Voltage detector and power conversion device with same

Abstract

A voltage detector (20) comprises: three-phase voltage dividing circuits (21-23) for each dividing a voltage between a three-phase AC voltage and a predetermined node (N1) to generate a three-phase AC signal; differential circuits (24-26) for each generating an analog signal having a level corresponding to the voltage of a difference between two-phase AC signals among the three-phase AC signals; and signal generating circuits (27-35) for generating a digital signal indicating a line-to-line voltage of the three-phase AC voltages on the basis of the analog signal. The predetermined node is insulated from the ground voltage (GND) and floated. Therefore, it is possible to prevent a leakage current from flowing from the three-phase AC voltages to the ground voltage via the three-phase voltage dividing circuits.

Description

Voltage detector and power conversion device including the same

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

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

[0003] Japanese Patent No. 6875607

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

[0005] Therefore, a 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.

[0006] The voltage detector according to the present disclosure includes: a three-phase voltage dividing circuit that divides a voltage between a three-phase alternating current voltage and a predetermined node to generate a three-phase alternating current signal; a differential circuit that generates an analog signal having a level corresponding to a voltage that is a difference between two-phase alternating current signals among the three-phase alternating current signal; and a signal generation circuit that generates a first digital signal indicating a line voltage of the three-phase alternating current voltage based on the analog signal. The predetermined node is insulated from the ground voltage and is in a floating state.

[0007] In the voltage detector according to the present disclosure, the predetermined node that is insulated from the ground voltage and is floating is provided, and the voltage between the three-phase alternating current voltage and the predetermined node is divided to generate the three-phase alternating current signal. Therefore, leakage current can be prevented from flowing from the three-phase alternating current voltage to the ground voltage via the three-phase voltage dividing circuit, and leakage current can be reduced.

[0008] This is a circuit block diagram showing the configuration of an uninterruptible power supply system according to one embodiment of the present disclosure. This is a circuit block diagram showing the configuration of the uninterruptible power supply device shown in Figure 1. This is a circuit block diagram showing the configuration of a voltage detector included in the control circuit shown in Figure 2. This is a circuit diagram showing the configuration of a voltage divider shown in Figure 3. This is a circuit block diagram showing the main part of the control circuit shown in Figure 2. This is a circuit block diagram showing the configuration of a power supply device that supplies power voltage to the voltage detector and control unit shown in Figure 5. This is a circuit block diagram showing the configuration of a voltage detector which is comparative example 1 of this embodiment. This is a circuit block diagram showing the configuration of a voltage detector which is another comparative example 2 of this embodiment.

[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 of 2 or more, 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 U1 to U6 may be collectively referred to as UPS U as a representative unit. The input terminal T1 of each UPS 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 the battery 3. The battery 3 stores DC power. A capacitor may be connected instead of the battery 3. The output terminal T3 of each UPS U is connected to the load 4. The 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 operate 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 the 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 the load 4 and stores it in the battery 3.

[0014] Furthermore, during operation, if AC power is not being supplied normally from the commercial AC power source 2 (when the commercial AC power source 2 is down), the uninterruptible power supply U converts the DC power from the battery 3 into AC power and supplies it to the load 4. Therefore, as long as DC power is stored in the battery 3, the load 4 can continue to operate even during a power outage. Uninterruptible power supply U that is not selected remains in standby mode 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, the uninterruptible power supply U1 comprises a converter 10, a DC line 11, a capacitor 12, a bidirectional chopper 13, an inverter 14, an operating unit 15, and a control circuit 16.

[0016] The instantaneous value of the AC input voltage VI appearing at input terminal T1 is detected by the control circuit 16. Based on the instantaneous value of the AC input voltage VI, it is determined whether or not a power outage has occurred. The converter 10 is controlled by the control circuit 16. When the commercial AC power supply 2 is functioning properly, 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 fails, the operation of the converter 10 is stopped.

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

[0018] The bidirectional chopper 13 is controlled by the control circuit 16. When the commercial AC power supply 2 is functioning properly, 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 fails, the bidirectional chopper 13 supplies the DC power from 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 functioning properly, the inverter 14 converts the DC power supplied from the converter 10 via the DC line 11 into AC power. When the commercial AC power supply 2 fails, 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 control unit 15 includes multiple buttons operated by the user of the uninterruptible power supply system, an image display unit that displays various information, and other components. By operating the control unit 15, the system user can operate the uninterruptible power supply U1 manually or automatically. The system user can also set the device number (in this case, 1) of the uninterruptible power supply U1 by operating the control unit 15. The control unit 15 outputs a signal including the set device number to the control circuit 16.

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

[0022] Furthermore, control circuit 16 is connected to the control circuits 16 of each other uninterruptible power supply U by communication cables 1, and exchanges various information with each other uninterruptible power supply U via communication cables 1. Based on this information, control circuit 16 controls the entire corresponding uninterruptible power supply U1. The configuration of each of the uninterruptible power supply U2 to UN is the same as that of uninterruptible power supply 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 to 23 divide the three-phase AC voltages VU, VV, and VW output from the inverter 14 to generate three-phase AC signals V1 to V3. Voltage dividers 21 to 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 resistive elements 36 and 37. Resistive element 36 is connected between terminals T11 and T12, and resistive element 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 to node N1 via three sets of resistors 36 and 37 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 an 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 of the digital signals D12, D23, and D31 corresponds to the reference voltage VS, and their "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 configured, for example, by a photocoupler.

[0039] The "L" level of each digital signal Duv, Dvw, and Dwu corresponds to the ground voltage GND, and its "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 is composed of a microcomputer driven by the power supply voltage VCC 5 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 a voltage detector 20 and a 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 each of the power supply voltages VCC2 and VCC3 may be the same voltage as the power supply voltage VCC1. In this case, the power supplies 42 and 43 can be eliminated. Further, the power supply voltage VCC4 may be the same voltage as the power supply voltage VCC5. In this case, the power supply 44 can be eliminated.

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

[0044] [Comparative Example 1] FIG. 7 is a circuit block diagram showing a configuration of a voltage detector 50 according to Comparative Example 1 of the present embodiment, and is a diagram contrasting with FIG. 3. Referring to FIG. 7, the voltage detector 50 differs from the voltage detector 20 in that ground voltage GND is supplied instead of reference voltage VS to each of voltage dividers 21 to 23, differential circuits 24 to 26, and A / D converters 27 to 29, and light-emitting units 30 to 32 and light-receiving units 33 to 35 are removed.

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

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

[0047] [Comparative Example 2] FIG. 8 is a circuit block diagram showing the configuration of a voltage detector 60 according to another Comparative Example 2 of the present embodiment, and is a diagram to be compared with FIG. 7. Referring to FIG. 8, voltage detector 60 differs from voltage detector 50 in that voltage dividers 21 to 23 and differential circuits 24 to 26 are replaced with transformers 61 to 63.

[0048] A first terminal and a second terminal of the primary winding of the transformer 61 receive AC voltages VU and VV, respectively. An analog signal V12 is output from a first terminal of the secondary winding of the transformer 61, and a second terminal of the secondary winding receives a ground voltage GND.

[0049] A first terminal and a second terminal of the primary winding of the transformer 62 receive AC voltages VV and VW, respectively. An analog signal V23 is output from a first terminal of the secondary winding of the transformer 62, and a second terminal of the secondary winding receives a ground voltage GND.

[0050] A first terminal and a second terminal of the primary winding of the transformer 63 receive AC voltages VW and VU, respectively. An analog signal V31 is output from a first terminal of the secondary winding of the transformer 63, and a second terminal of the secondary winding receives a ground voltage GND.

[0051] The analog signals V12, V23, V31 are converted into digital signals Duv, Dvw, Dwu by A / D converters 27 to 29, and are directly supplied to a control unit 38 (FIG. 5).

[0052] In this voltage detector 60, leakage current can be prevented from flowing from the three-phase AC voltages VU, VV, VW to the ground voltage GND line. However, since transformers 61 to 63 are more expensive than voltage dividers 21 to 23 and the like, there is a problem that this leads to increased cost of an uninterruptible power supply system.

[0053] As described above, in the present embodiment, a predetermined floating node N1 insulated from the ground voltage GND is provided, and voltages between the three-phase AC voltages VU, VV, VW and the predetermined node N1 are divided to generate three-phase AC signals V1 to V3. Therefore, compared with Comparative Example 1, leakage current flowing from the three-phase AC voltages VU, VV, VW to the ground voltage GND can be reduced. Further, compared with Comparative Example 2, the device 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.

[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 Operation 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 voltage detector comprising: a three-phase voltage divider 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 with a level corresponding to the voltage difference between two phase AC signals of the three-phase AC signal; and 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, wherein the predetermined node is isolated from the ground voltage and floats.

2. The voltage detector according to claim 1, wherein the signal generation circuit includes a signal conversion circuit that converts the analog signal into a second digital signal, and 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 a predetermined node and a first voltage different from the reference voltage, and the output circuit generates the first digital signal using the ground voltage and a second voltage different from the ground voltage.

3. The voltage detector according to claim 2, wherein the output circuit includes a light-emitting unit that outputs an optical signal in response to the second digital signal, and 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, and the light-receiving unit generates the first digital signal using the ground voltage and the second voltage.

4. The voltage detector according to claim 1, wherein the three-phase voltage divider circuit includes three voltage dividers, each corresponding to the three-phase AC voltage, and each voltage divider includes an output terminal for outputting an AC signal of the corresponding phase, a first resistive element whose first terminal receives the AC voltage of the corresponding phase and whose second terminal is connected to the output terminal, and a second resistive element whose first terminal is connected to the output terminal and whose second terminal is connected to the predetermined node.

5. A power conversion device comprising: a voltage detector according to claim 1; a power converter for performing power conversion; and a control unit for controlling the power converter based on the first digital signal.

6. The power conversion device according to claim 5, comprising a plurality of sets of voltage detectors, power converters, and control units, wherein the plurality of power converters are connected in parallel to a load.

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