No power outage device

Abstract

The converter (1) converts the AC power supplied from the AC power source (7) into DC power and outputs it to the DC line. The inverter (3) converts the DC power supplied from the DC line into AC power and supplies it to the load (10). The bidirectional chopper (2) exchanges DC power between the DC line and the first and second energy storage devices (8,9). The switching circuit (6) is provided between the bidirectional chopper (2) and the first and second energy storage devices (8,9). The first energy storage device (8) has a higher output density than the second energy storage device (9). The second energy storage device (9) has a higher energy density than the first energy storage device (8). The control device (5) controls the switching circuit (6) to allow charging of the first and second energy storage devices (8,9) and discharging of the first energy storage device (8) when the AC power supply (7) is healthy, and controls the switching circuit (6) to allow discharging of the first and second energy storage devices (8,9) when the AC power supply (7) is abnormal.

Description

Technical Field

[0001] The present disclosure relates to an uninterruptible power supply device.

Background Art

[0002] For example, International Publication No. 2020 / 026430 (Patent Document 1) discloses an uninterruptible power supply device including a converter, an inverter, and a bidirectional chopper. The converter supplies the AC power supplied from the AC power source to a DC line obtained by converting the AC power into DC power when the AC power source is normal. The bidirectional chopper supplies the DC power supplied from the power storage device to the DC line when the AC power source fails. The inverter converts the DC power received from the DC line into AC power and supplies it to the load.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a load with a large fluctuation in power consumption is connected to the uninterruptible power supply device, the power consumption of the load may temporarily exceed the rated load of the uninterruptible power supply device. Since the AC power supplied from the AC power source is limited to the rated load of the uninterruptible power supply device, the power corresponding to the excess is supplied from the power storage device to the load via the bidirectional chopper and the inverter. As a result, the stored power amount stored in the power storage device decreases. Therefore, in response to the power consumption of the load decreasing below the rated load, the bidirectional chopper stores the DC power supplied from the converter via the DC line in the power storage device.

[0005] When the uninterruptible power supply (UPS) becomes overloaded in this way, the energy storage device is discharged and charged. If the power consumption of the load fluctuates periodically, the discharge and charging of the energy storage device will also be repeated periodically, which raises concerns that it may accelerate the deterioration of the energy storage device.

[0006] To prevent overloading and overcharging of energy storage devices, one option is to select a larger capacity uninterruptible power supply (UPS) so that the maximum power consumption of the load is less than or equal to the UPS's rated load. In this case, the UPS would receive all the AC power equivalent to the maximum power consumption of the load from the AC power source. On the other hand, the contracted power would be determined by the maximum power consumption of the load, raising concerns that electricity costs will increase as the contracted power increases.

[0007] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide an uninterruptible power supply that can suppress the deterioration of the energy storage device while keeping the AC power supplied from the AC power source below the rated load. [Means for solving the problem]

[0008] An uninterruptible power supply (UPS) according to one aspect of this disclosure is connected between an AC power source and a load. The UPS comprises a converter, an inverter, a bidirectional chopper, a switching circuit, and a control device. The converter converts AC power supplied from the AC power source into DC power and outputs it to a DC line. The inverter converts DC power supplied from the DC line into AC power and supplies it to the load. The bidirectional chopper exchanges DC power between the DC line and the first and second energy storage devices. The switching circuit is provided between the bidirectional chopper and the first and second energy storage devices. The first energy storage device has a higher power density than the second energy storage device. The second energy storage device has a higher energy density than the first energy storage device. When the AC power source is healthy, the control device controls the switching circuit to allow charging of the first and second energy storage devices and discharging of the first energy storage device. When the AC power source is abnormal, the control device controls the switching circuit to allow discharging of the first and second energy storage devices. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide an uninterruptible power supply that can suppress the deterioration of the energy storage device while keeping the AC power supplied from the AC power source below the rated load. [Brief explanation of the drawing]

[0010] [Figure 1] This is a circuit block diagram showing the configuration of an uninterruptible power supply according to this embodiment. [Figure 2] This is a circuit diagram showing an example configuration of a bidirectional chopper and switching circuit. [Figure 3] This is a block diagram showing an example of the hardware configuration of a control device. [Figure 4] This is a block diagram showing the functional configuration of the control device. [Figure 5] This is a flowchart illustrating the control of the switching circuit in the switching control unit. [Figure 6] This is a block diagram showing the configuration of the part of the power conversion control unit that is related to the control of the converter. [Figure 7] This block diagram shows the configuration of the part of the power conversion control unit related to the control of the bidirectional chopper. [Figure 8] This is a block diagram showing the configuration of the control circuit. [Figure 9] This is a flowchart illustrating the control of the bidirectional chopper in the power conversion control unit. [Figure 10] This figure shows the power flow in an uninterruptible power supply according to this embodiment. [Figure 11] This figure shows the power flow in an uninterruptible power supply according to this embodiment. [Figure 12] This figure shows the power flow in an uninterruptible power supply according to this embodiment. [Figure 13] This figure shows the power flow in an uninterruptible power supply according to this embodiment. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle.

[0012] FIG. 1 is a circuit block diagram showing the configuration of an uninterruptible power supply device according to the present embodiment. As shown in FIG. 1, the uninterruptible power supply device 100 according to the present embodiment includes an AC input terminal T1, DC terminals T2, T3, and an AC output terminal T4.

[0013] The AC input terminal T1 receives an AC voltage VI of a predetermined frequency (for example, commercial frequency) from an AC power source 7. The AC power source 7 may be a commercial AC power source or a generator. The instantaneous value of the AC voltage VI (hereinafter also referred to as "AC input voltage VI") is detected by the control device 5. Based on the instantaneous value of the AC input voltage VI, the presence or absence of an abnormality in the AC power source 7 is determined.

[0014] The AC output terminal T4 is connected to a load 10. The load 10 is driven by the AC power supplied from the uninterruptible power supply device 100. The instantaneous value of the AC voltage VO (hereinafter also referred to as "AC output voltage VO") that appears at the AC output terminal T4 is detected by the control device 5.

[0015] Note that the uninterruptible power supply device 100 receives a three-phase AC voltage from the AC power source 7 and supplies a three-phase AC voltage to the load 10. However, for simplicity of the drawings and description, only a single-phase circuit is shown in FIG. 1.

[0016] The DC terminal T2 is connected to an electric double layer capacitor 8 (EDLC: Electric Double Layer Capacitor). The instantaneous value of the DC voltage VE of the DC terminal T2 (that is, the voltage VE between the terminals of the EDLC 8) is detected by the control device 5.

[0017] EDLC8 corresponds to one embodiment of the "first energy storage device" for storing DC power. Preferably, the first energy storage device is one with high power density (the amount of power that can be instantaneously extracted per unit weight or capacity). The energy stored in the first energy storage device is mainly used to supply the excess AC power to the load 10 when the power consumption of the load 10 exceeds the rated load of the uninterruptible power supply 100.

[0018] The DC terminal T3 is connected to the battery 9. The battery 9 corresponds to one embodiment of a "second energy storage device" that stores DC power. The instantaneous value of the DC voltage VB at the DC terminal T3 (i.e., the terminal voltage VB of the battery 9) is detected by the control device 5.

[0019] Battery 9 is a secondary battery such as a lead-acid battery, nickel-metal hydride battery, or lithium-ion battery. It is preferable to use a second energy storage device with a high energy density (amount of energy that can be stored per unit weight or capacity). The energy stored in the second energy storage device is mainly used to supply AC power to the load 10 in the event of an abnormality in the AC power supply 7.

[0020] In the example shown in Figure 1, the EDLC8 has a lower energy density than the battery 9, but a higher power density. Furthermore, the EDLC8 exhibits less performance degradation due to repeated high-current charging and discharging compared to the battery 9.

[0021] In the event of a malfunction in the AC power supply 7, a significant amount of energy is required to stably compensate for the operation of the load 10 for a predetermined power outage compensation period. The power outage compensation period is the time during which the uninterruptible power supply 100 can continuously supply power to the load 10 during a power outage. For this reason, the battery 9 is suitable as the second energy storage device. However, the second energy storage device is not particularly limited as long as it has a higher energy density than the first energy storage device.

[0022] On the other hand, in situations where the power consumption of load 10 increases sharply and becomes overloaded, the AC power supplied from AC power source 7 becomes insufficient, requiring the first energy storage device to discharge a large current instantaneously. For this reason, the EDLC 8 is suitable as the first energy storage device. However, the first energy storage device is not particularly limited as long as it has a higher power density than the second energy storage device.

[0023] The uninterruptible power supply 100 further comprises a converter 1, DC lines L1 to L3, a bidirectional chopper 2, an inverter 3, a switching circuit 6, current detectors CD1 to CD, an operating unit 4, and a control device 5.

[0024] Converter 1 has an AC terminal 1a, a positive voltage terminal 1b, a neutral voltage terminal 1c, and a negative voltage terminal 1d. Bidirectional chopper 2 has a DC terminal 2a, a positive voltage terminal 2b, a neutral voltage terminal 2c, and a negative voltage terminal 2d. Inverter 3 has an AC terminal 3a, a positive voltage terminal 3b, a neutral voltage terminal 3c, and a negative voltage terminal 3d.

[0025] The AC terminal 1a of converter 1 is connected to the AC input terminal T1. The current detector CD1 detects the instantaneous value of the current Ii (hereinafter also referred to as "AC input current Ii") flowing between the AC input terminal T1 and the AC terminal 1a of converter 1, and provides the control device 5 with a signal Iif indicating the detected value.

[0026] The DC terminal 2a of the bidirectional chopper 2 is connected to the switching circuit 6. The current detector CD2 detects the instantaneous value of the DC current Is flowing between the switching circuit 6 and the DC terminal 2a, and provides the control device 5 with a signal Isf indicating the detected value. The instantaneous value of the DC voltage VS appearing at the DC terminal 2a is detected by the control device 5.

[0027] The switching circuit 6 is connected between the DC terminal 2a of the bidirectional chopper 2 and the DC terminals T2 and T3. The switching circuit 6 is controlled by the control device 5 and allows charging and discharging of the EDLC 8 and the battery 9, respectively. The configuration of the switching circuit 6 will be explained in detail later.

[0028] The AC terminal 3a of the inverter 3 is connected to the AC output terminal T4. The current detector CD3 detects the instantaneous value of the current Io (hereinafter also referred to as "load current Io") flowing between the AC terminal 3a and the AC output terminal T4, and provides the control device 5 with a signal Iof indicating the detected value.

[0029] The first terminals of DC lines L1 to L3 are connected to the positive voltage terminal 1b, neutral voltage terminal 1c, and negative voltage terminal 1d of converter 1, respectively. The second terminals of DC lines L1 to L3 are connected to the positive voltage terminal 3b, neutral voltage terminal 3c, and negative voltage terminal 3d of inverter 3, respectively. In addition, DC lines L1 and L3 are connected to the positive voltage terminal 2b and negative voltage terminal 2d of bidirectional chopper 2, respectively.

[0030] Capacitor C1 is connected between DC lines L1 and L2 to stabilize and smooth the DC voltage Ep between DC lines L1 and L2. Capacitor C2 is connected between DC lines L2 and L3 to stabilize and smooth the DC voltage En between DC lines L2 and L3. Capacitors C1 and C2 are connected in series between DC lines L1 and L3 to stabilize and smooth the DC voltage VD = Ep + En between DC lines L1 and L3. The instantaneous values ​​of the DC voltages Ep and En are detected by the control device 5.

[0031] Capacitor C3 is connected between terminals 2b and 2c of the bidirectional chopper 2, stabilizing and smoothing the DC voltage between terminals 2b and 2c. Capacitor C4 is connected between terminals 2c and 2d of the bidirectional chopper 2, stabilizing and smoothing the DC voltage between terminals 2c and 2d. Capacitors C3 and C4 are connected in series between terminals 2b and 2d of the bidirectional chopper 2, stabilizing and smoothing the DC voltage VD = Ep + En between terminals 2b and 2d.

[0032] Converter 1 is a well-known converter comprising multiple transistors and multiple diodes, and is controlled by control device 5. When the AC input voltage VI is supplied normally from the AC power supply 7 (i.e., when the AC power supply 7 is healthy), converter 1 converts the AC input voltage VI supplied from the AC power supply 7 via the AC input terminal T1 into three levels of DC voltage V1 to V3, and outputs them to DC lines L1 to L3, respectively. That is, Ep = V1 - V2, En = V2 - V3. When the AC input voltage VI is not supplied normally from the AC power supply 7 (i.e., when the AC power supply 7 is abnormal), the operation of converter 1 is stopped.

[0033] The bidirectional chopper 2 is a well-known type containing multiple transistors and multiple diodes, and is controlled by the control device 5. When the AC power supply 7 is healthy, the bidirectional chopper 2 stores the DC power supplied from the converter 1 via the DC lines L1 and L3 into the EDLC 8 and battery 9 via the switching circuit 6.

[0034] When the AC power supply 7 is functioning normally, if the power consumption of the load 10 increases sharply and becomes overloaded, or if the AC power supply 7 malfunctions, the bidirectional chopper 2 converts the DC voltage VS supplied from the EDLC 8 or battery 9 via the switching circuit 6 into three levels of DC voltages V1 to V3 and outputs them to the positive voltage terminal 2b, the neutral voltage terminal 2c, and the negative voltage terminal 2d. DC voltages V1 and V3 are supplied to DC lines L1 and L3, respectively. The DC voltage (V1-V3) between DC lines L1 and L3 is divided by capacitors C1 and C2, and a neutral voltage V2 = (V1-V3) / 2 is generated on DC line L2. The DC voltage V2 on DC line L2 is supplied to the inverter 3.

[0035] The inverter 3 is a well-known inverter containing multiple transistors and multiple diodes, and is controlled by the control device 5. When the AC power supply 7 is healthy, the inverter 3 converts three levels of DC voltages V1 to V3 supplied from the converter 1 (or the converter 1 and the bidirectional chopper 2) via the DC lines L1 to L3 into an AC output voltage VO and supplies it to the load 10. When the AC power supply 7 is abnormal, the inverter 3 converts three levels of DC voltages V1 to V3 supplied from the EDLC 8 and battery 9 via the bidirectional chopper 2 and the DC lines L1 to L3 into an AC output voltage VO and supplies it to the load 10.

[0036] The control unit 4 includes multiple buttons operated by the user of the uninterruptible power supply 100, a display that shows various information, and other components. By operating the control unit 4, the user can turn the power of the uninterruptible power supply 100 on and off, and set various information.

[0037] The control device 5 controls the entire uninterruptible power supply 100 based on the AC input voltage VI, AC input current Ii, DC voltages Ep, En, VS, AC output voltage VO, DC current Is, load current Io, and signals from the control unit 4.

[0038] Figure 2 is a circuit diagram showing an example configuration of a bidirectional chopper 2 and a switching circuit 6. As shown in Figure 2, the bidirectional chopper 2 includes a reactor 21 and a semiconductor switch 23. The semiconductor switch 23 includes IGBT (Insulated Gate Bipolar Transistor) elements Q1 to Q4 connected in series between DC lines L1 and L3, and diodes D1 to D4 connected in antiparallel to the IGBT elements Q1 to Q4, respectively. In the example in Figure 2, IGBTs are used as semiconductor switching elements (hereinafter also simply referred to as "switching elements") Q1 to Q4. Not limited to IGBTs, self-extinguishing switching elements such as MOSFETs (Metal Oxide Field Effect Transistors) can be used for switching elements Q1 to Q4.

[0039] In the semiconductor switch 23, the first terminal of reactor 21P is connected to the connection point of IGBT elements Q1 and Q2, and the first terminal of reactor 21N is connected to the connection point of IGBT elements Q3 and Q4. The second terminal of reactor 21P is connected to the positive DC terminal 2aP, and the second terminal of reactor 21N is connected to the negative DC terminal 2aN.

[0040] In the example shown in Figure 2, reactor 21 has reactors 21P and 21N, but it may also be configured to have only one of the reactors 21P and 21N.

[0041] The switching circuit 6 includes IGBT elements Q5 and Q6 and diodes D5 and D6. In the example in Figure 2, IGBTs are used as switching elements Q5 and Q6. However, the switching elements Q5 and Q6 are not limited to IGBTs; self-extinguishing switching elements such as MOSFETs can also be used.

[0042] The IGBT element Q5 is connected between the positive DC terminal 2aP and the DC terminal T2 of the bidirectional chopper 2. The collector of the IGBT element Q5 is connected to the positive DC terminal 2aP, and the emitter of the IGBT element Q5 is connected to the DC terminal T2. The diode D5 is connected in antiparallel to the IGBT element Q5. The IGBT element Q5 and the diode D5 correspond to one embodiment of the "first switch". The IGBT element Q5 corresponds to one embodiment of the "first semiconductor switching element", and the diode D5 corresponds to one embodiment of the "first diode".

[0043] The IGBT element Q5 and EDLC8 are connected in series between the positive DC terminal 2aP and the negative DC terminal 2aN of the bidirectional chopper 2. In the example in Figure 2, the IGBT element Q5 is connected between the positive DC terminal 2aP of the bidirectional chopper 2 and the positive terminal of the EDLC8, but the IGBT element Q5 may also be connected between the negative terminal of the EDLC8 and the negative DC terminal 2aN of the bidirectional chopper 2.

[0044] The on / off state of the IGBT element Q5 is controlled by the control device 5. When the IGBT element Q5 is on, it is connected to allow current (i.e., the charging current for the EDLC 8) to flow from the bidirectional chopper 2 to the EDLC 8. When the IGBT element Q5 is off, the diode D5 is connected to allow current (i.e., the discharging current for the EDLC 8) to flow from the EDLC 8 to the bidirectional chopper 2.

[0045] The IGBT element Q6 is connected between the positive DC terminal 2aP and the DC terminal T3 of the bidirectional chopper 2. The emitter of the IGBT element Q6 is connected to the positive DC terminal 2aP, and the collector of the IGBT element Q6 is connected to the DC terminal T3. The diode D6 is connected in antiparallel to the IGBT element Q6. The IGBT element Q6 and the diode D6 correspond to one embodiment of the "second switch". The IGBT element Q6 corresponds to one embodiment of the "second semiconductor switching element", and the diode D6 corresponds to one embodiment of the "second diode".

[0046] The IGBT element Q6 and the battery 9 are connected in series between the positive DC terminal 2aP and the negative DC terminal 2aN of the bidirectional chopper 2. In the example shown in Figure 2, the IGBT element Q6 is connected between the positive DC terminal 2aP of the bidirectional chopper 2 and the positive terminal of the battery 9, but the IGBT element Q6 may also be connected between the negative terminal of the battery 9 and the negative DC terminal 2aN of the bidirectional chopper 2.

[0047] The on / off state of the IGBT element Q6 is controlled by the control device 5. When the IGBT element Q6 is on, it is connected to allow current (i.e., the discharge current of the battery 9) to flow from the battery 9 to the bidirectional chopper 2. When the IGBT element Q6 is off, the diode D6 is connected to allow current (i.e., the charging current of the battery 9) to flow from the bidirectional chopper 2 to the battery 9.

[0048] Figure 3 is a block diagram showing an example of the hardware configuration of the control device 5. Typically, the control device 5 can be configured using a microcomputer with a predetermined program pre-stored in it.

[0049] In the example shown in Figure 3, the control unit 5 includes a CPU (Central Processing Unit) 50, memory 52, and input / output (I / O) circuit 54. The CPU 50, memory 52, and I / O circuit 54 can exchange data with each other via a bus 56. A program is stored in a portion of the memory 52, and the CPU 50 can execute this program to realize various functions described later. The I / O circuit 54 inputs and outputs signals and data to and from the outside of the control unit 5.

[0050] Alternatively, unlike the example in Figure 3, at least a portion of the control device 5 can be configured using circuits such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit).

[0051] Figure 4 is a block diagram showing the functional configuration of the control device 5. As shown in Figure 4, the control device 5 is composed of an anomaly detector 60, a switching control unit 62, a power conversion control unit 64, an adder 66, and a subtractor 68. The functions of each block shown in Figure 4 can be realized by at least one of software processing and hardware processing by the control device 5.

[0052] The anomaly detector 60 detects whether an anomaly has occurred in the AC power supply 7 based on the AC input voltage VI supplied from the AC power supply 7, and outputs an anomaly detection signal φF indicating the detection result. When the AC power supply 7 is healthy, the anomaly detection signal φF is set to the deactivation level "L". When an anomaly occurs in the AC power supply 7, the anomaly detection signal φF is set to the activation level "H". For example, if the AC input voltage VI falls below the lower limit, the anomaly detector 60 determines that a power outage has occurred in the AC power supply 7 and sets the anomaly detection signal φF to the "H" level. Also, if the AC input voltage VI is higher than the upper limit, the anomaly detector 60 determines that an overvoltage has occurred in the AC power supply 7 and sets the anomaly detection signal φF to the "H" level.

[0053] The switching control unit 62 controls the switching circuit 6 based on the abnormality detection signal φF, DC voltage VD, VE, etc., provided by the abnormality detector 60. Figure 5 is a flowchart illustrating the control of the switching circuit 6 by the switching control unit 62. The flowchart shown in Figure 5 is repeatedly executed when the uninterruptible power supply 100 is in operation.

[0054] As shown in Figure 5, in step 11 (hereinafter simply referred to as "S"), the switching control unit 62 determines whether or not an abnormality has occurred in the AC power supply 7 based on the abnormality detection signal φF.

[0055] If the abnormality detection signal φF is at the "L" level, the switching control unit 62 determines that the AC power supply 7 is healthy (NO determination in S11). In this case, the switching control unit 62 turns on IGBT element Q5 and turns off IGBT element Q6 in S12.

[0056] When IGBT element Q5 is turned on, the switching circuit 6 can supply current (charging current to EDLC8) from the bidirectional chopper 2 to EDCL8. On the other hand, when IGBT element Q6 is turned off, the switching circuit 6 is unable to supply current (discharging current to battery 9) from battery 9 to bidirectional chopper 2. However, due to diode D6 connected in antiparallel to IGBT element Q6, the switching circuit 6 can supply current (i.e., charging current to battery 9) from the bidirectional chopper 2 to battery 9.

[0057] In S13, the switching control unit 62 determines whether the DC voltage VE (voltage VE across the terminals of the EDLC8) is greater than the discharge termination voltage VEmin of the EDLC8. If VE > VEmin (when S13 determines YES), the switching control unit 62 skips the processes in S14 to S16.

[0058] If VE ≤ VEmin (when NO is determined in S13), the switching control unit 62 turns on the IGBT element Q6 in S14. When the IGBT element Q6 is turned on, the switching circuit 6 is able to supply current (the discharge current of the battery 9) from the battery 9 to the bidirectional chopper 2.

[0059] In step S15, the switching control unit 62 compares the DC voltage VD with a predetermined threshold voltage VDth. The threshold voltage VDth is set to a voltage value lower than the reference DC voltage VD*, which is the target value of the DC voltage VD.

[0060] If VD ≤ VDth (when S15 determines NO), the switching control unit 62 keeps the IGBT element Q6 ON. On the other hand, if VD > VDth (when S15 determines YES), the switching control unit 62 turns off the IGBT element Q6 in S16.

[0061] Returning to S11, if the abnormality detection signal φF is at the "H" level, the switching control unit 62 determines that the AC power supply 7 is abnormal (YES determination in S11). In this case, the switching control unit 62 turns off IGBT element Q5 and turns on IGBT element Q6 in S17.

[0062] When IGBT element Q5 is turned off, the switching circuit 6 is unable to supply current (charging current to EDLC8) from the bidirectional chopper 2 to EDLC8. However, due to diode D5 connected in antiparallel to IGBT element Q5, the switching circuit 6 can supply current (discharging current to EDLC8) from EDLC8 to the bidirectional chopper 2. On the other hand, when IGBT element Q6 is turned on, the switching circuit 6 becomes able to supply current (discharging current to battery 9) from battery 9 to bidirectional chopper 2.

[0063] In this manner, the switching control unit 62 controls the switching circuit 6 to allow charging of the EDLC 8 and battery 9, and discharging of the EDLC 8, when the AC power supply 7 is healthy. However, if the terminal voltage VE of the EDLC 8 reaches the discharge termination voltage VEmin, the switching control unit 62 controls the switching circuit 6 to allow discharging of the battery 9.

[0064] On the other hand, in the event of an abnormality in the AC power supply 7, the switching control unit 62 controls the switching circuit 6 to allow the discharge of the EDLC 8 and the battery 9.

[0065] Returning to Figure 4, the adder 66 adds the DC voltage between DC lines L1 and L2 (i.e., the voltage across the terminals of capacitor C1) Ep and the DC voltage between DC lines L2 and L3 (i.e., the voltage across the terminals of capacitor C2) En to obtain the DC voltage between DC lines L1 and L3, VD = Ep + En. The subtractor 68 subtracts the DC voltage En from the DC voltage Ep to obtain the DC voltage ΔE = Ep - En.

[0066] The power conversion control unit 64 controls the converter 1, the bidirectional chopper 2, and the inverter 3 based on the abnormality detection signal φF, the DC voltages VD, ΔE, VE, VB, VS, the AC input voltage VI, the AC output voltage VO, and the output signals Iif, Isf, Iof from the current detectors CD1 to CD3.

[0067] Figure 6 is a block diagram showing the configuration of the part of the power conversion control unit 64 shown in Figure 4 that is related to the control of converter 1. As shown in Figure 6, the power conversion control unit 64 includes a reference voltage generation unit 20, subtractors 24 and 36, a filter 22, a DC voltage control unit 26, a load current feedforward (FF) unit 28, adders 30, 40, and 44, a multiplier 32, a divider 34, a current control unit 38, a balance control unit 42, and a PWM (Pulse Width Modulation) circuit 46.

[0068] The reference voltage generator 20 generates a reference DC voltage VD*. The filter 22 removes the AC component from the DC voltage VD from the adder 66 (Figure 4). The filter 22 is configured to include, for example, a moving average circuit. The moving average circuit calculates a moving average value of the DC voltage VD from the adder 66 over a predetermined moving average interval Tw. The moving average interval Tw is set to, for example, the reciprocal of the frequency f of the AC power supply 7 (Tw = 1 / f). Therefore, if the frequency f of the AC power supply 7 is 50 Hz, the moving average interval Tw = 20 ms.

[0069] The subtractor 24 calculates the difference ΔVD = VD* - VD between the reference DC voltage VD* and the DC voltage VD from the filter 22.

[0070] The DC voltage control unit 26 determines a feedback component Ifb to control the input current (AC input current Ii) of the converter 1 so that the deviation ΔVD becomes zero. The DC voltage control unit 26 determines a feedback component Ifb with a value corresponding to the voltage ΔVD, for example, by performing a proportional or proportional-integral operation on the deviation ΔVD. Feedback control is performed such that when the deviation ΔVD increases, the feedback component Ifb increases and the deviation ΔVD decreases, and when the deviation ΔVD decreases, the feedback component Ifb decreases and the deviation ΔVD disappears.

[0071] The load current FF unit 28 generates a feedforward component Iff of the current command value Ii* based on the load current Io indicated by the output signal Iof of the current detector CD3. The current command value Ii* corresponds to the command value of the input current (AC input current) Ii of the converter 1.

[0072] The load current FF section 28 is configured, for example, to include a moving average circuit. The moving average circuit calculates a moving average value over a predetermined moving average interval Tw for the output signal Iof from the current detector CD3. The moving average interval Tw is set, for example, to the reciprocal of the frequency f of the AC power supply 7 (Tw = 1 / f). If the frequency f of the AC power supply 7 is 50Hz, the moving average interval Tw = 20ms.

[0073] The adder 30 adds the feedback component Ifb from the DC voltage control unit 26 and the feedforward component Iff from the load current FF unit 28 to generate a current command value ID*=Ifb+Iff.

[0074] The multiplier 32 generates a DC power command value Pi* by multiplying the DC voltage VD from the filter 22 by the current command value ID*. The divider 34 generates a current command value Ii* by dividing the DC power command value Pi* by the AC input voltage VI. This generates a sinusoidal current command value Ii* that is in phase with the AC input voltage VI.

[0075] The subtractor 36 calculates the deviation ΔIi = Ii* - Ii between the current command value Ii* and the AC input current Ii detected by the current detector CD1.

[0076] The current control unit 38 generates a voltage command value VIa* such that the deviation ΔIi becomes 0. The current control unit 38 generates the voltage command value VIa* by, for example, amplifying the deviation ΔIi according to proportional control or proportional-integral control. The adder 40 adds the voltage command value VIa* and the AC input voltage VI to generate a voltage command value VIb*.

[0077] The balance control unit 42 generates a voltage command value VIc* based on the DC voltage ΔE = Ep - En from the subtractor 68. For example, the balance control unit 42 generates the voltage command value VIc* by performing a proportional or proportional-integral operation on the DC voltage ΔE. If ΔE = Ep - En > 0, the voltage command value VIc* is generated such that the charging time of capacitor C1 is shorter than the charging time of capacitor C2. If ΔEp = Ep - En < 0, the voltage command value VIc* is generated such that the charging time of capacitor C1 is longer than the charging time of capacitor C2.

[0078] The adder 44 adds the voltage command values ​​VIb* and V1c* to generate the voltage command value VI*. The PWM circuit 46 controls the converter 1 based on the sinusoidal voltage command value VI* when the abnormality detection signal φF from the abnormality detector 60 (Figure 4) is at the deactivation level "L" (when the AC power supply 7 is healthy). As a result, the DC voltage VD = Ep + En is maintained at the reference DC voltage VD*, and the DC voltage ΔE is maintained at 0.

[0079] Furthermore, the PWM circuit 46 stops the operation of the converter 1 when the abnormality detection signal φF is at the activation level "H" (indicating an abnormality in the AC power supply 7). This electrically disconnects the AC input terminal T1 from the DC lines L1 to L3.

[0080] By introducing a feedforward component Iff corresponding to the load current Io into the current command value ID* in this way, an AC input current Ii including the feedback component Ifb and the feedforward component Iff can be flowed from the AC power supply 7 to the converter 1.

[0081] According to this, the control is stabilized by controlling the feedback component Ifb at a low speed, while the feedforward component Iff enables a fast response to fluctuations in the load current Io. Furthermore, since the proportional gain of the feedback component Ifb can be set to a relatively small value, the proportional control or proportional-integral control in the DC voltage control unit 26 can be stabilized.

[0082] Furthermore, since the DC voltage VD can be stabilized by controlling converter 1, the capacitance of capacitors C1 and C2 can be reduced, allowing for miniaturization of capacitors C1 and C2. Therefore, it becomes possible to reduce the size and cost of the device.

[0083] In Figure 6, a configuration was described in which the feedforward component Iff is generated using the detected value of the load current Io detected by the current detector CD3. However, a configuration in which the feedforward component Iff is generated using the detected values ​​of the currents flowing through the DC lines L1 and L3 is also possible.

[0084] Figure 7 is a block diagram showing the configuration of the part of the power conversion control unit 64 shown in Figure 4 that is related to the control of the bidirectional chopper 2. As shown in Figure 7, the power conversion control unit 64 is composed of a comparator 640 and control circuits 642 and 644.

[0085] The comparator 640 detects a decrease in the DC voltage VD by comparing it with the threshold voltage VDth from the adder 66 (Figure 4). The threshold voltage VDth is set to a voltage value lower than the reference DC voltage VD* (first reference DC voltage).

[0086] The comparator 640 outputs a voltage drop detection signal φD. Specifically, when the DC voltage VD is below the threshold voltage VDth, the comparator 640 determines that a drop in the DC voltage VD has occurred and sets the voltage drop detection signal φD to the activation level "H". On the other hand, when the DC voltage VD is higher than the threshold voltage VDth, the comparator 640 determines that no drop in the DC voltage VD has occurred and sets the voltage drop detection signal φD to the deactivation level "L".

[0087] The control circuit 642 is activated when the voltage drop detection signal φD is at the deactivation level "L," and operates the bidirectional chopper 2 to supply DC power from DC lines L1 and L3 to the EDLC 8 and battery 9 based on the DC voltages VD, VS, VE, VB and the DC current Is indicated by the output signal Isf of the current detector CD2. Specifically, the control circuit 642 controls the bidirectional chopper 2 so that the DC voltage VS becomes the reference DC voltage VS* (second reference DC voltage). The reference DC voltage VS* is set based on the terminal voltages VE, VB when the EDLC 8 and battery 9 are in a predetermined fully charged state.

[0088] The control circuit 644 is activated when the voltage drop detection signal φD is at the activation level "H", and operates the bidirectional chopper 2 to supply DC power from the EDLC 8 and / or battery 9 to the DC lines L1 and L3 based on the DC voltages VD and VS, the DC current Is indicated by the output signal Isf of the current detector CD2, and the abnormality detection signal φF.

[0089] A drop in the DC voltage VD can occur when the power consumption of the load 10 increases sharply and becomes overloaded while the AC power supply 7 is functioning properly. When the power consumption of the load 10 exceeds the rated load of the uninterruptible power supply 100, the excess power is supplied to the inverter 3 from capacitors C1 and C2, causing the DC voltage VD to drop. In this case, the control circuit 644 controls the current of the bidirectional chopper 2 so that the excess power is supplied to the inverter 3 from the EDLC 8 (or battery 9).

[0090] Furthermore, a decrease in the DC voltage VD can also occur if there is a malfunction in the AC power supply 7. If a malfunction occurs in the AC power supply 7, the operation of the converter 1 is stopped and the AC input terminal T1 and the DC lines L1~L3 are electrically disconnected, causing the DC voltage VD to decrease. In this case, the control circuit 644 performs voltage control of the bidirectional chopper 2 so that the DC voltage VD becomes the reference DC voltage VD*.

[0091] Figure 8 is a block diagram showing the configuration of the control circuit 644 shown in Figure 7. As shown in Figure 8, the control circuit 644 includes a reference voltage generator 70, subtractors 74, 78, 86, 88, a filter 72, a voltage control unit 76, current control units 80, 90, a balance control unit 82, an adder 84, a switch 92, and a PWM circuit 94.

[0092] The reference voltage generation unit 70 generates a reference DC voltage VD*. The filter 72 removes the AC component from the DC voltage VD from the adder 66 (FIG. 4). The filter 72 is configured to include, for example, a moving average circuit. The moving average circuit obtains the moving average value of the DC voltage VD from the adder 66 over a predetermined moving average interval Tw. The moving average interval Tw is set, for example, to the reciprocal of the frequency f of the AC power supply 7 (Tw = 1 / f). Therefore, when the frequency f of the AC power supply 7 is 50 Hz, the moving average interval Tw is 20 ms.

[0093] The subtractor 74 obtains the deviation ΔVD = VD* - VD between the reference DC voltage VD* and the DC voltage VD from the filter 72.

[0094] The voltage control unit 76 obtains a current command value Is* at a level corresponding to the deviation ΔVD based on the DC voltage VS. The voltage control unit 76 obtains the current command value Is* by, for example, performing proportional operation or proportional integral operation on the deviation ΔVD.

[0095] The subtractor 78 obtains the deviation ΔIs = Is* - Is between the current command value Is* generated by the voltage control unit 76 and the DC current Is indicated by the output signal Isf of the current detector CD2. The current control unit 80 generates a voltage command value VDc based on the deviation ΔIs. The current control unit 80 obtains the voltage command value VDc by, for example, performing proportional operation or proportional integral operation on the deviation ΔIs.

[0096] The balance control unit 82 generates a voltage command value VDb based on the DC voltage ΔE = Ep - En from the subtractor 68 (FIG. 4). For example, the balance control unit 82 generates the voltage command value VDb by performing proportional operation or proportional integral operation on the DC voltage ΔE. For example, when Ep - En > 0, the balance control unit 82 sets the voltage command value VDb to a negative value. On the other hand, when Ep < En, the balance control unit 82 sets the voltage command value VDb to a positive value.

[0097] The adder 84 adds the voltage command values ​​VDc and VDb to generate the voltage command value VA*. The subtractor 86 subtracts the voltage command value VDb from the voltage command value VDc to generate the voltage command value VB*. The voltage command values ​​VA* and VB* are command values ​​for controlling the voltages of the upper and lower arms of the semiconductor switch 23, respectively, and are the command values ​​for voltages Ep and En to make the difference between voltages Ep and En zero.

[0098] The subtractor 88 calculates the difference ΔI = Io - Ii between the load current Io, indicated by the output signal Iof of the current detector CD3, and the AC input current Ii, indicated by the output signal Iif of the current detector CD1. The current control unit 90 generates a voltage command value VDa to supply a current corresponding to the difference ΔI from the bidirectional chopper 2 to the DC lines L1 and L3.

[0099] Switch 92 transmits the voltage command value VDa generated by the current control unit 90 to the PWM circuit 94 when the abnormality detection signal φF from the abnormality detector 60 (Figure 4) is at the "L" level, i.e., when the AC power supply 7 is healthy. As a result, when the AC power supply 7 is healthy and a drop in DC voltage VD occurs due to overload, the bidirectional chopper 2 is current-controlled so that a current equivalent to the difference ΔI between the load current Io and the AC input current Ii is supplied from the EDLC 8 (or battery 9) to the DC lines L1 and L3.

[0100] On the other hand, if the abnormality detection signal φF from the abnormality detector 60 is at the "H" level, that is, if the AC power supply 7 is abnormal, the switch 92 transmits the voltage command values ​​VA* and VB* to the PWM circuit 94. As a result, when the AC power supply 7 is abnormal, the bidirectional chopper 2 performs voltage control so that the DC voltage VD becomes the reference DC voltage VD*.

[0101] The PWM circuit 94 outputs signals to drive the IGBT elements Q1 to Q4 included in the semiconductor switch 23 based on the voltage command values ​​VA*, VB*, or VDa.

[0102] Figure 9 is a flowchart illustrating the control of the bidirectional chopper 2 in the power conversion control unit 64. The flowchart shown in Figure 9 is repeatedly executed when the uninterruptible power supply 100 is in operation.

[0103] As shown in Figure 9, in S01, the power conversion control unit 64 compares the DC voltage VD with the threshold voltage VDth. If the DC voltage VD is higher than the threshold voltage VDth (when S01 is judged as YES), the power conversion control unit 64 determines that no decrease in the DC voltage VD has occurred and sets the voltage drop detection signal φD to the deactivation level "L".

[0104] If the voltage drop detection signal φD is at the "L" level, the power conversion control unit 64 (control circuit 642) controls the bidirectional chopper 2 so that the DC voltages VE and VB equal the reference DC voltage VS*. Specifically, in S02, the power conversion control unit 64 compares the DC voltage VS with the reference DC voltage VS*. If the DC voltage VS is greater than or equal to the reference DC voltage VS* (when S02 determines YES), the power conversion control unit 64 stops the operation of the bidirectional chopper 2 in S03.

[0105] On the other hand, if the DC voltages VE and VB are less than the reference DC voltage VS* (when NO is determined in S02), the power conversion control unit 64 controls the bidirectional chopper 2 in S04 so that the DC power supplied from the converter 1 via the DC lines L1 and L3 is stored in the EDLC 8 and battery 9 via the switching circuit 6. In S04, voltage control of the bidirectional chopper 2 is performed so that the DC voltages VE and VB become the reference DC voltage VS*.

[0106] In S01, if the DC voltage VD is less than or equal to the threshold voltage VDth (when NO is determined in S01), the power conversion control unit 64 determines that a decrease in the DC voltage VD has occurred and sets the voltage drop detection signal φD to the activation level "H".

[0107] If the voltage drop detection signal φD is at the "H" level, the power conversion control unit 64 (control circuit 644) determines in S05 whether or not an abnormality has occurred in the AC power supply 7 based on the abnormality detection signal φF.

[0108] If the abnormality detection signal φF is at the "L" level, the power conversion control unit 64 determines that the AC power supply 7 is healthy (NO determination in S05). In this case, in S06, the power conversion control unit 64 controls the bidirectional chopper 2 to convert the DC voltage VS supplied from the EDLC 8 via the switching circuit 6 into three levels of DC voltage V1 to V3 and output them to the positive voltage terminal 2b, the neutral voltage terminal 2c, and the negative voltage terminal 2d. The bidirectional chopper 2 is current-controlled based on the difference between the load current Io and the AC input current Ii.

[0109] In S06, the power stored in the EDLC8 is preferentially used by the switching circuit 6. However, if the terminal voltage VE of the EDLC8 reaches the discharge termination voltage VEmin during the discharge of the EDLC8, the power stored in the battery 9 is used.

[0110] On the other hand, if the abnormality detection signal φF is at the "H" level, the power conversion control unit 64 determines that the AC power supply 7 is abnormal (YES determination in S05). In this case, in S09, the power conversion control unit 64 controls the bidirectional chopper 2 to convert the DC voltage VS supplied from the EDLC 8 and battery 9 via the switching circuit 6 into three levels of DC voltage V1 to V3 and output them to the positive voltage terminal 2b, the neutral voltage terminal 2c, and the negative voltage terminal 2d. The bidirectional chopper 2 is voltage-controlled based on the deviation ΔVD between the reference DC voltage VD* and the DC voltage VD.

[0111] As shown in Figure 5, when the AC power supply 7 is functioning normally, the switching circuit 6 is controlled to allow discharge of the EDLC 8. Therefore, when the AC power supply 7 is functioning normally, if the power consumption of the load 10 increases sharply and becomes overloaded, the bidirectional chopper 2 supplies the DC power stored in the EDLC 8 to the DC lines L1 and L3. Since the EDLC 8 can output a large current instantaneously, the uninterruptible power supply 100 can respond quickly to a sharp increase in the power consumption of the load 10.

[0112] Furthermore, if the energy stored in the EDLC 8 decreases and the terminal voltage VE of the EDLC 8 reaches the discharge termination voltage VEmin, the switching circuit 6 is controlled to allow the battery 9 to discharge. This ensures that even if an overload persists, the AC power supplied from the AC power source 7 is kept below the rated load of the uninterruptible power supply 100.

[0113] On the other hand, in the event of an abnormality in the AC power supply 7, the switching circuit 6 is controlled to allow the discharge of the battery 9 and EDLC 8. Therefore, in the event of an abnormality in the AC power supply 7, the bidirectional chopper 2 supplies the DC power stored in the EDLC 8 and battery 9 to the DC lines L1 and L3.

[0114] During the discharge of the EDLC 8 or battery 9, the power conversion control unit 64 determines in S07 whether the DC voltage VS has fallen below a predetermined discharge termination voltage VSmin. If the DC voltage VS has fallen below the discharge termination voltage VSmin (when S07 determines YES), the power conversion control unit 64 stops the operation of the bidirectional chopper 2 in S08.

[0115] Next, the operation of the uninterruptible power supply 100 according to this embodiment will be described. Figures 10 to 13 are diagrams showing the power flow in the uninterruptible power supply 100 according to this embodiment.

[0116] Figure 10 shows the power flow when the AC power supply 7 is functioning correctly, indicated by arrows. When the AC power supply 7 is functioning correctly, the converter 1 converts the AC power supplied from the AC power supply 7 into DC power and outputs that DC power to the DC lines L1 to L3.

[0117] The switching circuit 6 turns on IGBT element Q5 and turns off IGBT element Q6. In Figure 10, IGBT element Q5 is shown in the ON state, while the IGBT element Q6 in the OFF state is not shown.

[0118] The bidirectional chopper 2 stores the DC power supplied from the converter 1 via DC lines L1 to L3 in the EDLC 8 via the IGBT element Q5, and also stores it in the battery 9 via the diode D6. The EDLC 8 and battery 9 are charged to a predetermined full charge state.

[0119] The inverter 3 converts the DC power supplied from the converter 1 via the DC lines L1 to L3 into AC power, and supplies that AC power to the load 10.

[0120] When a load 10 with large fluctuations in power consumption is connected to an uninterruptible power supply 100, the power consumption of load 10 may temporarily exceed the rated load of the uninterruptible power supply 100. Figure 11 shows the power flow when the uninterruptible power supply 100 becomes overloaded while the AC power supply 7 is functioning normally, indicated by arrows.

[0121] The power supplied from the AC power source 7 is limited to the rated load of the uninterruptible power supply 100. The remaining power from the load 10's consumption is supplied to the load 10 from the EDLC 8 via diode D5, bidirectional chopper 2, and inverter 3.

[0122] Furthermore, since the IGBT element Q6 is turned off in the switching circuit 6, the DC power from the battery 9 is not supplied to the load 10, and the battery 9 is kept in a predetermined fully charged state. Therefore, when the power consumption of the load 10 fluctuates periodically, it is possible to prevent the battery 9 from deteriorating due to the periodic repeated discharge and charging of the battery 9.

[0123] However, if the overload persists and the terminal voltage VE reaches the discharge termination voltage VEmin during the discharge of the EDLC 8, the switching circuit 6 turns on the IGBT element Q6. In this case, as shown in Figure 12, the remaining power from the load 10's consumption is supplied to the load 10 from the battery 9 via the IGBT element Q6, the bidirectional chopper 2, and the inverter 3. By pre-selecting the capacity of the EDLC 8 according to fluctuations in the load 10's power consumption, the discharge of the battery 9 during overload can be suppressed.

[0124] During periods when the uninterruptible power supply (UPS) 100 is overloaded, the EDLC 8 is discharged preferentially. This keeps the power supplied from the AC power source 7 below the rated load of the UPS 100. Furthermore, because the EDLC 8 can output a large current instantaneously, the UPS 100 can respond quickly to sudden increases in power consumption. In addition, the EDLC 8 exhibits less performance degradation with repeated charging and discharging compared to the battery 9. Therefore, the power supply reliability of the UPS 100 can be maintained.

[0125] Figure 13 shows the power flow when the AC power supply 7 malfunctions, indicated by arrows. When the AC power supply 7 malfunctions, the converter 1 stops operating.

[0126] The switching circuit 6 turns off IGBT element Q5 and turns on IGBT element Q6. In Figure 13, IGBT element Q6 is shown in the ON state, while the IGBT element Q5 in the OFF state is not shown.

[0127] The bidirectional chopper 2 outputs DC power supplied from the EDLC 8 via diode D5 and DC power supplied from the battery 9 via IGBT element Q6 to DC lines L1 to L3.

[0128] The inverter 3 converts the DC power supplied from the bidirectional chopper 2 via DC lines L1 to L3 into AC power, and supplies that AC power to the load 10.

[0129] As described above, when the AC power supply 7 is functioning properly, the power stored in the EDLC 8 is used preferentially, so the battery 9 is kept in a predetermined fully charged state. Therefore, if an abnormality occurs in the AC power supply 7, the uninterruptible power supply 100 can use the power stored in the battery 9 to continuously supply power to the load 10 for a predetermined power outage compensation period.

[0130] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0131] 1 Converter, 2 Bidirectional Chopper, 3 Inverter, 4 Operating Unit, 5 Control Device, 6 Switching Circuit, 7 AC Power Supply, 8 EDLC, 9 Battery, 10 Load, 20, 70 Reference Voltage Generator, 21, 21P, 21N Reactor, 22, 72 Filter, 23 Semiconductor Switch, 24, 36, 68, 74, 78, 86, 88 Subtractor, 26 DC Voltage Control Unit, 30, 40, 44, 66, 84 Adder, 28 Load Current FF Unit, 32 Multiplier, 34 Divider, 38, 80, 90 Current Control Unit, 42, 82 Balance Control Unit, 46, 94 PWM Circuit, 50 CPU, 52 Memory, 54 I / O Circuit, 56 Bus, 60 Anomaly Detector, 62 Switching Control Unit, 64 Power Conversion Control Unit, 76 Voltage Control Unit, 92 Switch, 100 Uninterruptible power supply, 640 comparator, 642, 644 control circuit, T1 AC input terminal, T2, T3 DC terminals, T4 AC output terminal, L1~L3 DC lines, C1~C4 capacitors, CD1~CD3 current detectors, Q1~Q6 IGBT elements, D1~D6 diodes.

Claims

1. An uninterruptible power supply connected between an AC power source and a load, A converter that converts AC power supplied from the aforementioned AC power source into DC power and outputs it to a DC line, An inverter that converts the DC power supplied from the DC line into AC power and supplies it to the load, A bidirectional chopper for transferring DC power between the DC line and the first and second energy storage devices, A switching circuit is provided between the bidirectional chopper and the first and second energy storage devices, Equipped with a control device, The first energy storage device has a higher power density compared to the second energy storage device. The second energy storage device has a higher energy density than the first energy storage device. The control device is When the AC power supply is healthy, the switching circuit is controlled to allow charging of the first and second energy storage devices and discharging of the first energy storage device. An uninterruptible power supply that controls the switching circuit to allow the discharge of the first and second energy storage devices in the event of an abnormality in the AC power supply.

2. The switching circuit is, A first switch connected between the bidirectional chopper and the first energy storage device, It includes a second switch connected between the bidirectional chopper and the second energy storage device, The first switch is, A first semiconductor switching element is connected between the bidirectional chopper and the first energy storage device so as to allow current to flow from the bidirectional chopper to the first energy storage device when it is in the ON state, The first semiconductor switching element includes a first diode connected in antiparallel to the first semiconductor switching element, The second switch is, A second semiconductor switching element is connected between the bidirectional chopper and the second energy storage device so as to allow current to flow from the second energy storage device to the bidirectional chopper when it is in the ON state, The system includes a second diode connected in antiparallel to the second semiconductor switching element, The control device is When the AC power supply is healthy, the first semiconductor switching element is turned on and the second semiconductor switching element is turned off. The uninterruptible power supply according to claim 1, wherein in the event of an abnormality in the AC power supply, the first semiconductor switching element is turned off and the second semiconductor switching element is turned on.

3. The uninterruptible power supply according to claim 2, wherein the control device further turns on the second semiconductor switching element when the voltage of the first energy storage device reaches the discharge termination voltage while the AC power supply is functioning properly.

4. The first energy storage device is an electric double-layer capacitor, The uninterruptible power supply according to any one of claims 1 to 3, wherein the second energy storage device is a secondary battery.

5. A first current detector for detecting the input current of the converter, The system further comprises a second current detector for detecting the load current flowing from the inverter to the load, The uninterruptible power supply according to claim 1 or 2, wherein when the AC power supply is healthy, the control device controls the converter so that the input current, which includes a feedback component corresponding to the deviation between the DC voltage of the DC line and a first reference DC voltage, and a feedforward component corresponding to the load current detected by the second current detector, flows from the AC power supply to the converter.

6. The uninterruptible power supply according to claim 5, wherein, when the AC power supply is functioning properly, if the DC voltage of the DC line falls below a threshold voltage lower than the first reference DC voltage, the control device controls the bidirectional chopper to supply a current to the DC line corresponding to the difference between the load current and the input current.

7. The uninterruptible power supply according to claim 6, wherein, when the AC power supply is functioning properly, the DC voltage of the DC line is higher than the threshold voltage, the control device controls the bidirectional chopper so that the voltages of the first and second energy storage devices become the second reference DC voltage.

8. The uninterruptible power supply according to claim 5, wherein in the event of an abnormality in the AC power supply, the control device stops the operation of the converter and controls the bidirectional chopper so that the DC voltage of the DC line becomes the first reference DC voltage.

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