Uninterruptible power supply device

Abstract

Of the multiple power conversion modules (P), a number of power conversion modules (P) necessary to supply power to the load are put into an operating state, and the remaining power conversion modules (P) are put into a standby state. The power conversion modules (P) put into an operating state operate a converter (1), a bidirectional chopper (5), and an inverter (6) to supply power to the load. The power conversion module (P) put into a standby state stops the operation of the bidirectional chopper (5) and the inverter (6) and stands by without supplying power to the load, while operating the converter (1). If there are two or more power conversion modules (P) put into a standby state, any one of the two or more power conversion modules (P) put into a standby state further stops the operation of the converter (1) and performs a diagnostic operation to diagnose deterioration of the capacitor (3) based on the change over time in the DC voltage of the DC line (2).

Description

[Technical Field]

[0001] The present disclosure relates to an uninterruptible power supply, and more particularly to an uninterruptible power supply including a plurality of power conversion modules connected in parallel to a load. [Background technology]

[0002] For example, Japanese Patent Application Laid-Open Publication No. 2018-98960 (Patent Document 1) discloses an uninterruptible power supply system including a plurality of uninterruptible power supplies connected in parallel to a load. In this system, a necessary number of uninterruptible power supplies for supplying power to the load are selected from the plurality of uninterruptible power supplies. The selected uninterruptible power supplies are put into an operating state in which they supply power to the load, and unselected uninterruptible power supplies are put into a standby state in which they do not supply power to the load. In addition, the selected uninterruptible power supply is changed so that the operating times of the plurality of uninterruptible power supplies are equalized. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-98960 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above system, each uninterruptible power supply includes a DC line for transmitting DC power, a converter for converting AC power supplied from an AC power source into DC power and supplying it to the DC line, and an inverter for converting the DC power received from the DC line into AC power and supplying it to a load. A capacitor for smoothing the DC voltage of the DC line is connected to the DC line. The capacitor deteriorates over time, resulting in a decrease in capacitance. If a capacitor fails while the uninterruptible power supply is operating, the DC voltage of the DC line cannot be stabilized, raising concerns about a decrease in the reliability of power supply to the load.

[0005] Therefore, the main object of the present disclosure is to prevent failure of a capacitor connected to the DC line of a power conversion module in an operating state in an uninterruptible power supply having multiple power conversion modules connected in parallel to a load. [Means for solving the problem]

[0006] An uninterruptible power supply according to the present disclosure includes a plurality of power conversion modules connected in parallel to a load, and a control circuit. The control circuit is configured to operate a number of the plurality of power conversion modules required to supply power to the load, and to operate the remaining power conversion modules in a standby state. The power conversion modules include a DC line for transmitting DC power, a capacitor connected to the DC line, a discharge resistor connected in parallel to the capacitor, a converter for converting AC power supplied from an AC power source into DC power and supplying the DC power to the DC line, a bidirectional chopper for exchanging DC power between the DC line and a power storage device, and an inverter for converting DC power received from the DC line into AC power and supplying the AC power to the load.

[0007] The power conversion module in operation operates the converter, bidirectional chopper, and inverter to supply power to the load, while the power conversion module in standby mode stops operation of the bidirectional chopper and inverter and waits without supplying power to the load, while operating the converter.

[0008] If there are two or more power conversion modules in standby mode, any one of the two or more power conversion modules in standby mode further stops operation of the converter and performs a diagnostic operation to diagnose capacitor deterioration based on the change over time in the DC voltage of the DC line. [Effects of the Invention]

[0009] According to the present disclosure, in an uninterruptible power supply having a plurality of power conversion modules connected in parallel to a load, failure of a capacitor connected to a DC line of a power conversion module in an operating state can be prevented in advance. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a circuit block diagram showing an example of the configuration of an uninterruptible power supply according to an embodiment of the present invention; [Figure 2] FIG. 2 is a circuit block diagram showing the configuration of a power module. [Figure 3] FIG. 2 is a diagram illustrating the operation of the power module. [Figure 4] FIG. 10 is a diagram illustrating a standby operation of the power module. [Figure 5] FIG. 10 is a diagram illustrating a diagnostic operation of the power module. [Figure 6] FIG. 10 is a diagram showing an example of a change over time in a DC voltage of a DC line. [Figure 7] FIG. 2 is a block diagram showing a portion of a control circuit of the power module. [Figure 8] 10 is a time chart illustrating the operation of a selection unit; [Figure 9] 4 is a time chart illustrating the operation of a command unit. [Figure 10] FIG. 10 is a block diagram showing another part of the control circuit of the power module. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] Figure 1 is a circuit block diagram showing an example configuration of an uninterruptible power supply according to an embodiment of the present disclosure. As shown in Figure 1, the uninterruptible power supply includes a bypass module BP1, N power modules P1 to P6, and a communication cable 10. N is an integer equal to or greater than 3, and Figure 1 shows the case where N=6.

[0013] The bypass module BP1 includes an input terminal T11, an output terminal T12, and a switch (not shown) connected between the input terminal T11 and the output terminal T12.

[0014] Each of the power modules P1 to P6 is a "power conversion module" including a converter and an inverter. In the following description, the power modules P1 to P6 may be collectively referred to as a "power module P." The power module P includes an input terminal T1, a DC terminal T2, an output terminal T3, and a communication terminal T4.

[0015] An input terminal T1 of each power module P is connected to a commercial AC power supply 40. The commercial AC power supply 40 supplies AC power of a commercial frequency to the uninterruptible power supply.

[0016] The DC terminal T2 of each power module P is connected to a battery B. The battery B stores DC power. A capacitor may be connected instead of the battery B. The output terminal T3 of each power module P is connected to a load 41. The load 41 is driven by AC power supplied from the uninterruptible power supply.

[0017] The six power modules P1 to P6 are connected in parallel to a load 41. The communication terminal T4 of each power module P is connected to the communication terminal T4 of each of the other power modules P via a communication cable 10. Each power module P exchanges various information with each of the other power modules P via the communication cable 10.

[0018] 2 is a circuit block diagram showing the configuration of the power module P. As shown in Fig. 2, the power module P includes switches SW1 to SW3, capacitors C1, C3, and C2, reactors L1 and L2, a converter 1, a DC line 2, a discharge resistor 4, a bidirectional chopper 5, an inverter 6, current detectors CD1 and CD2, and a control circuit 7.

[0019] Switch SW1 and reactor L1 are connected in series between input terminal T1 and the AC node of converter 1. Capacitor C1 is connected to node N1 between switch SW1 and reactor L1. Switch SW1 is turned on during operation, on during standby, and off during diagnostic operation. The operation, standby, and diagnostic operations will be explained in detail later. The instantaneous value of the AC input voltage VI appearing at input terminal T1 is detected by control circuit 7. Whether a power outage has occurred is determined based on the instantaneous value of AC input voltage VI.

[0020] Capacitor C1 and reactor L1 constitute AC filter F1. AC filter F1 is a low-pass filter that passes commercial frequency AC power from commercial AC power supply 40 to converter 1 and prevents switching frequency signals generated in converter 1 from passing to commercial AC power supply 40. Current detector CD1 detects AC input current Ii flowing from commercial AC power supply 40 to power module P, and provides signal Iif indicating the detected value to control circuit 7.

[0021] The converter 1 is controlled by a control circuit 7. During operation, when the commercial AC power supply 40 is healthy, the converter 1 converts AC power supplied from the commercial AC power supply 40 into DC power and outputs it to the DC line 2. During operation, when the commercial AC power supply 40 experiences a power outage, the operation of the converter 1 is stopped. During standby operation, the converter 1 converts AC power supplied from the commercial AC power supply 40 into DC power and outputs it to the DC line 2. During diagnostic operation, the operation of the converter 1 is stopped.

[0022] Capacitor 3 is connected to DC line 2 and smooths the DC voltage VDC on DC line 2. The instantaneous value of DC voltage VDC appearing on DC line 2 is detected by control circuit 7. Discharge resistor 4 is connected in parallel to capacitor 3. Discharge resistor 4 is provided to reduce DC voltage VDC in the event of a failure in power module P, thereby protecting users of the uninterruptible power supply. The resistance value of discharge resistor 4 is set to a value that enables the voltage VDC across capacitor 3 to quickly reduce to 0 V when converter 1 operation is stopped.

[0023] The DC line 2 is connected to a high-voltage side node of the bidirectional chopper 5, and the low-voltage side node of the bidirectional chopper 5 is connected to the DC terminal T2 via the switch SW2. The switch SW2 is turned on during operation, turned off during standby operation, and turned off during diagnostic operation. The instantaneous value of the voltage VB between the terminals of the battery B (the voltage at the DC terminal T2) is detected by the control circuit 7.

[0024] The bidirectional chopper 5 is controlled by a control circuit 7. During operation, when the commercial AC power supply 40 is normal, the bidirectional chopper 5 stores the DC power supplied from the converter 1 via the DC line 2 in the battery B. During operation, when the commercial AC power supply 40 experiences a power outage, the bidirectional chopper 5 supplies the DC power of the battery B to the inverter 6 via the DC line 2. During standby operation and diagnostic operation, the operation of the bidirectional chopper 5 is stopped.

[0025] The inverter 6 is controlled by a control circuit 7. During operation, when the commercial AC power supply 40 is normal, the inverter 6 converts DC power supplied from the converter 1 via the DC line 2 into AC power. During operation, when the commercial AC power supply 40 is in a power outage, the inverter 6 converts DC power supplied from the battery B via the bidirectional chopper 5 into AC power. During standby operation and diagnostic operation, the operation of the inverter 6 is stopped.

[0026] An AC node of inverter 6 is connected to a first terminal of reactor L2, and a second terminal (node ​​N2) of reactor L2 is connected to output terminal T3 via switch SW3. Capacitor C2 is connected to node N2. Reactor L2 and capacitor C2 constitute AC filter F2.

[0027] The AC filter F2 is a low-pass filter that passes the commercial frequency AC power generated by the inverter 6 to the output terminal T3 and prevents the switching frequency signal generated by the inverter 6 from passing to the output terminal T3.

[0028] The switch SW3 is controlled by the control circuit 7 and is turned on during operation, on during standby, and off during diagnostic operation. The instantaneous value of the AC output voltage VO appearing at the node N2 is detected by the control circuit 7. The current detector CD2 detects the instantaneous value of the AC output current Io flowing from the node N2 through the switch SW3 to the output terminal T3, and provides the control circuit 7 with a signal Iof indicating the detected value.

[0029] The control circuit 7 controls the entire corresponding power module P based on the AC input voltage VI, the DC voltage VDC, the terminal voltage VB of the battery B, the AC output voltage VO, the AC input current Ii, and the AC output current Io.

[0030] The control circuit 7 is also connected to the control circuits 7 of the other power modules P by communication cables 10, and exchanges various information with the control circuits 7 of the other power modules P. Based on this information, the control circuit 7 executes operation, standby operation, or diagnostic operation.

[0031] Specifically, based on this information, M power modules P required to operate the load 41 are selected from the six power modules P1 to P6, where M is an integer equal to or less than N. Furthermore, the selected power modules P are changed at predetermined intervals so that the operating times of the six power modules P1 to P6 are equalized.

[0032] The selected power module P performs an operation to supply power to the load 41. FIG. 3 is a diagram illustrating the operation of the power module P. In FIG. 3, the flow of power when the commercial AC power supply 40 is normal during operation is indicated by solid arrows. The switches SW1 to SW3 are turned on. In this case, the selected power module P temporarily converts AC power from the commercial AC power supply 40 into DC power, converts the DC power into AC power, supplies it to the load 41, and stores it in the battery B.

[0033] Although not shown in the drawings, if the commercial AC power supply 40 experiences a power outage during operation, the selected power module P converts the DC power of the battery B into AC power and supplies it to the load 41. Therefore, the operation of the load 41 can be continued while DC power is stored in the battery B.

[0034] The power module P that is not selected to operate the load 41 executes a standby operation in which it waits without supplying current to the load 41. FIG. 4 is a diagram illustrating the standby operation of the power module P. In FIG. 4, the flow of power during the standby operation is indicated by solid arrows. During the standby operation, the switches SW1 and SW2 are turned on, and the switch SW3 is turned off.

[0035] During standby operation, when the commercial AC power supply 40 is healthy, the converter 1 converts AC power supplied from the commercial AC power supply 40 into DC power and outputs it to the DC line 2. The control circuit 7 controls the converter 1 so that the DC voltage VDC of the DC line 2 becomes equal to the reference DC voltage VDCR.

[0036] In contrast to Figure 4, when the converter 1 is stopped during standby, the DC voltage VDC drops due to the discharge resistor 4 connected in parallel to the capacitor 3. In this case, due to an increase in the number of power modules P required to operate the load 41, when the power modules P are transitioned from standby to operating, the DC voltage VDC drops, which can cause a problem in that the waveform of the AC output voltage VO of the inverter 6 becomes distorted. To prevent the DC voltage VDC from dropping, the control circuit 7 operates the converter 1 during standby.

[0037] On the other hand, the control circuit 7 fixes the switching elements constituting the bidirectional chopper 5 and the inverter 6 to the off state by supplying a gate block signal to the bidirectional chopper 5 and the inverter 6. The operation of the bidirectional chopper 5 and the inverter 6 is stopped.

[0038] During standby operation, if the power module P is selected as a diagnostic target, it executes a diagnostic operation to diagnose deterioration of the capacitor 3 connected to the DC line 2. Fig. 5 is a diagram illustrating the diagnostic operation of the power module P. In Fig. 5, the flow of power during the diagnostic operation is indicated by solid arrows.

[0039] During the diagnostic operation, the switches SW1, SW2, and SW3 are turned off. The control circuit 7 fixes the switching elements constituting the converter 1, bidirectional chopper 5, and inverter 6 in the off state by providing gate block signals to the converter 1, bidirectional chopper 5, and inverter 6. The operation of the converter 1, bidirectional chopper 5, and inverter 6 is stopped.

[0040] When the operation of the converter 1 is stopped, the charge stored in the capacitor 3 is discharged by the discharge resistor 4, as shown in FIG. 5. This causes the DC voltage VDC of the DC line 2 to drop. The behavior (change over time) of the DC voltage VDC at this time differs depending on the capacitance value of the capacitor 3. During the diagnostic operation, the power module P acquires the change over time of the DC voltage VDC and estimates the capacitance value of the capacitor 3 based on the acquired change over time of the DC voltage VDC.

[0041] 6 is a diagram showing an example of a change over time in the DC voltage VDC of the DC line 2. The horizontal axis of FIG. 6 represents time, and the vertical axis represents the DC voltage VDC. The DC voltage VDC has a voltage value of 1.0E when the converter 1 is operating. E is the rated voltage of the capacitor 3.

[0042] Before time 0, the power module P is in standby operation. As shown in Fig. 4, when the commercial AC power supply 40 is operating normally, the converter 1 converts AC power supplied from the commercial AC power supply 40 into DC power and supplies it to the DC line 2. The DC voltage VDC is maintained at a constant voltage (1.0E).

[0043] At time 0, the power module P starts a diagnostic operation. As shown in FIG. 5, during the diagnostic operation, the power module P stops the operation of the converter 1. Therefore, at time 0, the discharge of the capacitor 3 starts, and the DC voltage VDC begins to decrease. At this time, the DC voltage VDC decreases according to a time constant determined by the product of the capacitance value of the capacitor 3 and the resistance value of the discharge resistor 4. Specifically, if the capacitance value of the capacitor 3 is C and the resistance value of the discharge resistor 4 is R, VDC(t) at time t is given by the following equation (1). Time t corresponds to the elapsed time since the discharge of the capacitor 3 started. VDC(t)=E×exp(-t / RC) (1) At time t1, the DC voltage VDC drops to 80% of the rated voltage E of the capacitor 3. VDC(t1) at time t1 is 0.8E, and equation (2) holds. 0.8E=E×exp(-t1 / RC) (2) Equation (2) can be transformed into the following equation (3). t1=-RC×ln(0.8) (3) At time t2, which is later than time t1, the DC voltage VDC drops to 20% of the rated voltage E of the capacitor 3. VDC(t2) at time t2 is 0.2E, and equation (4) holds. 0.2E=E×exp(-t2 / RC) (4) Equation (4) can be transformed into the following equation (5). t2=-RC×ln(0.2) (5) From equations (3) and (5), the following equation (6) is obtained. t2-t1=-RC×(ln(0.2)-ln(0.8))···(6) From equation (6), the capacitance C of the capacitor 3 can be expressed as in the following equation (7). C=-(t2-t1) / (R×(ln(0.2)-ln(0.8)))...(7) Because the resistance value R of the discharge resistor 4 is a set value (known), the capacitance value C of the capacitor 3 can be estimated from the change over time in the DC voltage VDC according to equation (7). Specifically, the time t1 when the DC voltage VDC drops to 80% of the rated voltage E of the capacitor 3 and the time t2 when the DC voltage VDC drops to 20% of the rated voltage E of the capacitor 3 are determined, and the time difference between time t1 and time t2 (t2 - t1) is substituted into equation (7), thereby calculating the capacitance value C of the capacitor 3.

[0044] In the example of FIG. 6, a configuration has been described in which the capacitance value C of the capacitor 3 is estimated using the time t1 at which the DC voltage VDC drops to 80% of the rated voltage E of the capacitor 3 and the time t2 at which the DC voltage VDC drops to 20% of the rated voltage E of the capacitor 3. However, the times t1 and t2 used to estimate the capacitance value C are not limited to the times at which the DC voltage VDC drops to 80% and 20%, respectively, of the rated voltage E of the capacitor 3.

[0045] If it is determined that the estimated capacitance value C of the capacitor 3 is below a predetermined allowable value, the power module P notifies the user of the uninterruptible power supply of this fact. The user of the uninterruptible power supply replaces the capacitor 3 of the power module P with a new capacitor while driving the load 41 with the M power modules P.

[0046] In this embodiment, M selected power modules P out of N power modules P are put into operation, and (NM) unselected power modules P are put into standby. The above-described diagnostic operation is executed in any one power module P out of the (NM) power modules P when NM≧2, that is, when there are two or more power modules P put into standby.

[0047] This is because, when NM=1, that is, when there is one power module P in a standby state, if a diagnostic operation is performed on this one power module P, the DC voltage VDC of the DC line 2 will drop, and as the number M of power modules P required to operate the load 41 increases, a problem may occur in which the waveform of the AC output voltage VO of the inverter 6 will be distorted when the power module P is transitioned from the standby state to the operating state.

[0048] Furthermore, when NM≧2, that is, when there are two or more power modules P in a standby state, for the same reason, the diagnostic operation is not performed on all of the standby power modules P, but on one of the power modules P. When the number M of power modules P required to operate the load 41 increases, the power modules P other than the ones to be diagnosed are preferentially transitioned from the standby state to the operating state among the two or more standby power modules P, thereby making it possible to avoid affecting the operation of the load 41.

[0049] This allows the deterioration of the capacitor 3 to be diagnosed in the power module P that is in a standby state without affecting the operation of the load 41. Furthermore, by replacing the capacitor 3 that is diagnosed as being deteriorated with a new capacitor before the power module P is put into operation, it is possible to prevent the power module P in operation from failing and causing the operation of the load 41 to be stopped.

[0050] Next, the configuration of the control circuit 7 of the power module P will be described in detail. Fig. 7 is a block diagram showing a portion of the control circuit 7 of the power module P1. As shown in Fig. 7, the control circuit 7 includes a communication unit 21, a signal generation unit 22, a load current calculation unit 23, an appropriate operating unit number calculation unit 24, a shared current calculation unit 25, a timer 26, a selection unit 27, and a command unit 29. The control circuits 7 of the power modules P2 to P6 have the same configuration as the control circuit 7 of the power module P1.

[0051] The communication unit 21 exchanges various signals between the power module P1 and each of the other power modules P2 to P6 via the communication terminal T4 and the communication cable 10. The signal generation unit 22 receives fault detection signals φFp, φFc from the control unit 32 (described later) and an output signal Iof of the current detector CD2.

[0052] The fault detection signal φFp is a signal that is set to the inactive level "L" when the power module P1 is operating normally during operation, and is set to the active level "H" when it is determined that the power module P1 has failed.

[0053] The fault detection signal φFc is a signal that is set to the inactive level "L" if the capacitance value C of the capacitor 3 is diagnosed as exceeding the allowable value during diagnostic operation, and is set to the active level "H" if the capacitance value C of the capacitor 3 is diagnosed as being below the allowable value.

[0054] When the fault detection signals φFp and φFc are both at "L" level, the signal generating unit 22 generates signals D1 and φIo1. The signal D1 is a signal indicating that the power module P1 is included in an uninterruptible power supply. The signal φIo1 is a signal indicating the AC output current Io of the power module P1. The signals D1 and φIo1 are transmitted by the communication unit 21 to the control circuits 7 of the other power modules P2 to P6.

[0055] When at least one of the fault detection signals φFp, φFc is at the “H” level, the signal generating unit 22 does not generate the signals D1, φIo1. In this case, the power module P1 is not included in the uninterruptible power supply, and is not selected as the power module P that supplies power to the load 41.

[0056] The load current calculation unit 23 receives the output signal φIo1 from the signal generation unit 22 and signals φIo2 to φIo6 from the control circuits 7 of the other power modules P2 to P6 received by the communication unit 21. The received signals φIo1 to φIo6 indicate the AC output currents Io of the power modules P1 to P6, respectively. The load current calculation unit 23 adds up the AC output currents Io of the power modules P1 to P6 indicated by the signals φIo1 to φIo6 to determine the load current IL, and outputs a signal φIL indicating the load current IL.

[0057] The optimum number of operating units calculation unit 24 determines the optimum number M of operating power modules P required to supply the load current IL indicated by the signal φIL, and outputs a signal φM indicating the number M. The optimum number of operating units calculation unit 24 determines the optimum number M of operating units so as to maximize the efficiency of the uninterruptible power supply.

[0058] The shared current calculation unit 25 divides the load current IL indicated by the output signal φIL of the load current calculation unit 23 by the appropriate number of operating units M indicated by the output signal φM of the appropriate number of operating units calculation unit 24 to obtain the shared current Is of the power module P1 (=IL / M), and outputs a signal φIs indicating the shared current Is.

[0059] The timer 26 is connected to the timers 26 of the other power modules P2 to P6 via the communication unit 21, and operates in synchronization with the timers 26 of the power modules P2 to P6. The timer 26 raises the signal φ26 to the “H” level for a predetermined time each time a predetermined time has elapsed.

[0060] The selection unit 27 receives the signal D1 generated by the signal generation unit 22, the signals D2 to D6 from the control circuits 7 of the power modules P2 to P6 received by the communication unit 21, the output signal φM of the optimum number of operating units calculation unit 24, and the output signal φ26 of the timer 26, and outputs signals SE1 to SE6.

[0061] Signal D1 is a signal generated by signal generating unit 22 of power module P1. Signals D2 to D6 are signals generated by signal generating units 22 of power modules P2 to P6, respectively, and received by communication unit 21 of power module P1. Signals D1 to D6 indicate that the uninterruptible power supply includes six power modules P1 to P6 (N=6).

[0062] For example, if the power module P6 fails and the signal D6 is not received, the selector 27 outputs the signals SE1 to SE5 but does not output the signal SE6.

[0063] The appropriate number of operating units M indicated by the signal φM indicates the number of power modules P required to supply power to the load 41. M is, for example, 3. The signals SE1 to SE6 correspond to the power modules P1 to P6, respectively. When the signals SE1 to SE6 are set to the "H" level, which is the selection level, the power modules P1 to P6 are selected, respectively. When the signals SE1 to SE6 are set to the "L" level, which is the non-selection level, the power modules P1 to P6 are not selected, respectively.

[0064] The selection unit 27 sets the signals (for example, SE1 to SE3) of the number M (for example, 3) indicated by the signal φM among the signals SE1 to SE6 to the "H" level of the selection level, and sets the remaining signals (in this case, SE4 to SE6) to the "L" level of the non-selection level.

[0065] In this specification, the signals SE1 to SE6 may be collectively referred to as the signal SE. When the signal SE is set to the "H" level of the selection level, the power module P corresponding to the signal SE will execute the operation (Figure 3).

[0066] The selection unit 27 changes the signal SE to be at the selection level in response to the output signal φ26 of the timer 26 rising to the "H" level so that the operation times of the power modules P1 to P6 are equal.

[0067] Figure 8 is a time chart illustrating the operation of the selection unit 27. In Figure 8, (A) shows the waveform of the signal φ26, and (B) to (G) show the waveforms of the signals SE1 to SE6. The signal φ26 rises from the "L" level to the "H" level for a certain time Tb every time a predetermined time Ta elapses. Tb < Ta. In Figure 8, at each of the times t0 to t10, the signal φ26 is raised to the "H" level for a certain time Tb.

[0068] At time t0, in response to the rising edge of the signal φ26, the signals SE1 to SE3 are set to the "H" level, and the signals SE4 to SE6 are set to the "L" level. Next, at time t1, in response to the rising edge of the signal φ26, the signals SE2 to SE4 are set to the "H" level, and the signals SE5, SE6, SE1 are set to the "L" level. Next, at time t2, in response to the rising edge of the signal φ26, the signals SE3 to SE5 are set to the "H" level, and the signals SE6, SE1, SE2 are set to the "L" level.

[0069] Similarly, each time signal φ26 is set to "H" level, signals SE1 to SE6 are set to "L" level one by one in sequence. Therefore, the time that signals SE1 to SE6 are set to "H" level, which is the selection level, is equalized. Therefore, the operation time of power modules P1 to P6 is equalized.

[0070] The command unit 29 receives the output signal D1 from the signal generating unit 22 and the output signals SE1 to SE6 from the selecting unit 27, and outputs an operation command signal CMD1, a standby command signal CMD2, and a diagnosis command signal CMD3.

[0071] When the signal SE1 corresponding to the power module P1 indicated by the signal D1 is at the "H" level, the command unit 29 sets the operation command signal CMD1 to the "H" level, which is the activation level, to cause the power module P1 to perform the operation (Figure 3).

[0072] Furthermore, when the signal SE1 is at the "L" level, the command unit 29 sets the standby command signal CMD2 to the "H" level, which is the activation level, to cause the power module P1 to perform the standby operation (FIG. 4).

[0073] Furthermore, when the total number of signals SE that are at the non-selection level "L" is two or more and the standby command signal CMD2 is raised from "L" to "H", the command unit 29 sets the diagnosis command signal CMD3 to "H" level for a predetermined time, causing the power module P1 to perform a diagnostic operation (Figure 5).

[0074] Fig. 9 is a time chart illustrating the operation of the command unit 29. In Fig. 9, (A) to (D) show the waveforms of the signals SE1, CMD1, CMD2, and CMD3, respectively.

[0075] FIG. 9 shows a case where the signal SE1 falls from the "H" level to the "L" level at time t1 shown in FIG.

[0076] While the signal SE1 is at the selection level "H", the operation command signal CMD1 is at the activation level "H" and the standby command signal CMD2 is at the inactivation level "L".

[0077] Conversely, during the period when signal SE1 is at the non-selection level "L", the operation command signal CMD1 is set to the inactivation level "L" and the standby command signal CMD2 is set to the activation level "H".

[0078] At the rising edge of the standby command signal CMD2, if the total number of signals SE that are at the non-selection level "L" is two or more (i.e., if there are two or more power modules P that are in the standby state), the diagnosis command signal CMD3 is raised from "L" to "H" for a predetermined time Td (time t11). <Taである。

[0079] 10 is a block diagram showing other parts of the control circuit 7 of the power module P1. As shown in FIG. 10, the control circuit 7 includes a power failure detector 30, a control power supply 31, a control unit 32, and a notification unit 33.

[0080] The power failure detector 30 detects whether a power failure has occurred in the commercial AC power supply 40 based on the AC input voltage VI, and outputs a signal φ30 indicating the detection result. For example, the power failure detector 30 determines that the commercial AC power supply 40 is healthy when the AC input voltage VI is higher than a lower limit, and determines that a power failure has occurred in the commercial AC power supply 40 when the AC input voltage VI falls below the lower limit. When the commercial AC power supply 40 is healthy, the power failure detection signal φ30 is set to an inactive "H" level. When a power failure has occurred in the commercial AC power supply 40, the power failure detection signal φ30 is set to an active "L" level.

[0081] The control power supply 31 generates a power supply voltage VDS for the control unit 32 based on the DC voltage VDC. The control unit 32 is driven by the power supply voltage VDS and controls the switches SW1 to SW3 of the power module P1, the converter 1, the bidirectional chopper 5, and the inverter 6 based on the power failure detection signal φ30, the AC input voltage VI, the AC output voltage VO, the DC voltage VDC, the voltage VB between the terminals of the battery B, the output signal Iof of the current detector CD2, the output signal φIs of the shared current calculation unit 25, and the output signals CMD1 to CMD3 of the command unit 29, and outputs fault detection signals φFp and φFc.

[0082] When the operation command signal CMD1 is at the "H" level, the control unit 32 executes the operation. When the power failure detection signal φ30 is at the "L" level, which is the inactivation level, during the operation (when the commercial AC power supply 40 is normal), the control unit 32 turns on the switches SW1 to SW3 and operates the converter 1, the bidirectional chopper 5, and the inverter 6.

[0083] Specifically, as shown in FIG. 3, when the switches SW1 to SW3 are turned on, AC power is supplied from the commercial AC power supply 40 to the converter 1 via the switch SW1 and the AC filter F1, the low-voltage side node of the bidirectional chopper 5 is connected to the battery B via the switch SW2, and the inverter 6 is connected to the load 41 via the AC filter F2 and the switch SW3.

[0084] Converter 1 converts AC power supplied from a commercial AC power supply 40 via switch SW1 and AC filter F1 into DC power and outputs the DC power to DC line 2. Bidirectional chopper 5 stores the DC power supplied from converter 1 via DC line 2 in battery B via switch SW2. Inverter 6 converts the DC power supplied from converter 1 via DC line 2 into AC power and supplies it to load 41 via AC filter F2 and switch SW3.

[0085] At this time, the control unit 32 controls the converter 1 so that the DC voltage VDC of the DC line 2 becomes the reference DC voltage VDCR, controls the bidirectional chopper 5 so that the terminal voltage VB of the battery B becomes the reference DC voltage VBR, and controls the inverter 6 so that the AC output current Io becomes the shared current Is.

[0086] During operation, when the power outage detection signal φ30 is set to the activated level "L," that is, when a power outage occurs in the commercial AC power supply 40, the control unit 32 turns off the switch SW1 and stops the operation of the converter 1. This electrically disconnects the commercial AC power supply 40 from the DC line 2.

[0087] The bidirectional chopper 5 supplies DC power supplied from the battery B via the switch SW2 to the inverter 6 via the DC line 2. The inverter 6 converts the DC power supplied from the battery B via the switch SW2, the bidirectional chopper 5, and the DC line 2 into AC power and supplies it to the load 41 via the AC filter F2 and the switch SW3.

[0088] At this time, the control unit 32 controls the bidirectional chopper 5 so that the DC voltage VDC of the DC line 2 becomes the reference DC voltage VDCR, and controls the inverter 6 so that the AC output current Io becomes the shared current Is.

[0089] If the DC voltage VDC, the AC output current Io, or the like becomes an abnormal value during operation, the control unit 32 determines that the power module P1 has failed, raises the failure detection signal φFp from "L" level to "H" level, turns off the switches SW1 to SW3, and stops the operation of the converter 1, the bidirectional chopper 5, and the inverter 6. When the failure detection signal φFp is set to "H" level, the notification unit 33 notifies the user of the uninterruptible power supply that the power module P1 has failed.

[0090] Furthermore, when the standby command signal CMD2 is at the "H" level, the control unit 32 executes standby operation. During standby operation, when the power failure detection signal φ30 is at the "L" level, which is the inactivation level (when the commercial AC power supply 40 is normal), the control unit 32 turns on the switch SW1 and operates the converter 1. Specifically, as shown in FIG. 4 , the converter 1 converts AC power supplied from the commercial AC power supply 40 via the switch SW1 and the AC filter F1 into DC power and outputs it to the DC line 2.

[0091] At this time, the control unit 32 controls the converter 1 so that the DC voltage VDC of the DC line 2 becomes the reference DC voltage VDCR. The control unit 32 further turns off the switch SW2 and stops the operation of the bidirectional chopper 5 and the inverter 6.

[0092] Furthermore, when the diagnosis command signal CMD3 is set to "H" level during standby operation, the control unit 32 executes a diagnostic operation. During the diagnostic operation, the control unit 32 turns off the switches SW1 to SW3 and stops the operation of the converter 1, the bidirectional chopper 5, and the inverter 6, as shown in Fig. 5. When the operation of the converter 1 is stopped, the charge stored in the capacitor 3 is discharged by the discharge resistor 4, and the DC voltage VDC of the DC line 2 drops.

[0093] At this time, the control unit 32 diagnoses the deterioration of the capacitor 3 based on the change over time in the DC voltage VDC of the DC line 2. As described in Fig. 6, the control unit 32 determines the time t1 at which the DC voltage VDC drops to 80% of the rated voltage E of the capacitor 3 and the time t2 at which the DC voltage VDC drops to 20% of the rated voltage E of the capacitor 3. Then, the control unit 32 estimates the capacitance value C of the capacitor 3 by substituting the time difference (t2 - t1) between the time t1 and the time t2 into equation (7).

[0094] The control unit 32 diagnoses whether or not the capacitor 3 is faulty based on the estimated capacitance value C of the capacitor 3, and outputs a signal φFc indicating the diagnosis result. For example, the control unit 32 diagnoses that the capacitor 3 is not faulty if the capacitance value C of the capacitor 3 is higher than the allowable value, and diagnoses that the capacitor 3 is faulty if the capacitance value C of the capacitor 3 drops below the allowable value. If the control unit 32 diagnoses that the capacitor 3 is not faulty, the fault detection signal φFc is set to the inactivation level "L"; if the control unit 32 diagnoses that the capacitor 3 is faulty, the fault detection signal φFc is set to the activation level "H." When the fault detection signal φFc is set to the "H" level, the notification unit 33 notifies the user of the uninterruptible power supply that the capacitor 3 is faulty.

[0095] When the user is notified by the notification unit 33 that the power module P1 or the capacitor 3 has failed, the user turns off the switches SW1 to SW3 corresponding to the power module P1 to electrically separate the power module P1 from the other power modules P2 to P6. After repairing or replacing the power module P1 with a new power module P, or replacing the capacitor 3 with a new capacitor, the user turns on the switches SW1 to SW3. This allows the power module P1 to be re-installed in the uninterruptible power supply.

[0096] Each of the power modules P2 to P6 has the same configuration as the power module P1, and therefore the description thereof will not be repeated.

[0097] As described above, in this embodiment, M selected power modules out of N power modules are put into operation, and (NM) unselected power modules are put into standby. When NM≧2, that is, when there are two or more power modules put into standby, a diagnostic operation is performed on a capacitor connected to a DC line in any one of the (NM) power modules.

[0098] In this way, when the number M of power modules required to operate the load increases, among the two or more power modules in standby state, the power module other than the diagnosis target is preferentially transitioned from standby state to operating state, thereby avoiding affecting the operation of the load. Therefore, it is possible to diagnose the deterioration of the capacitors in the power modules in standby state without affecting the operation of the load.

[0099] Furthermore, by replacing a capacitor diagnosed as degraded with a new capacitor before the power module is put into operation, it is possible to prevent a power module in operation from failing and causing the operation of the load to be stopped.

[0100] In the above-described embodiment, the control circuit 7 included in each power module P has a "selection unit" that selects the number of power modules P1 to P6 required to supply power to the load. However, in the present disclosure, the "selection unit" may be realized by a control circuit separate from the control circuit 7 of each power module P. The control circuit is communicatively connected to the control circuits 7 of the power modules P1 to P6 and exchanges various information with each control circuit 7. Based on that information, the control circuit selects the number of power modules P required to supply power to the load from the power modules P1 to P6. Furthermore, the control circuit changes the selected power modules P at a predetermined cycle so that the operation times of the power modules P1 to P6 are equalized.

[0101] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0102] 1 converter, 2 DC line, 3, C1, C2 capacitors, 4 discharge resistor, 5 bidirectional chopper, 6 inverter, 7 control circuit, 10 communication cable, 21 communication unit, 22 signal generation unit, 23 load current calculation unit, 24 appropriate number of operating units calculation unit, 25 shared current calculation unit, 26 timer, 27 selection unit, 29 command unit, 30 power failure detector, 31 control power supply, 32 control unit, 33 alarm unit, 40 commercial AC power supply, 41 load, B battery, BP1 bypass module, CD1, CD2 current detector, F1, F2 AC filter, L1, L2 reactor, P, P1 to P6 power module, SW1 to SW3 switch, T1, T11 input terminal, T2 DC terminal, T3, T12 output terminal.

Claims

1. a plurality of power conversion modules connected in parallel to a load; a control circuit that sets a necessary number of power conversion modules among the plurality of power conversion modules to an operating state and sets the remaining power conversion modules to a standby state, The power conversion module includes: a DC line for transmitting DC power; a capacitor connected to the DC line; a discharge resistor connected in parallel to the capacitor; a converter that converts AC power supplied from an AC power source into DC power and supplies the DC power to the DC line; a bidirectional chopper that exchanges DC power between the DC line and a power storage device; an inverter that converts DC power received from the DC line into AC power and supplies the AC power to the load; The power conversion module that has been put into the operating state operates the converter, the bidirectional chopper, and the inverter to supply power to the load; The power conversion module placed in the standby state stops operation of the bidirectional chopper and the inverter and waits without supplying power to the load, while operating the converter; an uninterruptible power supply device, wherein, if there are two or more power conversion modules in the standby state, any one of the two or more power conversion modules in the standby state further stops operation of the converter and performs a diagnostic operation to diagnose deterioration of the capacitor based on the change over time in the DC voltage of the DC line.

2. 2. The uninterruptible power supply according to claim 1, wherein during the diagnostic operation, the power conversion module in the standby state estimates a capacitance value of the capacitor based on a change over time in the DC voltage of the DC line after operation of the converter has stopped.

3. 3. The uninterruptible power supply according to claim 2, wherein each of the power conversion modules diagnoses the capacitor as faulty when the capacitance value of the capacitor falls below an allowable value and notifies the user that the capacitor has failed.

4. 4. The uninterruptible power supply according to claim 1, wherein the control circuit changes the power conversion module to be put into the operating state at a predetermined cycle so that the operating times of the plurality of power conversion modules are equalized.

5. 5. The uninterruptible power supply according to claim 4, wherein when each of the power conversion modules transitions from the operating state to the standby state, if there are two or more of the power conversion modules in the standby state, the diagnostic operation is performed.

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