Instantaneous low compensation device

Abstract

To avoid a situation in which an instantaneous voltage drop compensation function for a motor is impaired when the motor is started in a momentary sag compensation device configured to power a motor.SOLUTION: A momentary sag compensation device 1 includes an HSS 6, a power converter 2, and a control device 100. The power converter 2 is provided between an output terminal T2 and a power storage device 3, and performs bidirectional power conversion. The control device 100 controls the HSS 6 and the power converter 2. The control device 100 starts a motor M by causing the power converter 2 to convert DC power of the power storage device 3 into AC power and supply it to the motor M while controlling the HSS 6 to be off. When the motor M is started, the control device 100 operates the power converter 2 using a variable voltage variable frequency control method such that the voltage and frequency of the AC power increase as the rotational speed of the motor M increases.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a voltage sag compensation device. [Background technology]

[0002] Patent Publication No. 2021-001994 (Patent Document 1) discloses a voltage sag compensation device. When connected to an electrical load, this voltage sag compensation device is used as a power supply to protect the electrical load from momentary voltage drops (voltage sags) and power outages in the AC power supply (voltage sag compensation function). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Re-tabled publication No. 2021-001994 Summary of the Invention [Problem to be solved by the invention]

[0004] When an electrical load starts, an inrush current may flow from the AC power supply through the voltage sag compensator to the electrical load. If a motor is used as the electrical load, the inrush current at motor startup is larger than the inrush current at startup of other electrical loads. Such a large inrush current is likely to overload the voltage sag compensator. As a result, the voltage sag compensator's ability to compensate for the motor's voltage sag may be impaired.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to prevent a situation in which the momentary sag compensation function for a motor is impaired when the motor is started in a momentary sag compensation device configured to supply power to the motor. [Means for solving the problem]

[0006] A momentary sag compensator according to the present disclosure is connected to an AC power supply and is configured to supply power to a motor. The momentary sag compensator includes a switch, a power converter, and a control device. The switch has an input terminal connected to the AC power supply and an output terminal connected to the motor. The power converter is provided between the output terminal and a power storage device and performs bidirectional power conversion. The control device controls the switch and the power converter. With the switch controlled to be off, the control device starts the motor by having the power converter convert DC power from the power storage device into AC power and supply it to the motor, and when the motor starts, operates the power converter using a variable voltage / variable frequency control method so that the voltage and frequency of the AC power increase as the rotational speed of the motor increases. [Effects of the Invention]

[0007] According to the present disclosure, in a voltage sag compensation device configured to supply power to a motor, it is possible to avoid a situation in which the voltage sag compensation function for the motor is impaired when the motor is started. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a configuration of a voltage sag compensation system including a voltage sag compensation device according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the flow of power when the AC power supply is in a normal state. [Figure 3] FIG. 1 is a diagram showing the flow of power when a voltage sag or power outage occurs. [Figure 4] FIG. 10 is a diagram illustrating the flow of power when an overload of the instantaneous sag compensator is detected. [Figure 5] 10 is a diagram for explaining control executed by the control device when an overcurrent is detected when an overload is detected by the instantaneous sag compensator. FIG. [Figure 6] FIG. 3 is a diagram for explaining control executed by the control device when the motor is started. [Figure 7] 4 is a flowchart showing an example of processing executed by the control device in the first embodiment. [Figure 8]FIG. 10 is a diagram showing the configuration of a voltage sag compensation system including a voltage sag compensation device according to a second embodiment. [Figure 9] 3 is a diagram for explaining control executed by the control device when starting the motor and the electric load. FIG. [Figure 10] 10 is a diagram for explaining control further executed by the control device after the voltage of the AC power from the power converter to the motor is synchronized with the voltage of the AC power supply. FIG. [Figure 11] 10 is a flowchart showing an example of processing executed by a control device in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0010] <First Embodiment> Fig. 1 is a diagram showing the configuration of a voltage sag compensation system including a voltage sag compensation device according to this embodiment 1. Referring to Fig. 1, voltage sag compensation system 150 includes an electric load 12 and a voltage sag compensation device 1. Electric load 12 is, for example, an important facility in an industrial plant, and operates by receiving AC power.

[0011] The instantaneous voltage sag compensator 1 is connected to an AC power source 11 (in this example, a commercial power source) and an electrical load 12, and is configured to supply power to the electrical load 12. The instantaneous voltage sag compensator 1 includes a high-speed switch (HSS) 6, a bypass path 10, circuit breakers 7 to 9, a compensatory power supply circuit 5, sensor units 13A and 13B, and a control device 100.

[0012] The HSS 6 is shown as an example of a switch that can be turned on and off. An input terminal T1 of the HSS 6 is connected to an AC power supply 11. An output terminal T2 of the HSS 6 is connected to an electrical load 12.

[0013] The bypass path 10 is electrically connected in parallel with the HSS 6 between the AC power source 11 and the electrical load 12. The bypass path 10 is a path through which power is supplied from the AC power source 11 when an overload of the instantaneous voltage sag compensator 1 is detected or when the HSS 6 or the compensatory power supply circuit 5 fails.

[0014] The circuit breaker 7 is provided on an electric path between the AC power supply 11 and the input terminal T1. The circuit breaker 8 is provided on an electric path between the output terminal T2 and the electric load 12. The circuit breaker 9 is provided on the bypass path 10.

[0015] The compensatory power supply circuit 5 is connected to the output terminal T2 and is connectable to the electrical load 12 via the circuit breaker 8. The compensatory power supply circuit 5 supplies power to the electrical load 12 when the AC power supply 11 experiences a voltage drop or power outage. The power supply from the compensatory power supply circuit 5 to the electrical load 12 is also referred to as "compensatory power supply." The compensatory power supply circuit 5 includes a power storage device 3, a power converter 2, and a transformer 4. The power storage device 3 is a rechargeable secondary battery that stores power to be supplied to the electrical load 12 when the AC power supply 11 experiences a voltage drop or power outage.

[0016] The power converter 2 is provided on an electric path between the output terminal T2 and the power storage device 3, and is configured to perform bidirectional power conversion. When an instantaneous drop or power outage occurs in the AC power supply 11, the power converter 2 converts the DC power of the power storage device 3 into AC power and supplies the AC power to the electrical load 12 via the transformer 4. When the AC power supply 11 is normal, the power converter 2 converts the AC power from the transformer 4 into DC power to charge the power storage device 3.

[0017] The transformer 4 is provided on an electric path between the output terminal T2 and the power converter 2. The transformer 4 is configured to convert (step down) the voltage of the AC power supplied from the AC power source 11 through the HSS 6 when the AC power source 11 is normal, and supply the AC power of the converted voltage to the power converter 2. The transformer 4 is configured to convert (step up) the voltage of the AC power supplied from the power storage device 3 through the power converter 2 when the AC power source 11 experiences an instantaneous voltage drop or power outage, and supply the AC power of the converted voltage to the electrical load 12.

[0018] Sensor unit 13A detects the current and voltage of the power supplied from AC power supply 11. Sensor unit 13B detects the current and voltage of the power supplied from AC power supply 11 to transformer 4 through HSS 6, and the current and voltage of the power supplied from power converter 2 to electrical load 12 through transformer 4. The detected values ​​of sensor units 13A and 13B are provided to control device 100.

[0019] The control device 100 includes a processor 21 and a memory 22. The processor 21 is, for example, a CPU (Central Processing Unit) and executes various types of arithmetic processing. The memory 22 includes a ROM (Read Only Memory) and a RAM (Random Access Memory) (neither of which are shown). The ROM stores programs executed by the processor 21. The RAM functions as a working memory.

[0020] The control device 100 controls the HSS 6, the circuit breakers 7 to 9, and the compensation power supply circuit 5. The control performed by the control device 100 will be described below.

[0021] Fig. 2 is a diagram showing the flow of power when the AC power supply 11 is in a normal state. Referring to Fig. 2, the control device 100 turns on the HSS 6, controls the circuit breakers 7 and 8 to a closed state, and controls the circuit breaker 9 to an open state so that AC power is supplied from the AC power supply 11 to the electrical load 12. Furthermore, the control device 100 controls the power converter 2 so that power is supplied from the AC power supply 11 to the power storage device 3 (so that the power storage device 3 is charged). The power supply from the AC power supply 11 to the electrical load 12 when the AC power supply 11 is in a normal state is also referred to as "normal power supply."

[0022] 3 is a diagram showing the flow of power when a voltage sag or power outage occurs (when AC power supply 11 is abnormal). Referring to FIG. 3, control device 100 controls HSS 6, circuit breakers 7 to 9, and compensatory power supply circuit 5 so that compensatory power supply is performed by compensatory power supply circuit 5. Specifically, control device 100 turns off HSS 6 and controls power converter 2 so that power is supplied from power storage device 3 to electrical load 12.

[0023] The control device 100 is configured to perform compensatory power supply by operating the power converter 2 using a constant voltage constant frequency (CVCF) control method. The CVCF control method is a method for controlling the power converter 2 so that the effective value and frequency of the AC voltage converted by the power converter 2 are both constant.

[0024] The control device 100 can also operate the power converter 2 using a variable voltage variable frequency (VVVF) control method. The VVVF control method controls the power converter 2 so that the effective value and frequency of the AC voltage converted by the power converter 2 are both changed. In this example, the VVVF control method maintains a constant ratio between the voltage and the frequency.

[0025] Fig. 4 is a diagram showing the flow of power when an overload of the momentary sag compensator 1 is detected. Referring to Fig. 4, the control device 100 is configured to detect an overload of the momentary sag compensator 1. For example, if the current detection value of sensor unit 13A or the current detection value of sensor unit 13B exceeds the rated current value of the momentary sag compensator 1 during normal power supply, the control device 100 detects an overload of the momentary sag compensator 1. The rated current value is stored in advance in the memory 22 of the control device 100.

[0026] When the control device 100 detects an overload of the voltage sag compensator 1, it controls the HSS 6, the circuit breakers 7-9, and the compensatory power supply circuit 5 so that power is supplied from the AC power source 11 to the electrical load 12 through the bypass path 10. Specifically, the control device 100 turns off the HSS 6, controls the circuit breakers 7 and 8 to an open state, controls the circuit breaker 9 to a closed state, and stops the power converter 2. The power supply from the AC power source 11 to the electrical load 12 through the bypass path 10 is also referred to as "bypass power supply." When bypass power supply is performed in this manner, the electrical load 12 is electrically disconnected from the compensatory power supply circuit 5. As a result, compensatory power supply cannot be performed. Therefore, in the event of a voltage sag or power outage in the AC power source 11, the electrical load 12 cannot be protected from the voltage sag or power outage (the function of the voltage sag compensator 1 to compensate for the voltage sag on the electrical load 12 is impaired).

[0027] 5 is a diagram illustrating the control executed by the control device 100 when an overcurrent is detected during overload detection (bypass power supply) of the instantaneous sag compensator 1. Referring to FIG. 5, if the current detection value of the sensor unit 13A exceeds the rated current value of the circuit breaker 9 during bypass power supply, the control device 100 switches the circuit breaker 9 from the closed state to the open state to protect the circuit breaker 9. As a result, the bypass power supply may be interrupted, and the operation of the electrical load 12 may be interrupted. This is undesirable.

[0028] When the electrical load 12 starts, an inrush current (starting current) may flow from the AC power supply 11 to the electrical load 12 through the instantaneous voltage sag compensator 1. When a motor is used as the electrical load 12, the starting current of the motor is larger than the starting current of other electrical loads. Therefore, when the motor starts, for example, a large current may be supplied to the motor from the AC power supply 11 through the instantaneous voltage sag compensator 1. Such a large starting current is likely to overload the instantaneous voltage sag compensator 1. As a result, the normal power supply switches to the bypass power supply (Fig. 4), which may impair the instantaneous voltage sag compensation function of the instantaneous voltage sag compensator 1 for the motor or interrupt the power supply to the electrical load 12 (Fig. 5).

[0029] The voltage sag compensating device 1 according to the first embodiment has a configuration for dealing with the above problem, which will be described in detail below.

[0030] Fig. 6 is a diagram for explaining the control executed by the control device 100 when the motor is started. Referring to Fig. 6, the motor M is an AC motor serving as the electric load 12 (Figs. 1 to 5), and is a synchronous motor or an induction motor configured to operate by receiving AC power from the instantaneous sag compensator 1.

[0031] The control device 100 controls the HSS 6 to be off, and with the circuit breakers 7 and 8 controlled to be in the closed state, causes the power converter 2 to convert the DC power of the storage device 3 into AC power and supply it to the motor M, thereby starting the motor M. Then, when starting the motor M, the control device 100 operates the power converter 2 using the VVVF control method so that the effective voltage and frequency of the AC power from the power converter 2 to the motor M gradually increase as the rotational speed of the motor M increases.

[0032] Specifically, the control device 100 starts power supply from the power converter 2 to the motor M in a state where the effective value and frequency of the AC voltage from the power converter 2 to the motor M are lower than the rated voltage and rated frequency, respectively, of the AC power supply 11. Then, the power converter 2 executes power supply to the motor M so that the effective value and frequency of the AC voltage from the power converter 2 to the motor M gradually approach the rated voltage and rated frequency, respectively, of the AC power supply 11. This executes a soft start of the motor M.

[0033] As a result, the starting current of the motor M is reduced compared to the starting current of the motor M when a soft start is not performed (for example, when normal power supply is performed). This reduces the load on the instantaneous sag compensating device 1 when the motor M starts. This makes it possible to avoid a situation in which bypass power supply is performed due to the detection of an overload in the instantaneous sag compensating device 1. As a result, it is possible to avoid a situation in which the instantaneous sag compensating function of the instantaneous sag compensating device 1 to the motor M is impaired. This makes it possible to improve the reliability of the instantaneous sag compensating device 1.

[0034] During operation of the power converter 2 using the VVVF control method, the control device 100 determines whether or not the voltage of the AC power from the power converter 2 to the motor M (more specifically, in this example, the AC power from the transformer 4 to the motor M) is synchronized (hereinafter also simply referred to as "synchronization") with the voltage of the AC power source 11. Specifically, the control device 100 determines whether the amplitude, frequency, and phase of these voltages match based on the detection values ​​of the sensor units 13A and 13B.

[0035] Once synchronization is established, the control device 100 switches the control method of the power converter 2 from VVVF control to CVCF control. This maintains synchronization after the control method is switched. As a result, AC power with a constant effective voltage and frequency is stably supplied from the power converter 2 to the motor M via the transformer 4. This enables stable operation of the motor M.

[0036] When synchronization is established, the control device 100 further turns on the HSS 6. This makes it possible to supply power from the AC power source 11 to the motor M while avoiding interference (occurrence of cross current) between the AC power from the compensation power supply circuit 5 and the AC power from the AC power source 11.

[0037] After turning on the HSS 6, the control device 100 controls the power converter 2 to convert AC power supplied from the AC power source 11 through the HSS 6 into DC power and charge the power storage device 3. That is, the control device 100 switches the control of the power converter 2 from the power supply control from the power converter 2 to the motor M using the CVCF control method to the power supply control from the power converter 2 to the power storage device 3. This makes it possible to increase again the amount of electricity stored in the power storage device 3, which decreased when the motor M started.

[0038] 7 is a flowchart showing an example of processing executed by the control device 100 in the first embodiment. Before the processing of this flowchart starts, it is assumed that the circuit breakers 7 to 9 are in the open state and the HSS 6 is off. The processing of this flowchart starts when the instantaneous sag compensator 1 is started.

[0039] 7, the control device 100 switches the circuit breakers 7 and 8 from an open state to a closed state (step S102). Next, the control device 100 starts the motor M by operating the power converter 2 using the VVVF control method (step S105). That is, the control device 100 performs a soft start of the motor M using the VVVF control of the power converter 2.

[0040] Next, the control device 100 determines whether or not synchronization has been established between the AC power from the compensation power supply circuit 5 to the motor M and the power from the AC power supply 11 (step S110). If synchronization has not been established (NO in step S110), the process returns to step S105. On the other hand, if synchronization has been established (YES in step S110), the process proceeds to step S115.

[0041] Next, the control device 100 switches the control method of the power converter 2 from the VVVF control method to the CVCF control method (step S115), and turns on the HSS 6 (step S120).

[0042] Next, the control device 100 controls the power converter 2 to convert the AC power supplied from the AC power source 11 through the HSS 6 into DC power and charge the power storage device 3 (step S125). Thereafter, the processing in FIG. 7 ends, and normal power supply is performed.

[0043] As described above, according to the first embodiment, the control device 100 performs a soft start of the motor M by executing VVVF control of the power converter 2 until synchronization is achieved. Then, after synchronization is achieved, the control device 100 switches the control method of the power converter 2 from VVVF control to CVCF control. This makes it possible to reduce the starting current of the motor M below the starting current of the motor M when the motor M is started by normal power supply. As a result, it is possible to avoid a situation in which the function of the momentary sag compensating device 1 to compensate for the momentary sag of the motor M is impaired due to an overload at the start of the motor M. This makes it possible to improve the reliability of the momentary sag compensating device 1.

[0044] <Embodiment 2> In this second embodiment, the instantaneous voltage sag compensator is configured to supply power to both the motor M and other electrical loads.

[0045] Fig. 8 is a diagram showing the configuration of a voltage sag compensation system including a voltage sag compensation device according to this embodiment 2. Referring to Fig. 8, voltage sag compensation system 150A includes motor M, electric load 17, and voltage sag compensation device 1A connected to AC power supply 11.

[0046] Electric load 17 is a different type of electric load 12 (FIG. 1) from motor M, for example, a CPU of a server external to momentary sag compensator 1A. In this example, it is preferable that the effective voltage and frequency of the power supplied from momentary sag compensator 1A to electric load 17 are constant to enable stable operation of electric load 17. The starting current of electric load 17 is smaller than the starting current of motor M, and an overload of momentary sag compensator 1A is not detected due to the starting current of electric load 17.

[0047] The voltage sag compensator 1A differs from the voltage sag compensator 1 in that the compensation power supply circuit 5 further includes a circuit breaker 14 (first circuit breaker). The circuit breaker 14 is provided on the electrical path between the output terminal T2 and the power converter 2.

[0048] The voltage sag compensating device 1A differs from the voltage sag compensating device 1 in that it further includes a compensatory power supply circuit 50 and circuit breakers 15 and 16.

[0049] The compensatory power supply circuit 50 is connected to the output terminal T2 and is electrically connected in parallel with the compensatory power supply circuit 5. The compensatory power supply circuit 50 is configured to supply power to the electrical load 17 when the AC power supply 11 experiences a voltage sag or power outage. The compensatory power supply circuit 50 includes a power storage device 30, a power converter 20, a transformer 40, and a circuit breaker 140. The power storage device 30 stores power to be supplied to the electrical load 17 when the AC power supply 11 experiences a voltage sag or power outage. The power converter 20 and the transformer 40 are similar to the power converter 2 and the transformer 4, respectively.

[0050] Circuit breaker 15 (second circuit breaker) is connected between power converter 2 and motor M. Specifically, circuit breaker 15 has a first end connected to power converter 2 via transformer 4, and a second end connected to motor M. Circuit breaker 16 (third circuit breaker) is provided in the electrical path between output terminal T2 and motor M.

[0051] Other hardware components of the voltage sag compensator 1A are similar to those of the voltage sag compensator 1. For example, the input terminal T1 is connected to an AC power supply 11 through a circuit breaker 7. The output terminal T2 is connected to an electrical load 17 through a circuit breaker 8. The power converter 2 is provided on an electrical path between the output terminal T2 and the power storage device 3, and is configured to perform bidirectional power conversion.

[0052] The control device 100 controls each device of the instantaneous voltage sag compensator 1A, such as the HSS 6, the power converters 2 and 20, and the circuit breakers 7, 8, 9, 14, 140, 15, and 16.

[0053] If normal power supply from the AC power supply 11 is performed to both the motor M and the electrical load 17 when they are both started, an overload of the instantaneous sag compensator 1A may be detected due to a large starting current of the motor M. This causes the normal power supply to be switched to bypass power supply, and the compensatory power supply circuits 5 and 50 are electrically disconnected from the electrical load 17 and the motor M, respectively. As a result, the instantaneous sag compensator 1A's ability to compensate for both the electrical load 17 and the motor M may be impaired.

[0054] Therefore, when starting the motor M, it is preferable to perform a soft start of the motor M from the viewpoint of preventing overload. That is, it is preferable that the effective voltage and frequency of the power supplied to the motor M gradually increase. On the other hand, when starting the electric load 17, it is preferable that the effective voltage and frequency of the power supplied to the electric load 17 be constant from the viewpoint of stable operation of the electric load 17.

[0055] The instantaneous sag compensating device 1A according to the second embodiment has a configuration for preventing overload and ensuring stable operation of the electric load 17 at the start of the motor M and the electric load 17. This point will be described in detail below.

[0056] FIG. 9 is a diagram for explaining the control executed by the control device 100 when the motor M and the electric load 17 are started.

[0057] 9, the control device 100 starts the electric load 17 by turning on the HSS 6 while controlling the circuit breakers 7, 8, and 140 to the closed state and the circuit breakers 9, 14, and 16 to the open state. As a result, electric power of a substantially constant effective voltage and a constant frequency is supplied from the AC power source 11 to the electric load 17 through the electric path P1 (normal power supply from the AC power source 11 to the electric load 17 is executed). As a result, the electric load 17 can operate stably from the start.

[0058] The control device 100 controls the power converter 20 to charge the power storage device 30 while power is being supplied from the AC power source 11 to the electrical load 17. Specifically, the control device 100 controls the power converter 20 to convert AC power supplied from the AC power source 11 through the HSS 6 and the circuit breaker 140 into DC power and charge the power storage device 30. This makes it possible to increase the amount of electricity stored in the power storage device 30 before a momentary drop or power outage of the AC power source 11 occurs. A method for starting the motor M will now be described.

[0059] With circuit breaker 14 in the open state and circuit breaker 15 in the closed state, control device 100 causes power converter 2 to convert the DC power of power storage device 3 into AC power and supply it to motor M through electric line P2, thereby starting motor M. Because circuit breaker 14 is in the open state, power is supplied from power converter 2 to motor M while electric line P2 is electrically isolated from electric line P1 (i.e., while avoiding interference between the AC power supplied to motor M from compensating power supply circuit 5 through electric line P2 and the AC power supplied to electrical load 17 from AC power source 11 through electric line P1).

[0060] When starting the motor M, the control device 100 operates the power converter 2 using the VVVF control method so that the effective voltage and frequency of the AC power from the power converter 2 to the motor M (more specifically, the AC power from the transformer 4 to the motor M in this example) gradually increase as the rotational speed of the motor M increases. This allows the motor M to be soft-started.

[0061] While the power converter 2 is operating using the VVVF control method, the control device 100 determines whether the voltage of the AC power from the power converter 2 to the motor M is synchronized with the voltage of the AC power source 11. If synchronization is established, the control device 100 switches the control method of the power converter 2 from the VVVF control method to the CVCF control method. This maintains synchronization after the control method is switched.

[0062] FIG. 10 is a diagram for explaining the control further executed by the control device 100 after the voltage of the AC power from the power converter 2 to the motor M and the voltage of the AC power supply 11 are synchronized.

[0063] 10, when synchronization is established, the control device 100 further switches the circuit breaker 16 from the open state to the closed state. As a result, power from the AC power supply 11 is supplied to the motor M through the HSS 6 and the electrical path P3 (normal power supply from the AC power supply 11 to the motor M is executed). As a result, normal power supply from the AC power supply 11 to both the electrical load 17 and the motor M is executed thereafter.

[0064] Then, after switching circuit breaker 14 from the open state to the closed state, control device 100 switches circuit breaker 15 from the closed state to the open state. As a result, after power converter 2 and motor M are electrically connected through circuit breakers 8 and 16, the electrical connection between power converter 2 and motor M through circuit breaker 15 is cut off.

[0065] The control device 100 switches the circuit breakers 15 and 16 so that both circuit breakers 15 and 16 are in the closed state during the period from when the circuit breaker 16 is switched to the closed state to when the circuit breaker 15 is switched to the open state (overlap switching of the circuit breakers 15 and 16). This allows the power supply to the motor M to be switched from the power supply from the compensation power supply circuit 5 to the normal power supply without momentary interruption.

[0066] After switching the circuit breaker 14 from an open state to a closed state, the control device 100 controls the power converter 2 to charge the power storage device 3. Specifically, the control device 100 controls the power converter 2 to convert AC power supplied from the AC power source 11 through the HSS 6 and the circuit breaker 14 into DC power and charge the power storage device 3. This makes it possible to increase again the amount of electricity stored in the power storage device 3 that was reduced when the motor M was started.

[0067] 11 is a flowchart showing an example of processing executed by the control device 100 in the second embodiment. Before the processing of this flowchart starts, it is assumed that the circuit breakers 7 to 9, 14, 15, 16, and 140 are in the open state and the HSS 6 is off. The processing of this flowchart starts when the instantaneous sag compensator 1 is started.

[0068] 11, this flowchart differs from the flowchart of the first embodiment (FIG. 7) in that the processes of steps S202 and S220 are executed instead of steps S102 and S120, respectively. The flowchart of FIG. 11 differs from the flowchart of FIG. 7 in that the processes of steps S203, S222, and S223 are added. The processes of steps S205 to S215 and S225 are the same as the processes of steps S105 to S115 and S125, respectively. In the following description, FIG. 9 and FIG. 10 will be referred to as appropriate.

[0069] The control device 100 switches the circuit breakers 7 and 8 from the open state to the closed state and turns on the HSS 6 (step S202). This allows normal power supply from the AC power source 11 to the electrical load 17. In addition, the control device 100 switches the circuit breaker 140 from the open state to the closed state and controls the power converter 20 to charge the power storage device 30.

[0070] Next, the control device 100 switches the circuit breaker 15 from an open state to a closed state (step S203), and starts the motor M by operating the power converter 2 using the VVVF control method (step S205). That is, the control device 100 performs a soft start of the motor M using the VVVF control of the power converter 2 while the electric circuit P2 is electrically isolated from the electric circuit P1. Then, after the processes of steps S210 and S215, the process proceeds to step S220.

[0071] Next, the control device 100 switches the circuit breaker 16 from the open state to the closed state (step S220), thereby executing normal power supply from the AC power supply 11 to the motor M through the electric line P3.

[0072] Next, the control device 100 switches the circuit breaker 14 from the open state to the closed state (step S222), and then switches the circuit breaker 15 from the closed state to the open state (step S223). This disconnects the electrical connection between the power converter 2 and the motor M via the circuit breaker 15. Then, after the processing of step S225, the processing of FIG. 11 ends.

[0073] As described above, according to the second embodiment, when starting both the electric load 17 and the motor M, the control device 100 executes normal power supply from the AC power supply 11 to the electric load 17 while also executing a soft start of the motor M through VVVF control of the power converter 2. This makes it possible to achieve both overload prevention and stable operation of the electric load 17 when starting the electric load 17 and the motor M. As a result, it is possible to avoid a situation in which bypass power supply is executed due to the detection of an overload, impairing the function of the instantaneous sag compensating device 1A to compensate for the power supply to both the electric load 17 and the motor M.

[0074] <Modification of the second embodiment> In the second embodiment, for the sake of simplicity, the instantaneous sag compensating device 1A supplies power to one motor and one electrical load other than the motor. In this modification, the instantaneous sag compensating device 1A is configured to supply power to one or more motors and one or more electrical loads. Each motor is connected to a compensating power supply circuit similar to the compensating power supply circuit 5. These motors and electrical loads are electrically connected in parallel.

[0075] The control device 100 may control the power converter of the compensation power supply circuit using a VVVF control method so that soft-start power (power with gradually increasing effective voltage and frequency) is supplied only to the motor among the motor and the electric load. That is, the control device 100 may soft-start only the motor among the motor and the electric load. On the other hand, the control device 100 may start the electric load by controlling the HSS 6 and each circuit breaker so that power (power with a constant effective voltage and a constant frequency) from the AC power supply 11 is supplied only to the electric load among the motor and the electric load.

[0076] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0077] 1,1A instantaneous voltage sag compensation device, 2,20 power converter, 3,30 storage device, 4,40 transformer, 5,50 compensation power supply circuit, 7,8,9,14,15,16,140 circuit breaker, 10 bypass path, 11 AC power source, 12,17 electrical load, 100 control device, 150,150A instantaneous voltage sag compensation system, M motor.

Claims

1. A momentary sag compensation device connected to an AC power source and configured to supply power to a motor, comprising: a switch having an input terminal connected to the AC power supply and an output terminal connected to the motor; and a bypass circuit breaker provided in a bypass path electrically connected in parallel with the switch between the AC power supply and the motor; an input circuit breaker provided between the input terminal and a first connection point to which the bypass path is connected in an electric path between the input terminal and the AC power supply; an output circuit breaker provided between the output terminal and a second connection point to which the bypass path is connected in an electric path between the output terminal and the motor; a power converter that is provided between the output terminal and the power storage device and is electrically connected to a third connection point between the output terminal and the output breaker, and performs bidirectional power conversion; a control device that controls the switch, the bypass circuit breaker, the input circuit breaker, the output circuit breaker, and the power converter, when the control device detects an overload of the instantaneous sag compensator, the control device opens the input circuit breaker and the output circuit breaker, turns off the switch, and closes the bypass circuit breaker so that power is supplied to the motor from the AC power supply through the bypass path; The control device starting the motor by causing the power converter to convert the DC power of the power storage device into AC power and supplying the AC power to the motor while controlling the switch to be off, the input circuit breaker and the output circuit breaker to be in a closed state, and the bypass circuit breaker to be in an open state; a momentary sag compensator that operates the power converter by a variable voltage and variable frequency control method when the motor is started so that the voltage and frequency of the AC power increase as the rotational speed of the motor increases;

2. 2. The instantaneous sag compensation device according to claim 1, wherein when synchronization between the voltage of the AC power and the voltage of the AC power supply is established during operation of the power converter using the variable voltage variable frequency control method, the control device switches the control method of the power converter from the variable voltage variable frequency control method to a constant voltage constant frequency control method.

3. The instantaneous sag compensating device according to claim 2 , wherein when the synchronization is established, the control device further turns on the switch.

4. 4. The instantaneous sag compensation device according to claim 3, wherein, after turning on the switch, the control device controls the power converter so as to convert AC power supplied from the AC power supply through the switch into DC power and charge the power storage device.

5. A momentary sag compensation device connected to an AC power source and configured to supply power to both a motor and an electrical load other than the motor, a switch having an input terminal connected to the AC power source and an output terminal connected to the electrical load; a bypass circuit breaker provided in a bypass path electrically connected in parallel with the switch between the AC power supply and the electrical load; an input circuit breaker provided between the input terminal and a first connection point to which the bypass path is connected in an electric path between the input terminal and the AC power supply; an output breaker provided between the output terminal and a second connection point to which the bypass path is connected in an electric path between the output terminal and the electric load; a power converter that is provided between the output terminal and the power storage device and is electrically connectable to a third connection point between the output terminal and the output breaker, and performs bidirectional power conversion; a first circuit breaker provided between the third connection point and the power converter; a second circuit breaker connected between the motor and a fourth connection point between the power converter and the first circuit breaker; a control device that controls the switch, the bypass circuit breaker, the input circuit breaker, the output circuit breaker, the power converter, the first circuit breaker, and the second circuit breaker, when the control device detects an overload of the instantaneous sag compensator, the control device opens the input circuit breaker and the output circuit breaker, turns off the switch, and closes the bypass circuit breaker so that power is supplied from the AC power supply to the electrical load through the bypass path; The control device starting the electric load by turning on the switch while controlling the bypass circuit breaker and the first circuit breaker to be in an open state and the input circuit breaker and the output circuit breaker to be in a closed state; starting the motor by causing the power converter to convert the DC power of the power storage device into AC power and supply the AC power to the motor while controlling the bypass circuit breaker and the first circuit breaker to the open state and controlling the second circuit breaker to the closed state; a momentary sag compensator that operates the power converter by a variable voltage and variable frequency control method when the motor is started so that the voltage and frequency of the AC power increase as the rotational speed of the motor increases;

6. 6. The instantaneous sag compensation device according to claim 5, wherein when synchronization between the voltage of the AC power and the voltage of the AC power supply is established during operation of the power converter using the variable voltage variable frequency control method, the control device switches the control method of the power converter from the variable voltage variable frequency control method to a constant voltage constant frequency control method.

7. a third circuit breaker provided between the second connection point and the motor; the control device starts the motor while controlling the third circuit breaker to an open state; When the synchronization is established, the control device further Switching the first circuit breaker from the open state to a closed state, The instantaneous sag compensator according to claim 6 , wherein the second circuit breaker is switched from the closed state to the open state after the third circuit breaker is switched from the open state to the closed state.

8. 8. The instantaneous sag compensation device according to claim 7, wherein, after switching the first circuit breaker from the open state to the closed state, the control device controls the power converter so as to convert AC power supplied from the AC power source through the switch and the first circuit breaker into DC power and charge the power storage device.

9. A momentary sag compensation device connected to an AC power source and configured to supply power to both a motor and an electrical load other than the motor, comprising: a switch having an input terminal connected to the AC power source and an output terminal connected to the electrical load; a power converter that is provided between the output terminal and the power storage device and performs bidirectional power conversion; a first circuit breaker provided between the output terminal and the power converter; a second circuit breaker connected between the power converter and the motor; a control device that controls the switch, the power converter, the first circuit breaker, and the second circuit breaker, The control device Starting the electric load by turning on the switch while controlling the first circuit breaker to an open state; starting the motor by causing the power converter to convert the DC power of the power storage device into AC power and supplying the AC power to the motor while controlling the first circuit breaker to the open state and the second circuit breaker to the closed state; When starting the motor, the power converter is operated by a variable voltage and variable frequency control method so that the voltage and frequency of the AC power increase as the rotational speed of the motor increases; when synchronization between the voltage of the AC power and the voltage of the AC power supply is established during operation of the power converter using the variable voltage variable frequency control method, the control device switches the control method of the power converter from the variable voltage variable frequency control method to a constant voltage constant frequency control method, The instantaneous sag compensation device includes: a third circuit breaker provided between the output terminal and the motor; the control device starts the motor while controlling the third circuit breaker to an open state; When the synchronization is established, the control device further Switching the first circuit breaker from the open state to a closed state, a momentary sag compensator that switches the second circuit breaker from the closed state to the open state after switching the third circuit breaker from the open state to the closed state;

10. 10. The instantaneous sag compensation device according to claim 9, wherein, after switching the first circuit breaker from the open state to the closed state, the control device controls the power converter so as to convert AC power supplied from the AC power source through the switch and the first circuit breaker into DC power and charge the power storage device.

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