JP2005223979A - Uninterruptible power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an uninterruptible power supply capable of sustaining operation without requiring any extra main circuit component even if an unbalance load is connected. <P>SOLUTION: The uninterruptible power supply comprises a converter 14 for converting an AC input into a DC output, a positive side and negative side smoothing capacitors 15 connected with the output of the converter to constitute a DC circuit, an inverter 16 connected across the smoothing capacitor and obtaining an AC output from its middle point and the middle point of the smoothing capacitor, a battery 18 for switching power supply when the AC input becomes abnormal, a bypass circuit 19 connected to output the AC input directly to the output side, a control section 3 for controlling the inverter, and a voltage detecting means for detecting the voltages being applied to the positive side and negative side smoothing capacitors, respectively. The control section 3 corrects the AC output voltage command of the inverter depending on a DC difference voltage, i.e. the difference between a voltage being applied to the positive side smoothing capacitor and a voltage being applied to the negative side smoothing capacitor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improved uninterruptible power supply.

  In general, the inverter circuit of a small uninterruptible power supply with single-phase output is often an inverter circuit having a half-bridge configuration that can share the input / output reference potential and has excellent noise resistance. However, in an uninterruptible power supply in which the inverter circuit has a half-bridge configuration, when a load requiring positive or negative unbalanced power is connected to the output, the positive DC voltage and the negative side of the main circuit are connected. DC voltage is unbalanced. Therefore, in the past, connection of a load requiring positive or negative unbalanced power was prohibited, and when a DC voltage imbalance occurred, it was determined that a circuit failure occurred, and the inverter circuit was stopped and switched to a bypass circuit.

  However, recently, the load connected to the uninterruptible power supply apparatus has increased the number of devices that actively control the input current as a countermeasure against harmonics. Depending on the input current control technique, positive or negative imbalance has occurred in the power required by the load device.

  Therefore, as an uninterruptible power supply, it has become necessary to take measures to continue operation as much as possible even if there is a positive or negative imbalance in the power required by the load equipment.

For this reason, a balance circuit for suppressing the above-mentioned imbalance is newly provided, and by controlling this balance circuit, an attempt is made to eliminate the imbalance between the positive DC voltage and the negative DC voltage of the main circuit. Proposals have been made (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2001-197757 (page 5-6, FIG. 1)

  However, the countermeasures by adding a balance circuit disclosed in Patent Document 1 have problems of increasing the size of the apparatus and increasing the cost due to an increase in parts.

  Also, in the event of a failure of the uninterruptible power supply, it is possible to continue supplying power to the load by stopping the inverter circuit and switching to the bypass circuit, but an abnormality has occurred in the switch used in the bypass circuit. If this happens, an abnormal voltage may be output to the load, which may damage the load equipment.

  The present invention has been made in view of the above problems, and its purpose is to enable operation to continue without adding main circuit components even when an unbalanced load is connected and to damage load equipment. It is to provide an uninterruptible power supply that is not given.

In order to achieve the above object, an uninterruptible power supply according to the present invention includes a half-bridge converter that converts AC input to DC, and a positive and negative smoothing connected to the output of the converter and constituting a series circuit. A capacitor and a half-bridge inverter connected to both ends of the positive and negative smoothing capacitors to obtain an AC output from a middle point thereof and a middle point of the positive and negative smoothing capacitors, and the AC input A battery connected to selectively switch power supply to the converter via a changeover switch when an abnormality occurs, and a bypass circuit connected to output the AC input directly to the output side of the inverter; A control unit for controlling the inverter; and voltage detection means for detecting voltages applied to the positive and negative smoothing capacitors, respectively. The AC output voltage command of the inverter is corrected according to the DC deviation voltage that is the difference between the voltage applied to the positive smoothing capacitor and the voltage applied to the negative smoothing capacitor. It is characterized by that.

  According to the present invention, control is performed so as to compensate for the detected value of DC voltage imbalance, so even if a load device with input current imbalance is connected without adding main circuit components. An uninterruptible power supply capable of continuing operation can be provided.

  Embodiments of an uninterruptible power supply according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a circuit configuration diagram of the uninterruptible power supply according to Embodiment 1 of the present invention.

  The uninterruptible power supply 1 supplies high-quality AC power to the load 2. The operation of the uninterruptible power supply 1 is controlled by the control circuit 3.

  The internal configuration of the uninterruptible power supply 1 will be described below. AC input is received by the breaker 11, and power is supplied to the input filter 13 via the changeover switch 12. The change-over switch 12 is for switching to power supply from the battery 18 when there is an abnormality in the AC input. The output of the input filter 13 becomes the input of the converter circuit 14, and the converter circuit 14 converts alternating current into direct current. The converter circuit 14 has a configuration in which a power device having a diode connected in antiparallel is half-bridge connected. When direct current is supplied from the battery 18, the input filter 13 and the converter circuit 14 operate a so-called boost chopper.

  The output of the converter circuit 14 is supplied to the smoothing capacitor 15. The smoothing capacitor 15 is divided into a positive side and a negative side with one side of the AC input as a reference potential. The output of the smoothing capacitor 15 is supplied to the inverter circuit 16, converted into alternating current again by the inverter circuit 16, and supplied to the load 2 through the output filter 17. The inverter circuit 16 also has a configuration in which a power device having a diode connected in antiparallel is half-bridge connected.

  Connected between the AC input and the output of the inverter circuit 16 is a bypass circuit 19 for switching so that the AC input is directly output when the conversion circuit portion of the uninterruptible power supply 1 fails.

  Next, the internal configuration of the control circuit 3 will be described. In the control circuit 3 of FIG. 1, only the portion related to the voltage control of the inverter circuit 16 related to the present invention is shown, and the other functions such as the portion related to current control are not shown.

  The output voltage reference Voutref and the output feedback voltage Vout of the uninterruptible power supply 1 are compared with each other by a comparator 31 and proportionally integral amplified by an amplifier 32 to obtain a sine wave output voltage command. Further, the voltage across the positive side smoothing capacitor 15, that is, the positive side DC voltage Vp, and the voltage across the negative side smoothing capacitor 15, that is, the negative side DC voltage Vn are compared by the comparator 33, and the DC deviation voltage is determined. ΔVdc is obtained. This DC deviation voltage ΔVdc is applied to the input of the amplifier 32 as a correction signal.

The output voltage command, which is the output of the amplifier 32, is compared with a carrier triangular wave for PWM (pulse width modulation) control by the comparator 34, and becomes a gate signal of the positive power device of the inverter circuit 16 via the dead time giving circuit 35. . Further, the gate signal of the negative power device is obtained through the dead time giving circuit 35 by inverting the signal compared by the comparator 34 by the inverting circuit 36.

  The operation in the above configuration will be described below.

  When unbalance occurs in the positive and negative values of the current flowing through the load 2, in the uninterruptible power supply 1 having the half-bridge type inverter circuit 16 as shown in FIG. There is a difference between the voltage Vp and the negative DC voltage Vn. For example, when the positive side current of the load 2 is large like the negative overcurrent shown in FIG. 1, the positive side DC voltage Vp decreases.

  When the AC input is normal, the balance of the main circuit DC voltage can be obtained by adding the DC deviation voltage ΔVdc, which is the difference between the positive DC voltage Vp and the negative DC voltage Vn, to the current reference of the converter circuit 14. However, when the AC input is abnormal, the input of the converter circuit 14 is switched to the battery 18 side by the changeover switch 12, and the converter circuit 14 operates as a step-up chopper. In this case, since the positive side DC voltage Vp and the negative side DC voltage Vn are collectively equalized voltage control, if the main circuit DC voltage is unbalanced by the load 2, it cannot be controlled on the boost chopper side. .

  Therefore, in the present invention, as shown in the control circuit 3 of FIG. 1, the DC deviation voltage ΔVdc, which is the difference between the positive DC voltage Vp and the negative DC voltage Vn, is added to the input of the amplifier 32 as a correction signal. Then, a DC bias for correction is applied to the output voltage command that is the output of the amplifier 32 to correct the unbalance of the DC voltage of the main circuit.

  As described above, according to the present invention, control is performed so as to compensate for the detected value of the DC voltage imbalance, so that the operation can be continued even when a load device having an input current imbalance is connected. It is possible to provide an uninterruptible power supply that can be used.

  FIG. 2 is a circuit configuration diagram of the uninterruptible power supply according to Embodiment 2 of the present invention. About each part of this Example 2, the same part as each part of the uninterruptible power supply concerning Example 1 of Drawing 1 is shown with the same numerals, and the explanation is omitted. The second embodiment is different from the first embodiment in that an unbalance excessive monitoring circuit 37 that receives the DC deviation voltage ΔVdc that is the output of the comparator 33 is provided, and the output is switched to the bypass operation. is there.

  When the above-described DC deviation voltage ΔVdc is large, there is a risk that the input transformer of the load 2 may be broken due to DC bias. In addition, the output voltage command is corrected with a DC bias so that the DC deviation voltage ΔVdc is zero, but this method is limited in its correction, although it depends on the relationship with the modulation factor that is initially set. There is.

  For this reason, when the DC deviation voltage ΔVdc exceeds a predetermined set value, the unbalance excessive monitoring circuit 37 gate-blocks the inverter circuit 16 of the uninterruptible power supply 1 and turns on the bypass circuit 19 to perform bypass operation. Switch.

  In this way, even when the DC deviation voltage ΔVdc increases beyond the control range, it is possible to continue the operation safely. In order to prevent malfunction due to noise or the like, switching to bypass operation may be performed when the DC deviation voltage ΔVdc exceeds a predetermined value for a predetermined time or more.

  FIG. 3 is a circuit configuration diagram of an uninterruptible power supply according to Embodiment 3 of the present invention. About each part of this Example 3, the same part as each part of the uninterruptible power supply concerning Example 2 of Drawing 2 is shown with the same numerals, and the explanation is omitted. The third embodiment is different from the second embodiment in that an abnormality detection circuit 38 that detects an abnormality by monitoring the output feedback voltage Vout, an output of the abnormality detection circuit 38, and a bypass switching signal are held by a hold circuit. An AND circuit 39 for obtaining an AND condition with the signal is provided, and the bypass operation is stopped by the output of the AND circuit 39.

  The bypass circuit 19 is constituted by a semiconductor switch, for example, an antiparallel circuit of a thyristor. The voltage supplied to the load 2 when the thyristor on one side of the anti-parallel connected thyristors occurs during the bypass operation of the load 2 requiring the unbalanced current in the state of the above-described second embodiment. Becomes a half-wave voltage, and the load 2 may be damaged due to direct current bias.

  Therefore, in order to solve the above problem, the abnormality detection circuit 38 monitors whether the output voltage Vout is in a half-wave state. If the output voltage Vout is in a half-wave state, the AND circuit 39 outputs a bypass operation stop command. Then, the thyristor of the bypass circuit 19 is turned off to stop the power supply to the load 2.

  Here, for example, the abnormality detection circuit 38 may output an abnormality output when the absolute value obtained by full-wave rectifying the output feedback voltage Vout when the bypass circuit 19 is on becomes equal to or less than a predetermined value, or The abnormality may be detected by A / D converting the output feedback voltage Vout and monitoring the lack of voltage for half a period from the time-series data. It is also possible to detect an abnormality by monitoring the output current instead of the output feedback voltage Vout.

  As described above, according to the present invention, when an unbalanced load is operated, an uninterruptible power supply apparatus that does not damage load equipment by applying an unbalanced voltage of half-wave rectification to the load. It becomes possible to provide.

The circuit block diagram which shows the uninterruptible power supply which concerns on Example 1 of this invention. The circuit block diagram which shows the uninterruptible power supply which concerns on Example 2 of this invention. The circuit block diagram which shows the uninterruptible power supply which concerns on Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uninterruptible power supply 2 Load 3 Control circuit 11 Breaker 12 Changeover switch 13 Input filter 14 Converter circuit 15 Smoothing capacitor 16 Inverter circuit 17 Output filter 18 Battery 31 Comparator 32 Amplifier 33 Comparator 34 Comparator 35 Dead time provision circuit 36 Inversion circuit 37 Overbalance monitoring circuit 38 Abnormality detection circuit 39 AND circuit

Claims (3)

A half-bridge converter that converts AC input to DC,
A smoothing capacitor on the positive side and the negative side connected to the output of this converter and constituting a series circuit,
An inverter of a half bridge configuration that is connected to both ends of the positive and negative smoothing capacitors and obtains an AC output from the middle point and the middle point of the positive and negative smoothing capacitors;
A battery connected to selectively switch power supply to the converter via a changeover switch when the AC input becomes abnormal;
A control unit for controlling the inverter;
Voltage detecting means for detecting voltages applied to the positive and negative smoothing capacitors, respectively.
The controller is
According to the DC deviation voltage, which is the difference between the voltage applied to the positive smoothing capacitor and the voltage applied to the negative smoothing capacitor,
An uninterruptible power supply, wherein an AC output voltage command of the inverter is corrected. And further comprising a bypass circuit connected to directly output the AC input to the output side of the inverter,
When the DC deviation voltage exceeds a predetermined value for a predetermined time,
The uninterruptible power supply according to claim 1, wherein the inverter is stopped and the bypass circuit is turned on. Furthermore, it comprises an output abnormality detecting means for monitoring and detecting whether the output voltage or current is in a half-wave state by monitoring the amount of electricity in the output
After turning on the bypass circuit,
When the output abnormality detection means detects an abnormality,
The uninterruptible power supply according to claim 2, wherein the bypass circuit is turned off.

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