Uninterruptible power supply device

Abstract

In an uninterruptible power supply (UPS) device, during the switching from bypass power supply mode to inverter power supply mode, the inverter (3) is activated by turning on the semiconductor switch (6), turning off the first electromagnetic contactor (5), and turning on the second electromagnetic contactor (4), thereby initiating the superimposed power supply mode and turning off the semiconductor switch to end the superimposed power supply mode. Therefore, the superimposed power supply mode can be ended in a short time, thus minimizing the rise in the inter-terminal voltage (VDC) of the capacitor (Cd) and preventing the inter-terminal voltage of the capacitor from exceeding the upper limit voltage (VDCH).

Description

Technical Field

[0001] This invention relates to uninterruptible power supply (UPS) devices, and more particularly to a UPS device comprising: a bypass power supply mode, supplying AC power from a bypass AC power source to a load; an inverter power supply mode, supplying AC power from an inverter to a load; and a superimposed power supply mode, supplying AC power from both the bypass AC power source and the inverter to the load. Background Technology

[0002] For example, Japanese Patent No. 6533357 (Patent Document 1) discloses an uninterruptible power supply (UPS) device having a bypass power supply mode, an inverter power supply mode, and a superimposed power supply mode. This UPS device includes: a first switch, one terminal of which receives a first AC voltage supplied from a bypass AC power source, and the other terminal of which is connected to a load; a rectifier, which converts a second AC voltage supplied from an industrial AC power source into a DC voltage; a capacitor, which smooths the DC output voltage of the rectifier; an inverter, which converts the voltage between the terminals of the capacitor into a third AC voltage; a second switch, one terminal of which receives the third AC voltage, and the other terminal of which is connected to a load; and a control device.

[0003] In bypass power supply mode, the control device turns on the first switch and turns off the second switch. Furthermore, in inverter power supply mode, the control device turns off the first switch and turns on the second switch. Moreover, in superimposed power supply mode, the control device turns on both the first and second switches. Superimposed power supply mode is executed during the switching process between the bypass power supply mode and the inverter power supply mode, where the power supply mode is changed to the other.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6533357 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] Typically, in such uninterruptible power supply (UPS) devices, the capacitor's terminal voltage is maintained at the reference voltage by allowing an alternating current, including a feedback component that corresponds to the deviation between the reference voltage and the capacitor's terminal voltage, to flow from the industrial AC power supply to the rectifier. In this method, to maintain the capacitor's terminal voltage at the reference voltage even under sudden changes in load current, the feedback component needs to be controlled at high speed. However, high-speed control of the feedback component leads to instability in the control process.

[0009] As a countermeasure, the following method can be considered: by allowing an AC current, including a feedback component and a feedforward component corresponding to the load current, to flow from the industrial AC power supply to the rectifier, the voltage between the capacitor terminals can be maintained at a reference voltage. According to this method, control stabilization can be achieved by controlling the feedback component at a low speed, and by introducing the feedforward component, sudden changes in load current can be addressed.

[0010] However, in this method, during the superimposed power supply mode, if the load current is supplied from both the bypass AC power source and the inverter, the rectifier output becomes larger compared to the inverter output, leading to a problem of increased inter-terminal voltage across the capacitors. During the switch from bypass power supply mode to inverter power supply mode, if the inter-terminal voltage across the capacitors exceeds the upper limit voltage, the inverter operation is stopped, and the load operation is also stopped.

[0011] Therefore, the main objective of this invention is to provide an uninterruptible power supply device that can minimize the rise in voltage between capacitor terminals during the switching from a first mode to a second mode.

[0012] Methods for solving problems

[0013] The uninterruptible power supply (UPS) device of the present invention comprises a first electromagnetic contactor, a semiconductor switch, a rectifier, a capacitor, an inverter, a second electromagnetic contactor, and a control device. The first terminal of the first electromagnetic contactor receives a first AC voltage supplied from a first AC power source, and its second terminal is connected to a load. The semiconductor switch is connected in parallel with the first electromagnetic contactor. The rectifier converts a second AC voltage supplied from a second AC power source into a DC voltage. The capacitor smooths the DC output voltage of the rectifier. The inverter converts the voltage between the terminals of the capacitor into a third AC voltage. The first terminal of the second electromagnetic contactor receives the third AC voltage, and its second terminal is connected to the load. The control device controls the UPS device.

[0014] In a first mode, when supplying a first AC voltage to the load, the control device turns on the first electromagnetic contactor and turns off the semiconductor switch and the second electromagnetic contactor. Furthermore, in a second mode, when supplying a third AC voltage to the load, the control device turns off the first electromagnetic contactor and the semiconductor switch and turns on the second electromagnetic contactor. Moreover, during the switching from the first mode to the second mode, the control device turns on the semiconductor switch and the second electromagnetic contactor, turns off the first electromagnetic contactor, activates the inverter, and then turns off the semiconductor switch.

[0015] Invention Effects

[0016] In the uninterruptible power supply device of the present invention, during the switching from the first mode to the second mode, the superimposed power supply mode is initiated by activating the inverter after the semiconductor switch and the second electromagnetic contactor are turned on and the first electromagnetic contactor is turned off, and the superimposed power supply mode is terminated by turning off the semiconductor switch. Therefore, the superimposed power supply mode can be terminated in a short time, thus minimizing the rise in the voltage between the capacitor terminals and preventing the voltage between the capacitor terminals from exceeding the upper limit voltage. Attached Figure Description

[0017] Figure 1 This is a circuit block diagram illustrating the configuration of an uninterruptible power supply device according to one embodiment of the present invention.

[0018] Figure 2 It means Figure 1 The circuit diagram shown illustrates the configuration of a semiconductor switch.

[0019] Figure 3 It means Figure 1 The circuit diagram shown illustrates the configuration of the converter and inverter.

[0020] Figure 4 It means Figure 1 The diagram shown is an equivalent circuit diagram of an industrial AC power supply.

[0021] Figure 5 It means Figure 1 The equivalent circuit diagram of the bypass AC power supply shown is shown.

[0022] Figure 6 It means Figure 4 The three-phase AC voltage of the industrial AC power supply shown is... Figure 5 The diagram shows the relationship between the three-phase AC voltages of the bypass AC power supply.

[0023] Figure 7 It is a circuit block diagram used to illustrate the circulating current flowing in the superimposed power supply mode.

[0024] Figure 8 This is another circuit block diagram used to illustrate the circulating current flowing in the superimposed power supply mode.

[0025] Figure 9 This is a circuit block diagram used to illustrate the problems in the superimposed power supply mode.

[0026] Figure 10 It is a circuit block diagram that shows the operation of the uninterruptible power supply device during the switching from bypass power supply mode to inverter power supply mode.

[0027] Figure 11This is another circuit block diagram representing the operation of the uninterruptible power supply device during the switching from bypass power supply mode to inverter power supply mode.

[0028] Figure 12 It means Figure 1 The circuit block diagram shown illustrates the components of the control device related to the control of the electromagnetic contactor and semiconductor switch.

[0029] Figure 13 It means Figure 1 The diagram shows the configuration of the parts related to the control of the converter in the control device.

[0030] Figure 14 It means Figure 1 The diagram shows the block diagram of the components related to the control of the inverter in the control device.

[0031] Figure 15 This is a timing diagram showing the operation of control device 8 during the switching from bypass power supply mode to inverter power supply mode.

[0032] Figure 16 This is a circuit block diagram illustrating a comparative example of the implementation method.

[0033] Figure 17 These are other circuit block diagrams illustrating comparative examples of implementation methods.

[0034] Figure 18 This is a timing diagram showing a comparative example of the implementation method. Detailed Implementation

[0035] Figure 1 This is a circuit block diagram illustrating the configuration of an uninterruptible power supply device according to one embodiment of the present invention. Figure 1 The uninterruptible power supply device includes capacitors C1 to C6 and Cd, reactors L1 to L6, current detectors CT1 to CT6, converter 1, DC positive bus Lp, DC negative bus Ln, bidirectional chopper 2, inverter 3, electromagnetic contactors 4 and 5, semiconductor switch 6, operation unit 7, and control device 8.

[0036] The uninterruptible power supply (UPS) receives three-phase AC power at the industrial frequency from the industrial AC power source 11 and the bypass AC power source 12, and supplies three-phase AC power at the industrial frequency to the load 13. The industrial AC power source 11 (second AC power source) outputs three-phase AC voltages Vu1, Vv1, and Vw1 (second AC voltages) to the AC output terminals 11a to 11c, respectively. The neutral point terminal 11d of the industrial AC power source 11 receives the ground voltage GND.

[0037] The instantaneous values ​​of the three-phase AC voltages Vu1, Vv1, and Vw1 are detected by the control device 8. Based on the AC output voltages Vu1, Vv1, and Vw1 of the industrial AC power supply 11, the control device 8 detects whether a power outage has occurred in the industrial AC power supply 11.

[0038] The bypass AC power supply 12 (first AC power supply) outputs three-phase AC voltages Vu2, Vv2, and Vw2 (first AC voltages) to AC output terminals 12a-12c, respectively. The neutral point terminal 12d of the bypass AC power supply 12 receives the ground voltage GND. The bypass AC power supply 12 is a household generator. The instantaneous values ​​of the three-phase AC voltages Vu2, Vv2, and Vw2 are detected by the control device 8. The AC input terminals 13a-13c of the load 13 receive three-phase AC voltage from the uninterruptible power supply (UPS). The load 13 is driven by three-phase AC power supplied by the UPS.

[0039] The first electrodes of capacitors C1 to C3 are connected to the AC output terminals 11a to 11c of the industrial AC power supply 11, and their second electrodes are connected to each other. The first terminals of reactors L1 to L3 are connected to the AC output terminals 11a to 11c of the industrial AC power supply 11, and their second terminals are connected to the three input nodes of converter 1, respectively.

[0040] Capacitors C1-C3 and reactors L1-L3 constitute AC filter F1. AC filter F1 is a low-pass filter that allows industrial frequency AC current to flow from industrial AC power supply 11 to converter 1, preventing switching frequency signals from flowing from converter 1 to industrial AC power supply 11. Current detectors CT1-CT3 detect the AC current I1-I3 flowing through reactors L1-L3 respectively, and provide signals representing the detected values ​​to control device 8.

[0041] The positive output node of converter 1 is connected to the positive input node of inverter 3 via the DC positive bus Lp. The negative output node of converter 1 is connected to the negative input node of inverter 3 via the DC negative bus Ln. A capacitor Cd is connected between buses Lp and Ln to smooth the DC voltage VDC between buses Lp and Ln. The instantaneous value of the DC voltage VDC is detected by control device 8.

[0042] The converter 1 is controlled by the control device 8 and converts the three-phase AC power from the industrial AC power source 11 into DC power when the industrial AC power source 11 is normally supplied with three-phase AC power (when the industrial AC power source 11 is normal). The DC power generated by the converter 1 is supplied to the bidirectional chopper 2 and the inverter 3 via buses Lp and Ln.

[0043] When the supply of three-phase AC power from industrial AC power source 11 is interrupted (when industrial AC power source 11 is de-energized), the operation of converter 1 stops. AC filter F1 and converter 1 correspond to one embodiment of a "rectifier" that converts three-phase AC power from industrial AC power source 11 into DC power. Current detectors CT1 to CT3 correspond to one embodiment of a "first current detector" that detects the AC current flowing from industrial AC power source 11 to the rectifier.

[0044] The bidirectional chopper 2 is controlled by the control device 8. When the industrial AC power supply 11 is normal, the DC power generated by the converter 1 is stored in battery B1. In the event of a power outage in the industrial AC power supply 11, the DC power from battery B1 is supplied to the inverter 3 via buses Lp and Ln. The instantaneous value of the inter-terminal voltage VB of battery B1 is detected by the control device 8.

[0045] Inverter 3, controlled by control device 8, converts the DC power supplied from converter 1 and bidirectional chopper 2 into three-phase AC power at industrial frequency. Electromagnetic contactor 4 includes three switches S1 to S3. These three switches S1 to S3 are controlled by control device 8 and are simultaneously turned on and off. Electromagnetic contactor 4 corresponds to one embodiment of the "second electromagnetic contactor".

[0046] The three output nodes of inverter 3 are connected to the first terminals of reactors L4 to L6, respectively. The second terminals of reactors L4 to L6 are connected to the first terminals of switches S1 to S3, respectively. The second terminals of switches S1 to S3 (nodes N1 to N3) are connected to the three AC input terminals 13a to 13c of load 13, respectively. The first electrodes of capacitors C4 to C6 are connected to the second terminals of reactors L4 to L6, respectively. The second electrodes of capacitors C4 to C6 are all connected to the second electrodes of capacitors C1 to C3.

[0047] Capacitors C4-C6 and reactors L4-L6 constitute AC filter F2. AC filter F2 is a low-pass filter that allows industrial frequency AC current to flow from inverter 3 to load 13, preventing switching frequency signals from flowing from inverter 3 to load 13. In other words, AC filter F2 converts the three-phase rectangular wave voltage output from inverter 3 into sinusoidal three-phase AC voltages Va, Vb, and Vc.

[0048] Inverter 3 and AC filter F2 correspond to one embodiment of an "inverter" that converts the inter-terminal voltage VDC of capacitor Cd into three-phase AC voltages Va to Vc. The instantaneous values ​​of the three-phase AC voltages Va to Vc are detected by control device 8.

[0049] The electromagnetic contactor 5 includes three switches S4 to S6. The three switches S4 to S6 are controlled by the control device 8 and are simultaneously turned on and off. The first terminals of switches S4 to S6 are respectively connected to the AC output terminals 12a to 12c of the bypass AC power supply 12, and their second terminals are respectively connected to the second terminals (nodes N1 to N3) of switches S1 to S3. Electromagnetic contactor 5 corresponds to one embodiment of the "first electromagnetic contactor".

[0050] Figure 2 This is a circuit diagram showing the configuration of semiconductor switch 6. Figure 2 In this embodiment, semiconductor switch 6 includes three thyristor switches S7 to S9. Thyristor switches S7 to S9 are connected in parallel with switches S4 to S6 of electromagnetic contactor 5, respectively. Each thyristor switch S7 to S9 includes a pair of thyristors connected in parallel in opposite directions. Thyristor switches S7 to S9 are controlled by control device 8 and are simultaneously turned on and off. Semiconductor switch 6 corresponds to one embodiment of a "semiconductor switch".

[0051] Furthermore, electromagnetic contactors 4 and 5 have the advantage of being inexpensive even with high rated current, but have the disadvantage of a long response time (around 100 milliseconds). In contrast, semiconductor switch 6 has the advantage of a short response time (below 10 milliseconds), but has the disadvantage of being expensive with a high rated current.

[0052] Therefore, in uninterruptible power supply (UPS) devices, electromagnetic contactors 4 and 5 with large rated current and semiconductor switches 6 with small rated current are typically used. Electromagnetic contactors 4 and 5 are used to conduct load current for extended periods, while semiconductor switches 6 are used to conduct load current only for short periods. Even with semiconductor switches 6 having small rated current, they can still conduct load current for short periods.

[0053] Refer again Figure 1 Current detector CT4 detects the AC current I4 flowing between node N1 and AC input terminal 13a of load 13, and provides a signal indicating the detected value to control device 8. Current detector CT5 detects the AC current I5 flowing between node N2 and AC input terminal 13b of load 13, and provides a signal indicating the detected value to control device 8. Current detector CT6 detects the AC current I6 flowing between node N3 and AC input terminal 13c of load 13, and provides a signal indicating the detected value to control device 8. Current detectors CT4 to CT6 correspond to one embodiment of a "second current detector" for detecting load currents I4 to I6.

[0054] The operation unit 7 includes multiple buttons operated by the user of the uninterruptible power supply (UPS), an image display unit for displaying various information, etc. By operating the operation unit 7, the user can turn the UPS on and off, or select either the bypass power supply mode or the inverter power supply mode.

[0055] The control device 8 controls the entire uninterruptible power supply based on signals from the operation unit 7, the AC output voltages Vu1, Vv1, and Vw1 of the industrial AC power supply 11, the AC input currents I1 to I3, the terminal voltage VDC of the capacitor Cd, the terminal voltage VB of the battery B1, the load currents I4 to I6, the AC output voltages Va to Vc of the inverter 3, and the AC output voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12.

[0056] That is, in the bypass power supply mode (first mode) where three-phase AC power from the bypass AC power supply 12 is supplied to the load 13, the control device 8 deactivates the inverter 3, disconnects the electromagnetic contactors 4 (i.e., switches S1 to S3) and the semiconductor switches 6 (i.e., thyristor switches S7 to S8), and connects the electromagnetic contactors 5 (i.e., switches S4 to S6). In this case, three-phase AC power is supplied from the bypass AC power supply 12 to the load 13 via the electromagnetic contactors 5.

[0057] In the inverter power supply mode (second mode) where the three-phase AC power generated by inverter 3 is supplied to load 13, control device 8 activates inverter 3, connects electromagnetic contactor 4, and disconnects electromagnetic contactor 5 and semiconductor switch 6. In this case, three-phase AC power is supplied from inverter 3 to load 13 via AC filter F2 and electromagnetic contactor 4.

[0058] In the event of a fault in inverter 3 during inverter power supply mode, control device 8 connects semiconductor switch 6 and electromagnetic contactor 5, disconnects electromagnetic contactor 4, and then disconnects semiconductor switch 6.

[0059] In this scenario, if inverter 3 malfunctions, the short-response semiconductor switch 6 is instantly switched on, supplying three-phase AC power from bypass AC power supply 12 to load 13 via semiconductor switch 6. Then, if the long-response electromagnetic contactor 5 is switched on, three-phase AC power is supplied from bypass AC power supply 12 to load 13 via the parallel connection of electromagnetic contactor 5 and semiconductor switch 6.

[0060] If electromagnetic contactor 5 is turned on, semiconductor switch 6 is turned off, and three-phase AC power is supplied from bypass AC power supply 12 to load 13 via electromagnetic contactor 5. Semiconductor switch 6 is turned on only briefly to allow the load current to flow, causing it to heat up and preventing damage.

[0061] Furthermore, during the switching from bypass power supply mode to inverter power supply mode, the control device 8 turns on the semiconductor switch 6 and the electromagnetic contactor 4, turns off the electromagnetic contactor 5, activates the inverter 3, and then turns off the semiconductor switch 6.

[0062] If inverter 3 is activated, three-phase AC power is supplied from inverter 3 to load 13 via AC filter F2 and electromagnetic contactor 4, and three-phase AC power is also supplied from bypass AC power supply 12 to load 13 via semiconductor switch 6, executing the superimposed power supply mode. If semiconductor switch 6 is deactivated, the power supply from bypass AC power supply 12 is stopped (i.e., the superimposed power supply mode is stopped), and inverter power supply mode is executed.

[0063] Therefore, compared to the past, the time of the superimposed power supply mode can be shortened, and the rise of the inter-terminal voltage VDC of capacitor Cd during switching can be minimized. This will be explained in detail later.

[0064] Furthermore, during the switching from inverter power supply mode to bypass power supply mode, control device 8 turns on electromagnetic contactor 5, turns off electromagnetic contactor 4, and then deactivates inverter 3.

[0065] If electromagnetic contactor 5 is turned on, three-phase AC power is supplied from inverter 3 to load 13 via AC filter F2 and electromagnetic contactor 4, and three-phase AC power is also supplied from bypass AC power supply 12 to load 13 via electromagnetic contactor 5, executing the superimposed power supply mode. If electromagnetic contactor 4 is turned off, the power supply from inverter 3 is stopped (i.e., the superimposed power supply mode is stopped), and the bypass power supply mode is executed.

[0066] In this case, even if the voltage VDC between the terminals of capacitor Cd rises and exceeds the upper limit voltage VDCH and the operation of inverter 3 is stopped in the superimposed power supply mode, there is no problem because the power supply to load 13 continues from the bypass AC power supply 12.

[0067] Furthermore, the control device 8 controls the converter 1 based on the AC input currents I1 to I3, the inter-terminal voltage VDC of capacitor Cd, and the load currents I4 to I6. In inverter power supply mode and bypass power supply mode, the control device 8 uses the inter-terminal voltage VDC of capacitor Cd as the reference voltage VDCr1 (first reference voltage) to make the three-phase AC currents I1 to I3 flow from the industrial AC power supply 11 to the converter 1. The three-phase AC currents I1 to I3 include a feedback component IFB corresponding to the deviation ΔVDC = VDCr1 - VDC between the reference voltage VDCr1 and the inter-terminal voltage VDC of capacitor Cd, and a feedforward component IFF obtained by multiplying the load currents I4 to I6 by a gain Kf (e.g., 1.0).

[0068] The purpose of directing the three-phase AC currents I1 to I3, including the feedforward component IFF (obtained by multiplying the load currents I4 to I6 by the gain Kf), to converter 1 is to improve the response speed of converter 1 to changes in the load currents I4 to I6. By introducing this feedforward component IFF, the feedback component IFB can be controlled at a low speed, thereby achieving control stabilization.

[0069] Furthermore, during the switching from either the inverter power supply mode or the bypass power supply mode to the other, the control device 8 causes the three-phase AC currents I1 to I3 to flow from the industrial AC power supply 11 to the converter 1 in such a way that the inter-terminal voltage VDC of the capacitor Cd becomes a reference voltage VDCr2 (second reference voltage) that is higher than the reference voltage VDCr1. The three-phase AC currents I1 to I3 include a feedback component IFB corresponding to the deviation ΔVDC = VDCr2 - VDC between the reference voltage VDCr2 and the inter-terminal voltage VDC of the capacitor Cd, and a feedforward component IFF obtained by multiplying the load currents I4 to I6 by the gain Kf.

[0070] During switching, the converter 1 is controlled such that the inter-terminal voltage VDC of capacitor Cd becomes a reference voltage VDCr2 that is higher than the reference voltage VDCr1 in order to prevent circulating current from flowing between the industrial AC power supply 11 and the bypass AC power supply 12.

[0071] The reference voltage VDCr1 is set to a voltage lower than twice the peak value of the three-phase AC voltages Vu1, Vv1, and Vw1 of the industrial AC power supply 11. The reference voltage VDCr2 is set to a voltage greater than or equal to twice the peak value of the three-phase AC voltages Vu1, Vv1, and Vw1 of the industrial AC power supply 11. The relationship between the reference voltages VDCr1 and VDCr2 and the circulating current is explained in detail below. Figures 3-8 ).

[0072] Furthermore, when the industrial AC power supply 11 is normal, the control device 8 controls the bidirectional chopper 2 with the terminal voltage VB of battery B1 as the reference voltage VBr. When the industrial AC power supply 11 is de-energized, the control device 8 controls the bidirectional chopper 2 with the terminal voltage VDC of capacitor Cd as the reference voltage VDCr1. Moreover, the control device 8 controls the inverter 3 in a synchronized manner with the AC output voltages Va to Vc of the inverter 3 and the AC output voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12.

[0073] Next, the reasons for the rise of the inter-terminal voltage VDC of capacitor Cd in such an uninterruptible power supply device during superimposed power supply mode and the means to suppress the rise of this DC voltage VDC will be explained in detail.

[0074] In the superimposed power supply mode, if power is supplied to the load 13 from both the inverter 3 and the bypass AC power supply 12, the load of the bypass AC power supply 12, which acts as a household generator, will change abruptly, and the frequency and phase of the output voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12 will change.

[0075] If the frequency and phase of the output voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12 change, the circulating current IC flows from the AC power supply of either the industrial AC power supply 11 or the bypass AC power supply 12 through the capacitor Cd to the AC power supply of the other. The circulating current IC charges the capacitor Cd, causing the DC voltage VDC to rise.

[0076] In this embodiment, as a countermeasure, the circulating current IC is reduced by setting the reference voltage VDCr2 during the switching between bypass power supply mode and inverter power supply mode to a higher voltage than the reference voltage VDCr1 during both bypass power supply mode and inverter power supply mode.

[0077] Furthermore, in the superimposed power supply mode, if the feedforward component IFF, obtained by multiplying the load currents I4 to I6 by the gain Kf, flows to converter 1, the input current of converter 1 becomes larger than the output current of inverter 3, and the DC voltage VDC rises. If the duration of the superimposed power supply mode is longer, the increase in DC voltage VDC becomes larger.

[0078] In this embodiment, as a countermeasure, the semiconductor switch 6 and the electromagnetic contactor 4 are turned on, the electromagnetic contactor 5 is turned off, the inverter 3 is activated, and then the semiconductor switch 6 is turned off, thereby shortening the time of the superimposed power supply mode and suppressing the rise of the DC voltage VDC.

[0079] First, the reasons for the circulating current IC flowing in the superimposed power supply mode and the countermeasures are explained in detail. Figure 3 This is a circuit diagram showing the configuration of converter 1 and inverter 3. Figure 3 In this converter 1, there are IGBTs (Insulated Gate Bipolar Transistors) Q1 to Q6 and diodes D1 to D6. The IGBTs constitute the switching elements. The collectors of IGBTs Q1 to Q3 are all connected to the DC positive bus Lp, and their emitters are connected to the input nodes 1a, 1b, and 1c, respectively.

[0080] Input nodes 1a, 1b, and 1c are respectively connected to reactors L1 to L3 ( Figure 1 The other terminal of the IGBT is connected. The collectors of IGBTs Q4 to Q6 are connected to input nodes 1a, 1b, and 1c, respectively, and their emitters are all connected to the DC negative bus Ln. Diodes D1 to D6 are connected in reverse parallel with IGBTs Q1 to Q6, respectively.

[0081] IGBTs Q1 and Q4 are controlled by gate signals A1 and B1, respectively; IGBTs Q2 and Q5 are controlled by gate signals A2 and B2, respectively; and IGBTs Q3 and Q6 are controlled by gate signals A3 and B3, respectively. Gate signals B1, B2, and B3 are the inversions of gate signals A1, A2, and A3, respectively.

[0082] IGBTs Q1 through Q3 are turned on when gate signals A1, A2, and A3 are set to "H" level, and turned off when gate signals A1, A2, and A3 are set to "L" level. IGBTs Q4 through Q6 are turned on when gate signals B1, B2, and B3 are set to "H" level, and turned off when gate signals B1, B2, and B3 are set to "L" level.

[0083] Gate signals A1, B1, A2, B2, A3, and B3 are pulse signal trains, which are PWM (Pulse Width Modulation) signals. The phases of gate signals A1 and B1, A2 and B2, and A3 and B3 are approximately 120 degrees apart. Gate signals A1, B1, A2, B2, A3, and B3 are generated by control device 8.

[0084] By using gate signals A1, B1, A2, B2, A3, and B3, IGBTs Q1 to Q6 are turned on and off at specified timings. By adjusting the turn-on times of IGBTs Q1 to Q6, the three-phase AC voltage supplied to input nodes 6a to 6c can be converted into the desired DC voltage VDC (the voltage between the terminals of capacitor Cd).

[0085] Inverter 3 includes IGBTs Q11-Q16 and diodes D11-D16. The IGBTs constitute the switching elements. The collectors of IGBTs Q11-Q13 are all connected to the DC positive bus Lp, and their emitters are connected to output nodes 3a, 3b, and 3c, respectively. Output nodes 3a, 3b, and 3c are connected to reactors L4-L6, respectively. Figure 1 The first terminal of the IGBT is connected. The collectors of IGBTs Q14 to Q16 are connected to output nodes 3a, 3b, and 3c, respectively, and their emitters are all connected to the DC negative bus Ln. Diodes D11 to D16 are connected in reverse parallel with IGBTs Q11 to Q16, respectively.

[0086] IGBTs Q11 and Q14 are controlled by gate signals X1 and Y1, respectively; IGBTs Q12 and Q15 are controlled by gate signals X2 and Y2, respectively; and IGBTs Q13 and Q16 are controlled by gate signals X3 and Y3, respectively. Gate signals Y1, Y2, and Y3 are the inversion signals of gate signals X1, X2, and X3, respectively.

[0087] IGBTs Q11 through Q13 are turned on when gate signals X1, X2, and X3 are set to "H" level, and turned off when gate signals X1, X2, and X3 are set to "L" level. IGBTs Q14 through Q16 are turned on when gate signals Y1, Y2, and Y3 are set to "H" level, and turned off when gate signals Y1, Y2, and Y3 are set to "L" level.

[0088] Gate signals X1, Y2, X3, Y1, X2, Y3 are a pulse signal train, which is a PWM signal. The phases of gate signals X1 and Y1, the phases of gate signals X2 and Y2, and the phases of gate signals X3 and Y3 are approximately 120 degrees apart. Gate signals X1, Y1, X2, Y2, X3, Y3 are generated by control device 8.

[0089] For example, if IGBTs Q11 and Q15 are turned on, the DC positive bus Lp is connected to the output node 3a via IGBT Q11, and the output node 3b is connected to the DC negative bus Ln via IGBT Q15, resulting in a positive voltage output between output nodes 3a and 3b.

[0090] Furthermore, if IGBTs Q12 and Q14 are turned on, the positive DC bus Lp is connected to the output node 3b via IGBT Q12, and the output node 3a is connected to the negative DC bus Ln via IGBT Q14, resulting in a negative voltage output between output nodes 3a and 3b.

[0091] The gate signals X1, Y1, X2, Y2, X3, and Y3 enable IGBTs Q11 to Q16 to be turned on and off at specified time intervals, and the turn-on time of each IGBT Q11 to Q16 is adjusted, thereby converting the DC voltage VDC between the bus Lp and Ln into three-phase AC voltages Va, Vb, and Vc.

[0092] Figure 4 This is an equivalent circuit diagram showing the configuration of the industrial AC power supply 11. Figure 4 In this embodiment, the industrial AC power supply 11 includes three-phase AC power supplies 11U, 11V, and 11W connected in a star (Y) configuration relative to the neutral point terminal 11d. AC power supply 11U is connected between AC output terminal 11a and neutral point terminal 11d, outputting AC voltage Vu1 to AC output terminal 11a. AC power supply 11V is connected between AC output terminal 11b and neutral point terminal 11d, outputting AC voltage Vv1 to AC output terminal 11b. AC power supply 11W is connected between AC output terminal 11c and neutral point terminal 11d, outputting AC voltage Vw1 to AC output terminal 11c.

[0093] AC voltages Vu1, Vv1, and Vw1 vary sinusoidally at an industrial frequency (e.g., 60Hz). The peak values ​​(√2 ​​times the effective value) of AC voltages Vu1, Vv1, and Vw1 are the same, and their phases are staggered by 120 degrees. AC power supplies 11U, 11V, and 11W correspond, for example, to the three-phase windings of the final stage of a three-phase transformer in the final stage of an industrial AC power supply 11.

[0094] Figure 5 This is an equivalent circuit diagram showing the configuration of the bypass AC power supply 12. Figure 5 In this configuration, the bypass AC power supply 12 includes three-phase AC power supplies 12U, 12V, and 12W connected in a star configuration relative to the neutral point terminal 12d. AC power supply 12U is connected between AC output terminal 12a and neutral point terminal 12d, outputting AC voltage Vu2 to AC output terminal 12a. AC power supply 12V is connected between AC output terminal 12b and neutral point terminal 12d, outputting AC voltage Vv2 to AC output terminal 12b. AC power supply 12W is connected between AC output terminal 12c and neutral point terminal 12d, outputting AC voltage Vw2 to AC output terminal 12c.

[0095] The AC voltages Vu2, Vv2, and Vw2 vary sinusoidally at industrial frequencies. The peak values ​​of Vu2, Vv2, and Vw2 are the same, but their phases are staggered by 120 degrees. AC power supplies of 12U, 12V, and 12W correspond, for example, to the three-phase coils of a household generator.

[0096] In both inverter power supply mode and bypass power supply mode, the phases (and peak values) of the AC voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12 are consistent with the phases (and peak values) of the AC voltages Vu1, Vv1, and Vw1 of the industrial AC power supply 11, respectively. In this state, no circulating current IC flows in the uninterruptible power supply device.

[0097] However, in the superimposed power supply mode where AC power is supplied to the load 13 from both the inverter 3 and the bypass AC power supply 12, the load current of the bypass AC power supply 12 fluctuates significantly, causing changes in the phase and peak value of the AC voltages Vu2, Vv2, and Vw2. Therefore, the AC voltages Vu2, Vv2, and Vw2 are inconsistent with the AC voltages Vu1, Vv1, and Vw1, respectively.

[0098] Figure 6 (A) to (C) are diagrams showing the relationship between the AC voltages Vu1, Vv1, and Vw1 of the industrial AC power supply 11 and the AC voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12. The AC voltages Vu1, Vv1, Vw1, Vu2, Vv2, and Vw2 are displayed as vectors. The phases of AC voltages Vu1, Vv1, and Vw1 are each staggered by 120 degrees, and the phases of AC voltages Vu2, Vv2, and Vw2 are each staggered by 120 degrees. Figure 6 (A) shows the cases where the phases of AC voltages Vu2, Vv2, and Vw2 are in line with the phases of AC voltages Vu1, Vv1, and Vw1, respectively.

[0099] Figure 6 (B) illustrates the cases where the phases of AC voltages Vu2, Vv2, and Vw2 are delayed by 60 degrees compared to the phases of AC voltages Vu1, Vv1, and Vw1, respectively. For example, the phase of AC voltage Vu1 is 180 degrees out of phase with AC voltage Vw2. When AC voltage Vu1 has a positive peak value and AC voltage Vw2 has a negative peak value, the voltage difference between AC voltages Vu1 and Vw2, ΔV12 = Vu1 - Vw2, becomes the sum of the peak values ​​of AC voltages Vu1 and Vw2. Conversely, when AC voltage Vu1 has a negative peak value and AC voltage Vw2 has a positive peak value, the voltage difference between AC voltage Vw2 and AC voltage Vu1, ΔV21 = Vw2 - Vu1, becomes the sum of the peak values ​​of AC voltages Vu1 and Vw2.

[0100] Figure 6(C) illustrates the cases where the phases of AC voltages Vu2, Vv2, and Vw2 lead the phases of AC voltages Vu1, Vv1, and Vv2 by 60 degrees, respectively. For example, the phase of AC voltage Vu1 is 180 degrees out of phase with AC voltage Vv2. When AC voltage Vu1 has a positive peak value and AC voltage Vv2 has a negative peak value, the voltage difference between AC voltages Vu1 and Vv2, ΔV12 = Vu1 - Vv2, becomes the sum of the peak values ​​of AC voltages Vu1 and Vv2. Conversely, when AC voltage Vu1 has a negative peak value and AC voltage Vv2 has a positive peak value, the voltage difference between AC voltages Vv2 and Vu1, ΔV21 = Vv2 - Vu1, becomes the sum of the peak values ​​of AC voltages Vu1 and Vv2.

[0101] If, during the superposition period, the voltage VDC across the terminals of capacitor Cd is less than the sum of the peak values ​​of AC voltages Vu1, Vv1, Vw1 and the peak values ​​of AC voltages Vu2, Vv2, Vw2, the following problem occurs. For example, as... Figure 6 As shown in (B), when the phases of AC voltages Vu1 and Vw2 are shifted by 180 degrees, and the voltage difference ΔV12 = Vu1 - Vw2 becomes the sum of the peak values ​​of AC voltages Vu1 and Vw2, then... Figure 7 The circulating current IC flows through the path shown.

[0102] That is, from the first terminal (AC output terminal 11a) of the AC power supply 11U via the input node 1a of the converter 1, diode D1 ( Figure 3 DC positive bus Lp, capacitor Cd, DC negative bus Ln, diode D16 ( Figure 3 The circulating current IC flows through the path from the output node 3c of inverter 3, AC power supply 12W, neutral point terminal 12d, ground voltage GND, and neutral point terminal 11d to the other terminal of AC power supply 11U. Additionally, in Figure 7 To simplify the accompanying drawings and explanations, the illustrations of filters F1 and F2, and the switched switches S1 to S9, etc., have been omitted.

[0103] Conversely, when the voltage difference ΔV21 = Vw2 - Vu1 between AC voltages Vw2 and Vu1 becomes the sum of the peak values ​​of AC voltages Vu1 and Vw2, in Figure 8 The circulating current IC flows through the path shown. That is, from the first terminal (AC output terminal 12c) of the AC power supply 12W, through the output node 3c of the inverter 3, and diode D13 ( Figure 3 DC positive bus Lp, capacitor Cd, DC negative bus Ln, diode D4 ( Figure 3The circulating current IC flows through the input node 1a of converter 1, AC power supply 11U, neutral point terminal 11d, ground voltage GND line and neutral point terminal 12d to the other terminal of AC power supply 12W.

[0104] If the circulating current IC is flowing, the following situation may occur: The capacitor Cd is charged by the circulating current IC, and the inter-terminal voltage VDC of capacitor Cd exceeds the upper limit voltage VDCH. The control device 8 identifies this as an abnormality and stops the operation of the uninterruptible power supply (UPS), thus stopping the operation of load 13. Furthermore, there may be a situation where the detection values ​​of current detectors CT1 to CT6 exceed the upper limit current IH, which the control device 8 also identifies as an abnormality, stopping the operation of the UPS and stopping the operation of load 13.

[0105] Therefore, in this embodiment, in the superimposed power supply mode, the inter-terminal voltage VDC of capacitor Cd is set by a reference voltage VDCr2 that is above the sum of the peak values ​​of AC voltages Vu1, Vv1, and Vw1 and the peak values ​​of AC voltages Vu2, Vv2, and Vw2, thereby preventing the circulating current IC from flowing in the uninterruptible power supply device.

[0106] Furthermore, in this embodiment, in both inverter power supply mode and bypass power supply mode, by setting the inter-terminal voltage VDC of capacitor Cd to a reference voltage VDCr1 that is lower than the sum of the peak values ​​of AC voltages Vu1, Vv1, Vw1 and the peak values ​​of AC voltages Vu2, Vv2, Vw2, the power consumption is reduced and the efficiency is improved.

[0107] When the bypass AC power supply 12 is stable, the AC output voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12 are consistent with the AC output voltages Vu1, Vv1, and Vw1 of the industrial AC power supply 11. Therefore, the sum of the peak values ​​of AC voltages Vu1, Vv1, and Vw1 and the peak values ​​of AC voltages Vu2, Vv2, and Vw2 is equal to twice the peak values ​​of AC voltages Vu1, Vv1, and Vw1. Furthermore, the peak values ​​of AC voltages Vu1, Vv1, and Vw1 are the same.

[0108] For example, the effective value of AC voltage Vu1 is 277V, and its peak value is 392V. Twice the peak value of AC voltage Vu1 is 784V. Reference voltage VDCr1 is set to 750V, which is lower than 784V. Reference voltage VDCr2 is set to 920V, which is higher than 784V. Furthermore, reference voltage VDCr2 is set to a value lower than the upper limit VDCH (e.g., 1000V) of the inter-terminal voltage VDC of capacitor Cd.

[0109] As a result, in the superimposed power supply mode, for example, even when AC voltage Vu1 has a positive peak (+392V) and AC voltage Vw2 has a negative peak (-392V), the inter-terminal voltage VDC = VDCr2 (920V) of capacitor Cd is higher than the sum of the peak values ​​of AC voltages Vu1 and Vw2 (784V). Therefore, diodes D1 and D16 ( Figure 3 The IC is not connected and the circulating current is not flowing.

[0110] Conversely, even when AC voltage Vu1 has a negative peak (-392V) and AC voltage Vw2 has a positive peak (+392V), the inter-terminal voltage VDC = VDCr2 (920V) of capacitor Cd is higher than the sum of the peak values ​​of AC voltages Vu1 and Vw2 (784V). Therefore, diodes D13 and D4 ( Figure 3 The IC is not connected and does not allow circulating current to flow. Because the IC does not allow circulating current to flow, overcurrent or overvoltage of capacitor Cd will not be detected, thus preventing the uninterruptible power supply from stopping operation and the operation of load 13 will not be stopped.

[0111] Next, a detailed explanation is given of the reasons why the input current of converter 1 becomes larger than the output current of inverter 3 in the superimposed power supply mode, causing the DC voltage VDC to rise, and the countermeasures therein. Figure 9 (A) to (C) are circuit block diagrams representing bypass power supply mode, superimposed power supply mode, and inverter power supply mode, respectively. Figure 9 To simplify the accompanying drawings and explanations, only the parts related to one of the three phases are shown, and the diagrams of switches S1 to S9, AC filters F1 and F2, current detectors CT1 to CT6, etc., are omitted.

[0112] like Figure 9 As shown in (A), in bypass power supply mode, load current I4 is supplied from bypass AC power supply 12 to load 13. Furthermore, converter 1 is controlled with the inter-terminal voltage VDC of capacitor Cd as the reference voltage VDCr1. A feedback component IFB, containing the deviation ΔVDC = VDCr1 - VDC between the reference voltage VDCr1 and the inter-terminal voltage VDC of capacitor Cd, and a feedforward component IFF = 1.0 × I4 obtained by multiplying the load current I4 by a gain Kf (e.g., 1.0), flows from industrial AC power supply 11 to converter 1.

[0113] With the voltage VDC across the terminals of capacitor Cd charging the reference voltage VDCr1, the feedback component IFB cancels out the feedforward component IFF, and the input current I1 of converter 1 becomes approximately 0A.

[0114] During the switching between bypass power supply mode and inverter power supply mode, a superimposed power supply mode is executed. In superimposed power supply mode, such as... Figure 9 As shown in (B), both inverter 3 and bypass AC power supply 12 are connected to load 13. Consequently, a sudden change in the load on bypass AC power supply 12 causes a frequency variation in its output voltage, resulting in a phase shift between the output voltage of bypass AC power supply 12 and the output voltage of inverter 3. Current I4 is supplied from both inverter 3 and bypass AC power supply 12 to load 13 in proportion to their phase difference. Figure 9 (B) shows the case where 60% of the load current I4 is supplied from inverter 3 and 40% of the load current I4 is supplied from bypass AC power supply 12.

[0115] If current flows from inverter 3 to load 13, the inter-terminal voltage VDC of capacitor Cd decreases, and the input current I1 = IFB + 1.0 × I4 of converter 1 increases. In this case, the input current I1 of converter 1 becomes too large compared to the output current 0.6 × I4 of inverter 3, making it impossible to follow the feedback control. The inter-terminal voltage VDC of capacitor Cd rises compared to the reference voltage VDCr2, raising concerns that it may exceed the upper limit voltage VDCH. In this embodiment, the rise of DC voltage VDC is suppressed by shortening the superimposed power supply mode time. The method for shortening the superimposed power supply mode time will be described later.

[0116] In inverter power supply mode, such as Figure 9 As shown in (C), a load current I4 is supplied from the inverter 3 to the load 13. The converter 1 is controlled with the inter-terminal voltage VDC of the capacitor Cd as the reference voltage VDCr1. The current I1 = IFB + Kf × I4, which includes the feedback component IFB corresponding to the deviation ΔVDC = VDCr1 - VDC between the reference voltage VDCr1 and the inter-terminal voltage VDC of the capacitor Cd, and the feedforward component IFF = Kf × I4 obtained by multiplying the load current I4 by the gain Kf, flows from the industrial AC power supply 11 to the converter 1.

[0117] In this case, by allowing the feedforward component IFF to flow through converter 1, the response speed of the feedback component IFB can be reduced, thereby stably controlling the inter-terminal voltage VDC of capacitor Cd, and the inter-terminal voltage VDC of capacitor Cd can be controlled at high speed in response to changes in the load current I4.

[0118] Figure 10 as well as Figure 11 This is a circuit block diagram illustrating the operation of the uninterruptible power supply (UPS) during the switching from bypass power supply mode to inverter power supply mode. Figure 9 (B) is a diagram illustrating a method for minimizing the rise of the DC voltage VDC. Figure 10 as well as Figure 11 To simplify the accompanying drawings and explanations, only the parts related to one of the three phases are shown, and the illustrations of AC filters F1 and F2, current detectors CT1 to CT6, etc. are omitted.

[0119] exist Figure 10 In (A), in bypass power supply mode, switch S4 of electromagnetic contactor 5 is turned on, supplying load current I4 from bypass AC power supply 12 to load 13 via switch S4. Thyristor switch S7 of semiconductor switch 6 is turned off, and the current flowing through thyristor switch S7 is 0A. Furthermore, inverter 3 is deactivated, switch S1 of electromagnetic contactor 4 is turned off, and the output current of inverter 3 is 0A.

[0120] exist Figure 10 In (B), if the instruction is to switch from bypass power supply mode to inverter power supply mode, the thyristor switch S7 is first turned on, and the load current I4 is supplied from the bypass AC power supply 12 to the load 13 via the parallel connection of switches S4 and S7. Figure 10 (B) shows the state in which 50% of the load current I4 flows through switches S4 and S7 respectively.

[0121] Next, as Figure 10 As shown in (C), switch S1 is turned on. At this time, inverter 3 is deactivated, therefore, no current flows through switch S1. Next, as... Figure 11 As shown in (A), switch S4 is open and inverter 3 is activated.

[0122] At that instant, the inverter 3 is controlled such that the phase of the AC output voltage of the inverter 3 is aligned with the phase of the AC output voltage of the bypass AC power supply 12, and the peak value of the AC output voltage of the inverter 3 becomes larger than the peak value of the AC output voltage of the bypass AC power supply 12. Therefore, the load current I4 is supplied from the inverter 3 to the load 13 via the switch S1, and the current flowing in the thyristor switch S7 becomes 0A.

[0123] However, if the load current I4 is supplied from the inverter 3, the load on the bypass AC power supply 12 suddenly becomes lighter. As a result, the frequency of the bypass AC power supply 12, which acts as a household generator, increases, creating a phase difference between the AC output voltage of the inverter 3 and the AC output voltage of the bypass AC power supply 12.

[0124] Therefore, as Figure 11 As shown in (B), current I4 is supplied from both the inverter 3 and the bypass AC power supply 12 to the bidirectional load 13 in proportion to its phase difference. Figure 11 (B) shows the case where 80% of the load current I4 is supplied from inverter 3 and 20% of the load current I4 is supplied from bypass AC power supply 12.

[0125] If current flows from inverter 3 to load 13, the inter-terminal voltage VDC of capacitor Cd decreases, and the input current I1 = IFB + 1.0 × I4 of converter 1 increases. In this case, the input current I1 of converter 1 becomes too large compared to the output current 0.8 × I4 of inverter 3, and cannot keep up with the feedback control, causing the inter-terminal voltage VDC of capacitor Cd to rise.

[0126] Next, as Figure 11 As shown in (C), the thyristor switch S7 is turned off. As a result, the output current of inverter 3 is consistent with the load current I4, the difference between the input current I1 of converter 1 and the output current I4 of inverter 3 becomes smaller, and following the feedback control, the voltage VDC between the terminals of capacitor Cd is maintained at the reference voltage VDCr1.

[0127] In this embodiment, the superimposed power supply mode is maintained from the activation of inverter 3 until the thyristor switch S7 is turned off. The response time of thyristor switch S7 is shorter than that of switch S4. Therefore, compared with the conventional method of stopping the superimposed power supply mode by turning off switch S4, the duration of the superimposed power supply mode can be shortened, thereby suppressing the rise of DC voltage VDC.

[0128] Figure 12 This is a circuit block diagram showing the configuration of the parts related to the control of switches S1 to S9 in control device 8. Figure 12 In this configuration, the control device 8 includes signal generation circuits 21 and 22 and a control unit 23. The electromagnetic contactor 4 includes switches S1 to S3 and an auxiliary switch SA. The auxiliary switch SA is linked to switches S1 to S3. Switches S1 to S3 and SA are controlled by a control signal φ4 from the control unit 23. When the control signal φ4 is at a "L" level, switches S1 to S3 and SA are all open. When the control signal φ4 is at a "H" level, switches S1 to S3 and SA are all closed.

[0129] The signal generation circuit 21 detects whether the auxiliary switch SA is on and outputs a signal φSA indicating the detection result. When the auxiliary switch SA is off, the signal φSA is set to the "L" level, and when the auxiliary switch SA is on, the signal φSA is set to the "H" level.

[0130] Similarly, in addition to switches S4 to S6, electromagnetic contactor 5 also includes an auxiliary switch SB. The auxiliary switch SB is linked to switches S4 to S6. Switches S4 to S6 and SB are controlled by a control signal φ5 from control unit 23. When control signal φ5 is at a "L" level, switches S4 to S6 and SB are all open. When control signal φ5 is at a "H" level, switches S4 to S6 and SB are all closed.

[0131] The signal generation circuit 22 detects whether the auxiliary switch SB is on and outputs a signal φSB indicating the detection result. When the auxiliary switch SB is off, the signal φSB is set to the "L" level, and when the auxiliary switch SB is on, the signal φSB is set to the "H" level.

[0132] Semiconductor switch 6 is controlled by control signal φ6 from control unit 23. When control signal φ6 is at the "L" level, thyristor switches S7 to S9 are all open. When control signal φ6 is at the "H" level, thyristor switches S7 to S9 are all closed.

[0133] Control unit 23 is based on data from operation unit 7 ( Figure 1 The mode selection signal MS and the output signals φSA and φSB of the signal generation circuits 21 and 22 generate control signals φ4 to φ6 and control signals EN for activating and deactivating the inverter 3.

[0134] When the user operation unit 7 of the uninterruptible power supply (UPS) selects the bypass power supply mode, the mode selection signal MS is set to the "L" level. When the user operation unit 7 of the UPS selects the inverter power supply mode, the mode selection signal MS is set to the "H" level.

[0135] When the mode selection signal MS is at the "L" level (in bypass power supply mode), the control unit 23 sets control signals φ4 and φ6 to the "L" level, causing the electromagnetic contactor 4 and semiconductor switch 6 to disconnect; sets control signal φ5 to the "H" level, causing the electromagnetic contactor 5 to connect; and sets control signal EN to the "L" level, deactivating the inverter 3. Thus, three-phase AC power is supplied from the bypass AC power supply 12 to the load 13 via the electromagnetic contactor 5.

[0136] When the mode selection signal MS is at the "H" level (inverter power supply mode), the control unit 23 sets control signals φ5 and φ6 to the "L" level, causing electromagnetic contactor 5 and semiconductor switch 6 to disconnect; sets control signal φ4 to the "H" level, causing electromagnetic contactor 4 to connect; and sets control signal EN to the "H" level, activating inverter 3. Thus, three-phase AC power is supplied from inverter 3 to load 13 via AC filter F2 and electromagnetic contactor 4.

[0137] During the switching period when the mode selection signal MS is switched from the "L" level to the "H" level (during the switching period from bypass power supply mode to inverter power supply mode), the control unit 23 sets the control signal φ6 to the "H" level to turn on the semiconductor switch 6, and sets the control signal φ4 to the "H" level to turn on the electromagnetic contactor 4.

[0138] Furthermore, in response to the signal φSA rising from the "L" level to the "H" level, control unit 23 sets control signal φ5 to the "L" level, causing electromagnetic contactor 5 to disconnect. Next, in response to the signal φSA rising from the "L" level to the "H" level, control unit 23 sets control signal EN to the "H" level, activating inverter 3, and then sets control signal φ6 to the "L" level, causing semiconductor switch 6 to disconnect. Thus, three-phase AC power is supplied from inverter 3 to load 13 via AC filter F2 and electromagnetic contactor 4.

[0139] During the switching period when the mode selection signal MS changes from "H" level to "L" level (the switching period from inverter power supply mode to bypass power supply mode), the control unit 23 sets the control signal φ5 to "H" level, thus turning on the electromagnetic contactor 5. Then, in response to the signal φSB rising from "L" level to "H" level, the control unit 23 sets the control signal φ4 to "L" level, thus turning off the electromagnetic contactor 4. As a result, three-phase AC power is supplied from the bypass AC power supply 12 to the load 13 via the electromagnetic contactor 5.

[0140] Furthermore, the control unit 23 generates control signals φ4 to φ6 and control signals EN for controlling the activation and deactivation of the inverter 3 based on the fault detection signal DT1 indicating that a fault has occurred in the inverter 3 and the output signals φSA and φSB of the signal generation circuits 21 and 22.

[0141] In inverter power supply mode, when inverter 3 is operating normally, the fault detection signal DT1 is set to the inactive level "L". When inverter 3 malfunctions, the fault detection signal DT1 is set to the active level "H".

[0142] In inverter power supply mode, when the fault detection signal DT1 is at the "L" level, the control unit 23 sets the control signals φ5 and φ6 to the "L" level, causing the electromagnetic contactor 5 and semiconductor switch 6 to disconnect, sets the control signal φ4 to the "H" level, causing the electromagnetic contactor 4 to connect, and sets the control signal EN to the "H" level, causing the inverter 3 to activate.

[0143] In inverter power supply mode, if the fault detection signal DT1 rises from the "L" level to the "H" level, the control unit 23 sets control signals φ5 and φ6 to the "H" level, control signal φ4 to the "L" level, and control signal EN to the "L" level. If control signal φ6 is set to the "H" level, semiconductor switch 6 is turned on momentarily; if control signal EN is set to the "L" level, inverter 3 is deactivated.

[0144] If control signal φ5 is set to "H" level, electromagnetic contactor 5 will turn on after a predetermined on-time, and signal φSB will rise from "L" level to "H" level. If control signal φ4 is set to "L" level, electromagnetic contactor 4 will turn off after a predetermined off-time, and signal φSA will drop from "H" level to "L" level. Control unit 23, in response to the rising edge of signal φSB, sets control signal φ6 to "L" level, causing semiconductor switch 6 to turn off.

[0145] Figure 13 This is a block diagram showing the configuration of the parts in the control device 8 related to the control of the converter 1. Figure 13 In the control device 8, there are timer 25, reference voltage generating circuit 26 and control unit 27.

[0146] Timer 25 generates a switching signal φC based on the level change of the mode selection signal MS. When the mode selection signal MS is maintained at either "L" or "H" level, the switching signal φC is maintained at "L" level. When the mode selection signal MS changes from "L" to "H" level, the switching signal φC is set to "H" level only for a specified time. Furthermore, when the mode selection signal MS changes from "H" to "L" level, the switching signal φC is set to "H" level only for a specified time.

[0147] The reference voltage generation circuit 26 outputs a reference voltage VDCr according to the switching signal φC. When the switching signal φC is at the "L" level, the reference voltage VDCr is set to reference voltage VDCr1. When the switching signal φC is at the "H" level, the reference voltage VDCr is set to reference voltage VDCr2, which is higher than reference voltage VDCr1.

[0148] Therefore, in both bypass power supply mode and inverter power supply mode, the reference voltage VDCr is set to reference voltage VDCr1. Furthermore, during the switching from either the bypass power supply mode or the inverter power supply mode to the other, the reference voltage VDCr is set to reference voltage VDCr2.

[0149] The control unit 27 generates gate signals A1-A3 and B1-B3 based on the reference voltage VDCr, DC voltage VDC, AC input voltages Vu1, Vv1, Vw1, AC input currents I1-I3, and load currents I4-I6. Figure 3 Thus, converter 1 is controlled by using DC voltage VDC as the reference voltage VDCr.

[0150] At this time, the control unit 27 controls the converter 1 to flow from the industrial AC power supply 11 to the converter 1 in such a way that the feedback component IFB, which includes the value corresponding to the deviation ΔVDC = VDCr - VDC of the reference voltage VDC and the DC voltage VDC, and the feedforward component IFF obtained by multiplying the load currents I4 to I6 by the gain Kf, flows to the converter 1.

[0151] Figure 14 This is a block diagram showing the configuration of the parts in control device 8 related to the control of inverter 3. Figure 14 In the control device 8, there is a control unit 30. The control unit 30 generates gate signals X1-X3 and Y1-Y3 based on the control signal EN from the control unit 23, the load currents I4-I6, the AC output voltages Va-Vc, and the AC voltages Vu2, Vv2, and Vw3 of the bypass AC power supply 12. Figure 3 ), thereby controlling inverter 3.

[0152] When the control signal EN is at the "L" level, the control unit 27 stops the output of gate signals X1~X3 and Y1~Y3, thus stopping the operation of inverter 3. At this time, the IGBTs Q11~Q16 of inverter 3 ( Figure 3 The inverter is kept in the off state. When the control signal EN is at the "H" level, the control unit 27 outputs gate signals X1~X3 and Y1~Y3 to operate the inverter 3. At this time, the IGBTs Q11~Q16 of the inverter 3 are turned on and off at predetermined times, and the inverter 3 outputs three-phase AC power.

[0153] Furthermore, the control unit 30 determines whether the inverter 3 is operating normally during its operation, and outputs a fault detection signal DT1 based on the determination result. Figure 12 The control unit 30, for example, is based on the AC output voltage Va to Vc of the inverter 3. Figure 1 The fault detection signal DT1 is used to identify whether there is a fault in inverter 3. When inverter 3 is operating normally, the fault detection signal DT1 is set to the inactive level "L". When inverter 3 has a fault, the fault detection signal DT1 is set to the active level "H".

[0154] Figure 15 This is a timing diagram showing the operation of control device 8 during the switching from bypass power supply mode to inverter power supply mode. Figure 15 In the diagram, (A) to (H) show the waveforms of the mode selection signal MS, control signal φ6, reference voltage VDCr, and signals φ4, φSA, φ5, φSB, and EN, respectively. Initially, the mode selection signal MS is set to "L" level, executing the bypass power supply mode.

[0155] In bypass power supply mode, control signal φ6 ( Figure 12 When the control signal φ4 is set to "L" level, semiconductor switch 6 is opened, and reference voltage VDCr is set to reference voltage VDCr1. Furthermore, when control signal φ5 is set to "H" level, electromagnetic contactor 4 is opened, and signal φSA is set to "L" level. Additionally, when control signal φ5 is set to "H" level, electromagnetic contactor 5 is opened, and signal φSB is set to "H" level. Finally, when control signal EN is set to "L" level, inverter 3 is deactivated.

[0156] At a certain moment t1, if the inverter power supply mode is selected and the mode selection signal MS rises from the "L" level to the "H" level, then the control unit 23 ( Figure 12 When the control signal φ6 rises from the "L" level to the "H" level, the semiconductor switch 6 is turned on, and through the timer 25 and the reference voltage generation circuit 26, the reference voltage VDC is set to a reference voltage VDCr2 that is higher than the reference voltage VDC1. The turn-on time of the semiconductor switch 6 is sufficiently short; therefore, if the control signal φ6 is set to the "H" level, the semiconductor switch 6 is turned on instantaneously.

[0157] Next, at time t2, the control signal φ4 rises from the "L" level to the "H" level. After a predetermined on-time has elapsed from the rising edge of the control signal φ4, the switches S1~S3 and SA of the electromagnetic contactor 4 are turned on, and the signal φSA rises from the "L" level to the "H" level (time t3).

[0158] In response to the rising edge of signal φSA, control signal φ5 drops from the "H" level to the "L" level (time t4). After a predetermined disconnection time has elapsed since the falling edge of control signal φ5, switches S4-S6 and SB of electromagnetic contactor 5 are disconnected, and signal φSB drops from the "H" level to the "L" level (time t5).

[0159] In response to the falling edge of signal φSB, control signal EN rises from "L" level to "H" level, activating inverter 3 (time t5). Thus, three-phase AC power is supplied from inverter 3 to load 13 via electromagnetic contactor 4, and three-phase AC power is also supplied from bypass AC power supply 12 to load 13 via semiconductor switch 6, executing a superimposed power supply mode.

[0160] At time t6, after a predetermined time elapsed from the falling edge of signal φSB, control signal φ6 drops from the "H" level to the "L" level, and semiconductor switch 6 is disconnected. This stops the power supply from bypass AC power supply 12 to load 13, ending the superimposed power supply mode. The superimposed power supply mode lasts from time t5 to time t6. Here, semiconductor switch 6 operates at a higher speed than electromagnetic contactors 4 and 5; therefore, the superimposed power supply mode time TL1 is shorter than before. Furthermore, at time t7, reference voltage VDCr drops from reference voltage VDCr2 to reference voltage VDCr1, completing the switch from bypass power supply mode to inverter power supply mode.

[0161] Next, the operation of the uninterruptible power supply (UPS) will be briefly explained. When the industrial AC power supply 11 is normal, and the inverter power supply mode is selected using the operation unit 7, the three-phase AC currents I1 to I3, including feedback and feedforward components, flow from the industrial AC power supply 11 to the converter 1, with the terminal voltage VDC of capacitor Cd serving as the reference voltage VDCr1. By directing the feedforward component to the converter 1, the converter 1 can be stably controlled, and the converter 1 can be controlled at high speed in response to changes in the load currents I4 to I6.

[0162] In addition, the bidirectional chopper 2 is controlled by using the inter-terminal voltage VB of battery B1 as the reference voltage VBr, and the inverter 3 is controlled by synchronizing the AC output voltages Va to Vc with the AC output voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12, respectively.

[0163] Furthermore, electromagnetic contactor 4 is turned on, and electromagnetic contactor 5 and semiconductor switch 6 are turned off. Inverter 3 is connected to load 13 via AC filter F2 and electromagnetic contactor 4. Thus, AC output voltage Va to Vc is supplied to load 13 via electromagnetic contactor 4, and load 13 is driven.

[0164] In the event of a power outage of the industrial AC power supply 11, the operation of the converter 1 is stopped, the bidirectional chopper 2 is controlled with the voltage VDC between the terminals of capacitor Cd as the reference voltage VDCr1, and the inverter 3 is controlled with the AC output voltages Va to Vc synchronized with the AC output voltages Vu2, Vv2, and Vw2 of the bypass AC power supply 12, respectively.

[0165] When the DC power of battery B1 is consumed and the inter-terminal voltage VB of battery B1 reaches the lower limit voltage, the operation of bidirectional chopper 2 and inverter 3 is stopped. Therefore, even in the event of a power outage of industrial AC power supply 11, load 13 can continue to operate until the inter-terminal voltage VB of battery B1 reaches the lower limit voltage.

[0166] Furthermore, in inverter power supply mode, in the event of a fault in inverter 3, semiconductor switch 6 is momentarily switched on, supplying three-phase AC power from bypass AC power supply 12 to load 13 via semiconductor switch 6, allowing load 13 to continue operating. Additionally, electromagnetic contactor 5 is switched on, and electromagnetic contactor 4 is switched off. After a predetermined time, semiconductor switch 6 is switched off, supplying three-phase AC power from bypass AC power supply 12 to load 13 via electromagnetic contactor 5.

[0167] Furthermore, in inverter power supply mode, when the bypass power supply mode is selected using the operation unit 7, the three-phase AC current I1 to I3, including feedback and feedforward components, flows from the industrial AC power supply 11 to the converter 1 in such a way that the inter-terminal voltage VDC of capacitor Cd becomes a reference voltage VDCr2 that is higher than the reference voltage VDCr1.

[0168] Furthermore, both electromagnetic contactors 4 and 5 are activated, supplying three-phase AC power to the load 13 from both the inverter 3 and the bypass AC power supply 12, executing a superimposed power supply mode. At this time, since VDC = VDCr2, circulating current can be prevented from flowing between the industrial AC power supply 11 and the bypass AC power supply 12.

[0169] Next, electromagnetic contactor 4 is disconnected, and only electromagnetic contactor 5 is connected. The operation of inverter 3 is stopped, and three-phase AC power is supplied to load 13 only from bypass AC power supply 12. In addition, the voltage VDC between the terminals of capacitor Cd is reduced to the reference voltage VDCr1, controlling converter 1, thus completing the switch from inverter power supply mode to bypass power supply mode.

[0170] Furthermore, during the switching from inverter power supply mode to bypass power supply mode, there is a concern that the superimposed power supply mode may take longer, causing the DC voltage VDC to rise and exceed the upper limit voltage VDCH, potentially halting the operation of inverter 3. However, even if inverter 3 is stopped during this switching period, load 13 can continue to operate via three-phase AC power from bypass AC power supply 12, therefore, there is no problem.

[0171] Furthermore, in bypass power supply mode, when the inverter power supply mode is selected using the operation unit 7, the three-phase AC current I1 to I3, including feedback and feedforward components, flows from the industrial AC power supply 11 to the converter 1 in such a way that the inter-terminal voltage VDC of capacitor Cd becomes a reference voltage VDCr2 that is higher than the reference voltage VDCr1.

[0172] In addition, such as Figure 15As shown, semiconductor switch 6 and electromagnetic contactor 4 are turned on, electromagnetic contactor 5 is turned off, inverter 3 is activated, and then semiconductor switch 6 is turned off. If inverter 3 is activated, three-phase AC power is supplied from inverter 3 and bypass AC power supply 12 to load 13 via electromagnetic contactor 4 and semiconductor switch 6. At this time, since VDC = VDCr2, the circulating current IC will not flow to the uninterruptible power supply device.

[0173] Furthermore, if semiconductor switch 6 is disconnected, three-phase AC power is supplied from inverter 3 to load 13 via electromagnetic contactor 4. Here, semiconductor switch 6 operates at a higher speed than electromagnetic contactors 4 and 5, thus shortening the superimposed power supply mode time TL1 compared to the past, and minimizing the rise of the inter-terminal voltage VDC of capacitor Cd during superimposed power supply mode. Afterwards, converter 1 lowers the inter-terminal voltage VDC of capacitor Cd to the reference voltage VDCr1, completing the switch from bypass power supply mode to inverter power supply mode.

[0174] As described above, in this embodiment, during the switching from bypass power supply mode to inverter power supply mode, with semiconductor switch 6 and electromagnetic contactor 4 turned on and electromagnetic contactor 5 turned off, the superimposed power supply mode is started by activating inverter 3 and ended by turning off semiconductor switch 6. Therefore, the superimposed power supply mode can be ended in a short time, thus minimizing the rise in the inter-terminal voltage VDC of capacitor Cd and preventing the inter-terminal voltage VDC of capacitor Cd from exceeding the upper limit voltage VDCH.

[0175] Furthermore, by allowing the AC currents I1 to I3, which include the feedback component IFB and the feedforward component IFF, to flow into converter 1, the control can be stabilized by controlling the feedback component IFB at a low speed, and the load currents I4 to I6 can be handled by the feedforward component IFF.

[0176] Furthermore, during switching, the converter 1 is controlled such that the inter-terminal voltage VDC of capacitor Cd becomes a reference voltage VDCr2, which is higher than the reference voltage VDCr1, thereby preventing circulating current IC from flowing through the path containing capacitor Cd, etc. Therefore, even when both the neutral point terminal 11d of the industrial AC power supply 11 and the neutral point terminal 12d of the bypass AC power supply 12 are grounded, the flow of circulating current IC can be prevented.

[0177] [Comparative Example]

[0178] Hereinafter, in order to make the effects of the above embodiments clear, a comparative example of the above embodiments will be described. Figure 16 as well as Figure 17This is a circuit block diagram illustrating the operation of the uninterruptible power supply device used as a comparative example, and is related to... Figure 10 as well as Figure 11 A comparison chart. In Figure 16 as well as Figure 17 The diagram illustrates the operation of a comparative example during the switching from bypass power supply mode to inverter power supply mode. In this comparative example, semiconductor switches 6 (i.e., thyristor switches S7 to S9) are not used during the switching period and are fixed in the open state.

[0179] exist Figure 16 In (A), in bypass power supply mode, switch S4 of electromagnetic contactor 5 is turned on, and load current I4 is supplied from bypass AC power supply 12 to load 13 via switch S4. In addition, inverter 3 is deactivated, switch S1 of electromagnetic contactor 4 is turned off, and the output current of inverter 3 is 0A.

[0180] If the instruction indicates a switch from bypass power supply mode to inverter power supply mode, then as follows: Figure 16 As shown in (B), first, switch S1 is turned on. Then, as... Figure 16 As shown in (C), inverter 3 is activated.

[0181] At the instant inverter 3 is activated, inverter 3 is controlled such that the phase of the AC output voltage of inverter 3 is synchronized with the phase of the AC output voltage of bypass AC power supply 12, and the peak value of the AC output voltage of inverter 3 becomes larger than the peak value of the AC output voltage of bypass AC power supply 12. Therefore, load current I4 is supplied from inverter 3 to load 13 via switch S1, and the current flowing through switch S4 becomes 0A.

[0182] However, if the load current I4 is supplied from the inverter 3, the load on the bypass AC power supply 12 is suddenly reduced. As a result, the frequency of the bypass AC power supply 12, which acts as a household generator, increases, creating a phase difference between the AC output voltage of the inverter 3 and the AC output voltage of the bypass AC power supply 12.

[0183] Therefore, as Figure 17 As shown in (A), current I4 is supplied from both the inverter 3 and the bypass AC power supply 12 to the bidirectional load 13 in proportion to its phase difference. Figure 17 (A) shows the case where 60% of the load current I4 is supplied from inverter 3 and 40% of the load current I4 is supplied from bypass AC power supply 12.

[0184] If current flows from inverter 3 to load 13, the inter-terminal voltage VDC of capacitor Cd decreases, and the input current I1 = IFB + 1.0 × I4 of converter 1 increases. In this case, the input current I1 of converter 1 becomes too large compared to the output current 0.6 × I4 of inverter 3, and cannot follow the feedback control, causing the inter-terminal voltage VDC of capacitor Cd to rise. Then, as... Figure 17 As shown in (C), switch S4 is opened, completing the switch from bypass power supply mode to inverter power supply mode.

[0185] Figure 18 It means Figure 16 as well as Figure 17 The timing diagram shown is related to the operation of the uninterruptible power supply device. Figure 15 A comparison chart. In Figure 18 In the diagram, (A) through (F) show the waveforms of the mode selection signal MS, signals φ4, φSA, φ5, φSB, and EN, respectively. In this comparative example, during the switching from bypass power supply mode to inverter power supply mode, semiconductor switch 6 is not used and is fixed in the off state. In the initial state, the mode selection signal MS is set to the "L" level, and bypass power supply mode is executed.

[0186] In bypass power supply mode, control signal φ4 is set to "L" level, electromagnetic contactor 4 is disconnected, and signal φSA is set to "L" level. Furthermore, control signal φ5 is set to "H" level, electromagnetic contactor 5 is connected, and signal φSB is set to "H" level. Consequently, control signal EN is set to "L" level, and inverter 3 is deactivated.

[0187] At a certain time t11, if the inverter power supply mode is selected and the mode selection signal MS rises from the "L" level to the "H" level, then at time t12, the control signal φ4 rises from the "L" level to the "H" level. After a specified on-time has elapsed from the rising edge of the control signal φ4, the switches S1~S3 and SA of the electromagnetic contactor 4 are turned on, and the signal φSA rises from the "L" level to the "H" level (time t13).

[0188] In response to the rising edge of signal φSA, control signal EN rises from "L" level to "H" level, and inverter 3 is activated (time t13). As a result, three-phase AC power is supplied from inverter 3 to load 13 via electromagnetic contactor 4, and three-phase AC power is also supplied from bypass AC power supply 12 to load 13 via semiconductor switch 6, executing superimposed power supply mode.

[0189] Furthermore, in response to the rising edge of signal φSA, control signal φ5 drops from the "H" level to the "L" level (time t14). After a predetermined disconnection time has elapsed since the falling edge of control signal φ5, switches S4-S6 and SB of electromagnetic contactor 5 open, and signal φSB drops from the "H" level to the "L" level (time t15). Thus, the power supply from bypass AC power supply 12 is stopped, the superimposed power supply mode ends, and the switch from bypass power supply mode to inverter power supply mode is completed. The period from time t13 to time t15 is the superimposed power supply mode.

[0190] In this comparative example, during the switch from bypass power supply mode to inverter power supply mode, with electromagnetic contactors 4 and 5 closed, the superimposed power supply mode is initiated by activating inverter 3 and terminated by disengaging electromagnetic contactor 5. Therefore, the execution time TL2 of the superimposed power supply mode is longer than the disengagement time of electromagnetic contactor 5. Consequently, there is a concern that in the superimposed power supply mode, the inter-terminal voltage VDC of capacitor Cd may rise above the upper limit voltage VDCH, causing the operation of inverter 3 to stop and the operation of load 13 to cease.

[0191] In contrast, in this embodiment, with the semiconductor switch 6 and the electromagnetic contactor 4 turned on, the superimposed power supply mode is started by activating the inverter 3, and ended by turning off the semiconductor switch 6. Therefore, the superimposed power supply mode time TL1 can be shortened, thus minimizing the rise of the inter-terminal voltage VDC of the capacitor Cd in the superimposed power supply mode and preventing the inter-terminal voltage VDC of the capacitor Cd from exceeding the upper limit voltage VDCH.

[0192] The embodiments disclosed herein should be considered illustrative rather than limiting in all respects. The invention is defined by the claims, rather than by the foregoing description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0193] Explanation of reference numerals in the attached figures

[0194] C1~C6, Cd capacitors, L1~L6 reactors, CT1~CT6 current detectors, 1 converter, Lp DC positive bus, Ln DC negative bus, 2 bidirectional chopper, 3 inverter, 4, 5 electromagnetic contactors, S1~S6 switches, SA, SB auxiliary switches, 6 semiconductor switches, S7~S9 thyristor switches, 7 operating unit, 8 control device, 11 industrial AC power supply, 11d, 12d neutral point terminals, 11U, 11V, 11W, 12U, 12V, 12W AC power supply, 12 bypass AC power supply, 13 load, Q1~Q6, Q11~Q16 IGBTs, D1~D6, D11~D16 diodes, 21, 22 signal generation circuits, 23, 27, 30 control unit, 25 timer, 26 reference voltage generation circuit.

Claims

1. An uninterruptible power supply device, wherein, have: The first electromagnetic contactor has a first terminal that receives a first AC voltage supplied from a first AC power source, and a second terminal that is connected to a load. A semiconductor switch is connected in parallel with the first electromagnetic contactor; The rectifier converts the second AC voltage supplied from the second AC power source into a DC voltage. The capacitor smooths the DC output voltage of the rectifier. An inverter converts the voltage between the terminals of the capacitor into a third AC voltage; The second electromagnetic contactor has a first terminal that receives the third AC voltage and a second terminal that is connected to the load. as well as The control device controls the uninterruptible power supply device. The control device (i) In the first mode of supplying the first AC voltage to the load, the first electromagnetic contactor is turned on, and the semiconductor switch and the second electromagnetic contactor are turned off. (ii) In the second mode of supplying the third AC voltage to the load, the first electromagnetic contactor and the semiconductor switch are disconnected, and the second electromagnetic contactor is turned on. (iii) During the switching from the first mode to the second mode, the semiconductor switch and the second electromagnetic contactor are turned on, the first electromagnetic contactor is turned off, the inverter is activated, and then the semiconductor switch is turned off. The uninterruptible power supply device also includes: A first current detector detects the alternating current flowing between the second AC power supply and the rectifier; and The second current detector detects the load current. The control device The rectifier is controlled based on the detection results of the first and second current detectors. With the terminal voltage of the capacitor as a reference voltage, an alternating current, including a feedback component corresponding to the deviation between the reference voltage and the terminal voltage of the capacitor, and a feedforward component obtained by multiplying the load current by a gain, flows from the second AC power source to the rectifier.

2. The uninterruptible power supply device of claim 1, wherein, It also has: The bidirectional chopper stores the DC power generated by the rectifier in a power storage device when the second AC power supply is normal, and supplies the DC power from the power storage device to the inverter when the second AC power supply fails.

3. An uninterruptible power supply device, wherein, have: The first electromagnetic contactor has a first terminal that receives a first AC voltage supplied from a first AC power source, and a second terminal that is connected to a load. A semiconductor switch is connected in parallel with the first electromagnetic contactor; The rectifier converts the second AC voltage supplied from the second AC power source into a DC voltage. The capacitor smooths the DC output voltage of the rectifier. An inverter converts the voltage between the terminals of the capacitor into a third AC voltage; The second electromagnetic contactor has a first terminal that receives the third AC voltage and a second terminal that is connected to the load. as well as The control device controls the uninterruptible power supply device. The control device (i) In the first mode of supplying the first AC voltage to the load, the first electromagnetic contactor is turned on, and the semiconductor switch and the second electromagnetic contactor are turned off. (ii) In the second mode of supplying the third AC voltage to the load, the first electromagnetic contactor and the semiconductor switch are disconnected, and the second electromagnetic contactor is turned on. (iii) During the switching from the first mode to the second mode, the semiconductor switch and the second electromagnetic contactor are turned on, the first electromagnetic contactor is turned off, the inverter is activated, and then the semiconductor switch is turned off. The uninterruptible power supply device also includes: A first current detector detects the alternating current flowing between the second AC power supply and the rectifier; and The second current detector detects the load current. The control device The rectifier is controlled based on the detection results of the first and second current detectors. In the first and second modes, with the voltage between the terminals of the capacitor serving as the first reference voltage, an AC current, including a feedback component corresponding to the deviation between the first reference voltage and the voltage between the terminals of the capacitor, and a feedforward component obtained by multiplying the load current by a gain, flows from the second AC power supply to the rectifier. During the switching process, an AC current, comprising a feedback component corresponding to the deviation between the second reference voltage and the capacitor's terminal voltage, and a feedforward component obtained by multiplying the load current by a gain, is configured such that the voltage between the capacitor's terminals becomes a second reference voltage higher than the first reference voltage. This prevents circulating current from either the first or second AC power source to the other AC power source via the capacitor. The first and second AC power supplies each comprise three-phase AC power supplies that are star-connected relative to the neutral point. The neutral points of both the first and second AC power supplies are grounded. The first to third AC voltages each comprise three-phase AC voltages. The first electromagnetic contactor includes three first terminals that receive the three-phase AC voltage contained in the first AC voltage and three second terminals connected to the load. The semiconductor switch includes three first terminals that accept the three-phase AC voltage contained in the first AC voltage and three second terminals connected to the load. The second electromagnetic contactor includes three first terminals for receiving the three-phase AC voltage contained in the third AC voltage and three second terminals connected to the load. The first reference voltage is lower than twice the peak value of the second AC voltage. The second reference voltage is greater than or equal to twice the peak value of the second AC voltage.

4. The uninterruptible power supply device according to claim 3, wherein, The first AC power source is a generator. The second AC power source is an industrial AC power source.

5. The uninterruptible power supply device of claim 3, wherein, It also has: The bidirectional chopper stores the DC power generated by the rectifier in a power storage device when the second AC power supply is normal, and supplies the DC power from the power storage device to the inverter when the second AC power supply fails.

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