Power converter

Abstract

To provide a power conversion device which can stabilize AC voltage of a distribution line.SOLUTION: An uninterruptible power supply device 6 comprises: a converter 11 which converts AC power to be received from a distribution line 4 into DC power; an inverter 13 which converts the DC power into the AC power to be supplied to a load 8; and a control device 15 which controls the converter 11 to absorb reactive power for compensating a changed portion ΔVS of AC voltage VS of the distribution line 4 from the distribution line 4 when the AC voltage VS of the distribution line 4 changes.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a power conversion device, and more particularly to a power conversion device including a forward converter and a reverse converter.

Background Art

[0002] For example, Japanese Patent Application Laid-Open No. 2011-55570 discloses a power conversion device including a forward converter that converts AC power received from a distribution line into DC power, a reverse converter that converts DC power into AC power and supplies it to a first load, and a control device that controls the forward converter to supply reactive power for compensating for a change in the AC voltage of the distribution line from the forward converter to the distribution line to make the power factor 1, which is consumed by a second load connected to the distribution line.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional power conversion device, when the power consumption of the second load fluctuates, the AC voltage of the distribution line fluctuates, which has a problem of affecting the power system adversely.

[0005] Therefore, the main object of the present disclosure is to provide a power conversion device capable of stabilizing the AC voltage of the distribution line.

Means for Solving the Problems

[0006] The power conversion device according to the present disclosure includes a forward converter that converts AC power received from a distribution line into DC power, a reverse converter that converts DC power into AC power and supplies it to a first load, and a control device that controls the forward converter to absorb reactive power for compensating for a change in the AC voltage of the distribution line from the distribution line when the AC voltage of the distribution line changes. [Effects of the Invention]

[0007] In the power converter according to this disclosure, when the AC voltage of the distribution line changes, the forward converter is controlled to absorb reactive power from the distribution line to compensate for the change in the AC voltage of the distribution line. Therefore, the AC voltage of the distribution line can be stabilized. [Brief explanation of the drawing]

[0008] [Figure 1] This is a circuit block diagram showing the main components of a power system according to Embodiment 1 of the present disclosure. [Figure 2] Figure 1 is a circuit block diagram showing the configuration of the uninterruptible power supply (UPS). [Figure 3] Figure 2 is a circuit diagram showing the configuration of the converter and inverter. [Figure 4] This block diagram shows the configuration of the control device as shown in Figure 1. [Figure 5] The block diagram shows the configuration of the control circuit as shown in Figure 4. [Figure 6] Figure 5 is a block diagram showing the configuration of the control unit 32. [Figure 7] Figure 6 shows the operation of the AC voltage control unit and limiter. [Figure 8] This is a circuit block diagram showing the main parts of a control unit included in a power system according to Embodiment 2 of the present disclosure. [Figure 9] Figure 8 shows the operation of the AC voltage control unit and limiter. [Modes for carrying out the invention]

[0009] [Embodiment 1] Figure 1 is a circuit block diagram showing the main components of a power system according to Embodiment 1 of the present disclosure. In this power system, three-phase AC voltage is actually supplied, but for the sake of simplicity in the drawings and explanation, only the parts related to single-phase AC voltage are shown in Figure 1. In Figure 1, the power system comprises a commercial AC power source 1, a transmission line 2, an interconnection transformer 3, a distribution line 4, loads 5, 8, an uninterruptible power supply 6, and a battery 7.

[0010] Commercial AC power source 1 supplies AC power at commercial frequency to transmission line 2. Transmission line 2 is connected to distribution line 4 via interconnection transformer 3. Load 5 (second load) is driven by AC power received from distribution line 4.

[0011] The uninterruptible power supply (UPS) 6 (power converter) converts the AC power received from the distribution line 4 into DC power when the commercial AC power supply 1 is functioning properly. It stores this DC power in the battery 7 and also converts it back into AC power at the commercial frequency to supply to the load 8. The battery 7 (power storage device) stores DC power. A capacitor may be connected instead of the battery 7. The load 8 (first load) is driven by the AC power supplied by the UPS 6.

[0012] Furthermore, in the event of a power outage of the commercial AC power supply 1, the uninterruptible power supply 6 converts the DC power from the battery 7 into AC power at the commercial frequency and supplies it to the load 8. Therefore, even if a power outage occurs in the commercial AC power supply 1, the operation of the load 8 can continue as long as DC power is stored in the battery 7.

[0013] Furthermore, if the AC voltage VS of the distribution line 4 changes due to a change in the power consumption of the load 5, the uninterruptible power supply 6 absorbs reactive power from the distribution line 4 to compensate for that change and stabilizes the AC voltage VS of the distribution line 4.

[0014] That is, when the AC voltage VS of the distribution line 4 drops, the uninterruptible power supply device 6 absorbs the leading reactive power from the distribution line 4 to raise the AC voltage VS of the distribution line 4. Further, when the AC voltage VS of the distribution line 4 rises, the uninterruptible power supply device 6 absorbs the lagging reactive power from the distribution line 4 to lower the AC voltage VS of the distribution line 4.

[0015] Note that absorbing the leading reactive power from the distribution line 4 is synonymous with supplying the lagging reactive power to the distribution line 4. Also, absorbing the lagging reactive power from the distribution line 4 is synonymous with supplying the leading reactive power to the distribution line 4.

[0016] FIG. 2 is a circuit block diagram showing the configuration of the uninterruptible power supply device 6. In FIG. 2, this uninterruptible power supply device 6 includes an AC input terminal T1, a battery terminal T2, and an AC output terminal T3. The AC input terminal T1 receives commercial frequency AC power from the distribution line 4. The battery terminal T2 is connected to the battery 7. The AC output terminal T3 is connected to the load 8.

[0017] Note that this uninterruptible power supply device actually receives three-phase AC voltages VU, VV, VW from three distribution lines 4 and supplies a three-phase AC voltage to the load 8. However, for the sake of simplicity of the drawing and description, only the part related to the single-phase AC voltage VS is shown in FIG. 2. The AC voltage VS corresponds to any one of the three-phase AC voltages VU, VV, VW (for example, VU).

[0018] This uninterruptible power supply device 6 further includes switches S1 to S3, capacitors C1 to C3, reactors L1 to L3, current detectors CD1 to CD3, a converter 11, a DC line DL, a bidirectional chopper 12, an inverter 13, an operation unit 14, and a control device 15.

[0019] Switch S1 and reactor L1 are connected in series between the AC input terminal T1 and the AC node 11a of the converter 11. Switch S1 is controlled by the control device 15. When AC power is supplied normally from the commercial AC power supply 1 (when the commercial AC power supply 1 is healthy), switch S1 is turned on. When AC power is no longer supplied normally from the commercial AC power supply 1 (when the commercial AC power supply 1 fails), switch S1 is turned off.

[0020] The current detector CD1 detects the current Ii flowing between the power distribution line 4 and the converter 11, and outputs a signal Iif indicating the detected value to the control device 15. The instantaneous value of the AC input voltage VS appearing at the AC input terminal T1 is detected by the control device 15. Based on the detected value of the AC input voltage VS, the control device 15 determines whether or not a power outage has occurred. The control device 15 also controls the converter 11 and other components based on the detected value of the AC input voltage VS.

[0021] Capacitor C1 is connected between node N1, which is between switch S1 and reactor L1, and the neutral point NP. Capacitor C1 and reactor L1 constitute an AC filter. This AC filter is a low-pass filter that allows commercial frequency AC power to pass through, preventing switching frequency signals generated in converter 11 from passing through the power distribution line 4.

[0022] The converter 11 is a well-known type containing multiple transistors and multiple diodes, and is controlled by the control device 15. When the commercial AC power supply 1 is healthy, the converter 11 converts the AC power received by the AC node 11a into DC power and outputs it to the DC node 11b. The DC node 11b is connected to the DC line DL. The output voltage of the converter 11 is controllable to a desired value. When the commercial AC power supply 1 fails, the operation of the converter 11 is stopped.

[0023] Furthermore, when the commercial AC power supply 1 is functioning normally, if the power consumption of the load 5 fluctuates and the AC voltage VS of the distribution line 4 decreases or increases, the converter 11 absorbs leading or lagging reactive power from the AC node 11a to increase or decrease the AC voltage VS of the distribution line 4. At this time, the converter 11 operates as the main circuit of a self-excited SVC (Static Var Compensator).

[0024] Capacitor C1, reactor L1, and converter 11 constitute a forward converter that converts AC power to DC power. Capacitor C2 is connected to the DC line DL and smooths the voltage of the DC line DL. The instantaneous value of the DC voltage VD appearing on the DC line DL is detected by the control device 15.

[0025] The control device 15 controls the converter 11 so that when the commercial AC power supply 1 is functioning properly, the DC voltage VD of the DC line DL becomes the reference voltage VDR, and the amplitude VSA of the AC voltage VS of the distribution line 4 becomes the reference voltage VSR. When the commercial AC power supply 1 fails, the control device 15 stops the operation of the converter 11. When the amplitude VSA of the AC voltage VS of the distribution line 4 becomes the reference voltage VSR, the effective value of the AC voltage VS is the rated voltage.

[0026] The DC line DL is connected to the high-voltage side node 12a of the bidirectional chopper 12, and the low-voltage side node 12b of the bidirectional chopper 12 is connected to the battery terminal T2 via the reactor L2 and switch S2. Switch S2 is turned on when the uninterruptible power supply is in use and turned off, for example, when the uninterruptible power supply and battery 7 are being maintained. The reactor L2 smooths the current Ib that flows between the bidirectional chopper 12 and the battery 7.

[0027] The bidirectional chopper 12 is a well-known type including multiple transistors and multiple diodes, and is controlled by the control device 15. When the commercial AC power supply 1 is functioning properly, the bidirectional chopper 12 stores the DC power received from the DC line DL in the battery 7, and when the commercial AC power supply 1 fails, it supplies the DC power from the battery 7 to the DC line DL.

[0028] When the bidirectional chopper 12 stores DC power in the battery 7, it steps down the DC voltage VD of the DC line DL and supplies it to the battery 7. Also, when the bidirectional chopper 12 supplies DC power from the battery 7 to the inverter 13, it steps up the terminal voltage VB of the battery 7 and outputs it to the DC line DL.

[0029] The current detector CD2 detects the current Ib flowing between the bidirectional chopper 12 and the battery 7, and outputs a signal Ibf indicating the detected value to the control device 15. The instantaneous value of the terminal voltage VB of the battery 7, which appears at the battery terminal T2, is detected by the control device 15.

[0030] When the commercial AC power supply 1 is functioning properly, the control device 15 controls the bidirectional chopper 12 so that the battery voltage VB becomes the reference voltage VBR. When the commercial AC power supply 1 fails, the control device 15 controls the bidirectional chopper 12 so that the DC voltage VD of the DC line DL becomes the reference voltage VDR.

[0031] The inverter 13 is a well-known inverter comprising multiple transistors and multiple diodes, and is controlled by the control device 15. The inverter 13 converts the DC power received from the DC line DL via the DC node 13a into AC power at commercial frequency and outputs it to the AC node 13b. The output voltage of the inverter 13 is controllable to a desired value.

[0032] The AC node 13b of the inverter 13 is connected to one terminal (node ​​N2) of the switch S3 via the reactor L3, and the other terminal of the switch S3 is connected to the AC output terminal T3. Capacitor C3 is connected between node N2 and the neutral point NP.

[0033] The reactor L3 and capacitor C3 constitute an AC filter. This AC filter is a low-pass filter that allows the commercial frequency AC power generated by the inverter 13 to pass through the AC output terminal T3, while preventing the switching frequency signal generated by the inverter 13 from passing through the AC output terminal T3. The inverter 13, reactor L3, and capacitor C3 constitute an inverse converter that converts DC power to AC power.

[0034] Switch S3 is controlled by the control device 15 and is turned on when the uninterruptible power supply 6 is in operation, and turned off when the uninterruptible power supply 6 is shut down. The instantaneous value of the AC output voltage VO that appears at the AC output terminal T3 is detected by the control device 15.

[0035] The current detector CD3 detects the current Io flowing between the inverter 13 and the load 8, and provides the control device 15 with a signal Iof indicating the detected value. The control device 15 controls the inverter 13 so that the AC output voltage VO becomes a sinusoidal reference voltage VOR.

[0036] The control unit 14 includes multiple buttons operated by the user of the uninterruptible power supply 6, an image display unit that displays various information, and other components. By operating the control unit 14, the user can set various voltages VDR, VBR, and VOR, turn the power of the uninterruptible power supply 6 on and off, and operate the uninterruptible power supply 6 automatically or manually.

[0037] Furthermore, the control device 15 controls the entire uninterruptible power supply 6 based on the AC input voltage VS, AC input current Ii, DC voltage VD, battery voltage VB, battery current Ib, AC output voltage VO, AC output current Io, reference voltages VDR, VBR, VOR, and signals from the operation unit 14.

[0038] Figure 3 is a circuit diagram showing the configuration of the converter 11 and inverter 13. While Figures 1 and 2 only show the portion related to one phase AC voltage of the three-phase AC voltage, Figure 3 shows the portion related to all three phases of AC voltage. Also, while Figure 2 only shows the positive DC line DL, Figure 3 also shows the negative DC line DLn.

[0039] In Figure 3, the converter 11 includes IGBTs (Insulated Gate Bipolar Transistors) Q1-Q6 and diodes D1-D6. The IGBTs constitute the switching elements. The collectors of IGBTs Q1-Q3 are all connected to the positive DC line DL via DC node 11b, and their emitters are connected to AC nodes 11a, 11c, and 11d, respectively.

[0040] AC nodes 11a, 11c, and 11d are provided, each corresponding to the three-phase AC voltage supplied from the commercial AC power supply 1. The collectors of IGBTQ4 to Q6 are connected to AC nodes 11a, 11c, and 11d, respectively, and their emitters are both connected to the negative DC line DLn. Diodes D1 to D6 are connected in antiparallel to IGBTQ1 to Q6, respectively. Capacitor C2 is connected between DC lines DL and DLn.

[0041] IGBTQ1 and Q4 are controlled by gate signals A1 and B1, respectively; IGBTQ2 and Q5 are controlled by gate signals A2 and B2, respectively; and IGBTQ3 and Q6 are controlled by gate signals A3 and B3, respectively. Gate signals B1, B2, and B3 are the inverse signals of gate signals A1, A2, and A3, respectively.

[0042] IGBTQ1~Q3 turns on when gate signals A1, A2, and A3 are set to the "H" level, respectively, and turns off when gate signals A1, A2, and A3 are set to the "L" level, respectively. IGBTQ4~Q6 turns on when gate signals B1, B2, and B3 are set to the "H" level, respectively, and turns off when gate signals B1, B2, and B3 are set to the "L" level, respectively.

[0043] Each of the gate signals A1, B1, A2, B2, A3, and B3 is a pulse signal train and is a PWM (Pulse Width Modulation) signal. The phases of gate signals A1 and B1, A2 and B2, and A3 and B3 are basically shifted by 120 degrees each. The gate signals A1, B1, A2, B2, A3, and B3 are generated by the control device 15.

[0044] By using gate signals A1, B1, A2, B2, A3, and B3 to turn each of IGBTQ1 to Q6 on and off at predetermined timings, and by adjusting the on-time of each of IGBTQ1 to Q6, it is possible to convert the three-phase AC voltage applied to AC nodes 11a, 11c, and 11d into a desired DC voltage VD (voltage across the terminals of capacitor C2).

[0045] Conversely, by using gate signals A1, B1, A2, B2, A3, and B3 to turn each of IGBTQ1 to Q6 on and off at predetermined timings, and by adjusting the on-time of each of IGBTQ1 to Q6, it is possible to convert the DC voltage VD into a three-phase AC voltage with a desired phase and amplitude and output it to AC nodes 11a, 11c, and 11d.

[0046] In other words, by using gate signals A1, B1, A2, B2, A3, and B3 to turn each of IGBTQ1 to Q6 on and off at predetermined timings, and by adjusting the on-time of each of IGBTQ1 to Q6, it is possible to absorb active power of a desired polarity (positive or negative) from AC nodes 11a, 11c, and 11d, as well as reactive power of a desired polarity (lagging or leading) from AC nodes 11a, 11c, and 11d.

[0047] The inverter 13 includes IGBTs Q11 to Q16 and diodes D11 to D16. The IGBTs constitute the switching elements. The collectors of IGBTs Q11 to Q13 are all connected to the positive DC line DL via DC node 13a, and their emitters are connected to AC nodes 13b, 13c, and 13d, respectively.

[0048] AC nodes 13b, 13c, and 13d are provided, each corresponding to the three-phase AC voltage supplied to the load 8. The collectors of IGBTQ14 to Q16 are connected to AC nodes 13b, 13c, and 13d, respectively, and their emitters are both connected to the negative DC line DLn. Diodes D11 to D16 are connected in antiparallel to IGBTQ11 to Q16, respectively.

[0049] IGBTQ11 and Q14 are controlled by gate signals X1 and Y1, respectively; IGBTQ12 and Q15 are controlled by gate signals X2 and Y2, respectively; and IGBTQ13 and Q16 are controlled by gate signals X3 and Y3, respectively. Gate signals Y1, Y2, and Y3 are the inverse signals of gate signals X1, X2, and X3, respectively.

[0050] IGBTQ11~Q13 are turned on when gate signals X1, X2, and X3 are set to the "H" level, respectively, and turned off when gate signals X1, X2, and X3 are set to the "L" level, respectively. IGBTQ14~Q16 are turned on when gate signals Y1, Y2, and Y3 are set to the "H" level, respectively, and turned off when gate signals Y1, Y2, and Y3 are set to the "L" level, respectively.

[0051] Each of the gate signals X1, Y1, X2, Y2, X3, and Y3 is a pulse signal train and is a PWM signal. The phases of gate signals X1, Y1, gate signals X2, Y2, and gate signals X3, Y3 are basically shifted by 120 degrees each. The gate signals X1, Y1, X2, Y2, X3, and Y3 are generated by the control device 15.

[0052] For example, when IGBTQ11 and Q15 are turned on, DC line DL is connected to AC node 13b via IGBTQ11, and AC node 13c is connected to DC line DLn via IGBTQ15, and a positive voltage is output between AC nodes 13b and 13c.

[0053] Furthermore, when IGBTQ12 and Q14 are turned on, the DC line DL is connected to the AC node 13c via IGBTQ12, and the AC node 13b is connected to the DC line DLn via IGBTQ14, and a negative voltage is output between output nodes 13b and 13c.

[0054] By using gate signals X1, Y1, X2, Y2, X3, and Y3 to turn each of the IGBTQ11 to Q16 on and off at predetermined timings, and by adjusting the on-time of each of the IGBTQ11 to Q16, it is possible to convert the DC voltage VD between the DC lines DL and DLn into a three-phase AC voltage and output it to the AC nodes 13b, 13c, and 13d.

[0055] Figure 4 is a block diagram showing the main components of the control device 15. In Figure 4, the control device 15 includes voltage detectors 21-24, a power failure detector 25, and a control circuit 26. Voltage detector 21 detects the instantaneous value of the AC input voltage VS received from the power distribution line 4 and outputs a signal VSf indicating the detected value to the power failure detector 25 and the control circuit 26. Voltage detector 22 detects the instantaneous value of the AC output voltage VO supplied to the load 8 and outputs a signal VOf indicating the detected value to the control circuit 26.

[0056] The voltage detector 23 detects the instantaneous value of the DC voltage VD of the DC line DL and outputs a signal VDf indicating the detected value to the control circuit 26. The voltage detector 24 detects the instantaneous value of the terminal voltage VB of the battery 7 and outputs a signal VBf indicating the detected value to the control circuit 26.

[0057] The power outage detector 25 detects whether a power outage has occurred in the commercial AC power supply 1 based on the output signal VSF of the voltage detector 21, and outputs a signal φ25 indicating the detection result to the control circuit 26. If the commercial AC power supply 1 is healthy, the signal φ25 is set to the "H" level. If a power outage has occurred in the commercial AC power supply 1, the signal φ25 is set to the "L" level.

[0058] For example, if the AC input voltage VS is higher than the lower limit, the power outage detector 25 determines that the commercial AC power supply 1 is healthy and sets the signal φ25 to the "H" level. Also, if the AC input voltage VS is lower than the lower limit, the power outage detector 25 determines that a power outage has occurred in the commercial AC power supply 1 and sets the signal φ25 to the "L" level.

[0059] The output signals Iif, Ibf, and Iof from current detectors CD1 to CD3 (Figure 1) are supplied to the control circuit 26. The control circuit 26 controls switches S1 to S3, converter 11, bidirectional chopper 12, and inverter 13 based on the output signals VSf, VOf, VDf, and VBf from voltage detectors 21 to 24, the output signal φ25 from power failure detector 25, the output signals Iif, Ibf, and Iof from current detectors CD1 to CD3, and signals from the operation unit 14.

[0060] Figure 5 is a block diagram showing the main components of the control circuit 26. In Figure 5, the control circuit 26 includes control units 31-34 and a communication line 35. The control units 31-34 and the operation unit 14 are connected to each other by the communication line 35. The control units 31-34 send and receive various signals via the communication line 35 and cooperate with each other to control the entire uninterruptible power supply 6.

[0061] The control unit 31 controls switches S1 to S3 based on the output signal φ25 from the power outage detector 25 and the signal from the operation unit 14. When the signal φ25 is at the "H" level (when the commercial AC power supply 1 is healthy), the control unit 31 turns on switches S1 to S3.

[0062] When signal φ25 is at the "L" level (during a power outage of commercial AC power supply 1), the control unit 31 turns off switch S1 and keeps switches S2 and S3 in the ON state. In addition, the control unit 31 individually turns on and off switches S1 to S3 during manual operation according to the signal from the operation unit 14.

[0063] The control unit 32 generates gate signals A1-A3 and B1-B3 (Figure 3) based on the output signals VSf and VDf from the voltage detectors 21 and 23, the output signal Iif from the current detector CD1, the output signal φ25 from the power failure detector 25, and the signal from the operation unit 14, and controls the converter 11.

[0064] When signal φ25 is at the "H" level (when commercial AC power supply 1 is healthy), the control unit 32 controls the converter 11 based on signals VSf, VDf, and Iif so that the DC voltage VD of the DC line DL becomes the reference voltage VDR and the amplitude VSA of the AC input voltage VS becomes the reference voltage VSR.

[0065] When signal φ25 is at the "L" level (during a power outage of commercial AC power supply 1), the control unit 32 stops the operation of the converter 11. At this time, gate signals A1~A3 and B1~B3 are both set to the "L" level, and IGBTQ1~Q6 (Figure 3) of the converter 11 are both turned off. In addition, the control unit 32 starts or stops the converter 11 during manual operation according to the signal from the operation unit 14.

[0066] The control unit 33 controls the bidirectional chopper 12 based on the output signals VDf and VBf from the voltage detectors 23 and 24, the output signal Ibf from the current detector CD2, the output signal φ25 from the power failure detector 25, and the signal from the operation unit 14.

[0067] When signal φ25 is at the "H" level (when commercial AC power supply 1 is healthy), the control unit 33 controls the bidirectional chopper 12 based on signals VBf and Ibf so that the battery voltage VB becomes the reference voltage VBR.

[0068] When signal φ25 is at the "L" level (during a power outage of commercial AC power supply 1), the control unit 33 controls the bidirectional chopper 12 based on signals VBf and Ibf so that the DC voltage VD of the DC line DL becomes the reference voltage VDR. The control unit 33 also starts or stops the bidirectional chopper 12 during manual operation according to the signal from the operation unit 14.

[0069] The control unit 34 generates gate signals X1~X3, Y1~Y3 (Figure 3) based on the output signals VSf, VOf from the voltage detectors 21, 22, the output signal Iof from the current detector CD3, the output signal φ25 from the power failure detector 25, and the signal from the operation unit 14, and controls the inverter 13.

[0070] The control unit 34 operates in synchronization with the signal VSF and controls the inverter 13 based on the signals VOf and Iof so that the AC output voltage VO becomes a sinusoidal reference voltage VOR. The control unit 34 also operates or stops the inverter 13 according to the signal from the operation unit 14.

[0071] Here, we will explain the operation of the power system shown in Figures 1 to 5. When the commercial AC power source 1 (Figure 1) is functioning properly, AC power is supplied from the commercial AC power source 1 to the load 5 and the uninterruptible power supply 6 via the transmission line 2, the interconnection transformer 3, and the distribution line 4. The load 5 is driven by the AC power received from the distribution line 4.

[0072] The uninterruptible power supply (UPS) 6 converts the AC power received from the power distribution line 4 into DC power and stores it in the battery 7. It then converts that DC power back into AC power and supplies it to the load 8. The load 8 is driven by the AC power supplied by the UPS 6.

[0073] In other words, in the uninterruptible power supply 6, the output signal φ25 of the power failure detector 25 (Figure 4) is set to the "H" level, and the control unit 31 (Figure 5) turns on switch S1 (Figure 2) and keeps switches S2 and S3 in the ON state.

[0074] Furthermore, the control unit 32 (Figure 5) operates the converter 11, and the AC power received from the distribution line 4 is converted into DC power by the converter 11 (Figures 2 and 3) and supplied to the DC line DL. At this time, the control unit 32 generates gate signals A1 to A3 and B1 to B3 (Figure 3) to control the converter 11 so that the DC voltage VD of the DC line DL becomes the reference voltage VDR, and the amplitude VSA of the AC voltage VS of the distribution line 4 becomes the reference voltage VSR.

[0075] Furthermore, the control unit 33 (Figure 5) operates the bidirectional chopper 12 (Figure 2), and the DC power generated by the converter 11 is stored in the battery 7 by the bidirectional chopper 12. At this time, the control unit 33 controls the bidirectional chopper 12 so that the battery voltage VB becomes the reference voltage VBR.

[0076] Furthermore, the control unit 34 (Figure 5) operates the inverter 13 (Figure 2), and the DC power generated by the converter 11 is converted into AC power by the inverter 13 and supplied to the load 8. At this time, the control unit 34 generates gate signals X1~X3, Y1~Y3 (Figure 3) to control the inverter 13 so that the AC voltage VO applied to the load 8 becomes a sinusoidal reference voltage VOR.

[0077] When the commercial AC power supply 1 (Figure 1) experiences a power outage, the supply of AC power from the commercial AC power supply 1 to the transmission line 2 is stopped, and the operation of load 5 is halted. The uninterruptible power supply 6 converts the DC power in battery 7 into AC power and supplies it to load 8. Therefore, as long as DC power is stored in battery 7, the operation of load 8 can continue.

[0078] In other words, in the uninterruptible power supply 6, the output signal φ25 of the power failure detector 25 (Figure 4) is set to the "L" level, the control unit 31 (Figure 5) turns off the switch S1 (Figure 2), and the power distribution line 4 and the converter 11 are electrically disconnected.

[0079] Furthermore, the control unit 32 (Figure 5) stops the operation of the converter 11. At this time, the control unit 32 sets all gate signals A1~A3, B1~B3 (Figure 3) to the "L" level and turns off the IGBTQ1~Q6 of the converter 11.

[0080] Furthermore, the control unit 33 (Figure 5) operates the bidirectional chopper 12 (Figure 2), and DC power from the battery 7 is supplied to the inverter 13 via the bidirectional chopper 12 and the DC line DL. At this time, the control unit 33 controls the bidirectional chopper 12 so that the DC voltage VD of the DC line DL becomes the reference voltage VDR.

[0081] Furthermore, the control unit 34 (Figure 5) operates the inverter 13 (Figure 2), and the DC power supplied from the battery 7 via the bidirectional chopper 12 and DC line DL is converted into AC power by the inverter 13 and supplied to the load 8. At this time, the control unit 34 controls the inverter 13 so that the AC voltage VO applied to the load 8 becomes a sinusoidal reference voltage VOR.

[0082] Next, the control method for the converter 11 will be described in more detail. Figure 6 is a block diagram showing the configuration of the control unit 32. In Figure 6, the control unit 32 includes a DC voltage command unit 41, subtractors 42, 46, 53, 56, a DC voltage control unit 43, limiters 44, 55, a current component detection unit 45, an active current control unit 47, an AC voltage command unit 51, an amplitude detection unit 52, an AC voltage control unit 54, a reactive current control unit 57, a coordinate transformation unit 58, and a PWM control unit 59.

[0083] The DC voltage command unit 41 generates a reference voltage VDR, which is the target value for the DC voltage VD of the DC line DL (Figure 2). The subtractor 42 calculates the deviation ΔVD = VDR - VD between the reference voltage VDR and the DC voltage VD of the DC line DL, which is indicated by the output signal VDf of the voltage detector 23.

[0084] The DC voltage control unit 43 generates an effective current command value Idc corresponding to the deviation ΔVD obtained by the subtractor 42. The DC voltage control unit 43 determines the effective current command value Idc by, for example, performing a proportional or proportional-integral operation on the deviation ΔVD. The limiter 44 generates the effective current command value Idc1 by limiting the magnitude of the effective current command value Idc to a range below a predetermined value.

[0085] The current component detection unit 45 detects the active current Id and reactive current Iq of the AC current Ii based on the AC current Ii indicated by the output signal Iif of the current detector CD1 (Figure 2) and the AC voltage VS of the power distribution line 4 indicated by the output signal VSf of the voltage detector 21.

[0086] The subtractor 46 calculates the deviation ΔId = Idc1 - Id between the active current command value Idc1 generated by the limiter 44 and the active current Id detected by the current component detection unit 45.

[0087] The active current control unit 47 generates an active current control value Vdc corresponding to the deviation ΔId obtained by the subtractor 46. The active current control unit 47 obtains the active voltage control value Vdc by, for example, performing a proportional or proportional-integral operation on the deviation ΔId.

[0088] The AC voltage command unit 51 generates a reference voltage VSR, which is the target value for the amplitude of the AC voltage VS of the power distribution line 4 (Figures 1 and 2). The amplitude detection unit 52 detects the amplitude VSA of the AC voltage VS of the power distribution line 4, indicated by the output signal VSf of the voltage detector 21 (Figure 4). The subtractor 53 calculates the deviation ΔVS = VSR - VSA between the reference voltage VSR and the amplitude VSA of the AC voltage VS of the power distribution line 4 detected by the amplitude detection unit 52.

[0089] The AC voltage control unit 54 generates a reactive current command value Iqc corresponding to the deviation ΔVS obtained by the subtractor 53. The AC voltage control unit 54 determines the reactive current command value Iqc by, for example, performing a proportional or proportional-integral operation on the deviation ΔVS. The limiter 55 generates a reactive current command value Iqc1 by limiting the magnitude of the reactive current command value Iqc to a range below a predetermined value.

[0090] Figure 7 shows the operation of the AC voltage control unit 54 and the limiter 55. In Figure 7, the horizontal axis represents the deviation ΔVS obtained by the subtractor 53, and the vertical axis represents the reactive current command value Iqc1 generated by the limiter 55.

[0091] The reactive current command value Iqc generated by the AC voltage control unit 54 increases in proportion to the magnitude of the deviation ΔVS, as shown by the dotted line in Figure 7. The reactive current command value Iqc1 generated by the limiter 55 is limited to a predetermined range, as shown by the solid line in Figure 7. That is, if -α ≤ ΔVS ≤ α, Iqc1 = Iqc; if α < ΔVS, Iqc1 = β; and if ΔVS < -α, Iqc1 = -β.

[0092] Referring again to Figure 6, the subtractor 56 calculates the deviation ΔIq = Iqc1 - Iq between the reactive current command value Iqc1 generated by the limiter 55 and the reactive current Iq detected by the current component detection unit 45.

[0093] The reactive current control unit 57 generates a reactive current control value Vqc that corresponds to the deviation ΔIq obtained by the subtractor 56. The reactive current control unit 57 obtains the reactive voltage control value Vqc by, for example, performing a proportional or proportional-integral operation on the deviation ΔIq.

[0094] The coordinate transformation unit 58 converts the active voltage control value Vdc and the reactive voltage control value Vqc to two-phase / three-phase AC voltage control values ​​VUc, VVc, and VWc based on the AC voltage VS of the power distribution line 4 indicated by the output signal VSf of the voltage detector 21 (Figure 4).

[0095] When the output signal φ25 of the power outage detector 25 is at the "H" level (when the commercial AC power supply 1 is healthy), the PWM control unit 59 generates gate signals A1, B1, gate signals A2, B2, and gate signals A3, B3 (Figure 3) according to the AC voltage control values ​​VUc, VVc, and VWc, respectively.

[0096] In this case, the converter 11 (Figure 3) is driven by gate signals A1-A3 and B1-B3 generated by the PWM control unit 59, and outputs three-phase AC voltages VU, VV, and VW to AC nodes 11a, 11c, and 11d. Note that the AC voltage VS of the distribution line 4 corresponds to one of the three-phase AC voltages VU, VV, and VW (for example, VU).

[0097] Furthermore, if the output signal φ25 of the power outage detector 25 is at the "L" level (during a power outage of the commercial AC power supply 1), the PWM control unit 59 sets all gate signals A1~A3 and B1~B3 to the "L" level and stops the operation of the converter 11. In this case, all IGBTQ1~Q6 included in the converter 11 are kept in the OFF state.

[0098] Next, the operation of the control unit 32 shown in Figure 6 will be explained. The DC voltage command unit 41 generates a reference voltage VDR, and the subtractor 42 calculates the deviation ΔVD = VDR - VD between the reference voltage VDR and the DC voltage VD of the DC line DL.

[0099] The DC voltage control unit 43 generates an effective current command value Idc corresponding to the deviation ΔVD, and the limiter 44 limits the magnitude of the effective current command value Idc to a range below a predetermined value, thereby generating the effective current command value Idc1.

[0100] The current component detection unit 45 detects the active current Id and reactive current Iq contained in the AC current Ii flowing between the distribution line 4 and the converter 11. The subtractor 46 calculates the deviation ΔId = Idc1 - Id between the active current command value Idc1 and the active current Id, and the active current control unit 47 calculates the active voltage control value Vdc corresponding to the deviation ΔId.

[0101] Furthermore, the AC voltage command unit 51 generates a reference voltage VSR, the amplitude detection unit 52 detects the amplitude VSA of the AC voltage VS of the power distribution line 4, and the subtractor 53 calculates the difference between the reference voltage VSR and the amplitude VSA, ΔVS = VSR - VSA.

[0102] The AC voltage control unit 54 generates an reactive current command value Iqc corresponding to the deviation ΔVS, and the limiter 55 limits the magnitude of the reactive current command value Iqc to a range of less than or equal to a predetermined value β, thereby generating the reactive current command value Iqc1.

[0103] The subtractor 56 calculates the deviation ΔIq = Iqc1 - Iq between the reactive current command value Iqc1 and the reactive current Iq, and the reactive current control unit 57 calculates the reactive voltage control value Vqc corresponding to the deviation ΔIq.

[0104] The coordinate transformation unit 58 converts the active voltage control value Vdc and the reactive voltage control value Vqc to two-phase / three-phase AC voltage control values ​​VUc, VVc, and VWc based on the AC voltage VS.

[0105] When the output signal φ25 of the power outage detector 25 is at the "H" level (when the commercial AC power supply 1 is healthy), the PWM control unit 59 generates gate signals A1~A3, B1~B3 (Figure 3) according to the AC voltage control values ​​VUc, VVc, VWc, and the converter 11 is operated.

[0106] When the output signal φ25 of the power outage detector 25 is at the "L" level (during a power outage of the commercial AC power supply 1), the PWM control unit 59 sets all gate signals A1~A3 and B1~B3 to the "L" level, stopping the operation of the converter 11.

[0107] When the commercial AC power supply 1 is functioning properly, if the DC voltage VD of the DC line DL falls below the reference voltage VDR, the deviation ΔVD increases in the positive direction, and the active current control value Idc increases in the positive direction. Furthermore, the active current control value Idc1 increases in the positive direction, the deviation ΔId increases in the positive direction, and the active voltage control value Vdc increases in the positive direction. As a result, the positive active current Id absorbed from the distribution line 4 to the converter 11 increases, and the DC voltage VD of the DC line DL rises.

[0108] Conversely, if the DC voltage VD of the DC line DL rises above the reference voltage VDR, the deviation ΔVD increases in the negative direction, and the effective current control value Idc increases in the negative direction. Furthermore, the effective current control value Idc1 increases in the negative direction, the deviation ΔId increases in the negative direction, and the effective voltage control value Vdc increases in the negative direction.

[0109] This increases the negative active current Id absorbed from the distribution line 4 to the converter 11, causing the DC voltage VD of the DC line DL to decrease. Therefore, the DC voltage VD of the DC line DL is maintained at the reference voltage VDR.

[0110] Furthermore, when the commercial AC power supply 1 is functioning normally, if the power consumption of load 5 increases and the amplitude VSA of the AC voltage VS of distribution line 4 falls below the reference voltage VSR, the deviation ΔVS increases in the positive direction, and the reactive current control value Iqc increases in the positive direction. In addition, the reactive current control value Iqc1 increases in the positive direction, the deviation ΔIq increases in the positive direction, and the reactive voltage control value Vqc increases in the positive direction. As a result, the leading reactive current Iq absorbed from distribution line 4 to converter 11 increases, and the amplitude VSA of the AC voltage VS of distribution line 4 rises.

[0111] Conversely, if the power consumption of load 5 decreases, or if regenerative power is supplied from load 5 to distribution line 4, causing the amplitude VSA of the AC voltage VS in distribution line 4 to rise above the reference voltage VSR, the deviation ΔVS increases in the negative direction, and the reactive current control value Iqc increases in the negative direction. Furthermore, the reactive current control value Iqc1 increases in the negative direction, the deviation ΔIq increases in the negative direction, and the reactive voltage control value Vqc increases in the negative direction. As a result, the lagging reactive current Iq absorbed from distribution line 4 to converter 11 increases, and the amplitude VSA of the AC voltage VS in distribution line 4 decreases. Therefore, the amplitude VSA of the AC voltage VS is maintained at the reference voltage VSR.

[0112] As described above, in this embodiment 1, when the AC voltage VS of the power distribution line 4 changes, the converter 11 is controlled to absorb reactive power from the power distribution line 4 to compensate for the change in the AC voltage VS of the power distribution line 4. Therefore, the AC voltage VS of the power distribution line 4 can be stabilized.

[0113] [Embodiment 2] In Embodiment 1, when the AC voltage VS of the power distribution line 4 changed, the converter 11 was controlled to absorb reactive power from the power distribution line 4 to compensate for the change. However, if the AC voltage VS remains low for an extended period, the reactive power flowing through the converter 11 may become excessive. Embodiment 2 aims to solve this problem.

[0114] Figure 8 is a block diagram showing the main parts of a control unit 32A included in a power system according to Embodiment 2 of the present disclosure, and is shown in comparison with Figure 6. Referring to Figure 8, the difference between the control unit 32A and the control unit 32 (Figure 6) is that the AC voltage control unit 54 and limiter 55 are replaced by a clock generation unit 61, latch circuits 62, 63, subtractor 64, AC voltage control unit 65, polarity determination unit 66, and limiter 67.

[0115] The clock generation unit 61 generates a clock signal CLK of a predetermined frequency. The latch circuit 62 acquires the amplitude VSA of the AC voltage VS of the power distribution line 4 detected by the amplitude detection unit 52 (Figure 6) in response to the rising edge of the clock signal CLK, and holds and outputs the acquired amplitude VSA as amplitude VSA1.

[0116] The latch circuit 63 receives the amplitude VSA1 output from the latch circuit 62 in response to the falling edge of the clock signal CLK, and holds and outputs the received amplitude VSA1 as amplitude VSA2.

[0117] The subtractor 64 calculates the deviation ΔVSA = VSA2 - VSA1 between the previously detected amplitude VSA2 and the currently detected amplitude VSA1. The AC voltage control unit 65 generates a reactive current command value Iqc corresponding to the deviation ΔVSA obtained by the subtractor 64. The AC voltage control unit 54 calculates the reactive current command value Iqc, for example, by performing a proportional or proportional-integral operation on the deviation ΔVSA.

[0118] The polarity determination unit 66 determines the polarity (positive or negative) of the deviation ΔVS obtained by the subtractor 53 (Figure 6) and outputs a signal φ66 indicating the determination result. If the deviation ΔVS is positive, the signal φ66 is set to the "H" level. If the deviation ΔVS is negative, the signal φ66 is set to the "L" level. The limiter 67 generates the reactive current command value Iqc1 by limiting the magnitude of the reactive current command value Iqc within a predetermined range. The limiting range of the limiter 67 is changed by the signal φ66.

[0119] Figure 9 shows the operation of the AC voltage control unit 65 and the limiter 67. In Figure 9, (A) shows the case where the deviation ΔVS is positive, and (B) shows the case where the deviation ΔVS is negative. In both (A) and (B), the horizontal axis shows the deviation ΔVSA obtained by the subtractor 64, and the vertical axis shows the reactive current command value Iqc1 generated by the limiter 67.

[0120] The reactive current command value Iqc generated by the AC voltage control unit 65 increases in proportion to the magnitude of the deviation ΔVSA, as shown by the dotted lines in Figures 9(A) and (B). When ΔVS > 0, the reactive current command value Iqc is limited by the limiter 67 to become the reactive current command value Iqc1, as shown by the solid line in Figure 9(A). That is, when 0 ≤ ΔVSA ≤ α, Iqc1 = Iqc; when α < ΔVSA, Iqc1 = β; and when ΔVSA < 0, Iqc = 0.

[0121] The reason for setting Iqc1=0 when ΔVS>0 and ΔVSA<0 is that even if the current detected value VSA1 is higher than the previous detected value VSA2 (ΔVSA<0), if the amplitude VSA of the AC voltage VS of distribution line 4 is lower than the reference voltage VSR (ΔVS>0), there is no need to reduce the amplitude VSA of the AC voltage VS.

[0122] Conversely, when ΔVS < 0, the reactive current command value Iqc is limited by the limiter 67 to Iqc1, as shown by the solid line in Figure 9(B). That is, when -α ≤ ΔVSA ≤ 0, Iqc1 = Iqc; when ΔVSA < -α, Iqc = -β; and when 0 < ΔVSA, Iqc = 0.

[0123] The reason for setting Iqc1=0 when ΔVS<0 and 0<ΔVSA is that even if the current detected value VSA1 is lower than the previous detected value VSA2 (0<ΔVSA), if the amplitude VSA of the AC voltage VS of distribution line 4 is higher than the reference voltage VSR (ΔVS<0), there is no need to increase the amplitude VSA of the AC voltage VS.

[0124] The reactive current command value Iqc1 generated by the limiter 67 is supplied to the subtractor 56 (Figure 6). The other configurations and operations are the same as in Embodiment 1, so their description will not be repeated.

[0125] As described above, in this second embodiment, the amplitude VSA of the AC voltage VS of the power distribution line 4 is detected at a predetermined period, the deviation ΔVSA = VSA2 - VSA1 between the previously detected amplitude VSA2 and the currently detected amplitude VSA1 is calculated, and the converter 11 absorbs a reactive current Iq corresponding to the deviation ΔVSA. Therefore, since the converter 11 absorbs the reactive current Iq only when the amplitude VSA of the AC voltage VS changes, the amount of reactive power absorbed by the converter 11 can be reduced compared to the first embodiment.

[0126] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The present invention is indicated by the claims rather than by the foregoing description, and all modifications are intended to be in the sense and scope equivalent to the claims. [Explanation of symbols]

[0127] 1 Commercial AC power supply, 2 Transmission line, 3 Interconnection transformer, 4 Distribution line, 5,8 Load, 6 Uninterruptible power supply, 7 Battery, T1 AC input terminal, T2 Battery terminal, T3 AC output terminal, S1~S3 Switch, C1~C3 Capacitor, L1~L3 Reactor, CD1~CD3 Current detector, 11 Converter, DL,DLn DC line, 12 Bidirectional chopper, 13 Inverter, 14 Operating unit, 15 Control unit, Q1~Q6,Q11~Q16 IGBT, D1~D6,D11~D16 Diode, 21~24 Voltage detector, 25 Power failure detector, 26 Control circuit, 31~34 Control unit, 35 Communication line, 41 DC voltage command unit, 42,46,53,56,64 Subtractor, 43 DC voltage control unit, 44, 55, 67 limiter, 45 current component detection unit, 47 active current control unit, 51 AC voltage command unit, 52 amplitude detection unit, 54, 65 AC voltage control unit, 57 reactive current control unit, 58 coordinate transformation unit, 59 PWM control unit, 61 clock generation unit, 62, 63 latch circuit, 66 polarity determination unit.

Claims

1. A forward converter that converts AC power received from a power distribution line into DC power, An inverse converter that converts DC power to AC power and supplies it to the first load, The system includes a control device that controls the forward converter to absorb reactive power from the distribution line to compensate for the change in the AC voltage of the distribution line when the AC voltage of the distribution line changes, The control device is The AC voltage of the distribution line is detected at a predetermined interval, The difference between the AC voltage detected last time and the AC voltage detected this time is calculated. Based on that deviation, the reactive power is calculated, A power converter that controls the forward converter to absorb the reactive power obtained.

2. The power conversion device according to claim 1, wherein the control device controls the forward converter to absorb leading or lagging reactive power that causes the AC voltage of the distribution line to increase or decrease when the AC voltage of the distribution line decreases or increases.

3. A second load is connected to the aforementioned power distribution line. The power conversion device according to claim 1, wherein the AC voltage of the power distribution line changes in response to a change in the power consumption of the second load.

4. The aforementioned power distribution line is connected between the AC power source and the forward converter. When the AC power supply is functioning properly, the DC power generated by the forward converter is stored in the power storage device and converted back into AC power by the reverse converter. The power conversion device according to claim 1, wherein in the event of a power outage of the AC power supply, the operation of the forward converter is stopped and the DC power of the power storage device is converted to AC power by the reverse converter.

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