Voltage detector and power converter equipped therewith

Abstract

This voltage detector (20) includes a three-phase voltage divider circuit (21-23) that divides the voltage between a three-phase AC voltage and a predetermined node (N1) to generate a three-phase AC signal, a differential circuit (24-26) that generates an analog signal with a level corresponding to the voltage difference between two of the three-phase AC signals, and a signal generation circuit (27-35) that generates a digital signal indicating the line-to-line voltage of the three-phase AC voltage based on the analog signal. The predetermined node is isolated from the ground voltage (GND) and is floating. Therefore, leakage current from the three-phase AC voltage to the ground voltage via the three-phase voltage divider circuit can be prevented.

Description

Technical Field

[0001] The present disclosure relates to a voltage detector and a power conversion device including the same, and particularly to a voltage detector that detects the line voltage of a three-phase AC voltage and a power conversion device including the same.

Background Art

[0002] For example, Japanese Patent No. 6875607 (Patent Document 1) discloses a voltage detector that divides the voltage between a three-phase AC voltage and a ground voltage to generate a three-phase AC signal, and detects the line voltage of the three-phase AC voltage based on the voltage difference between two of the three-phase AC signals.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, conventional voltage detectors have a problem that a large leakage current flows from the three-phase AC voltage to the ground voltage.

[0005] Therefore, the main object of the present disclosure is to provide a voltage detector capable of reducing leakage current and a power conversion device using the same.

Means for Solving the Problems

[0006] The voltage detector according to the present disclosure includes a three-phase voltage dividing circuit that divides the voltage between a three-phase AC voltage and a predetermined node to generate a three-phase AC signal, a differential circuit that generates an analog signal having a level corresponding to the voltage difference between two of the three-phase AC signals, and a signal generation circuit that generates a first digital signal indicating the line voltage of the three-phase AC voltage based on the analog signal. The predetermined node is insulated from the ground voltage and floated. [Effects of the Invention]

[0007] The voltage detector according to this disclosure includes a predetermined node that is isolated from the ground voltage and floats, and generates a three-phase AC signal by dividing the voltage between the three-phase AC voltage and the predetermined node. Therefore, it is possible to prevent leakage current from flowing from the three-phase AC voltage to the ground voltage via the three-phase voltage divider circuit, and leakage current can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1] This is a circuit block diagram showing the configuration of an uninterruptible power supply system according to one embodiment of the present disclosure. [Figure 2] Figure 1 is a circuit block diagram showing the configuration of the uninterruptible power supply (UPS). [Figure 3] Figure 2 is a circuit block diagram showing the configuration of the voltage detector included in the control circuit shown. [Figure 4] Figure 3 is a circuit diagram showing the configuration of the voltage divider. [Figure 5] Figure 2 is a circuit block diagram showing the main components of the control circuit. [Figure 6] Figure 5 is a circuit diagram showing the configuration of a power supply unit that supplies power voltage to the voltage detector and control unit. [Figure 7] This is a circuit block diagram showing the configuration of a voltage detector that is a comparative example 1 of this embodiment. [Figure 8] This is a circuit block diagram showing the configuration of a voltage detector, which is another comparative example 2 of this embodiment. [Modes for carrying out the invention]

[0009] Figure 1 is a circuit block diagram showing the configuration of an uninterruptible power supply system according to one embodiment of the present disclosure. In Figure 1, the uninterruptible power supply system comprises N uninterruptible power supply units U1 to UN and a communication cable 1. N is a natural number greater than or equal to 2, and Figure 1 shows the case where N=6.

[0010] Each uninterruptible power supply (UPS) U includes an input terminal T1, a DC terminal T2, an output terminal T3, and a communication terminal T4. In this specification, UPS units U1 to U6 may be collectively referred to as UPS unit U. The input terminal T1 of each UPS unit U is connected to a commercial AC power supply 2. The commercial AC power supply 2 supplies AC power at commercial frequency to the UPS system.

[0011] The DC terminal T2 of each uninterruptible power supply (UPS) U is connected to battery 3. Battery 3 stores DC power. A capacitor may be connected instead of battery 3. The output terminal T3 of each UPS U is connected to load 4. Load 4 is driven by AC power supplied from the UPS system.

[0012] The communication terminal T4 of each uninterruptible power supply (UPS) U is connected to the communication terminal T4 of each other UPS U via a communication cable 1. Each UPS U exchanges various information with each other UPS U via the communication cable 1. Based on this information, M UPS U units are selected from among the N UPS U1 to UN units to power load 4. M is a natural number less than or equal to N, for example, 5. In addition, the selected UPS U units are changed at predetermined intervals so that the operating times of the N UPS U1 to UN units are equalized.

[0013] The selected uninterruptible power supply (UPS) U performs an operation to supply power to load 4. During operation, if AC power is being supplied normally from the commercial AC power supply 2 (when the commercial AC power supply 2 is healthy), the UPS U first converts the AC power from the commercial AC power supply 2 to DC power, then converts that DC power back to AC power to supply to load 4 and stores it in battery 3.

[0014] During the operation, when the AC power supply 2 is not supplying AC power normally (i.e., during a power outage of the commercial AC power supply 2), the uninterruptible power supply U converts the DC power of the battery 3 into AC power and supplies it to the load 4. Therefore, during the period when DC power is stored in the battery 3, the operation of the load 4 can be continued even during a power outage. The unselected uninterruptible power supply U waits without supplying power to the load 4.

[0015] Figure 2 is a circuit block diagram showing the configuration of the uninterruptible power supply U1. In Figure 2, this uninterruptible power supply U1 includes a converter 10, a DC line 11, a capacitor 12, a bidirectional chopper 13, an inverter 14, an operation unit 15, and a control circuit 16.

[0016] The instantaneous value of the AC input voltage VI appearing at the input terminal T1 is detected by the control circuit 16. Based on the instantaneous value of the AC input voltage VI, the presence or absence of a power outage is discriminated. The converter 10 is controlled by the control circuit 16. When the commercial AC power supply 2 is normal, the converter 10 converts the AC power supplied from the commercial AC power supply 2 into DC power and outputs it to the DC line 11. When the commercial AC power supply 2 experiences a power outage, the operation of the converter 10 is stopped.

[0017] The capacitor 12 is connected to the DC line 11 and smoothes the voltage VD of the DC line 11. The instantaneous value of the DC voltage VD appearing on the DC line 11 is detected by the control circuit 16. The DC line 11 is connected to the high-voltage side node of the bidirectional chopper 13, and the low-voltage side node of the bidirectional chopper 13 is connected to the DC terminal T2. The instantaneous value of the terminal voltage VB of the battery 3 appearing at the DC terminal T2 is detected by the control circuit 16.

[0018] The bidirectional chopper 13 is controlled by the control circuit 16. When the commercial AC power supply 2 is normal, the bidirectional chopper 13 stores the DC power supplied from the converter 10 via the DC line 11 in the battery 3. When the commercial AC power supply 2 experiences a power outage, the bidirectional chopper 13 supplies the DC power of the battery 3 to the inverter 14 via the DC line 11.

[0019] The inverter 14 is controlled by the control circuit 16. When the commercial AC power supply 2 is normal, the inverter 14 converts the DC power supplied from the converter 10 via the DC line 11 into AC power. When a power outage occurs in the commercial AC power supply 2, the inverter 14 converts the DC power supplied from the battery 3 via the bidirectional chopper 13 into AC power. The instantaneous value of the AC output voltage VO appearing at the output terminal T3 is detected by the control circuit 16.

[0020] The operation unit 15 includes a plurality of buttons operated by the user of the uninterruptible power supply system, an image display unit for displaying various information, and the like. The user of the system can manually operate or automatically operate the uninterruptible power supply device U1 by operating the operation unit 15. Further, the user of the system can set the device number (in this case, number 1) of the uninterruptible power supply device U1 by operating the operation unit 15. The operation unit 15 outputs a signal including the set device number to the control circuit 16.

[0021] Based on signals from the operation unit 15, the AC input voltage VI, the DC voltage VD, the battery voltage VB, the AC output voltage VO, etc., the control circuit 16 controls the entire corresponding uninterruptible power supply device U1.

[0022] Also, the control circuits 16 of the other uninterruptible power supply devices U are connected to each other by the communication cable 1, and exchange various information with the other uninterruptible power supply devices U via the communication cable 1. Based on that information, etc., the control circuit 16 controls the entire corresponding uninterruptible power supply device U1. The configuration of each of the uninterruptible power supply devices U2 to UN is the same as that of the uninterruptible power supply device U1.

[0023] Incidentally, in Figures 1 and 2, only the part related to one phase of the three-phase AC voltage was explained in order to simplify the diagrams and explanations. However, in reality, an uninterruptible power supply system receives three-phase AC voltage from a commercial AC power source 2 and supplies three-phase AC voltage to the load 4. For this reason, the control circuit 16 is equipped with a voltage detector 20 for detecting the line voltages Vuv, Vvw, and Vwu of the three-phase AC voltages VU, VV, and VW.

[0024] Figure 3 is a circuit block diagram showing the configuration of such a voltage detector 20. In Figure 3, the voltage detector 20 includes voltage dividers 21-23, differential circuits 24-26, A / D converters 27-29, light-emitting units 30-32, and light-receiving units 33-35.

[0025] Voltage dividers 21-23 divide the three-phase AC voltages VU, VV, and VW output from inverter 14 to generate three-phase AC signals V1-V3. Voltage dividers 21-23 constitute a three-phase voltage divider circuit.

[0026] Figure 4 is a circuit diagram showing the configuration of voltage dividers 21 to 23. In Figure 4, each of the voltage dividers 21 to 23 includes an input terminal T11, an output terminal T12, a common terminal T13, and resistors 36 and 37. Resistor 36 is connected between terminals T11 and T12, and resistor 37 is connected between terminals T12 and T13. The input terminal T11 of the voltage dividers 21 to 23 receives three-phase AC voltages VU, VV, and VW, respectively.

[0027] The common terminal T13 of voltage dividers 21 to 23 is connected to a predetermined node N1. Node N1 is isolated from the ground voltage GND and is floating. The sum of the instantaneous values ​​of the three-phase AC currents IU, IV, and IW flowing from the three input terminals T11 of voltage dividers 21 to 23 through three sets of resistors 36 and 37 to node N1 is 0A. Therefore, the reference voltage VS appearing at node N1 is 0V.

[0028] If the resistance values ​​of resistors 36 and 37 are R1 and R2 respectively, then the voltage division ratio K of voltage dividers 21 to 23 is K = R2 / (R1 + R2). Voltage divider 21 divides the voltage (VU - VS) between the AC voltage VU and node N1 to generate the AC signal V1 = K × (VU - VS) = K × VU.

[0029] Voltage divider 22 divides the voltage between the AC voltage VV and node N1 (VV-VS) to generate the AC signal V2 = K × (VV-VS) = K × VV. Voltage divider 23 divides the voltage between the AC voltage VW and node N1 (VW-VS) to generate the AC signal V3 = K × (VW-VS) = K × VW.

[0030] Referring again to Figure 3, the differential circuit 24 is driven by the power supply voltage VCC1 and the reference voltage VS, and generates an analog signal V12 whose level corresponds to the voltage difference between the two-phase AC signals V1 and V2 output from the voltage dividers 21 and 22.

[0031] The differential circuit 25 is driven by the power supply voltage VCC1 and the reference voltage VS, and generates an analog signal V23 whose level corresponds to the voltage difference between the two-phase AC signals V2 and V3 output from the voltage dividers 22 and 23. The differential circuit 26 is driven by the power supply voltage VCC1 and the reference voltage VS, and generates an analog signal V31 whose level corresponds to the voltage difference between the two-phase AC signals V3 and V1 output from the voltage dividers 23 and 21.

[0032] The A / D converter 27 (signal conversion circuit) is driven by the power supply voltage VCC2 and the reference voltage VS. It samples the voltage of the analog signal V12 output from the differential circuit 24 at a predetermined period and converts each sampled voltage into a multi-bit digital signal D12 (second digital signal). The predetermined period is sufficiently shorter than the period of the AC signal V12.

[0033] The A / D converter 28 is driven by the power supply voltage VCC2 and the reference voltage VS, samples the voltage of the analog signal V23 output from the differential circuit 25 at a predetermined period, and converts each sampled voltage into a multi-bit digital signal D23.

[0034] The A / D converter 29 is driven by the power supply voltage VCC2 and the reference voltage VS, samples the voltage of the analog signal V23 output from the differential circuit 26 at a predetermined period, and converts each sampled voltage into a multi-bit digital signal D31.

[0035] The "L" level of each digital signal D12, D23, and D31 corresponds to the reference voltage VS, and its "H" level corresponds to the DC voltage between the power supply voltage VCC2 and the reference voltage VS.

[0036] Light-emitting unit 30 is driven by the power supply voltage VCC3 and the reference voltage VS, and converts the digital signal D12 output from the A / D converter 27 into an optical signal P12. Light-emitting unit 31 is driven by the power supply voltage VCC3 and the reference voltage VS, and converts the digital signal D23 output from the A / D converter 28 into an optical signal P23. Light-emitting unit 32 is driven by the power supply voltage VCC3 and the reference voltage VS, and converts the digital signal D31 output from the A / D converter 29 into an optical signal P31.

[0037] The light-receiving unit 33 is driven by the power supply voltage VCC4 and the ground voltage GND, and converts the optical signal P12 output from the light-emitting unit 30 into a digital signal Duv (first digital signal). The light-receiving unit 34 is driven by the power supply voltage VCC4 and the ground voltage GND, and converts the optical signal P23 output from the light-emitting unit 31 into a digital signal Dvw. The light-receiving unit 35 is driven by the power supply voltage VCC4 and the ground voltage GND, and converts the optical signal P31 output from the light-emitting unit 32 into a digital signal Dwu.

[0038] The light-emitting unit 30 and the light-receiving unit 33 constitute an output circuit. This output circuit is composed of, for example, a photocoupler.

[0039] The "L" level of the digital signals Duv, Dvw, and Dwu corresponds to the ground voltage GND, and the "H" level corresponds to the DC voltage between the power supply voltage VCC4 and the ground voltage GND. The digital signals Duv, Dvw, and Dwu are signals that represent the line voltages Vuv, Vvw, and Vwu of the three-phase AC voltages VU, VV, and VW, respectively.

[0040] Figure 5 is a circuit block diagram showing the main components of the control circuit 16. In Figure 5, the control circuit 16 includes a voltage detector 20 (Figure 3) and a control unit 38. The control unit 38 consists of a microcomputer driven by the power supply voltage VCC5 and the ground voltage GND. The control unit 38 controls the inverter 14 (power converter) based on the digital signals Duv, Dvw, and Dwu output from the voltage detector 20.

[0041] Figure 6 is a circuit diagram showing the configuration of a power supply unit 40 that supplies power supply voltages VCC1 to VCC5 to the voltage detector 20 and the control unit 38. In Figure 6, the power supply unit 40 includes power supplies 41 to 45. The negative terminals of power supplies 41 to 43 are both connected to node N1 and receive a reference voltage VS. Power supply voltages VCC1 to VCC3 are output from the positive terminals of power supplies 41 to 43, respectively. The negative terminals of power supplies 44 and 45 both receive the ground voltage GND. Power supply voltages VCC4 and VCC5 are output from the positive terminals of power supplies 44 and 45, respectively. Node N1 and the ground voltage GND are isolated from each other.

[0042] Note that power supply voltages VCC2 and VCC3 may each be the same voltage as power supply voltage VCC1. In this case, power supplies 42 and 43 can be removed. Also, power supply voltage VCC4 may be the same voltage as power supply voltage VCC5. In this case, power supply 44 can be removed.

[0043] Furthermore, if only two power supply voltages, VCC1 and VCC5, power supply voltage VCC1 may be generated using power supply 45 and a flyback converter. In this case, power supply 41 can be eliminated.

[0044] [Comparative Example 1] Figure 7 is a circuit block diagram showing the configuration of a voltage detector 50, which is comparative example 1 of this embodiment, and is shown in comparison with Figure 3. Referring to Figure 7, the differences between the voltage detector 50 and the voltage detector 20 are that a ground voltage GND is provided instead of a reference voltage VS to each of the voltage dividers 21-23, differential circuits 24-26, and A / D converters 27-29, and the light-emitting units 30-32 and light-receiving units 33-35 have been removed.

[0045] In this voltage detector 50, the "L" level of the output signals D12, D23, and D31 from the A / D converters 27-29 corresponds to the ground voltage GND, and the "H" level corresponds to the DC voltage between the power supply voltage VCC2 and the ground voltage GND. Therefore, the digital signals D12, D23, and D31 are directly supplied to the control unit 38 (Figure 5) as digital signals Duv, Dvw, and Dwu, which represent the line voltages Vuv, Vvw, and Vwu of the three-phase AC voltages VU, VV, and VW.

[0046] On the other hand, since the common terminal T13 of the voltage dividers 21-23 is connected to the ground voltage GND line, leakage current flows from the three-phase AC voltages VU, VV, VW to the ground voltage GND line via the voltage dividers 21-23. The uninterruptible power supply system shown in Figure 1 has N uninterruptible power supply units U1-UN connected in parallel, so the leakage current of the entire system becomes large. This leakage current flows into other electronic components via the ground voltage GND line, which may reduce the reliability of the operation of the electronic components.

[0047] [Comparative Example 2] Figure 8 is a circuit block diagram showing the configuration of a voltage detector 60, which is another comparative example 2 of this embodiment, and is shown in comparison with Figure 7. Referring to Figure 8, the difference between the voltage detector 60 and the voltage detector 50 is that the voltage dividers 21-23 and differential circuits 24-26 are replaced by transformers 61-63.

[0048] The first and second terminals of the primary winding of transformer 61 receive AC voltages VU and VV, respectively. The first terminal of the secondary winding of transformer 61 outputs an analog signal V12, and its second terminal receives the ground voltage GND.

[0049] The first and second terminals of the primary winding of transformer 62 receive AC voltages VV and VW, respectively. The first terminal of the secondary winding of transformer 62 outputs an analog signal V23, and its second terminal receives the ground voltage GND.

[0050] The first and second terminals of the primary winding of transformer 63 receive AC voltages VW and VU, respectively. The first terminal of the secondary winding of transformer 63 outputs an analog signal V31, and its second terminal receives the ground voltage GND.

[0051] The analog signals V12, V21, and V31 are converted into digital signals Duv, Dvw, and Dwu by A / D converters 27-29 and directly supplied to the control unit 38 (Figure 5).

[0052] This voltage detector 60 can prevent leakage current from flowing from the three-phase AC voltages VU, VV, and VW to the ground voltage GND line. However, since transformers 61-62 are more expensive than voltage dividers 21-23, etc., there is a problem that this leads to higher costs for the uninterruptible power supply system.

[0053] As described above, in this embodiment, a predetermined node N1 is provided that is isolated from the ground voltage GND and floats, and the voltage between the three-phase AC voltages VU, VV, VW and the predetermined node N1 is divided to generate three-phase AC signals V1 to V3. Therefore, compared to Comparative Example 1, the leakage current flowing from the three-phase AC voltages VU, VV, VW to the ground voltage GND can be reduced. Also, compared to Comparative Example 2, the equipment cost can be reduced.

[0054] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0055] U1~UN Uninterruptible power supply, 1 Communication cable, T1 Input terminal, T2 DC terminal, T3 Output terminal, T4 Communication terminal, 2 Commercial AC power supply, 3 Battery, 4 Load, 10 Converter, 11 DC line, 12 Capacitor, 13 Bidirectional chopper, 14 Inverter, 15 Operating unit, 16 Control circuit, 20, 50, 60 Voltage detector, 21~23 Voltage divider, 24~26 Differential circuit, 27~29 A / D converter, 30~32 Light-emitting unit, 33~35 Light-receiving unit, T11 Input terminal, T12 Output terminal, T13 Common terminal, 36, 37 Resistor element, N1 Node, 38 Control unit, 40 Power supply unit, 41~45 Power supply, 61~63 Transformer.

Claims

1. A three-phase voltage divider circuit generates a three-phase AC signal by dividing the voltage between a three-phase AC voltage and a predetermined node, A differential circuit that generates an analog signal with a level corresponding to the voltage difference between two phase AC signals of the three-phase AC signal, The system includes a signal generation circuit that generates a first digital signal indicating the line-to-line voltage of the three-phase AC voltage based on the analog signal, The aforementioned predetermined node is a voltage detector that is isolated from and floating from the ground voltage.

2. The aforementioned signal generation circuit is A signal conversion circuit that converts the aforementioned analog signal into a second digital signal, The system includes an output circuit that outputs the first digital signal in response to the second digital signal, The signal conversion circuit generates the second digital signal using a reference voltage appearing at the predetermined node and a first voltage different from the reference voltage. The voltage detector according to claim 1, wherein the output circuit generates the first digital signal using the ground voltage and a second voltage different from the ground voltage.

3. The output circuit described above is A light-emitting unit that outputs an optical signal in response to the second digital signal, It includes a light receiving unit that outputs the first digital signal in response to the optical signal, The light-emitting unit generates the optical signal using the reference voltage and a third voltage different from the reference voltage. The voltage detector according to claim 2, wherein the light receiving unit generates the first digital signal using the ground voltage and the second voltage.

4. The three-phase voltage divider circuit includes three voltage dividers, each corresponding to one of the three-phase AC voltages. Each voltage divider is, Output terminals for outputting AC signals of the corresponding phase, A first resistive element whose first terminal receives an AC voltage of the corresponding phase, and whose second terminal is connected to the output terminal, The voltage detector according to claim 1, further comprising a second resistive element having a first terminal connected to the output terminal and a second terminal connected to the predetermined node.

5. A voltage detector according to claim 1, A power converter that performs power conversion, A power conversion device comprising a control unit that controls the power converter based on the first digital signal.

6. The system comprises multiple sets of the voltage detectors, the power converters, and the control unit, The power conversion device according to claim 5, wherein the multiple power converters are connected in parallel to the load.

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