JP2014093900A - Electric power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power conversion system capable of stably supplying AC power even if a failure occurs in an AC power supply.SOLUTION: The electric power conversion system 1 includes a switching section 2 and a low-pass filter 3 between an AC power supply 6 and a primary winding 4a of a transformer 4. A load apparatus 7 of a secondary winding 4b of the transformer 4 is connected with a load apparatus 7 and IGBTQ1, Q2 of the switching section 2 are turned on/off so that an output voltage V3 becomes a target voltage Vt. Thus, even if an instantaneous drop occurs in an AC voltage V1 from the AC power supply 6, AC power can be stably supplied to the load apparatus 7.

Description

  The present invention relates to a power converter, and more particularly to a power converter that stably supplies AC power to a load device.

  An uninterruptible power supply device is known as one example to which a power conversion device is applied (see, for example, Patent Document 1). The uninterruptible power supply device is roughly classified into an uninterruptible power supply device of a constant commercial power supply method and an uninterruptible power supply device of a constant inverter power supply method. The power conversion efficiency of the uninterruptible power supply device of the constant commercial power supply system is higher than the power conversion efficiency of the uninterruptible power supply apparatus of the constant inverter power supply system.

  In the uninterruptible power supply of the commercial power supply system, an AC switch is provided between the AC power supply and the load device. In addition, an AC / DC converter for mutually converting AC power and DC power and a power storage device capable of charging / discharging DC power are connected in parallel with the AC switch to the AC power source.

  When the AC power supply is normal, the AC switch is turned on, and AC power is supplied from the AC power supply to the load device via the AC switch. Moreover, AC power is converted into DC power by the AC / DC converter and stored in the power storage device.

  When an abnormality such as a power failure occurs in the AC power supply, the AC switch is turned off, and the AC power supply and the load device are disconnected. Moreover, the DC power of the power storage device is converted into AC power by the AC / DC converter and supplied to the load device. Therefore, even when an abnormality occurs in the AC power supply, the operation of the load device can be continued during the period in which the DC power is stored in the power storage device.

JP 2006-187089 A

  However, in the conventional uninterruptible power supply, when switching the supply of AC power to the load device from the AC power supply to the AC / DC converter, there is a problem that a so-called instantaneous drop occurs, in which the AC voltage drops for a moment. .

  Therefore, a main object of the present invention is to provide a power conversion device that can stably supply AC power to a load device even when an abnormality occurs in the AC power supply.

  The power conversion device according to the present invention includes a plurality of input terminals that receive a first AC voltage from an AC power source, a plurality of output terminals that are connected to the load device, and a plurality of input terminals each of which includes a plurality of input terminals. And a plurality of terminals of the primary winding connected to second electrodes of the plurality of semiconductor switching elements, respectively, and a plurality of terminals of the secondary winding respectively connected to a plurality of output terminals. And a controller that turns on and off the plurality of semiconductor switching elements so that the second AC voltage appearing at the plurality of output terminals becomes a target voltage.

  Preferably, it further includes a low-pass filter interposed between the second electrodes of the plurality of semiconductor switching elements and the plurality of terminals of the primary winding.

  In addition, preferably, when the first AC voltage is higher than the first lower limit voltage, the AC power is converted to DC power and stored in the power storage device when the first AC voltage is higher than the first lower limit voltage. Is lower than the first lower limit voltage, an AC / DC converter is provided that converts the DC power of the power storage device into AC power and outputs the AC power to the output terminal. The control unit controls the semiconductor switching element and the AC / DC converter so that the second AC voltage becomes the target voltage.

  Preferably, the control unit fixes the plurality of semiconductor switching elements in an OFF state when the first AC voltage is lower than a second lower limit voltage lower than the first lower limit voltage.

  Preferably, the AC voltage output from the plurality of terminals of the secondary winding is higher than the AC voltage applied to the plurality of terminals of the primary winding.

  In the power converter according to the present invention, a plurality of semiconductor switching elements are connected in parallel between the AC power supply and a plurality of terminals of the primary winding of the transformer, and a plurality of terminals of the secondary winding of the transformer are used as a load device. The plurality of semiconductor switching elements are turned on / off so that the output voltage becomes the target voltage. Therefore, even if an abnormality occurs in the AC power supply, AC power can be stably supplied to the load device.

It is a circuit block diagram which shows the structure of the power converter device which concerns on Embodiment 1 of this invention. It is a time chart which shows the PWM control system performed with the power converter device shown in FIG. It is a figure which shows the waveform of the PWM control signal shown in FIG. 2 is a time chart showing a relationship between a duty ratio of a PWM control signal shown in FIG. 1 and an AC voltage V2. It is a time chart which shows the effect of the power converter device shown in FIG. It is a circuit block diagram which shows the structure of the power converter device which concerns on Embodiment 2 of this invention. It is a circuit block diagram which shows the structure of the control part shown in FIG. It is another time chart which shows the effect of the power converter device shown in FIG. FIG. 10 is a circuit block diagram showing a modification of the second embodiment. FIG. 6 is a circuit block diagram illustrating a configuration of a power conversion device according to a third embodiment. FIG. 6 is a circuit block diagram illustrating a configuration of a power conversion device according to a fourth embodiment.

[Embodiment 1]
As shown in FIG. 1, the power conversion device 1 according to the first embodiment of the present invention includes input terminals TI1, TI2, output terminals TO1, TO2, a switching unit 2, a low-pass filter 3, a transformer 4, and a control unit. 5 is provided. Switching unit 2 includes IGBTs (Insulated Gate Bipolar Transistors) Q1, Q2 and diodes D1, D2. Low-pass filter 3 includes reactors L1 and L2 and a capacitor C1. The transformer 4 includes a primary winding 4a and a secondary winding 4b.

  The input terminals TI1 and TI2 are connected to output terminals 2a and 2b of the single-phase two-wire AC power source 6, respectively. The output terminals TO1 and TO2 are connected to the input terminals 7a and 7b of the single-phase two-wire load device 7, respectively.

  The collectors of IGBTs Q1 and Q2 are connected to input terminals TI1 and TI2, respectively. Diodes D1 and D2 are connected in antiparallel to IGBTs Q1 and Q2, respectively. The IGBTs Q1 and Q2 are turned on / off in a cycle sufficiently shorter than the cycle of the AC voltage V1 from the AC power supply 6 in response to PWM (pulse width modulation) control signals S1 and S2 from the control unit 5, respectively. Turn off. When the IGBTs Q1 and Q2 are turned on / off, the AC voltage V1 from the AC power supply 6 is converted into a pulse voltage string Vp.

  Reactors L1 and L2 have one terminals connected to the emitters of IGBTs Q1 and Q2, respectively, and the other terminals connected to two terminals at both ends of primary winding 4a of transformer 4, respectively. Capacitor C1 is connected between the other terminals of reactors L1 and L2. The low-pass filter 3 converts the pulse voltage train Vp generated by the switching unit 2 into an alternating voltage V2. The amplitude of the AC voltage V2 is smaller than the amplitude of the AC voltage V1 output from the AC power supply 6. Further, the amplitude of the AC voltage V2 can be adjusted by adjusting the duty ratio of the PWM control signals S1 and S2.

  Two terminals of the secondary winding 4b of the transformer 4 are connected to output terminals TO1 and TO2, respectively. The number of turns of the secondary winding 4b is set to be larger than the number of turns of the primary winding 4a, and the secondary winding 4b has a higher amplitude than the amplitude of the AC voltage V2 applied between the two terminals of the primary winding 4a. The amplitude of the AC voltage V3 appearing between the two terminals is larger. The transformer 4 boosts the AC voltage V2 that has passed through the low-pass filter 3 and outputs the boosted voltage to the output terminals TO1 and TO2. In normal times, the amplitude of the AC voltage V1 from the AC power supply 6 is equal to the amplitude of the AC voltage V3 output from the transformer 4.

  The control unit 5 generates PWM control signals S1 and S2 based on the AC voltage V1 between the input terminals TI1 and TI2 and the AC voltage V3 between the output terminals TO1 and TO2. The waveforms of the PWM control signals S1 and S2 are the same. The control unit 5 operates in synchronization with the input voltage V1, and adjusts the duty ratio of the PWM control signals S1 and S2 so that the amplitude of the output voltage V3 becomes the target voltage Vt. The target voltage Vt is equal to the amplitude of the AC voltage V1 when the AC power supply 6 is normal.

  When the AC power supply 6 is normal, the duty ratio of the PWM control signals S1 and S2 is maintained at a predetermined value, the amplitude of the AC voltage V1 from the AC power supply 6, the target voltage Vt, and the AC output from the power converter 1. The amplitude of the voltage V3 is equal. When an abnormality occurs in the AC power supply 6 and the amplitude of the AC voltage V1 decreases below the rated value, the duty ratio of the PWM control signals S1 and S2 becomes larger than a predetermined value, and the AC output from the power conversion device 1 The amplitude of the voltage V3 is maintained at the target voltage Vt.

  2A and 2B are time charts showing the PWM control method. As shown in FIG. 2A, the AC voltage V1 from the AC power supply 6 changes in a sine wave shape. The IGBTs Q1 and Q2 are turned on / off at a predetermined cycle. The sinusoidal AC voltage V1 passes through the switching unit 2 only when the IGBTs Q1 and Q2 are turned on, and becomes a pulse voltage string Vp.

  When the duty ratio of the PWM control signals S1 and S2 is reduced, the pulse width of the pulse voltage train Vp is narrowed, and the amplitude of the AC voltage V2 is reduced as shown by a one-dot chain line in FIG. When the duty ratio of the PWM control signals S1 and S2 is increased, the pulse width of the pulse voltage train Vp is increased, and the amplitude of the AC voltage V2 is increased as shown by the solid line in FIG. Therefore, the amplitude of AC voltage V2 can be adjusted by adjusting the duty ratio of PWM control signals S1 and S2.

  FIG. 3 is a time chart showing waveforms of the PWM control signals S1 and S2. In FIG. 3, when the PWM control signals S1 and S2 are at “H” level, the IGBTs Q1 and Q2 are turned on, and when the PWM control signals S1 and S2 are at “L” level, the IGBTs Q1 and Q2 are turned off. The sum of the on time A and the off time B of the IGBTs Q1 and Q2 is a switching period λ. The switching period λ is kept constant. The ratio A / λ between the ON time A and the switching period λ is the duty ratio DR. As the ON time A is shortened from the predetermined value A1, the pulse width of the pulse voltage train Vp becomes narrower and the AC voltage V2 decreases. Conversely, as the ON time A is increased, the pulse width of the pulse voltage train Vp becomes wider and the AC voltage V2 increases.

  When the AC power supply 6 is normal, the ratio of the on time A and the off time B is determined by the winding ratio between the primary winding 4a and the secondary winding 4b of the transformer 4. For example, when the turns ratio of the primary winding 4a and the secondary winding 4b of the transformer 4 is 1: 2, the ratio of the on time A1 to the off time B is 1: 1, and the duty ratio DR is 1 / 2. When the winding ratio of the primary winding 4a and the secondary winding 4b of the transformer 4 is 2: 3, the ratio of the on time A1 to the off time B is 2: 1, and the duty ratio DR is 2 / 3 When the AC power supply 6 becomes abnormal and the AC voltage V1 decreases, the duty ratio DR is increased so that the AC voltage V2 becomes the target voltage Vt.

  FIG. 4 is a waveform diagram showing the relationship between the AC voltage V2 on the primary winding 4a side of the transformer 4 and the duty ratio DR. When the amplitude of the input voltage V1 is constant, the amplitude of the AC voltage V2 could be changed from 15.6% to 75.7% of the maximum value by changing the duty ratio DR from 0.2 to 0.8. . Thus, when the amplitude of the input voltage V1 is constant, the amplitude of the AC voltage V2 can be adjusted by adjusting the duty ratio DR. Further, when the amplitude of the input voltage V1 decreases, the amplitude of the AC voltage V2 can be maintained at the target voltage Vt by adjusting the duty ratio DR.

  FIG. 5 is a diagram illustrating waveforms of the AC voltages V1 and V3 when the instantaneous drop occurs. In the period Td of FIG. 5, the AC voltage V1 from the AC power supply 6 is instantaneously decreased, but no instantaneous voltage decrease occurs in the AC voltage V3 output from the power converter 1.

  In the first embodiment, the switching unit 2 and the low-pass filter 3 are provided between the AC power source 6 and the primary winding 4a of the transformer 4, and the secondary winding 4b of the transformer 4 is connected to the load device 7. The IGBTs Q1 and Q2 of the switching unit 2 are turned on / off so that the output voltage V3 becomes the target voltage Vt. Therefore, even if an abnormality occurs in the AC power supply 6, AC power can be stably supplied to the load device 7.

[Embodiment 2]
FIG. 6 is a circuit block diagram showing the configuration of the uninterruptible power supply 10 according to the second embodiment of the present invention, and is a diagram contrasted with FIG. Referring to FIG. 6, this uninterruptible power supply 10 is obtained by adding a storage battery B1, an AC / DC converter 11, and a low-pass filter 12 to the power converter 1 of FIG.

  AC / DC converter 11 includes IGBTs Q11 to Q14 and diodes D11 to D14. The IGBTs Q11 and Q12 are connected in series between the positive electrode and the negative electrode of the storage battery B1. The IGBTs Q13 and Q14 are connected in series between the positive electrode and the negative electrode of the storage battery B1. Diodes D11-D14 are connected in antiparallel to IGBTs Q11-Q14, respectively. IGBTs Q11 to Q14 are turned on / off in a cycle sufficiently shorter than the cycle of AC voltage V1 from AC power supply 6 in response to PWM control signals S11 to S14 from control unit 5, respectively. For example, a positive voltage can be applied to the load device 7 by turning on the IGBTs Q11 and Q14 and turning off the IGBTs Q12 and Q13. Further, a negative voltage can be applied to the load device 7 by turning on the IGBTs Q12 and Q13 and turning off the IGBTs Q11 and Q14.

  The AC / DC converter 11 is controlled by the control unit 5, converts the AC power from the transformer 4 into DC power and stores it in the storage battery B1 in the charging mode, and stores the DC power of the storage battery B1 in the discharging mode in the AC mode. It is converted into electric power and supplied to the load device 7.

  Low-pass filter 12 includes a reactor L11 and a capacitor C11. Reactor L11 is connected between the emitter of IGBT Q11 and output terminal TO1. The emitter of the IGBT Q13 is connected to the output terminal TO2. The capacitor C11 is connected between the output terminals TO1 and TO2. The low-pass filter 12 allows the AC voltage V3 from the transformer 4 to pass through the AC / DC converter 11 and blocks noise of the switching frequency generated by the AC / DC converter 11.

  The control unit 5 has a first lower limit voltage VL1 and a second lower limit voltage VL2 that is lower than the first lower limit voltage VL1. The first lower limit voltage VL1 is set to 85% of the rated voltage, for example, and the first lower limit voltage VL2 is set to 60% of the rated voltage, for example. When the AC voltage V1 from the AC power supply 6 is higher than the first lower limit voltage VL1 in the first case (V1> VL1), the control unit 5 sets the AC voltage V1 to the first and second lower limit voltages VL1 and VL2. The switching unit 2 and the AC / DC conversion are divided into a second case (VL1> V1> VL2) and a third case (VL2> V1) in which the AC voltage V1 is lower than the second lower limit voltage VL2. The device 11 is controlled.

  In the first case (V1> VL1), the control unit 5 performs on / off control of the IGBTs Q1 and Q2 of the switching unit 2 so that the output AC voltage V3 matches the target voltage Vt, and the AC / DC converter 11 Set to charging mode. At this time, the AC / DC converter 11 converts AC power into DC power and stores it in the storage battery B1.

  In the second case (VL1> V1> VL2), the control unit 5 performs on / off control of the IGBTs Q1 and Q2 of the switching unit 2 so that the output AC voltage V3 matches the target voltage Vt, and AC / DC conversion. The vessel 11 is set to the discharge mode. At this time, the AC / DC converter 11 converts the DC power of the storage battery B1 into AC power and supplies it to the output terminals TO1 and TO2.

  In the third case (VL2> V1), the control unit 5 fixes the IGBTs Q1 and Q2 of the switching unit 2 to the OFF state and sets the AC / DC converter 11 to the discharge mode. At this time, the AC / DC converter 11 converts the DC power of the storage battery B1 into AC power and supplies it to the output terminals TO1 and TO2.

  In the first and second cases, it is determined that there is a possibility that the AC power supply 6 may return to a normal state because of the instantaneous drop, and the IGBTs Q1 and Q2 are turned on / off. In the third case, it is determined that the AC power supply 6 is not expected to return to the normal state, and the IGBTs Q1 and Q2 are fixed in the off state.

  FIG. 7 is a circuit block diagram illustrating the configuration of the control unit 5 shown in FIG. In FIG. 7, the control unit 5 includes a sine wave reference unit 15, subtractors 16, 18, 20, a voltage controller 17, a limiter 19, a current controller 21, a PWM control circuit 22, and an adjustment controller 23. The uninterruptible power supply 10 also includes current sensors 24 and 25. Current sensor 24 detects a current flowing through reactors L1 and L2. The current sensor 25 detects a load current.

  The sine wave reference unit 15 generates a voltage command value based on the AC voltage V <b> 1 from the AC power supply 6. This voltage command value changes sinusoidally with the same phase as the AC voltage V1. The subtracter 16 obtains a deviation between the voltage command value generated by the sine wave reference unit 15 and the AC voltage V3. The voltage controller 17 generates a current command value based on the deviation generated by the subtracter 16. The subtracter 18 obtains a deviation between the current command value generated by the voltage controller 17 and the load current detected by the current sensor 24. The limiter 19 generates a current control reference signal value for flowing a current equal to or lower than the upper limit value based on the deviation generated by the subtracter 18.

  The subtracter 20 obtains a deviation between the current control reference signal value generated by the limiter 19 and the current detected by the current sensor 24. The current controller 21 generates a voltage command value based on the deviation generated by the subtracter 20. The PWM control circuit 22 generates the PWM control signals S1 and S2 based on the AC voltage V1 and the voltage command value from the current controller 21. The adjustment controller 23 also generates PWM control signals S11 to S14 based on the AC voltages V1 and V3 and the detection result of the current sensor 25.

  FIG. 8 is a diagram illustrating waveforms of AC voltages V1 and V3 at the time of a power failure. In FIG. 8, the AC voltage V <b> 1 from the AC power supply 6 gradually decreases, but no voltage decrease occurs in the AC voltage V <b> 3 output from the power converter 1.

  In the second embodiment, the same effect as in the first embodiment can be obtained, and since the storage battery B1, the AC / DC converter 11, and the low-pass filter 12 are provided, even if a power failure occurs, the storage battery B1 The operation of the load device 7 can be continued while the DC power is stored.

  As shown in FIG. 9, the storage battery B <b> 1 may be replaced with a double layer capacitor 26. The double layer capacitor 26 can be easily downsized as compared to the storage battery B1, and can save space. Further, since the double layer capacitor 26 is hardly deteriorated by repeated charge and discharge, it is possible to reduce the trouble of maintenance such as replacement and to improve the economic efficiency.

[Embodiment 3]
FIG. 10 is a circuit block diagram showing the configuration of the power conversion device 31 according to the third embodiment of the present invention, and is a diagram compared with FIG. The power conversion device 1 in FIG. 1 is a single-phase type, whereas the power conversion device 31 is a three-phase type.

  That is, the power conversion device 10 includes input terminals TI1 to TI3, output terminals TO1 to TO3, a switching unit 32, a low-pass filter 33, a transformer 34, and a control unit 35. Switching unit 2 includes IGBTs Q1 to Q3 and diodes D1 to D3. Low-pass filter 33 includes reactors L1 to L3 and capacitors C1 to C3. The transformer 34 includes a primary winding 34a and a secondary winding 34b.

  The input terminals TI <b> 1 to TI <b> 3 are connected to three output terminals of a three-phase three-wire AC power supply 36, respectively. The output terminals TO1 to TO3 are connected to three input terminals of a three-phase three-wire load device 37, respectively.

  The collectors of IGBTs Q1 to Q3 are connected to input terminals TI1 to TI3, respectively. Diodes D1-D3 are connected in antiparallel to IGBTs Q1-Q3, respectively. The IGBTs Q1 to Q3 are turned on / off in a cycle sufficiently shorter than the cycle of the AC voltage V1 from the AC power supply 36 in response to the PWM control signals S1 to S3 from the control unit 5, respectively. When the IGBTs Q1 to Q3 are turned on / off, the AC voltage V1 from the AC power supply 36 is converted into a pulse voltage string Vp.

  Reactors L1-L3 have one terminals connected to the emitters of IGBTs Q1-Q3, respectively, and the other terminals connected to the three terminals of primary winding 34a of transformer 34, respectively. Capacitor C1 is connected between the other terminals of reactors L1 and L2. Capacitor C2 is connected between the other terminals of reactors L2 and L3. Capacitor C3 is connected between the other terminals of reactors L3 and L1. The low-pass filter 33 including the reactors L1 to L3 and the capacitors C1 to C3 converts the pulse voltage string Vp generated by the switching unit 32 into an AC voltage V2. The amplitude of the AC voltage V2 is smaller than the amplitude of the AC voltage V1 output from the AC power supply 36. Further, the amplitude of the AC voltage V2 can be adjusted by adjusting the duty ratio of the PWM control signals S1 to S3.

  Three terminals of the secondary winding 34b of the transformer 34 are connected to output terminals TO1 to TO3, respectively. The number of turns of the secondary winding 34b is set to be larger than the number of turns of the primary winding 34a, and the secondary winding 34b is larger than the amplitude of the AC voltage V2 applied between the three terminals of the primary winding 34a. The amplitude of the AC voltage V3 appearing between these three terminals is larger. The transformer 34 boosts the AC voltage V2 that has passed through the low-pass filter 33 and outputs the boosted voltage to the output terminals TO1 to TO3. In normal times, the amplitude of the AC voltage V1 from the AC power source 36 is equal to the amplitude of the AC voltage V3 output from the transformer 34.

  The control unit 35 generates PWM control signals S1 to S3 based on the AC voltage V1 between the input terminals TI1 to TI3 and the AC voltage V3 between the output terminals TO1 to TO3. The waveforms of the PWM control signals S1 to S3 are the same. The control unit 35 operates in synchronization with the input voltage V1 and adjusts the duty ratio of the PWM control signals S1 to S3 so that the amplitude of the output voltage V3 becomes the target voltage Vt. The target voltage Vt is equal to the amplitude of the AC voltage V1 when the AC power supply 36 is normal.

  When the AC power supply 36 is normal, the duty ratio of the PWM control signals S1 to S3 is maintained at a predetermined value, the amplitude of the AC voltage V1 from the AC power supply 36, the target voltage Vt, and the AC output from the power converter 31. The amplitude of the voltage V3 is equal. When an abnormality occurs in the AC power supply 36 and the amplitude of the AC voltage V1 is lower than the rated value, the duty ratio of the PWM control signals S1 to S3 becomes larger than a predetermined value, and the AC output from the power conversion device 31. The amplitude of the voltage V3 is maintained at the target voltage Vt. Since other configurations and operations are the same as those in the first embodiment, description thereof will not be repeated. In the third embodiment, the same effect as in the first embodiment can be obtained.

[Embodiment 4]
FIG. 11 is a circuit block diagram showing the configuration of the uninterruptible power supply 40 according to the fourth embodiment of the present invention, and is a diagram compared with FIG. Referring to FIG. 11, uninterruptible power supply 40 is obtained by adding storage battery B1, AC / DC converter 41, and low-pass filter 42 to power converter 31 in FIG.

  AC / DC converter 41 includes IGBTs Q11 to Q16 and diodes D11 to D16. The IGBTs Q11 and Q12 are connected in series between the positive electrode and the negative electrode of the storage battery B1. The IGBTs Q13 and Q14 are connected in series between the positive electrode and the negative electrode of the storage battery B1. The IGBTs Q15 and Q16 are connected in series between the positive electrode and the negative electrode of the storage battery B1. Diodes D11-D16 are connected in antiparallel to IGBTs Q11-Q16, respectively. IGBTs Q11 to Q16 are turned on / off in a cycle sufficiently shorter than the cycle of AC voltage V1 from AC power supply 36 in response to PWM control signals S11 to S14 from control unit 5, respectively. By turning on / off the IGBTs Q11 to Q16 at a predetermined timing, it is possible to convert the DC power of the storage battery B1 into three-phase AC power.

  The AC / DC converter 41 is controlled by the control unit 35. In the charging mode, the AC power from the transformer 34 is converted into DC power and stored in the storage battery B1, and in the discharging mode, the DC power of the storage battery B1 is AC. It is converted into electric power and supplied to the load device 37.

  Low-pass filter 42 includes reactors L11 to L13 and capacitors C11 to C13. Reactors L11-L13 have one terminals connected to the emitters of IGBTs Q11, Q13, Q15, respectively, and the other terminals connected to output terminals TO1-TO3, respectively. The capacitor C11 is connected between the output terminals TO1 and TO2. The capacitor C12 is connected between the output terminals TO2 and TO3. The capacitor C13 is connected between the output terminals TO3 and TO1. The low-pass filter 42 allows the AC voltage V3 from the transformer 34 to pass through the AC / DC converter 41 and blocks noise of the switching frequency generated by the AC / DC converter 41.

  The control unit 35 has a first lower limit voltage VL1 and a second lower limit voltage VL2 that is lower than the first lower limit voltage VL1. The first lower limit voltage VL1 is set to 85% of the rated voltage, for example, and the first lower limit voltage VL2 is set to 60% of the rated voltage, for example. When the AC voltage V1 from the AC power supply 6 is higher than the first lower limit voltage VL1 in the first case (V1> VL1), the control unit 5 sets the AC voltage V1 to the first and second lower limit voltages VL1 and VL2. The switching unit 32 and the AC / DC conversion are divided into a second case (VL1> V1> VL2) in between and a third case (VL2> V1) in which the AC voltage V1 is lower than the second lower limit voltage VL2. The device 41 is controlled.

  In the first case (V1> VL1), the control unit 35 performs on / off control of the IGBTs Q1 to Q3 of the switching unit 32 so that the output AC voltage V3 matches the target voltage Vt, and the AC / DC converter 41. Set to charging mode. At this time, the AC / DC converter 41 converts AC power into DC power and stores it in the storage battery B1.

  In the second case (VL1> V1> VL2), the control unit 35 performs on / off control of the IGBTs Q1 to Q3 of the switching unit 32 so that the output AC voltage V3 matches the target voltage Vt, and AC / DC conversion. The device 41 is set to the discharge mode. At this time, the AC / DC converter 41 converts the DC power of the storage battery B1 into three-phase AC power and supplies it to the output terminals TO1 to TO3.

  In the third case (VL2> V1), the control unit 35 fixes the IGBTs Q1 to Q3 of the switching unit 32 in the off state and sets the AC / DC converter 41 to the discharge mode. At this time, the AC / DC converter 41 converts the DC power of the storage battery B1 into three-phase AC power and supplies it to the output terminals TO1 to TO3.

  In the first and second cases, it is determined that there is a possibility that the AC power source 36 may return to a normal state because of the instantaneous drop, and the IGBTs Q <b> 1 to Q <b> 3 are controlled on / off. In the third case, it is determined that the AC power supply 36 is not expected to return to the normal state, and the IGBTs Q1 to Q3 are fixed to the off state. In the fourth embodiment, the same effect as in the second embodiment can be obtained.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1,31 power converter, 2,32 switching unit, 3,12,33,42 low-pass filter, 4,34 transformer, 4a, 34a primary winding, 4b, 34b secondary winding, 5,35 control 6, 36 AC power supply, 3, 37 load device, 10, 40 uninterruptible power supply device, 11, 41 AC / DC converter, 15 sine wave reference unit, 16, 18, 20 subtractor, 17 voltage controller, 19 limiter, 21 current controller, 22 PWM control circuit, 23 adjustment controller, 24, 25 current sensor, 26 double layer capacitor, TI1-TI3 input terminal, TO1-TO3 output terminal, Q1-Q3, Q11-Q16 IGBT, D1-D3, D11-D16 diode, L1-L3, L11-L13 reactor, C1-C3, C11-C13 capacitor, B1 storage battery.

Claims (5)

A plurality of input terminals receiving a first AC voltage from an AC power source;
A plurality of output terminals connected to the load device;
A plurality of semiconductor switching elements each having a first electrode connected to the plurality of input terminals;
A transformer in which a plurality of terminals of a primary winding are respectively connected to second electrodes of the plurality of semiconductor switching elements, and a plurality of terminals of a secondary winding are respectively connected to the plurality of output terminals;
A power converter comprising: a controller that turns on and off the plurality of semiconductor switching elements so that the second AC voltage appearing at the plurality of output terminals becomes a target voltage.   Furthermore, the power converter device of Claim 1 provided with the low-pass filter inserted between the 2nd electrode of these semiconductor switching elements, and the some terminal of the said primary winding. Furthermore, when the first AC voltage is higher than the first lower limit voltage, the AC power is converted into DC power and stored in the power storage device when the first AC voltage is connected to the plurality of output terminals, and the first AC voltage is An AC / DC converter that converts the DC power of the power storage device into AC power and outputs it to the output terminal when lower than the first lower limit voltage;
The power converter according to claim 1 or 2, wherein the control unit controls the semiconductor switching element and the AC / DC converter so that the second AC voltage becomes the target voltage.   4. The control unit according to claim 3, wherein the control unit fixes the plurality of semiconductor switching elements in an OFF state when the first AC voltage is lower than a second lower limit voltage lower than the first lower limit voltage. 5. Power converter.   5. The power according to claim 1, wherein an alternating voltage output from a plurality of terminals of the secondary winding is higher than an alternating voltage applied to the plurality of terminals of the primary winding. Conversion device.

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