JP2002010528A - Momentary voltage drop compensating device and initial charging method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a momentary voltage drop compensating decide and an initial charging method thereof, capable of preventing overcurrent from flowing through a capacitor immediately after the startup of an inverter during initial charging of the capacitor. SOLUTION: This momentary voltage drop compensating device, compensating for load voltage during a momentary voltage drop by providing a power storing capacitor 4 on the DC side of the inverter 3 connected between a system power source 1 and a load 2, and supplying the charging voltage of the capacitor 4 to the load 2 through the inverter 3 if a momentary voltage drop occurs in the system power source 1, is provided with a booster chopper 8 boosting the DC voltage of the capacitor 4 to compensate for a peak voltage difference between the power source voltage and the output voltage of the inverter 3 when the capacitor 4 is initially charged by a phase difference between the power source voltage and the output voltage of the inverter 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an instantaneous voltage drop compensating device and an initial charging method thereof, and is applied to, for example, an uninterruptible power supply system (UPS). The present invention relates to an instantaneous voltage drop compensating device for compensating voltage and an initial charging method thereof.

[0002]

2. Description of the Related Art In recent years, with the spread of various control devices using a CPU, an obstacle due to an instantaneous voltage drop (hereinafter simply referred to as an instantaneous voltage drop) due to a lightning strike or the like has become a problem. For this reason,
For important load equipment such as bank online, traffic control, computer control and industrial manufacturing equipment, and power supply for measurement and control, the power supply voltage that should be detected immediately in the system power supply and supplied to the load equipment ( An uninterruptible power supply (UPS) or the like that compensates for the load voltage has been introduced.

As a device for compensating for a load voltage when a voltage sag occurs, for example, there is a device having a configuration as shown in FIG. This sag compensator comprises a system power supply 1 and a load 2 as shown in FIG.
An electrolytic capacitor 4 (hereinafter, simply referred to as a capacitor) is provided on the DC side of the inverter 3 connected between the inverter 3 and the power supply 1. 2, the load voltage during the sag is compensated. A main thyristor switch 5 is provided between the system power supply 1 and the load 2 for disconnecting the system power supply 1 from the power system when an instantaneous voltage drop occurs in the system power supply 1.

The inverter 3 comprises a bridge-structured switching element (for example, IGBT or the like), and has a circuit configuration in which a reflux diode is connected in parallel to each switching element. The inverter 3 is a bidirectional AC / DC converter having an inverter function and a rectifying function.
The operation is switched between a rectifying operation in which the AC power from the DC converter is converted to a DC and charging the capacitor 4 and an inverter operation in which the DC power charged in the capacitor 4 is converted to the AC and supplied to the system bus 6.

In this instantaneous sag compensator, power is supplied from the system power supply 1 to the load 2 in a steady state with the main thyristor switch 5 turned on. When this occurs, the main thyristor switch 5 is turned off.
Simultaneously with the FF, the charging voltage of the capacitor 4 is converted to AC by the inverter operation of the inverter 3 and the AC output of the inverter 3 is supplied to the load 2 so that the charging voltage of the capacitor 4 compensates for the load voltage during the sag. I have to.

As described above, the capacitor 4 is initially charged when the power of the sag compensator is turned on so that the load voltage during the sag can be compensated by the charging voltage of the capacitor 4 when the sag of the system power supply 1 occurs. There is a need. Therefore, in the instantaneous sag compensator, a diode rectifier circuit 7 is connected between the system bus 6 and the capacitor 4, and when the power of the sag compensator is started, the power supply voltage from the system power supply 1 The conversion is performed so that the capacitor 4 is initially charged.

[0007]

The initial charging in the above-described conventional sag compensator is specifically performed in the following manner. When the voltage sag compensator is powered on, an initial charge start command is output from a control circuit (not shown) of the voltage sag compensator, and the diode rectifier circuit 7 is operated based on the initial charge start command to operate the capacitor. 4 is started. When the DC voltage charged in the capacitor 4 reaches about 90% of the peak value of the power supply voltage, the inverter 3 is started by a start command from the control circuit. Note that the charging of the capacitor 4 with the DC voltage by the diode rectifier circuit 7 is limited to about 90% of the peak value of the power supply voltage as described above.

When the inverter 3 is started, the phase of the output voltage of the inverter 3 which is in phase with the power supply voltage is gradually shifted by the rectification operation of the inverter 3, thereby increasing the voltage to a voltage equal to or higher than the peak value of the power supply voltage. The initial charging is completed by charging the capacitor 4.

By the way, since the DC voltage of the capacitor 4 can be charged only up to about 90% of the peak value of the power supply voltage by the diode rectification circuit 7 as described above, the peak of the power supply voltage Initial charging is performed in a state where the DC voltage charged in the capacitor 4 with respect to the value is insufficient.

Therefore, if the capacitor 4 is charged with a peak voltage difference between the power supply voltage and the output voltage of the inverter 3, an overcurrent (rush current) flows through the capacitor 4. When such an overcurrent flows, there occurs a problem that the instantaneous sag compensator having a small capacity is stopped.

In view of the above, the present invention has been proposed in view of the above-described problems. It is an object of the present invention to prevent an overcurrent from flowing into the capacitor immediately after the inverter is started during the initial charging of the capacitor. It is an object of the present invention to provide a sag compensating device and an initial charging method for the sag preventing device.

[0012]

According to a first aspect of the present invention, as a technical means for achieving the above object, a capacitor is provided on a DC side of an inverter connected between a system power supply and a load. When an instantaneous voltage drop occurs in a power supply, a voltage sag compensator that compensates for a load voltage during voltage sag by supplying a charging voltage of the capacitor to a load via an inverter,
When the capacitor is initially charged by a phase difference between a power supply voltage and an inverter output voltage, a boost chopper that boosts a DC voltage of the capacitor is provided to compensate for a peak voltage difference between the power supply voltage and the inverter output voltage. I do.

According to a second aspect of the present invention, a capacitor is provided on the DC side of an inverter connected between a system power supply and a load, and when an instantaneous voltage sag occurs in the system power supply, the charging voltage of the capacitor is transferred via the inverter. A voltage sag compensator for compensating a load voltage during a sag by supplying the load to the load by initializing the capacitor based on a phase difference between the power supply voltage and the inverter output voltage. It is characterized in that the DC voltage of the capacitor is boosted immediately before the start of the inverter so as to compensate for the peak voltage difference.

According to the first and second aspects of the present invention, the peak voltage difference between the power supply voltage and the inverter output voltage is compensated by boosting the DC voltage of the capacitor immediately before starting the inverter during the initial charging of the capacitor. If the inverter is started in this state, a voltage substantially equal to the peak value of the power supply voltage can be output from the inverter, so that an overcurrent does not occur immediately after the start of the inverter.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the sag compensator and the initial charging method according to the present invention will be described in detail below. The same or corresponding parts as those in FIG. 2 are denoted by the same reference numerals.

The instantaneous sag compensator of the embodiment shown in FIG. 1 is provided with an electrolytic capacitor 4 (hereinafter simply referred to as a capacitor) on the DC side of an inverter 3 connected between a system power supply 1 and a load 2. When a voltage sag occurs in the power supply 1, the charging voltage of the capacitor 4 is supplied to the load 2 via the inverter 3 to compensate for the load voltage during the voltage sag. Note that a main thyristor switch 5 is provided between the system power supply 1 and the load 2 to disconnect the system power supply 1 from the power system when an instantaneous voltage drop occurs.

The inverter 3 includes a bridge-structured switching element (for example, an IGBT), and has a circuit configuration in which a reflux diode is connected in parallel to each switching element. The inverter 3 is a bidirectional AC / DC converter having an inverter function and a rectifying function.
The operation is switched between a rectifying operation in which the AC power from the DC converter is converted to a DC and charging the capacitor 4 and an inverter operation in which the DC power charged in the capacitor 4 is converted to the AC and supplied to the system bus 6.

In this instantaneous sag compensator, in a steady state, power is supplied from the system power supply 1 to the load 2 while the main thyristor switch 5 is turned on. When this occurs, the main thyristor switch 5 is turned off.
Simultaneously with the FF, the charging voltage of the capacitor 4 is converted to AC by the inverter operation of the inverter 3 and the AC output of the inverter 3 is supplied to the load 2 so that the charging voltage of the capacitor 4 compensates for the load voltage during the sag. I have to.

The capacitor 4 must be initially charged when the power of the sag compensator is turned on so that the load voltage during the sag can be compensated by the charging voltage of the capacitor 4 when the sag of the system power supply 1 occurs. . Therefore, in the instantaneous sag compensator of this embodiment, the diode rectifier circuit 7 is connected between the system bus 6 and the capacitor 4, and the step-up chopper 8 is interposed between the diode rectifier circuit 7 and the capacitor 4. I do. When the power supply of the sag compensator is turned on, the capacitor 4 is connected to the diode rectifier circuit 7 and the boost chopper 8.
The initial charge. The boost chopper 8
Is constituted by a short-circuit switching element 9 such as a transistor, a reactor 10 and a diode 11.

The initial charging in the instantaneous sag compensator of this embodiment is performed in the following manner. When an initial charging start command is output from a control circuit (not shown) of the voltage sag compensator when the power supply of the voltage sag compensating device is turned on, the diode rectifier circuit 7 is operated based on the initial charging start command. To start the initial charging of the capacitor 4. Here, since the DC voltage of the capacitor 4 can be charged only up to about 90% of the peak value of the power supply voltage by the diode rectifier circuit 7, the DC voltage charged in the capacitor 4 with respect to the peak value of the power supply voltage is reduced. The voltage is insufficient, and there is a peak voltage difference between the power supply voltage and the output voltage of the inverter 3.

Therefore, in the instantaneous sag compensator of this embodiment, the initial charging of the capacitor 4 is started by the operation of the diode rectifier circuit 7, and the DC voltage charged in the capacitor 4 is about 90% of the peak value of the power supply voltage. Is reached, the step-up chopper 8 is operated by the step-up command from the control circuit.
To work. The boost chopper 8 boosts the DC voltage of the capacitor 4 by flowing the current flowing in the reactor 10 through the diode 11 to the capacitor 4 by the chopping operation of the switching element 9. This boost chopper 8 causes the DC voltage of the capacitor 4 to reach almost the same level as the peak value of the power supply voltage.

After the DC voltage of the capacitor 4 is boosted by the boost chopper 8, the inverter 3 is started by a start command from the control circuit. When the inverter 3 is started, the phase of the output voltage of the inverter 3 that is in phase with the power supply voltage is gradually shifted by the rectification operation of the inverter 3, whereby the capacitor 4 is switched to a voltage equal to or higher than the peak value of the power supply voltage. The initial charging is completed by charging. Immediately after the start of the inverter, since the DC voltage of the capacitor 4 has reached almost the same level as the peak value of the power supply voltage by the boost chopper 8 as described above, the output voltage of the inverter 3 is the same as the peak value of the power supply voltage. Voltage.

As described above, immediately after the start of the inverter 3, the output voltage of the inverter 3 is the same as the peak value of the power supply voltage. The disadvantage of stopping even with a low compensation device can be solved.

In the above embodiment, the inverter 3 and the diode rectifier circuit 7 are configured separately, but the inverter 3 and the diode rectifier circuit 7 can be incorporated in one package.

[0025]

According to the present invention, a power storage capacitor is provided on the DC side of an inverter connected between a system power supply and a load, and when an instantaneous voltage drop occurs in the system power supply, the charging voltage of the capacitor is controlled by the inverter. In the sag compensator for compensating for the load voltage during sag by supplying to the load through the power supply, when the capacitor is initially charged by the phase difference between the power supply voltage and the inverter output voltage, the peak of the power supply voltage and the inverter output voltage By providing a boost chopper to boost the DC voltage of the capacitor to compensate for the voltage difference, the power supply voltage and the output voltage of the inverter are increased by boosting the DC voltage of the capacitor immediately before starting the inverter during the initial charging of the capacitor. To compensate for the peak voltage difference. If the inverter is started in this state, the output voltage of the inverter will be almost the same as the peak value of the power supply voltage. Since no trouble occurs, the reliability can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a sag compensator according to the present invention.

FIG. 2 is a circuit diagram showing a conventional sag compensator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 System power supply 2 Load 3 Inverter 4 Power storage capacitor 8 Step-up chopper

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02M 7/48 H02M 7/48 N

Claims (2)

[Claims] 1. A power storage capacitor is provided on a DC side of an inverter connected between a system power supply and a load, and when an instantaneous voltage drop of the system power supply occurs, a charging voltage of the capacitor is supplied to the load via the inverter. In the instantaneous voltage drop compensating device for compensating the load voltage during the instantaneous voltage drop, when initially charging the capacitor by the phase difference between the power supply voltage and the inverter output voltage, the peak voltage difference between the power supply voltage and the inverter output voltage is calculated. An instantaneous voltage drop compensator comprising a boost chopper for boosting a DC voltage of a capacitor for compensation. 2. A power storage capacitor is provided on a DC side of an inverter connected between a system power supply and a load, and when an instantaneous voltage drop of the system power supply occurs, a charging voltage of the capacitor is supplied to the load via the inverter. A method for initially charging the capacitor by a phase difference between a power supply voltage and an inverter output voltage, wherein the peak voltage of the power supply voltage and the inverter output voltage is compensated. An initial charging method for an instantaneous voltage drop compensating device, wherein a DC voltage of a capacitor is boosted immediately before activation of an inverter so as to compensate for a difference.