Uninterruptible power supply device

Abstract

An uninterruptible power supply device according to the present disclosure comprises 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 phases of an input voltage and an input current of the converter (1) match each other and the DC voltage of DC lines (L1, L3) reaches a first reference voltage. The control device (5) controls the converter (1) so that the input current including 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 a load current detected by the second current detector (CD2) flows from the AC power supply to the converter (1).

Description

Uninterruptible power supply device

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

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

[0003] International Publication No. 2020 / 026430

[0004] In such an uninterruptible power supply device, the control device controls the converter so as to average and stabilize the DC voltage of the DC line and make the power factor of the input power to the uninterruptible power supply device equal to 1. Further, 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 device due to the ripple voltage including high-frequency components and the characteristics of the load.

[0005] On the other hand, from the viewpoints of miniaturization and cost reduction of the device size, miniaturization of the capacitor is required. However, when the capacitor is miniaturized and the capacitance of the capacitor is reduced, the capacitance of the capacitor becomes insufficient for load fluctuations, and it becomes difficult to stabilize the DC voltage of the DC line. Further, there is a concern that the distortion of the waveform of the input current of the converter increases due to the generation of a ripple voltage in the DC voltage of the DC line, resulting in a decrease in efficiency.

[0006] Therefore, the main object of the present disclosure is to provide a small and highly efficient uninterruptible power supply device.

[0007] An uninterruptible power supply according to this disclosure comprises 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 the input current of the converter. The second current detector detects the load current flowing from the inverter to the load. The control device controls the converter so that the phases of the input voltage and input current of the converter match and the DC voltage of the DC line is a first reference voltage. The control device controls the converter so that an input current flows from the AC power source to the converter, which includes 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.

[0008] According to this disclosure, it is possible to provide a compact and highly efficient uninterruptible power supply.

[0009] This is a circuit block diagram showing the configuration of an uninterruptible power supply according to Embodiment 1. This is a block diagram showing an example of the hardware configuration of the control device. This is a block diagram showing the configuration of the part of the control device related to the control of the converter. This is a block diagram showing the configuration of the control circuit shown in Figure 3. This is a circuit block diagram showing the configuration of an uninterruptible power supply according to Embodiment 2. This is a block diagram showing the configuration of the part of the control device related to the control of the converter shown in Figure 5. This is a block diagram showing the configuration of the control circuit shown in Figure 6. This is a flowchart for explaining the control of the switch by the switch control unit. This is a flowchart for explaining the control of the load current FF section. This is a circuit block diagram showing the configuration of an uninterruptible power supply according to Embodiment 1.

[0010] Embodiments of this disclosure will be described in detail below 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 descriptions will not be repeated in principle.

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

[0012] Input terminal T1 receives an AC voltage VI from the 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. Based on the instantaneous value of the AC input voltage VI, it is determined whether or not a power outage has occurred in the AC power supply 6.

[0013] The DC terminal T2 is connected to the 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] Output terminal T3 is connected to load 8. Load 8 is driven by AC power supplied from an uninterruptible power supply. The instantaneous value of the AC voltage VO (hereinafter also referred to as "AC output voltage VO") appearing at output terminal T3 is detected by control device 5.

[0015] The uninterruptible power supply (UPS) receives three-phase AC voltage from the AC power source 6 and supplies three-phase AC voltage to the load 8. However, for the sake of simplicity in the diagrams and explanations, only the circuit for one phase is shown in Figure 1.

[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] The AC terminal 1a of converter 1 is connected to the 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 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.

[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 the 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] 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.

[0021] 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.

[0022] 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.

[0023] 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 6 (i.e., when the AC power supply 6 is healthy), converter 1 converts the AC input voltage VI supplied from the AC power supply 6 via input terminal T1 into three levels of DC voltages 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 6 (i.e., when the AC power supply 6 fails), the operation of converter 1 is stopped.

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

[0025] In the event of a power outage in the AC power supply 6, the bidirectional chopper 2 converts the DC voltage VB of the battery 7 into three levels of DC voltages V1 to V3, which are output to the positive voltage terminal 2b, the neutral voltage terminal 2c, and the negative voltage terminal 2d, respectively. 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, generating a neutral voltage V2 = (V1 - V3) / 2 on DC line L2. The DC voltage V2 on DC line L2 is supplied to the inverter 3.

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

[0027] The control unit 4 includes multiple buttons operated by the user of the uninterruptible power supply, an image display unit that displays various information, and other components. By operating the control 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] Figure 2 is a block diagram showing an example of the hardware configuration of the control device 5. As shown in Figure 2, the control device 5 can typically be configured with a microcomputer that has a predetermined program pre-stored in it.

[0030] In the example shown in Figure 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, 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 device 5.

[0031] Alternatively, unlike the example in Figure 2, 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).

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

[0033] Furthermore, when the AC power supply 6 is functioning properly, the control device 5 controls the bidirectional chopper 2 so that the DC voltage VB becomes the reference voltage VBR. In the event of a power outage of the AC power supply 6, 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] Figure 3 is a block diagram showing the configuration of the part of the control device 5 related to the control of the converter 1. As shown in Figure 3, the control device 5 is composed of a power failure detector 10, an adder 11, a subtractor 12, and a control circuit 13. The function of each block shown in Figure 3 can be realized by at least one of software processing and hardware processing by the control device 5.

[0036] The power outage detector 10 detects whether a power outage 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 outage detection signal φF indicating the detection result. The power outage detection signal φF is set to the deactivation level "L" when the AC power supply 6 is healthy. When a power outage occurs in the AC power supply 6, the power outage detection signal φF is set to the activation level "H". For example, the power outage detector 10 determines that a power outage has occurred in the AC power supply 6 when the AC input voltage VI falls below the lower limit.

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

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

[0039] If a power outage occurs in the AC power supply 6 and the power outage detection signal φF reaches the "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 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] Figure 4 is a block diagram showing the configuration of the control circuit 13 shown in Figure 3. As shown in Figure 4, the control circuit 13 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.

[0041] The reference voltage generation unit 20 generates a reference voltage VD*. The filter 22 removes an AC component from the DC voltage VD from the adder 11. The filter 22 is configured to include, for example, a moving average circuit. The moving average circuit obtains a moving average value of the DC voltage VD from the adder 11 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 6 (Tw = 1 / f). Therefore, when the frequency f of the AC power supply 6 is 50 Hz, the moving average interval Tw becomes 20 ms.

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

[0043] The DC voltage control unit​​​​​​​​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.

[0047] The multiplier 32 multiplies the DC voltage VD from the filter 22 by the current command value ID* to generate a DC power command value Pi*. The divider 34 divides the DC power command value Pi* by the AC input voltage VI to generate a current command value Ii*. As a result, a sinusoidal current command value Ii* that is in phase with the AC input voltage VI is generated.

[0048] The 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* such that the deviation ΔIi becomes 0. The current control unit 38 generates the voltage command value VIa* by amplifying the deviation ΔIi according to, for example, 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*.

[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 proportional calculation or proportional integral calculation on the DC voltage ΔE. When ΔE = Ep - En > 0, the voltage command value VIc* is generated such 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 such that the charging time of the capacitor C1 is longer than the charging time of the capacitor C2.

[0051] 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 power outage detection signal φF from the power outage detector 10 is at the deactivation level "L" (when the AC power supply 6 is healthy). 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, the PWM circuit 46 stops the operation of the converter 1 when the power outage detection signal φF is at the activation level "H" (when the AC power supply 6 is powered off). This electrically disconnects the input terminal T1 from the DC lines L1 to L3.

[0053] As described above, in Embodiment 1, by introducing a feedforward component Iff corresponding to the load current Io into the current command value ID*, an AC input current Ii including a feedback component Ifb and a feedforward component Iff can be flowed from the AC power supply 6 to the converter 1.

[0054] According to this, the control is stabilized by controlling the feedback component Ifb at a low speed, and 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.

[0055] Furthermore, since the DC voltage VD can be stabilized by controlling the 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.

[0056] In Figure 4, 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.

[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 is equipped with input terminals T1a, T1b and a switch (SW) 9.

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

[0059] Switch 9 is connected between input terminals T1a and T1b and AC terminal 1a of converter 1. Switch 9 is controlled by control device 5 and configured to connect either input terminals T1a or T1b to AC terminal 1a of converter 1. In other words, the uninterruptible power supply according to embodiment 2 is configured to switch between AC system 6A and generator 6B as AC power sources.

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

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

[0062] The SOC detector 14 detects the State of Charge (SOC) of the battery 7. SOC is a value that indicates the amount of charge stored in the battery 7, for example, it is the current amount of charge stored as a percentage of the battery 7's full charge capacity. The SOC detector 14 detects the SOC of the battery 7 based on the detected value of the terminal voltage VB of the battery 7. For the method of detecting SOC, known methods can be used, such as the method using the OCV-SOC curve that shows the relationship between the open circuit voltage (OCV) of the battery 7 and SOC. The SOC detector 14 transmits a signal SOCf indicating the detected value of SOC to the control circuit 13.

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

[0064] In Embodiment 2, the power outage detector 10 detects whether a power outage has occurred in the AC power source (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 of the converter 1, and outputs a power outage detection signal φF indicating the detection result. When the AC power source is healthy, the power outage detection signal φF is set to the "L" level. When a power outage occurs in the AC power source, the power outage detection signal φF is set to the "H" level.

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

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

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

[0068] If the AC power system 6A is healthy (YES in S01), the switch control unit 48 controls the switch 9 in S02 to connect the AC power system 6A to the AC terminal 1a of the converter 1. In S02, the switch control unit 48 generates a control signal φSW to control 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 its 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 power system 6A.

[0069] If a power outage occurs 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 above a predetermined SOC lower limit (SOCmin) based on the output signal SOCf of the SOC detector 14. SOCmin is a determination value set to prevent over-discharge of the battery 7. If the SOC drops below SOCmin during the discharge of the battery 7, the discharge 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, the AC system 6A is connected to the uninterruptible power supply when the SOC of the battery 7 ≥ SOCmin. However, since AC power is not supplied normally from the AC system 6A, the power outage detector 10 outputs a power outage detection signal φF at the "H" level. Therefore, the PWM circuit 46 of the control circuit 13 stops the operation of the converter 1.

[0071] Meanwhile, the bidirectional chopper 2 converts the DC voltage VB of the battery 7 into three levels of DC voltage V1 to V3 and outputs them to DC lines L1 to L3, respectively. The inverter 3 converts the three levels of DC voltage V1 to V3 supplied from the battery 7 via the bidirectional chopper 2 and DC lines L1 to L3 into an AC output voltage VO and supplies it to the load 8. Therefore, the operation of the load 8 can be continued as long as the state of charge (SOC) of the battery 7 is ≥ SOCmin.

[0072] If S03 shows SOC < SOCmin (NO in S03), the switch control unit 48 controls the switch 9 in S04 to connect the generator 6B to the AC terminal 1a of the converter 1. In 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] As a result, the uninterruptible power supply 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 state of charge (SOC) of the battery 7 rises from SOCmin.

[0074] In step S05, the switch control unit 48 determines, based on the output signal SOCf of the SOC detector 14, whether the SOC of the battery 7 is equal to or greater than a predetermined SOC reference value (SOCbackup). SOCbackup is the SOC that ensures the function of the uninterruptible power supply as a backup power source in the event of an AC power outage (power outage compensation function).

[0075] SOCbackup is set to be equal to or greater than the power storage amount for power outage compensation. "Power storage amount for power outage compensation" is the amount of stored energy necessary to continue supplying power from battery 7 to load 8 for a predetermined compensation time when an AC power outage occurs. The power storage amount for power outage compensation is calculated based on the rated current and compensation time of the uninterruptible power supply, assuming that load 8 is at its rated load when an AC power outage occurs. In order for the uninterruptible power supply to guarantee its power outage compensation function, the SOC of battery 7 must be kept equal to or greater than SOCbackup when the AC power supply is healthy.

[0076] If S05 is SOC < SOCbackup (NO in 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 (UPS) first converts the AC power from the generator 6B to DC power, supplies that DC power to the battery 7, and also converts that DC power to AC power of a predetermined frequency and supplies it to the load 8.

[0077] If S05 is SOC ≥ SOCbackup (YES in S05), the switch control unit 48 selects the switch 9 as the AC power source so that the AC system 6A is connected to the AC terminal 1a of the converter 1, and generates a signal φSW indicating the selection result and outputs it to the switch 9.

[0078] In this case, even if the AC power system 6A is experiencing a power outage and the converter 1 is not operating, the operation of the load 8 can continue as long as the battery 7's SOC ≥ SOCmin, thanks to the power outage compensation function described above. When the AC power system 6A is restored, a YES determination is made in S01, and the control circuit 13 restarts the operation of the converter 1. Therefore, the uninterruptible power supply (UPS) first converts the AC power from the AC power system 6A into DC power, supplies that DC power to the battery 7, and then converts that DC power back into AC power of a predetermined frequency and supplies it to the load 8.

[0079] As described above, the uninterruptible power supply according to Embodiment 2 includes a 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 if a power outage occurs 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 so that an AC input current Ii, including a feedback component Ifb and a feedforward component Iff, flows from the generator 6B to the converter 1. However, if the capacity of the generator 6B is sufficiently small compared to the AC system 6A, the generator 6B has a problem in that it is difficult to make its output current follow the AC input current Ii at high speed. If the response speed of the generator 6B is increased in order to make the output current follow the AC input current Ii at high speed, the generator 6B may fail.

[0081] In response to these concerns, the load current FF section 28 in the control circuit 13 is configured to set the feedforward component If to 0 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 a low speed so that an 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 failing.

[0083] Specifically, as shown in Figure 7, the load current FF unit 28 receives the control signal φSW of switch 9 from the switch control unit 48. Based on the load current Io indicated by the output signal Iof of the current detector CD3 and the control signal φSW, the load current FF unit 28 generates a feedforward component Iff of the current command value Ii*. Figure 9 is a flowchart illustrating the control of the load current FF unit 28. The flowchart in Figure 9 is repeatedly executed by the load current FF unit 28 during the operation of the uninterruptible power supply.

[0084] As shown in Figure 9, in S10, the load current FF unit 28 determines whether the AC system 6A is connected to the AC terminal 1a of the converter 1 based on the control signal φSW obtained 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 If in S11 based on the load current Io indicated by the output signal Iof of the current detector CD3. In S11, the load current FF unit 28 generates the feedforward component If by, for example, calculating the moving average value of the output signal Iof from the current detector CD3 over a predetermined moving average interval Tw (Tw = 20 ms).

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

[0086] As described above, in Embodiment 2, when the AC system 6A is connected to the AC terminal 1a of the converter 1, an AC input current Ii including a feedback component Ifb and a feedforward component Iff is allowed to flow into the converter 1, while when the generator 6B is connected to the AC terminal 1a of the converter 1, an AC input current Ii including only the feedback component Ifb is allowed 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 a low speed, thereby preventing the generator 6B from failing.

[0088] In the above-described Embodiment 1, the case in which the uninterruptible power supply according to this disclosure is applied to a three-level uninterruptible power supply equipped with three DC lines L1 to L3 and four capacitors C1 to C4 was explained, but it is not limited to this. It is also possible to configure each of the converter 1 and inverter 3 as a two-level circuit or a multi-level circuit of four or more levels. For example, the uninterruptible power supply according to this disclosure is also applicable to a two-level uninterruptible power supply equipped with two DC lines L1 and L3 and two capacitors C5 and C6, as shown in Figure 10.

[0089] In the uninterruptible power supply shown in Figure 10, the control device 5 controls the converter 1 so that when the AC power supply 6 is healthy, the DC voltage VD between 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 an AC input current Ii, which includes a feedback component Ifb corresponding to the deviation ΔVD between the DC voltage VD between DC lines L1 and L3 and the reference voltage VD*, and a feedforward component Iff corresponding to the load current Io, flows into the converter 1. Therefore, the same effects as in the first embodiment described above can be obtained.

[0090] 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 and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

[0091] 1 Converter, 2 Bidirectional chopper, 3 Inverter, 4 Operating 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 control unit, 28 Load current FF unit, 32 Multiplier, 34 Divider, 38 Current control unit, 42 Balance control unit, 42, 46 PWM circuit, 48 Switch control unit, 50 CPU, 52 Memory, 54 I / O circuit, 56 Bus, C1-C4 Capacitors, CD1-CD3 Current detectors, L1-L3 DC lines.

Claims

1. An uninterruptible power supply comprising: a converter that converts AC power supplied from an AC power source into DC power and supplies it 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 it to a load; a first current detector that detects the input current of the converter; a second current detector that detects the load current flowing from the inverter to the load; and a control device that controls the converter such that the phases of the input voltage of the converter and the input current match and the DC voltage of the DC line becomes a first reference voltage, wherein the control device controls the converter such that the input current, which includes 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, flows from the AC power source to the converter.

2. The uninterruptible power supply according to claim 1, wherein the control device calculates the feedback component by performing a control calculation with input to the deviation between the DC voltage of the DC line and the first reference voltage; calculates the feedforward component by obtaining a moving average value of the AC power supply over one period with respect to the detected value of the second current detector; generates a current command value based on the sum of the feedback component and the feedforward component and the input voltage of the converter; and controls the converter so that the deviation between the current command value and the input current detected by the first current detector is zero.

3. The uninterruptible power supply according to claim 1 or 2, wherein the control device calculates the feedforward component corresponding to the load current detected by the second current detector when the AC power supply is an AC system, and sets the feedforward component to 0 when the AC power supply is a generator.

4. The uninterruptible power supply according to claim 1 or 2, further comprising a switch configured to connect either an AC system or a generator to the AC terminal of the converter, wherein the control device calculates the feedforward component from the load current detected by the second current detector when the AC system is connected to the AC terminal by the switch, and sets the feedforward component to 0 when the generator is connected to the AC terminal by the switch.

5. The uninterruptible power supply according to claim 4, further comprising a bidirectional chopper for sending and receiving DC power between the DC line and the power storage device, wherein when the AC system is healthy, the control device connects the AC system to the AC terminals by the switch, controls the converter so that the phases of the input voltage and input current of the converter match and the DC voltage of the DC line becomes the first reference voltage, controls the bidirectional chopper so that the terminal voltage of the power storage device becomes the second reference voltage, and in the event of a power outage in the AC system, the control device connects the AC system to the AC terminals by the switch if the amount of power stored in the power storage device is above a reference value, while connecting the generator to the AC terminals by the switch if the amount of power stored in the power storage device is below a lower limit.

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