Uninterruptible power supply device

Abstract

In the present invention, a converter (1) converts alternating-current power supplied from an alternating-current power source (10) to direct-current power and supplies the direct-current power to a direct-current line (2). An inverter (6) converts the direct-current power supplied from the direct-current line (2) to alternating-current power and supplies the alternating-current power to a load (13). A first bidirectional chopper (4) transfers first direct-current power between the direct-current line (2) and a first power storage device (11). A second bidirectional chopper (5) has a lower capacity than the first bidirectional chopper (4) and transfers second direct-current power between the direct-current line (2) and a second power storage device (12). During an overload, a control device (8) operates the second bidirectional chopper (5) to supply the second direct-current power from the second power storage device (12) to the direct-current line (2). During a power failure of the alternating-current power source (10), the control device (8) operates the first bidirectional chopper (4) to supply the first direct-current power from the first power storage device (11) to the direct-current line (2).

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, an inverter, and a bidirectional chopper. The converter supplies AC power supplied from an 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 DC power supplied from a 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 a load.

[0003] International Publication No. 2020 / 026430

[0004] When a load with a large fluctuating 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 amount of power stored in the power storage device decreases. Therefore, in response to the power consumption of the load dropping 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] In this way, when the uninterruptible power supply device becomes overloaded, the power storage device is discharged and charged. When the power consumption of the load fluctuates periodically, the discharge and charge of the power storage device are also repeated periodically, and there is concern that the deterioration of the power storage device is accelerated.

[0006] In order to prevent the charge and discharge of the battery 11 due to overload, it is conceivable to select a larger-capacity uninterruptible power supply device so that the maximum power consumption of the load is below the rated load of the uninterruptible power supply device. According to this, the uninterruptible power supply device receives all of the AC power corresponding to the maximum power consumption of the load from the AC power source. On the other hand, the contract power is determined by the maximum power consumption of the load, and there is concern that the electricity bill will increase due to an increase in the contract power.

[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.

[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 includes a converter that converts AC power supplied from the AC power source into DC power and outputs it to a DC line, an inverter that converts DC power supplied from the DC line into AC power and supplies it to the load, a first bidirectional chopper that exchanges first DC power between the DC line and a first energy storage device, and a second bidirectional chopper that exchanges second DC power between the DC line and a second energy storage device. The second bidirectional chopper has a lower capacity than the first bidirectional chopper. The UPS further includes a control device. When the power consumption of the load exceeds the rated load of the UPS, the control device operates the second bidirectional chopper to supply second DC power from the second energy storage device to the DC line. When the AC power source fails, the control device stops the operation of the converter. The control device operates the first bidirectional chopper to supply first DC power from the first energy storage device to the DC line.

[0009] According to this disclosure, it is possible to suppress the deterioration of the energy storage device while keeping the AC power supplied from the AC power source below the rated load.

[0010] This is a circuit block diagram showing the configuration of an uninterruptible power supply according to this embodiment. This is a block diagram showing an example of the hardware configuration of the control device. This is a diagram showing the power flow during overload in an uninterruptible power supply according to this embodiment. This is a diagram showing the temporal change of the load's power consumption and the AC input power supplied from the AC power source. This is a block diagram showing the part of the control device related to the control of the converter and the bidirectional chopper. This is a flowchart showing the operation of the control unit. This is a diagram showing an example of the temporal change of the load's power consumption, the AC input power from the AC power source, the DC voltage of the DC line, the terminal voltage of the battery, and the terminal voltage of the EDLC. This is a diagram showing another example of the temporal change of the load's power consumption, the AC input power from the AC power source, the DC voltage of the DC line, the terminal voltage of the battery, and the terminal voltage of the EDLC. This is a circuit block diagram showing the schematic configuration of a conventional uninterruptible power supply. This is a diagram showing an example of the temporal change of the load's power consumption.

[0011] 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.

[0012] Figure 1 is a circuit block diagram showing the configuration of an uninterruptible power supply according to this embodiment. As shown in Figure 1, the uninterruptible power supply 100 includes an AC input terminal T1, DC terminals T2 and T3, and an AC output terminal T4. The AC input terminal T1 receives AC power at a predetermined frequency (for example, commercial frequency) from an AC power source 10. The AC power source 10 may be a commercial AC power source or a generator.

[0013] The AC output terminal T4 is connected to the load 13. The load 13 is driven by AC power supplied from the uninterruptible power supply 100.

[0014] The DC terminal T2 is connected to the battery 11. The battery 11 corresponds to one embodiment of the "first energy storage device" that stores DC power. The battery 11 is a secondary battery such as a lead-acid battery, nickel-metal hydride battery, or lithium-ion battery. It is preferable to use an energy storage device with high energy density (amount of energy that can be stored per unit weight or volume) for the first energy storage device. The energy stored in the first energy storage device is mainly used to supply AC power to the load 13 in the event of a power outage of the AC power supply 10.

[0015] The DC terminal T3 is connected to an electric double-layer capacitor (EDLC) 12. The EDLC 12 corresponds to one embodiment of a "second energy storage device" that stores DC power. Preferably, the second energy storage device is one with a high power density (the amount of power that can be instantaneously extracted per unit weight or volume). The energy stored in the second energy storage device is mainly used to supply excess AC power to the load 13 when the power consumption of the load 13 exceeds the rated load of the uninterruptible power supply 100.

[0016] In the example shown in Figure 1, the EDLC 12 has a lower energy density than the battery 11, but a higher power density. Furthermore, the EDLC 12 exhibits less performance degradation due to repeated high-current charging and discharging compared to the battery 11.

[0017] When the AC power supply 10 is interrupted, a significant amount of energy is required to stably compensate for the operation of the load 13 over a predetermined interruption compensation period. The interruption compensation period is the time during which the uninterruptible power supply 100 can continuously supply power to the load 13 during an interruption. For this reason, the battery 11 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 energy density than the second energy storage device.

[0018] On the other hand, in situations where the power consumption of load 13 increases sharply and becomes overloaded, the AC power supplied from AC power source 10 becomes insufficient, requiring the second energy storage device to discharge a large current instantaneously. For this reason, the EDLC 12 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 power density than the first energy storage device.

[0019] The uninterruptible power supply 100 further comprises switches S1 to S4, a converter 1, a DC line 2, a capacitor 3, bidirectional choppers 4 and 5, an inverter 6, an operating unit 7, current detectors CD1 to CD4, and a control device 8.

[0020] Switch S1 is connected between the AC input terminal T1 and the AC node of the converter 1. Switch S1 is controlled by the control device 8. When the AC power supply 10 is healthy, switch S1 is turned on, and AC power is supplied from the AC power supply 10 to the converter 1 via switch S1. When the AC power supply 10 fails, switch S1 is turned off, and the connection between the AC power supply 10 and the converter 1 is interrupted.

[0021] The instantaneous value of the AC input voltage VI supplied from the AC power supply 10 is detected by the control device 8. Based on the instantaneous value of the AC input voltage VI, the control device 8 determines whether or not the AC voltage is being supplied normally from the AC power supply 10. The current detector CD1 detects the AC input current Ii flowing between the AC power supply 10 and the converter 1, and provides the control device 8 with a signal Iif indicating the detected value.

[0022] Converter 1 is controlled by control device 8. When the AC power supply 10 is functioning properly, converter 1 converts the AC power received at the AC input terminal T1 into DC power and outputs it to DC line 2. Control device 8 controls converter 1 so that the DC voltage VD of DC line 2 becomes the reference DC voltage VDR. In the event of a power outage at the AC power supply 10, control device 8 stops the operation of converter 1. Converter 1 is a well-known type including multiple semiconductor switching elements and multiple diodes.

[0023] Capacitor 3 is connected to DC line 2 and smooths and stabilizes the DC voltage VD of DC line 2. The instantaneous value of the DC voltage VD of DC line 2 is detected by control device 8.

[0024] DC line 2 is connected to the high-voltage side node of the bidirectional chopper 4. The low-voltage side node of the bidirectional chopper 4 is connected to DC terminal T2 via switch S2. Switch S2 is controlled by control device 8. Switch S2 is turned on when the uninterruptible power supply 100 is in use and turned off, for example, when the uninterruptible power supply 100 and battery 11 are being maintained.

[0025] The bidirectional chopper 4 is controlled by the control device 8 and exchanges DC power between the DC line 2 and the battery 11. The bidirectional chopper 4 is a well-known type that includes multiple semiconductor switching elements and multiple diodes. The bidirectional chopper 4 corresponds to one embodiment of the "first bidirectional chopper".

[0026] When the AC power supply 10 is functioning properly, the bidirectional chopper 4 stores the DC power supplied from the converter 1 via the DC line 2 in the battery 11. At this time, the control device 8 controls the bidirectional chopper 4 so that the terminal voltage VB of the battery 11 becomes the reference DC voltage VBR.

[0027] In the event of a power outage in the AC power supply 10, the bidirectional chopper 4 supplies DC power from the battery 11 to the DC line 2. At this time, the control device 8 controls the bidirectional chopper 4 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR.

[0028] Furthermore, if the DC power of the EDLC 12 becomes insufficient during an overload, the bidirectional chopper 4 assists the bidirectional chopper 5 by supplying DC power from the battery 11 to the DC line 2. At this time, the control device 8 controls the bidirectional chopper 4 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR.

[0029] The instantaneous value of the terminal voltage VB of the battery 11 is detected by the control device 8. The current detector CD2 detects the DC current IB flowing between the battery 11 and the bidirectional chopper 4 and provides the control device 8 with a signal IBf indicating the detected value.

[0030] DC line 2 is connected to the high-voltage side node of the bidirectional chopper 5. The low-voltage side node of the bidirectional chopper 5 is connected to DC terminal T3 via switch S3. Switch S3 is controlled by control device 8. Switch S3 is turned on when the uninterruptible power supply 100 is in use and turned off, for example, when the uninterruptible power supply 100 and EDLC 12 are being maintained.

[0031] The bidirectional chopper 5 is controlled by the control device 8 and exchanges DC power between the DC line 2 and the EDLC 12. The bidirectional chopper 5 is a well-known type that includes multiple semiconductor switching elements and multiple diodes. The bidirectional chopper 5 corresponds to one embodiment of the "second bidirectional chopper".

[0032] When the AC power supply 10 is functioning properly and the power consumption of the load 13 is low, the bidirectional chopper 5 stores the DC power supplied from the converter 1 via the DC line 2 in the EDLC 12. At this time, the control device 8 controls the bidirectional chopper 5 so that the terminal voltage VE of the EDLC 12 becomes the reference DC voltage VER.

[0033] When the AC power supply 10 is functioning properly, and the power consumption of the load 13 increases sharply, causing an overload, the bidirectional chopper 5 supplies DC power from the EDLC 12 to the DC line 2. At this time, the control device 8 controls the bidirectional chopper 5 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR.

[0034] The instantaneous value of the terminal voltage VE of the EDLC 12 is detected by the control device 8. The current detector CD3 detects the DC current IE flowing between the EDLC 12 and the bidirectional chopper 5, and provides the control device 8 with a signal IEf indicating the detected value.

[0035] Thus, the uninterruptible power supply 100 is equipped with two bidirectional choppers 4 and 5. As described above, the bidirectional chopper 4 (the first bidirectional chopper) is configured to charge the battery 11 when the AC power supply 10 is functioning properly, and to discharge the battery 11 when the AC power supply 10 fails. Therefore, the bidirectional chopper 4 has the capacity to continuously output the rated load of the uninterruptible power supply 100 for the duration of the power outage compensation period.

[0036] In contrast, the bidirectional chopper 5 (second bidirectional chopper), as described above, is configured to discharge the EDLC 12 when the AC power supply 10 is healthy and overloaded, and to charge the EDLC 12 when it is lightly loaded. Therefore, the bidirectional chopper 5 only needs to have a capacity that can output power for the short time (for example, a few milliseconds to about one second) when the uninterruptible power supply 100 is overloaded. For this reason, a bidirectional chopper with a smaller rated capacity than bidirectional chopper 4 can be used for bidirectional chopper 5. Therefore, the size of bidirectional chopper 5 can be made smaller than the size of bidirectional chopper 4.

[0037] DC line 2 is connected to the DC node of inverter 6, and the AC node of inverter 6 is connected to the AC output terminal T4 via switch S4. Inverter 6 is controlled by control device 8 and converts DC power supplied from converter 1 or bidirectional choppers 4, 5 via DC line 2 into AC power and outputs it to the AC node. Inverter 6 is a well-known type including multiple semiconductor switching elements and multiple diodes.

[0038] When the AC power supply 10 is functioning properly, the inverter 6 converts the DC power supplied from the converter 1 (or both the converter 1 and the bidirectional chopper 5) via the DC line 2 into AC power of a predetermined frequency (e.g., commercial frequency). When the AC power supply 10 fails, the inverter 6 converts the DC power supplied from the bidirectional chopper 4 via the DC line 2 into AC power of a predetermined frequency. The control device 8 controls the inverter 6 so that the AC output voltage VO becomes the reference AC voltage VOR.

[0039] Switch S4 is controlled by the control device 8. Switch S4 is turned on in inverter power supply mode when AC power generated by the inverter 6 is supplied to the load 13. Switch S4 is turned off in bypass power supply mode when AC power from a bypass AC power source (not shown) is supplied to the load 13.

[0040] The instantaneous value of the AC output voltage VO appearing at the AC output terminal T4 is detected by the control device 8. The current detector CD4 detects the AC output current Io flowing between the inverter 6 and the AC output terminal T4, and provides the control device 8 with a signal Iof indicating the detected value.

[0041] The control unit 7 includes a number of buttons operated by the user of the uninterruptible power supply 100, and a display that shows various information. By operating the control unit 7, the user can turn the power of the uninterruptible power supply 100 on and off. In addition, by operating the control unit 7, the user can store various information in the control device 8. The various information includes information related to the discharge operation of the EDLC 12 (threshold voltage VDth1, discharge termination voltage VEmin), and a reference DC voltage VER for charging the EDLC 12, information related to the discharge operation of the battery 11 (threshold voltage VDth2, discharge termination voltage VBmin), and a reference DC voltage VBR for charging the battery 11.

[0042] The control device 8 controls the entire uninterruptible power supply 100 based on the AC input voltage VI, AC input current Ii, DC voltage VD, terminal voltage VB of the battery 11, DC current IB, terminal voltage VE of the EDLC 12, DC current IE, AC output voltage VO, and AC output current Io.

[0043] Figure 2 is a block diagram showing an example of the hardware configuration of the control device 8. Typically, the control device 8 can be configured using a microcomputer with a predetermined program pre-stored in it.

[0044] As shown in FIG. 2, the control device 8 includes a CPU (Central Processing Unit) 80, a memory 82, and an input / output (I / O) circuit 84. The CPU 80, the memory 82, and the I / O circuit 84 can exchange data with each other via a bus 86. A program is stored in a partial area of the memory 82, and by executing the program by the CPU 80, various functions described later can be realized. The I / O circuit 84 exchanges signals and data with the outside of the control device 8.

[0045] Alternatively, different from the example of FIG. 2, at least a part of the control device 8 can be configured using a circuit such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Also, at least a part of the control device 8 can be configured by an analog circuit.

[0046] Next, the operation of the uninterruptible power supply device 100 will be described. In the following description, first, the technical problems of the conventional uninterruptible power supply device will be described.

[0047] FIG. 9 is a circuit block diagram showing a schematic configuration of a conventional uninterruptible power supply device. As shown in FIG. 9, the conventional uninterruptible power supply device 200 includes a converter 1, a bidirectional chopper 4, and an inverter 6. The uninterruptible power supply device 200 is different from the uninterruptible power supply device 100 according to the present embodiment in that there is one bidirectional chopper.

[0048] When the AC power supply 10 is normal, the converter 1 converts the AC power supplied from the AC power supply 10 into DC power and outputs the DC power to the DC line 2. The bidirectional chopper 4 stores the DC power supplied from the converter 1 via the DC line 2 in the battery 11. The inverter 6 converts the DC power supplied from the converter 1 via the DC line 2 into AC power and supplies the AC power to the load 13.

[0049] When the AC power supply 10 fails, the converter 1 stops operating. The bidirectional chopper 4 supplies DC power from the battery 11 to the inverter 6 via the DC line 2. The inverter 6 converts the DC power supplied from the bidirectional chopper 4 via the DC line 2 into AC power and supplies that AC power to the load 13.

[0050] When a load 13, whose power consumption fluctuates significantly, is connected to an uninterruptible power supply (UPS) 200, the power consumption of load 13 may temporarily exceed the rated load of the UPS 200. Figure 10 shows an example of the temporal change in the power consumption of load 13. In Figure 10, the power consumption of load 13 is expressed as a load factor (%). A load factor of 100% corresponds to the rated load of the UPS 200.

[0051] In the example shown in Figure 10, the power consumption of load 13 fluctuates periodically. The power consumption fluctuation period has a length of several seconds. Within one fluctuation period, there is a period (approximately several tens of milliseconds) during which the power consumption exceeds the rated load. During this period, the uninterruptible power supply 200 becomes temporarily overloaded. The maximum power consumption of load 13 is approximately 150% of the rated load of the uninterruptible power supply 200.

[0052] In Figure 9, the power flow when the power consumption of load 13 is at its maximum is shown by arrows. The AC power supplied from the AC power supply 10 is supplied to load 13 via converter 1 and inverter 6. The power supplied from the AC power supply 10 is limited to the rated load (100%) of the uninterruptible power supply 200. Therefore, the remaining power, which corresponds to 50% of the rated load, is supplied to load 13 from battery 11 via bidirectional chopper 4 and inverter 6.

[0053] When DC power from battery 11 is supplied to load 13, the amount of charge stored in battery 11 decreases. Therefore, in response to the power consumption dropping below the rated load, the bidirectional chopper 4 stores DC power supplied from converter 1 via DC line 2 in battery 11.

[0054] As the uninterruptible power supply 200 becomes overloaded, the battery 11 is discharged and charged. Because the power consumption of the load 13 fluctuates periodically, the discharge and charging of the battery 11 are also repeated periodically. This repeated charging and discharging is a factor that accelerates the degradation of the battery 11.

[0055] Here, by selecting a larger capacity uninterruptible power supply (UPS) 200 such that the maximum power consumption of load 13 is less than or equal to the rated load of the UPS 200, it is possible to prevent the battery 11 from being charged or discharged due to overload. In this case, the UPS 200 will receive all the AC power equivalent to the maximum power consumption of load 13 from the AC power supply 10. On the other hand, the contracted power will be determined by the maximum power consumption of load 13. Since the basic charge for electricity is calculated based on the contracted power, there is a concern that the electricity bill will rise as the contracted power increases.

[0056] Figure 3 is a diagram showing the power flow during overload in an uninterruptible power supply 100 according to this embodiment, and is shown in comparison with Figure 9. The uninterruptible power supply 100 is equipped with two bidirectional choppers 4 and 5. Bidirectional chopper 4 is connected to a battery 11 and supplies DC power from the battery 11 to the inverter 6 via the DC line 2 when the AC power supply 10 fails. Bidirectional chopper 5 is connected to an EDLC 12 and supplies DC power from the EDLC 12 to the inverter 6 via the DC line 2 when overloaded.

[0057] In Figure 3, the power flow when the power consumption of load 13 is at its maximum is indicated by arrows. Note that when battery 11 is fully charged, almost 100% of the power supplied from the AC power source 10 is supplied to load 13 via converter 1 and inverter 6.

[0058] As shown in Figure 3, the power supplied from the AC power source 10 is limited to the rated load of the uninterruptible power supply 100. The remaining power, equivalent to 50% of the rated load, is supplied from the EDLC 12 to the load 13 via the bidirectional chopper 5 and inverter 6.

[0059] Figure 4 shows the temporal changes in the power consumption of load 13 and the AC input power supplied from AC power source 10. The temporal changes in the power consumption of load 13 shown in Figure 4 are the same as those shown in Figure 10.

[0060] As shown in Figure 4, during the period when the power consumption of load 13 exceeds the rated load, the bidirectional chopper 5 performs the discharge operation of the EDLC 12. During this period, the AC input power is limited to the rated load of the uninterruptible power supply 100.

[0061] During periods when the power consumption of load 13 is low, the bidirectional chopper 5 performs a charging operation of the EDLC 12. This allows the EDLC 12's stored energy to be restored in preparation for the next overload.

[0062] In this embodiment, during overload, the power supplied from the AC power source 10 can be kept below the rated load of the uninterruptible power supply 100. Furthermore, since the DC power from the battery 11 is not supplied to the load 13, repeated charging and discharging of the battery 11 can be suppressed.

[0063] Furthermore, since the EDLC 12 can output a large current instantaneously, the uninterruptible power supply 100 can quickly respond to a sudden increase in power consumption. In addition, since the EDLC 12 experiences less performance degradation due to repeated charging and discharging compared to the battery 11, the power supply reliability of the uninterruptible power supply 100 can be maintained.

[0064] The control configuration of the uninterruptible power supply 100 for realizing the above-described operation will be explained below. Figure 5 is a block diagram showing the portion of the control device 8 related to the control of the converter 1 and the bidirectional choppers 4 and 5. As shown in Figure 5, the control device 8 includes a power failure detector 20 and a control unit 22.

[0065] The power outage detector 20 detects whether a power outage has occurred in the AC power supply 10 based on the AC input voltage VI supplied from the AC power supply 10, and outputs a detection signal φPF indicating the detection result. When the AC power supply 10 is healthy, the detection signal φPF is set to an L (logic low) level. When a power outage occurs in the AC power supply 10, the detection signal φPF is set to an H (logic high) level. For example, the power outage detector 20 determines that a power outage has occurred in the AC power supply 10 when the AC input voltage VI falls below a lower limit.

[0066] The control unit 22 controls the converter 1 and the bidirectional choppers 4 and 5 based on the detection signal φPF from the power outage detector 20, the DC voltage VD of the DC line 2, the AC input voltage VI, the terminal voltage VB of the battery 11, the terminal voltage VE of the EDLC 12, the AC input current Ii indicated by the output signal Iif of the current detector CD1, the DC current IB indicated by the output signal IBf of the current detector CD2, the DC current IE indicated by the output signal IEf of the current detector CD3, and the AC output current Io indicated by the output signal Iof of the current detector CD4.

[0067] Figure 6 is a flowchart showing the operation of the control unit 22 shown in Figure 4. The flowchart shown in Figure 6 is repeatedly executed when the uninterruptible power supply 100 is in operation.

[0068] As shown in Figure 6, in step S01 (hereinafter simply referred to as "S"), the control unit 22 determines whether or not a power outage has occurred in the AC power supply 10 based on the detection signal φPF from the power outage detector 20.

[0069] If the detection signal φPF is at an L level, i.e., the AC power supply 10 is healthy (NO determination in S01), the control unit 22 operates the converter 1 in S02. In S02, the control unit 22 controls the converter 1 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR.

[0070] In step S03, the control unit 22 determines whether the DC voltage VD of the DC line 2 has fallen below the threshold voltage VDth1. When the power consumption of the load 13 is less than or equal to the rated load of the uninterruptible power supply 100, the DC voltage VD of the DC line 2 is maintained at approximately the reference DC voltage VDR by the power supplied from the AC power supply 10 via the converter 1. However, if the power consumption of the load 13 increases sharply and exceeds the rated load of the uninterruptible power supply 100, the power equivalent to the excess is supplied from the capacitor 3 to the inverter 6, causing the DC voltage VD to decrease. The threshold voltage VDth1 corresponds to the "first threshold voltage" for determining whether the uninterruptible power supply 100 is overloaded.

[0071] If the DC voltage VD is greater than or equal to the threshold voltage VDth1 (when NO is determined in S03), the control unit 22 determines that the uninterruptible power supply 100 is not overloaded. In this case, the control unit 22 proceeds to S04 and operates the bidirectional chopper 4 to charge the battery 11 with DC power supplied from the converter 1 via the DC line 2. The control unit 22 controls the bidirectional chopper 4 so that the terminal voltage VB of the battery 11 becomes the reference DC voltage VBR.

[0072] In S05, the control unit 22 determines whether the load 13 is a light load. In S05, the control unit 22 compares the AC output current Io detected by the current detector CD4 with the threshold current. If the AC output current Io is less than the threshold, the control unit 22 determines that the load 13 is a light load.

[0073] If the load 13 is a light load (when S05 is judged as YES), the control unit 22 operates the bidirectional chopper 5 in S06 to store the DC power supplied from the converter 1 via the DC line 2 in the EDLC 12. The control unit 22 controls the bidirectional chopper 5 so that the terminal voltage VE of the EDLC 12 becomes the reference DC voltage VER. If the load 13 is not a light load (when S05 is judged as NO), the control unit 22 skips the process in S06 and does not charge the EDLC 12.

[0074] If the DC voltage VD in S03 is less than the threshold voltage VDth1 (when S03 is judged as YES), the control unit 22 further determines in S07 whether the DC voltage VD of the DC line 2 has fallen below the threshold voltage VDth2. The threshold voltage VDth2 corresponds to the "second threshold voltage" used to determine whether the uninterruptible power supply 100 is overloaded. The threshold voltage VDth2 is set to a voltage value lower than the threshold voltage VDth1.

[0075] If the DC voltage VD is less than the threshold voltage VDth1 and greater than or equal to the threshold voltage VDth2 (when NO is determined in S07), the control unit 22 determines that the uninterruptible power supply 100 is overloaded. In this case, the control unit 22 proceeds to S08 and operates the bidirectional chopper 5 to supply DC power from the EDLC 12 to the inverter 6 via the DC line 2. The control unit 22 controls the bidirectional chopper 5 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR.

[0076] During the discharge of the EDLC 12, the control unit 22 determines in S09 whether the terminal voltage VE of the EDLC 12 has fallen below the discharge termination voltage VEmin. If the terminal voltage VE of the EDLC 12 has fallen below the discharge termination voltage VEmin (YES determination in S09), the control unit 22 stops the operation of the bidirectional chopper 5 in S10. On the other hand, if the terminal voltage VE of the EDLC 12 is greater than the discharge termination voltage VEmin (NO determination in S09), the control unit 22 returns to S03.

[0077] If the DC voltage VD falls below the threshold voltage VDth2 (when YES is determined in S07), the control unit 22 operates the bidirectional chopper 4 in S11 to supply DC power from the battery 11 to the inverter 6 via the DC line 2. The control unit 22 controls the bidirectional chopper 4 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR. Then, the control unit 22 returns to S03.

[0078] Returning to S01, if the detection signal φPF is at the H level, i.e., if a power outage occurs in the AC power supply 10 (when S01 is determined to be YES), the control unit 22 stops the operation of the converter 1 in S12.

[0079] In step S13, the control unit 22 operates the bidirectional chopper 4 to supply DC power from the battery 11 to the inverter 6 via the DC line 2. The control unit 22 controls the bidirectional chopper 4 so that the DC voltage VD of the DC line 2 becomes the reference DC voltage VDR.

[0080] During the discharge of the battery 11, the control unit 22 determines in S14 whether the terminal voltage VB of the battery 11 has fallen below the discharge termination voltage VBmin. If the terminal voltage VB of the battery 11 has fallen below the discharge termination voltage VBmin (YES determination in S14), the control unit 22 stops the operation of the bidirectional chopper 4 in S15.

[0081] Figure 7 shows an example of the temporal changes in the power consumption of the load 13, the AC input power from the AC power supply 10, the DC voltage VD of the DC line 2, the terminal voltage VB of the battery 11, and the terminal voltage VE of the EDLC 12.

[0082] The temporal change in the power consumption of load 13 shown in Figure 7 is the same as that shown in Figures 10 and 4. As shown in Figure 7, during the period from time t0 to t1 when the power consumption of load 13 is less than the rated load, the DC voltage VD of DC line 2 is maintained at the reference DC voltage VDR by the converter 1.

[0083] The terminal voltages VB of the battery 11 and VE of the EDLC 12 are maintained at reference DC voltages VBR and VER, respectively. The reference DC voltage VBR corresponds to the terminal voltage VB when the battery 11 is fully charged. The reference DC voltage VER corresponds to the terminal voltage VE when the EDLC 12 is fully charged.

[0084] When the power consumption of load 13 increases sharply at time t1, the power stored in capacitor 3 is supplied to inverter 6, causing the DC voltage VD of DC line 2 to start to decrease. If the power consumption exceeds the rated load and the DC voltage VD drops to threshold voltage VDth1 at time t2, the control unit 22 operates the bidirectional chopper 5 to supply DC power from EDLC 12 to inverter 6 via DC line 2.

[0085] Since the DC line 2 receives DC power from the EDLC 12 in addition to the DC power generated by the converter 1, the DC voltage VD rises. When the voltage VE across the terminals of the EDLC 12 decreases due to this discharge operation and reaches the discharge termination voltage VEmin (time t3), the control unit 22 stops the operation of the bidirectional chopper 5.

[0086] At time t4, which is after time t3, when the load 13 becomes a light load, the control unit 22 operates the bidirectional chopper 5 to store the DC power supplied from the converter 1 via the DC line 2 in the EDLC 12.

[0087] In the example shown in Figure 7, the bidirectional chopper 5 performs a discharge operation on the EDLC 12 during overload, so the AC input power during overload is limited to the rated load of the uninterruptible power supply 100. Furthermore, since the battery 11 does not discharge during overload, deterioration of the battery 11 due to repeated charging and discharging can be suppressed.

[0088] Furthermore, under light load conditions, the bidirectional chopper 5 performs a charging operation on the EDLC 12, allowing the EDLC 12's charge level to be restored in preparation for the next overload.

[0089] Figure 8 shows another example of the temporal changes in the power consumption of load 13, the AC input power from AC power supply 10, the DC voltage VD of DC line 2, the terminal voltage VB of battery 11, and the terminal voltage VE of EDLC 12. Figure 8 differs from Figure 7 in that the length of the period during which the uninterruptible power supply 100 is overloaded.

[0090] In Figure 8, as in Figure 7, the power consumption of the load 13 increases sharply at time t1, and when the DC voltage VD drops to the threshold voltage VDth1 at time t2, the control unit 22 operates the bidirectional chopper 5 to supply DC power from the EDLC 12 to the inverter 6 via the DC line 2. Then, when the terminal voltage VE of the EDLC 12 drops to the discharge termination voltage VEmin at time t3, the control unit 22 stops the operation of the bidirectional chopper 5.

[0091] However, since the power consumption of load 13 exceeds the rated load even after time t3, the DC voltage VD of DC line 2 begins to decrease again. If the DC voltage VD drops to the threshold voltage VDth2 at time t4, the control unit 22 operates the bidirectional chopper 4 to supply DC power from battery 11 to inverter 6 via DC line 2.

[0092] Because DC line 2 receives DC power from battery 11 in addition to the DC power generated by converter 1, the DC voltage VD rises again. This discharge operation causes the terminal voltage VB of battery 11 to decrease.

[0093] When the power consumption of load 13 drops to below the rated load at time t5, the control unit 22 operates the bidirectional chopper 4 to store the DC power supplied from converter 1 via DC line 2 in battery 11. As a result, the terminal voltage VB of battery 11 recovers to the reference DC voltage VBR (time t6).

[0094] Furthermore, at time t7, when the load 13 becomes a light load, the control unit 22 operates the bidirectional chopper 5 to store the DC power supplied from the converter 1 via the DC line 2 in the EDLC 12. As a result, the terminal voltage VE of the EDLC 12 recovers to the reference DC voltage VER (time t8).

[0095] As described above, in this embodiment, in the event of an overload, the bidirectional chopper 5 supplies power stored in the EDLC 12 to the inverter 6 via the DC line 2. This makes it possible to keep the power supplied from the AC power source 10 below the rated load of the uninterruptible power supply 100. In addition, since DC power from the battery 11 is not supplied to the load 13 in the event of an overload, repeated charging and discharging of the battery 11 can be suppressed.

[0096] However, in the event of an overload, if the DC power supplied from the EDLC 12 to the inverter 6 via the DC line 2 is insufficient, the bidirectional chopper 4 supplies power stored in the battery 11 to the inverter 6 via the DC line 2. In this way, the bidirectional chopper 4 assists the bidirectional chopper 5, enabling a stable power supply to the load 13 while maintaining the power supplied from the AC power source 10 below the rated load of the uninterruptible power supply 100.

[0097] Furthermore, by acquiring information regarding the maximum power consumption and overload operating time of the load 13 in advance, and selecting the capacity of the EDLC 12 based on this information, it becomes possible to suppress the assist operation of the bidirectional chopper 4.

[0098] 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.

[0099] 1 Converter, 2 DC line, 3 Capacitor, 4, 5 Bidirectional chopper, 6 Inverter, 7 Operating unit, 8 Control unit, 10 AC power supply, 11 Battery, 12 EDLC, 13 Load, 20 Power failure detector, 22 Control unit, 80 CPU, 82 Memory, 84 I / O circuit, 86 Bus, 100, 200 Uninterruptible power supply, CD1-CD4 Current detector, S1-S4 Switch, T1 AC input terminal, T2, T3 DC terminals, T4 AC output terminal.

Claims

1. An uninterruptible power supply connected between an AC power source and a load, comprising: a converter that converts AC power supplied from the AC power source into DC power and outputs it to a DC line; an inverter that converts DC power supplied from the DC line into AC power and supplies it to the load; a first bidirectional chopper that exchanges first DC power between the DC line and a first energy storage device; a second bidirectional chopper that exchanges second DC power between the DC line and a second energy storage device, wherein the second bidirectional chopper has a lower capacity than the first bidirectional chopper; and further comprising a control device, wherein when the power consumption of the load exceeds the rated load of the uninterruptible power supply, the control device operates the second bidirectional chopper to supply second DC power from the second energy storage device to the DC line. An uninterruptible power supply (UPS) that, in the event of a power outage of the AC power supply, stops the operation of the converter and operates the first bidirectional chopper to supply the first DC power from the first energy storage device to the DC line.

2. The uninterruptible power supply according to claim 1, wherein the first energy storage device has a higher energy density than the second energy storage device, and the second energy storage device has a higher output density than the first energy storage device.

3. The uninterruptible power supply according to claim 2, wherein the first energy storage device is a secondary battery, and the second energy storage device is an electric double-layer capacitor.

4. When the AC power supply is healthy, the control device operates the first bidirectional chopper to supply first DC power from the DC line to the first energy storage device, the uninterruptible power supply according to any one of claims 1 to 3.

5. The uninterruptible power supply according to claim 4, wherein the control device operates the first bidirectional chopper to supply the first DC power from the first energy storage device to the DC line when the second DC power supplied from the second energy storage device is insufficient during the overload.

6. The uninterruptible power supply according to claim 5, wherein, 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 DC voltage; when the DC voltage of the DC line falls below a first threshold voltage lower than the reference DC voltage, the control device operates the second bidirectional chopper to supply the second DC power from the second energy storage device to the DC line; and when the DC voltage of the DC line falls below a second threshold voltage lower than the first threshold voltage, the control device operates the first bidirectional chopper to supply the first DC power from the first energy storage device to the DC line.

7. When the AC power supply is healthy and the uninterruptible power supply is operating at a load smaller than the rated load, the control device operates the second bidirectional chopper to supply the second DC power to the second energy storage device from the DC line, as described in claim 4.

8. The uninterruptible power supply according to claim 1, wherein the second bidirectional chopper is smaller in size than the first bidirectional chopper.

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