Uninterruptible power source device

Abstract

In the present invention, among a plurality of power conversion modules (P), a number of the power conversion modules (P) necessary to supply power to a load are placed in an operational state, and the remaining power conversion modules (P) are placed in a standby state. The power conversion modules (P) in the operational state operate a converter (1), a bidirectional chopper (5), and an inverter (6) to supply power to the load. The power conversion modules (P) in the standby state stop operation of the bidirectional chopper (5) and the inverter (6) and stand by without supplying power to the load, but do operate the converter (1). If there are two or more power conversion modules (P) in the standby state, then one power conversion module (P) of the two or more power conversion modules (P) in the standby state stops operation of the converter (1), and executes diagnostic operation for diagnosing degradation of a capacitor (3) on the basis of change over time in the direct current voltage of a direct current line (2).

Description

Uninterruptible power supply device

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

[0002] For example, Japanese Patent Application Laid-Open No. 2018-98960 (Patent Document 1) discloses an uninterruptible power supply system including a plurality of uninterruptible power supply devices connected in parallel to a load. In this system, the number of uninterruptible power supply devices necessary to supply power to the load among the plurality of uninterruptible power supply devices is selected. The selected uninterruptible power supply device is set to an operating state of supplying power to the load, and the unselected uninterruptible power supply devices are set to a standby state of not supplying power to the load. Further, the selected uninterruptible power supply device is changed so that the operating times of the plurality of uninterruptible power supply devices become equal.

[0003] Japanese Patent Application Laid-Open No. 2018-98960

[0004] In the above system, each uninterruptible power supply device 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 DC power received from the DC line into AC power and supplying it to the load. A capacitor for smoothing the DC voltage of the DC line is connected to the DC line. The capacitor deteriorates over time and its capacitance value decreases. When a failure of the capacitor occurs in the operating uninterruptible power supply device, the DC voltage of the DC line cannot be stabilized, so there is a concern that the power supply reliability to the load may decrease.

[0005] Therefore, the main object of the present disclosure is to prevent a failure of a capacitor connected to the DC line of a power conversion module in an operating state in an uninterruptible power supply device including a plurality of power conversion modules connected in parallel to a load.

[0006] An uninterruptible power supply according to this disclosure comprises a plurality of power conversion modules connected in parallel to a load, and a control circuit. The control circuit is configured to put the number of power conversion modules necessary to supply power to the load into an operational state, and the remaining power conversion modules into 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 it to the DC line, a bidirectional chopper that exchanges DC power between the DC line and the power storage device, and an inverter that converts the DC power received from the DC line into AC power and supplies it to the load.

[0007] A power conversion module in operation runs the converter, bidirectional chopper, and inverter to supply power to the load. A power conversion module in standby mode stops the bidirectional chopper and inverter and does not supply power to the load, while operating the converter.

[0008] If there are two or more power conversion modules in standby mode, one of those two or more power conversion modules will further stop the operation of its converter and perform a diagnostic operation to diagnose capacitor degradation based on the time change of the DC voltage in the DC line.

[0009] According to this disclosure, in an uninterruptible power supply (UPS) equipped with multiple power conversion modules connected in parallel to a load, it is possible to prevent failure of capacitors connected to the DC lines of power conversion modules in operation.

[0010] This is a circuit block diagram showing an example configuration of an uninterruptible power supply according to this embodiment. This is a circuit block diagram showing the configuration of a power module. This is a diagram illustrating the operating operation of the power module. This is a diagram illustrating the standby operation of the power module. This is a diagram illustrating the diagnostic operation of the power module. This is a diagram showing an example of the time variation of the DC voltage of a DC line. This is a block diagram showing a part of the control circuit of the power module. This is a time chart illustrating the operation of the selection unit. This is a time chart illustrating the operation of the command unit. This is a block diagram showing other parts of the control circuit of the power module.

[0011] Embodiments of this disclosure will be described in detail below with reference to the drawings. In the following, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their descriptions will not be repeated in principle.

[0012] Figure 1 is a circuit block diagram showing 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 comprises a bypass module BP1, N power modules P1 to P6, and a communication cable 10. N is an integer of 3 or more, 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" that includes a converter and an inverter. In the following description, power modules P1 to P6 may be collectively referred to as "power module P". Power module P includes an input terminal T1, a DC terminal T2, an output terminal T3, and a communication terminal T4.

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

[0016] The DC terminal T2 of each power module P is connected to the 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 the load 41. The load 41 is driven by AC power supplied from an uninterruptible power supply.

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

[0018] Figure 2 is a circuit block diagram showing the configuration of power module P. As shown in Figure 2, power module P comprises switches SW1 to SW3, capacitors C1, 3, C2, reactors L1, L2, converter 1, DC line 2, discharge resistor 4, bidirectional chopper 5, inverter 6, current detectors CD1, CD2, and 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 operation, and off during diagnostic operation. Operation, standby operation, and diagnostic operation 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. Based on the instantaneous value of the AC input voltage VI, it is determined whether or not a power outage has occurred.

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

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

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

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

[0024] The bidirectional chopper 5 is controlled by the control circuit 7. When the commercial AC power supply 40 is functioning properly during operation, the bidirectional chopper 5 stores the DC power supplied from the converter 1 via the DC line 2 in the battery B. When the commercial AC power supply 40 fails during operation, the bidirectional chopper 5 supplies the DC power from the battery B to the inverter 6 via the DC line 2. During standby and diagnostic operations, the bidirectional chopper 5 is shut down.

[0025] The inverter 6 is controlled by the control circuit 7. When the commercial AC power supply 40 is functioning properly during operation, the inverter 6 converts the DC power supplied from the converter 1 via the DC line 2 into AC power. When the commercial AC power supply 40 fails during operation, the inverter 6 converts the DC power supplied from the battery B via the bidirectional chopper 5 into AC power. During standby and diagnostic operation, the inverter 6 is shut down.

[0026] The AC node of inverter 6 is connected to the first terminal of reactor L2, and the 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 allows the AC power of commercial frequency generated by the inverter 6 to pass through to the output terminal T3, while preventing the switching frequency signal generated by the inverter 6 from passing through to the output terminal T3.

[0028] 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 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 node N2 to output terminal T3 via switch SW3 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, DC voltage VDC, terminal voltage VB of battery B, AC output voltage VO, AC input current Ii, and AC output current Io.

[0030] Furthermore, the control circuit 7 is connected to the control circuits 7 of each other power module P by a communication cable 10, and exchanges various information with the control circuits 7 of each other power module P. Based on this information, the control circuit 7 performs operation, standby operation, or diagnostic operation.

[0031] Specifically, based on that information, M power modules P are selected from among the six power modules P1 to P6 to operate the load 41. M is an integer less than or equal to N. In addition, 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. Figure 3 is a diagram illustrating the operation of the power module P. In Figure 3, the power flow of the commercial AC power supply 40 when it is healthy during operation is shown by solid arrows. Switches SW1 to SW3 are turned on. In this case, the selected power module P first converts the AC power from the commercial AC power supply 40 into DC power, then converts that DC power back into AC power to supply to the load 41, and also stores it in the battery B.

[0033] Although not shown in the diagram, in the event of a power outage of the commercial AC power supply 40 during operation, the selected power module P converts the DC power from battery B into AC power and supplies it to the load 41. Therefore, the operation of load 41 can continue as long as DC power is stored in battery B.

[0034] Power modules P that were not selected to operate load 41 perform a standby operation, remaining idle without supplying current to load 41. Figure 4 illustrates the standby operation of power modules P. In Figure 4, the power flow during standby operation is shown by solid arrows. During standby operation, switches SW1 and SW2 are turned on, and switch SW3 is turned off.

[0035] When the commercial AC power supply 40 is healthy during standby operation, the converter 1 converts the 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 the reference DC voltage VDDR.

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

[0037] Meanwhile, the control circuit 7 provides gate block signals to the bidirectional chopper 5 and inverter 6, thereby fixing the switching elements constituting the bidirectional chopper 5 and inverter 6 in the off state. The operation of the bidirectional chopper 5 and inverter 6 is stopped.

[0038] During standby operation, if selected as the target for diagnosis, the power module P performs a diagnostic operation to diagnose the degradation of the capacitor 3 connected to the DC line 2. Figure 5 illustrates the diagnostic operation of the power module P. In Figure 5, the power flow during the diagnostic operation is shown by solid arrows.

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

[0040] As the operation of converter 1 is stopped, the charge stored in capacitor 3 is discharged by the discharge resistor 4, as shown in Figure 5. As a result, the DC voltage VDC of DC line 2 decreases. The behavior (time variation) of the DC voltage VDC at this time differs depending on the capacitance value of capacitor 3. During diagnostic operation, power module P acquires the time variation of the DC voltage VDC and estimates the capacitance value of capacitor 3 based on the acquired time variation of the DC voltage VDC.

[0041] Figure 6 shows an example of the time variation of the DC voltage VDC in DC line 2. In Figure 6, the horizontal axis represents time, and the vertical axis represents the DC voltage VDC. The DC voltage VDC is set to 1.0E when converter 1 is in operation. E is the rated voltage of capacitor 3.

[0042] Before time 0, the power module P is performing standby operation. As shown in Figure 4, when the commercial AC power supply 40 is functioning properly, the converter 1 converts the 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, power module P starts a diagnostic operation. As shown in Figure 5, during the diagnostic operation, power module P stops the operation of converter 1. Therefore, at time 0, the discharge of capacitor 3 begins, 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 capacitor 3 and the resistance value of discharge resistor 4. Specifically, if the capacitance value of capacitor 3 is C and the resistance value of discharge resistor 4 is R, then VDC(t) at time t is given by the following equation (1). Time t corresponds to the elapsed time since the discharge of capacitor 3 began. VDC(t) = E × exp(-t / RC) ... (1) At time t1, the DC voltage VDC decreases to 80% of the rated voltage E of 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 after time t1, the DC voltage VDC drops to 20% of the rated voltage E of 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 value C of capacitor 3 can be expressed as follows: C = -(t2 - t1) / (R × (ln(0.2) - ln(0.8))) ... (7) Since the resistance value R of the discharge resistor 4 is a set value (known), according to equation (7), the capacitance value C of capacitor 3 can be estimated from the time change of the DC voltage VDC. Specifically, the time t1 when the DC voltage VDC drops to 80% of the rated voltage E of capacitor 3 and the time t2 when the DC voltage VDC drops to 20% of the rated voltage E of capacitor 3 can be determined, and the capacitance value C of capacitor 3 can be calculated by substituting the time difference between time t1 and time t2 (t2 - t1) into equation (7).

[0044] In the example of FIG. 6, the configuration for estimating the capacitance value C of the capacitor 3 using 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 has been described. However, the times t1 and t2 used for estimating the capacitance value C are not limited to the times when the DC voltage VDC drops to 80% and 20% of the rated voltage E of the capacitor 3, respectively.

[0045] When it is diagnosed 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 device to that effect. The user of the uninterruptible power supply device replaces the capacitor 3 of the power module P with a new capacitor while driving the load 41 by M power modules P.

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

[0047] This is because when N - M = 1, that is, when there is one power module P in the standby state, if the diagnostic operation is executed in this one power module P, the DC voltage VDC of the DC line 2 drops. Therefore, when the power module P is transitioned from the standby state to the operating state in response to an increase in the number M of power modules P required to drive the load 41, a problem may occur in that the waveform of the AC output voltage VO of the inverter 6 is distorted.

[0048] Also, when N - M ≥ 2, that is, even when there are two or more power modules P in the standby state, for the same reason, the diagnostic operation is not executed for all the power modules P in the standby state, and the diagnostic operation is executed for any one of the power modules P. When the number M of power modules P required to operate the load 41 increases, among the two or more power modules P in the standby state, by preferentially transitioning the power modules P other than the diagnostic target from the standby state to the operating state, it is possible to avoid affecting the operation of the load 41.

[0049] According to this, it is possible to diagnose the deterioration of the capacitor 3 in the power module P in the standby state without affecting the operation of the load 41. Further, by replacing the capacitor 3 diagnosed as deteriorated with a new capacitor before the power module P is put into the operating state, it is possible to prevent the power module P in the operating state from failing and the operation of the load 41 from being 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 part 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 operation number calculation unit 24, a shared current calculation unit 25, a timer 26, a selection unit 27, and a command unit 29. Note that 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 the fault detection signals φFp, φFc from the control unit 32 described later and the output signal Iof of the current detector CD2.

[0052] The fault detection signal φFp is set to an inactive level "L" when the power module P1 is operating normally during operation, and to an active level "H" when the power module P1 is determined to be faulty.

[0053] The fault detection signal φFc is set to the deactivation level "L" if it is determined during the diagnostic operation that the capacitance value C of capacitor 3 exceeds the allowable value, and to the activation level "H" if it is determined that the capacitance value C of capacitor 3 falls below the allowable value.

[0054] The signal generation unit 22 generates signals D1 and φIo1 when both fault detection signals φFp and φFc are at the "L" level. Signal D1 indicates that power module P1 is included in the uninterruptible power supply. Signal φIo1 indicates the AC output current Io of power module P1. 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] If at least one of the fault detection signals φFp and φFc is at the "H" level, the signal generation unit 22 does not generate signals D1 and 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, which are received by the communication unit 21. The received signals φIo1 to φIo6 each represent the AC output current I of the power modules P1 to P6. The load current calculation unit 23 adds the AC output currents I of the power modules P1 to P6, which are represented by signals φIo1 to φIo6, to obtain the load current IL, and outputs a signal φIL that represents the load current IL.

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

[0058] The current distribution 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 current distribution Is = IL / M for the power module P1, and outputs a signal φIs indicating the current distribution Is.

[0059] Timer 26 is coupled to the timers 26 of other power modules P2 to P6 via the communication unit 21 and operates in synchronization with the timers 26 of power modules P2 to P6. Timer 26 raises the signal φ26 to the "H" level for a predetermined period of time each time a predetermined period of 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 from the appropriate number of operating units calculation unit 24, and the output signal φ26 from the timer 26, and outputs signals SE1 to SE6.

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

[0062] Furthermore, if, for example, power module P6 malfunctions and signal D6 is not received, the selection unit 27 will output signals SE1 to SE5, but will not output signal SE6.

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

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

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

[0066] The selection unit 27 changes the signal SE to be set to the selection level in accordance with the fact that the output signal φ26 of the timer 26 has been raised to the "H" level, so that the operating 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 signal φ26, and (B) to (G) show the waveforms of signals SE1 to SE6. Signal φ26 is raised from the "L" level to the "H" level by a certain amount of time Tb each time a predetermined time Ta has elapsed. Tb < Ta. In Figure 8, at each of the times t0 to t10, signal φ26 is raised to the "H" level by a certain amount of time Tb.

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

[0069] Similarly, each time signal φ26 is set to the "H" level, signals SE1 to SE6 are sequentially set to the "L" level one by one. As a result, the time that signals SE1 to SE6 are at the selected "H" level is equalized. Therefore, the operating times of power modules P1 to P6 are equalized.

[0070] The command unit 29 receives the output signal D1 from the signal generation unit 22 and the output signals SE1 to SE6 from the selection unit 27, and outputs the operation command signal CMD1, the standby command signal CMD2, and the diagnostic command signal CMD3.

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

[0072] Furthermore, if signal SE1 is at the "L" level, the command unit 29 sets the standby command signal CMD2 to the activation level "H" level, causing the power module P1 to perform a standby operation (Figure 4).

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

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

[0075] Figure 9 shows the case where signal SE1 is lowered from the "H" level to the "L" level at time t1 shown in Figure 8.

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

[0078] If, at the rising edge of the standby command signal CMD2, the total number of signals SE set to the non-selected "L" level is two or more (i.e., there are two or more power modules P in standby mode), the diagnostic command signal CMD3 is raised from the "L" level to the "H" level for a predetermined time Td (time t11). Td < Ta.

[0079] Figure 10 is a block diagram showing other parts of the control circuit 7 of the power module P1. As shown in Figure 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 outage detector 30 detects whether or not a power outage 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 outage detector 30 determines that the commercial AC power supply 40 is healthy if the AC input voltage VI is higher than the lower limit, and determines that a power outage has occurred in the commercial AC power supply 40 if the AC input voltage VI falls below the lower limit. If the commercial AC power supply 40 is healthy, the power outage detection signal φ30 is set to the deactivation level "H". If a power outage occurs in the commercial AC power supply 40, the power outage detection signal φ30 is set to the activation level "L".

[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 terminal voltage VB of the battery B, the output signal Iof of the current detector CD2, the output signal φIs of the current distribution calculation unit 25, and the output signals CMD1 to CMD3 of the command unit 29, and also outputs fault detection signals φFp and Fc.

[0082] The control unit 32 executes an operation when the operation command signal CMD1 is at the "H" level. During operation, if the power outage detection signal φ30 is at the deactivation level "L" (when the commercial AC power supply 40 is healthy), the control unit 32 turns on switches SW1 to SW3 and operates the converter 1, the bidirectional chopper 5, and the inverter 6.

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

[0084] Converter 1 converts AC power supplied from commercial AC power supply 40 via switch SW1 and AC filter F1 into DC power and outputs it to DC line 2. Bidirectional chopper 5 stores the DC power supplied from converter 1 via DC line 2 into 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 VDDR, 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] When the power outage detection signal φ30 is set to the activation level "L" during operation, 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 from the battery B via switch SW2 to the inverter 6 via DC line 2. The inverter 6 converts the DC power supplied from the battery B via switch SW2, bidirectional chopper 5, and DC line 2 into AC power and supplies it to the load 41 via AC filter F2 and 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 VDDR, and controls the inverter 6 so that the AC output current Io becomes the shared current Is.

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

[0090] Furthermore, the control unit 32 performs a standby operation when the standby command signal CMD2 is at the "H" level. During the standby operation, the control unit 32 turns on the switch SW1 and operates the converter 1 when the power outage detection signal φ30 is at the deactivation level "L" (when the commercial AC power supply 40 is healthy). Specifically, as shown in Figure 4, the converter 1 converts the 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 VDDR. The control unit 32 further turns off the switch SW2 and stops the operation of the bidirectional chopper 5 and inverter 6.

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

[0093] At this time, the control unit 32 diagnoses the deterioration of the capacitor 3 based on the time change of the DC voltage VDC of the DC line 2. As explained in Figure 6, the control unit 32 determines 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. Then, the control unit 32 estimates the capacitance value C of the capacitor 3 by substituting the time difference (t2-t1) between time t1 and time t2 into equation (7).

[0094] The control unit 32 diagnoses whether capacitor 3 is faulty based on the estimated capacitance value C of capacitor 3 and outputs a signal φFc indicating the diagnosis result. For example, the control unit 32 diagnoses that capacitor 3 is not faulty if the capacitance value C of capacitor 3 is higher than the allowable value, and diagnoses that capacitor 3 is faulty if the capacitance value C of capacitor 3 falls below the allowable value. If it is diagnosed that capacitor 3 is not faulty, the fault detection signal φFc is set to the deactivation level "L", and if it is diagnosed that 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 capacitor 3 is faulty.

[0095] When the user receives notification from the notification unit 33 that power module P1 or capacitor 3 is faulty, they turn off switches SW1 to SW3 corresponding to power module P1 to electrically disconnect power module P1 from the other power modules P2 to P6. After repairing power module P1 or replacing it with a new power module P, or replacing capacitor 3 with a new capacitor, the user turns on switches SW1 to SW3. As a result, power module P1 is re-integrated into the uninterruptible power supply.

[0096] Since each of the power modules P2 to P6 has the same configuration as power module P1, the explanation will not be repeated.

[0097] As described above, in this embodiment, M selected power modules out of N power modules are put into operation mode, and the remaining (N-M) power modules are put into standby mode. If N-M ≥ 2, that is, if there are two or more power modules in standby mode, a diagnostic operation for the capacitor connected to the DC line is performed on any one of the (N-M) power modules.

[0098] In this way, if the number of power modules M required to operate the load increases, the system can prioritize transitioning the power modules other than the one being diagnosed from the standby state to the operational state, thereby avoiding any impact on the operation of the load. Therefore, capacitor degradation in the power modules in the standby state can be diagnosed without affecting the operation of the load.

[0099] Furthermore, by replacing capacitors diagnosed as degraded with new ones before the power module is put into operation, it is possible to prevent the power module from failing while in operation and causing the load to stop.

[0100] In the embodiment described above, a configuration was described in which the control circuit 7 included in each power module P has a "selection unit" that selects the number of power modules from among the multiple power modules P1 to P6 necessary to supply power to the load. However, in this disclosure, the "selection unit" may be implemented by a control circuit separate from the control circuit 7 of each power module P. This control circuit is connected to the control circuits 7 of the multiple power modules P1 to P6 in communication and exchanges various information with each control circuit 7. Based on this information, the control circuit selects the number of power modules P from among the multiple power modules P1 to P6 necessary to supply power to the load. Furthermore, the control circuit changes the selected power modules P at predetermined intervals so that the operating times of the multiple power modules P1 to P6 are equalized.

[0101] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

[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 Current distribution calculation unit, 26 Timer, 27 Selection unit, 29 Command unit, 30 Power outage detector, 31 Control power supply, 32 Control unit, 33 Notification unit, 40 Commercial AC power supply, 41 Load, B Battery, BP1 Bypass module, CD1, CD2 Current detectors, F1, F2 AC filters, L1, L2 Reactors, P, P1-P6 Power modules, SW1-SW3 Switches, T1, T11 Input terminals, T2 DC terminal, T3, T12 Output terminals.

Claims

1. The power conversion module comprises a plurality of power conversion modules connected in parallel to a load, and a control circuit that puts the number of power conversion modules necessary to supply power to the load into an operating state and the remaining power conversion modules into a standby state, wherein 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 it to the DC line, a bidirectional chopper that exchanges DC power between the DC line and a power storage device, and an inverter that converts the DC power received from the DC line into AC power and supplies it to the load, wherein the power conversion module in the operating state operates the converter, the bidirectional chopper and the inverter to supply power to the load, and the power conversion module in the standby state stops the operation of the bidirectional chopper and the inverter and remains in standby without supplying power to the load, while operating the converter. If there are two or more of the power conversion modules in standby mode, the uninterruptible power supply further stops the operation of the converter in any one of the two or more power conversion modules in standby mode and performs a diagnostic operation to diagnose the deterioration of the capacitor based on the time change of the DC voltage of the DC line.

2. During the diagnostic operation, the power conversion module, which is in standby mode, estimates the capacitance value of the capacitor based on the time change of the DC voltage in the DC line after the converter has stopped operating, according to claim 1.

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

4. The uninterruptible power supply according to any one of claims 1 to 3, wherein the control circuit changes the power conversion module to be in operation at a predetermined period so that the operating time of the plurality of power conversion modules is equal.

5. The uninterruptible power supply according to claim 4, wherein each power conversion module performs the diagnostic operation when it transitions from the operating state to the standby state, and there are two or more power conversion modules in the standby state.

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