Uninterruptible power supply device

Abstract

A converter (10) converts AC power supplied from an AC power supply (80) into DC power and outputs the DC power to a DC line (20). An inverter (40) converts the DC power supplied from the DC line (20) into AC power and supplies the AC power to a load (84). An electricity storage device (82) is connected to the DC line (20). The converter (10) includes a plurality of converter units (12) connected in parallel. The inverter (40) includes a plurality of inverter units (42) connected in parallel. When the AC power supply (80) is normal, a control device (50) determines an appropriate number of inverter units (42) to be operated on the basis of the output current of the inverter (40). The control device (50) determines an appropriate number of converter units (12) to be operated on the basis of AC power supplied from the AC power supply (80) to the converter (10). The control device (50) operates the determined appropriate numbers of inverter units (42) and converter units (12) to be operated.

Description

Uninterruptible power supply device

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

[0002] For example, Japanese Unexamined Patent Application Publication No. 2020-005410 (Patent Document 1) discloses an uninterruptible power supply system including a plurality of uninterruptible power supply devices. The plurality of uninterruptible power supply devices are connected in parallel between an AC power supply and a load. An appropriate number of operating units required to supply a load current is determined, and an appropriate number of uninterruptible power supply devices among the plurality of uninterruptible power supply devices are brought into an operating state to supply the load current, and the remaining uninterruptible power supply devices are brought into a standby state.

[0003] Japanese Unexamined Patent Application Publication No. 2020-005410

[0004] In Patent Document 1, the converters and inverters belonging to the uninterruptible power supply device in the operating state are operated. Also, the operation of the converters and inverters belonging to the uninterruptible power supply device in the stopped state is stopped. That is, the number of inverters determined based on the load current and the same number of converters are each operated.

[0005] Therefore, when a load with a low power factor is connected to the uninterruptible power supply system, while each inverter can be operated with high operating efficiency, the number of operating units of the converters may be excessive with respect to the AC power supplied from the AC power supply (corresponding to the power consumption of the load). In this case, since the operating efficiency of each converter decreases, there is a concern that the power supply efficiency of the entire uninterruptible power supply system will decrease.

[0006] Therefore, a main object of the present disclosure is to provide an uninterruptible power supply device capable of improving the power supply efficiency.

[0007] An uninterruptible power supply (UPS) according to this disclosure comprises a converter that converts AC power supplied from an 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 a load, and a control device that controls the converter and the inverter. A power storage device that stores the DC power of the DC line is connected to the DC line. The converter includes a plurality of converter units connected in parallel between the AC power source and the DC line. The inverter includes a plurality of inverter units connected in parallel between the DC line and the load. When the AC power source is healthy, the control device determines the appropriate number of inverter units to operate based on the output current of the inverter. The control device determines the appropriate number of converter units to operate based on the AC power supplied from the AC power source to the converter. The control device operates the determined appropriate number of inverter units and converter units.

[0008] According to this disclosure, it is possible to provide an uninterruptible power supply that can improve power supply efficiency.

[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 flowchart showing the operation flow of the control device. This is a block diagram showing the configuration of the part of the control device related to inverter control. This is a block diagram showing the configuration of the part of the control device related to bidirectional chopper control. This is a block diagram showing the configuration of the part of the control device related to converter control. This is a diagram showing an example of the operation of the uninterruptible power supply when the AC power supply is healthy. This is a diagram showing an example of the operation of the uninterruptible power supply when the AC power supply is down. This is a diagram showing an example of the operation of the uninterruptible power supply when the AC power supply is restored. This is a circuit block diagram showing the configuration of an uninterruptible power supply according to Embodiment 2.

[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 100 includes an AC input terminal T1, a DC terminal T2, and an AC output terminal T3. The AC input terminal T1 receives AC power at a predetermined frequency (for example, commercial frequency) from an AC power source 80. The AC power source 80 may be a commercial AC power source or a generator.

[0012] The DC terminal T2 is connected to the battery 82. The battery 82 corresponds to one embodiment of an "energy storage device" that stores DC power. The battery 82 is a secondary battery such as a lead-acid battery, nickel-metal hydride battery, or lithium-ion battery. Instead of the battery 82, an electric double-layer capacitor or a flywheel may be connected.

[0013] The AC output terminal T3 is connected to the load 84. The load 84 is driven by AC power supplied from the uninterruptible power supply 100.

[0014] The uninterruptible power supply 100 further includes switches S1 to S3, a converter 10, current detectors CD1 to CD3, a DC line 20, capacitors C1, C2, 22, reactors L1, L2, a bidirectional chopper 30, an inverter 40, and a control device 50.

[0015] Switch S1 and reactor L1 are connected in series between the AC input terminal T1 and the AC node of the converter 10. Switch S1 is controlled by the control device 50. When the AC power supply 80 is healthy, switch S1 is turned on, and AC power is supplied from the AC power supply 80 to the converter 10 via switch S1. When the AC power supply 80 fails, switch S1 is turned off, and the connection between the AC power supply 80 and the converter 10 is interrupted.

[0016] The instantaneous value of the AC input voltage VI supplied from the AC power supply 80 is detected by the control device 50. Based on the instantaneous value of the AC input voltage VI, the control device 50 determines whether or not the AC voltage VI is being supplied normally from the AC power supply 80. The current detector CD1 detects the AC input current Ii flowing between the AC power supply 80 and the converter 10 and provides the control device 50 with a signal Iif indicating the detected value.

[0017] Capacitor C1 is connected to the node between switch S1 and reactor L1. Capacitor C1 and reactor L1 constitute an AC filter F1. The AC filter F1 is a low-pass filter that allows AC power of a predetermined frequency to pass from the AC power supply 80 to the converter 10, and prevents switching frequency signals generated in the converter 10 from passing through to the AC power supply 80.

[0018] The converter 10 is controlled by the control device 50. When the AC power supply 80 is functioning properly, the converter 10 converts the AC power received by the AC input terminal T1 into DC power and outputs it to the DC line 20. The output voltage of the converter 10 can be controlled to a desired value. In the event of a power outage of the AC power supply 80, the operation of the converter 10 is stopped.

[0019] The converter 10 includes multiple converter units 12_1, 12_2, and 12_3, and multiple switches 11_1, 11_2, and 11_3. In the following description, the multiple converter units 12_1, 12_2, and 12_3 may be collectively referred to as "converter unit 12," and the multiple switches 11_1, 11_2, and 11_3 may be collectively referred to as "switch 11." The number L of each of the converter units 12 and switches 11 is not limited to 3, but can be any number.

[0020] Multiple converter units 12_1, 12_2, and 12_3 are connected in parallel between the AC node and the DC node of converter 10. The converter unit 12 is a well-known type including multiple semiconductor switching elements and multiple diodes, and is controlled by the control device 50. The converter unit 12 converts the AC power input from the AC node via the corresponding switch 11 into DC power and outputs it to the DC node.

[0021] Multiple switches 11_1, 11_2, and 11_3 are provided corresponding to multiple converter units 12_1, 12_2, and 12_3, respectively. Switch 11 is connected in series with the corresponding converter unit 12 between the AC node and DC node of the converter 10. Switch 11 is controlled by the control device 50, and is turned on when the corresponding converter unit 12 is put into operation, and turned off when the corresponding converter unit 12 is put into a stopped state.

[0022] Capacitor 22 is connected to the DC line 20 and smooths the voltage of the DC line 20. The instantaneous value of the DC voltage VD appearing on the DC line 20 is detected by the control device 50.

[0023] The DC line 20 is connected to the high-voltage side node of the bidirectional chopper 30, and the low-voltage side node of the bidirectional chopper 30 is connected to the DC terminal T2 via switch S2. 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 82 are being maintained.

[0024] The bidirectional chopper 30 is controlled by the control device 50 and exchanges DC power between the DC line 20 and the battery 82. When the AC power supply 80 is functioning properly, the bidirectional chopper 30 stores the DC power supplied from the converter 10 via the DC line 20 in the battery 82. In the event of a power outage of the AC power supply 80, the bidirectional chopper 30 supplies the DC power from the battery 82 to the inverter 40 via the DC line 20.

[0025] The current detector CD2 detects the current IB (hereinafter also referred to as "battery current") flowing between the bidirectional chopper 30 and the battery 82, and provides a signal IBf indicating the detected value to the control device 50. The instantaneous value of the terminal voltage VB of the battery 82 (hereinafter also referred to as "battery voltage") appearing at the DC terminal T2 is detected by the control device 50.

[0026] The bidirectional chopper 30 includes multiple chopper units 32_1, 32_2, 32_3 and multiple switches 31_1, 31_2, 31_3. In the following description, the multiple chopper units 32_1, 32_2, 32_3 may be collectively referred to as "chopper unit 32," and the multiple switches 31_1, 31_2, 31_3 may be collectively referred to as "switch 31." The number M of each chopper unit 32 and switch 31 is not limited to 3, but can be any number.

[0027] Multiple chopper units 32_1, 32_2, and 32_3 are connected in parallel between the high-voltage side node and the low-voltage side node of the bidirectional chopper 30. The chopper units 32 are well-known ones that include multiple semiconductor switching elements and multiple diodes, and are controlled by the control device 50. When storing DC power in the battery 82, the chopper unit 32 steps down the DC voltage VD of the DC line 20 and supplies it to the battery 82 via the corresponding switch 31. Also, when supplying DC power from the battery 82 to the inverter 40, the chopper unit 32 steps up the battery voltage VB input via the corresponding switch 31 and outputs it to the DC line 20.

[0028] Multiple switches 31_1, 31_2, and 31_3 are provided corresponding to multiple chopper units 32_1, 32_2, and 32_3, respectively. Switch 31 is connected in series with the corresponding chopper unit 32 between the high-voltage side node and the low-voltage side node of the bidirectional chopper 30. Switch 31 is controlled by the control device 50, and is turned on when the corresponding chopper unit 32 is put into operation, and turned off when the corresponding chopper unit 32 is put into a stopped state.

[0029] The DC line 20 is connected to the DC node of the inverter 40. The inverter 40 is controlled by the control device 50 and converts the DC power supplied from the converter 10 or the bidirectional chopper 30 via the DC line 20 into AC power and outputs it to the AC node. That is, when the AC power supply 80 is healthy, the inverter 40 converts the DC power supplied from the converter 10 via the DC line 20 into AC power, and when the AC power supply 80 fails, it converts the DC power supplied from the bidirectional chopper 30 via the DC line 20 into AC power. The output voltage of the inverter 40 is controllable to a desired value.

[0030] The inverter 40 includes multiple inverter units 42_1, 42_2, 42_3 and multiple switches 41_1, 41_2, 41_3. In the following description, the multiple inverter units 42_1, 42_2, 42_3 may be collectively referred to as "inverter unit 42," and the multiple switches 41_1, 41_2, 41_3 may be collectively referred to as "switch 41." The number N of each inverter unit 42 and switch 41 is not limited to 3, but can be any number.

[0031] Multiple inverter units 42_1, 42_2, and 42_3 are connected in parallel between the DC node and the AC node of the inverter 40. The inverter unit 42 is a well-known type including multiple semiconductor switching elements and multiple diodes, and is controlled by the control device 50. The inverter unit 42 converts the DC power input from the DC node via the corresponding switch 41 into AC power and outputs it to the AC node.

[0032] Multiple switches 41_1, 41_2, and 41_3 are provided corresponding to multiple inverter units 42_1, 42_2, and 42_3, respectively. Switch 41 is connected in series with the corresponding inverter unit 42 between the DC node and the AC node of the inverter 40. Switch 41 is controlled by the control device 50, and is turned on when the corresponding inverter unit 42 is put into operation, and turned off when the corresponding inverter unit 42 is put into a stopped state.

[0033] The AC node of the inverter 40 is connected to the first terminal of the switch S3 via the reactor L2, and the second terminal of the switch S3 is connected to the AC output terminal T3. Capacitor C2 is connected to the first terminal of the switch S3. The reactor L2 and capacitor C2 constitute an AC filter F2. The AC filter F2 is a low-pass filter that allows AC power of a predetermined frequency generated by the inverter 40 to pass through to the AC output terminal T3, and prevents the switching frequency signal generated by the inverter 40 from passing through to the AC output terminal T3.

[0034] Switch S3 is controlled by the control device 50 and is turned on in inverter power supply mode when AC power generated by the inverter 40 is supplied to the load 84, and turned off in bypass power supply mode when AC power from a bypass AC power source (not shown) is supplied to the load 84.

[0035] The instantaneous value of the AC output voltage VO appearing at node N2 is detected by the control device 50. The current detector CD3 detects the current Io (hereinafter also referred to as "load current") flowing between the inverter 40 and the AC output terminal T3, and provides the control device 50 with a signal Iof indicating the detected value.

[0036] The control device 50 controls the entire uninterruptible power supply 100 based on the AC input voltage VI, AC input current Ii, DC voltage VD, battery voltage VB, battery current IB, AC output voltage VO, and load current Io.

[0037] Figure 2 is a block diagram showing an example of the hardware configuration of the control device 50. Typically, the control device 50 can be configured using a microcomputer with a predetermined program pre-stored in it.

[0038] As shown in Figure 2, the control device 50 includes a CPU (Central Processing Unit) 52, a memory 54, and an input / output (I / O) circuit 56. The CPU 52, memory 54, and I / O circuit 56 can exchange data with each other via a bus 58. A program is stored in a portion of the memory 54, and the CPU 52 can execute this program to realize various functions described later. The I / O circuit 56 exchanges signals and data with the outside of the control device 50.

[0039] The data provided to the control device 50 from outside includes information on the number of power conversion units contained in each power converter of the converter 10, bidirectional chopper 30, and inverter 40, as well as information on the rated output and operating efficiency of each power conversion unit of the converter unit 12, chopper unit 32, and inverter unit 42. This acquired data is stored in the memory 54.

[0040] Alternatively, unlike the example in Figure 2, at least a portion of the control device 50 can be configured using circuits such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit). Furthermore, at least a portion of the control device 50 can also be configured using analog circuits.

[0041] Next, the operation of the uninterruptible power supply 100 will be described. As shown in Figure 1, in the uninterruptible power supply 100, each power converter, including the converter 10, the bidirectional chopper 30, and the inverter 40, is configured to include a plurality of power conversion units (converter unit 12, chopper unit 32, and inverter unit 42) connected in parallel. The control device 50 is configured to individually control the number of power conversion units operating in each power converter according to the operating state of the uninterruptible power supply 100.

[0042] FIG. 3 is a flowchart showing the flow of operations of the control device 50. The flowchart shown in FIG. 3 is repeatedly executed every time a predetermined condition is satisfied (every predetermined period) during the operation of the uninterruptible power supply device 100.

[0043] As shown in FIG. 3, the control device 50 first detects whether or not a power failure has occurred in the AC power supply 80 (step S01). In S01, the control device 50 determines that a power failure has occurred in the AC power supply 80 when, for example, the instantaneous value of the AC input voltage VI supplied from the AC power supply 80 drops below the lower limit value.

[0044] When the AC power supply 80 is normal (when the determination in S01 is NO), the control device 50 determines the appropriate number of operating power conversion units in each of the power converters of the converter 10, the bidirectional chopper 30, and the inverter 40 (steps S02 to S04).

[0045] Specifically, the control device 50 determines the appropriate number of operating units X of the inverter unit 42 for the inverter 40 (step S02). In S02, the control device 50 determines the appropriate number of operating units X of the inverter unit 42 based on the output current of the inverter 40 (that is, the load current Io). X is an integer of 1 or more and N or less. N is the number of inverter units 42 included in the inverter 40 (the total number of units). The control device 50 determines the appropriate number of operating units X of the inverter unit 42 so that the inverter unit 42 operates at a high load factor with high operating efficiency. The method for determining the appropriate number of operating units X will be described in detail later.

[0046] Further, the control device 50 determines the appropriate number of operating units Y of the chopper unit 32 for the bidirectional chopper 30 (step S03). In S03, the control device 50 determines the appropriate number of operating units Y of the chopper unit 32 based on the charging current required to charge the battery 82. Y is an integer of 0 or more and M or less. M is the number of chopper units 32 included in the bidirectional chopper 30 (the total number of units). The control device 50 determines the appropriate number of operating units Y of the chopper unit 32 so that the minimum number of chopper units 32 required to charge the battery 82 operates. The method for determining the appropriate number of operating units Y will be described in detail later.

[0047] Further, the control device 50 determines the appropriate number of operating units Z of the converter unit 12 for the converter 10 (step S04). In S04, the control device 50 determines the appropriate number of operating units Z of the converter unit 12 based on the AC power supplied from the AC power source 80 to the converter 10. Z is an integer greater than or equal to 1 and less than or equal to L. L is the number of converter units 12 included in the converter 10 (total number of units). The AC power supplied from the AC power source 80 to the converter 10 corresponds to the total power of the AC power consumed by the load 84 (power consumption of the load 84) and the AC power supplied to the battery 82 (charging power of the battery 82). The control device 50 determines the appropriate number of operating units Z of the converter unit 12 so that the converter unit 12 operates at a high load factor with high operating efficiency. The method for determining the appropriate number of operating units Z will be described in detail later.

[0048] When the appropriate number of operating units of the power conversion unit in each power converter is determined, the control device 50 controls the operations of the converter 10, the bidirectional chopper 30, and the inverter 40 based on the determined appropriate number of operating units (step S05). In S05, the control device 50 sets the power conversion units with the appropriate number of operating units among the plurality of power conversion units to the operating state and turns on the corresponding switches in each power converter. Also, the control device 50 sets the remaining power conversion units to the stopped state and turns off the corresponding switches.

[0049] Returning to step S01, when a power outage of the AC power source 80 occurs (when the determination in S01 is YES), the control device 50 does not perform the determination of the appropriate number of operating units in steps S02 to S04. The control device 50 sets the appropriate number of operating units X of the inverter unit 42 of the inverter 40 to the total number of units N (step S06). That is, the control device 50 sets all the plurality of inverter units 42 to the operating state.

[0050] Also, the control device 50 sets the appropriate number of operating units Y of the chopper unit 32 of the bidirectional chopper 30 to the total number of units M (step S07). That is, the control device 50 sets all the plurality of chopper units 32 to the operating state.

[0051] On the other hand, the control device 50 sets the appropriate number of operating converter units 12 Z to 0 for the converter 10 (step S08). In other words, the control device 50 stops the operation of the converter 10 by stopping all of the converter units 12.

[0052] The control device 50 controls the operation of the bidirectional chopper 30 and inverter 40 based on the appropriate number of operating units determined in steps S06 and S07 (step S09). In S09, the control device 50 puts all of the multiple power conversion units in the bidirectional chopper 30 and inverter 40 into operation, and turns on all of the multiple switches.

[0053] In this way, when the AC power supply 80 is interrupted, all inverter units 42 of the inverter 40 and all chopper units 32 of the bidirectional chopper 30 are operated, thereby maintaining the reliability of power supply to the load 84 during the power outage.

[0054] Next, we will explain how to determine the appropriate number of power conversion units to operate in steps S02 to S04 of Figure 3.

[0055] Figure 4 is a block diagram showing the configuration of the part of the control device 50 related to the control of the inverter 40. As shown in Figure 4, the control device 50 includes a power outage detector 60, a unit number calculation unit 44, a selection unit 45, and a control unit 46.

[0056] The power outage detector 60 detects whether a power outage has occurred in the AC power supply 80 based on the AC input voltage VI supplied from the AC power supply 80, and outputs a detection signal φPF indicating the detection result. For example, the power outage detector 60 determines that a power outage has occurred in the AC power supply 80 when the instantaneous value of the AC input voltage VI falls below a lower limit. When the AC power supply 80 is healthy, the detection signal φPF is set to an L (logic low) level. When a power outage occurs in the AC power supply 80, the detection signal φPF is activated to an H (logic high) level.

[0057] The unit number calculation unit 44 receives the output signal Iof from the current detector CD3 and the detection signal φPF from the power failure detector 60. When the detection signal φPF is at the L level (when the AC power supply 80 is healthy), the unit number calculation unit 44 determines the appropriate number of inverter units 42 to operate X based on the load current Io indicated by the output signal Iof.

[0058] Specifically, the operating unit calculation unit 44 obtains information about the inverter 40 from the memory 54. The information about the inverter 40 includes the number of inverter units 42 included in the inverter 40 (total number of units) N, the rated output A of the inverter units 42, and the load characteristics of the inverter units 42. The load characteristics of the inverter units 42 represent the relationship between the load factor and the operating efficiency of the inverter units 42. The load characteristics of the inverter units 42 are stored in the memory 54 in the form of a mathematical formula or map.

[0059] As shown in Figure 4, the operating efficiency of the inverter unit 42 changes depending on the load factor. In the example in Figure 4, the highest operating efficiency can be obtained when the load factor is R1 (%), but when the load factor falls below R1 (%), the operating efficiency drops sharply.

[0060] When N inverter units 42 are operated in parallel, the load current Io is equally distributed among the N inverter units 42, and the current distributed to each inverter unit 42 is Io / N. When N inverter units 42 are operated in parallel, if the load factor of each inverter unit 42 falls below R1 (%) and the operating efficiency is low, the current distributed to each inverter unit 42 can be increased by stopping the operation of N-X inverter units 42, thereby improving the operating efficiency of each inverter unit 42. Therefore, by controlling the number of inverter units 42 in operation to achieve a high-efficiency load factor R1 (%), the overall operating efficiency of the inverter 40 can be improved.

[0061] The number of operating units calculation unit 44 determines the output power of the inverter 40 based on the load current Io indicated by the output signal Iof. The number of operating units calculation unit 44 also determines the output power R1 × A of the inverter unit 42 when the load factor is R1 (%) based on the load characteristics of the inverter unit 42. Then, the number of operating units calculation unit 44 divides the output power of the inverter 40 by the output power R1 × A of the inverter unit 42. For example, if the output power of the inverter 40 corresponds to α% of the rated output N × A of the inverter 40, the quotient will be (α × N × A) / (R1 × A). The number of operating units calculation unit 44 determines the appropriate number of operating units X to be the integer closest to this quotient α × N / R1.

[0062] On the other hand, when the detection signal φPF is at the H level (when the AC power supply 80 is shut off), the operating unit calculation unit 44 sets the appropriate operating number X of the inverter unit 42 to the total number of units N (corresponding to S06 in Figure 3).

[0063] The number of operating units calculation unit 44 provides a signal φX indicating the appropriate number of operating units X to the selection unit 45. Based on the output signal φX from the number of operating units calculation unit 44, the selection unit 45 selects whether to put each of the N inverter units 42 into an operating state or a stopped state.

[0064] In certain situations, the N inverter units 42 have a predetermined priority order for when they should be in operation. The selection unit 45 selects whether to put each inverter unit 42 into operation or stopped state based on the signal φX and this priority order. The selection unit 45 provides the control unit 46 with signals SE1 to SEN indicating the selection result for each of the N inverter units 42.

[0065] Signal SEi, which indicates the selection result of inverter unit 42_i, which has priority number i, is set to H level when inverter unit 42_i is selected to be in operation. When inverter unit 42_i is selected to be in stopped state, signal SEi is set to L level. If the appropriate number of operating units X is equal to the total number of units N, signals SE1 to SEN are all set to H level.

[0066] For example, if the current number of operating units is 2 and the appropriate number of operating units X is 3, the selection unit 45 selects the inverter unit 42 with the highest priority among the stopped inverter units 42 to be put into operation. Conversely, if the current number of operating units is 3 and the appropriate number of operating units X is 2, the selection unit 45 selects the inverter unit 42 with the highest priority among the 3 inverter units 42 that are currently in operation to be put into operation.

[0067] The control device 50 may include a timer 48 for measuring the time each inverter unit 42 has been in operation. In this case, the selection unit 45 can select an inverter unit 42 to be in a stopped state when the measured operating time for that inverter unit 42 reaches a predetermined time, and can also select the inverter unit 42 with the highest priority among the stopped inverter units 42 to be in operation. In this way, the inverter units 42 that are put into operation are rotated, so the operating time of the N inverter units 42 can be equalized. As a result, the occurrence of failure in each inverter unit 42 can be delayed.

[0068] The control unit 46 controls a plurality of switches 41 and a plurality of inverter units 42 based on the output signals SE1 to SEN of the selection unit 45, the output signal Iof of the current detector CD3, and the AC output voltage VO.

[0069] Specifically, when the signal SEi is at an L level, the control unit 46 stops the operation of the corresponding inverter unit 42_i and turns off the corresponding switch 41_i.

[0070] On the other hand, if the signal SEi is at a high level, the control unit 46 operates the corresponding inverter unit 42_i and turns on the corresponding switch 41_i. The control unit 46 controls the inverter unit 42_i so that the AC output voltage VO becomes a sinusoidal reference voltage VOR.

[0071] Figure 5 is a block diagram showing the configuration of the part of the control device 50 related to the control of the bidirectional chopper 30. As shown in Figure 5, the control device 50 includes a subtractor 33, a charging current calculation unit 34, a number of operating units calculation unit 35, a selection unit 36, and a control unit 38.

[0072] The subtractor 33 calculates the deviation ΔVB = VBR - VB between the battery voltage VB and the reference voltage VBR. The reference voltage VBR corresponds to the target value of the battery voltage VB when charging the battery 82.

[0073] The charging current calculation unit 34 calculates a current command value IBc to control the current flowing to the battery 82 so that the deviation ΔVB becomes 0. The charging current calculation unit 34 calculates the current command value IBc by, for example, performing a proportional or proportional-integral operation on the deviation ΔVB. The current command value IBc corresponds to the current required to charge the battery 82.

[0074] The unit number calculation unit 35 receives the current command value IBc and the detection signal φPF from a power outage detector 60 (not shown). When the detection signal φPF is at the L level (when the AC power supply 80 is healthy), the unit number calculation unit 35 determines the appropriate number of chopper units 32 to operate Y based on the current command value IBc.

[0075] Specifically, the number of operating units calculation unit 35 obtains information about the bidirectional chopper 30 from the memory 54. The information about the bidirectional chopper 30 includes the number of chopper units 32 included in the bidirectional chopper 30 (total number of units) M, and the rated current B of the chopper units 32. The number of operating units calculation unit 35 divides the current command value IBc by the rated current B. Then, the number of operating units calculation unit 35 determines the appropriate number of operating units Y to be the integer closest to this quotient IBc / B.

[0076] In Figure 5, the current command value IBc is divided by the rated current B of the chopper unit 32. However, the current command value IBc may also be divided by the current that the chopper unit 32 can charge the battery 82 with.

[0077] On the other hand, when the detection signal φPF is at the H level (when the AC power supply 80 is shut off), the operating unit calculation unit 35 sets the appropriate operating number Y of the chopper unit 32 to the total number of units M (corresponding to S07 in Figure 3).

[0078] The number of operating units calculation unit 35 provides a signal φY indicating the appropriate number of operating units Y to the selection unit 36. Based on the output signal φY of the number of operating units calculation unit 35, the selection unit 36 ​​selects whether to put each of the M chopper units 32 into an operating state or a stopped state.

[0079] In certain situations, similar to the inverter 40, the bidirectional chopper 30 also has a pre-set priority order for the M-unit chopper 32 to enter the operating state. The selection unit 36 ​​selects whether to enter the operating state or the stopped state for each chopper unit 32 based on the signal φX and this priority order. The selection unit 36 ​​provides the control unit 38 with signals SE1 to SEM indicating the selection result for each of the M-unit chopper 32.

[0080] Signal SEk, which indicates the selection result of chopper unit 32_k having priority number k, is set to H level when chopper unit 32_k is selected to be in operation. When chopper unit 32_k is selected to be in stopped state, signal SEk is set to L level. If the appropriate number of operating units Y is equal to the total number of units M, signals SE1 to SEM are all set to H level.

[0081] The control device 50 may include a timer 37 for measuring the time each chopper unit 32 has been in operation. In this case, the selection unit 36 ​​can select a chopper unit 32 to be stopped when the measured operating time for that chopper unit 32 reaches a predetermined time, and at the same time select the chopper unit 32 with the highest priority among the stopped chopper units 32 to be in operation. In this way, the chopper units 32 that are put into operation are rotated, so the operating time of the M units of chopper units 32 can be equalized. As a result, the occurrence of failure in each chopper unit 32 can be delayed.

[0082] The control unit 38 controls a plurality of switches 31 and a plurality of chopper units 32 based on the output signals SE1 to SEM from the selection unit 36, the output signal IBf from the current detector CD2, the battery voltage VB, the DC voltage VD, and the detection signal φPF.

[0083] Specifically, when the signal SEk is at an L level, the control unit 46 stops the operation of the corresponding chopper unit 32_k and turns off the corresponding switch 31_k.

[0084] On the other hand, if the signal SEk is at the H level, the control unit 38 operates the corresponding chopper unit 32_k and turns on the corresponding switch 31_k. If the detection signal φPF is at the L level (when the AC power supply 80 is healthy), the control unit 38 controls the chopper unit 32_k so that the battery voltage VB becomes the reference voltage VBR.

[0085] When the detection signal φPF is at the H level (during a power outage of the AC power supply 80), the control unit 38 controls the chopper unit 32_k so that the DC voltage VD of the DC line 20 becomes the reference voltage VDR. In addition, during a power outage of the AC power supply 80, all M units of chopper unit 32 are selected to be in operation, so the control unit 38 controls the M units of chopper unit 32 so that the DC voltage VD of the DC line 20 becomes the reference voltage VDR.

[0086] Figure 6 is a block diagram showing the configuration of the part of the control device 50 related to the control of the converter 10. As shown in Figure 6, the control device 50 includes a load power calculation unit 13, a charging power calculation unit 14, an adder 15, a number of operating units calculation unit 16, a selection unit 17, and a control unit 19.

[0087] The load power calculation unit 13 calculates the AC power PL (power consumption of the load 84) consumed by the load 84 based on the AC output voltage VO and the output signal Iof of the current detector CD3. Specifically, the load power calculation unit 13 calculates the power consumption (active power) PL from the AC output voltage VO and the load current Io indicated by the output signal Iof using the following equation (1): PL = VOrms × Iorms × cosθ ... (1) Here, VOrms is the RMS voltage applied to the load 84, Iorms is the RMS current applied to the load 84, and θ represents the phase difference between the load current Io and the AC output voltage VO. cosθ means the power factor.

[0088] The charging power calculation unit 14 calculates the AC power PB (charging power of the battery 82) supplied to the battery 82 based on the battery voltage VB and the output signal IBf of the current detector CD2. Specifically, the charging power calculation unit 14 calculates the charging power PB based on the product of the battery voltage VB and the battery current IB indicated by the output signal IBf.

[0089] The adder 15 calculates the total power PB+PL, which is the sum of the power consumption PL indicated by the signal φPL and the charging power PB indicated by the signal φPB. This total power PB+PL corresponds to the AC power supplied from the AC power source 80 to the converter 10.

[0090] The operating unit calculation unit 16 receives the output signal from the adder 15 and the detection signal φPF from the power failure detector 60. When the detection signal φPF is at the L level (when the AC power supply 80 is healthy), the operating unit calculation unit 16 determines the appropriate number of operating units Z for the converter unit 12 based on the total power PL + PB (AC power supplied from the AC power supply 80 to the converter 10) indicated by the output signal from the adder 15.

[0091] Specifically, the operating unit calculation unit 16 obtains information about the converter 10 from the memory 54. The information about the converter 10 includes the number of converter units 12 included in the converter 10 (total number of units) L, the rated output C of the converter units 12, and the load characteristics of the converter units 12. The load characteristics of the converter units 12 represent the relationship between the load factor and the operating efficiency of the converter units 12. The load characteristics of the converter units 12 are stored in the memory 54 in the form of a mathematical formula or map.

[0092] As shown in Figure 6, the operating efficiency of the converter unit 12 changes depending on the load factor. In the example in Figure 6, the highest operating efficiency can be obtained when the load factor is R2 (%), but when the load factor falls below R2 (%), the operating efficiency drops sharply.

[0093] When L converter units 12 are operated in parallel, the AC input current Ii is evenly distributed among the L converter units 12, and the current distributed to each converter unit 12 is Ii / L. When L converter units 12 are operated in parallel, and the load factor of each converter unit 12 falls below R2 (%), resulting in low operating efficiency, the operation of L-Z converter units 12 can be stopped to increase the current distributed to each converter unit 12, thereby improving the operating efficiency of each converter unit 12. Therefore, by controlling the number of operating converter units 12 to achieve a high-efficiency load factor R2 (%), the overall operating efficiency of the converter 10 can be improved.

[0094] The number of operating units calculation unit 16 calculates the output power R2 × C of the converter unit 12 when the load factor is R2 (%), based on the load characteristics of the converter unit 12. Then, the number of operating units calculation unit 16 divides the total power PL + PB by the output power R2 × C of the converter unit 12. For example, if the total power PL + PB corresponds to β% of the rated output L × C of the converter 10, the quotient will be (β × L × C) / (R2 × C). The number of operating units calculation unit 16 determines the appropriate number of operating units Z to be the integer closest to this quotient β × L / R2.

[0095] On the other hand, when the detection signal φPF is at the H level (when the AC power supply 80 is shut off), the operating unit calculation unit 16 sets the appropriate operating unit Z of the converter unit 12 to 0 (corresponding to S08 in Figure 3).

[0096] The number of operating units calculation unit 16 provides a signal φZ indicating the appropriate number of operating units Z to the selection unit 17. Based on the output signal φZ of the number of operating units calculation unit 16, the selection unit 17 selects whether to put each of the L converter units 12 into an operating state or a stopped state.

[0097] In certain situations, similar to the inverter 40 and the bidirectional chopper 30, the converter 10 also has a predetermined priority order for the L converter units 12 to enter the operating state. The selection unit 17 selects whether to enter the operating state or the stopped state for each converter unit 12 based on the signal φZ and this priority order. The selection unit 17 provides the control unit 19 with signals SE1 to SEL indicating the selection result for each of the L converter units 12.

[0098] Signal SEj, which indicates the selection result of converter unit 12_j, which has priority number j, is set to H level when converter unit 12_j is selected to be in operation. When converter unit 12_j is selected to be in stopped state, signal SEj is set to L level. If the appropriate number of operating units Z is equal to the total number of units L, signals SE1 to SEL are all set to H level.

[0099] The control device 50 may include a timer 18 for measuring the time each converter unit 12 has been in operation. In this case, the selection unit 17 can select a converter unit 12 to be stopped when the measured operating time for that converter unit 12 reaches a predetermined time, and can also select the converter unit 12 with the highest priority among the stopped converter units 12 to be in operation. In this way, the converter units 12 that are put into operation are rotated, so the operating time of the L converter units 12 can be equalized. As a result, the occurrence of failure in each converter unit 12 can be delayed.

[0100] The control unit 19 controls a plurality of switches 11 and a plurality of converter units 12 based on the output signals SE1 to SEL of the selection unit 17, the output signal Iif of the current detector CD1, the battery voltage VB, the DC voltage VD, and the detection signal φPF.

[0101] Specifically, when the signal SEj is at an L level, the control unit 19 stops the operation of the corresponding converter unit 12_k and turns off the corresponding switch 11_j.

[0102] On the other hand, if the signal SEj is at the H level, the control unit 19 operates the corresponding converter unit 12_j and turns on the corresponding switch 11_j. The control unit 19 controls the converter unit 12_j so that the DC voltage VD of the DC line 20 becomes the reference voltage VDR.

[0103] In the event of a power outage to the AC power supply 80, all L-unit converter units 12 are selected to be in a stopped state, and the control unit 19 stops the operation of the converter 10.

[0104] Next, an example of the operation of the uninterruptible power supply 100 will be described with reference to Figures 7 to 9. In each of Figures 7 to 9, the operating power conversion unit of the converter 10, bidirectional chopper 30, and inverter 40 is represented by a solid line, and the stopped power conversion unit is represented by a dashed line. Also, in each figure, the arrows represent the flow of power.

[0105] Figure 7 shows an example of the operation of the uninterruptible power supply 100 when the AC power supply 80 is functioning properly. In Figure 7, the load 84 is an electrical device with a low power factor cosθ. The battery 82 is fully charged.

[0106] In this case, the power consumption PL (PL = VOrms × Iorms × cosθ) of the load 84 becomes smaller than the AC power output by the inverter 40 (apparent power = VOrms × Iorms). Also, since the battery 82 is fully charged, the charging power PB required to maintain the battery voltage VB at the reference voltage VBR also becomes smaller. In other words, the AC power supplied from the AC power source 80 to the converter 10 (total power PB + PL) also becomes smaller.

[0107] In this situation, the optimal number of operating units for the converter unit 12, Z (for example, Z=1), and the optimal number of operating units for the chopper unit 32, Y (for example, Y=1), can be reduced relative to the optimal number of operating units X (for example, X=3) for the inverter unit 42.

[0108] In conventional uninterruptible power supply (UPS) systems configured by connecting multiple UPS units in parallel, the appropriate number of UPS units to operate is determined based on the load current Io. Therefore, the same number of converter units and chopper units are operated as the number of inverter units determined from the load current Io. Consequently, when the load has a low power factor and the battery is fully charged, the number of operating converter units becomes excessive relative to the amount of AC power supplied from the AC power source, resulting in low overall converter efficiency. Similarly, the number of operating chopper units becomes excessive relative to the amount of battery charge, leading to low bidirectional chopper efficiency. As a result, there are concerns that the power supply efficiency of the UPS system may be reduced.

[0109] In contrast, in this embodiment, the number of inverter units 42 operating X, the number of chopper units 32 operating Y, and the number of converter units 12 operating Z can be controlled individually. Therefore, it is possible to operate an appropriate number of inverter units 42 for the magnitude of the load current Io, an appropriate number of converter units 12 for the magnitude of the AC power supplied from the AC power source 80, and the number of chopper units 32 necessary to charge the battery 82. Consequently, as shown in Figure 7, when the load 84 has a low power factor and the battery 82 is fully charged, the inverter 40, the bidirectional chopper 30, and the converter 10 can each be operated with high operating efficiency. As a result, it is possible to improve the power supply efficiency of the uninterruptible power supply 100.

[0110] Figure 8 shows an example of the operation of the uninterruptible power supply 100 during a power outage of the AC power supply 80. As shown in Figure 8, when a power outage of the AC power supply 80 occurs, the control device 50 sets the appropriate number of operating converter units 12 Z to 0 and stops the operation of the converter 10. In addition, the control device 50 operates all chopper units 32 included in the bidirectional chopper 30 and all inverter units 42 included in the inverter 40.

[0111] In this way, even if the load 84 fluctuates during a power outage of the AC power supply 80, AC power can be supplied stably to the load 84. Therefore, the reliability of the power supply to the load 84 can be maintained.

[0112] Figure 9 shows an example of the operation of the uninterruptible power supply 100 when the AC power supply 80 is restored. In Figure 9, the load 84 is a light load. The battery 82 has a reduced charge capacity because it supplied power to the load 84 during the power outage.

[0113] In this case, the AC power output by the inverter 40 decreases, and the power consumption PL of the load 84 also decreases. On the other hand, because the amount of charge stored in the battery 82 is small, the charging power PB required to maintain the battery voltage VB at the reference voltage VBR increases. Therefore, the AC power supplied from the AC power source 80 to the converter 10 (total power PB + PL) also increases.

[0114] In this situation, the appropriate number of inverter units 42 in operation, Z (for example, Z=2), and the appropriate number of chopper units 32 in operation, Y (for example, Y=3), can be increased relative to the appropriate number of inverter units 42 in operation, X (for example, X=1). As a result, when the AC power supply 80 is restored, the battery 82 can be quickly charged and its stored energy restored while operating an appropriate number of inverter units 42 for the magnitude of the load current Io.

[0115] [Embodiment 2] Figure 10 is a circuit block diagram showing the configuration of an uninterruptible power supply according to Embodiment 2. As shown in Figure 10, the uninterruptible power supply 110 according to Embodiment 2 differs from the uninterruptible power supply 100 shown in Figure 1 in that it does not have a bidirectional chopper 30.

[0116] In the uninterruptible power supply 110, the control device 50 is configured to include the control configuration shown in Figures 4 and 6. Specifically, when the AC power supply 80 is healthy, the control device 50 determines the appropriate number of inverter units 42 to operate X based on the output current of the inverter 40 (i.e., the load current Io). The control device 50 also determines the appropriate number of converter units 12 to operate Z based on the AC power supplied from the AC power supply 80 to the converter 10.

[0117] In the event of a power outage of the AC power supply 80, the control device 50 sets the appropriate number of operating converter units 12 Z to 0 and stops the operation of the converter 10. The control device 50 also sets the appropriate number of operating inverter units 42 X to the total number of units N and operates all inverter units 42 included in the inverter 40.

[0118] Therefore, the same effects as in Embodiment 1 can be obtained in Embodiment 2 as well.

[0119] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

[0120] 10 Converter, 11, 31, 41, S1-S3 Switch, 12 Converter unit, 13 Load power calculation unit, 14 Charging power calculation unit, 15 Adder, 16, 35, 44 Number of operating units calculation unit, 17, 36, 45 Selection unit, 18, 37, 48 Timer, 19, 38, 46 Control unit, 20 DC line, 22, C1, C2 Capacitors, 30 Bidirectional chopper, 32 Chopper unit, 33 Subtractor, 34 Charging current calculation unit, 40 Inverter, 42 Inverter unit, 50 Control device, 52 CPU, 54 Memory, 56 I / O circuit, 60 Power failure detector, 80 AC power supply, 82 Battery, 84 Load, 100, 110 Uninterruptible power supply, CD1-CD3 Current detector, T1 AC input terminal, T2 DC terminal, T3 AC output terminal, L1, L2 reactors, F1, F2 AC filters.

Claims

1. An uninterruptible power supply comprising: a converter that converts AC power supplied from an 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 a load; and a control device that controls the converter and the inverter, wherein a power storage device for storing the DC power of the DC line is connected to the DC line; the converter includes a plurality of converter units connected in parallel between the AC power source and the DC line; the inverter includes a plurality of inverter units connected in parallel between the DC line and the load; and the control device, when the AC power source is healthy, determines the appropriate number of inverter units to operate based on the output current of the inverter, determines the appropriate number of converter units to operate based on the AC power supplied from the AC power source to the converter, and operates the determined appropriate number of inverter units and converter units.

2. The uninterruptible power supply according to claim 1, wherein the control device calculates the total power of the power consumption of the load and the charging power supplied to the energy storage device from the DC line, and calculates the appropriate number of converter units to operate from the total power by referring to the relationship between the load factor and the operating efficiency of the converter unit.

3. The uninterruptible power supply according to claim 1 or 2, wherein the control device calculates the appropriate number of inverter units to operate from the output current of the inverter, by referring to the relationship between the load factor and the operating efficiency of the inverter unit.

4. The uninterruptible power supply according to claim 1, wherein the control device stops the operation of the converter and operates all of the plurality of inverter units in the event of a power outage of the AC power supply.

5. The uninterruptible power supply according to claim 1, wherein the control device has a timer for measuring the time each of the inverter units is in operation, and rotates the inverter units to be in operation based on the time measured by the timer.

6. The uninterruptible power supply according to claim 1, wherein the control device has a timer for measuring the time each of the converter units is in operation, and rotates the converter units to be in operation based on the time measured by the timer.

7. The uninterruptible power supply according to claim 1, further comprising a bidirectional chopper for sending and receiving DC power between the DC line and the energy storage device, wherein the bidirectional chopper is configured to charge the energy storage device with DC power from the DC line when the AC power supply is healthy, the bidirectional chopper includes a plurality of chopper units connected in parallel between the DC line and the energy storage device, and the control device determines the appropriate number of chopper units to operate based on the charging current required to charge the energy storage device when the AC power supply is healthy.

8. The uninterruptible power supply according to claim 7, wherein the control device determines the appropriate number of chopper units to operate based on the charging current and the rated current of the chopper unit.

9. The uninterruptible power supply according to claim 7 or 8, wherein the bidirectional chopper is configured to supply DC power from the energy storage device to the DC line in the event of a power outage of the AC power supply, and the control device operates all of the plurality of chopper units in the event of a power outage of the AC power supply.

10. The uninterruptible power supply according to claim 7, wherein the control device has a timer for measuring the time each of the chopper units is in operation, and rotates the chopper units to be in operation based on the time measured by the timer.

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