Instantaneous voltage drop compensator

Abstract

To provide an instantaneous voltage drop compensator that suppresses a load overvoltage generated along with turn-off of a thyristor switch that opens and closes a power line.SOLUTION: An instantaneous voltage drop compensator 100 is provided between a power system PS and a load PL and compensates for voltage drop occurring due to abnormality such as instantaneous voltage drop, and comprises a thyristor switch 1, a main power converter 3a, and a sub-power converter 3b. When abnormality occurs in the power system PS, the instantaneous voltage drop compensator operates in a dropped voltage compensation mode for applying an extinction voltage of arc to turn off the thyristor switch 1 and feeding power from the main power converter 3a to the load PL to compensate for the dropped voltage of the load PL. In turning off the thyristor switch 1 in the dropped voltage compensation mode, the instantaneous voltage drop compensator performs a first extinction operation of outputting the extinction voltage of arc from the main power converter 3a through a main injection transformer 4a, and subsequently performs control of switching to a second extinction operation of outputting the extinction voltage of arc from the sub-power converter 3b through a sub-injection transformer 4b.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an instantaneous voltage drop compensation device provided between a power system and a load, which compensates for a voltage drop caused by an instantaneous voltage drop in the power system.

Background Art

[0002] This type of instantaneous voltage drop compensation device is installed between a power system and a load, for example, as shown in Patent Document 1. It includes a thyristor switch that opens and closes a power line for supplying power from the power system to the load, a power storage unit that accumulates compensation energy, and a power converter that is connected to the power line via an injection transformer so as to be in parallel with the thyristor switch, and converts the DC power output from the power storage unit into AC power and supplies it to the power line. This instantaneous voltage drop compensation device operates in a normal commercial power supply mode in which the thyristor switch is turned on to supply power from the power system to the load during normal operation of the power system. On the other hand, during an abnormal operation of the power system, the thyristor switch is turned off, and the power converter supplies power to the load to operate in a voltage drop compensation mode for compensating for the voltage drop of the load.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described momentary voltage dip compensator, when detecting an abnormality in the power system such as a momentary voltage dip and always shifting from the commercial power supply mode to the reduced voltage compensation mode, a pulsed reverse voltage (arc extinction voltage) is applied to the thyristor switch from the power converter to reduce the thyristor current (current flowing from the anode to the cathode) to below a predetermined holding current and force arc extinction. At this time, the pulsed (several hundred μs) arc extinction voltage for extinguishing the thyristor switch is superimposed on the system voltage, and a pulsed overvoltage is applied to the load. For example, when the voltage drop width due to a momentary voltage dip is small, the peak value of the overvoltage (load overvoltage) applied to the load becomes excessively large, and depending on the load capacity of the connected load, the protection operation may be activated due to this load overvoltage and the load may stop (trip).

[0005] Therefore, the present invention has been made in view of the above problems, and in a momentary voltage dip compensator that compensates for a voltage drop caused by an abnormality such as a momentary voltage dip in a power system, the main problem is to suppress the load overvoltage generated when turning off a thyristor switch that opens and closes a power line.

Means for Solving the Problems

[0006] That is, the momentary voltage dip compensation device according to the present invention is provided between a power system and a load, and compensates for a voltage drop caused by an abnormality such as a momentary voltage dip in the power system. It includes a thyristor switch for opening and closing a power line that supplies power from the power system to the load, and is connected to the power line via a main injection transformer having a predetermined rated secondary voltage so as to be in parallel with the thyristor switch, and a main power converter that converts DC power output from a power storage unit into AC power and supplies the AC power to the power line, and is connected to the power line via a sub-injection transformer having a rated secondary voltage smaller than that of the main injection transformer so as to be in parallel with the thyristor switch, and a sub-power converter that converts DC power output from the power storage unit into AC power and supplies the AC power to the power line. When an abnormality occurs in the power system, an arc extinction voltage is applied to the thyristor switch to turn it off, and it operates in a voltage drop compensation mode in which power is supplied from the main power converter to the load to compensate for the voltage drop of the load. In this voltage drop compensation mode, when turning off the thyristor switch, after performing a first arc extinction operation of outputting an arc extinction voltage from the main power converter via the main injection transformer, it is switched to a second arc extinction operation of outputting an arc extinction voltage from the sub-power converter via the sub-injection transformer, which is characterized by this.

[0007] In order to completely extinguish the arc of the thyristor switch, it is necessary to continue applying a reverse voltage for several hundred microseconds even after the thyristor current has dropped below the holding current. If a large arc extinction voltage is continuously applied in a state where the current is below the holding current, it will be superimposed on the system voltage and the peak value of the load overvoltage will become excessively large. With the above configuration, when turning off the thyristor switch, first, an arc extinction voltage is applied from the main power converter via the main injection transformer having a relatively large rated secondary voltage, and an arc extinction voltage is applied from the sub-power converter via the sub-injection transformer having a relatively small rated secondary voltage. Therefore, for example, in a state where it is not necessary to apply a large arc extinction voltage to the thyristor switch, such as after the thyristor current has dropped below the holding current, a relatively small arc extinction voltage can be applied from the sub-power converter, and it is possible to prevent the peak value of the load overvoltage superimposed on the system voltage from becoming excessively large.

[0008] In the step-down voltage compensation mode, it is preferable that the transient voltage compensation device switches from the first arc extinguishing operation to the second arc extinguishing operation when the current value flowing through the thyristor switch drops to the holding current value. In this way, by switching from the first arc extinguishing operation to the second arc extinguishing operation at the timing when the current value flowing through the thyristor switch drops to the holding current value, while rapidly reducing the current value of the thyristor switch to the holding current value, the peak value of the superimposed load overvoltage can be suppressed.

[0009] As a specific embodiment of the transient voltage compensation device, examples include those in which the main injection transformer and the secondary injection transformer have equal rated primary voltages.

[0010] Furthermore, it is preferable that the transient voltage compensation device has a secondary power converter with a smaller rated capacity than the main power converter. As described above, by using a secondary injection transformer with a rated voltage smaller than that of the main injection transformer, it becomes possible to select a secondary power converter connected thereto with a smaller rated capacity than the main power converter. Thereby, the size of the secondary power converter can be reduced and the manufacturing cost can be suppressed.

[0011] Also, it is preferable that the transient voltage compensation device has the main power converter and the secondary power converter connected to a common power storage unit. In this way, for example, by sharing a power storage unit composed of a capacitor bank or the like between the main power converter and the secondary power converter, the size can be reduced.

[0012] As a specific embodiment of the transient voltage compensation device, in the step-down voltage compensation mode, after the thyristor switch turns off, the main power converter outputs the voltage drop of the load, and the secondary power converter outputs zero voltage.

[0013] As a specific embodiment of the momentary voltage dip compensation device, in the step-down voltage compensation mode, after the thyristor switch turns off, the step-down voltage of the load is output from the main power converter and the auxiliary power converter at a ratio according to their respective rated capacities.

Advantages of the Invention

[0014] According to the present invention configured as described above, in a momentary voltage dip compensation device that compensates for voltage dips caused by abnormalities such as momentary voltage dips in a power system, it is possible to suppress the load overvoltage that occurs when the thyristor switch for opening and closing the power line turns off.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0016] Hereinafter, an embodiment of the momentary voltage dip compensation device 100 according to the present invention will be described with reference to the drawings.

[0017] The momentary voltage dip compensation device 100 in this embodiment is provided between the power system (6.6 kV) PS and the critical load PL (hereinafter also referred to as the load), and has a voltage compensation function for compensating for the voltage drop caused by the momentary voltage dip (hereinafter also referred to as the momentary dip) in the power system PS. When the power system PS is normal, this momentary voltage dip compensation device 100 operates in a normal commercial power supply mode in which the power system PS and the load PL are electrically connected and power is supplied from the power system PS to the load PL. On the other hand, when a voltage abnormality such as a momentary dip occurs in the power system PS (hereinafter also referred to as the abnormal time), the thyristor switch 1 provided on the power line L for supplying power from the power system PS to the load PL is turned off, and at the same time, it shifts to a reduced voltage compensation mode in which power is supplied from the power storage unit 2 to the load PL to compensate for the reduced voltage of the load PL and operates. Note that although the power system PS supplies three-phase power, only a single-phase portion is shown in FIG. 1 for simplicity.

[0018] Specifically, as shown in FIG. 1, this momentary voltage dip compensation device 100 includes a thyristor switch 1 that opens and closes the power line L for supplying power from the power system PS to the load PL, a power storage unit 2 that accumulates compensation energy, a power converter 3 that converts the DC power output from the power storage unit 2 into AC power and supplies power, an injection transformer 4 that transforms the AC power supplied from the power converter 3 and injects it into the power line L, a system voltage measurement unit 5 that measures the voltage (input voltage) on the power system PS side, a switch current measurement unit 6 that measures the current (switch current) flowing through the thyristor switch 1, and a control device 7.

[0019] The thyristor switch 1 is provided on the power line L for supplying power from the power system PS to the load PL, and is driven by a drive circuit (not shown) to switch the opening and closing of the power line L. Specifically, it is the thyristor switch 1. This thyristor switch 1 is in an on state (conducting state) in the normal commercial power supply mode, and becomes an off state (non-conducting state) when shifting to the reduced voltage compensation mode.

[0020] Specifically, the power storage unit 2 is a power storage device such as a capacitor bank. In the continuous commercial power supply mode, the power storage unit 2 is in a charged state in which compensation energy is stored, and when the power storage unit 2 transitions to the voltage drop compensation mode, the power storage unit 2 supplies the stored compensation energy to the power converter 3 as DC power.

[0021] The power converter 3 is a so-called inverter that switches the input direct current using semiconductor switches such as IGBTs and transistors to supply an alternating current voltage. The power converter 3 is connected to the power line L via an injection transformer 4 so as to be connected in parallel to the thyristor switch 1. The power converter 3 is in a stopped standby state in the continuous commercial power supply mode, and when it shifts to the voltage drop compensation mode, it converts the direct current power supplied from the power storage unit 2 into alternating current power and supplies it to the power line L.

[0022] The injection transformer 4 is provided between the power converter 3 and the power line L, and transforms (steps up or down) the AC power output from the power converter 3 and injects it into the power line L; it is a so-called transformer.

[0023] The system voltage measuring unit 5 measures the voltage (input voltage) input from the power system PS, and outputs the measured voltage value to the control device 7. Specifically, the system voltage measuring unit 5 is connected to the power line L on the power system PS side relative to the thyristor switch 1. This system voltage measuring unit 5 individually measures the input voltage values ​​of the three phases (U phase, V phase, W phase) input from the power system PS.

[0024] The switch current measuring unit 6 measures the current flowing through the thyristor switch 1 and outputs the measured current value to the control device 7. Specifically, the switch current measuring unit 6 is connected in series to the thyristor switch 1 in the power line L. The switch current measuring unit 6 measures the current values ​​of the three phases (U phase, V phase, W phase) flowing through the thyristor switch 1 individually.

[0025] The control device 7 is a general-purpose or dedicated computer equipped with a CPU, a memory, an input / output interface, etc. By causing the CPU and peripheral devices to cooperate according to a predetermined program stored in its memory, as shown in FIG. 2, it at least exhibits the function as the operation mode switching unit 71.

[0026] Based on the system voltage measured by the system voltage measurement unit 5, the operation mode switching unit 71 controls the thyristor switch 1 and the power converter 3 to constantly switch between the commercial power supply mode and the low voltage compensation mode.

[0027] Specifically, when an abnormality occurs in the power system PS such as an instantaneous voltage drop, the operation mode switching unit 71 controls the thyristor switch 1 and the power converter 3 to switch from the commercial power supply mode to the low voltage compensation mode. Specifically, the operation mode switching unit 71 acquires the system voltage from the system voltage measurement unit 5, determines that there is an abnormality in the power system PS when the acquired system voltage is outside a predetermined range, and applies the arc extinction voltage, which is a pulsed reverse voltage, from the power converter 3 to the thyristor switch 1 to turn it off (arc extinction), and at the same time, supplies power from the power converter 3 to the load PL to compensate for the drop in the system voltage from the power converter 3.

[0028] When the system voltage recovers, the operation mode switching unit 71 controls the thyristor switch 1 and the power converter 3 to switch the operation mode from the low voltage compensation mode to the commercial power supply mode. Specifically, when the operation mode switching unit 71 determines that the acquired system voltage has recovered, it turns on (arcs) the thyristor switch 1 and blocks the gate of the power converter 3. Thereby, the power system PS and the load PL are electrically connected, and the current output by the power converter 3 is set to 0. Note that "the system voltage recovers" means that the state where the system voltage is equivalent to the rated voltage continues for a certain period of time.

[0029] When the momentary low voltage compensation device 100 of the present embodiment shifts to the step-down voltage compensation mode, in order to suppress the load overvoltage when the thyristor switch 1 is turned off, as shown in FIGS. 1 and 3, as a power converter, it includes a main power converter 3a having a predetermined rated capacity and a sub-power converter 3b having a rated capacity smaller than that of the main power converter 3a. As an injection transformer, it includes a main injection transformer 4a having a predetermined rated voltage and a sub-injection transformer 4b having a rated voltage smaller than that of the main injection transformer 4a.

[0030] The main power converter 3a is connected to the power line L via the main injection transformer 4a so as to be in parallel with the thyristor switch 1. The sub-power converter 3b is also connected to the power line L via the sub-injection transformer 4b so as to be in parallel with the thyristor switch 1. The main injection transformer 4a and the sub-injection transformer 4b are connected to the power line L so as to be in parallel with the thyristor switch 1 and in series with each other.

[0031] The rated primary voltage of the main injection transformer 4a is equal to the rated primary voltage of the sub-injection transformer 4b. On the other hand, the rated secondary voltage of the main injection transformer 4a is larger than the rated secondary voltage of the sub-injection transformer 4b. In the present embodiment, the main injection transformer 4a has a rated primary voltage of 440V and a rated secondary voltage of 3800V. On the other hand, the sub-injection transformer 4b has a rated primary voltage of 440V and a rated secondary voltage of 200V.

[0032] Also in the present embodiment, the rated capacity of the main power converter 3a is 2000 kVA for three phases, and the rated capacity of the sub-power converter 3b is 106 kVA, but it is not limited to this.

[0033] And in the present embodiment, as shown in FIG. 3, the main power converter 3a and the sub-power converter 3b are connected to a common power storage unit 2. The power storage unit 2 of the present embodiment is composed of a DC capacitor bank with an output voltage of 700V.

[0034] Then, when turning off the thyristor switch 1 in the step-down voltage compensation mode, the transient low compensation device 100 of the present embodiment first performs a first arc extinction operation of outputting an arc extinction voltage from the main power converter 3a via the main injection transformer 4a, and then switches to a second arc extinction operation of outputting an arc extinction voltage from the auxiliary power converter 3b via the auxiliary injection transformer 4b.

[0035] Specifically, the operation mode switching unit 71 performs the first arc extinction operation and the second arc extinction operation by controlling the main power converter 3a and the auxiliary power converter 3b. In the first arc extinction operation, a pulsed arc extinction voltage is output and generated from the main power converter 3a, and the auxiliary power converter 3b outputs a zero voltage. On the other hand, in the second arc extinction operation, a pulsed arc extinction voltage is output and generated from the auxiliary power converter 3b, and the main power converter 3a outputs a zero voltage. That is, the operation mode switching unit 71 alternately outputs (in order) the arc extinction voltage from the main power converter 3a and the auxiliary power converter 3b to turn off the thyristor switch 1.

[0036] Then, the operation mode switching unit 71 determines the timing to start the first arc extinction operation and the timing to switch from the first arc extinction operation to the second arc extinction operation based on the measured voltage value measured by the system voltage measurement unit 5 and the current value of the thyristor current measured by the switch current measurement unit 6. Specifically, when it is determined that momentary voltage dip has occurred because the measured voltage value is outside the predetermined range as described above, the operation mode switching unit 71 starts the first arc extinction operation. The operation mode switching unit 71 stores in advance the holding current value specific to the thyristor switch 1, compares the stored holding current value with the measured current value of the thyristor current, and determines the timing to switch from the first arc extinction operation to the second arc extinction operation. Specifically, when the current value of the thyristor current decreases and reaches the holding current value, the operation mode switching unit 71 switches from the first arc extinction operation to the second arc extinction operation. After that, the operation mode switching unit 71 continues the second arc extinction operation for a predetermined turn-off time (several hundred microseconds) specific to the thyristor switch 1. When the turn-off time elapses, the operation mode switching unit 71 terminates the second arc extinction operation with the zero voltage output of the secondary power converter 3b. This turn-off time is the time from when the thyristor current value becomes less than or equal to the holding current until the switch 1 is completely extinguished while the reverse voltage is continuously applied, and is stored in advance. Then, at the timing when the second arc extinction operation ends (that is, the timing when the thyristor switch 1 is completely extinguished), the operation mode switching unit 71 supplies power from the main power converter 3a to the load PL to compensate for the decrease in the system voltage from the power converter 3.

[0037] Next, the voltage drop compensation operation of the momentary voltage dip compensation device 100 according to the present embodiment will be described with reference to FIG. 5. This reduced voltage compensation operation starts with the thyristor switch 1 in the on state and both the main power converter 3a and the auxiliary power converter 3b in a zero voltage output state. When the grid voltage goes out of the predetermined range and a momentary dip is detected (step S1), with the auxiliary power converter 3b remaining in zero voltage output, first a pulsed arc extinction voltage is output from the main power converter 3a (step S2). As a result, the thyristor current value drops rapidly. When the thyristor current value drops to the holding current value (step S3), the main power converter 3a switches to zero voltage output and an arc extinction voltage is output from the auxiliary power converter 3b (step S4). After the turn-off time elapses since the arc extinction voltage is output from the auxiliary power converter 3b (step S5), the auxiliary power converter 3b is set to zero voltage output and the amount of voltage drop of the grid voltage is output from the main power converter 3a (step S6). Thereafter, when the recovery of the power voltage is detected, the thyristor switch 1 is turned on and both the main power converter 3a and the auxiliary power converter 3b are turned off (step S7).

[0038] According to the momentary dip compensation device 100 of this embodiment configured as described above, when turning off the thyristor switch 1, first an arc extinction voltage is applied from the main power converter 3a via the main injection transformer 4a with a relatively large rated secondary voltage, and an arc extinction voltage is applied from the auxiliary power converter 3b via the auxiliary injection transformer 4b with a relatively small rated secondary voltage. Therefore, in a state where it is not necessary to apply a large arc extinction voltage to the thyristor switch 1, such as after the thyristor current has dropped below the holding current, a relatively small arc extinction voltage can be applied from the auxiliary power converter 3b, preventing the peak value of the load overvoltage superimposed on the grid voltage from becoming excessively large.

[0039] Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, the main power converter 3a and the auxiliary power converter 3b were connected to the common power storage unit 2, but it is not limited to this. In other embodiments, as shown in FIG. 6, the main power converter 3a and the auxiliary power converter 3b may be connected to individual power storage units 2a and 2b, respectively.

[0040] Furthermore, in the momentary voltage drop compensation mode of the momentary voltage drop compensation device 100 of the above embodiment, after the thyristor switch 1 is completely turned off, all of the voltage drop of the load PL was output from the main power converter 3a, but it is not limited to this. In other embodiments, the voltage drop of the load PL may be shared and output by the main power converter 3a and the auxiliary power converter 3b. For example, the voltage drop of the load PL may be output from the main power converter 3a and the auxiliary power converter 3b in a ratio corresponding to their respective rated capacities.

[0041] Needless to say, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit thereof.

Explanation of Reference Numerals

[0042] 100 ··· Momentary voltage drop compensation device 1 ··· Thyristor switch 2 ··· Power storage unit 3a ··· Main power converter 3b ··· Auxiliary power converter 4a ··· Main injection transformer 4b ··· Auxiliary injection transformer 5 ··· System voltage measurement unit 6 ··· Switch current measurement unit 7 ··· Control device L ··· Power line PS ··· Power system PL ··· Load

Claims

1. It is provided between a power system PS and a load, and compensates for a voltage drop caused by an abnormality such as an instantaneous voltage dip in the power system PS. A thyristor switch that opens and closes a power line for supplying power from the power system PS to the load. A main power converter that is connected to the power line via a main injection transformer having a predetermined rated secondary voltage so as to be in parallel with the thyristor switch, converts DC power output from a power storage unit into AC power, and supplies the AC power to the power line. A sub-power converter that is connected to the power line via a sub-injection transformer having a rated secondary voltage smaller than that of the main injection transformer so as to be in parallel with the thyristor switch, converts DC power output from a power storage unit into AC power, and supplies the AC power to the power line. When an abnormality occurs in the power system PS, it operates in a voltage drop compensation mode in which an arc extinction voltage is applied to the thyristor switch to turn it off, and power is supplied from the main power converter to the load to compensate for the voltage drop of the load. An instantaneous voltage dip compensation device that, in the voltage drop compensation mode, when turning off the thyristor switch, performs a first arc extinction operation of outputting an arc extinction voltage from the main power converter via the main injection transformer, and then switches to a second arc extinction operation of outputting an arc extinction voltage from the sub-power converter via the sub-injection transformer.

2. The instantaneous voltage dip compensation device according to claim 1, wherein in the voltage drop compensation mode, when the current value flowing through the thyristor switch drops to a holding current value, it switches from the first arc extinction operation to the second arc extinction operation.

3. The instantaneous voltage dip compensation device according to claim 1, wherein the main injection transformer and the sub-injection transformer have equal rated primary voltages.

4. The instantaneous voltage dip compensation device according to claim 1, wherein the sub-power converter has a rated capacity smaller than that of the main power converter.

5. The instantaneous voltage dip compensation device according to claim 1, wherein the main power converter and the sub-power converter are connected to a common power storage unit.

6. The instantaneous voltage dip compensation device according to claim 1, wherein in the voltage drop compensation mode, after the thyristor switch is turned off, the main power converter outputs the voltage drop of the load, and the sub-power converter outputs a zero voltage.

7. The transient voltage compensation device according to claim 1, wherein, in the low voltage compensation mode, after the thyristor switch is turned off, the voltage drop of the load is output from the main power converter and the auxiliary power converter in a ratio corresponding to their respective rated capacitances.

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