active current and the reactive current according to the detection result, and in the second control mode, , a constant reactive power corresponding to the input reactive current command value can be output to the load system 102 .

FIG. 3 is a block diagram schematically showing a switching circuit according to the embodiment;
As shown in FIG. 3, the switching circuit 26 has switch circuits 41 to 44, arithmetic circuits 45 and 46, and a delay circuit 47.

The switch circuit 41 has two input terminals 41a and 41b and an output terminal 41c. An active current command value for the first control mode is input to the input terminal 41a. An active current command value for the second control mode is input to the input terminal 41b. As described above, the command value of the active current in the second control mode is 0 pu, for example.

A switching signal is input to the switch circuit 41 . The switch circuit 41 selectively outputs one of the active current command value for the first control mode and the active current command value for the second control mode from the output terminal 41c according to the input switching signal. do.

The switching signal is, for example, a binary signal of 0 (Low) or 1 (High). For example, a switching signal of 0 corresponds to the first control mode, and a switching signal of 1 corresponds to the second control mode. The switch circuit 41 outputs an active current command value for the first control mode when the switching signal is 0, and outputs an active current command value for the second control mode when the switching signal is 1. The output terminal 41 c is connected to the arithmetic circuit 45 . The switch circuit 41 selectively inputs either one of the active current command value for the first control mode and the active current command value for the second control mode to the arithmetic circuit 45 . Note that the configuration of the switching signal and the switch circuit 41 is not limited to the above, and may be any configuration that can appropriately switch between the first control mode and the second control mode.

Arithmetic circuit 45 performs a computation to gradually change the input command value. In other words, the arithmetic circuit 45 performs an operation on the input command value to suppress changes in the command value by a predetermined value or more per unit time. That is, the arithmetic circuit 45 performs an arithmetic operation that suppresses sharp changes in the input command value. The arithmetic circuit 45 is, for example, a first-order lag circuit. The arithmetic circuit 45 gradually changes the input command value by performing a first-order lag operation on the input command value. The arithmetic circuit 45 inputs the calculated effective current command value to the switch circuit 42 .

The switch circuit 42 has two input terminals 42a and 42b and an output terminal 42c. An active current command value for the first control mode is input to the input terminal 42a. The command value calculated by the arithmetic circuit 45 is input to the input terminal 42b.

A switching signal is input to the switch circuit 42 . The switch circuit 42 selectively outputs either one of the command value of the active current for the first control mode and the command value of the active current after calculation by the arithmetic circuit 45 from the output terminal 42c according to the input switching signal. Output. The output of the output terminal 42c is the output of the switching circuit 26, in other words.

The switch circuit 43 has two input terminals 43a and 43b and an output terminal 43c. Similarly, the switch circuit 44 has two input terminals 44a, 44b and an output terminal 44c. The configurations of the switch circuits 43 and 44 and the arithmetic circuit 46 are substantially the same as those of the switch circuits 41 and 42 and the arithmetic circuit 45 except that the input command value is the reactive current command value. Therefore, detailed description is omitted.

A switching signal is input to the delay circuit 47 . The delay circuit 47 delays the switching timing of the input switching signal from the second control mode to the first control mode by a predetermined time. In this example, a switching signal of 0 corresponds to the first control mode, and a switching signal of 1 corresponds to the second control mode. In this case, the delay circuit 47 delays the fall timing of the switching signal by a predetermined time. The delay circuit 47 is, for example, an off-delay circuit. As a result, the timing of switching from the second control mode to the first control mode of the input switching signal can be delayed by a predetermined time.

Contrary to the above, when 0 of the switching signal corresponds to the second control mode and 1 of the switching signal corresponds to the first control mode, the rise timing of the switching signal may be delayed by a predetermined time. The configuration of the delay circuit 47 may be any configuration capable of delaying the switching timing of the input switching signal from the second control mode to the first control mode by a predetermined time.

Switching signals before being input to the delay circuit 47 are input to the switch circuits 41 and 43 . The switching signals output from the delay circuit 47 are input to the switch circuits 42 and 44 . Therefore, the switching timing of the switch circuits 42 and 44 from the second control mode to the first control mode is delayed by a predetermined time from the switching timing of the switch circuits 41 and 43 from the second control mode to the first control mode.

4(a) to 4(e) are graphs schematically showing an example of the operation of the reactive power compensator according to the embodiment.
FIG. 4A shows an example of a switching signal.
FIG. 4B shows an example of the reactive current command value for the first control mode.
FIG. 4(c) shows an example of the reactive current command value for the second control mode.
FIG. 4D shows an example of the reactive current command value output from the switching circuit 26 .
FIG. 4(e) represents an example of the output current I _SVC output from the self-commutated converter 12 (var compensator).

In FIG. 4, in a state where the reactive current command value for the first control mode is 0 pu and the reactive current command value for the second control mode is 1 pu, the first control mode and the second control of the control device 14 An example of a reactive current command value output from the switching circuit 26 when the mode is switched is shown.

When the first control mode is selected by the switching signal, the switch circuit 42 outputs the active current command value for the first control mode, and the switch circuit 44 outputs the reactive current command value for the first control mode. to output Therefore, when the first control mode is selected by the switching signal, the switching circuit 26 outputs the active current command value for the first control mode and the reactive current command value for the first control mode. (timing t0 in FIG. 4). As a result, when the first control mode is selected by the switching signal, the load system is controlled based on the active current command value and the reactive current command value calculated by the current command value calculation circuit 24 according to the detection result. 102 voltage flicker is suppressed.

Further, when the first control mode is selected by the switching signal, the switch circuit 41 outputs the command value of the active current for the first control mode, and the switch circuit 43 outputs the reactive current command value for the first control mode. Output command value. Therefore, when the first control mode is selected by the switching signal, the active current command value for the first control mode is input to the arithmetic circuit 45, and the reactive current command value for the first control mode is input. A command value is input to the arithmetic circuit 46 .

When the switching signal switches from the first control mode to the second control mode, the output of the switch circuit 41 switches from the active current command value for the first control mode to the active current command value for the second control mode. The output of circuit 43 switches from the reactive current command value for the first control mode to the reactive current command value for the second control mode. Therefore, when the switching signal switches from the first control mode to the second control mode, the input to the arithmetic circuit 45 changes from the active current command value for the first control mode to the active current command value for the second control mode. Then, the input of the arithmetic circuit 46 is switched from the reactive current command value for the first control mode to the reactive current command value for the second control mode.

When the switching signal switches from the first control mode to the second control mode, the output of the switch circuit 42 switches from the command value of the active current for the first control mode to the command value calculated by the arithmetic circuit 45. , the output of the switch circuit 44 is switched from the reactive current command value for the first control mode to the command value calculated by the arithmetic circuit 46 .

Therefore, when the switching signal switches from the first control mode to the second control mode, the command value of the active current for the second control mode after being calculated by the arithmetic circuit 45 and the command value of the active current for the second control mode after being calculated by the arithmetic circuit 46 A reactive current command value for the two control modes is output from the switching circuit 26 (timing t1 in FIG. 4).

As a result, when the first control mode is switched to the second control mode, the control device 14 changes the active current command value for the first control mode and the reactive current command value to the active current command value for the second control mode. When switching to the command value and the reactive current command value, the active current command value for the first control mode is gradually changed to the active current command value for the second control mode, and the reactive current command value for the first control mode is changed. The current command value is gradually changed to the reactive current command value for the second control mode. After that, when the second control mode is selected by the switching signal, a constant reactive power corresponding to the input command value of the reactive current for the second control mode is output to the load system 102 .

When the switching signal switches from the second control mode to the first control mode again, the output of the switch circuit 41 switches from the active current command value for the second control mode to the active current command value for the first control mode, The output of the switch circuit 43 is switched from the reactive current command value for the second control mode to the reactive current command value for the first control mode (timing t2 in FIG. 4). Therefore, when the switching signal switches from the second control mode to the first control mode, the input to the arithmetic circuit 45 changes from the active current command value for the second control mode to the active current command value for the first control mode. Then, the input of the arithmetic circuit 46 is switched from the reactive current command value for the second control mode to the reactive current command value for the first control mode.

On the other hand, due to the operation of the delay circuit 47, the switching timing of the switch circuits 42 and 44 from the second control mode to the first control mode is the same as the switching timing of the switch circuits 41 and 43 from the second control mode to the first control mode. A predetermined time delay from the timing. Therefore, for a predetermined time from the timing when the switching signal switches from the second control mode to the first control mode, the command value of the active current for the first control mode calculated by the calculation circuit 45 and the calculation circuit 46 The command value of the reactive current for the first control mode after being calculated by is output from the switching circuit 26 (timings t2 to t3 in FIG. 4).

As a result, when the second control mode is switched to the first control mode, the control device 14 changes the active current command value for the second control mode and the reactive current command value to the active current command value for the first control mode. When switching to the command value and the reactive current command value, the active current command value for the second control mode is gradually changed to the active current command value for the first control mode, and the reactive current command value for the second control mode is changed. The current command value is gradually changed to the reactive current command value for the first control mode.

When a predetermined time elapses from the timing when the switching signal switches from the second control mode to the first control mode, the output of the switch circuit 42 is changed from the command value calculated by the arithmetic circuit 45 to the effective current for the first control mode. , and the output of the switch circuit 44 is switched from the command value calculated by the arithmetic circuit 46 to the reactive current command value for the first control mode (timing t3 in FIG. 4).

Therefore, after a predetermined time has passed since the switching signal switched from the second control mode to the first control mode, the active current command value for the first control mode before being calculated by the arithmetic circuits 45 and 46 and The reactive current command value for the first control mode is directly output from the switching circuit 26 .

In this way, in the first control mode, the control device 14 gradually changes by the arithmetic circuits 45 and 46 until a predetermined time elapses from the timing of switching from the second control mode to the first control mode. The operation of the self-commutated converter 12 is controlled based on the command value for which the calculation for causing the change is performed. to control the operation of the self-commutated converter 12.

FIGS. 5(a) to 5(e) are graphs schematically showing an example of reference operation of the reactive power compensator.
The signal items represented by the graphs of FIGS. 5A to 5E are the same as the signal items represented by the graphs of FIGS. 4A to 4E.

5(a) to 5(e), when the first control mode is switched to the second control mode, the command value used for controlling the self-commutated converter 12 is the reactive current for the first control mode. (eg, 0 pu) to the reactive current command value (eg, 1 pu) for the second control mode (timing t11 in FIG. 5).

When the command value used to control the self-commutated converter 12 changes abruptly in this manner, the output current I _SVC of the self-commutated converter 12 cannot follow the command value as shown in FIG. Otherwise, it may overshoot and exceed the overcurrent detection level at which the controller 14 stops the operation of the self-commutated converter 12 . That is, there is a possibility that the control device 14 will detect an overcurrent of the output current I _SVC and stop the operation of the self-commutated converter 12 .

On the other hand, in the reactive power compensator 10 according to the present embodiment, the controller 14 switches from the first control mode to the second control mode as shown at timing t1 in FIG. When switching from the active current command value and reactive current command value for the first control mode to the active current command value and reactive current command value for the second control mode, the active current command value for the first control mode to the command value of the active current for the second control mode, and the command value of the reactive current for the first control mode is gradually changed to the command value of the reactive current for the second control mode. .

By suppressing abrupt changes in the command value in this manner, overshoot of the output current _ISVC can be suppressed, and occurrence of overcurrent can be suppressed. Therefore, it is possible to suppress unintended stoppage of operation of the self-commutated converter 12 due to overcurrent.

Further, in the reactive power compensator 10 according to the present embodiment, as shown at timing t2 in FIG. 4D, the control device 14 switches from the second control mode to the first control mode, When switching from the active current command value and reactive current command value for the second control mode to the active current command value and reactive current command value for the first control mode, the active current command value for the second control mode is changed to the second The active current command value for the first control mode is gradually changed, and the reactive current command value for the second control mode is gradually changed to the reactive current command value for the first control mode. As a result, even when switching from the second control mode to the first control mode, it is possible to suppress sharp changes in the command value. Therefore, unintended stoppage of operation of the self-commutated converter 12 due to overcurrent can be suppressed more reliably.

Furthermore, in the reactive power compensator 10 according to the present embodiment, the control device 14 in the first control mode until a predetermined time elapses from the timing of switching from the second control mode to the first control mode, The operation of the self-commutated converter 12 is controlled based on the command value that has been calculated to be gradually changed by the arithmetic circuits 45 and 46. The operation of the self-commutated converter 12 is controlled based on the command value before the calculation for changing is performed.

In the second control mode, for example, the command value is substantially constant unless there is an instruction to change the command value from a higher-level controller. Therefore, in the second control mode, even if the command values output from the arithmetic circuits 45 and 46 are used to control the operation of the self-commutated converter 12, the substantial influence is small.

On the other hand, in the first control mode, in order to suppress the voltage flicker of the load system 102 due to the operation of the electric furnace 100, the command value changes as needed based on the detection results of the voltage detectors 110, 112 and the current detector 114. do. Therefore, in the first control mode, when the command values output from the arithmetic circuits 45 and 46 are used to control the operation of the self-commutated converter 12, the calculation for gradually changing the command value can be performed at a high speed of control. It is feared that it will affect sexuality.

Therefore, in the first control mode, the control device 14 causes the arithmetic circuits 45 and 46 to gradually change the control mode until a predetermined time elapses from the timing of switching from the second control mode to the first control mode. Based on the calculated command value, the operation of the self-commutated converter 12 is controlled. Based on this, the operation of the self-commutated converter 12 is controlled. As a result, it is possible to suppress unintended stoppage of operation of the self-commutated converter 12 due to overcurrent while suppressing a decrease in high-speed control in the first control mode.

The predetermined time may be set according to, for example, the time constants of the arithmetic circuits 45 and 46 that perform first-order lag calculations. The predetermined time is preferably set to, for example, the longest time during which the command value gradually changes or longer. As a result, it is possible to prevent the command value from being switched to the pre-computation command value during the gradual change. The longest time during which the command value gradually changes is, for example, the time during which the command value changes gradually from 0 pu to 1 pu. Also, the predetermined time is preferably set to, for example, twice or less the longest time during which the command value gradually changes. As a result, it is possible to further suppress the influence of the calculation for gradually changing the command value on the high-speed control.

In the above-described embodiment, the switching circuit 26 switches the transmission path of the command value so that the command value changes gradually according to the switching of each mode. The configuration of the control device 14 is not limited to this, and may be any configuration that can gradually change the command value according to the switching of each mode.

In the above embodiment, the active current command value and the reactive current command value output from the self-commutated converter 12 to the load system 102 are exemplified as an example of the command value related to the output current _ISVC to be output to the load system 102. ing. The command value related to the output current I _SVC is not limited to this, and may be, for example, a command value for active power or a command value for reactive power output from the self-commutated converter 12 to the load system 102 . A command value related to the output current I _SVC may be, for example, a command value for the voltage output from the self-commutated converter 12 to the load system 102 . The gradual command value can be any command value related to the output current _ISVC .

6(a) and 6(b) are graphs schematically showing a modification of the operation of the reactive power compensator according to the embodiment.
In the above embodiment, the command value is exponentially and gradually changed by the first-order lag calculation. The gradual change in the command value is not limited to an exponential change, and may be, for example, a linear change as shown in FIG. 6(a). Such a linear function change can be realized, for example, by a change rate limiter that suppresses a change of the command value beyond a predetermined change rate.

Also, the gradual change of the command value may be, for example, a step-like change as shown in FIG. 6(b). Such a stair-like change can be realized, for example, by a limiter or the like that suppresses a change in a specified value exceeding a predetermined value per unit time.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

2 Electric furnace system 10 Reactive power compensator 12 Self-commutated converter 14 Control device 20 Synchronization detection circuit 22 dq conversion circuit 24 Current command value calculation circuit 26 Switching circuit 28 Current command value arithmetic circuit 30 Inverse dq conversion circuit 32 Control circuit 41 to 44 Switch circuit 45 Arithmetic circuit 46 Arithmetic circuit 47 Delay circuit 100 Electric furnace 102 Load System 104 Transformer 106 Power receiving system 108 Power system 110 Voltage detector 112 Voltage detector 114 Current detector 116 Current detector 118 Harmonic filter

Claims (4)

a self-commutated converter connected to a load system to which an electric furnace is connected and outputting reactive power to the load system to suppress fluctuations in the voltage of the load system caused by the operation of the electric furnace;
A control device for controlling the operation of the self-commutated converter in accordance with a command value related to the output current output from the self-commutated converter to the load system, wherein the voltage flicker of the load system caused by the operation of the electric furnace is reduced. a first control mode for controlling the operation of the self-commutated converter so as to suppress and a second control mode for controlling the operation of the self-commutated converter so as to output constant reactive power to the load system; a controller having
with
When the control device switches from the command value for the first control mode to the command value for the second control mode with switching from the first control mode to the second control mode, the A reactive power compensator for gradually changing the command value for the first control mode to the command value for the second control mode. When the control device switches from the command value for the second control mode to the command value for the first control mode with switching from the second control mode to the first control mode, the 2. A reactive power compensator according to claim 1, wherein said command value for said second control mode is gradually changed to said command value for said first control mode. The control device has an arithmetic circuit that performs an arithmetic operation to gradually change the command value, and in the first control mode, a predetermined time elapses from the timing of switching from the second control mode to the first control mode. Until the predetermined time elapses, the operation of the self-commutated converter is controlled based on the command value that has been calculated to be gradually changed by the arithmetic circuit, and after the predetermined time elapses, the calculation 3. A reactive power compensator according to claim 2, wherein the operation of the self-commutated converter is controlled based on the command value before the circuit gradually changes the calculation. 4. A reactive power compensator according to claim 3, wherein said arithmetic circuit gradually changes said command value by performing a first-order lag operation on said input command value.

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