JP6394316B2 - Reactive power compensator control method and control apparatus - Google Patents

Description

  The present invention relates to a control method and a control device for a reactive power compensator linked to a power system in order to suppress voltage flicker generated by a reactive power fluctuation of a load such as an electric furnace connected to the power system.

  FIG. 2 shows an example of the reactive power compensator. In FIG. 2, 1 is a reactive power compensator, 2 is a power system, 3 is a system impedance included in the power system, and 4 is a load such as an electric furnace (arc furnace) that generates voltage flicker. The reactive power compensator 1 connected between the system impedance 3 and the load 4 includes a thyristor 5, a reactor 6, a capacitor 7, a transformer 8, a current transformer 9, and a control device 13, and suppresses voltage flicker. Therefore, the reactive power generated by the load 4 is compensated. That is, if the reactive power generated by the load 4 is Qf, the reactive power of the reactive power compensator 1 is Qt, and the reactive power of the system is Qs, the reactive power compensator is controlled so that Qt = Qf. The reactive power becomes Qs = 0, voltage fluctuation of the system voltage can be suppressed, and voltage flicker can be suppressed.

A specific configuration example of the control device 13 of FIG. 2 is shown in FIG. 3 controls the reactive power compensator according to the reactive power of the load, and the reactive power component (for example, around 10 Hz) that changes the reactive power of the load abruptly changes relatively slowly. It is a control device that detects reactive power components (for example, 1 Hz or less) separately and commands reactive power to be compensated based on both reactive power components, and this type of control device is known (for example, a patent) Reference 1 and Patent Document 2).
The transformer 8 and the current transformer 9 in FIG. 3 correspond to those in FIG. 2, the transformer 8 detects the system voltage Vs, and the current transformer 9 detects the load current If. The control device 13 includes reactive power detection circuits 10 and 11, a subtractor 14, a surplus capacity calculator 15, and a firing angle control circuit 12.

  From the system voltage Vs detected by the transformer 8 and the load current If detected by the current transformer 9, the reactive power detection circuit 10 calculates the reactive power Q1 including a steep fluctuation component of the load 4, and the reactive power. The detection circuit 11 calculates the reactive power Q2 of the base component of the load 4 that changes relatively slowly. Therefore, the subtractor 14 subtracts the relatively slowly varying reactive power Q2 calculated by the reactive power detection circuit 11 from the reactive power Q1 of the load 4 calculated by the reactive power detection circuit 10, thereby making the load 4 steep. Can be obtained. As a result, the reactive power Q1 of the load 4 includes the reactive power ΔQ that varies steeply and the reactive power Q2 that varies relatively slowly, and the reactive power Q1 of the load varies rapidly. It can be said that it is detected separately as ΔQ and reactive power Q2 that fluctuates relatively slowly.

  Here, in compensating reactive power, there are two methods: a method of compensating reactive power Q1 (= ΔQ + Q2) of the load 4 and a method of compensating reactive power ΔQ of the load 4 that varies sharply. In the case of flicker compensation, the reactive power ΔQ that fluctuates rapidly may be compensated. However, since the reactive power Q2 that changes relatively slowly remains, the power factor after compensation does not improve. Further, when the reactive power Q1 of the load 4 is compensated, the power factor is improved, but the compensation capacity of the reactive power compensator 1 is not sufficient for flicker compensation because there is a limit in terms of economical design. For this reason, the conventional technique uses a method in which flicker compensation is performed by compensating for a rapidly changing reactive power, and if the remaining capacity of the reactive power compensator 1 has a surplus capacity, the power factor is compensated.

  For this purpose, a surplus capacity calculation circuit 15 is provided as shown in FIG. The surplus capacity calculation circuit 15 calculates the surplus capacity of the reactive power compensator 1 using the calculation outputs of both the reactive power detectors 10 and 11, and the ineffective capacity fluctuating relatively slowly within the limits of the calculated surplus capacity. At least a part of the power Q2 is input to the adder 16 as an additional compensation component. The surplus capacity calculation circuit 15 calculates a surplus capacity value of the reactive power compensator 1 when only the reactive power ΔQ that varies sharply is compensated, and fluctuates relatively slowly so as not to exceed the surplus capacity value. Although it can be configured with a limiting unit that limits and outputs reactive power Q2, refer to Patent Document 1 cited above for a specific configuration example.

  The adder 16 adds the additional compensation calculated by the remaining capacity calculation circuit 15 to the reactive power ΔQ that fluctuates rapidly, thereby obtaining a command value of reactive power to be compensated. Based on this command value, the firing angle control circuit 12 calculates a firing angle command α, and the thyristor 5 of the reactive power compensator 1 is controlled to fire according to the firing angle command α. For example, when the additional compensation calculated by the surplus capacity calculation circuit 15 is zero, that is, when there is no surplus power, only the reactive power component ΔQ that varies steeply is compensated. Not only the power ΔQ but also at least a part of the reactive power Q2 that changes relatively slowly is compensated according to the additional compensation calculated by the capacity calculation circuit 15.

  On the other hand, the load 4 shown in FIG. 2 shows an electric furnace as equipment for melting and recycling scrap iron or the like by an arc, and an example of this electric furnace is shown in more detail in FIG. The electric furnace 4 in FIG. 4 includes a series reactor 19, a furnace transformer 31, an electrode 33, a furnace body 34, a current transformer 17, a transformer 18, an electrode lifting device 30 that lifts and lowers the electrode 33, and an electrode lifting device 30. It is comprised by the electrode raising / lowering control apparatus 35 which supplies the electric power required for the speed control of the electrode 33 to the electric motor to perform.

  In the electrode raising / lowering control device 35 shown in FIG. 4, the arc voltage is detected by the transformer 18 and the arc current is detected by the current transformer 17, and the arc impedance is calculated from the arc voltage and arc current. A speed command value is outputted to raise or lower the electrode 33 so as to be constant, and the electrode lifting device 30 is controlled.

  The series reactor 19 is configured as a tap-switching series reactor having taps that can be switched in order to switch circuit impedance in accordance with the amount of electric power supplied to the electric furnace. In order to switch a plurality of taps in a non-voltage state, the series reactor 19 is provided with circuit breakers 21 and 22 and a switching controller 20. In addition to this no-voltage tap switching method, there is a tap switching method at the time of loading. Generally, a non-voltage tap switching method that operates in a no-voltage state is adopted because the device can be miniaturized and is inexpensive. .

  The no-voltage tap switching of the series reactor 19 is performed in the following procedure. Normally, a current flows through the series reactor 19, the circuit breaker 21, and the furnace transformer 31, but when switching the tap, the circuit breaker 22 is “closed” and the circuit breaker 21 is “opened”. The tap is switched so that no current is passed through. Thereafter, the circuit breaker 21 is “closed” and the circuit breaker 22 is “opened” to complete the tap switching operation. At the time of this tap switching, especially when the circuit breaker 22 is “closed” in order to short-circuit the series reactor 19, the circuit impedance becomes extremely small, so that the fluctuating current flowing in the electric furnace becomes large. It became clear that many occur.

  The above-described conventional control device has two compensation modes: a mode for compensating the reactive power ΔQ of the load 4 for compensating flicker and the power factor, and a mode for compensating the reactive power Q2 of the load 4. However, at least one of the reactive powers Q2 that changes relatively slowly within the limit of the remaining capacity of the device while calculating the remaining capacity of the reactive power compensator while compensating for the reactive power ΔQ that varies abruptly at all times. Therefore, the mode switching is switched from the reactive power of the load 4 according to the device remaining capacity. However, in this case, it takes time to calculate the device remaining capacity, etc., and at the time when the reactive power of the steep fluctuation should be compensated for originally, the switching of the compensation mode is delayed, so that the optimum flicker compensation cannot be performed. There is a concern that the compensation performance may be reduced.

JP 2005-80368 A JP 2014-87207 A

  Accordingly, an object of the present invention is to improve flicker compensation performance by preventing the occurrence of flicker that may occur due to a reactor short-circuit during a series reactor tap switching operation.

  As for the method invention, the reactive power compensator linked to the power system in order to suppress the voltage flicker generated by the reactive power fluctuation of the load connected to the power system via the tap-switchable series reactor. In this control method, the reactive power of the load is detected separately from the reactive power that changes abruptly and the reactive power that changes relatively slowly, and the reactive power that changes rapidly and the reactive power that changes slowly are always detected. This is solved by a control method for a reactive power compensator, which compensates only for reactive power that changes steeply for a certain period of time when the series reactor tap is switched.

  Furthermore, the problem is that, with regard to the device invention, the reactive power connected to the power system in order to suppress voltage flicker generated by the reactive power fluctuation of the load connected to the power system via the tap-switchable series reactor. In the control device of the compensator, the reactive power detecting means for detecting the reactive power of the load separately from the reactive power that changes suddenly and the reactive power that changes relatively slowly, and the reactor that is generated at the time of tap switching of the series reactor In response to the short-circuit command signal, a time-limit means for generating a time-limited signal that lasts for a certain period of time, and a reactive power that changes abruptly and a reactive power that fluctuates relatively slowly are selected as compensation reactive power command values. Switching means for selecting only the reactive power that changes sharply as the compensation reactive power command value while the means generates the timed signal, Is solved by a control device of the reactive power compensator, characterized in that it comprises a control means for generating a control signal for the reactive power compensator based on the compensated reactive power command value selected by the switch means.

  According to the present invention, reactive power of a load is detected separately from reactive power that changes abruptly and reactive power that changes relatively slowly. Normally, reactive power that changes rapidly and reactive power that changes slowly By compensating only the reactive power that fluctuates sharply for a certain time when the reactor short-circuit command is issued at the time of tap switching of the tap-switching series reactor provided in the previous stage of the load, Flicker that may occur due to a reactor short-circuit during the series reactor tap switching operation can be prevented, and flicker compensation performance can be improved. This is because the circuit impedance becomes extremely small due to the reactor short circuit, so that the fluctuating current flowing through the load increases, but according to the present invention, when the reactor short circuit command is issued, the reactive power that fluctuates sharply for a certain period of time. This is because, by switching so as to compensate for only the variable current, it is possible to quickly compensate for the fluctuation current using the entire capacity of the reactive power compensator.

FIG. 1 is a block diagram showing an embodiment of a control device for a reactive power compensator according to the present invention. FIG. 2 is a block diagram illustrating a schematic configuration example of the reactive power compensator. FIG. 3 is a block diagram showing a conventional embodiment of a control device for a reactive power compensator. FIG. 4 is a block diagram illustrating a schematic configuration example of an electric furnace including a series reactor.

  FIG. 1 shows an embodiment of a control device for a reactive power compensator according to the present invention. Components corresponding to each other in FIGS. 1 to 4 are denoted by the same reference numerals. In FIG. 1, reference numeral 1 denotes a reactive power compensator, the main circuit of which is composed of a thyristor 5, a reactor 6 and a capacitor 7 as shown in FIG. 2. In a power system 2 having a system inductance 3, a load 4 Are connected in parallel.

  The load 4 is shown as an electric furnace as a facility for melting and regenerating scrap iron or the like by an arc. Similar to the electric furnace 4 shown in FIG. 4, the tap-switchable series reactor 19 and the breakers 21 and 22 are shown. , Switching controller 20, furnace transformer 31, electrode 33, furnace body 34, current transformer 17, transformer 18, electrode lifting device 30, and electrode lifting control device 35. Furthermore, as will be described later, in some cases, a delay circuit 23 not shown in FIG. 4 is added.

  The control device 13 of the reactive power compensator 1 includes two power detection circuits 10 and 11, a subtractor 14, and a firing angle control circuit 12, as in the conventional example shown in FIG. 3. Therefore, the power detection circuit 10 calculates the reactive power Q1 of the load 4 from the system voltage Vs detected by the transformer 8 and the load current If detected by the current transformer 9. Further, the power detection circuit 11 calculates the reactive power Q2 of the load 4 that varies relatively slowly from the system voltage Vs detected by the transformer 8 and the load current If detected by the current transformer 9. The subtractor 14 subtracts the reactive power Q2 calculated by the reactive power detection circuit 11 from the reactive power Q1 of the load 4 calculated by the reactive power detection circuit 10 to substantially change the load 4. The reactive power ΔQ to be obtained is obtained. Therefore, the transformer 8 and the current transformer 9, the two reactive power detection circuits 10 and 11, and the subtractor 14 change relatively slowly with the reactive power component ΔQ that rapidly changes the reactive power Q1 of the load 4. Reactive power detecting means for detecting the reactive power component Q2 separately is configured.

  Further, the control device 13 according to the present invention includes a timer 36 and a switch 37, unlike the conventional example shown in FIG. The timer 36 receives a reactor short-circuit command signal that is issued when the series reactor 19 is switched from a switching controller 20 that controls switching of the circuit breakers 21 and 22 of the series reactor 19 provided in the electric furnace 4. The timer 36 operates in response to the reactor short-circuit command signal and generates an output signal that lasts for a preset fixed time. Therefore, the timer 36 is a time limit means for generating a time signal that lasts for a predetermined time in response to the reactor short-circuit command signal when the series reactor 19 provided in the electric furnace 4 is switched.

  The switch 37 always selects the output value Q1 of the power detection circuit 10, and selects and selects the output value ΔQ of the subtractor 14 for a certain period of time during which the timer 36 operates and generates an output signal. The output value Q1 or ΔQ is input to the firing angle control circuit 12 as a compensation reactive power command value. Accordingly, the switching device 37 normally selects the reactive power Q1 of the load including the reactive power ΔQ that changes sharply and the reactive power Q2 that changes relatively slowly as the compensation reactive power command value, and the time limit means (timer 36) is a switching means for selecting only the reactive power ΔQ that fluctuates sharply as the compensation reactive power command value while the time signal is being generated.

  The compensation reactive power command value is a command value of reactive power to be compensated by the reactive power compensator 1, and the firing angle control circuit 12 compensates the reactive power at the firing angle α corresponding to the compensation reactive power command value. The thyristor 5 in the apparatus 1 is controlled to be fired. Therefore, the firing angle control circuit 12 is a control unit that generates a control signal for the reactive power compensator 1 based on the compensation reactive power command value selected by the switching unit (switch 37).

  On the electric furnace 4 side, the reactor command signal from the switching controller 20 is delayed by a preset time by the delay circuit 23 and transmitted to the circuit breakers 21 and 22, whereby the circuit breaker 22 is turned on and the circuit breaker is disconnected. 21 is opened. In this state, the no-voltage tap switching of the series reactor 19 is executed. After completion of the tap switching, the circuit breaker 21 is turned on again by the switching controller 20, and the circuit breaker 22 is opened. The delay circuit 23 is not necessary when the switching time of the switching device 37 of the control device 13 is shorter than the time from the short-circuit command from the switching controller 20 until the breaker 22 is closed.

  In the timer 36, once a short-circuit command is input, a fixed time is set in advance from that point in time until the tap of the series reactor 19 is switched and the current fluctuation is settled. Accordingly, the timer 36 immediately responds to the short-circuit command and is turned on, so that the switch 37 is switched, and the reactive power ΔQ that changes rapidly in the load 4 is selected as the compensation reactive power command value. Therefore, during the fixed time set by the timer 36, an operation for continuously compensating the reactive power ΔQ of the load 4 that is abruptly changed is performed. When the timer 36 is turned off after the lapse of a certain time, the switch 37 switches to the original state, and always compensates the reactive power Q1 of the load including the reactive power ΔQ that changes sharply and the reactive power Q2 that changes slowly. Return to operation.

  According to the present invention, the reactive power compensator 1 normally compensates for the flicker compensation simultaneously with the flicker compensation by compensating the reactive power Q1 of the load including the reactive power ΔQ that varies sharply and the reactive power Q2 that varies slowly. It can also contribute to rate improvement. However, in that case, when the reactor is short-circuited for tap switching of the series reactor 19 provided in the electric furnace 4, the circuit impedance becomes extremely small and the fluctuation current flowing through the electric furnace 4 becomes large. The reactive power compensator 1 cannot immediately respond to such a large fluctuation current, and as a result, flicker occurs. Therefore, according to the present invention, the total capacity of the reactive power compensator 1 can be immediately increased by switching so as to compensate only for the reactive power ΔQ that sharply fluctuates for a certain time when the reactor short-circuit command is issued. Can be used for compensation of the fluctuation current, so that flicker that may occur due to the reactor short-circuit can be prevented and flicker compensation performance can be improved.

  The control method according to the present invention can be used in combination with the flicker compensation improvement techniques disclosed in Patent Document 1 and Patent Document 2 described above, and thereby, the flicker compensation performance can be significantly improved comprehensively. . For example, in the case of constant-time operation that compensates for reactive power that varies abruptly and reactive power that varies slowly, compensation of reactive power that varies slowly, as disclosed in Patent Document 1, While calculating the remaining capacity of the apparatus, reactive power that varies relatively slowly within the limit of the apparatus remaining capacity may be compensated. Further, as described in Patent Document 2, when the speed command value of the electrode calculated for the electrode raising / lowering control of the electric furnace exceeds a preset limit value, it fluctuates sharply for a certain time. It may be added to switch the reactive power to be compensated so that only the reactive power is compensated.

1 Reactive Power Compensator 2 Power System 3 System Impedance 4 Load 5 Thyristor 6 Reactor 7 Capacitor 8 Transformer 9 Current Transformer 10 Reactive Power Detection Circuit 11 Reactive Power Detection Circuit 12 Firing Angle Control Circuit 13 Controller 14 Subtractor 15 Surplus Power Capacity calculator 16 Adder 17 Current transformer 18 Transformer 19 Series reactor 20 Switching controller 21 Breaker 22 Breaker 23 Delay circuit 28 Setting device 29 Lift control circuit 30 Electrode lifting device 31 Furnace transformer 33 Electrode 34 Furnace body 35 Electrode lifting / lowering control device 36 Timer 37 selector

Claims (2)

In a control method of a reactive power compensator linked to a power system in order to suppress voltage flicker generated by a reactive power fluctuation of a load connected to the power system via a tap-switchable series reactor,
The reactive power of the load is detected separately from a reactive power that changes abruptly and a reactive power that changes relatively slowly. Normally, the reactive power that changes rapidly and a reactive power that changes slowly are compensated, and the series A control method for a reactive power compensator, wherein only reactive power that changes sharply for a certain period of time when a reactor is switched is compensated. In a control device for a reactive power compensator linked to a power system in order to suppress voltage flicker generated by a reactive power fluctuation of a load connected to the power system via a tap-switchable series reactor,
Reactive power detection means for detecting reactive power of the load separated into reactive power that changes rapidly and reactive power that changes relatively slowly; and
Timing means for generating a timed signal that lasts for a predetermined time in response to a reactor short-circuit command signal issued at the time of tap switching of the series reactor;
Normally, reactive power that fluctuates sharply and reactive power that fluctuates relatively slowly are selected as compensation reactive power command values. Switching means for selecting as a compensation reactive power command value;
Control means for generating a control signal for the reactive power compensator based on the compensation reactive power command value selected by the switching means;
A control device for a reactive power compensator, comprising:

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