Uninterruptible power supply device

An uninterruptible power supply device includes a switch, a power converter, and another power converter. The switch includes a first electrode that receives AC power from an AC power supply and a second electrode connected to a load via an AC bus, and is turned on during a normal operation and turned off during a power failure. The power converter converts DC power from a DC power supply into AC power and outputs it to the AC bus during a power failure. The other power converter converts the AC power received from the AC bus into DC power and stores it in a lithium-ion battery when the load is performing regeneration running, and converts the DC power of the lithium-ion battery into AC power and supplies it to the AC bus when the load is performing power running.

TECHNICAL FIELD

The present invention relates to uninterruptible power supply devices, and particularly, to an uninterruptible power supply device of a standby power system.

BACKGROUND ART

Japanese Patent Laying-Open No. 11-341686 (PTD 1) discloses an uninterruptible power supply device of a standby power system. This uninterruptible power supply device includes a switch having a first electrode that receives AC power from a commercial AC power supply and a second electrode connected to a load, and a power converter connected to the load. When the commercial AC power supply supplies AC power normally, the switch is turned on, so that AC power from the commercial AC power supply is supplied to the load via the switch. When the commercial AC power supply does not supply AC power normally, the switch is turned off, so that DC power supplied from a DC power supply is converted into AC power by the power converter and the AC power is supplied to the load.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

According to PTD 1, at the occurrence of regenerated power in the load, the regenerated power is returned to the commercial AC power supply via the switch. When the uninterruptible power supply device is connected to an independent power generator in place of the commercial AC power supply, however, the regenerated power generated in the load may return to the independent power generator, leading to a failure of the independent power generator.

A main object of the present invention is therefore to provide an uninterruptible power supply device capable of preventing or reducing a return of regenerated power generated in a load to an AC power supply.

Solution to Problem

An uninterruptible power supply device according to the present invention is an uninterruptible power supply device that supplies AC power from an AC power supply to a load in a first case in which the AC power supply supplies AC power normally, and converts DC power from a DC power supply into AC power and supplies the AC power to the load in a second case in which the AC power supply does not supply AC power normally. The uninterruptible power supply device includes a switch, an AC bus, a first power converter, a second power converter, and a control circuit. The switch has a first electrode that receives AC power from the AC power supply, and is configured to be turned on in the first case and turned off in the second case. The AC bus is connected between a second electrode of the switch and the load. The first power converter is configured to convert DC power from the DC power supply into AC power and output the AC power to the AC bus in the second case. The second power converter has a charge mode in which the second power converter converts AC power received from the AC bus into DC power and supplies the DC power to a first power storage device and a discharge mode in which the second power converter converts DC power of the first power storage device into AC power and outputs the AC power to the AC bus. The control circuit is configured to execute a first mode. In the first mode, the control circuit causes the second power converter to execute the charge mode when the load is performing regeneration running and causes the second power converter to execute the discharge mode when the load is performing power running.

Another uninterruptible power supply device according to the present invention is an uninterruptible power supply device that supplies AC power from an AC power supply to a first load in a first case in which the AC power supply supplies AC power normally, and converts DC power from a DC power supply into AC power and supplies the AC power to the first load in a second case in which the AC power supply does not supply AC power normally. The uninterruptible power supply device includes a first terminal, a second terminal, a first switch, an AC bus, a power converter, a second switch, and a control circuit. The first terminal is connected to the first load. The second terminal is connected to a second load caused to consume regenerated power generated in the first load. The first switch has a first electrode that receives AC power from the AC power supply, and is configured to be turned on in the first case and turned off in the second case. The AC bus is connected between a second electrode of the first switch and the first terminal. The power converter is configured to convert DC power from the DC power supply into AC power and output the AC power to the AC bus in the second case. The second switch is connected between the first terminal and the second terminal. The control circuit is configured to execute a first mode. In the first mode, the control circuit turns on the second switch when the first load is performing regeneration running and turns off the second switch when the first load is performing power running.

Advantageous Effects of Invention

In the uninterruptible power supply device according to the present invention, the second power converter is provided between the AC bus and the first power storage device, and the first power storage device is charged during regeneration running of the load. This can prevent or reduce of a return of the regenerated power generated in the load to the AC power supply. Additionally, the first power storage device is discharged during power running of the load, allowing the regenerated power generated in the load to be used effectively, which increases an input efficiency of the uninterruptible power supply device.

In another uninterruptible power supply device according to the present invention, the first switch is connected between the first terminal connected with the first load and the second terminal connected with the second load that consumes the regenerated power generated in the first load, and the first switch is turned on during regeneration running of the first load and the first switch is turned off during power running of the first load. The regenerated power generated in the load can thus be consumed by the second load, preventing or reducing a return of the regenerated power to the AC power supply.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a circuit block diagram showing a configuration of an uninterruptible power supply device according to Embodiment 1 of the present invention. With reference toFIG. 1, the uninterruptible power supply device is an uninterruptible power supply device of a standby power system and includes input terminals TI1to TI3, output terminals TO1to TO3, switches1ato1c, AC buses2ato2c, control circuits3and4, power converters5and6, filters7and8, and current detectors9ato9c.

Input terminals TI1to TI3each receive three-phase AC power supplied from AC power supply51. AC power supply51may be a commercial AC power supply or an independent power generator. AC power supply51supplies, for example, AC power of a commercial frequency to the uninterruptible power supply device. Output terminals TO1to TO3are connected to a load52. Load52is, for example, a motor and is driven by the AC power supplied from the uninterruptible power supply device. In Embodiment 1, the case in which load52is subjected to power running and the case in which load52is subjected to regeneration running are performed alternately.

Switches1ato1chave first electrodes each connected to a corresponding one of input terminals TI1to TI3and second electrodes connected respectively to first terminals of AC buses2ato2c, and the second terminals of AC buses2ato2care connected respectively to output terminals TO1to TO3. Each of switches1ato1cincludes, for example, a pair of thyristors. One of the pair of thyristors has an anode and a cathode connected respectively to the first electrode and the second electrode, and the other thyristor has an anode and a cathode connected respectively to the second electrode and the first electrode. Each of switches1ato1cmay be formed of a mechanical switch.

Switches1ato1care controlled by control circuit3, and are turned on in a normal operation in which AC power supply51supplies three-phase AC power normally and are turned off in the case in which AC power supply51does not supply three-phase AC power normally (e.g., during a power failure).

Power converter5is connected to AC buses2ato2cvia filter7and is also connected to DC power supply53. DC power supply53supplies DC power to power converter5. Power converter5is controlled by a pulse width modulation (PWM) signal supplied from control circuit3and is driven by the DC power supplied from DC power supply53. Power converter5is brought to the standby state in which no current is output during the normal operation in which AC power supply51supplies three-phase AC power normally.

If an abnormality occurs in the three-phase AC power supplied from AC power supply51(e.g., if a power failure occurs), power converter5applies a reverse bias voltage to switches1ato1cto rapidly turn off switches1ato1c, and subsequently, converts the DC power supplied from DC power supply53into three-phase AC power and then supplies the three-phase AC power to AC buses2ato2cvia filter7.

Filter7is provided between power converter5and AC buses2ato2c. Filter7, which is a low pass filter, allows three-phase AC power of a commercial frequency to pass therethrough and prohibits a signal of a switching frequency which is generated in power converter5from passing therethrough. In other words, filter7shapes a rectangular-wave AC voltage generated in power converter5into a sine-wave AC voltage.

Control circuit3determines whether AC power supply51normally supplies three-phase AC power based on the voltages at input terminals TI1to TI3(i.e., three-phase AC voltage supplied from AC power supply51), and controls switches1ato1cand power converter5based on the determination result.

For example, when the three-phase AC voltage supplied from AC power supply51is within an allowable range, control circuit3determines that AC power supply51supplies three-phase AC power normally. When the three-phase AC voltage supplied from AC power supply51deviates from the allowable range, control circuit3determines that AC power supply51does not supply three-phase AC power normally.

When AC power supply51supplies three-phase AC power normally, control circuit3turns on switches1ato1cand also brings power converter5to the standby state. When AC power supply51does not supply three-phase AC power normally, control circuit3turns off switches1ato1cand also causes power converter5to generate three-phase AC power.

For example, when AC power supply51supplies three-phase AC power normally, control circuit3stores the phase and voltage value of the three-phase AC voltage from AC power supply51. When the three-phase AC power from AC power supply51is abnormal, control circuit3controls power converter5based on the stored phase and voltage value of the three-phase AC voltage.

Power converter6is connected to first ends of AC buses2ato2cvia filter8and is also connected to lithium-ion battery54. Power converter6is controlled by a PWM signal supplied from control circuit4and gives and receives power between AC buses2ato2cand lithium-ion battery54.

Power converter6executes a charge mode when load52is performing regeneration running and executes a discharge mode when load52is performing power running. During the charge mode, power converter6converts the three-phase AC power supplied from AC buses2ato2cvia filter8into DC power and stores the DC power in lithium-ion battery54. During the discharge mode, power converter6converts the DC power of lithium-ion battery54into three-phase AC power and outputs the three-phase AC power to AC buses2ato2cvia filter8.

Lithium-ion battery54is disadvantageous in that it is expensive compared with a storage battery; advantageously, lithium-ion battery54deteriorates less due to charging and discharging and can be charged and discharged many times. Lithium-ion battery54is thus used as a battery that is charged and discharged every time load52is switched between regeneration running and power running.

Filter8is provided between power converter6and AC buses2ato2c. Filter8, which is a low pass filter, allows three-phase AC power of a commercial frequency to pass therethrough and prohibits a signal of a switching frequency generated in power converter5from passing therethrough. In other words, filter8shapes a rectangular-wave AC voltage generated in power converter6into a sine-wave AC voltage. In addition, filter8causes regenerated power generated in load52to pass therethrough.

Current detectors9ato9crespectively detect the instantaneous values of the currents flowing through the second ends of AC buses2ato2cand output signals indicating the detected values. Control circuit4controls power converter6based on the output signals of current detectors9ato9cand the three-phase AC voltages of AC buses2ato2c. Control circuit4determines whether load52is performing regeneration running or power running based on the output signals of current detectors9ato9c.

Control circuit4subjects three-phase AC currents obtained from the output signals of three current detectors9ato9cto three-phase to two-phase conversion (i.e., dq conversion) to obtain an effective current and a reactive current. Control circuit4determines that load52is performing power running when the effective current has a positive value (i.e., the effective current flows into load52) and determines that load52is performing regeneration running when the effective current has a negative value (i.g., the effective current flows out of load52).

When load52is performing regeneration running, control circuit4causes power converter6to execute the charge mode to charge lithium-ion battery54. When load52is performing power running, control circuit4causes power converter6to execute the discharge mode to discharge lithium-ion battery54.

Transistors Q1to Q3have collectors connected together to the positive electrode of DC power supply53and emitters connected respectively to the collectors of transistors Q4to Q6, and emitters of transistors Q4to Q6are connected together to the negative electrode of DC power supply53. Diodes D1to D6are connected respectively in anti-parallel with transistors Q1to Q6.

Each of transistors Q1to Q6is controlled to be turned on/off by control circuit3ofFIG. 1. When AC power supply51does not supply three-phase AC power normally, control circuit3turns on transistors Q1to Q6for each predetermined period of time in a predetermined order to convert the output voltage of DC power supply53into a three-phase AC voltage.

Reactors L1to L3have first terminals connected respectively to the emitters of transistors Q1to Q3and second terminals connected respectively to AC buses2ato2c. Capacitors C1to C3have first electrodes connected respectively to AC buses2ato2cand second electrodes connected respectively to AC buses2b,2c, and2a. Reactors L1to L3and capacitors C1to C3constitute a low pass filter, and the low pass filter converts a rectangular-wave AC voltage generated by transistors Q1to Q6into a sine-wave AC voltage and supplies the sine-wave AC voltage to AC buses2ato2c.

Transistors Q11to Q13have collectors connected together to the positive electrode of lithium-ion battery54and emitters connected respectively to the collectors of transistors Q14to Q16, and emitters of transistors Q14to Q16are connected together to the negative electrode of lithium-ion battery54. Diodes D11to D16are connected respectively in anti-parallel with transistors Q11to Q16.

Reactors L11to L13have first terminals connected respectively to the emitters of transistors Q11to Q13and second terminals connected respectively to AC buses2ato2c. Capacitors C11to C13have first electrodes connected respectively to AC buses2ato2cand second electrodes connected respectively to AC buses2b,2c, and2a.

Reactors L11to L13and capacitors C11to C13constitute a low pass filter, and the low pass filter converts a rectangular-wave AC voltage generated in transistors Q11to Q16into a sine-wave AC voltage and supplies the sine-wave AC voltage to AC buses2ato2c.

Each of transistors Q11to Q16is controlled to be turned on/off by control circuit4ofFIG. 1. When load52is performing regeneration running, control circuit4turns on transistors Q11to Q16for each predetermined period of time in a predetermined order and converts the regenerated power (three-phase AC power) supplied from AC buses2ato2cvia filter8into DC power to charge lithium-ion battery54.

For example, the phase of a three-phase AC voltage that appears in the emitters of transistors Q11to Q13when transistors Q11to Q16are controlled to be turned on/off is delayed from the phase of the three-phase AC voltage that appears in AC buses2ato2c, thereby causing a current to flow from AC buses2ato2cto lithium-ion battery54to charge lithium-ion battery54.

When load52is performing power running, control circuit4turns on transistors Q11to Q16for each predetermined period of time in a predetermined order, and converts the DC power of lithium-ion battery54into three-phase AC power to discharge lithium-ion battery54.

For example, the phase of a three-phase AC voltage that appears in the emitters of transistors Q11to Q13when transistors Q11to Q16are controlled to be turned on/off is advanced from the phase of a three-phase AC voltage that appears in AC buses2ato2c, thereby causing a current to flow from lithium-ion battery54to AC buses2ato2cto discharge lithium-ion battery54.

The operation of this uninterruptible power supply device will now be described. When AC power supply51supplies three-phase AC power normally, control circuit3turns on switches1ato1c, so that the three-phase AC power from AC power supply51is supplied to load52via switches1ato1cand AC buses2ato2c. In this case, power converter5is brought to the standby state.

When load52performs regeneration running, regenerated power is generated in load52, causing an effective current to flow from load52to AC buses2ato2c. The effective current is detected by current detectors9ato9cand control circuit4, so that control circuit4causes power converter6to execute the charge mode. This causes the regenerated power generated in load52to be converted into DC power by power converter6to be stored in lithium-ion battery54.

When load52performs power running, an effective current flows from AC buses2ato2cinto load52. The effective current is detected by current detectors9ato9cand control circuit4, so that control circuit4causes power converter6to execute the discharge mode. That is to say, the DC power of lithium-ion battery54is converted into three-phase AC power by power converter6, and the three-phase AC power is supplied to load52via filter8and AC buses2ato2c. This allows effective use of the regenerated power generated in load52, increasing the input efficiency of the uninterruptible power supply device. Further, as a result of the discharge of lithium-ion battery54, the regenerated power to be generated in load52next is prepared to be stored in lithium-ion battery54.

When the three-phase AC power from AC power supply51is abnormal, control circuit3turns off switches1ato1cand the DC power from DC power supply53is converted into three-phase AC power by power converter5, and the three-phase AC power is supplied to load52via filter7and AC buses2ato2c. The operation of load52can thus be continued during a period in which DC power supply53supplies DC power.

Also in this case, when load52is performing regeneration running, the regenerated power generated in load52is converted into DC power, and the DC power is stored in lithium-ion battery54; when load52is performing power running, the DC power of lithium-ion battery54is converted into three-phase AC power, and the three-phase AC power is supplied to load52.

As described above, in Embodiment 1, AC buses2ato2care connected to lithium-ion battery54via power converter6, lithium-ion battery54is charged when load52is performing regeneration running and is discharged when the load is performing power running. A return of the regenerated power generated in load52to AC power supply51can thus be prevented or reduced. In addition, the regenerated power generated in load52can be used effectively, thus improving the efficiency of the uninterruptible power supply device.

An electric double layer capacitor or an electrolytic capacitor may be provided in place of lithium-ion battery54.

Further, although DC power supply53for driving power converter5is provided in Embodiment 1, a storage battery (power storage device) may be provided as DC power supply53. When the three-phase AC voltage supplied from AC power supply51is normal, control circuit3controls power converter5such that the voltage between the terminals of the storage battery reaches a target voltage. Power converter5is controlled by control circuit3to convert three-phase AC power supplied from AC power supply51via switches1ato1cinto DC power and store the DC power in the storage battery.

When the three-phase AC voltage supplied from AC power supply51is abnormal, power converter5converts the DC power of the storage battery into three-phase AC power and supplies the three-phase AC power to load52via filter7and AC buses2ato2c. Even when a power failure occurs, thus, the operation of load52can be continued during a period in which storage battery stores DC power. A capacitor may be provided in place of the storage battery.

Advantageously, the storage battery is inexpensive compared with lithium-ion battery54; the storage battery is disadvantageous in that it deteriorates severely due to charge and discharge and cannot be charged and discharged many times. Since large power is required during a power failure though a power failure occurs less frequently, an inexpensive storage battery is preferably used as the battery for storing DC power used during a power failure.

An uninterruptible power supply device is frequently connected with a load that does not perform regeneration running, and is less frequently connected with a load that performs regeneration running. When the load that does not perform regeneration running is connected to the uninterruptible power supply device, the uninterruptible power supply device of Embodiment 1 does not use control circuit4, power converter6, filter8, current detectors9ato9c, and lithium-ion battery54, leading to waste. Embodiment 2 aims to solve this problem.

FIG. 3is a circuit block diagram showing a configuration of an uninterruptible power supply device according to Embodiment 2 of the present invention, which is compared withFIG. 1. With reference toFIG. 3, this uninterruptible power supply device differs from the uninterruptible power supply device ofFIG. 1in that control circuits3and4are replaced respectively by control circuits3A and4A.

Control circuit3A determines whether a three-phase AC voltage supplied from AC power supply51is normal, and brings an abnormality detection signal φ3to “L” level that is the deactivation level when the three-phase AC voltage is normal and brings abnormality detection signal φ3to “H” level that is an activation level when the three-phase AC voltage is not normal.

In other words, abnormality detection signal φ3enters “L” level that is the deactivation level when the three-phase AC power supplied from AC power supply51is normal, and abnormality detection signal φ3enters “H” level that is the activation level when the three-phase AC power supplied from AC power supply51is not normal.

Control circuit4A determines whether load52is performing regeneration running or power running based on the output signals of current detectors9ato9cas in the case of control circuit4ofFIG. 1. Control circuit4A operates similarly to control circuit4ofFIG. 1(i.e., executes the first mode) when regeneration running of load52is performed within a predetermined period of time. Control circuit4A causes power converter6to execute the charge mode to charge lithium-ion battery54when load52is performing regeneration running, and causes power converter6to execute the discharge mode to discharge lithium-ion battery54when load52is performing power running. This is because when a time interval in which regeneration running of load52is performed is within the predetermined period of time, load52that performs regeneration running is estimated to be connected to output terminals TO1to TO3.

When regeneration running of load52is not performed within the predetermined period of time, control circuit4A operates similarly to control circuit3ofFIG. 1(i.e., executes the second mode). That is to say, control circuit4A causes power converter6to execute the charge mode to charge lithium-ion battery54when abnormality detection signal φ3is at “L” level that is the deactivation level, and causes power converter6to execute the discharge mode to discharge lithium-ion battery54when abnormality detection signal φ3is at “H” level that is the activation level. This is because when regeneration running of load52is not performed even after a lapse of the predetermined period of time, it is estimated that load52that performs power running alone is connected. The other configuration and operation are the same as those of Embodiment 1, which will not be described repetitively.

Embodiment 2 can achieve effects similar to those of Embodiment 1, and even when load52that performs power running alone is connected, power converter6, lithium-ion battery54, and the like can be used effectively, increasing the power that can be supplied during a power failure.

In Embodiment 2, whether load52is performing regeneration running or power running is determined based on the detection results of current detectors9ato9c, and when the period of time in which load52is not performing regeneration running exceeds the predetermined period of time, lithium-ion battery54is used as a battery for supplying power during a power failure. However, when whether load52performs regeneration running is evident without operating load52, the operation of determining whether the period of time in which whether load52is not performing regeneration running exceeds the predetermined period of time leads to waste, and control circuit4A may wastefully consume current. Embodiment 3 aims to solve this problem.

FIG. 4is a circuit block diagram showing a configuration of an uninterruptible power supply device according to Embodiment 3 of the present invention, which is compared withFIG. 3. With reference toFIG. 4, this uninterruptible power supply device differs from the uninterruptible power supply device ofFIG. 3in that control circuit4A is replaced by a control circuit4B and that a setting unit10is added.

Setting unit10includes, for example, a button operated by a user of the uninterruptible power supply device and is used to determine whether load52is configured to perform regeneration running. Setting unit10brings a control signal CNT to “L” level when it is set that load52is configured to perform regeneration running. Setting unit10brings control signal CNT to “H” level when it is set that load52is not configured to perform regeneration running. Setting unit10forms a selection unit that selects any one mode of a first mode and a second mode.

When control signal CNT is at “L” level (i.e., when the first mode is selected), control circuit4B determines whether load52is performing regeneration running or power running based on the output signals of current detectors9ato9cas in control circuit4ofFIG. 1. Control circuit4B causes power converter6to execute the charge mode to charge lithium-ion battery54when load52is performing regeneration running, and causes power converter6to execute the discharge mode to discharge lithium-ion battery54when load52is performing power running.

When control signal CNT is at “H” level (i.e., when the second mode is selected), control circuit4B operates similarly to control circuit3ofFIG. 1. That is to say, control circuit4B causes power converter6to execute the charge mode to charge lithium-ion battery54when abnormality detection signal φ3is at “H” level that is the deactivation level, and causes power converter6to execute the discharge mode to discharge lithium-ion battery54when abnormality detection signal φ3is at “H” level that is the activation level. The other configuration and operation are the same as those of Embodiment 1, which will not be described repetitively.

Embodiment 3 achieves the same effects as those of Embodiment 2, and when load52that performs power running alone is connected, the operation of control circuit4B can be simplified, thus reducing the current consumed by control circuit4B.

Although lithium-ion battery54is used as the battery for storing the power to be used during a power failure when control signal CNT is brought to “H” level in Embodiment 3, the present invention is not limited to this. When load52performs regeneration running even in the case in which control signal CNT has been brought to “H” level, lithium-ion battery54can be used as the battery for storing regenerated power when load52performs regeneration running. In this modification example, even when any one load of the load that performs regeneration running and the load that does not perform regeneration running is connected and one load is subsequently changed to the other load, the operation of control circuit4B can be switched without operating setting unit10. Even when the operation of setting unit10is forgot in the case in which one load has been changed to the other load, the operation of control circuit4B can be switched automatically.

FIG. 5is a circuit block diagram showing a configuration of an uninterruptible power supply device according to Embodiment 4 of the present invention, which is compared withFIG. 1. With reference toFIG. 5, this uninterruptible power supply device differs from the uninterruptible power supply device ofFIG. 1in that setting unit10, a control circuit20, switches21ato21c, and load terminals TL1to TL3are provided in place of control circuit4, power converter6, and filter8.

Load terminals TL1to TL3are connected with a load55caused to consume regenerated power generated in load52. For example, load55includes three resistance elements or three inductors. The three resistance elements (or three inductors) have first terminals connected respectively to load terminals TL1to TL3and second terminals connected to each other.

Switches21ato21chave first terminals connected respectively to output terminals TO1to TO3and second terminals connected respectively to load terminals TL1to TL3. Switches21ato21care controlled by control circuit20.

Setting unit10includes, for example, a button operated by a user of the uninterruptible power supply device and is used to determine whether load52is configured to perform regeneration running. Setting unit10brings a control signal CNT to “L” level when the user sets load52as being a load that performs regeneration running. Setting unit10brings control signal CNT to “H” level when the user sets load52as not being a load that performs regeneration running.

When control signal CNT is at “L” level, control circuit20determines whether load52is performing regeneration running or power running based on the output signals of current detectors9ato9cas in control circuit4ofFIG. 1. Control circuit20turns on switches21ato21csuch that the regenerated power is consumed in load55when load52is performing regeneration running, and turns off switches21ato21csuch that load55is electrically isolated from load52when load52is performing power running. When control signal CNT is at “H” level, control circuit20brings switches21ato21cto off state. The other configuration and operation are the same as those of Embodiment 1, which will not be described repetitively.

Since switches21ato21care turned on such that the regenerated power is consumed in load55when the regenerated power is generated in load52in Embodiment 4, a return of regenerated power to AC power supply51can be prevented or reduced. Even when an independent power generator is used as AC power supply51, thus, a failure of the independent power generator due to the regenerated power generated in load52can be prevented. Further, when load52that performs power running alone is connected, setting unit10is used to bring control signal CNT to “H” level, simplifying the operation of control circuit20, which reduces the current consumed by control circuit20.

Although switches21ato21care brought to off state when control signal CNT is brought to “H” level in Embodiment 4, the present invention is not limited to this. Also in the case where control signal CNT has been brought to “H” level, switches21ato21ccan be turned on when load52performs regeneration running. In this modification example, even when any one load of the load that performs regeneration running and the load that does not perform regeneration running is connected and one load is subsequently changed to the other load, the operation of control circuit4B can be switched without operating setting unit10. Even when the operation of setting unit10is forgot in the case where one load has been changed to the other load, thus, the operation of control circuit20can be switched automatically.

FIG. 6is a circuit block diagram showing a configuration of an uninterruptible power supply device according to Embodiment 5 of the present invention, which is compared withFIG. 5. With reference toFIG. 6, this uninterruptible power supply device differs from the uninterruptible power supply device ofFIG. 5in that control circuit20is replaced by control circuit25and that switches22ato22cand load terminals TL4to TL6are added.

Load terminals TL4to TL6are connected with a load56caused to consume the regenerated power generated in load52. For example, load56includes three resistance elements or three inductors. The three resistance elements (or three inductors) have first terminals each connected to a corresponding one of load terminals TL4to TL6and second terminals connected to each other.

Switches22ato22chave first terminals connected respectively to output terminals TO1to TO3and second terminals connected respectively to load terminals TL4to TL6. Switches21ato21cand22ato22care controlled by control circuit25.

When control signal CNT is at “L” level, control circuit25obtains an effective current flowing through load52based on the output signals of current detectors9ato9c, and determines that load52is performing regeneration running when the effective current has a negative value (i.e., when the effective current flows out of load52) and determines that load52is performing power running when the effective current has a positive value (i.e., when the effective current flows into load52).

In the case in which load52is performing regeneration running, control circuit25turns on switches21ato21calone among switches21ato21cand22ato22cwhen the absolute value of the effective current is smaller than a threshold current and turns on all of switches21ato21cand22ato22cwhen the absolute value of the effective current is greater than the threshold current. This allows the regenerated current generated in load52to be consumed in load55alone when the regenerated current generated in load52is relatively small and allows the regenerated current to be consumed in loads55and56when the regenerated current generated in load52is relatively large. The other configuration and operation are the same as those of Embodiment 4, which will not be described repetitively.

Embodiment 5 achieves the same effects as those of Embodiment 4. Additionally, since the number of loads for the consumption of regenerated power is changed depending on the magnitude of the regenerated current generated in load52, Embodiment 5 can reduce variations in the voltages at output terminals TO1to TO3associated with on/off of switches21ato21cand22ato22c.

Although two pairs of switches21ato21cand22ato22cand loads55and56are provided in Embodiment 5, the present invention is not limited to this. Three or more pairs of switches and loads may be provided, and the number of switches that are turned on can be changed depending on the magnitude of the regenerated current generated in load52.

It should be construed that the embodiments disclosed herein are given by way of illustration in all respects, not by way of limitation. It is therefore intended that the scope of the present invention is defined by claims, not only by the embodiments described above, and encompasses all modifications and variations equivalent in meaning and scope to the claims.

REFERENCE SIGNS LIST