Power conversion device

Abstract

The uninterruptible power supply device (1) has a bidirectional chopper (5) that converts a first direct-current voltage (VB) supplied from a battery (22) into a second direct-current voltage (VDC) and supplies the second direct-current voltage to an inverter (8) when a commercial AC power source (21) is out of operation. The bidirectional chopper includes capacitors (C11, C12) that stabilize the second direct-current voltage. The uninterruptible power supply device also has a current detector (6) that detects an output current (Ib) of the battery and a control circuit (7) that calculates a temperature rise estimation value (Ta) of the capacitors every prescribed time (Δt) based on a detection result of the current detector and stops operation of the bidirectional chopper when the calculated temperature rise estimation value is higher than an upper limit value (Th).

Description

Technical Field

[0001] This invention relates to a power conversion device, and more particularly to a power conversion device having a capacitor that stabilizes the output voltage of a chopper. Background Technology

[0002] For example, International Publication No. 2010 / 100737 (Patent Document 1) discloses a power conversion device comprising: a chopper that converts a first DC voltage supplied from a DC power source into a second DC voltage for supplying to a DC load; and a capacitor that stabilizes the second DC voltage.

[0003] Prior technology documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2010 / 100737 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In such power conversion devices, the capacitor temperature gradually rises once the chopper starts operating. If the temperature rise exceeds the upper limit, thermal runaway occurs, and the capacitor is damaged. Previously, to prevent capacitor damage, large-capacity capacitors were used to avoid exceeding the upper limit of temperature saturation. This resulted in larger device sizes and higher costs.

[0008] Therefore, the main objective of this invention is to provide a small and low-cost power conversion device.

[0009] Solution for solving the problem

[0010] The power conversion device of the present invention comprises: a chopper that converts a first DC voltage supplied from a DC power source into a second DC voltage and supplies it to a DC load; a capacitor that stabilizes the second DC voltage; a current detector that detects the output current of the DC power source; and a control circuit that, based on the detection result of the current detector, estimates the temperature rise of the capacitor at predetermined intervals, and stops the operation of the chopper if the estimated temperature rise exceeds an upper limit value.

[0011] The effects of the invention

[0012] In the power conversion device of this invention, based on the detection results of the current detector, the temperature rise of the capacitor is estimated after a predetermined time interval. If the estimated temperature rise exceeds the upper limit, the chopper operation is stopped. Therefore, small-capacity capacitors can be used, enabling miniaturization and cost reduction of the device. Attached Figure Description

[0013] Figure 1 This is a circuit block diagram showing the structure of the uninterruptible power supply device according to Embodiment 1.

[0014] Figure 2 It means Figure 1 The circuit diagram shown is of the structure of a bidirectional chopper.

[0015] Figure 3 It means Figure 2 The block diagram of the structure of the control circuit 7 shown is shown.

[0016] Figure 4 It means Figure 3 The diagram shows the structure of the discharge detector.

[0017] Figure 5 It is used for explanation Figure 4 A diagram showing the stored contents of the storage section.

[0018] Figure 6 It means Figure 5 The diagram shows the time series of the temperature rise of the electrolytic capacitor.

[0019] Figure 7 This is an example in Figure 5 and Figure 6 The figure illustrates the experimental results.

[0020] Figure 8 It means Figure 7 The graph shows the relationship between DC current and temperature rise saturation value.

[0021] Figure 9 It is used for explanation Figure 4 The timing diagram shown illustrates the operation of the arithmetic unit.

[0022] Figure 10 It is used for explanation Figure 4 The timing diagram of the operation of the discharge detector is shown.

[0023] Figure 11 It means Figure 3 The diagram shows the structure of the PWM control unit.

[0024] Figure 12 It is used for explanation Figure 11 The timing diagram of the operation of the PWM control unit is shown.

[0025] Figure 13 This is a circuit block diagram illustrating the structure of the uninterruptible power supply device according to Embodiment 2.

[0026] Figure 14 It means Figure 13 The circuit diagram shown is of the structure of a bidirectional chopper. Detailed Implementation

[0027] [Implementation Method 1]

[0028] Figure 1 This is a circuit block diagram illustrating the structure of the uninterruptible power supply device 1 according to Embodiment 1. Figure 1 The uninterruptible power supply device 1 includes current detectors 2, 6, and 9, a converter 3, DC lines L1 to L3, capacitors C1, C2, and 11, control circuits 4, 7, and 14, a bidirectional chopper 5, an inverter 8, a reactor 10, and electromagnetic contactors 12 and 13.

[0029] The uninterruptible power supply 1 is driven by commercial frequency AC power supplied from commercial AC power source 21. The instantaneous value of the AC input voltage Vi supplied from commercial AC power source 21 is detected by control circuit 4. Current detector 2 detects the AC input current Ii flowing from commercial AC power source 21 to converter 3 and sends a signal Iif representing its detected value to control circuit 4.

[0030] Converter 3 (forward converter) is controlled by control circuit 4. When AC power is normally supplied from commercial AC power source 21 (when commercial AC power source 21 is working normally), converter 3 converts AC power into DC power and outputs it to DC lines L1, L2, and L3. When the supply of AC power from commercial AC power source 21 stops (when commercial AC power source 21 is de-energized), the operation of converter 3 stops.

[0031] When the commercial AC power supply 21 is operating normally, the converter 3 generates three-level DC voltages Vdc1, Vdc2, and Vdc3 based on the AC voltage Vi supplied from the commercial AC power supply 21, and outputs DC voltages Vdc1 to Vdc3 to DC lines L1 to L3 respectively. DC voltage Vdc1 is a positive voltage, DC voltage Vdc2 is a negative voltage, and DC voltage Vdc3 is the ground voltage (0V). VDC1 = Vdc1 - Vdc3, VDC2 = Vdc3 - Vdc2, and VDC1 = VDC2. When Vdc1 - Vdc2 = VDC, then VDC1 + VDC2 = VDC.

[0032] Capacitor C1 is connected between DC lines L1 and L3 to smooth the DC voltage VDC1 between them. Capacitor C2 is connected between DC lines L3 and L2 to smooth the DC voltage VDC2 between them. The instantaneous value of the DC voltage VDC between DC lines L1 and L2 is detected by control circuit 4.

[0033] Control circuit 4 detects whether the commercial AC power supply 21 has experienced a power outage based on the detected value of the AC input voltage Vi. When the commercial AC power supply 21 is operating normally, control circuit 4 controls converter 3 based on the AC input voltage Vi, AC input current Ii, and DC voltage VDC, causing the DC voltage VDC to become a specified reference DC voltage VDCr (e.g., 660V). When the commercial AC power supply 21 experiences a power outage, control circuit 4 stops the operation of converter 3.

[0034] DC lines L1, L2, and L3 are connected to inverter 8 and to the high-voltage side nodes 5a, 5b, and 5c of bidirectional chopper 5, respectively. The low-voltage side nodes 5d and 5e of bidirectional chopper 5 are connected to the positive and negative terminals of battery 22, respectively. Battery 22 (power storage device) stores DC power.

[0035] The bidirectional chopper 5 is controlled by the control circuit 7. When the commercial AC power supply 21 is working normally, the DC power generated by the converter 3 is stored in the battery 22. When the commercial AC power supply 21 fails, the DC power of the battery 22 is supplied to the inverter 8 through the DC lines L1 to L3.

[0036] The instantaneous value of the DC voltage VDC between DC lines L1 and L2 is detected by control circuit 7. Alternatively, the instantaneous value of the DC voltage VDC1 between DC lines L1 and L3 can be added to the instantaneous value of the DC voltage VDC2 between DC lines L3 and L2 to obtain the instantaneous value of the DC voltage VDC between DC lines L1 and L2.

[0037] Current detector 6 detects the DC current Ib flowing between the low-voltage side node 5d of bidirectional chopper 5 and the positive terminal of battery 22, and provides a signal Ibf representing its detected value to control circuit 7. The instantaneous value of the inter-terminal voltage VB of battery 22 is detected by control circuit 7.

[0038] The control circuit 7 controls the bidirectional chopper 7 based on the DC voltage VDC, the DC current Ib, and the inter-terminal voltage VB of the battery 22. The control circuit 7 determines whether the commercial AC power supply 21 has experienced a power outage based on the polarity of the DC current Ib.

[0039] When the commercial AC power supply 21 is operating normally, the control circuit 7 controls the bidirectional chopper 5 so that the DC power generated by the converter 3 is stored in the battery 22, and the inter-terminal voltage VB of the battery 22 becomes a specified reference DC voltage VBr (e.g., 480V).

[0040] In addition, in response to a power outage in the commercial AC power supply 21, the control circuit 7 controls the bidirectional chopper 5 to supply DC power from the battery 22 to the inverter 8, and the DC voltage VDC between the DC lines L1 and L2 becomes a specified reference DC voltage VDCr (e.g., 660V).

[0041] In addition, the control circuit 7 stores information relating the DC current Ib, the time constant of the temperature rise of the capacitor included in the bidirectional chopper 5, and the temperature rise saturation value of the capacitor. When the commercial AC power supply 21 fails, the control circuit 7 calculates the estimated temperature rise of the capacitor every specified time interval based on the DC power supply Ib and the stored information, and stops the operation of the bidirectional chopper 5 if the calculated estimated temperature rise exceeds the upper limit value.

[0042] Inverter 8, controlled by control circuit 14, converts the DC power supplied from converter 3 or bidirectional chopper 5 via DC lines L1-L3 into commercial frequency AC power before outputting it. Specifically, when commercial AC power supply 21 is operating normally, inverter 8 converts the DC power supplied from converter 3 via DC lines L1-L3 into AC power; conversely, if commercial AC power supply 21 experiences a power outage, it converts the DC power supplied from battery 22 via bidirectional chopper 5 into AC power. The AC output voltage of inverter 8 can be controlled to a desired value.

[0043] At this time, inverter 8 generates AC output voltage Vo based on the DC voltages Vdc1 to Vdc3 of DC lines L1 to L3. Control circuit 14 controls inverter 8 based on AC output voltage Vo and AC output current Io, so that AC output voltage Vo becomes a specified reference AC voltage Vor.

[0044] The output node of inverter 8 is connected to one terminal of reactor 10, and the other terminal of reactor 10 (node ​​N1) is connected to load 23 via electromagnetic contactor 12. Capacitor 11 is connected between node N1 and DC line L3. The ground terminal 23a of load 23 is connected to DC line L3.

[0045] Reactor 10 and capacitor 11 form a low-pass filter, allowing the commercial frequency AC power generated by inverter 8 to pass through load 23, while preventing signals at the switching frequency generated by inverter 8 from passing through load 23. Inverter 8, reactor 10, and capacitor 11 constitute an inverter converter. Inverter 8, reactor 10, capacitor 11, and load 23 (AC load) constitute a DC load.

[0046] Current detector 9 detects the instantaneous value of the output current Io of inverter 8 and provides a signal Iof representing its detected value to control circuit 14. The instantaneous value of the AC output voltage Vo appearing at node N1 is detected by control circuit 14. Control circuit 14 controls inverter 8 based on AC output voltage Vo and AC output current Io, so that AC output voltage Vo becomes a specified reference AC voltage Vor.

[0047] When the inverter power supply mode supplies AC power generated by the inverter 8 to the load 23, the electromagnetic contactor 12 is turned on; when the bypass power supply mode supplies AC power from the commercial AC power supply 21 to the load 23, the electromagnetic contactor 12 is turned off.

[0048] Electromagnetic contactor 13 is connected between commercial AC power supply 21 and load 23. It is disconnected in inverter power supply mode and connected in bypass power supply mode. In addition, in inverter power supply mode, if inverter 8 fails, electromagnetic contactor 13 is connected and electromagnetic contactor 12 is disconnected, so that AC power from commercial AC power supply 21 is supplied to load 23.

[0049] Figure 2 This is a circuit diagram showing the structure of the bidirectional chopper 5. Figure 2 In the bidirectional chopper 5, there are IGBTs Q1 to Q4, diodes D1 to D4, reactors X1 and X2, and capacitors C11 and C12.

[0050] The collector of IGBT Q1 is connected to the high-voltage side node 5a. The emitter of IGBT Q1 is connected to the low-voltage side node 5d via reactor X1 and is also connected to the collector of IGBT Q2. The emitter of IGBT Q2 is connected to the high-voltage side node 5c and is also connected to the collector of IGBT Q3. The emitter of IGBT Q3 is connected to the low-voltage side node 5e via reactor X2 and is also connected to the collector of IGBT Q4. The emitter of IGBT Q4 is connected to the high-voltage side node 5b.

[0051] Diodes D1 to D4 are connected in reverse parallel with IGBTs Q1 to Q4, respectively. Capacitor C11 is connected between high-voltage side nodes 5a and 5c to stabilize the DC voltage VDC1 between high-voltage side nodes 5a and 5c. Capacitor C12 is connected between high-voltage side nodes 5c and 5b to stabilize the DC voltage VDC2 between high-voltage side nodes 5c and 5b.

[0052] IGBT Q1 (first switching element) and IGBT Q4 (fourth switching element) are switched on and off at a specified frequency when the commercial AC power supply 21 is operating normally, storing the DC power generated by the converter 3 into the battery 22. When the commercial AC power supply 21 is operating normally, IGBTs Q2 and Q3 are always in the off state.

[0053] IGBTs Q1 and Q4 are controlled by a gating signal S1 from control circuit 7. The gating signal S1 is alternately set to "H" level and "L" level at a specified frequency. If the gating signal S1 is set to "H" level, IGBTs Q1 and Q4 are turned on; if the gating signal S1 is set to "L" level, IGBTs Q1 and Q4 are turned off.

[0054] When the commercial AC power supply 21 is working normally, if IGBT Q1 and Q4 are turned on when VDC>VB, a current Ib flows through the path from DC line L1 through IGBT Q1, reactor X1, battery 22, reactor X2 and IGBT Q4 to DC line L2. The battery 22 is charged and the reactors X1 and X2 store electromagnetic energy.

[0055] If IGBTs Q1 and Q4 are disconnected, current flows through the path from one terminal of reactor X1 (the terminal on the side of battery 22) through battery 22, reactor X2 and diodes D3 and D2 to the other terminal of reactor X1. Battery 22 is charged and the electromagnetic energy of reactors X1 and X2 is released.

[0056] The ratio of the time (pulse width) during which the gating signal S1 is set to "H" level to one cycle is called the duty cycle. By adjusting the duty cycle of the gating signal S1, the inter-terminal voltage VB of battery 22 can be adjusted to a specified reference DC voltage VBr. The DC voltage VDC = VDC1 + VDC2 between DC lines L1 and L2 is stepped down and supplied to battery 22, becoming VB. <VDC。

[0057] IGBT Q2 (second switching element) and IGBT Q3 (third switching element) are switched on and off at a specified frequency in response to a power outage of the commercial AC power supply 21, supplying DC power from the battery 22 to the inverter 8.

[0058] IGBTs Q2 and Q3 are controlled by a gating signal S2 from control circuit 7. The gating signal S2 is alternately set to "H" and "L" levels at a fixed frequency. If the gating signal S2 is set to "H" level, IGBTs Q2 and Q3 are turned on; if the gating signal S2 is set to "L" level, IGBTs Q2 and Q3 are turned off.

[0059] If the supply of AC power from the commercial AC power source 21 stops and the DC voltage VDC between the DC lines L1 and L2 drops below the voltage VB between the terminals of the battery 22, the IGBTs Q1 and Q4 are fixed in the off state, and the IGBTs Q2 and Q3 start to turn on and off.

[0060] If the IGBTs Q2 and Q3 are on, current flows from the positive electrode of the battery 22 through the reactors X1, the IGBTs Q2 and Q3, and the reactor X2 to the negative electrode of the battery 22, and the reactors X1 and X2 store electromagnetic energy. If the IGBTs Q2 and Q3 are off, the current that originally flowed from the reactor X1 to the IGBT Q2 instead flows from the reactor X1 to the diode D1, through the capacitors C11 and C12, the diode D4, and the reactor X2 to the negative electrode of the battery 22, the capacitors C11 and C12 are charged, and the electromagnetic energy of the reactors X1 and X2 is released.

[0061] The ratio of the time (pulse width) when the gate signal S2 is set to the "H" level to one cycle is called the duty ratio. By adjusting the duty ratio of the gate signal S2, the DC voltage VDC = VDC1 + VDC2 between the DC lines L1 and L2 can be adjusted to a specified reference DC voltage VDCR. The voltage VB between the terminals of the battery 22 is boosted and supplied between the DC lines L1 and L2, becoming VB < VDC.

[0062] The IGBTs Q1 to Q4, the diodes D1 to D4, and the reactors X1 and X2 constitute a chopper that converts the DC voltage VB into the DC voltage VDC when the commercial AC power source 21 is out of power, and the C11 and C12 constitute capacitors that stabilize the output voltage of the chopper.

[0063] The control circuit 7 detects whether a power outage has occurred in the commercial AC power source 21 based on the output signal Ibf of the current detector 6. That is, if a power outage occurs in the commercial AC power source 21, the operation of the converter 3 stops, DC power is supplied from the capacitors C1, C2, C11, and C\alpha to the inverter 8, and the DC voltage VDC between the DC lines L1 and L2 drops. If VDC = VB, no current flows through the IGBTs Q1 and Q4 even if the IGBTs Q1 and Q4 are turned on and off, and if further VDC < VB, the current Ib flows from the positive electrode of the battery 22 through the reactor X1, the diode D1, the capacitors C11 and C12, the diode D4, and the reactor X2 to the negative electrode of the battery 22.

[0064] Therefore, if the commercial AC power supply 21 experiences a power outage, the polarity of the current Ib flowing from the low-voltage side node 5d of the bidirectional chopper 5 to the positive terminal of the battery 22 will reverse. If the polarity of the current Ib flowing from the low-voltage side node 5d of the bidirectional chopper 5 to the positive terminal of the battery 22 is set to negative, the control circuit 7 will detect a power outage of the commercial AC power supply 21 when the polarity of the current Ib reverses from negative to positive. Furthermore, a current detector 6 can also be installed within the bidirectional chopper 5. For example, the current detector 6 can also detect the current Ib flowing between the emitter of the IGBT Q1 and the reactor X1.

[0065] For such a bidirectional chopper 5, when the commercial AC power supply 21 fails and DC power is supplied to the inverter 8 from the battery 22, ripple current flows through capacitors C11 and C12, causing their temperatures to rise. If the temperature rise of capacitors C11 and C12 exceeds the specified upper limit, thermal runaway occurs, and capacitors C11 and C12 are damaged. To minimize the temperature rise of capacitors C11 and C12, their capacitance values ​​need to be large.

[0066] Previously, the capacitance values ​​of capacitors C11 and C12 were set such that, under the condition of a stable flow of the maximum current Ib when the commercial AC power supply 21 is interrupted, the temperature rise saturation value of capacitors C11 and C12 would not exceed the upper limit. Therefore, the capacitance values ​​of capacitors C11 and C12 became excessively large, leading to larger devices and increased costs. This embodiment 1 aims to solve this problem.

[0067] Figure 3 This is a block diagram showing the structure of control circuit 7. Figure 3 In the control circuit 7, there are reference voltage generation units 31 and 36, correction units 32 and 39, voltage detectors 33 and 37, subtractors 34 and 38, voltage control units 35 and 40, polarity determiner 41, discharge determiner 42, and PWM (Pulse Width Modulation) control unit 43.

[0068] The reference voltage generation unit 31 generates a reference DC voltage VBr, which serves as the target voltage VB between the terminals of the battery 22. The correction unit 32, based on the current detector 6 (… Figure 2 The correction unit 32 operates by outputting the signal Ibf, and corrects the reference DC voltage VBr based on the current Ib flowing into the battery 22, outputting a reference voltage correction value VBr1. For example, the correction unit 32 monitors the magnitude of the current Ib while adjusting the reference voltage correction value VBr1 to prevent excessive current Ib from flowing through the battery 22 during initial charging.

[0069] Voltage detector 33 detects the inter-terminal voltage VB of battery 22 and outputs a signal VBf representing the detected value. Subtractor 34 calculates the deviation ΔVB = VBr1 - VB between the reference voltage correction value VBr1 and the inter-terminal voltage VB of battery 22 represented by the output signal VBf of voltage detector 33. Voltage control unit 35 adds a value proportional to the deviation ΔVB and the integral value of the deviation ΔVB to generate a voltage command value VBc.

[0070] The correction unit 32, the subtractor 34, and the voltage control unit 35 constitute a first voltage command unit that generates a voltage command value VBc so that the inter-terminal voltage VB of the battery 22 becomes a reference DC voltage VBr.

[0071] The reference voltage generation unit 36 ​​generates a reference DC voltage VDCr, which serves as the target voltage for the DC voltage VDC between DC lines L1 and L2. The voltage detector 37 detects the DC voltage VDC between DC lines L1 and L2 and outputs a signal VDCf representing the detected value. The subtractor 38 calculates the deviation ΔVDC = VDCr - VDC between the reference DC voltage VDCr and the DC voltage VDC represented by the output signal VDCf of the voltage detector 37.

[0072] The calibration unit 39 is based on the current detector 6 ( Figure 2 The correction unit 39 operates by monitoring the magnitude of the current Ib flowing from the battery 22 and adjusting the deviation ΔVDC based on the output signal Ibf, and outputs a deviation correction value ΔVDC1. For example, the correction unit 39 adjusts the deviation correction value ΔVDC1 while monitoring the magnitude of the current Ib to prevent excessive current Ib from flowing during the initial discharge of the battery 22. The voltage control unit 40 generates a voltage command value VDCc by adding a value proportional to the deviation correction value ΔVDC1 and the integral value of the deviation correction value ΔVDC1.

[0073] The subtractor 38, the correction unit 39, and the voltage control unit 40 constitute a second voltage command unit that generates the voltage command value VDCc by changing the DC voltage VDC between DC lines L1 and L2 to the reference DC voltage VDCr.

[0074] Polarity determiner 41 is based on current detector 6 ( Figure 2 The output signal Ibf is used to determine the polarity of the DC current Ib flowing between the low-voltage side node 5d of the bidirectional chopper 5 and the positive terminal of the battery 22, and the output signal DT1 represents the determination result.

[0075] When the DC current Ib flows from the low-voltage side node 5d of the bidirectional chopper 5 towards the positive terminal of the battery 22 (when the commercial AC power supply 21 is working normally), the DC current Ib is determined to be negative, and the signal DT1 is set to the "L" level. Conversely, when the DC current Ib flows from the positive terminal of the battery 22 towards the low-voltage side node 5d of the bidirectional chopper 5 (when the commercial AC power supply 21 is de-energized), the DC current Ib is determined to be positive, and the signal DT1 is set to the "H" level.

[0076] When the discharge detector 42 is at the "H" level (when the commercial AC power supply 21 is interrupted), it determines the discharge based on the output signal VBf of the voltage detector 33 and the current detector 6. Figure 1 , Figure 2 The output signal IBf is used to determine whether the DC power of battery 22 can be discharged, and the output signal DT2 represents the determination result. If the DC power of battery 22 can be discharged, the signal DT2 is set to the "H" level. If the DC power of battery 22 cannot be discharged, the signal DT2 is set to the "L" level.

[0077] Figure 4 This is a block diagram showing the structure of the discharge detector 42. Figure 4 In the discharge determination unit 42, there are a voltage determination unit 51, a storage unit 52, an arithmetic unit 53, a temperature determination unit 54, and an AND gate 55.

[0078] Voltage determination unit 51 corresponds to voltage detector 33 ( Figure 3 The output signal VBf represents the DC voltage VB and the battery 22 ( Figure 1 , Figure 2 The DC voltage VB is compared with the discharge termination voltage VBE, and a signal φ51 representing the comparison result is output. When the DC voltage VB is higher than the discharge termination voltage VBE, the signal φ51 is set to the "H" level. When the DC voltage VB is lower than the discharge termination voltage VBE, the signal φ51 is set to the "L" level.

[0079] The storage unit 52 stores information representing the relationship between the DC current Ib when the commercial AC power supply 21 is interrupted, the time constant τ of the temperature rise of capacitors C11 and C12, and the temperature rise saturation value Ts of capacitors C11 and C12.

[0080] Here, the experimental method for obtaining information representing the relationship between Ib, τ, and Ts is described. Capacitors C11 and C12 each consist of multiple electrolytic capacitors connected in parallel. For example... Figure 5As shown, the electrolytic capacitor 60 with the largest temperature rise among these electrolytic capacitors (e.g., the electrolytic capacitor located in the center among multiple electrolytic capacitors) is selected, and a temperature sensor 61 is arranged inside the selected electrolytic capacitor 60 to detect the internal temperature T1 of the electrolytic capacitor 60.

[0081] In addition, a temperature sensor 62 is disposed outside the selected electrolytic capacitor 60 to detect the ambient temperature T2 of the electrolytic capacitor 60. The difference between the internal temperature T1 of the electrolytic capacitor 60, represented by the output signal T1f of the temperature sensor 61, and the ambient temperature T2 of the electrolytic capacitor 60, represented by the output signal T2f of the temperature sensor 62, is taken as the temperature rise value T = T1 - T2 of the electrolytic capacitor 60.

[0082] Furthermore, the electrolytic capacitor 60, which has an internal temperature sensor 61, has a short lifespan, so it is practically impossible to detect the internal temperature T1 of the electrolytic capacitor 60 while the uninterruptible power supply device 1 is running.

[0083] Additionally, a fixed-capacity load 23 (e.g., 400kW) is connected to the uninterruptible power supply 1, and a DC power supply with adjustable output voltage VB is connected instead of the battery 22. The output voltage VB of the DC power supply is set to a specified value, and the bidirectional chopper 5 and inverter 8 are operated in the same way as when the commercial AC power supply 21 is interrupted.

[0084] The DC current Ib is detected by current detector 6, and the temperature rise T(K) of electrolytic capacitor 60 is detected by temperature sensors 61 and 62. The temperature rise T(K) gradually increases over time, so the bidirectional chopper 5 and inverter 8 are kept running until the temperature rise T(K) saturates, and a curve representing the time change of the temperature rise T(K) is plotted.

[0085] Figure 6 This is a time series graph showing the time variation of the temperature rise T (K) of an electrolytic capacitor 60. Figure 6 In the initial state (time t0), Ib = 0 (A) and T = 0 (k). The DC voltage VB is set to a specified value. At time t1, if the bidirectional chopper 5 and inverter 8 start operating, the DC current Ib flows, and the temperature rise T (K) gradually increases. At time t3, the temperature rise T (K) saturates, reaching the temperature rise saturation value Ts (K).

[0086] The time it takes for the temperature rise T(K) to reach 62.3% of the temperature rise saturation value Ts(K) from 0(K) is defined as the time constant τ = t2 - t1. The DC voltage VB is varied in multiple stages, and a temperature rise curve A is plotted for each DC voltage VB. The DC voltage VB(V), DC current Ib, temperature rise saturation value Ts, and time constant τ are recorded.

[0087] Figure 7 This is an example Figure 5 and Figure 6 The experimental results are illustrated in the figure. Figure 7 The following scenario is illustrated: the power consumption PL of load 23 is fixed at 400 kW, and the DC voltage VB varies in four stages: 400, 420, 440, and 480 V. When the DC voltage VB varies to 400, 420, 440, and 480 V, the DC current Ib is 1000.0, 952.4, 909.1, and 833.3 A, respectively, and the temperature rise saturation value Ts is 51, 48, 44, and 39 K, respectively. The time constant τ is approximately 15 minutes in all cases.

[0088] Figure 8 It means Figure 7 The graph shows the relationship between the DC current Ib and the temperature rise saturation value Ts. Figure 8 In the diagram, curve B passes through the origin (Ib = 0, Ts = 0) and four points: P1 (Ib = 833.3, Ts = 39), P2 (Ib = 909.1, Ts = 44), P3 (Ib = 952.4, Ts = 48), and P4 (Ib = 1000.0, Ts = 51). The temperature rise saturation value Ts as a function of the DC current Ib can be approximated by the expression Ts = f(Ib). This expression Ts = f(Ib) and the time constant τ are stored in the storage unit 52 beforehand.

[0089] Refer again Figure 4 The arithmetic unit 53 is activated when the signal DT1 is at the "H" level (when the commercial AC power supply 21 is interrupted). Based on the DC current Ib represented by the output signal Ibf of the current detector 6 and the stored contents of the storage unit 52, it calculates the estimated temperature rise Ta of capacitors C11 and C12 every predetermined time interval Δt.

[0090] Figure 9 This is a timing diagram used to illustrate the operation of the arithmetic unit 53. Figure 9 In the diagram, (A) represents the time-varying temperature rise T(K) of capacitors C11 and C12, and (B) represents the time-varying DC current Ib(A).

[0091] exist Figure 9The following situation is illustrated: at a certain time t0, a DC current Ib flows at 833.3 (A), and at time t1 after time t0, the DC current Ib increases to 1000 (A). At time t0, the temperature rise T0 (K) of capacitors C11 and C12 is 39 (K). The arithmetic unit 53 calculates the estimated temperature rise Ta at time t2 after a predetermined time Δt from time t1.

[0092] That is, the arithmetic unit 53 first calculates the temperature rise saturation value Ts = f(1000) = 51 (K) based on the DC current Ib = 1000 (A) at time t1. The estimated temperature rise value T (K) increases along the curve C, represented by the time constant τ, toward the calculated temperature rise saturation value Ts = 51 (K). The arithmetic unit 53 calculates the estimated temperature rise value Ta at time t2 according to the following formula (1). N is a positive integer that increments by (+1) in each calculation.

[0093] Ta=T0+(Ts-T0)×[1-exp(-Δt×N / τ)]…(1)

[0094] The temperature determination unit 54 compares the estimated temperature rise Ta calculated by the calculation unit 53 with the upper limit value Th, and outputs a signal φ54 indicating the comparison result. If the estimated temperature rise Ta is smaller than the upper limit value Th, the signal φ54 is set to "H" level. If the estimated temperature rise Ta is larger than the upper limit value Th, the signal φ54 is set to "L" level. The upper limit value Th is, for example, 45 (K).

[0095] AND gate 55 outputs signals φ51 and φ54, which are logically ANDed with signal DT2. When the DC voltage VB is higher than the discharge termination voltage VBE and the estimated temperature rise Ta is lower than the upper limit Th, signal DT2 is at a "H" level, allowing battery 22 to discharge. When the DC voltage VB drops below the discharge termination voltage VBE, or when the estimated temperature rise Ta rises above the upper limit Th, signal DT2 is at a "L" level, preventing battery 22 from discharging.

[0096] Figure 10 This is a timing diagram used to illustrate the operation of the discharge detector 42. Figure 10 In the diagram, (A) represents the time variation of the temperature rise saturation value Ts and the temperature rise estimate Ta, (B) represents the time variation of the terminal voltage VB (DC voltage VB) of battery 22, and (C) represents the time variation of the discharge current Ib (DC current Ib) of battery 22. Figure 10 The horizontal axis represents the discharge time of battery 22.

[0097] exist Figure 10If battery 22 begins to discharge, the inter-terminal voltage VB of battery 22 gradually decreases from an initial value (e.g., 470V). Since the power consumption of load 23 is a fixed value (e.g., 400kW), as the inter-terminal voltage VB of battery 22 decreases, the discharge current Ib of battery 22 gradually increases from an initial value (e.g., 851A).

[0098] The calculation unit 53 calculates the temperature rise saturation value Ts and the temperature rise estimate Ta every specified time interval Δt (e.g., 1 minute). As the discharge current Ib of battery 22 gradually increases, the temperature rise saturation value Ts also gradually increases from its initial value (e.g., 40K). The temperature rise estimate Ta gradually increases from its initial value (0K).

[0099] exist Figure 10 In the case shown, approximately 35 minutes after the start of discharge, the estimated temperature rise Ta becomes higher than the upper limit Th (e.g., 45K), and approximately 26 minutes after the start of discharge, the inter-terminal voltage VB of battery 22 becomes lower than the discharge termination voltage (e.g., 400V). Therefore, in this case, approximately 26 minutes after the start of discharge, the voltage determination unit 51 ( Figure 4 The output signal φ51 is reduced to the "L" level and the signal DT2 is reduced to the "L" level, thus preventing the battery 22 from discharging.

[0100] Refer again Figure 3 When the output signal DT1 of the polarity determiner 41 is at the "L" level (when the commercial AC power supply 21 is working normally), the PWM control unit 43 generates the gating signal S1 based on the comparison result between the voltage command value VBc from the voltage control unit 35 and the triangular wave signal CW of the specified frequency, and fixes the gating signal S2 at the "L" level.

[0101] In addition, when the output signal DT1 of the polarity determiner 41 is at the "H" level and the output signal DT2 of the discharge determiner 42 is at the "H" level (when the commercial AC power supply 21 is interrupted, the DC voltage VB is higher than the discharge termination voltage VBE and the estimated temperature rise Ta is lower than the upper limit value Th), the PWM control unit 43 generates the gating signal S2 based on the comparison result between the voltage command value VDCc from the voltage control unit 40 and the triangular wave signal CW of the specified frequency, and fixes the gating signal S1 at the "L" level.

[0102] In addition, when the output signal DT1 of the polarity determiner 41 is at the "H" level and the output signal DT2 of the discharge determiner 42 is at the "L" level (when the commercial AC power supply 21 is interrupted, the DC voltage VB is lower than the discharge termination voltage VBE, or the temperature rise estimate Ta is higher than the upper limit value Th), the PWM calculation unit 43 fixes the gating signals S1 and S2 at the "L" level.

[0103] Figure 11 is a block diagram showing the structure of the PWM operation unit 43. In Figure 11 the PWM operation unit 43 includes a triangular wave generator 71, comparators 72, 73, a selector 74, and signal output circuits 75, 76.

[0104] The triangular wave generator 71 generates a triangular wave signal CW with a specified frequency. The comparator 72 compares the voltage command value VBc from the voltage control unit 35 ( Figure 3 ) with the level of the triangular wave signal CW, and outputs a PWM signal φ1 indicating the comparison result. When VBc > CW, the PWM signal φ1 is set to the "H" level, and when VBc < CW, the PWM signal φ1 is set to the "L" level.

[0105] The comparator 73 compares the voltage command value VDCc from the voltage control unit 40 ( Figure 3 ) with the level of the triangular wave signal CW, and outputs a PWM signal φ2 indicating the comparison result. When VDCc > CW, the PWM signal φ2 is set to the "H" level, and when VDCc < CW, the PWM signal φ2 is set to the "L" level.

[0106] When the output signal DT1 of the polarity discriminator 41 ( Figure 3 ) is at the "L" level, the selector 74 selects the PWM signal φ1 among the PWM signals φ1 and φ2, and provides the selected PWM signal φ1 as the PWM signal φ1A to the signal output circuit 75, and provides the PWM signal φ2A fixed at the "L" level to the signal output circuit 76.

[0107] In addition, when the output signal DT1 of the polarity discriminator 41 ( Figure 3 ) is at the "H" level, the selector 74 selects the PWM signal φ2 among the PWM signals φ1 and φ2, and provides the selected PWM signal φ2 as the PWM signal φ2A to the signal output circuit 76, and provides the PWM signal φ1A fixed at the "L" level to the signal output circuit 75.

[0108] The signal output circuit 75 is activated when the signal DT2 is at the "H" level, performs amplification and level conversion processing on the PWM signal φ1A from the selector 74, generates a gate signal S1 with the same waveform as the PWM signal φ1A, and provides it to the gates of the IGBTs Q1, Q4 of the bidirectional chopper 5. When the signal DT2 is at the "L" level, the signal output circuit 75 fixes the gate signal S1 at the "L" level.

[0109] The signal output circuit 76 is activated when the signal DT2 is at the "H" level. It amplifies and levels the PWM signal φ2A from the selector 74, generating a gating signal S2 with the same waveform as the PWM signal φ2A, and provides it to the gates of IGBTs Q2 and Q3 of the bidirectional chopper 5. When the signal DT2 is at the "L" level, the signal output circuit 76 fixes the gating signal S2 at the "L" level.

[0110] Figure 12 This is a timing diagram used to illustrate the operation of the PWM control unit 43. Figure 12 In the diagram, (A) is a timing diagram representing the waveforms of the voltage command value VDCc, the triangular wave signal CW, and the PWM signal φ2. For example... Figure 12 As shown in (A), the triangular wave signal CW varies at a fixed frequency between the negative and positive peak values. The voltage command value VDCc varies between the negative and positive peak values. Figure 12 (A) shows the case where the voltage command value VDCc changes linearly from a negative value to a positive value.

[0111] like Figure 12 As shown in (A) and (B), when the voltage command value VDCc is greater than the triangular wave signal CW, the PWM signal φ2 becomes "H" level, and when the voltage command value VDCc is less than the triangular wave signal CW, the PWM signal φ2 becomes "L" level. Therefore, as the voltage command value VDCc increases, the duty cycle of the PWM signal φ2 increases.

[0112] The waveforms of the voltage command value VBc, the triangular wave signal CW, and the PWM signal φ1 are the same as those of the voltage command value VDCc, the triangular wave signal CW, and the PWM signal φ2, so their descriptions will not be repeated.

[0113] Next, the explanation Figures 1-12 The operation of the uninterruptible power supply device 1 is shown. Assume that the inverter power supply mode is selected, the electromagnetic contactor 12 is connected, and the electromagnetic contactor 13 is disconnected. When the commercial AC power supply 21 is operating normally, the AC power supplied from the commercial AC power supply 21 is converted to DC power by the converter 3, and this DC power is converted back to AC power by the inverter 8 and supplied to the load 23, causing the load 23 to operate.

[0114] Additionally, a portion of the DC power generated by converter 3 is stored in battery 22 via bidirectional chopper 5. At this time, for control circuit 7 ( Figure 3 The voltage command value VBc is generated to make the inter-terminal voltage VB of battery 22 become the reference DC voltage VBr, and the polarity determiner 41 sets the signal DT1 to the "L" level.

[0115] For PWM control unit 43 ( Figure 11 This generates a PWM signal φ1 representing the comparison result between the triangular wave signal CW and the voltage command value VBc, and generates a gating signal S1 with the same waveform as the PWM signal φ1. This gating signal S1 is used to enable the IGBTs Q1 and Q4 of the bidirectional chopper 5. Figure 2 The circuit is switched on and off, which reduces the DC voltage VDC between DC lines L1 and L2 to supply the battery 22.

[0116] If the commercial AC power supply 21 experiences a power outage, the converter 3 stops operating, and the DC power from the battery 22 is supplied to the inverter 8 via the bidirectional chopper 5, where it is converted into AC power and supplied to the load 23.

[0117] That is, if the converter 3 stops operating and the DC voltage VDC between DC lines L1 and L2 drops, the current Ib flows from the positive terminal of battery 22 towards the low-voltage side node 5d of bidirectional chopper 5. Figure 2 As the current flows, the polarity of the current Ib reverses from negative to positive, and the polarity determiner 41 ( Figure 3 The output signal DT1 of the control circuit becomes "H" level. Additionally, for control circuit 7 ( Figure 3 This generates a voltage command value VDCc to make the DC voltage VDC between DC lines L1 and L2 become the reference DC voltage VDCr.

[0118] For PWM control unit 43 ( Figure 11 This generates a PWM signal φ2 representing the comparison result between the triangular wave signal CW and the voltage command value VDCc, and generates a gating signal S2 with the same waveform as the PWM signal φ2. This gating signal S2 is used to enable the IGBTs Q2 and Q3 of the bidirectional chopper 5. Figure 2 The circuit switches on and off, boosting the voltage VB between the terminals of battery 22 and supplying it to inverter 8 via DC lines L1 and L2.

[0119] Additionally, if the commercial AC power supply 21 experiences a power outage, the arithmetic unit 53 ( Figure 4 At regular intervals Δt, the estimated temperature rise Ta of capacitors C11 and C12 is calculated. If the calculated estimated temperature rise Ta exceeds the upper limit Th, the temperature determination unit 54 causes signal φ54 to drop to the "L" level and signal DT2 to drop to the "L" level.

[0120] Furthermore, when the voltage VB between the terminals of battery 22 drops below the discharge termination voltage VBE, the temperature determination unit 54 causes signal φ51 to drop to the "L" level and signal DT2 to drop to the "L" level. If signal DT2 becomes the "L" level, signals S1 and S2 are fixed at the "L" level by signal output circuits 75 and 76, and the discharge of battery 22 stops.

[0121] As described above, in this embodiment 1, based on the detection results of the current detector 6 and the stored content of the storage unit 52, the estimated temperature rise value Ta of capacitors C11 and C12 is calculated every predetermined time Δt. If the calculated estimated temperature rise value Ta is higher than the upper limit value Th, the operation of the bidirectional chopper 5 is stopped. Therefore, smaller capacity capacitors C11 and C12 can be used compared to the past, enabling miniaturization and cost reduction of the device.

[0122] Furthermore, in this embodiment 1, the case where capacitors C1 and C2 are independently provided for stabilizing the output voltage of the converter 3 and capacitors C11 and C12 are provided for stabilizing the output voltage of the bidirectional chopper 5 is described. However, it is not limited to this; the same effect can be obtained when capacitors C1 and C2 include capacitors C11 and C12. Here, capacitors C1 and C2 each include multiple electrolytic capacitors connected in parallel, therefore, it is necessary to select the electrolytic capacitor 60 (which has the largest temperature rise among these electrolytic capacitors). Figure 5 The internal temperature T1 and ambient temperature T2 of the selected electrolytic capacitor 60 are detected.

[0123] [Implementation Method 2]

[0124] Figure 13 This is a circuit block diagram showing the structure of the uninterruptible power supply device 81 in Embodiment 2, and is related to... Figure 1 Comparison chart. (Refer to the original text.) Figure 13 The uninterruptible power supply device 81 and Figure 1 The difference of the uninterruptible power supply device 1 is that the converter 3, inverter 8 and bidirectional chopper 5 are replaced by converter 3A, inverter 8A and bidirectional chopper 5A respectively, the control circuits 4, 7 and 14 are replaced by control circuits 4A, 7A and 14A respectively, the capacitors C1 and C2 are replaced by capacitor C3, and the DC line L3 is removed.

[0125] Converter 3A is controlled by control circuit 4A. When the commercial AC power supply 21 is operating normally, it converts AC power into DC power and outputs it to DC lines L1 and L2. When the commercial AC power supply 21 is de-energized, converter 3A stops operating. The DC output voltage VDC of converter 3A can be controlled to the desired value.

[0126] Capacitor C3 is connected between DC lines L1 and L2 to smooth and stabilize the voltage between them. The instantaneous value of the DC voltage VDC between DC lines L1 and L2 is detected by control circuit 4A.

[0127] Control circuit 4A detects whether the commercial AC power supply 21 has experienced a power outage based on the detected value of the AC input voltage Vi. When the commercial AC power supply 21 is operating normally, control circuit 4A controls converter 3A based on the AC input voltage Vi, AC input current Ii, and DC voltage VDC, causing the DC voltage VDC to become a specified reference DC voltage VDCr (e.g., 660V). When the commercial AC power supply 21 experiences a power outage, control circuit 4A stops the operation of converter 3A.

[0128] DC lines L1 and L2 are connected to inverter 8A, and to the high-voltage side nodes 5a and 5b of bidirectional chopper 5A, respectively. The low-voltage side nodes 5d and 5e of bidirectional chopper 5A are connected to the positive and negative terminals of battery 22, respectively.

[0129] The bidirectional chopper 5A is controlled by the control circuit 7A. When the commercial AC power supply 21 is working normally, it stores the DC power generated by the converter 3A into the battery 22. When the commercial AC power supply 21 fails, it supplies the DC power of the battery 22 to the inverter 8A through the DC lines L1 and L2.

[0130] The instantaneous value of the DC voltage VDC between DC lines L1 and L2 is detected by control circuit 7A. Current detector 6 detects the DC current Ib flowing between the low-voltage side node 5c of bidirectional chopper 5 and the positive terminal of battery 22, and provides a signal Ibf representing its detected value to control circuit 7A. The instantaneous value of the inter-terminal voltage VB of battery 22 is detected by control circuit 7A.

[0131] Control circuit 7A controls bidirectional chopper 5A based on DC voltage VDC, DC current Ib, and the inter-terminal voltage VB of battery 22. Control circuit 7A determines whether commercial AC power supply 21 has experienced a power outage based on the polarity of DC current Ib.

[0132] When the commercial AC power supply 21 is operating normally, the control circuit 7A controls the bidirectional chopper 5A so that the DC power generated by the converter 3A is stored in the battery 22, and the inter-terminal voltage VB of the battery 22 becomes a specified reference DC voltage VBr (e.g., 480V).

[0133] In addition, in response to a power outage in the commercial AC power supply 21, the control circuit 7A controls the bidirectional chopper 5A to supply DC power from the battery 22 to the inverter 8A, and the DC voltage VDC between the DC lines L1 and L2 becomes a specified reference DC voltage VDCr (e.g., 660V).

[0134] In addition, control circuit 7A stores information representing the relationship between DC current Ib, the time constant τ of temperature rise of capacitor C11 included in bidirectional chopper 5A, and the temperature rise saturation value Ts of capacitor C11. When commercial AC power supply 21 fails, control circuit 7A calculates the estimated temperature rise value Ta of capacitor C11 every predetermined time interval Δt based on DC power supply Ib and the stored information. If the calculated estimated temperature rise value Ta exceeds the upper limit value Th, the operation of bidirectional chopper 5A is stopped.

[0135] Inverter 8A, controlled by control circuit 14A, converts the DC power supplied from converter 3A or bidirectional chopper 5A via DC lines L1 and L2 into commercial frequency AC power for output. Specifically, when commercial AC power supply 21 is operating normally, inverter 8A converts the DC power supplied from converter 3A via DC lines L1 and L2 into AC power. Conversely, if commercial AC power supply 21 experiences a power outage, inverter 8A converts the DC power supplied from battery 22 via bidirectional chopper 5A into AC power. The AC output voltage of inverter 8A can be controlled to a desired value.

[0136] Figure 14 This is a circuit diagram showing the structure of the bidirectional chopper 5A, which is related to... Figure 2 A comparison chart. In Figure 14 In the bidirectional chopper 5A, there are IGBTs Q1 and Q2, diodes D1 and D2, reactor X1 and capacitor C11.

[0137] The collector of IGBT Q1 is connected to the high-voltage side node 5a. The emitter of IGBT Q1 is connected to the low-voltage side node 5d via reactor X1, and is also connected to the collector of IGBT Q2. The emitter of IGBT Q2 is connected to both the high-voltage side node 5b and the low-voltage side node 5e. Diodes D1 and D2 are connected in reverse parallel with IGBTs Q1 and Q2, respectively. Capacitor C11 is connected between the high-voltage side nodes 5a and 5b to stabilize the DC voltage VDC between them.

[0138] IGBT Q1 (the first switching element) turns on and off at a specified frequency when the commercial AC power supply 21 is operating normally, storing the DC power generated by converter 3A into battery 22. When the commercial AC power supply 21 is operating normally, IGBT Q2 is always in the off state.

[0139] IGBT Q1 is controlled by a strobe signal S1 from control circuit 7A. The strobe signal S1 is at a specified frequency between "H" and "L" levels. If the strobe signal S1 is at the "H" level, IGBT Q1 is turned on; if the strobe signal S1 is at the "L" level, IGBT Q1 is turned off.

[0140] When the commercial AC power supply 21 is working normally, if IGBT Q1 is turned on when VDC>VB, a current Ib flows through the path from DC line L1 through IGBT Q1, reactor X1 and battery 22 to DC line L2. The battery 22 is charged and the reactor X1 stores electromagnetic energy.

[0141] If IGBT Q1 is disconnected, current flows through the path from one terminal of reactor X1 (the terminal on the side of battery 22) through battery 22 and diode D2 to the other terminal of reactor X1, charging battery 22 and releasing electromagnetic energy of reactor X1.

[0142] The ratio of the time (pulse width) during which the gating signal S1 is at the "H" level to one cycle is called the duty cycle. By adjusting the duty cycle of the gating signal S1, the inter-terminal voltage VB of battery 22 can be adjusted to a specified reference DC voltage VBr. The DC voltage VDC between DC lines L1 and L2 is stepped down and supplied to battery 22, becoming VB. <VDC。

[0143] IGBT Q2 (second switching element) is switched on and off at a specified frequency in response to a power outage of commercial AC power supply 21, supplying DC power from battery 22 to inverter 8A.

[0144] IGBT Q2 is controlled by a strobe signal S2 from control circuit 7A. The strobe signal S2 is at a specified frequency between "H" and "L" levels. If the strobe signal S2 is at the "H" level, IGBT Q2 is turned on; if the strobe signal S2 is at the "L" level, IGBT Q2 is turned off.

[0145] If the AC power supply from the commercial AC power source 21 is stopped and the DC voltage VDC between DC lines L1 and L2 drops below the terminal voltage VB of battery 22, then IGBT Q1 remains in the off state, and IGBT Q2 begins to turn on and off.

[0146] When IGBT Q2 is turned on, current flows from the positive terminal of battery 22 through reactor X1 and IGBT Q2 to the negative terminal of battery 22, and reactor X1 stores electromagnetic energy. When IGBT Q2 is turned off, the current that originally flowed from reactor X1 to IGBT Q2 flows from reactor X1 to diode D1, through capacitor C11 to the negative terminal of battery 22, charging battery 22, and releasing the electromagnetic energy stored in reactor X1.

[0147] The ratio of the time (pulse width) during which the strobe signal S2 becomes the "H" level to one cycle is called the duty ratio. By adjusting the duty ratio of the strobe signal S2, the DC voltage VDC between the DC lines L1 and L2 can be adjusted to a specified reference DC voltage VDCR. The voltage VB between the terminals of the battery 22 is boosted and supplied between the DC lines L1 and L2, and VB < VDC.

[0148] The control circuit 7A detects whether a power outage has occurred in the commercial AC power supply 21 based on the output signal Ibf of the current detector 6. That is, if a power outage has occurred in the commercial AC power supply 21, the operation of the converter 3A stops, and DC power is supplied from the capacitor C3 to the inverter 8A, and the DC voltage VDC between the DC lines L1 and L2 decreases. If VDC = VB, even if the IGBT Q1 is turned on and off, current no longer flows through the IGBT Q1. If further VDC < VB, the current Ib flows from the positive electrode of the battery 22 through the reactor X1, the diode D1, and the capacitor C1 to the negative electrode of the battery 22.

[0149] Therefore, if a power outage has occurred in the commercial AC power supply 21, the polarity of the current Ib flowing from the low-voltage side node 5d of the bidirectional chopper 5A to the positive electrode of the battery 22 is reversed. If the polarity of the current Ib flowing from the low-voltage side node 5d of the bidirectional chopper 5A to the positive electrode of the battery 22 is set to negative, the control circuit 7A determines that a power outage has occurred in the commercial AC power supply 21 when the polarity of the current Ib changes from negative to positive. Other structures and operations are the same as those in the first embodiment, so the description thereof will not be repeated.

[0150] In the second embodiment, the same effects as those in the first embodiment are also obtained.

[0151] In addition, in the second embodiment, it is described that the capacitor C3 for stabilizing the output voltage of the converter 3A and the capacitor C11 for stabilizing the output voltage of the bidirectional chopper 5A are provided independently, but this is not limited thereto, and the same effects are also obtained when the capacitor C3 includes the capacitor C11. Among them, since the capacitor C3 includes a plurality of electrolytic capacitors connected in parallel, it is necessary to select the electrolytic capacitor 60 ( Figure 5 ) with the largest temperature rise among these electrolytic capacitors, and detect the internal temperature T1 and the ambient temperature T2 of the selected electrolytic capacitor 60.

[0152] It should be considered that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The present invention is represented by the claims, rather than by the above description, and intends to include all modifications within the meaning and scope equivalent to the claims.

[0153] Description of Reference Numerals

[0154] 1. 81: Uninterruptible power supply (UPS); 2. 6, 9: Current detectors; 3. 3A: Converter; L1~L3: DC circuits; C1~C3, C11, C12: Capacitors; 4. 4A, 7. 7A, 14, 14A: Control circuits; 5. 5A: Bidirectional chopper; 8. 8A: Inverter; 10. X1, X2: Reactors; 12, 13: Electromagnetic contactors; Q1~Q4: IGBTs; D1~D4: Diodes; X1, X2: Reactors; 21: Commercial AC power supply; 22: Battery; 23: Load; 3 1, 36: Reference voltage generation unit; 32, 39: Correction unit; 33, 37: Voltage detector; 34, 38: Subtractor; 35, 40: Voltage control unit; 41: Polarity determiner; 42: Discharge determiner; 43: PWM control unit; 51: Voltage determination unit; 52: Storage unit; 53: Arithmetic unit; 54: Temperature determination unit; 55: AND gate; 60: Electrolytic capacitor; 61, 62: Temperature sensor; 71: Triangle wave generator; 72, 73: Comparator; 74: Selector; 75, 76: Signal output circuit.

Claims

1. A power conversion device, comprising: A chopper converts a first DC voltage supplied from a DC power source into a second DC voltage, which is then supplied to the DC load. A capacitor that stabilizes the second DC voltage; A current detector that detects the output current of the DC power supply; as well as The control circuit, based on the detection results of the current detector, estimates the temperature rise of the capacitor at predetermined intervals, and stops the chopper from operating if the estimated temperature rise exceeds an upper limit. The control circuit includes: The storage unit stores information representing the relationship between the output current of the DC power supply, the time constant of the temperature rise of the capacitor, and the temperature rise saturation value of the capacitor. The arithmetic unit, based on the detection result of the current detector and the stored content of the storage unit, calculates an estimated value of the temperature rise of the capacitor every predetermined time interval; and The control unit controls the chopper to change the voltage between the terminals of the capacitor to a reference voltage when the estimated temperature rise is lower than the upper limit value, and stops the operation of the chopper when the estimated temperature rise is higher than the upper limit value.

2. The power conversion device according to claim 1, wherein, The DC power supply is a power storage device that stores DC power. When the voltage between the terminals of the power storage device drops to the discharge termination voltage, the control circuit also stops the operation of the chopper.

3. The power conversion device according to claim 2, wherein, The chopper and the capacitor together constitute a bidirectional chopper. The power conversion device also has: A forward converter, which converts AC power supplied from an AC power source into DC power; and An inverting converter converts the DC power supplied from the forward converter or the bidirectional chopper into AC power for supplying to an AC load. The inverter and the AC load constitute the DC load. When the AC power supply is working normally, the bidirectional chopper stores a portion of the DC power generated by the forward converter into the power storage device. When the AC power supply fails, the bidirectional chopper supplies the DC power from the power storage device to the reverse converter.

4. The power conversion device according to claim 3, wherein, The capacitor includes a first secondary capacitor and a second secondary capacitor connected in series. The bidirectional chopper includes: A first switching element and a second switching element are connected in series between the positive and negative terminals of the first secondary capacitor; A third and a fourth switching element are connected in series between the positive and negative terminals of the second secondary capacitor; The first diode and the fourth diode are respectively connected in reverse parallel with the first switching element to the fourth switching element; A first reactor connected between the positive terminal of the power storage device and the first node between the first switching element and the second switching element; and A second reactor connected between the second node between the third and fourth switching elements and the negative terminal of the power storage device. When the AC power supply is operating normally, the control circuit connects and disconnects the first and fourth switching elements. When the AC power supply fails, the control circuit connects and disconnects the second and third switching elements. When the operation of the bidirectional chopper is stopped, the control circuit disconnects the first to the fourth switching elements.

5. The power conversion device according to claim 3, wherein, The bidirectional chopper includes: A first switching element and a second switching element are connected in series between the positive and negative terminals of the capacitor; The first diode and the second diode are respectively connected in reverse parallel with the first switching element and the second switching element; and A reactor connected between the positive terminal of the power storage device and the node between the first switching element and the second switching element. When the AC power supply is operating normally, the control circuit turns the first switching element on and off. When the AC power supply fails, the control circuit switches the second switching element on and off. When the operation of the bidirectional chopper is stopped, the first switching element and the second switching element are disconnected.

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