Uninterruptible power supply device

Abstract

An uninterruptible power supply according to the present disclosure includes a converter (1), capacitors (C1, C2), an inverter (3), a first current detector (CD1), a second current detector (CD3), and a control device (5). The control device (5) controls the converter (1) so that the input voltage and input current of the converter (1) are in phase and the DC voltage of the DC lines (L1, L3) is equal to a first reference voltage. The control device (5) controls the converter (1) so that the input current, which includes a feedback component corresponding to the deviation between the DC voltage of the DC lines (L1, L3) and the first reference voltage and a feedforward component corresponding to the load current detected by the second current detector (CD2), flows from the AC power source to the converter (1).

Description

[Technical Field]

[0001] The present disclosure relates to uninterruptible power supplies. [Background technology]

[0002] For example, International Publication No. 2020 / 026430 (Patent Document 1) discloses an uninterruptible power supply including a converter, a capacitor, an inverter, and a control device. When the AC power supply is healthy, the converter converts AC power supplied from the AC power supply into DC power and supplies it to a DC line. The capacitor is connected to the DC line. The inverter converts DC power received from the DC line into AC power and supplies it to a load. When the AC power supply is healthy, the control device controls the converter so that the DC voltage of the DC line becomes a reference voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 026430 Summary of the Invention [Problem to be solved by the invention]

[0004] In such an uninterruptible power supply, the control device controls the converter to stabilize the DC voltage of the DC line on average and to make the power factor of the input power to the uninterruptible power supply 1. The capacitance of the capacitor is set to a sufficiently large value according to the load specifications so that the capacitor can absorb fluctuations in the output power of the uninterruptible power supply due to ripple voltage containing high-frequency components and load characteristics.

[0005] On the other hand, miniaturization of capacitors is required from the viewpoint of miniaturization and cost reduction of equipment. However, if the capacitor is miniaturized and its capacitance is reduced, the capacitance will be insufficient to cope with load fluctuations, making it difficult to stabilize the DC voltage of the DC line. Furthermore, there is a concern that ripple voltage will occur in the DC voltage of the DC line, which will increase distortion of the waveform of the input current of the converter and reduce efficiency.

[0006] Therefore, a primary object of the present disclosure is to provide a compact and highly efficient uninterruptible power supply. [Means for solving the problem]

[0007] An uninterruptible power supply according to the present disclosure includes a converter, a capacitor, an inverter, a first current detector, a second current detector, and a control device. The converter converts AC power supplied from an AC power source into DC power and supplies it to a DC line. The capacitor is connected to the DC line. The inverter converts DC power received from the DC line into AC power and supplies it to a load. The first current detector detects an input current to the converter. The second current detector detects a load current flowing from the inverter to the load. The control device controls the converter so that the input voltage and input current of the converter are in phase and the DC voltage of the DC line is equal to a first reference voltage. The control device controls the converter so that an input current flows from the AC power source to the converter, the input current including a feedback component corresponding to the deviation between the DC voltage of the DC line and the first reference voltage and a feedforward component corresponding to the load current detected by the second current detector. [Effects of the Invention]

[0008] According to the present disclosure, a small and highly efficient uninterruptible power supply can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit block diagram showing a configuration of an uninterruptible power supply according to a first embodiment. [Figure 2] FIG. 2 is a block diagram illustrating an example of a hardware configuration of a control device. [Figure 3] FIG. 2 is a block diagram showing the configuration of a portion of the control device that is related to the control of the converter. [Figure 4] FIG. 4 is a block diagram showing the configuration of a control circuit shown in FIG. 3. [Figure 5] FIG. 10 is a circuit block diagram showing a configuration of an uninterruptible power supply according to a second embodiment. [Figure 6] 6 is a block diagram showing the configuration of a portion of the control device shown in FIG. 5 that is related to the control of a converter. FIG. [Figure 7] FIG. 7 is a block diagram showing the configuration of a control circuit shown in FIG. 6. [Figure 8] 10 is a flowchart illustrating the control of a switch by a switch control unit. [Figure 9] 10 is a flowchart for explaining control of the load current FF unit. [Figure 10] 1 is a circuit block diagram showing a configuration of an uninterruptible power supply according to a first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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 will be denoted by the same reference numerals, and their description will not be repeated in principle.

[0011] [Embodiment 1] Fig. 1 is a circuit block diagram showing the configuration of an uninterruptible power supply according to embodiment 1. As shown in Fig. 1, the uninterruptible power supply includes an input terminal T1, a DC terminal T2, an output terminal T3, a converter 1, current detectors CD1-CD3, DC lines L1-L3, capacitors C1-C4, a bidirectional chopper 2, an inverter 3, an operation unit 4, and a control device 5.

[0012] The input terminal T1 receives an AC voltage VI from an AC power supply 6. The instantaneous value of the AC voltage VI (hereinafter also referred to as "AC input voltage VI") is detected by the control device 5. Whether or not a power outage has occurred in the AC power supply 6 is determined based on the instantaneous value of the AC input voltage VI.

[0013] The DC terminal T2 is connected to a battery 7 (power storage device). The battery 7 stores DC power. A capacitor may be connected instead of the battery 7. The instantaneous value of the DC voltage VB at the DC terminal T2 (i.e., the terminal voltage VB of the battery 7) is detected by the control device 5.

[0014] The output terminal T3 is connected to a load 8. The load 8 is driven by AC power supplied from the uninterruptible power supply. The instantaneous value of the AC voltage VO (hereinafter also referred to as "AC output voltage VO") appearing at the output terminal T3 is detected by the control device 5.

[0015] The uninterruptible power supply receives a three-phase AC voltage from an AC power source 6 and supplies the three-phase AC voltage to a load 8, but for the sake of simplicity of the drawing and explanation, only a circuit for one phase is shown in FIG.

[0016] 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.

[0017] An AC terminal 1a of the converter 1 is connected to an input terminal T1. A current detector CD1 detects the instantaneous value of a current Ii (hereinafter also referred to as "AC input current Ii") flowing between the input terminal T1 and the AC terminal 1a of the converter 1, and provides a signal Iif indicating the detected value to the control device 5.

[0018] The DC terminal 2a of the bidirectional chopper 2 is connected to the DC terminal T2. The current detector CD2 detects the instantaneous value of the DC current IB flowing between the DC terminal T2 and the DC terminal 2a, and provides the control device 5 with a signal IBf indicating the detected value.

[0019] The AC terminal 3a of the inverter 3 is connected to the output terminal T3. The current detector CD3 detects the instantaneous value of a current Io (hereinafter also referred to as "load current Io") flowing between the AC terminal 3a and the output terminal T3, and provides the control device 5 with a signal Iof indicating the detected value.

[0020] First terminals of the DC lines L1 to L3 are respectively connected to the positive voltage terminal 1b, neutral voltage terminal 1c, and negative voltage terminal 1d of the converter 1. Second terminals of the DC lines L1 to L3 are respectively connected to the positive voltage terminal 3b, neutral voltage terminal 3c, and negative voltage terminal 3d of the inverter 3. Furthermore, the DC lines L1 and L3 are respectively connected to the positive voltage terminal 2b and negative voltage terminal 2d of the bidirectional chopper 2.

[0021] Capacitor C1 is connected between DC lines L1 and L2 and stabilizes and smooths the DC voltage Ep between DC lines L1 and L2. Capacitor C2 is connected between DC lines L2 and L3 and stabilizes and smooths the DC voltage En between DC lines L2 and L3. Capacitors C1 and C2 are connected in series between DC lines L1 and L3 and stabilize and smooth the DC voltage VD = Ep + En between DC lines L1 and L3. The instantaneous values ​​of each of the DC voltages Ep and En are detected by the control device 5.

[0022] Capacitor C3 is connected between terminals 2b and 2c of bidirectional chopper 2 and stabilizes and smooths the DC voltage between terminals 2b and 2c. Capacitor C4 is connected between terminals 2c and 2d of bidirectional chopper 2 and stabilizes and smooths the DC voltage between terminals 2c and 2d. Capacitors C3 and C4 are connected in series between terminals 2b and 2d of bidirectional chopper 2 and stabilize and smooth the DC voltage VD=Ep+En between terminals 2b and 2d.

[0023] Converter 1 is a well-known device including multiple transistors and multiple diodes, and is controlled by control device 5. When AC input voltage VI is normally supplied from AC power supply 6 (i.e., when AC power supply 6 is functioning properly), converter 1 converts AC input voltage VI, supplied from AC power supply 6 via input terminal T1, into three-level DC voltages V1 to V3 and outputs them to DC lines L1 to L3, respectively. That is, Ep=V1-V2, En=V2-V3. When AC input voltage VI is not normally supplied from AC power supply 6 (i.e., when AC power supply 6 is in a power outage), operation of converter 1 is stopped.

[0024] The bidirectional chopper 2 is a well-known device including a plurality of transistors and a plurality of diodes, and is controlled by a control device 5. When the AC power supply 6 is normal, the bidirectional chopper 2 stores in the battery 7 the DC power supplied from the converter 1 via the DC lines L1 and L3.

[0025] In the event of a power outage at the AC power source 6, the bidirectional chopper 2 converts the DC voltage VB of the battery 7 into three-level DC voltages V1 to V3 and outputs them to the positive voltage terminal 2b, neutral voltage terminal 2c, and negative voltage terminal 2d, respectively. The DC voltages V1 and V3 are applied to the DC lines L1 and L3, respectively. The DC voltage (V1-V3) between the DC lines L1 and L3 is divided by the capacitors C1 and C2, and a neutral voltage V2=(V1-V3) / 2 is generated on the DC line L2. The DC voltage V2 on the DC line L2 is supplied to the inverter 3.

[0026] The inverter 3 is a well-known device including a plurality of transistors and a plurality of diodes, and is controlled by the control device 5. When the AC power supply 6 is operating normally, the inverter 3 converts three-level DC voltages V1 to V3 supplied from the converter 1 via the DC lines L1 to L3 into an AC output voltage VO and supplies this to the load 8. When the AC power supply 6 is in a power outage, the inverter 3 converts three-level DC voltages V1 to V3 supplied from the battery 7 via the bidirectional chopper 2 and the DC lines L1 to L3 into an AC output voltage VO and supplies this to the load 8.

[0027] The operation unit 4 includes a plurality of buttons operated by the user of the uninterruptible power supply, an image display unit that displays various information, etc. By operating the operation unit 4, the user can turn the power of the uninterruptible power supply on and off and set various information.

[0028] The control device 5 controls the entire uninterruptible power supply based on the AC input voltage VI, AC input current Ii, DC voltages Ep, En, VB, AC output voltage VO, load current Io, and signals from the operation unit 4.

[0029] Fig. 2 is a block diagram showing an example of the hardware configuration of the control device 5. As shown in Fig. 2, the control device 5 can be typically configured by a microcomputer in which a predetermined program is stored in advance.

[0030] 2, the control device 5 includes a CPU (Central Processing Unit) 50, a memory 52, and an input / output (I / O) circuit 54. The CPU 50, the memory 52, and the I / O circuit 54 can exchange data with one another via a bus 56. Programs are stored in a partial area of ​​the memory 52, and the CPU 50 executes these programs to realize various functions described below. The I / O circuit 54 inputs and outputs signals and data to and from the outside of the control device 5.

[0031] Alternatively, unlike the example of FIG. 2, at least a part of the control device 5 can be configured using a circuit such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0032] When the AC power supply 6 is operating normally, the control device 5 controls the converter 1 so that the DC voltage VD=Ep+En between the DC lines L1 and L3 becomes the reference voltage VD*, the input current (AC input current Ii) of the converter 1 matches the phase of the AC input voltage VI, and the difference ΔE=Ep-En between the DC voltages Ep and En becomes 0. When the AC power supply 6 fails, the control device 5 stops the operation of the converter 1.

[0033] Furthermore, when the AC power supply 6 is healthy, the control device 5 controls the bidirectional chopper 2 so that the DC voltage VB becomes the reference voltage VBR. When the AC power supply 6 experiences a power outage, the control device 5 controls the bidirectional chopper 2 so that the DC voltage VD between the DC lines L1 and L3 becomes the reference voltage VD*.

[0034] Furthermore, the control device 5 controls the inverter 3 so that the AC output voltage VO becomes a sinusoidal reference voltage VO*.

[0035] 3 is a block diagram showing the configuration of a portion of the control device 5 that is related to the control of the converter 1. As shown in FIG. 3, the control device 5 includes a power failure detector 10, an adder 11, a subtractor 12, and a control circuit 13. The function of each block shown in FIG. 3 can be realized by at least one of software processing and hardware processing by the control device 5.

[0036] The power failure detector 10 detects whether a power failure has occurred in the AC power supply 6 based on the AC input voltage VI supplied from the AC power supply 6, and outputs a power failure detection signal φF indicating the detection result. When the AC power supply 6 is healthy, the power failure detection signal φF is set to an inactive "L" level. When a power failure occurs in the AC power supply 6, the power failure detection signal φF is set to an active "H" level. For example, the power failure detector 10 determines that a power failure has occurred in the AC power supply 6 when the AC input voltage VI drops below a lower limit value.

[0037] An adder 11 adds the DC voltage Ep between the DC lines L1 and L2 (i.e., the voltage across the capacitor C1) and the DC voltage En between the DC lines L2 and L3 (i.e., the voltage across the capacitor C2) to obtain the DC voltage VD between the DC lines L1 and L3 (VD=Ep+En). A subtractor 12 subtracts the DC voltage En from the DC voltage Ep to obtain the DC voltage ΔE=Ep-En.

[0038] When the power failure detection signal φF is at the “L” level, the control circuit 13 controls the converter 1 based on the AC input voltage VI, the AC input current Ii, the DC voltages VD and ΔE, and the load current Io so that the DC voltage VD becomes the reference voltage VD* and the DC voltage ΔE becomes 0.

[0039] When a power outage occurs in the AC power supply 6 and the power outage detection signal φF becomes "H" level, the control circuit 13 stops the operation of the converter 1. When the operation of the converter 1 is stopped, all of the multiple transistors included in the converter 1 are turned off, and the input terminal T1 and the DC lines L1 to L3 are electrically disconnected.

[0040] Fig. 4 is a block diagram showing the configuration of the control circuit 13 shown in Fig. 3. As shown in Fig. 4, the control circuit 13 includes a reference voltage generating 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.

[0041] The reference voltage generating unit 20 generates a reference voltage VD*. The filter 22 removes AC components from the DC voltage VD from the adder 11. The filter 22 includes, for example, a moving average circuit. The moving average circuit calculates a moving average value of the DC voltage VD from the adder 11 within 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 6 (Tw=1 / f). Therefore, when the frequency f of the AC power supply 6 is 50 Hz, the moving average interval Tw is 20 ms.

[0042] The subtractor 24 calculates the deviation ΔVD=VD*−VD between the reference voltage VD* and the DC voltage VD from the filter 22 .

[0043] DC voltage control unit 26 determines a feedback component Ifb for controlling the input current (AC input current Ii) of converter 1 so that deviation ΔVD becomes zero. DC voltage control unit 26 determines feedback component Ifb of a value corresponding to voltage ΔVD, for example, by performing a proportional operation or a proportional-integral operation on deviation ΔVD. Feedback control is performed so that when deviation ΔVD increases, feedback component Ifb increases and deviation ΔVD decreases, and when deviation ΔVD decreases, feedback component Ifb decreases and deviation ΔVD disappears.

[0044] 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 a command value for the input current (AC input current) Ii of the converter 1.

[0045] The load current FF unit 28 is configured to include, for example, a moving average circuit. The moving average circuit calculates a moving average value of the output signal Iof from the current detector CD3 within 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 6 (Tw=1 / f). When the frequency f of the AC power supply 6 is 50 Hz, the moving average interval Tw=20 ms.

[0046] 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 together to generate a current command value ID*=Ifb+Iff.

[0047] A multiplier 32 generates a DC power command value Pi* by multiplying the DC voltage VD from the filter 22 by a current command value ID*. A 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.

[0048] A subtractor 36 obtains a deviation ΔIi=Ii*−Ii between the current command value Ii* and the AC input current Ii detected by the current detector CD1.

[0049] The current control unit 38 generates a voltage command value VIa* so that the deviation ΔIi becomes 0. The current control unit 38 generates the voltage command value VIa* by amplifying the deviation ΔIi according to proportional control or proportional-integral control, for example. The adder 40 adds the voltage command value VIa* and the AC input voltage VI to generate a voltage command value VIb*.

[0050] The balance control unit 42 generates a voltage command value VIc* based on the DC voltage ΔE=Ep-En from the subtractor 12. For example, the balance control unit 42 generates the voltage command value VIc* by performing a proportional operation or a proportional-integral operation on the DC voltage ΔE. When ΔE=Ep-En>0, the voltage command value VIc* is generated so that the charging time of the capacitor C1 is shorter than the charging time of the capacitor C2. When ΔEp=Ep-En<0, the voltage command value VIc* is generated so that the charging time of the capacitor C1 is longer than the charging time of the capacitor C2.

[0051] An adder 44 adds together voltage command values ​​VIb* and V1c* to generate a voltage command value VI*. When the power outage detection signal φF from the power outage detector 10 is at the inactivation level "L" (when the AC power supply 6 is healthy), the PWM circuit 46 controls the converter 1 based on the sinusoidal voltage command value VI*. As a result, the DC voltage VD=Ep+En is maintained at the reference voltage VD*, and the DC voltage ΔE is maintained at 0.

[0052] Furthermore, when the power failure detection signal φF is at the activated "H" level (when the AC power supply 6 is in a power failure state), the PWM circuit 46 stops the operation of the converter 1. This electrically disconnects the input terminal T1 from the DC lines L1 to L3.

[0053] As described above, in the first embodiment, by introducing the feedforward component Iff corresponding to the load current Io into the current command value ID*, it is possible to cause the AC input current Ii including the feedback component Ifb and the feedforward component Iff to flow from the AC power supply 6 to the converter 1.

[0054] This allows the feedback component Ifb to be controlled at a low speed to stabilize the control, and the feedforward component Iff to quickly respond 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.

[0055] Furthermore, because the DC voltage VD can be stabilized by controlling the converter 1, the capacitance of the capacitors C1 and C2 can be reduced, allowing the capacitors C1 and C2 to be made smaller, thereby enabling the device to be made smaller and less expensive.

[0056] Although FIG. 4 illustrates a configuration in which the feedforward component Iff is generated using the detected value of the load current Io detected by the current detector CD3, the feedforward component Iff may also be generated using the detected value of the current flowing through the DC lines L1 and L3.

[0057] [Embodiment 2] Figure 5 is a circuit block diagram showing the configuration of an uninterruptible power supply according to embodiment 2. As shown in Figure 5, the uninterruptible power supply according to embodiment 2 differs from the uninterruptible power supply shown in Figure 1 in that it includes input terminals T1a and T1b and a switch (SW) 9.

[0058] The input terminal T1a receives an AC voltage VIA from the AC system 6A. The instantaneous value of the AC voltage VIA is detected by the control device 5. Whether or not a power outage has occurred in the AC system 6A is determined based on the instantaneous value of the AC voltage VIA. The input terminal T1b receives an AC voltage VIB from the generator 6B.

[0059] The switch 9 is connected between the input terminals T1a, T1b and the AC terminal 1a of the converter 1. The switch 9 is controlled by the control device 5 and is configured to connect either the input terminal T1a or T1b to the AC terminal 1a of the converter 1. That is, the uninterruptible power supply according to the second embodiment is configured to be able to switch between the AC system 6A and the generator 6B as the AC power supply.

[0060] When the switch 9 connects the AC system 6A to the AC terminal 1a of the converter 1, the AC input voltage VI becomes the output voltage VIA of the AC system 6A. When the switch 9 connects the generator 6B to the AC terminal 1a of the converter 1, the AC input voltage VI becomes the output voltage VIB of the generator 6B.

[0061] Fig. 6 is a block diagram showing the configuration of a portion of the control device 5 shown in Fig. 5 that is related to the control of the converter 1. As shown in Fig. 6, the control device 5 differs from the control device 5 shown in Fig. 2 in that it includes an SOC detector 14 and a power outage detector 15.

[0062] The SOC detector 14 detects the SOC (State Of Charge) of the battery 7. The SOC is a value indicating the amount of charge stored in the battery 7, and is, for example, expressed as a percentage of the current amount of charge relative to the fully charged capacity of the battery 7. The SOC detector 14 detects the SOC of the battery 7 based on a detected value of the terminal voltage VB of the battery 7. The SOC can be detected by a known method, such as a method using an OCV-SOC curve that indicates the relationship between the open circuit voltage (OCV) of the battery 7 and the SOC. The SOC detector 14 transmits a signal SOCf indicating the detected SOC value to the control circuit 13.

[0063] The power failure detector 15 detects whether a power failure has occurred in the AC system 6A based on the AC voltage VIA supplied from the AC system 6A, and outputs a power failure detection signal φFA indicating the detection result. When the AC system 6A is healthy, the power failure detection signal φFA is set to an inactive "L" level. When a power failure occurs in the AC system 6A, the power failure detection signal φFA is set to an active "H" level. For example, the power failure detector 15 determines that a power failure has occurred in the AC system 6A when the AC voltage VIA drops below a lower limit value.

[0064] In the second embodiment, the power failure detector 10 detects whether a power failure has occurred in the AC power supply (AC system 6A or generator 6B) connected to the AC terminal 1a of the converter 1 based on the AC input voltage VI supplied to the AC terminal 1a, and outputs a power failure detection signal φF indicating the detection result. When the AC power supply is healthy, the power failure detection signal φF is set to "L" level. When a power failure occurs in the AC power supply, the power failure detection signal φF is set to "H" level.

[0065] Fig. 7 is a block diagram showing the configuration of control circuit 13 shown in Fig. 6. As shown in Fig. 7, control circuit 13 differs from control circuit 13 shown in Fig. 4 in that it includes a switch control unit 48.

[0066] The switch control unit 48 controls the switch 9 based on the power failure detection signal φFA from the power failure detector 15 and the output signal SOCf of the SOC detector 14. Fig. 8 is a flowchart for explaining an example of the control of the switch 9 by the switch control unit 48. The flowchart in Fig. 8 is repeatedly executed by the switch control unit 48 when the uninterruptible power supply is in operation.

[0067] 8, in step (hereinafter simply referred to as "S") 01, the switch control unit 48 determines whether the AC system 6A is healthy or not based on the power failure detection signal φFA from the power failure detector 15. In S01, the switch control unit 48 determines that the AC system 6A is healthy when the power failure detection signal φFA is at an "L" level, and determines that a power failure has occurred in the AC system 6A when the power failure detection signal φFA is at an "H" level.

[0068] If the AC system 6A is healthy (YES in S01), the switch control unit 48 controls the switch 9 in S02 to connect the AC system 6A to the AC terminal 1a of the converter 1. In S02, the switch control unit 48 generates a control signal φSW for controlling the switching of the switch 9 and outputs it to the switch 9. In response to the control signal φSW from the switch control unit 48, the switch 9 connects the input terminal T1a to the AC terminal 1a of the converter 1. As a result, the uninterruptible power supply receives AC power from the AC system 6A.

[0069] When a power outage has occurred in the AC system 6A (NO in S01), the switch control unit 48 determines whether the SOC of the battery 7 is equal to or greater than a predetermined SOC lower limit (SOCmin) based on the output signal SOCf of the SOC detector 14. The SOCmin is a determination value set to prevent over-discharge of the battery 7. If the SOC drops below the SOCmin during discharge of the battery 7, discharging of the battery 7 is prohibited.

[0070] If SOC≧SOCmin (YES in S03), the switch control unit 48 controls the switch 9 in S02 to connect the AC system 6A to the AC terminal 1a of the converter 1. That is, even if a power outage occurs in the AC system 6A, if the SOC of the battery 7 is equal to or greater than SOCmin, the AC system 6A is connected to the uninterruptible power supply. However, because AC power is not normally supplied from the AC system 6A, the power outage detector 10 outputs a power outage detection signal φF of “H” level. Therefore, the PWM circuit 46 of the control circuit 13 stops the operation of the converter 1.

[0071] On the other hand, the bidirectional chopper 2 converts the DC voltage VB of the battery 7 into three-level DC voltages V1 to V3 and outputs them to the DC lines L1 to L3, respectively. The inverter 3 converts the three-level DC voltages V1 to V3 supplied from the battery 7 via the bidirectional chopper 2 and the DC lines L1 to L3 into an AC output voltage VO and supplies it to the load 8. Therefore, during the period when the SOC of the battery 7 is ≧SOCmin, the operation of the load 8 can be continued.

[0072] When SOC < SOCmin at S03 (NO at S03), the switch control unit 48 controls the switch 9 to connect the generator 6B to the AC terminal 1a of the converter 1 at S04. At S04, in response to the control signal φSW from the switch control unit 48, the input terminal T1b is connected to the AC terminal 1a of the converter 1.

[0073] Thereby, the uninterruptible power supply device receives AC power from the generator 6B. The converter 1 converts the AC power supplied from the generator 6B into DC power and supplies it to the DC lines L1 and L3. The bidirectional chopper 2 stores the DC power supplied from the converter 1 via the DC lines L1 and L3 in the battery 7. Therefore, the SOC of the battery 7 rises from SOCmin.

[0074] At S05, the switch control unit 48 determines whether or not the SOC of the battery 7 is equal to or higher than a predetermined SOC reference value (SOCbackup) based on the output signal SOCf of the SOC detector 14. SOCbackup is the SOC for ensuring the function (power outage compensation function) as a backup power supply when the AC power supply fails, which the uninterruptible power supply device has.

[0075] The SOC backup is set to be not less than the power storage capacity for power outage compensation. The "power storage capacity for power outage compensation" is the power storage capacity required to continuously supply power from the battery 7 to the load 8 for a predetermined compensation time when a power outage of the AC power supply occurs. The power storage capacity for power outage compensation is calculated based on the rated current and compensation time of the uninterruptible power supply assuming that the load 8 at the time of the power outage of the AC power supply is the rated load. In order for the uninterruptible power supply to ensure the power outage compensation function, it is necessary to keep the SOC of the battery 7 not less than the SOC backup when the AC power supply is normal.

[0076] If the SOC < SOC backup at S05 (NO at S05), the switch control unit 48 returns to S04 and continues to control the switch 9 to connect the generator 6B to the AC terminal 1a of the converter 1. The uninterruptible power supply temporarily converts the AC power from the generator 6B into DC power, supplies the DC power to the battery 7, and converts the DC power into AC power of a predetermined frequency and supplies it to the load 8.

[0077] If the SOC ≥ SOC backup at S05 (YES at S05), the switch control unit 48 selects the switch 9 to the AC power supply so as to connect the AC system 6A to the AC terminal 1a of the converter 1 according to S02, generates a signal φSW indicating the selection result, and outputs it to the switch 9.

[0078] In this case, even if the AC system 6A is in a power outage and the operation of the converter 1 has stopped, during the period when the SOC of the battery 7 ≥ SOC min due to the operation of the power outage compensation function described above, the operation of the load 8 can be continued. When the AC system 6A is restored, a YES determination is made at S01 and the control circuit 13 restarts the operation of the converter 1. Therefore, the uninterruptible power supply temporarily converts the AC power from the AC system 6A into DC power, supplies the DC power to the battery 7, and converts the DC power into AC power of a predetermined frequency and supplies it to the load 8.

[0079] As described above, the uninterruptible power supply according to the second embodiment includes the switch SW configured to connect either the AC system 6A or the generator 6B to the AC terminal 1a of the converter 1. Therefore, even in the event of a power outage in the AC system 6A, the converter 1 can receive AC power from the generator 6B and generate DC power.

[0080] When the generator 6B is connected to the AC terminal 1a of the converter 1, the control circuit 13 controls the converter 1, causing an AC input current Ii including a feedback component Ifb and a feedforward component Iff to flow from the generator 6B to the converter 1. However, if the capacity of the generator 6B is sufficiently smaller than that of the AC system 6A, it is difficult for the generator 6B to quickly change its output current to match the AC input current Ii. Increasing the response speed of the generator 6B in order to quickly change the output current to match the AC input current Ii could result in a breakdown of the generator 6B.

[0081] In response to such concerns, in the control circuit 13, the load current FF unit 28 is configured to set the feedforward component Iff to zero when the generator 6B is connected to the AC terminal 1a of the converter 1.

[0082] According to this, the output current of the generator 6B is controlled to be slow so that the AC input current Ii containing only the feedback component Ifb flows into the converter 1. Since the output current of the generator 6B can be stably controlled, it is possible to prevent the generator 6B from breaking down.

[0083] Specifically, as shown in Fig. 7, the load current FF unit 28 obtains a control signal φSW for the switch 9 from the switch control unit 48. 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 and the control signal φSW. Fig. 9 is a flowchart for explaining the control of the load current FF unit 28. The flowchart in Fig. 9 is repeatedly executed by the load current FF unit 28 during operation of the uninterruptible power supply.

[0084] 9, in S10, the load current FF unit 28 determines whether or not the AC system 6A is connected to the AC terminal 1a of the converter 1 based on the control signal φSW acquired from the switch control unit 48. If the AC system 6A is connected to the AC terminal 1a of the converter 1 (YES in S10), the load current FF unit 28 generates a feedforward component Iff based on the load current Io indicated by the output signal Iof of the current detector CD3 in S11. In S11, the load current FF unit 28 generates the feedforward component Iff by, for example, calculating a moving average value of the output signal Iof from the current detector CD3 over a predetermined moving average interval Tw (Tw=20 ms).

[0085] When the AC system 6A is not connected to the AC terminal 1a of the converter 1, that is, when the generator 6B is connected to the AC terminal 1a of the converter 1 (NO in S10), the load current FF unit 28 sets the feedforward component Iff to 0 in S12.

[0086] As described above, in the second embodiment, when the AC system 6A is connected to the AC terminal 1a of the converter 1, the AC input current Ii including the feedback component Ifb and the feedforward component Iff is made to flow into the converter 1, whereas when the generator 6B is connected to the AC terminal 1a of the converter 1, the AC input current Ii including only the feedback component Ifb is made to flow into the converter 1.

[0087] According to this, when the AC system 6A is connected to the AC terminal 1a of the converter 1, the DC voltage VD can be controlled at high speed in response to fluctuations in the load current. On the other hand, when the generator 6B is connected to the AC terminal 1a of the converter 1, the output current of the generator 6B can be controlled at low speed, thereby preventing the generator 6B from breaking down.

[0088] In the first embodiment described above, the uninterruptible power supply according to the present disclosure is applied to a three-level uninterruptible power supply having three DC lines L1 to L3 and four capacitors C1 to C4, but the present disclosure is not limited to this. Each of the converter 1 and the inverter 3 can also be configured as a two-level circuit or a multi-level circuit having four or more levels. For example, the uninterruptible power supply according to the present disclosure can also be applied to a two-level uninterruptible power supply having two DC lines L1 and L3 and two capacitors C5 and C6 as shown in FIG. 10.

[0089] 10, when the AC power supply 6 is healthy, the control device 5 controls the converter 1 so that the DC voltage VD between the DC lines L1 and L3 becomes the reference voltage VD* and the phase of the input current (AC input current Ii) of the converter 1 matches the phase of the AC input voltage VI. Specifically, the control device 5 controls the converter 1 so that the AC input current Ii including the feedback component Ifb corresponding to the deviation ΔVD between the DC voltage VD between the DC lines L1 and L3 and the reference voltage VD* and the feedforward component Iff corresponding to the load current Io flows into the converter 1. Therefore, the same effects as those of the first embodiment described above can be obtained.

[0090] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0091] 1 converter, 2 bidirectional chopper, 3 inverter, 4 operation unit, 5 control device, 6 AC power supply, 6A AC system, 6B generator, 7 battery, 8 load, 9 switch, 10, 15 power failure detector, 11, 30, 40, 44 adder, 12, 24, 36 subtractor, 13 control circuit, 14 SOC detector, 20 reference voltage generator, 22 filter, 26 DC voltage controller, 28 load current FF unit, 32 multiplier, 34 divider, 38 current controller, 42 balance controller, 42, 46 PWM circuit, 48 switch controller, 50 CPU, 52 memory, 54 I / O circuit, 56 bus, C1 to C4 capacitors, CD1 to CD3 current detectors, L1 to L3 DC lines.

Claims

1. a converter that converts AC power supplied from an AC power source into DC power and supplies the DC power to a DC line; a capacitor connected to the DC line; an inverter that converts DC power received from the DC line into AC power and supplies the AC power to a load; a first current detector for detecting an input current of the converter; a second current detector that detects a load current flowing from the inverter to the load; a control device that controls the converter so that an input voltage and an input current of the converter are in phase with each other and so that a DC voltage of the DC line becomes a first reference voltage; the control device controls the converter so that the input current, which includes a feedback component corresponding to a deviation between the DC voltage of the DC line and the first reference 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; The control device calculating the feedback component by a control calculation using a deviation between the DC voltage of the DC line and the first reference voltage as an input; calculating the feedforward component by obtaining a moving average value of one cycle of the AC power supply with respect to the detection value of the second current detector; generating a current command value based on a sum of the feedback component and the feedforward component and the input voltage of the converter; an uninterruptible power supply that controls the converter so that a deviation between the current command value and the input current detected by the first current detector becomes zero;

2. The control device When the AC power supply is an AC system, the feedforward component is calculated according to the load current detected by the second current detector; 2. The uninterruptible power supply according to claim 1, wherein the feedforward component is set to zero when the AC power source is a generator.

3. a switch configured to connect either an AC system or a generator to an AC terminal of the converter; The control device When the AC system is connected to the AC terminal by the switch, the feedforward component is calculated from the load current detected by the second current detector; 2. The uninterruptible power supply according to claim 1, wherein the feedforward component is set to zero when the generator is connected to the AC terminal by the switch.

4. a bidirectional chopper that exchanges DC power between the DC line and a power storage device; When the AC system is healthy, the control device The switch connects the AC system to the AC terminal; controlling the converter so that the input voltage and the input current of the converter are in phase and the DC voltage of the DC line becomes the first reference voltage; controlling the bidirectional chopper so that the voltage between the terminals of the power storage device becomes a second reference voltage; When a power outage occurs in the AC system, the control device 4. The uninterruptible power supply according to claim 3, wherein when the amount of stored power in the power storage device is equal to or greater than a reference value, the switch connects the AC system to the AC terminal, and when the amount of stored power in the power storage device is less than a lower limit value, the switch connects the generator to the AC terminal.

5. A converter that converts AC power supplied from an AC power source into DC power and supplies the DC power to a DC line; a capacitor connected to the DC line; an inverter that converts DC power received from the DC line into AC power and supplies the AC power to a load; a first current detector for detecting an input current of the converter; a second current detector that detects a load current flowing from the inverter to the load; a control device that controls the converter so that an input voltage and an input current of the converter are in phase with each other and so that a DC voltage of the DC line becomes a first reference voltage; the control device controls the converter so that the input current, which includes a feedback component corresponding to a deviation between the DC voltage of the DC line and the first reference 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; The control device When the AC power supply is an AC system, the feedforward component is calculated according to the load current detected by the second current detector; An uninterruptible power supply, wherein the feedforward component is set to 0 when the AC power source is a generator.

6. A converter that converts AC power supplied from an AC power source into DC power and supplies the DC power to a DC line; a capacitor connected to the DC line; an inverter that converts DC power received from the DC line into AC power and supplies the AC power to a load; a first current detector for detecting an input current of the converter; a second current detector that detects a load current flowing from the inverter to the load; a control device that controls the converter so that an input voltage and an input current of the converter are in phase with each other and so that a DC voltage of the DC line becomes a first reference voltage; the control device controls the converter so that the input current, which includes a feedback component corresponding to a deviation between the DC voltage of the DC line and the first reference 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; a switch configured to connect either an AC system or a generator to an AC terminal of the converter; The control device When the AC system is connected to the AC terminal by the switch, the feedforward component is calculated from the load current detected by the second current detector; An uninterruptible power supply device, wherein the feedforward component is set to 0 when the generator is connected to the AC terminal by the switch.

7. a bidirectional chopper that exchanges DC power between the DC line and a power storage device; When the AC system is healthy, the control device The switch connects the AC system to the AC terminal; controlling the converter so that the input voltage and the input current of the converter are in phase and the DC voltage of the DC line becomes the first reference voltage; controlling the bidirectional chopper so that the voltage between the terminals of the power storage device becomes a second reference voltage; When a power outage occurs in the AC system, the control device 7. The uninterruptible power supply according to claim 6, wherein when the amount of stored power in the power storage device is equal to or greater than a reference value, the switch connects the AC system to the AC terminal, and when the amount of stored power in the power storage device is less than a lower limit value, the switch connects the generator to the AC terminal.

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