JP4438778B2 - Instantaneous voltage drop compensation device - Google Patents

Description

  The present invention always supplies power from the commercial system to the load. When an instantaneous power failure or the like occurs in the commercial system, the load is disconnected from the commercial system and supplied to the load from the power storage unit via the inverter. The present invention relates to a voltage sag compensator that switches from inverter power supply to commercial power supply, and more particularly to inverter output control when switching from inverter power supply to commercial power supply.

  The main circuit configuration of this type of voltage sag compensator is shown in FIG. A high-speed switch 3 is inserted between the commercial system 1 and the load 2, and the high-speed switch 3 is closed at all times to supply power from the commercial system 1 to the load 2. When it occurs, the load 2 is disconnected from the commercial system 1 by opening the high-speed switch 3. The inverter 4 starts up the power storage unit 5 as a DC power source and supplies power to the load 2 when a power failure occurs in the commercial system 1. The high-speed switch 3 is configured by using a power semiconductor element or combined with an electromagnetic contactor. The battery 5 is a battery or an electric double layer capacitor.

  In the conventional voltage sag compensator, the commercial system is restored, and the following control procedure is used to switch the power supply from the inverter power supply to the commercial power supply.

  (S1) In a state where the commercial system 1 has a power failure, the high-speed switch 3 disconnects the load from the commercial system, and power is supplied from the inverter 4 to the load 2. At this time, the inverter 4 performs voltage control so as to maintain the output voltage constant.

  (S2) When the power of the commercial system 1 is restored, the amplitude and phase of the commercial system voltage and the inverter output voltage are matched, and at the same time, the high-speed switch 3 is turned on and at the same time the operation of the inverter 4 is stopped to supply power to the load 2 Is switched from the inverter 4 to the commercial system 1.

  (S3) The inverter 4 changes its control from voltage control to current control and restarts, and starts precharging the power storage unit 5 with a predetermined current using the commercial system 1 as a power source.

  When switching from inverter power supply to commercial power supply by the above procedure, changes in load power, system power, and inverter power are as shown in FIG. Here, the control at the time of inverter power supply is a completely different control of constant voltage control and the current control of the inverter at the time of commercial power supply. Therefore, when switching from inverter power supply to commercial power supply, all load power is applied to the commercial system at once. Therefore, when the impedance of the commercial system is high, the AC voltage temporarily decreases, and this voltage decrease may be erroneously detected as a power failure and may return to inverter power feeding again.

To solve this inconvenience, the load current is detected by a current detector, and the inverter output current ratio with respect to the total load current is gradually reduced from “1” to “0” when power is restored. An inverter output control method has been proposed in which the power supply of the inverter is gradually switched from the inverter to the commercial system (see, for example, Patent Document 1).
JP 2005-229664 A

  In the inverter output current control method according to Patent Document 1, the load current is detected by a current detector, and when the power is restored, the inverter output current command is gradually reduced from the current full load current to zero by the limiter. The given current control PI amplifier performs a proportional integral (PI) operation on the deviation from the inverter output current, and feedback controls the inverter output current.

  In this system, when switching from inverter power supply to commercial power supply, the inverter switches from current voltage control to current control, and depending on the standby state of the current control system that is feedback controlled and the response at the time of startup, There was a problem that the load voltage became unstable. This is particularly problematic when the operating conditions of the commercial system (for example, the emergency generator is operating / stopped) and the load conditions (non-linear load / inductive load / capacitive load such as a rectifier) change.

  In the conventional system, a dedicated load current detector is required for switching control from the commercial system to the inverter.

  The object of the present invention is to minimize the sudden change in the load voltage regardless of the operating conditions and load conditions of the commercial system, and to switch the power from the inverter to the commercial system (load transfer) with high accuracy. It is an object of the present invention to provide a voltage sag compensator that eliminates the need for a dedicated load current detector.

  In order to solve the above problems, the present invention detects inverter output power (= load power) at the time of inverter power feeding, sets this output power as the initial value of the inverter output power command value, and the inverter output power control system. The output is initialized to “0”, and when the inverter power supply is switched to the commercial power supply, the inverter output power is feedforward controlled by the output power command value, and the feedback control by the output power control system is started. Thereafter, the output power command value is gradually reduced to gradually shift the power supply to the load from the inverter to the commercial system, and has the following configuration.

(1) Normally, power is supplied from the commercial system to the load. When an instantaneous power failure occurs in the commercial system, the load is disconnected from the commercial system, and the load is supplied from the power storage unit via the inverter. In the sag compensation device that switches from power supply to commercial power supply,
The inverter control device comprises:
The inverter output power that is being fed from the inverter to the load is detected, this output power is used as the initial value of the inverter output power command value, and the output of the inverter output power control system is initialized to “0”. At the time of switching from power supply to commercial power supply, the inverter output power is feedforward controlled by the output power command value, and feedback control by the output power control system is started. Thereafter, the output power command value is gradually increased to the power set value. It is characterized by comprising control means for gradually shifting the power supply to the load from the inverter to the commercial system.

  (2) The control means performs the feedforward control and the feedback control separately for the active power P and the reactive power Q.

  (3) The power setting value is charging power when charging the power storage unit from a commercial system via an inverter.

  (4) The feedforward control is characterized in that an output current command value is obtained by dividing by an effective value of a load voltage.

  As described above, according to the present invention, regardless of the operating conditions and load conditions of the commercial system, a sudden change in load voltage can be suppressed to a minimum, and the power can be switched from the inverter to the commercial system (load transition) with high accuracy. Furthermore, a dedicated load current detector for switching the power supply is not necessary. Specifically, the following effects are obtained.

  -Since power control is comprised of a combination of feedforward control and feedback control, both high speed and accuracy of control can be achieved. That is, the feedforward control is effective immediately after switching from the inverter power supply to the commercial power supply, and the output power fluctuation due to the switching can be minimized. In the feedback control, the output power can be controlled with high accuracy by correcting the output current command value by the difference between the output power set value and the output power detection value during steady operation.

  By performing feedforward control and feedback control separately for active power P and reactive power Q, power control according to load conditions becomes possible.

  The power set value is the charging power when charging the power storage unit from the commercial system via the inverter, so that continuous power control from the inverter power supply control to the power storage unit charging control can be performed.

  ・ Feedforward control can be compensated by fluctuations in commercial system voltage by dividing the effective value of the load voltage to obtain the output current command value.

  FIG. 1 is a configuration diagram of a voltage sag compensator showing an embodiment of the present invention. The main circuit configuration is the same as that in FIG. 3, and power is supplied from the commercial system 1 to the load 2 at all times. When the load is disconnected from the commercial system by the high-speed switch 3 and fed from the inverter 4 and returned from the inverter feeding to the commercial feeding, the load power is gradually transferred from the inverter output to the commercial system in the same manner as in Patent Document 1.

  The control device of the inverter 4 is based on a PI (proportional integration) calculation according to the deviation between the set voltage and the detection voltage by the voltage control amplifier 6 or a PI calculation according to the deviation between the current command and the detection current by the current control amplifier 7. Then, an output voltage control command for the inverter 4 is obtained, and the PWM control of the inverter 4 is performed by the PWM control unit 8 in accordance with the voltage control command.

  In the control device of the present embodiment, the inverter output power being fed from the inverter to the load is detected, this output power is set as the initial value of the inverter output power command value, and the output of the inverter output power control system is set to “0”. When the inverter power supply is switched to the commercial power supply, the inverter output power is feedforward controlled by the output power command value, and the feedback control by the output power control system is started. Thereafter, the output power By gradually reducing the command value, the power supply to the load is gradually shifted from the inverter to the commercial system, which minimizes sudden changes in the load voltage regardless of the commercial system operating conditions and load conditions. Enables power switching (load transfer) from the inverter to the commercial system with accuracy.

  The output power control system of the inverter is configured to control the output power of the inverter 4 separately for the active power P and the reactive power Q, and is realized by the following control means.

  The active power / reactive power calculation unit 11 obtains the active power P and the reactive power Q of the output of the inverter 4 from the load voltage detection value by the voltage transformer VT and the inverter output current detection value by the current transformer CT. In the ramp function generators 12P and 12Q, the output is held at the active power P and the reactive power Q obtained by the active power / reactive power calculation unit 11 at the reset, and the active power set value Ps and the reactive power set value Qs at the reset release. A ramp voltage that changes with a certain slope is generated with the target value as the target value, and these lamp voltage outputs are set to the active power command value and the reactive power command value. The active power set value Ps and the reactive power set value Qs are set to values for charging the power storage unit 5 from the commercial system through the inverter 4 after switching from the inverter power supply to the commercial system power supply.

  The PI control units 13P and 13Q for automatic power control include the active / reactive power command values generated by the ramp function generators 12P and 12Q, the active power P and the reactive power Q detected by the active power / reactive power calculation unit 11, and Is calculated to obtain command values of active current and reactive current (feedback control). These PI controllers 13P and 13Q can force the output to “0” by the reset.

  The current correction units 14P and 14Q divide the active / reactive power command value generated by the ramp function generators 12P and 12Q by the voltage effective value obtained by the effective value calculation unit 15 to include correction of fluctuations in the load voltage. The valid / reactive current command value is obtained (feed forward control).

  The coordinate conversion unit 16 synthesizes an invalid / effective current command value obtained by adding the current command value from the PI control units 13P and 13Q and the current command value from the voltage correction units 14P and 14Q in a vector manner, and thereby a current control amplifier. 7 is obtained.

  The semiconductor element configuration changeover switch 17 changes the output of the voltage control amplifier 6 and the output of the current control amplifier 7 to obtain an output voltage command value of the PWM control unit 8.

  The operation of the sag compensation control configured as described above will be described with reference to FIG. This control includes detection of occurrence of power failure and recovery of commercial system, various settings of voltage / power, reset and release control of lamp function generators 12P and 12Q, reset and release control of PI controllers 13P and 13Q, changeover switch The control means (computer etc.) which performs 17 switching control etc. is provided.

(A) Control at the time of inverter power supply The commercial system is switched to the inverter power supply, and the control constant is initialized in the output voltage control state of the inverter 4 by the voltage control amplifier 6. In this initialization, the ramp function generators 12P and 12Q are reset, and the current active power P and the reactive power Q obtained by the active power / reactive power calculation unit 11 are used as output power command values of the ramp function generators 12P and 12Q. Keep it as In addition, the PI control units 13P and 13Q are reset and their outputs are set to “0”.

  By these initializations, the output current command value of the coordinate conversion unit 16 is held at a value corresponding to the inverter output power at the time of switching.

(B) Control when switching to commercial power supply (time t1 in FIG. 2)
The high-speed switch 3 is turned on, and the output of the current control amplifier 7 is switched to the output voltage command of the PWM control unit 8 by switching the switch 17 to switch from inverter power supply to commercial power supply. At this time, the reset of the PI control units 13P and 13Q is released to enable the PI calculation operation. At the same time, the ramp function generators 12P and 12Q are released from reset to enable the ramp function generation operation.

  When these resets are released, the output of the PI control units 13P and 13Q = 0, the output of the ramp function generators 12P and 12Q = the inverter output power immediately before the switching control, and the inverter output current control is started from this state To do. This current control starts with feedforward control that initially uses an output current command value through the current correction units 14P and 14Q, and then feedforward control in which the output is added in response to the PI control units 13P and 13Q. Control is combined with feedback control.

  Therefore, immediately after switching, a load shift of the commercial system is prevented by starting load transition with power (initial value) that matches the inverter output immediately before switching, and in addition, high response is achieved by performing feedforward control in the initial stage. The load can be transferred with a high degree of accuracy by performing the control including

(C) Control after switching to commercial power supply (period T in FIG. 2)
The output of the ramp function generators 12P and 12Q gradually decreases according to the active / reactive power setting values Ps and Qs, and the power supplied to the load 2 gradually shifts from the inverter 4 to the commercial system. After the output becomes zero (time t2 in FIG. 2), the control proceeds to the charging current control from the commercial system to the power storage unit 5, and finally the power storage unit with the electric power corresponding to the active / reactive power set values Ps and Qs. 5 is continued (after time t3 in FIG. 2).

1 is a configuration diagram of a voltage sag compensator showing an embodiment of the present invention. Power recovery switching characteristic diagram in the embodiment. The conventional main circuit block diagram. The conventional power recovery switching characteristic diagram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial system 2 Load 3 High speed switch 4 Inverter 5 Power storage body 6 Voltage control amplifier 7 Current control amplifier 8 PWM control part 11 Active power / reactive power calculation part 12P, 12Q Ramp function generator 13P, 13Q PI control part 14P, 14Q Current Correction unit 15 Effective value detection unit 16 Coordinate conversion unit 17 Changeover switch

Claims (4)

Normally, power is supplied from the commercial system to the load, and when an instantaneous power failure occurs in the commercial system, the load is disconnected from the commercial system, and the load is supplied from the power storage unit via the inverter. In the voltage sag compensator that switches to grid power supply,
The inverter control device comprises:
The inverter output power that is being fed from the inverter to the load is detected, this output power is used as the initial value of the inverter output power command value, and the output of the inverter output power control system is initialized to “0”. At the time of switching from power supply to commercial power supply, the inverter output power is feedforward controlled by the output power command value, and feedback control by the output power control system is started. Thereafter, the output power command value is gradually increased to the power set value. A voltage sag compensator comprising control means for gradually shifting power supply to a load from an inverter to a commercial system by focusing on   2. The voltage sag compensator according to claim 1, wherein the control unit performs the feedforward control and the feedback control separately for the active power P and the reactive power Q. 3.   3. The voltage sag compensator according to claim 1, wherein the power set value is charging power when charging the power storage unit from a commercial system via an inverter. 4. 4. The voltage sag compensator according to claim 1, wherein the feedforward control obtains an output current command value by dividing by an effective value of a load voltage. 5.

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