JP2008092719A - Instantaneous voltage drop compensation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a variation of an output voltage at the switching of operation modes, and to stably switch a system linkage operation to an autonomous operation. <P>SOLUTION: When an instantaneous voltage drop occurs at a system power supply, the voltage drop of a load is compensated by a control output of a system linkage operation part 11A by autonomously current-controlling a main circuit 6A of a PWM power converter which uses a DC power supply as a power supply, and when instantaneous power interruption occurs at the system power supply, a load voltage is controlled by a control output of an autonomous operation part 12A by autonomous voltage control. A PWM command is obtained by adding a common base voltage made to be a rated voltage to the control output at the system linkage operation and the control output at the autonomous operation by an adding part 15. This instantaneous voltage drop compensation device includes a constitution which autonomously adjusts the base voltage to a voltage equivalent to the rated voltage on the basis of the voltage of the DC power supply of the power converter. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an instantaneous voltage drop compensator that supplies power to a load in a grid-operated operation or a self-sustained operation with a system power supply, and compensates for the load voltage when the system power supply voltage drops instantaneously.

  FIG. 3 shows a configuration example of a power receiving system provided with an instantaneous voltage drop compensator (hereinafter referred to as “instantaneous voltage compensator”). For the power receiving system that feeds power to the general load (air conditioner or electric device) 2 with the received power from the system power source 1 and further feeds the important load (computer etc.) 4 through the high speed switch 3, the important load 4 has a high speed. When the bidirectional power converter 6 connected through the switch 5 is connected to the grid power supply 1 and an instantaneous voltage drop occurs in the system power supply 1, the voltage drop is compensated from the bidirectional power converter 6 using the DC power supply 7 as a power source. Supply power. Furthermore, when the instantaneous power failure of the system power supply 1 occurs, the high-speed switch 3 is dissociated and power is supplied to the important load by the self-sustaining operation of the bidirectional power converter 6 (see, for example, Patent Document 1).

  In the bidirectional power converter 6, the main circuit 6A is configured as a PWM rectifier circuit using a semiconductor switch element, and each switch element is PWM gate-controlled by the PWM controller 6B. This control obtains an output compensated for voltage by DC-AC conversion from the DC power source 7 when the voltage of the system power source 1 is lowered during the interconnection operation with the system power source 1, and AC- when the voltage of the system power source 1 is normal. The DC power supply 7 is charged by DC conversion. Further, during the independent operation due to the instantaneous power failure of the system power supply 1, the DC power supply 7 is used as a power supply to supply power to the important load 4 with a specified voltage. The DC power source 7 employs a general secondary battery or an electric double layer capacitor, and is adapted to the power capacity of the important load 4.

  In this way, the voltage sag compensator can be switched between two operation modes of grid interconnection operation and independent operation, and switching of this operation mode (system interconnection operation → independent operation, independent operation → system interconnection operation). ), The control device 6B has a circuit configuration capable of suppressing voltage fluctuation and abnormal voltage.

  FIG. 4 shows a block configuration of the PWM controller 6B in the voltage sag compensator. The PWM control device normally performs ACR (automatic current control) by the grid interconnection operation unit 11 and switches to AVR (automatic voltage control) by the independent operation unit 12 when a sag occurs. Perform grid-connected operation. During the grid connection operation, the current (charge / discharge current) that the main circuit 6A takes in and out is controlled. During the independent operation, the output voltage of the main circuit 6A is controlled. In the grid connection / independent operation mode switching, the PWM command value is switched by the changeover switch 13, and the PWM control unit 14 obtains a PWM waveform gate signal by comparing the PWM command value with a triangular wave (carrier signal).

  In the current technology, the self-supporting operation unit 12 is controlled by a control method of an AC / DC converter that performs voltage control such as CVCF. The grid interconnection operation unit 11 is controlled by a control method of an AC / DC converter that performs current control such as a PWM rectifier circuit. Each PWM command value is generated by the sum of the PI controller output (AVR output or ACR output) and the base voltage.

  In the self-sustained operation, the base voltage is added to reduce the AVR burden. Since the responsiveness deteriorates when the control amount of AVR becomes small, the base voltage is generally a value of about 0.5 p.u (1 p.u is a rated voltage). In grid-connected operation, the charge / discharge current becomes zero if the device outputs the exact same voltage as the grid. Therefore, the charge / discharge current is controlled by ACR by adding a value of 1 p.u as the base voltage.

For the base voltage value, the simplest method is to use a value calculated by feedforward as a fixed value, and it is often used.
JP 2002-101576 A

  In the voltage sag compensator, when a voltage sag is detected, the system is instantaneously switched from grid interconnection operation to independent operation. At this time, if the response of AVR is delayed, the output voltage is lowered. If the response is made faster, the output voltage may become unstable when the mode is switched. In general CVCF, since the output voltage is soft-started from zero when the apparatus is activated, there is no need to worry about such a problem. Since the responsiveness improves as the AVR control range is increased, the base voltage is set to about 0.5 p.u.

  In the voltage sag compensator, when the system voltage recovers from the voltage sag (hereinafter referred to as power recovery), the operation is instantaneously switched from the independent operation to the system interconnection operation. At this time, if the ACR response is delayed, the charging / discharging current of the device becomes unstable. In addition, in the case of a device in which the DC voltage greatly fluctuates, such as a voltage sag compensator (hereinafter referred to as a capacitor type voltage sag compensator) in which an electric double layer capacitor is applied to the DC power source 7, the control amount of the ACR becomes large and unstable. It is easy to become. When a general storage battery is used for the DC power source 7, the DC voltage hardly fluctuates, so there was no problem even if the base voltage was fixed.

  For example, a capacitor type voltage sag compensator with an output voltage of three-phase 220 V and a DC voltage range of 375 V to 625 V (rated 625 V) is taken as an example. As shown in FIG. 5, when a PWM gate signal is generated by comparing a triangular wave with an amplitude of 1 and a PWM command value to control the voltage sag compensator, the DC voltage and From the relationship of the crest factor of AC voltage,

Thus, if a sine wave having an amplitude of 0.57 p.u is given to the PWM command value, a voltage of 220 V is output.

  Consider switching from grid-connected operation to independent operation. In order to output a voltage of 220 V, the amplitude is 0.57 p. The sine wave of u must be output. Since the base voltage during self-sustained operation is about 0.5 p.u (0.29), the AVR output must be instantaneously set to 0.29. However, since it takes time to stabilize, the output voltage is It will decline.

  Consider a case where the voltage drop compensation operation is performed and the DC voltage is reduced to 375 V, and then the operation is switched to the grid interconnection operation. To output a voltage of 220V when the DC voltage is 375V,

The base voltage is required. When the base voltage is set to a fixed value, the base voltage is 0.57 p. u.

  For this reason, a value having a range of about 0.39 p.u has to be controlled by ACR, which tends to be unstable when switching.

  An object of the present invention is to provide an instantaneous voltage drop compensator that can suppress fluctuations in output voltage at the time of operation mode switching and that can be stably switched from grid-connected operation to independent operation.

  In order to solve the above-mentioned problems, the present invention has a configuration in which the base voltage of the independent operation and the grid connection operation is used as a rated voltage, and the base voltage is a voltage corresponding to the rated voltage based on the detection voltage of the DC power supply. It is configured to automatically adjust to the above, and has the following configuration.

(1) When an instantaneous voltage drop occurs in the system power supply, the load voltage drop is compensated by the grid-connected operation by automatic current control of the PWM power converter that uses DC power as the power supply, and an instantaneous power failure occurs in the system power supply When this is an instantaneous voltage drop compensator that controls the load voltage by self-sustaining operation by automatic voltage control of the PWM power converter,
The configuration is characterized in that a PWM command is obtained by adding a common base voltage set to a rated voltage to the control output during the grid interconnection operation and the control output during the independent operation.

  (2) The base voltage is automatically adjusted to a voltage corresponding to a rated voltage based on the voltage of the DC power supply.

  As described above, according to the present invention, the base voltage of the self-sustained operation and the grid connection operation is set to the common rated voltage, and the base voltage is automatically set to a voltage corresponding to the rated voltage based on the detection voltage of the DC power supply. Because it is configured to adjust, when switching from grid-connected operation to independent operation, the PWM command value with the base voltage added becomes the rated voltage even if the automatic voltage control output is zero, so the fluctuation in output voltage when switching the operation mode is suppressed be able to.

  Moreover, even when the voltage of the DC power supply is smaller than the rating, an output equivalent to 1 p.u can be obtained.

(Embodiment 1)
FIG. 1 is a control block of a PWM control apparatus showing an embodiment of the present invention. The grid interconnection operation unit 11A outputs a result obtained by calculating a deviation between the output current command value and the detected value by a PI (proportional integration) controller as a PWM command value. The independent operation unit 12A outputs a result obtained by calculating a deviation between the output voltage command value and the detected value by a PI (proportional integration) controller as a PWM command value. The changeover switch 13 switches the PWM command value from the grid interconnection operation unit 11A and the independent operation unit 12A. The base voltage adding unit 15 adds the base voltage to the PWM command value that is output from the changeover switch 13 to obtain a PWM command value to the PWM control unit 14.

  That is, in the present embodiment, the base voltage component in the PWM command value for the self-sustained operation / system interconnection operation is shared, and this base voltage is a value (fixed value) that outputs 1 p.u in the DC voltage rating.

  With this configuration, when switching from grid-connected operation to independent operation, the PWM command value obtained by adding the base voltage becomes the rated voltage even when the AVR output is zero, so that fluctuations in output voltage at the time of operation mode switching can be suppressed.

  However, when the voltage of the DC power supply 7 is smaller than the rating, the output voltage is also reduced. However, it is rare to switch from grid-connected operation to independent operation when the DC voltage is lower than the rating. For example, when a voltage sag is repeatedly generated in the voltage sag compensator and the discharge due to the self-sustaining operation is advanced, the DC power supply voltage is lowered, but such a control state is extremely small.

  In the present embodiment, when switching from the independent operation to the grid interconnection operation, the base voltage is 1 p.u, and the performance is not different from the conventional technology. Further, since the base voltage is shared, the control circuit configuration can be simplified as compared with the prior art.

(Embodiment 2)
FIG. 2 is a control block of the PWM control apparatus showing the embodiment of the present invention. 1 is different from FIG. 1 in that the base voltage is automatically adjusted according to the DC voltage of the DC power supply 7 instead of a fixed value. The base voltage calculation unit 16 obtains a base voltage according to the DC voltage detection value of the DC power supply 7 and sets this as the base voltage of the base voltage addition unit 15. The calculation by the base voltage calculation unit 16 obtains the base voltage by the following equation. That is, an output of 1 p.u can be obtained as the PWM command value regardless of the change in the DC voltage Vdc.

  According to this embodiment, when switching from grid-connected operation to independent operation, the rated voltage is output even when the AVR output is zero, so that the output voltage fluctuation at the time of operation mode switching can be suppressed. Moreover, an output equivalent to 1 p.u can be obtained even when the DC voltage is smaller than the rating.

  In addition, when switching from independent operation to grid interconnection operation, since the output current is zero when the ACR output is zero, the switching can be performed stably.

  Further, compared with the first embodiment, the addition of the base voltage calculation unit 16 is required and the control becomes complicated. However, when the PWM control device 6B is configured by a control computer, the base voltage value at each DC voltage is calculated in advance. However, if the data is written in the ROM, the calculation is merely to measure the DC voltage and read the value, and the calculation load does not increase so much.

The control block of the PWM control apparatus which shows Embodiment 1 of this invention. The control block of the PWM control apparatus which shows Embodiment 2 of this invention. The structural example of the power receiving system which provided the instantaneous voltage drop compensation apparatus. The block block diagram of the PWM control apparatus 6B in a sag compensator (conventional). The waveform diagram of PWM control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 System power supply 3, 5 High speed switch 6 Power converter 6A Main circuit 6B PWM controller 7 DC power supply 11 System interconnection operation part 12 Independent operation part 13 Changeover switch 14 PWM control part 15 Addition part 16 Base voltage calculation part

Claims (2)

When an instantaneous voltage drop occurs in the system power supply, the voltage drop of the load is compensated for by the grid-connected operation by automatic current control of the PWM power converter that uses the DC power supply as a power supply, and when an instantaneous power failure occurs in the system power supply An instantaneous voltage drop compensation device for controlling a load voltage by a self-sustaining operation by automatic voltage control of a PWM power converter,
An instantaneous voltage drop compensator, characterized in that a PWM command is obtained by adding a common base voltage, which is a rated voltage, to a control output during grid interconnection operation and a control output during autonomous operation.   2. The instantaneous voltage drop compensator according to claim 1, wherein the base voltage is automatically adjusted to a voltage corresponding to a rated voltage based on a voltage of the DC power supply.

Images