Instantaneous voltage drop compensator

Abstract

To provide an instantaneous voltage drop compensator that is provided between a power system and a load and compensates for voltage drop occurring due to instantaneous voltage drop in the power system.SOLUTION: An instantaneous voltage drop compensator 100 is provided between a three-phase power system and a load and compensates for voltage drop occurring due to abnormality such as instantaneous voltage drop in the power system, and comprises: a thyristor switch 1; a power converter 3; a line voltage measuring unit 5 that measures the line voltage of the power system, and can switch among three operation modes of a normal commercial power supply mode in a normal time of the power system, a dropped voltage compensation mode when abnormality occurs in the power system, and a compensation function test mode for outputting a test voltage to test a voltage compensation function; and a control unit 8 including an operation mode switching unit 81 that switches the operation mode. When switching from the normal commercial power supply mode to the compensation function test mode, the operation mode switching unit 81 synchronizes the timing to output the extinction voltage of arc for extinguishing the arc of the thyristor switch 1 from the power converter 3, with the phase of the measured line voltage.SELECTED DRAWING: Figure 2

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, for example, as shown in Patent Document 1, between a power system and a load, and includes a thyristor switch that opens and closes a power line for feeding 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 DC power output from the power storage unit into AC power and feeds 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, while in the event of an abnormality in the power system, the thyristor switch is turned off and power is supplied from the power converter to the load to compensate for the voltage drop of the load in a voltage drop compensation mode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the momentary voltage dip compensator described above, a voltage compensation function test for checking the soundness of the voltage compensation function (specifically, whether the power converter functions correctly) is periodically performed. This voltage compensation function test is performed by instantaneously turning off the thyristor switch while being connected between the power system and the load and with the power system being normal. Specifically, in this voltage compensation function test, a reverse voltage (arc extinction voltage) for turning off (extinguishing the arc) the thyristor switch is generated from the power converter, and after the thyristor switch is completely extinguished, a voltage deficiency (specifically, zero voltage output) is output for about 0.1 seconds. At this time, a pulsed (several hundred μs) arc extinction voltage for extinguishing the thyristor switch is superimposed on the injection transformer, and a pulsed overvoltage is applied to the load. Then, thereafter, the thyristor switch is turned on (arced), and the power converter is turned off, and the momentary voltage dip compensator always returns to the commercial power supply mode.

[0005] Conventionally, such a voltage compensation function test is configured such that an arc extinction voltage is immediately generated at the timing when an inspector presses a test execution button provided on a control panel or the like, and the thyristor switch is turned off. Therefore, for example, as shown in FIG. 5, when an inspector presses the test execution button at the timing when the line voltage of the power system reaches its peak, the peak value of the overvoltage (load overvoltage) applied to the load due to the pulsed arc extinction voltage becomes excessively large, and depending on the load capacity of the connected load, there is a risk that the protective operation will act and the load will stop (trip) due to the influence of this load overvoltage.

[0006] 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 that occurs during the test execution of the voltage compensation function.

Means for Solving the Problems

[0007] That is, the instantaneous voltage dip compensation device according to the present invention is provided between a power system that supplies three-phase power and a load, and compensates for a voltage drop caused by an abnormality such as an instantaneous voltage dip in the power system. It includes a thyristor switch that opens and closes a power line that supplies power from the power system to the load, and a power converter that is connected to the power line via an injection transformer so as to be parallel to the thyristor switch, converts DC power output from a power storage unit that accumulates compensation energy into AC power, and supplies the AC power to the power line. In the normal state of the power system, there is a normal commercial power supply mode in which the thyristor switch is turned on to supply power from the power system to the load, a voltage drop compensation mode in which, when the power system is abnormal, the thyristor switch is turned off and power is supplied from the power converter to the load to compensate for the voltage drop of the load, and a compensation function test mode in which, when the power system is normal, the thyristor switch is turned off and a test voltage is output from the power converter to test the voltage compensation function. The instantaneous voltage dip compensation device is configured to be able to switch between these three operation modes, and includes a phase detection unit that detects the phase of the line voltage of the power system, and an operation mode switching unit that controls the operations of the thyristor switch and the power converter to switch the operation mode. The operation mode switching unit is characterized in that, when switching from the normal commercial power supply mode to the compensation function test mode, the timing for generating an arc extinction voltage that extinguishes the thyristor switch from the power converter is synchronized with the phase of the line voltage.

[0008] With such a configuration, when switching from the normal commercial power supply mode to the compensation function test mode, the timing for generating the arc extinction voltage for extinguishing the thyristor switch from the power converter is synchronized with the phase of the line voltage. Therefore, the peak value of the load overvoltage generated during the test execution of the voltage compensation function can be suppressed. That is, instead of generating the arc extinction voltage at the timing when the inspector presses the test execution button as in the conventional case, the arc extinction voltage is generated in synchronization with the phase of the line voltage. Thus, by presetting to generate the arc extinction voltage at a phase where the line voltage becomes low, such as a voltage zero point where the line voltage becomes zero, even if the timing when the inspector presses the test execution button overlaps with the timing when the line voltage of the power system reaches its peak, the arc extinction voltage can be generated at the timing when the line voltage becomes low. Thereby, the peak value of the overvoltage (load overvoltage) applied to the load by the pulse-shaped arc extinction voltage can be suppressed.

[0009] Further, in the momentary voltage dip compensation device, the phase detection unit detects the phase of the voltage zero point where the line voltage of the power system becomes zero, and when the operation mode switching unit switches from the normal commercial power supply mode to the compensation function test mode, it is preferable to synchronize the timing for generating the arc extinction voltage from the power converter with the phase where the line voltage becomes the voltage zero point. By doing so, since the arc extinction voltage is generated at the timing when the line voltage becomes the voltage zero point, the peak value of the load overvoltage can be suppressed to the maximum extent.

[0010] As a specific aspect of the momentary voltage dip compensation device, it further includes a command signal receiving unit that receives a test command signal for instructing the execution of the test of the voltage compensation function, and the operation mode switching unit synchronizes the timing for generating the arc extinction voltage from the power converter with the phase where the line voltage becomes the voltage zero point within a predetermined time after receiving the test command signal.

[0011] In addition, since the peak value of the load overvoltage generated by applying the arc extinction voltage increases in inverse proportion to the load capacity of the connected load, in order to suppress the peak value of the load overvoltage, it is desirable not to apply the arc extinction voltage during light load. Therefore, the momentary voltage dip compensation device further includes a load power calculation unit that measures the load power value of the load, and the operation mode switching unit compares the measured load power value with a predetermined set power value, and when the load power value is equal to or greater than the set power value, it is preferable to generate the arc extinction voltage from the power converter. In this way, when the load power value is equal to or greater than the set power value, that is, when the load capacity is relatively large, the arc extinction voltage is generated from the power converter, so that the peak value of the load overvoltage can be further suppressed.

Advantages of the Invention

[0012] 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 generated during the test execution of the voltage compensation function.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0014] Hereinafter, an embodiment of the instantaneous voltage drop compensation device 100 according to the present invention will be described with reference to the drawings.

[0015] The instantaneous voltage drop compensation device 100 in this embodiment is provided between the power system PS and the important load PL (hereinafter also referred to as the load), and has a voltage compensation function for compensating for the voltage drop caused by the instantaneous voltage drop (hereinafter also referred to as the instantaneous voltage drop) in the power system PS. When the power system PS is normal, this instantaneous voltage drop 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 an instantaneous voltage drop 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, the power storage unit 2 supplies power to the load PL and shifts to a reduced voltage compensation mode for compensating 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.

[0016] Specifically, as shown in FIG. 1, this instantaneous voltage drop 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 it to the power line L, a system voltage measurement unit 5 that measures the voltage (input voltage) on the power system PS side, a load voltage measurement unit 6 that measures the voltage (output voltage) on the load PL side, a load current measurement unit 7 that measures the current flowing through the load PL, and a control device 8.

[0017] 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.

[0018] The power storage unit 2 is specifically a power storage device (power storage device) such as a capacitor. This power storage unit 2 is in a charged state with accumulated compensation energy in the normal commercial power supply mode, and when it shifts to the low voltage compensation mode, it supplies the accumulated compensation energy as DC power to the power converter 3.

[0019] The power converter 3 uses semiconductor switches such as IGBTs and transistors to switch the input DC and supply an AC voltage, and is a so-called inverter. This power converter 3 is connected to the power line L via the injection transformer 4 so as to be connected in parallel with the thyristor switch 1. The power converter 3 is in a standby state in the stopped state in the normal commercial power supply mode, and when it shifts to the low voltage compensation mode, it converts the DC power supplied from the power storage unit 2 into AC power and supplies power to the power line L.

[0020] The system voltage measurement unit 5 measures the voltage (input voltage) input from the power system PS and outputs the measured voltage value to the control device 8. Specifically, the system voltage measurement unit 5 is connected to the power line L on the power system PS side of the thyristor switch 1. This system voltage measurement unit 5 individually measures the input voltage values of the three phases (U phase, V phase, W phase) input from the power system PS.

[0021] The load voltage measurement unit 6 measures the voltage (output voltage) output to the load PL and outputs the measured voltage value to the control device 8. Specifically, the load voltage measurement unit 6 is connected to the power line L on the load PL side of the thyristor switch 1. This load voltage measurement unit 6 individually measures the output voltage values of the three phases (U phase, V phase, W phase) output to the load PL.

[0022] The load current measurement unit 7 measures the current supplied to the load PL and outputs the measured current value to the control device 8. Specifically, the load current measurement unit 7 is connected to the power line L on the load PL side of the thyristor switch 1. This load voltage measurement unit 6 individually measures the current values of the three phases (U phase, V phase, W phase) supplied to the load PL.

[0023] The control device 8 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 functions as an operation mode switching unit 81.

[0024] Based on the system voltage measured by the system voltage measurement unit 5, the operation mode switching unit 81 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.

[0025] Specifically, when an abnormality occurs in the power system PS such as an instantaneous voltage drop, the operation mode switching unit 81 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 81 acquires the system voltage from the system voltage measurement unit 5. When the acquired system voltage is outside a predetermined range, it determines that there is an abnormality in the power system PS, applies an arc extinguishing voltage, which is a pulsed reverse voltage, to the thyristor switch 1 to turn it off, and supplies power from the power converter 3 to the load PL to compensate for the decrease in the system voltage from the power converter 3.

[0026] When the system voltage recovers, the operation mode switching unit 81 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 81 determines that the acquired system voltage has recovered, it turns on 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 equal to the rated voltage continues for a certain period of time.

[0027] Also, this momentary voltage dip compensator 100 has a compensation function test mode which is an operation mode for confirming the soundness of the voltage compensation function. In this compensation function test mode, when the power system PS is normal, the momentary voltage dip compensator 100 applies a pulsed (several hundred μs) arc extinction voltage from the power converter 3 to the thyristor switch 1 to turn off the thyristor switch 1, and operates to output a test voltage (specifically, zero voltage output) from the power converter 3 to the power line L.

[0028] As shown in FIG. 2, the control device 8 functions as a command signal reception unit 82 that receives a test command signal for instructing the execution of the voltage compensation function test. When the command signal reception unit 82 receives the test command signal, it outputs this to the operation mode switching unit 81, and the operation mode switching unit 81 always switches the operation mode of the momentary voltage dip compensator 100 from the commercial power supply mode to the compensation function test mode. Note that the test command signal is output when an inspector presses a test execution button 9 provided on a control panel or the like.

[0029] And in order to suppress the load overvoltage that occurs during the execution of the voltage compensation function test, the momentary voltage dip compensator 100 of this embodiment is configured such that the operation mode switching unit 81 synchronizes the timing of generating the arc extinction voltage from the power converter 3 with the phase of the line voltage when switching from the commercial power supply mode to the compensation function test mode.

[0030] In order to realize such an operation, the control device 8 of the present embodiment further functions as a phase detection unit 83 that detects the phase of the line voltage of the power system PS as shown in FIG. 2. As shown in FIG. 3, this phase detection unit 83 calculates the line voltages between U-V, V-W, and W-U from the input voltage values of each phase measured by the system voltage measurement unit 5, and detects the phase of the voltage waveform of each of the line voltages. More specifically, this phase detection unit 83 detects the phase (voltage zero-phase) at which the voltage waveform of each line voltage passes through the voltage zero point. As soon as the phase detection unit 83 detects the voltage zero-phase, it outputs a zero-point detection signal indicating that the voltage zero-phase has been detected to the operation mode switching unit 81. The phase detection unit 83 detects the voltage zero-phase for each of the plurality of line voltages, and outputs a zero-point detection signal every time the voltage zero-phase is detected by any of the line voltages.

[0031] When the operation mode switching unit 81 receives the zero-point detection signal from the phase detection unit 83, it generates a pulsed arc extinguishing voltage (reverse voltage) from the power converter 3. That is, the operation mode switching unit 81 synchronizes the timing of generating the arc extinguishing voltage (reverse voltage) from the power converter 3 with the phase at which the voltage waveform of the line voltage crosses the voltage zero point. More specifically, as shown in FIG. 3, the operation mode switching unit 81 generates the arc extinguishing voltage at the timing when it receives the zero-point detection signal within a predetermined time after receiving the test command signal. Here, the operation mode switching unit 81 is configured to generate the arc extinguishing voltage at the timing when it first receives the zero-point detection signal after receiving the zero-point detection signal.

[0032] Further, the momentary voltage drop compensation device 100 of the present embodiment has an interlock function that prevents the voltage compensation function test from being executed when the load power at the load PL is small. Specifically, in this embodiment, the control device 8 further functions as a load power calculation unit 84 that measures the load power value at the connected load PL.

[0033] This load power calculation unit 84 calculates the load power value at the load PL based on the output voltage value measured by the load voltage measurement unit 6 and the supply current value measured by the load current measurement unit 7, and constantly outputs this to the operation mode switching unit 81. The operation mode switching unit 81 stores a predetermined set power value in advance, compares the set power value with the load power value, and is configured to generate an arc extinction voltage from the power converter 3 only when the load power value is equal to or greater than the set power value. That is, the momentary voltage dip compensation device 100 of the present embodiment is configured to receive a zero-crossing detection signal within a predetermined time after receiving a test command signal, and further generate an arc extinction voltage when the load power value is equal to or greater than the set power value. The set power value is set such that the attenuation rate of the arc extinction pulse voltage determined by the output impedance composed of the power converter 3 and the injection transformer 4 and the impedance of the load PL is approximately 0.8.

[0034] Next, the operation of the momentary voltage dip compensation device 100 of the present embodiment during the execution of the compensation function test will be described with reference to FIG. 4.

[0035] The voltage compensation function test starts when an inspector presses a test execution button 9 provided on a control panel or the like in a state where no abnormality such as a momentary voltage dip occurs in the power system PS, that is, in a state where the momentary voltage dip compensation device 100 is constantly operating in the commercial power supply mode, and a test command signal is output to the control device 8 (specifically, the operation mode switching unit 81) (step S1).

[0036] When the operation mode switching unit 81 receives a test command signal, it then receives the input of the zero point detection signal from the phase detection unit 83 for a predetermined time period (step S2). When the operation mode switching unit 81 receives the zero point detection signal and detects the zero point of the line voltage, it compares the load power value at the load PL with the power setting value stored in advance (step S3). Here, when the load power value is less than the power setting value, the operation mode switching unit 81 cancels the execution of the voltage compensation function test without applying the arc extinction voltage, which is a reverse voltage, to the thyristor switch 1 (step S4). On the other hand, when the load power value is equal to or greater than the power setting value, the operation mode switching unit 81 generates a pulsed arc extinction voltage from the power converter 3 and turns off the thyristor switch 1 (step S5). Then, after the thyristor switch 1 is completely extinguished, the operation mode switching unit 81 causes the power converter 3 to output a test voltage (zero voltage) (step S6).

[0037] Thereafter, the operation mode switching unit 81 turns on the thyristor switch 1 and turns off the power converter 3 to switch the operation mode to the commercial power supply mode at all times.

[0038] According to the momentary low compensation device 100 of the present embodiment configured as described above, when switching from the commercial power supply mode to the compensation function test mode at all times, the timing for generating the arc extinction voltage for extinguishing the thyristor switch 1 from the power converter 3 is synchronized with the phase at which the line voltage becomes the voltage zero point. Therefore, even if the timing when the inspector presses the test execution button 9 overlaps with the timing when the line voltage of the power system PS reaches the peak, the arc extinction voltage can be generated at the timing when the line voltage becomes the zero voltage. Thus, the peak value of the overvoltage (load overvoltage) applied to the load PL due to the pulsed arc extinction voltage can be suppressed.

[0039] In addition, the operation mode switching unit 81 compares the measured load power value with a predetermined set power value, and generates a quenching voltage from the power converter 3 only when the load power value is equal to or greater than the set power value, that is, only in a situation where the load capacity is relatively large. Therefore, the peak value of the load overvoltage can be further suppressed.

[0040] Note that the present invention is not limited to the above-described embodiment.

[0041] For example, in the momentary voltage dip compensator 100 of the above-described embodiment, there is an interlock function that prevents the voltage compensation function test from being executed when the load power at the load PL is small, but the present invention is not limited to this. In other embodiments, such an interlock function may not be provided, and the quenching voltage may be generated from the power converter 3 regardless of the load power value at the load PL at the timing when a test command signal and a zero-cross detection signal are received.

[0042] Also, in the momentary voltage dip compensator 100 of the above-described embodiment, the timing for generating the quenching voltage is synchronized with the voltage zero phase at which the voltage waveform of the line voltage passes through the voltage zero point, but the present invention is not limited to this. In other embodiments, the timing for generating the quenching voltage may be synchronized with the phases before and after being shifted from the voltage zero phase. The timing for generating the quenching voltage may be any timing as long as the load overvoltage related to the load PL can be suppressed to about 200% or less (within 1 ms) of the peak value of the rated voltage by generating the quenching voltage.

[0043] Needless to say, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

Explanation of Reference Numerals

[0044] 100 ··· Momentary voltage dip compensator 1 ··· Thyristor switch 2 ··· Power storage unit 3 ··· Power converter 4 ··· Injection transformer 81 ··· Operation mode switching unit 83 ··· Phase detection unit L ··· Power line PS ··· Power system PL ··· Load

Claims

1. It is provided between a power system that supplies three-phase power and a load, and compensates for a voltage drop caused by an abnormality such as an instantaneous voltage dip in the power system. A thyristor switch that opens and closes a power line for supplying power from the power system to the load. A power converter that is connected to the power line via an injection transformer so as to be parallel to the thyristor switch, converts DC power output from a power storage unit that accumulates compensation energy into AC power, and supplies the AC power to the power line. A normal commercial power supply mode in which the thyristor switch is turned on to supply power from the power system to the load when the power system is normal. A voltage drop compensation mode in which when the power system is abnormal, the thyristor switch is turned off, and power is supplied from the power converter to the load to compensate for the voltage drop of the load. A momentary voltage dip compensation device configured to be able to switch between three operation modes: a compensation function test mode in which when the power system is normal, the thyristor switch is turned off and a test voltage is output from the power converter to test the voltage compensation function. A phase detection unit that detects the phase of the line voltage of the power system. An operation mode switching unit that controls the operations of the thyristor switch and the power converter to switch the operation mode. A momentary voltage dip compensation device in which when the operation mode switching unit switches from the normal commercial power supply mode to the compensation function test mode, the timing for generating an arc extinction voltage from the power converter to extinguish the arc of the thyristor switch is synchronized with the phase of the line voltage.

2. The phase detection unit detects the phase of the voltage zero point at which the line voltage of the power system becomes zero. The momentary voltage dip compensation device according to claim 1, wherein when the operation mode switching unit switches from the normal commercial power supply mode to the compensation function test mode, the timing for generating the arc extinction voltage from the power converter is synchronized with the phase at which the line voltage becomes the voltage zero point.

3. Further comprising a command signal receiving unit that receives a test command signal for instructing the execution of the test of the voltage compensation function. The momentary voltage dip compensation device according to claim 2, wherein when the operation mode switching unit receives the test command signal, the timing for generating the arc extinction voltage from the power converter is synchronized with the phase at which the line voltage becomes the voltage zero point within a predetermined time.

4. Further comprising a load power calculation unit that measures the load power value at the load. The instantaneous low compensation device according to claim 1, wherein the operation mode switching unit compares the measured load power value with a predetermined set power value, and generates the arc extinction voltage from the power converter when the load power value is equal to or greater than the set power value.

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