Monitoring circuit and power conversion system

Abstract

To increase the reliability of a monitoring circuit.SOLUTION: A monitoring circuit for monitoring an AC voltage includes: a primary-side circuit in which the AC voltage is input; a secondary-side circuit for outputting a pulse signal of a cycle according to the AC voltage; and a plurality of conversion units for converting the AC voltage to the pulse signal. The conversion units are connected in parallel to each other in a part included in the primary-side circuit and in a part included in the secondary-side circuit.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a monitoring circuit and a power conversion system.

Background Art

[0002] A monitoring circuit for monitoring an AC voltage provided from a commercial power system or the like is known. For example, Patent Document 1 discloses a power failure detection circuit for detecting a power failure of an input power supply. The power failure detection circuit of Patent Document 1 has a configuration in which a primary side circuit of an input power supply system and a secondary side circuit of a DC power supply system are insulated by a first photocoupler. In Patent Document 1, when the input power supply is at or above a power failure detection voltage level, the first photocoupler turns ON and a low-level output is made to the secondary side circuit. When the input power supply has a power failure or drops to the power failure detection voltage level, the first photocoupler turns OFF and a high-level output is made to the secondary side circuit.

[0003] Patent Document 2 discloses a power frequency detection circuit that generates a pulse synchronized with the waveform of an AC power supply. In the power frequency detection circuit of Patent Document 2, light emitting diodes included in two photocouplers are connected in parallel, and phototransistors included in the two photocouplers are connected in series.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] If an element in the monitoring circuit fails, it may become difficult to continue monitoring the AC power supply. For example, if the first photocoupler in Patent Document 1 fails, the power outage detection circuit in Patent Document 1 will not be able to continue detecting the power outage. Also, in the power frequency detection circuit in Patent Document 2, if either of the two photocouplers included in the power frequency detection circuit fails, it will not be possible to continue detecting the power frequency.

[0006] In light of these challenges, this disclosure aims to improve the reliability of monitoring circuits in order to more reliably continue monitoring of AC power supplies. [Means for solving the problem]

[0007] The monitoring circuit of this disclosure is a monitoring circuit for monitoring an AC voltage, comprising: a primary circuit to which the AC voltage is input; a secondary circuit that outputs a pulse signal with a period corresponding to the AC voltage; and a plurality of conversion units that convert the AC voltage into the pulse signal, wherein the plurality of conversion units are connected in parallel to each other in both the portion included in the primary circuit and the portion included in the secondary circuit. [Effects of the Invention]

[0008] According to this disclosure, the reliability of the monitoring circuit can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows an example of the configuration of a power conversion system according to an embodiment. [Figure 2] Figure 2 is a circuit diagram showing an example of a monitoring circuit according to the embodiment. [Figure 3] Figure 3 is a waveform diagram illustrating the operation of the monitoring circuit shown in Figure 2. [Figure 4] Figure 4 is a waveform diagram illustrating the operation of the monitoring circuit shown in Figure 2. [Figure 5] Figure 5 is a graph illustrating the relationship between AC voltage and duty cycle according to the embodiment. [Figure 6]Figure 6 is a flowchart illustrating the detection operation according to the embodiment. [Figure 7] Figure 7 is a circuit diagram showing a monitoring circuit according to a modified example. [Figure 8] Figure 8 is a circuit diagram showing a monitoring circuit according to a modified example. [Figure 9] Figure 9 is a circuit diagram showing a monitoring circuit according to a modified example. [Figure 10] Figure 10 is a waveform diagram illustrating the operation of the monitoring circuit shown in Figure 9. [Figure 11] Figure 11 is a circuit diagram showing a conventional monitoring circuit. [Figure 12] Figure 12 is a waveform diagram illustrating the operation of the monitoring circuit shown in Figure 11. [Modes for carrying out the invention]

[0010] [Description of Embodiments in this Disclosure] Embodiments of this disclosure include, in essence, at least the following:

[0011] (1) The monitoring circuit of the present disclosure is a monitoring circuit for monitoring an AC voltage, comprising: a primary circuit to which the AC voltage is input; a secondary circuit to which a pulse signal with a period corresponding to the AC voltage is output; and a plurality of conversion units to convert the AC voltage into the pulse signal, wherein the plurality of conversion units are connected in parallel to each other in both the portion included in the primary circuit and the portion included in the secondary circuit.

[0012] With this configuration, even if at least one of the multiple conversion units fails, the remaining functioning conversion units can continue to output the pulse signal. Therefore, the monitoring circuit can continue to monitor the AC voltage, improving the reliability of the monitoring circuit.

[0013] (2) In the monitoring circuit of (1) above, the plurality of the conversion units may include a first conversion unit and a second conversion unit. In this case, the first conversion unit may include a first element included in the primary side circuit and configured to output when an AC voltage of positive polarity greater than or equal to a first threshold value is applied, and a first transistor included in the secondary side circuit and configured such that the collector and the emitter are energized by the output of the first element. The second conversion unit may include a second element connected in parallel with the first element in the primary side circuit and configured to output when an AC voltage of negative polarity less than or equal to a second threshold value is applied, and a second transistor connected in parallel with the first transistor in the secondary side circuit and configured such that the collector and the emitter are energized by the output of the second element. The pulse signal may be output from a first connection point where the emitters of the first transistor and the second transistor are connected to each other, or a second connection point where the collectors of the first transistor and the second transistor are connected to each other.

[0014] By configuring in this way, even if one of the first conversion unit and the second conversion unit fails, the other conversion unit can continue to output the pulse signal. Therefore, for example, the monitoring circuit can continue to monitor the AC voltage even while waiting for the repair of the monitoring circuit. Thus, by redundantly providing the first conversion unit and the second conversion unit, the reliability of the monitoring circuit can be improved.

[0015] (3) In the monitoring circuit described in (2) above, the primary side circuit may include one or more first resistors connected in series with the first element, and one or more second resistors connected in series with the second element and in parallel with the one or more first resistors.

[0016] By redundantly providing one or more first resistors and one or more second resistors, the reliability of the monitoring circuit can be improved.

[0017] (4) In the monitoring circuit of (3) above, the primary circuit may include a plurality of first resistors and a plurality of second resistors. In this case, the first end of the first element is connected to the ungrounded wire of the primary circuit, the second end of the first element is connected to the grounded wire of the primary circuit, the third end of the second element is connected to the ungrounded wire of the primary circuit, and the fourth end of the second element is connected to the grounded wire of the primary circuit. The plurality of first resistors may be connected in series, at least one each to the first and second ends of the first element, and the plurality of second resistors may be connected in series, at least one each to the third and fourth ends of the second element.

[0018] This configuration allows for protection of the first and second elements from both positive and negative surge currents.

[0019] (5) In any of the monitoring circuits described in (2) to (4) above, the first element and the second element are each light-emitting diodes, the first transistor may be a phototransistor whose collector and emitter are energized by the light emitted by the first element, and the second transistor may be a phototransistor whose collector and emitter are energized by the light emitted by the second element.

[0020] This configuration allows for monitoring of the AC voltage while keeping the primary and secondary circuits isolated from each other.

[0021] (6) In any of the monitoring circuits described in (2) to (4) above, the first element and the second element are each operational amplifiers, the first transistor may be a transistor whose collector and emitter are energized by the output of the first element, and the second transistor may be a transistor whose collector and emitter are energized by the output of the second element.

[0022] This configuration allows for monitoring of AC voltage while keeping the primary and secondary circuits non-isolated.

[0023] (7) In the monitoring circuit of (1) above, the AC voltage is a three-phase voltage supplied from a first AC power supply, a second AC power supply, and a third AC power supply, and the plurality of conversion units may include a first conversion unit, a second conversion unit, and a third conversion unit. In this case, the first conversion unit includes a first element included in the primary circuit that outputs when a voltage of predetermined polarity and an absolute value greater than or equal to a predetermined threshold is applied by the first AC power supply, and a first transistor connected to the secondary circuit, the collector and emitter of which are energized by the output of the first element, and the second conversion unit includes a second element connected in parallel with the first element in the primary circuit that outputs when a voltage of predetermined polarity and an absolute value greater than or equal to the predetermined threshold is applied by the second AC power supply, and the first The third conversion unit includes a second transistor connected in parallel with the transistor, the collector and emitter of which are energized by the output of the second element, and the third conversion unit may also include a third element connected in parallel with the first and second elements in the primary circuit, which outputs when a voltage of a predetermined polarity and with an absolute value greater than or equal to a predetermined threshold is applied by the third AC power supply, and a third transistor connected in parallel with the first and second transistors in the secondary circuit, the collector and emitter of which are energized by the output of the third element. Furthermore, the pulse signal may be output from a first connection point where the emitters of the first transistor, the second transistor, and the third transistor are connected to each other, or from a second connection point where the collectors of the first transistor, the second transistor, and the third transistor are connected to each other.

[0024] With this configuration, even if one or two of the first, second, and third converters fail, the remaining converters can continue to output pulse signals. Therefore, for example, the monitoring circuit can continue monitoring the AC voltage while waiting for repairs to be completed. In this way, the reliability of the monitoring circuit can be improved by providing redundant first, second, and third converters.

[0025] (8) Any monitoring circuit described in (2) to (6) above may further include a detection unit that detects that the first element or the second element is faulty when the frequency of the pulse signal is equal to the frequency of the AC voltage.

[0026] This configuration allows for the detection of a failure in either the first or second element, enabling smoother maintenance and inspection of the monitoring circuit.

[0027] (9) In the monitoring circuit of (8), the detection unit may acquire the effective value of the AC voltage based on the duty cycle of the pulse signal.

[0028] By configuring it in this way, the effective value of the AC voltage can be obtained.

[0029] (10) In the monitoring circuit of (9) above, the detection unit may determine that the power system providing the AC voltage is normal if the frequency of the pulse signal is one or two times the frequency of the AC voltage and the effective value is equal to or greater than the lower limit that the AC voltage should maintain.

[0030] This configuration allows for a more favorable determination of the power system's state.

[0031] (11) In the monitoring circuit of (10), the detection unit may determine that the power system is experiencing a power outage if the pulse signal is maintained at a high level or a low level for a predetermined period of time longer than the period of the AC voltage, or it may determine that the power system is in a low-voltage state if the effective value is less than the lower limit value.

[0032] By configuring it in this way, it is possible to determine the state of the power system by taking into account not only whether or not there is a power outage, but also whether or not the power system is in a low-voltage state.

[0033] (12) The monitoring circuit of (11) may further include a control unit that controls a relay circuit for connecting and disconnecting the power system and the load. In this case, the control unit may control the relay circuit to connect the power system and the load when the detection unit determines that the power system is normal, or it may control the relay circuit to disconnect the power system and the load when the detection unit determines that the power system is experiencing a power outage or is in a low voltage state.

[0034] This configuration allows the relay circuit to be controlled according to the state of the power system.

[0035] (13) The power conversion system of the present disclosure comprises the monitoring circuit of (12), the relay circuit, and a power conversion device that converts DC power provided from a DC power source into AC power and supplies it to the power system or a load, and converts AC power provided from the power system into DC power and supplies it to the DC power source, wherein the power conversion device converts DC power provided from the DC power source into AC power and supplies it to the load when the power system and the load are disconnected by the relay circuit.

[0036] This configuration allows for independent operation as needed, depending on the state of the power grid.

[0037] [Details of the embodiments of this disclosure] Specific examples of the monitoring circuit and power conversion system described herein will be explained below with reference to the drawings.

[0038] [1. Problems that the embodiment aims to solve] [1.1 Conventional Circuit Configuration] First, the problems that this embodiment aims to solve will be explained with reference to Figures 11 and 12. Figure 11 is a circuit diagram showing a conventional monitoring circuit 90. The circuit diagram in Figure 11 is a power supply frequency detection circuit shown in Patent Document 2. Figure 12 is a waveform diagram illustrating the operation of the monitoring circuit 90 in Figure 11.

[0039] The monitoring circuit 90 is a circuit that converts the AC voltage Vin applied between input terminals T91 and T92 into a pulse signal Vout. The monitoring circuit 90 consists of two resistors R91 and R92 and two photocouplers PC91 and PC92.

[0040] The light-emitting diodes D91 and D92 contained in the two photocouplers PC91 and PC92 are connected in parallel with their polarity reversed in the primary circuit (the circuit to which the AC voltage Vin is applied).

[0041] The phototransistors Tr91 and Tr92, contained within the two photocouplers PC91 and PC92, are connected in series in the secondary circuit (the circuit from which the pulse signal Vout is output). A voltage V1 is applied to the collector of phototransistor Tr91, and the emitter of phototransistor Tr91 is connected to the collector of phototransistor Tr92. The emitter of phototransistor Tr92 is connected to a common potential point. The pulse signal Vout is output from the connection point between the emitter of phototransistor Tr91 and the collector of phototransistor Tr92.

[0042] In Figure 12, (a) shows the input AC voltage Vin, and (b) shows the output pulse signal Vout. For example, when a positive AC voltage Vin greater than or equal to a predetermined first threshold Th91 is applied between input terminals T91 and T92, current flows through light-emitting diode D91 without current flowing through light-emitting diode D92, and phototransistor Tr91 turns ON while phototransistor Tr92 is OFF. As a result, a voltage V1 is output as a pulse signal Vout, and a charge based on the voltage V1 is charged into the capacitance C9.

[0043] On the other hand, when a negative AC voltage Vin below a predetermined second threshold Th92 is applied between input terminals T91 and T92, current flows through light-emitting diode D92 without current flowing through light-emitting diode D91, and phototransistor Tr92 turns ON while phototransistor Tr91 remains OFF. As a result, a zero voltage (0V) is output as a pulse signal Vout, and the charge stored in capacitance C9 is discharged.

[0044] As a result of the above operation, the monitoring circuit 90 outputs a pulse signal Vout with the same frequency as the AC voltage Vin by having the two photocouplers PC91 and PC92 alternately turn ON according to the polarity of the AC voltage Vin.

[0045] [1.2 Challenges of Conventional Circuits] If any element in the monitoring circuit 90 fails, it becomes impossible to continue monitoring the AC voltage Vin. Since the two photocouplers PC91 and PC92 are connected in series in the secondary circuit, if at least one of the two photocouplers PC91 or PC92 fails, the pulse signal Vout will remain constant at voltage V1 or zero voltage, and no pulse output will be produced.

[0046] Furthermore, if at least one of the two resistors R91 and R92 fails (for example, an open circuit failure), the AC voltage Vin will not be applied to either of the two photocouplers PC91 and PC92. As a result, the pulse signal Vout will remain constant at voltage V1, and no pulse output will be produced.

[0047] Thus, in the conventional monitoring circuit 90, if one of the multiple elements (two photocouplers PC91 and PC92, and two resistors R91 and R92) failed, it became difficult to continue monitoring the AC voltage Vin.

[0048] Therefore, in the monitoring circuit 10 of this embodiment, two photocouplers PC1 and PC2 are connected in parallel in both the primary circuit 11 and the secondary circuit 12, and multiple resistors R11, R12, R13, R21, R22, and R23 are connected in parallel in the primary circuit 11. This increases the redundancy of the elements against failure, thereby improving the reliability of the monitoring circuit 10.

[0049] The power conversion system 1 of this embodiment will be described below.

[0050] [2. Power Conversion System 1] [2.1 Configuration of Power Conversion System 1] Figure 1 shows an example of the configuration of a power conversion system 1 according to an embodiment. The power conversion system 1 is a system that monitors the AC voltage Vin supplied from the power grid 50. More specifically, the power conversion system monitors the status of the power grid 50 (e.g., power outage and power restoration). The power grid 50 is, for example, a commercial power grid, but may be any other power grid. The power conversion system 1 comprises a monitoring circuit 10, a relay circuit 20, a power conversion device 30, and a DC power supply 40.

[0051] The relay circuit 20 has a contact 21 and a coil 22. The monitoring circuit 10 controls the opening and closing of the contact 21 by supplying current to the coil 22.

[0052] The power converter 30 includes, for example, a bidirectional inverter circuit. The power converter 30 converts DC power supplied from the DC power supply 40 into grid-connectable AC power. The power converter 30 also converts AC power supplied from the power grid 50 into DC power.

[0053] The DC power supply 40 is, for example, an energy storage device. In this case, the DC power supply 40 may be a lithium-ion battery or another type of energy storage battery. The DC power supply 40 may also be a solar cell or a combination of an energy storage device and a solar cell. If the DC power supply 40 includes an energy storage device, it is charged by DC power converted by the power converter 30 or by power generated by the solar cell.

[0054] The power conversion system 1 supplies power from the power grid 50 or power from the DC power supply 40 to a load 60 installed at a consumer (e.g., a general household or factory). The monitoring circuit 10 monitors the status of the power grid 50, and if the power grid 50 is operating normally, it closes the relay circuit 20 to supply power from the power grid 50 to the load 60.

[0055] On the other hand, the monitoring circuit 10 disconnects the load 60 from the power system 50 by opening the relay circuit 20 when the power system 50 is experiencing a power outage. In this state, the power converter 30 converts the DC power from the DC power supply 40 into AC power and supplies it to the load 60. As a result, the load 60 can receive power even when the power system 50 is experiencing a power outage (standalone operation).

[0056] Subsequently, when the monitoring circuit 10 detects the restoration of power to the power system 50, the monitoring circuit 10 closes the relay circuit 20, thereby resuming the power supply from the power system 50 to the load 60. In parallel with the power supply from the power system 50 to the load 60, power may also be supplied to the load 60 from the DC power supply 40 and the power converter 30.

[0057] [2.2 Configuration of the monitoring circuit 10] Figure 2 is a circuit diagram showing an example of a monitoring circuit 10 according to the embodiment. The monitoring circuit 10 is a circuit that converts the AC voltage Vin of the power system 50 applied between input terminals T1 and T2 into a pulse signal Vout. The monitoring circuit 10 comprises a primary circuit 11 to which the AC voltage Vin is applied, a secondary circuit 12 that outputs a pulse signal Vout with a period corresponding to the AC voltage Vin, and a plurality of conversion units PC1 and PC2 that convert the AC voltage Vin into a pulse signal Vout. As will be described later, the plurality of conversion units PC1 and PC2 are connected in parallel to each other in both the portion included in the primary circuit 11 and the portion included in the secondary circuit 12.

[0058] The multiple conversion units PC1 and PC2 include a first conversion unit PC1 and a second conversion unit PC2. The first conversion unit PC1 and the second conversion unit PC2 are each photocouplers. In this case, the primary circuit 11 and the secondary circuit 12 are isolated by the first conversion unit PC1 and the second conversion unit PC2.

[0059] The first conversion unit PC1 (hereinafter referred to as "photocoupler PC1") includes a first element D12 (in this example, a light-emitting diode, hereinafter referred to as "light-emitting diode D12") included in the primary circuit 11 and a first transistor Tr1 (in this example, a phototransistor, hereinafter referred to as "phototransistor Tr1") included in the secondary circuit 12. , Da The diode D11 is connected in antiparallel to the light-emitting diode D12.

[0060] The second conversion unit PC2 (hereinafter referred to as "photocoupler PC2") includes a second element D22 (in this example, a light-emitting diode, hereinafter referred to as "light-emitting diode D22") included in the primary circuit 11 and a second transistor Tr2 (in this example, a phototransistor, hereinafter referred to as "phototransistor Tr2") included in the secondary circuit 12. , Da The diode D21 is connected in antiparallel to the light-emitting diode D22.

[0061] Photocoupler PC2 is connected in parallel to photocoupler PC1 in both the primary circuit 11 and the secondary circuit 12. Specifically, the light-emitting diode D22 of photocoupler PC2 is connected in parallel to the light-emitting diode D12 of photocoupler PC1 with the polarity reversed. That is, the cathode of light-emitting diode D12 is connected to the anode of light-emitting diode D22, and the anode of light-emitting diode D12 is connected to the cathode of light-emitting diode D22.

[0062] Furthermore, the phototransistor Tr2 of photocoupler PC2 is connected in parallel with the phototransistor Tr1 of photocoupler PC1. That is, the collector of phototransistor Tr2 is connected to the collector of phototransistor Tr1, and the emitter of phototransistor Tr2 is connected to the emitter of phototransistor Tr1.

[0063] The primary circuit 11 includes six resistors R11, R12, R13, R21, R22, and R23. In the example in Figure 2, the anode (first terminal of the first element) of the light-emitting diode D12 is connected to the ungrounded side (input terminal T1 side) wire of the primary circuit 11, and the cathode (second terminal of the first element) of the light-emitting diode D12 is connected to the grounded side (input terminal T2 side) wire of the primary circuit 11. Resistor R11 is connected in series with the anode of the light-emitting diode D12. Resistor R12 is connected in series with the cathode of the light-emitting diode D12. The two resistors R11 and R12 connected in series with the light-emitting diode D12 in this way are "current-limiting resistors" that suppress surge current from the power system 50 from flowing to the photocoupler PC1, and are an example of the "first resistor" in this disclosure. Therefore, for the two resistors R11 and R12, resistors with relatively high resistance values ​​(for example, 200kΩ) are selected, depending on the characteristics of the photocoupler PC1.

[0064] Resistor R13 is connected in parallel with the light-emitting diode D12. Resistor R13 is a "threshold determination resistor" that determines the voltage threshold at which the photocoupler PC1 turns ON (i.e., the light-emitting diode D12 lights up). A resistor with an appropriate resistance value (e.g., 2.7kΩ) is selected for resistor R13 depending on the characteristics of the photocoupler PC1 and the effective value of the AC voltage Vin. The resistance values ​​of the two resistors R11 and R12 are higher than the resistance value of resistor R13.

[0065] The two resistors R21 and R22 are current-limiting resistors for the photocoupler PC2 and are an example of the "second resistor" in this disclosure. The two resistors R21 and R22 are connected in parallel with the two resistors R11 and R12 (first resistors). Specifically, in the example in Figure 2, the cathode of the light-emitting diode D22 (the third terminal of the second element) is connected to the wire on the ungrounded side (input terminal T1 side) of the primary circuit 11, and the anode of the light-emitting diode D22 (the fourth terminal of the second element) is connected to the wire on the grounded side (input terminal T2 side) of the primary circuit 11. The resistor R21 is connected in series with the cathode of the light-emitting diode D22. The resistor R22 is connected in series with the anode of the light-emitting diode D22. Similar to the two resistors R11 and R12, resistors with relatively high resistance values ​​are selected for the two resistors R21 and R22.

[0066] Resistor R23 is the threshold determination resistor for the photocoupler PC2 and is connected in parallel to resistor R13. Specifically, resistor R23 is connected in parallel to the light-emitting diode D22. Similar to resistor R13, a resistor with an appropriate resistance value can be selected for resistor R23.

[0067] In this way, in the monitoring circuit 10, the photocoupler PC2 is connected in parallel to the photocoupler PC1, and the current limiting resistors (resistors R21, R22) and threshold determination resistor (resistor R23) of the photocoupler PC2 are connected in parallel to the current limiting resistors (resistors R11, R12) and threshold determination resistor (resistor R13) of the photocoupler PC1, respectively.

[0068] The secondary circuit 12 includes a detection unit 13 for detecting a pulse signal Vout, a control unit 14 for controlling the relay circuit 20 based on the detection result of the detection unit 13, a power line 15 to which a DC voltage V1 is applied, and a resistor R51 for adjusting the voltage of the pulse signal Vout.

[0069] The collectors of the two phototransistors Tr1 and Tr2 are connected to the power supply line 15. The emitters of the two phototransistors Tr1 and Tr2 are connected at the first connection point X1. A line is drawn from the first connection point X1 to the detection unit 13 to output a pulse signal Vout, and the first end of resistor R51 is connected to the middle of this line. The second end of resistor R51, opposite to the first end, is connected to a common potential point.

[0070] The detection unit 13 has an integrated circuit that includes a logic circuit (e.g., a logic IC) and a memory circuit (e.g., a memory IC). The detection unit 13 receives an AC voltage Vin and a pulse signal Vout as inputs. Based on the AC voltage Vin and the pulse signal Vout, the detection unit 13 detects power outages and restorations in the power system 50 and outputs the detection signal to the control unit 14.

[0071] The control unit 14, like the detection unit 13, has an integrated circuit that includes logic circuits and memory circuits. The control unit 14 controls the relay circuit 20 based on the detection signal sent from the detection unit 13.

[0072] [2.3 Monitoring method using monitoring circuit 10] Next, the monitoring method performed by the monitoring circuit 10 will be described. The monitoring circuit 10 generates a pulse signal Vout according to the state of the power system 50 and the state of the monitoring circuit 10. The detection unit 13 of the monitoring circuit 10 determines the state of the power system 50 and the state of the monitoring circuit 10 based on the pulse signal Vout. After describing the pulse signal Vout generated by the monitoring circuit 10, the determination operation in the detection unit 13 and the control operation in the control unit 14 will be described below.

[0073] [2.3.1 About the pulse signal Vout] Figure 3 is a waveform diagram illustrating the operation of the monitoring circuit 10. In Figure 3, (a) shows the AC voltage Vin input to the input terminals T1 and T2 and the detection unit 13, and (b) to (d) show the pulse signal Vout, respectively.

[0074] Specifically, in Figure 3, (b) shows the pulse signal Vout during "normal operation" when the power system 50 is operating normally and each element of the monitoring circuit 10 is operating normally; (c) shows the pulse signal Vout during "failure" when the power system 50 is operating normally and the photocoupler PC2 is malfunctioning; and (d) shows the pulse signal Vout during "power outage" when the power system 50 is experiencing a power outage.

[0075] First, let's explain the pulse signal Vout under normal conditions. When a positive AC voltage Vin of a predetermined first threshold Th1 (where Th1 is a positive value) or higher is applied between input terminals T1 and T2, current does not flow through the light-emitting diode D22 but flows through the light-emitting diode D12, and phototransistor Tr1 turns ON while phototransistor Tr2 is OFF. In other words, photocoupler PC1 turns ON while photocoupler PC2 is OFF. As a result, a value (high level) based on the voltage V1 and resistor R51 is output as the pulse signal Vout.

[0076] When a negative polarity AC voltage Vin, which is less than or equal to a predetermined second threshold Th2 (where Th2 is a negative value), is applied between input terminals T1 and T2, current does not flow through the light-emitting diode D12 but current flows through the light-emitting diode D22, and phototransistor Tr1 is OFF while phototransistor Tr2 is ON. In other words, photocoupler PC2 is ON while photocoupler PC1 is OFF. As a result, a value (high level) based on voltage V1 and resistor R51 is output as a pulse signal Vout, similar to when a positive polarity AC voltage Vin, which is greater than or equal to the first threshold Th1, is applied between input terminals T1 and T2.

[0077] When an AC voltage Vin greater than the second threshold Th2 and less than the first threshold Th1 is applied between input terminals T1 and T2, no current flows through either of the two light-emitting diodes D12 and D22, and both phototransistors Tr1 and Tr2 turn OFF. In other words, both photocouplers PC1 and PC2 turn OFF. As a result, the voltage at the common potential point (low level) is output as a pulse signal Vout.

[0078] Thus, under normal conditions, when the AC voltage Vin is positive, photocoupler PC1 turns ON, and when it is negative, photocoupler PC2 turns ON, causing the two photocouplers PC1 and PC2 to alternately output a high level as a pulse signal Vout. In other words, under normal conditions, the monitoring circuit 10 outputs a pulse signal Vout with a frequency twice that of the AC voltage Vin. For example, if the frequency of the AC voltage Vin is 60Hz, the frequency of the pulse signal Vout will be 120Hz.

[0079] Here, the first threshold Th1 (Th1>0) is a value (detection voltage) determined based on the threshold determination resistor (resistor R13) of the photocoupler PC1. Specifically, the first threshold Th1 is calculated by the following equation (1).

[0080] Th1=Ic1×Rx1 / CTR1+Vf1×(1+Rx1 / R13) ···(1)

[0081] Here, Ic1: Output current of photocoupler PC1 (current flowing through phototransistor Tr1) CTR1: Current transfer rate of photocoupler PC1 Vf1: Forward voltage of light-emitting diode D12 Rx1: Sum of resistors R11 and R12

[0082] Furthermore, the second threshold Th2 (Th2<0) is a value determined based on the threshold determination resistor (resistor R23) of the photocoupler PC2. Specifically, the second threshold Th2 is calculated by the following equation (2).

[0083] Th2=-Ic2×Rx2 / CTR2+Vf2×(1+Rx2 / R23)...(2)

[0084] Here, Ic2: Output current of photocoupler PC2 (current flowing through phototransistor Tr2) CTR2: Current transfer rate of photocoupler PC2 Vf2: Forward voltage of light-emitting diode D22 Rx2: Sum of resistors R21 and R22

[0085] For the two resistors R13 and R23, resistors are selected such that the first threshold Th1 is equal to the absolute value of the second threshold Th2 (Th1 = |Th2|). This makes it possible to match the duty cycle of the pulse signal Vout when the AC voltage Vin is positive polarity with the duty cycle of the pulse signal Vout when the AC voltage Vin is negative polarity, thus enabling the output of a more stable pulse signal Vout.

[0086] Next, we will explain the pulse signal Vout in the event of a malfunction. In this example, the photocoupler PC1 and the three resistors R11, R12, and R13 operate normally. Therefore, when a positive AC voltage Vin of first threshold Th1 or higher is applied between input terminals T1 and T2, the photocoupler PC1 turns ON while the photocoupler PC2 remains OFF, as in normal operation. As a result, a high level is output as the pulse signal Vout.

[0087] A failure in photocoupler PC2 is, for example, a short circuit failure in light-emitting diode D22. In this case, since light-emitting diode D22 will no longer emit light, even if a negative polarity AC voltage Vin below the second threshold Th2 is applied to photocoupler PC2, photocoupler PC2 will remain in the OFF state. Therefore, when a negative polarity AC voltage Vin below the second threshold Th2 is applied between input terminals T1 and T2, both photocouplers PC1 and PC2 will turn OFF. As a result, the voltage at the common potential point (low level) is output as a pulse signal Vout.

[0088] Thus, in the event of a failure, the photocoupler PC2 remains in the OFF state, and the photocoupler PC1 outputs a high level pulse signal Vout only when the AC voltage Vin is positive. In other words, in the event of a failure, the monitoring circuit 10 outputs a pulse signal Vout with the same frequency as the AC voltage Vin. For example, if the frequency of the AC voltage Vin is 60Hz, the frequency of the pulse signal Vout will be 60Hz.

[0089] In the above explanation, the failure of the photocoupler PC2 was used as an example of a failure, but the pulse signal Vout shown in Figure 3(c) will also occur if at least one of the three resistors R21, R22, and R23 fails as follows. For example, if at least one of the two resistors R21 and R22 has an open circuit failure, no current will flow to the photocoupler PC2, and the photocoupler PC2 will remain in the OFF state. Similarly, if resistor R23 has a short circuit failure, no current will flow to the photocoupler PC2, and the photocoupler PC2 will remain in the OFF state.

[0090] Furthermore, if photocoupler PC2 and the three resistors R21, R22, and R23 are functioning normally, but photocoupler PC1 and at least one of the three resistors R11, R12, and R13 fail, photocoupler PC1 will remain in the OFF state. In this case, photocoupler PC2 will output a high level pulse signal Vout only when the AC voltage Vin is negative. In this case as well, the monitoring circuit 10 will output a pulse signal Vout with the same frequency as the AC voltage Vin.

[0091] Next, we will explain the pulse signal Vout during a power outage. The state of power system 50 being out of service includes not only the state in which the AC voltage Vin is at zero voltage, but also the state in which the effective value of the AC voltage Vin is less than a predetermined value Z1 (extremely low voltage state). Specifically, the extremely low voltage state is the state in which the peak voltage of the positive polarity of the AC voltage Vin is less than the first threshold Th1, and the peak voltage of the negative polarity of the AC voltage Vin is greater than the second threshold Th2.

[0092] During a power outage, both photocouplers PC1 and PC2 remain in the OFF state. As a result, the voltage at the common potential point (low level) is output as a pulse signal Vout, as shown in Figure 3(d).

[0093] Next, we will explain the pulse signal Vout in a state where the AC voltage Vin is higher than the voltage in the extremely low voltage state, but lower than the normal voltage (low voltage state).

[0094] Figure 4 is a waveform diagram illustrating the operation of the monitoring circuit 10 under low voltage conditions. In Figure 4(a), the AC voltage Vin (=Vin2) under low voltage conditions is shown by a solid line, and the AC voltage Vin (=Vin1) under normal conditions is shown by a dashed line. In Japan, the lower limit Z2 that the AC voltage Vin should maintain is stipulated by laws such as the Electricity Business Act. For example, if the standard voltage of the AC voltage Vin is 100V, the lower limit Z2 is 95V, and if the standard voltage of the AC voltage Vin is 200V, the lower limit Z2 is 182V.

[0095] Furthermore, to allow for some margin, the lower limit Z2 may be set to a value higher than that stipulated by law. For example, if the standard voltage of AC voltage Vin is 100V, the lower limit Z2 may be set to a value greater than 95V (e.g., 97V), and if the standard voltage of AC voltage Vin is 200V, the lower limit Z2 may be set to a value greater than 182V (e.g., 190V).

[0096] In this embodiment, a low-voltage state means a state in which the effective value of the AC voltage Vin is lower than the lower limit Z2 and greater than or equal to a predetermined value Z1 (the effective value of the AC voltage Vin in an extremely low-voltage state). For example, if the effective value of the AC voltage Vin under normal conditions is 202V, then the effective value of the AC voltage Vin in a low-voltage state is less than 182V and greater than or equal to the predetermined value Z1.

[0097] In Figure 4 (b), the pulse signal Vout is shown during "low voltage" operation, when the power system 50 is in a low voltage state and each element of the monitoring circuit 10 is operating normally. The operation of the monitoring circuit 10 during low voltage is basically the same as the operation of the monitoring circuit 10 during normal operation. However, because the effective value of the AC voltage Vin is lower than during normal operation, the period during which the AC voltage Vin is above the first threshold Th1 in the positive polarity and the period during which the AC voltage Vin is below the second threshold Th2 in the negative polarity are both shorter than during normal operation. As a result, the period during which the two photocouplers PC1 and PC2 are ON is shorter compared to normal operation, and the duty cycle becomes smaller.

[0098] Figure 5 is a graph illustrating the relationship between the RMS value of the AC voltage Vin input to the monitoring circuit 10 and the duty cycle of the pulse signal Vout output by the monitoring circuit 10. In Figure 5, the horizontal axis represents the RMS value of the AC voltage Vin, and the vertical axis represents the duty cycle of the pulse signal Vout.

[0099] As shown in Figure 5, the larger the effective value of the AC voltage Vin, the larger the duty cycle of the pulse signal Vout. In other words, the effective value of the AC voltage Vin can be estimated based on the duty cycle of the pulse signal Vout.

[0100] For example, multiple plotted PLs shown in the graph of Figure 5 are measured by test. Then, a function F1 representing the multiple plotted PLs is calculated. Function F1 only needs to approximate the multiple plotted PLs and may be a linear function, a quadratic function, or a step function. Function F1 may be calculated by linear regression or by a moving average. Function F1 is stored, for example, in the memory circuit of the detection unit 13.

[0101] [2.3.2 Determination operation in the detection unit 13] Next, the determination operation in the detection unit 13 will be explained. Figure 6 is a flowchart illustrating the detection operation performed by the detection unit 13 (specifically, the logic circuit of the detection unit 13).

[0102] The detection unit 13 first monitors whether the pulse signal Vout contains a high-level output (step S11). For example, if the input pulse signal Vout remains at a low level for a predetermined period of time sufficiently longer than the period of the AC voltage Vin under normal conditions (e.g., 1 second) (NO in step S11), the detection unit 13 determines that the power system 50 is experiencing a power outage (power outage determination: step S12), and terminates the detection operation.

[0103] If the input pulse signal Vout contains a high-level output (YES in step S11), the detection unit 13 obtains the duty cycle of the pulse signal Vout (step S13). Then, the detection unit 13 obtains the RMS value of the AC voltage Vin based on the obtained duty cycle and function F1 (step S14). Function F1 takes the duty cycle as a variable and the RMS value of the AC voltage Vin as its solution. Therefore, the detection unit 13 calculates the RMS value of the AC voltage Vin by substituting the obtained duty cycle into function F1.

[0104] Next, the detection unit 13 monitors whether the effective value of the acquired AC voltage Vin is greater than or equal to the lower limit Z2 that the AC voltage Vin should maintain (step S15). If the effective value of the AC voltage Vin is less than the lower limit Z2 (NO in step S15), the detection unit 13 determines that the power system 50 is in a low voltage state (low voltage determination: step S16) and proceeds to the next step S17. If the effective value of the AC voltage Vin is greater than or equal to the lower limit Z2 (YES in step S15), the detection unit 13 skips step S16 and proceeds to the next step S17.

[0105] Next, the detection unit 13 compares the frequency FR2 of the pulse signal Vout with the frequency FR1 of the AC voltage Vin under normal conditions (step S17). Here, the frequency FR1 of the AC voltage Vin under normal conditions is stored in the memory circuit of the detection unit 13. The logic circuit of the detection unit 13 reads the frequency FR1 from the memory circuit and compares it with the frequency FR2 of the input pulse signal Vout.

[0106] If the frequency FR2 of the pulse signal Vout is twice the frequency FR1 of the AC voltage Vin (FR2 = 2 × FR1), the detection unit 13 terminates its detection operation.

[0107] If the frequency FR2 of the pulse signal Vout is 1 times the frequency FR1 of the AC voltage Vin (FR2 = FR1), the detection unit 13 determines that there is a fault in the element included in the monitoring circuit 10 (fault determination: step S18), and terminates the detection operation.

[0108] In fault detection (step S18), the detection unit 13 may estimate which element in the monitoring circuit 10 has failed. For example, the detection unit 13 compares the period during which the input AC voltage Vin has a predetermined polarity with the period during which the pulse signal Vout is maintained at a low level. When the AC voltage Vin is negative and the pulse signal Vout is maintained at a low level, the photocoupler PC2, which should normally be ON, is OFF. Therefore, the detection unit 13 determines that the photocoupler PC2 and at least one of the three resistors R21, R22, and R23 in the monitoring circuit 10 have failed.

[0109] Furthermore, when the AC voltage Vin is positive and the pulse signal Vout is maintained at a low level, the photocoupler PC1, which should normally be ON, is OFF. Therefore, the detection unit 13 determines that the photocoupler PC1 and at least one of the three resistors R11, R12, and R13 in the monitoring circuit 10 are faulty.

[0110] If the frequency FR2 of the pulse signal Vout is neither twice nor exactly the same as the frequency FR1 of the AC voltage Vin (FR2 ≠ 2 × FR1 and FR2 ≠ FR1), the detection unit 13 determines that an abnormality has occurred in the monitoring circuit 10 or the power system 50 (abnormality determination: step S19), and terminates the detection operation. For example, if a failure occurs in which at least one of the two phototransistors Tr1 and Tr2 is always ON, the pulse signal Vout will be maintained at a high level output, making it impossible to measure the frequency FR2 of the pulse signal Vout. In such a case, the detection unit 13 performs an abnormality determination.

[0111] If, at the end of the detection operation, no power outage, low voltage, or abnormality determination has been made, the detection unit 13 may determine that the power system 50 is normal (normal determination).

[0112] As a result, the detection unit 13 can detect the state of the power system 50 (power outage, low voltage, abnormal, or normal) and the state of the monitoring circuit 10 (fault, abnormal, or normal). The detection unit 13 outputs these determination results to the control unit 14.

[0113] [2.3.3 Control operation in the control unit 14] If the detection unit 13 detects a power outage, low voltage, or abnormality, the control unit 14 opens the relay circuit 20 to disconnect the power system 50 from the load 60. If the detection unit 13 does not detect a power outage, low voltage, or abnormality, or if the detection unit 13 detects normal operation (i.e., the power system 50 is operating normally), the control unit 14 closes the relay circuit 20 to connect the power system 50 to the load 60.

[0114] If the detection unit 13 performs a fault detection or abnormality detection, the control unit 14 transmits the detection result to the outside of the monitoring circuit 10 from a communication unit (not shown). For example, the control unit 14 transmits the detection result to the administrator responsible for maintenance and inspection of the power conversion system 1, or to the terminal of a user using the power conversion system 1 (e.g., a server, personal computer, smartphone, or tablet terminal). The administrator or user performs maintenance and inspection of the monitoring circuit 10 based on the detection result received at the terminal.

[0115] [2.4 Effects of Power Conversion System 1] In the monitoring circuit 10, photocoupler PC2 is connected in parallel to photocoupler PC1 in both the primary circuit 11 and the secondary circuit 12. Therefore, even if one of the two photocouplers PC1 and PC2 fails, the other photocoupler can continue to output the pulse signal Vout, as shown in Figure 3(c). For this reason, for example, while waiting for the monitoring circuit 10 to be repaired, the monitoring circuit 10 can continue to monitor whether the power system 50 is experiencing a power outage. In this way, the reliability of the monitoring circuit 10 can be improved by providing redundant photocouplers PC1 and PC2.

[0116] Furthermore, in the monitoring circuit 10, the current limiting resistors (resistors R21, R22) and threshold determination resistor (resistor R23) of photocoupler PC2 are connected in parallel to the current limiting resistors (resistors R11, R12) and threshold determination resistor (resistor R13) of photocoupler PC1, respectively. Therefore, even if any one of these six resistors R11, R12, R13, R21, R22, R23 fails, the output of the pulse signal Vout can continue from one of the photocouplers (PC1 or PC2). In other words, the monitoring circuit 10 provides redundancy not only in the two photocouplers PC1 and PC2, but also in the six resistors R11, R12, R13, R21, R22, R23. As a result, monitoring of whether or not the power system 50 is experiencing a power outage can be continued more reliably, thereby improving the reliability of the monitoring circuit 10.

[0117] Furthermore, in the monitoring circuit 10, two resistors R11 and R12 are connected in series, one each to both ends (first and second ends) of the light-emitting diode D12. This protects the light-emitting diode D12 from both positive and negative surge currents. Note that at least one resistor is required to be connected in series to each end of the light-emitting diode D12, but two or more may be used. For example, instead of resistor R11, two resistors may be connected in series to the anode of the light-emitting diode D12.

[0118] Furthermore, in the monitoring circuit 10, two resistors R21 and R22 are connected in series, one each, to both ends (third and fourth terminals) of the light-emitting diode D22. This protects the light-emitting diode D22 from both positive and negative surge currents. Note that the resistors connected in series to each end of the light-emitting diode D22 only need to be at least one, but there may be two or more.

[0119] Furthermore, since the monitoring circuit 10 uses photocouplers as the first element PC1 and the second element PC2, it is possible to monitor the AC voltage Vin while the primary circuit 11 and the secondary circuit 12 are isolated from each other.

[0120] Here, when the power system 50 is restored after a power outage, it may be in a low-voltage state for a certain period of time before returning to normal operation. In this case, if the load 60 is connected to the power system 50 in a low-voltage state, the operation of the load 60 may become unstable. For this reason, it is preferable to connect the load 60 to the power system 50 when the power system 50 is operating normally (i.e., when the voltage has returned to normal).

[0121] The monitoring circuit 10 calculates the AC voltage Vin based on the duty cycle of the pulse signal Vout, which allows it to determine not only whether the power system 50 is experiencing a power outage, but also whether the power system 50 is in a low-voltage state. Therefore, with the power conversion system 1, the load 60 can be connected to the power system 50 after power has been restored and it has returned to normal operation (i.e., after low-voltage detection is no longer required), allowing the load 60 to be used more stably.

[0122] [3. Variant] While embodiments of this disclosure have been described above, various modifications are possible to this disclosure in addition to the forms described above. Hereinafter, modifications of embodiments of this disclosure will be described. In the following modifications, components similar to those in the embodiments are denoted by the same reference numerals and their descriptions are omitted.

[0123] [3.1 Monitoring circuit 10a related to a modified example] In the monitoring circuit 10 according to this embodiment, redundancy is provided to the two photocouplers PC1 and PC2 by connecting them in parallel, and redundancy is also provided to the current limiting resistors and threshold determination resistors of the two photocouplers PC1 and PC2 by connecting them in parallel.

[0124] However, the two photocouplers PC1 and PC2 may share the same current limiting resistor and threshold determination resistor. In other words, in the monitoring circuit 10, the current limiting resistor and threshold determination resistor of the two photocouplers PC1 and PC2 do not need to be connected in parallel.

[0125] Figure 7 is a circuit diagram showing a modified monitoring circuit 10a. The monitoring circuit 10a differs from the monitoring circuit 10 of the embodiment in that three resistors R1, R2, and R3 are provided in the primary circuit 11a instead of six resistors R11, R12, R13, R21, R22, and R23, but all other aspects are the same.

[0126] The two resistors R1 and R2 are connected in series to the two photocouplers PC1 and PC2, respectively. The two resistors R1 and R2 function as current limiting resistors for both photocoupler PC1 and photocoupler PC2.

[0127] Specifically, the first end of resistor R1 is connected to input terminal T1. The second end of resistor R1, opposite the first end, is connected in series with the anode of light-emitting diode D12 and in series with the cathode of light-emitting diode D22.

[0128] Furthermore, the first end of resistor R2 is connected to input terminal T2. The second end of resistor R2, opposite to the first end, is connected in series with the cathode of light-emitting diode D12 and in series with the anode of light-emitting diode D22.

[0129] Resistor R3 is connected in parallel to the two photocouplers PC1 and PC2, respectively. Resistor R3 functions as a threshold determination resistor for both photocoupler PC1 and photocoupler PC2.

[0130] Specifically, the first end of resistor R3 is connected to the second end of resistor R1, the anode of light-emitting diode D12, and the cathode of light-emitting diode D22, respectively. The second end of resistor R3, opposite the first end, is connected to the second end of resistor R2, the cathode of light-emitting diode D12, and the anode of light-emitting diode D22, respectively.

[0131] In monitoring circuit 10a, similar to monitoring circuit 10, photocoupler PC2 is connected in parallel to photocoupler PC1 in both the primary circuit 11 and the secondary circuit 12. Therefore, even if one of the two photocouplers PC1 and PC2 fails, monitoring circuit 10a can continue to monitor whether or not the power system 50 is experiencing a power outage.

[0132] Furthermore, in the monitoring circuit 10a, the two photocouplers PC1 and PC2 share current limiting resistors (resistors R1 and R2) and threshold determination resistor (resistor R3), thus reducing the number of resistors used compared to the monitoring circuit 10. This reduces the manufacturing cost of the monitoring circuit 10a.

[0133] On the other hand, if any one of the three resistors R1, R2, or R3 fails, the power outage monitoring of the power system 50 in the monitoring circuit 10a may stop. However, resistors generally have a longer lifespan than photocouplers and are less prone to failure than photocouplers, so simply providing redundancy in the two photocouplers PC1 and PC2 is sufficient to improve the reliability of the monitoring circuit 10a.

[0134] [3.2 Monitoring circuit 10b related to modified example] In the monitoring circuit 10 according to this embodiment, a photocoupler was used as an example of a plurality of conversion units PC1, PC2 that transmit signals from the primary circuit 11 to the secondary circuit 12. However, elements other than photocouplers may be used as conversion units. For example, the conversion unit may be a comparator including an operational amplifier.

[0135] Figure 8 is a circuit diagram showing a modified monitoring circuit 10b. The monitoring circuit 10b comprises a primary circuit 11b, a secondary circuit 12b, and a plurality of conversion units CM1 and CM2. The plurality of conversion units CM1 and CM2 include a first conversion unit CM1 and a second conversion unit CM2. The first conversion unit CM1 and the second conversion unit CM2 are comparators, and will be referred to as "comparator CM1" and "comparator CM2" respectively below. In the monitoring circuit 10b, the primary circuit 11b and the secondary circuit 12b are not isolated from each other.

[0136] The primary circuit 11b consists of four resistors R31, R32, R33, R34 and two no Da Includes iodine D1, D2 and . The diode D1, resistor R31, and resistor R32 are connected in parallel between input terminals T1 and T2 in this order. . Iode D1 anode It is connected to input terminal T1. , Da Iode D1 Cathode It is connected to resistor R31. . Iode D1 has the function of suppressing the application of reverse voltage to comparator CM1.

[0137] Da The diode D2, resistor R33, and resistor R34 are connected in parallel between input terminals T1 and T2 in this order. , Da The set of Iode D2, resistor R33 and resistor R34 is , Da The set of diode D1, resistor R31, and resistor R32 is connected in parallel. . The cathode of Iode D2 is connected to input terminal T1. , Da The anode of diode D2 is connected to resistor R33. .Iode D2 has the function of suppressing the application of reverse voltage to comparator CM2.

[0138] Comparator CM1 includes operational amplifier A1, which is included in the primary circuit 11b, and transistor Tr3, which is included in the secondary circuit 12b. The non-inverting input T11 of operational amplifier A1 is connected between resistors R31 and R32. The inverting input T12 of operational amplifier A1 is connected to a common potential point via a DC power supply that provides a voltage of the first threshold Th1 (Th1>0). The output of operational amplifier A1 is connected to the base of transistor Tr3.

[0139] When a positive voltage greater than or equal to the first threshold Th1 is applied to the non-inverting input T11 of operational amplifier A1, operational amplifier A1 outputs a predetermined voltage and transistor Tr3 turns ON. If the applied voltage is less than the first threshold Th1, operational amplifier A1 does not output the predetermined voltage, and transistor Tr3 remains OFF.

[0140] The two resistors R31 and R32 are "current-limiting resistors" that suppress surge current from the power system 50 from flowing to the comparator CM1, and are an example of the first resistors in this disclosure. For this reason, resistors with relatively high resistance values ​​are selected for the two resistors R31 and R32.

[0141] Comparator CM2 includes operational amplifier A2, which is included in the primary circuit 11b, and transistor Tr4, which is included in the secondary circuit 12b. The inverting input T21 of operational amplifier A2 is connected between resistors R33 and R34.

[0142] The two resistors R33 and R34 are "current-limiting resistors" that suppress surge current from the power system 50 from flowing to the comparator CM2, and are an example of the second resistor in this disclosure. For this reason, resistors with relatively high resistance values ​​are selected for the two resistors R33 and R34.

[0143] The non-inverting input T22 of op-amp A2 is connected to a common potential point via a DC power supply that provides a second threshold voltage Th2 (Th2<0). The output of op-amp A2 is connected to the base of transistor Tr4.

[0144] When a negative voltage less than or equal to the second threshold Th2 is applied to the inverting input T21 of operational amplifier A2, operational amplifier A2 outputs a predetermined voltage and transistor Tr4 turns ON. If the applied voltage is greater than the second threshold Th2, operational amplifier A2 does not output the predetermined voltage, and transistor Tr4 remains OFF.

[0145] Thus, the non-inverting input T11 of op-amp A1 is connected between input terminals T1 and T2, and the inverting input T21 of op-amp A2, which is opposite to the non-inverting input T22, is also connected between input terminals T1 and T2. In other words, op-amp A2 is connected in antiparallel to op-amp A1.

[0146] The secondary circuit 12b includes a detection unit 13, a control unit 14, a power supply line 15, and a resistor R52 for adjusting the voltage of the pulse signal Vout. The resistor R52 is provided on the power supply line 15. The first end of the resistor R52 is connected to a power supply that provides a DC voltage V1. The second end of the resistor R52, opposite the first end, is connected to the detection unit 13 via a second connection point X2.

[0147] Transistor Tr4 of comparator CM2 is connected in parallel with transistor Tr3 of comparator CM1. The collectors of the two transistors Tr3 and Tr4 are connected to the second connection point X2. The emitters of the two transistors Tr3 and Tr4 are connected to a common potential point. In this way, comparator CM2 is connected in parallel with comparator CM1 in both the primary circuit 11b and the secondary circuit 12b.

[0148] In monitoring circuit 10b, the frequency FR2 of the output pulse signal Vout is the same as in monitoring circuit 10 of the embodiment, and the high and low levels of the pulse signal Vout are the opposite of those in monitoring circuit 10.

[0149] Under normal conditions, when the AC voltage Vin applied to the primary circuit 11b is greater than the second threshold Th2 and less than the first threshold Th1, both transistors Tr3 and Tr4 remain in the OFF state, and the second connection point X2 becomes a value based on the voltage V1 and resistor R52. Therefore, a high level is output as the pulse signal Vout.

[0150] When a positive AC voltage Vin greater than or equal to the first threshold Th1 is applied to the primary circuit 11b, transistor Tr4 remains OFF while transistor Tr3 turns ON. As a result, the second connection point X2 becomes the potential of the common potential point. Therefore, a low level is output as the pulse signal Vout.

[0151] When a negative AC voltage Vin below the second threshold Th2 is applied to the primary circuit 11b, transistor Tr3 remains OFF while transistor Tr4 turns ON. As a result, the second connection point X2 becomes the same potential as the common potential point. Therefore, a low level is output as the pulse signal Vout.

[0152] Therefore, under normal circumstances, the frequency FR2 of the output pulse signal Vout is twice the frequency FR1 of the AC voltage Vin.

[0153] Next, consider the case where op-amp A2 fails and transistor Tr4 remains OFF even when an AC voltage Vin below the second threshold Th2 is applied to the primary circuit 11b. In this case, the pulse signal Vout will be low level only when an AC voltage Vin above the first threshold Th1 is applied to the primary circuit 11b, and high level in all other cases. Therefore, the frequency FR2 of the output pulse signal Vout will be equal to the frequency FR1 of the AC voltage Vin.

[0154] Similarly, if op-amp A1 fails, the frequency FR2 of the output pulse signal Vout will be equal to the frequency FR1 of the AC voltage Vin. Also, if any one of the current limiting resistors (R31, R32, R33, R34) of the two op-amps A1 and A2 fails, the frequency FR2 of the output pulse signal Vout will be equal to the frequency FR1 of the AC voltage Vin.

[0155] In this way, even if an element included in the monitoring circuit 10b fails, the monitoring circuit 10b can continue to monitor whether or not the power system 50 is experiencing a power outage, thereby improving the reliability of the monitoring circuit 10b.

[0156] Furthermore, since the monitoring circuit 10b uses comparators as multiple conversion units CM1 and CM2, it is possible to monitor the AC voltage Vin while the primary circuit 11b and the secondary circuit 12b are not isolated from each other.

[0157] [3.3 Monitoring circuit 10c related to modified example] The monitoring circuit 10 according to this embodiment monitors a single-phase power system 50. However, this disclosure can also be used to monitor a three-phase power system 50a.

[0158] Figure 9 is a circuit diagram showing a modified monitoring circuit 10c. The monitoring circuit 10b comprises a primary circuit 11c, a secondary circuit 12c, and a plurality of conversion units PC11, PC12, and PC13. The plurality of conversion units PC11, PC12, and PC13 include a first conversion unit PC11, a second conversion unit PC12, and a third conversion unit PC13. The first conversion unit PC11, the second conversion unit PC12, and the third conversion unit PC13 are each photocouplers, and will be referred to as "photocoupler PC11," "photocoupler PC12," and "photocoupler PC13" respectively below. In the monitoring circuit 10c, the primary circuit 11c and the secondary circuit 12c are isolated from each other. Note that the plurality of conversion units PC11, PC12, and PC13 may each be comparators.

[0159] Power system 50a includes three AC power supplies L1, L2, and L3, each with a phase difference of 120 degrees. AC power supply L1 applies an AC voltage between input terminals T31 and T34. AC power supply L2 applies an AC voltage between input terminals T32 and T34. AC power supply L3 applies an AC voltage between input terminals T33 and T34.

[0160] The three photocouplers PC11, PC12, and PC13 each turn ON only when a positive voltage of a predetermined threshold Th3 or higher is applied to them. The threshold Th3 is higher than the voltage Vc1 at which a predetermined one phase (e.g., AC voltage L1) crosses with the other two phases (e.g.) in positive polarity, and lower than the peak voltage.

[0161] The photocoupler PC11 includes a light-emitting diode D32 connected between input terminals T31 and T34 of the primary circuit 11c, and a phototransistor Tr5 connected to the secondary circuit 12c. , Da LED D31 is connected in antiparallel to LED D32. Additionally, resistor R41 is connected in series with LED D32 as a current-limiting resistor to suppress surge current flow through LED D32.

[0162] The photocoupler PC12 includes a light-emitting diode D42 connected between input terminals T32 and T34 of the primary circuit 11c, and a phototransistor Tr6 connected to the secondary circuit 12c. , Da LED D41 is connected in antiparallel to LED D42. Additionally, resistor R42 is connected in series with LED D42 as a current-limiting resistor.

[0163] The photocoupler PC13 includes a light-emitting diode D52 connected between input terminals T33 and T34 of the primary circuit 11c, and a phototransistor Tr7 connected to the secondary circuit 12c. , DaLED D51 is connected in antiparallel to LED D52. Additionally, resistor R43 is connected in series with LED D52 as a current-limiting resistor.

[0164] The three light-emitting diodes D32, D42, and D52 are connected in parallel in the primary circuit 11c. The anodes of the three light-emitting diodes D32, D42, and D52 are connected to input terminals T31, T32, and T33, respectively, and the cathode is connected to input terminal T34.

[0165] The secondary circuit 12c includes a detection unit 13, a control unit 14, a power line 15, and a resistor R52. The first end of resistor R52 is connected to a power supply that provides a DC voltage V1. The second end of resistor R52, opposite the first end, is connected to the detection unit 13 via a second connection point X3.

[0166] The three phototransistors Tr5, Tr6, and Tr7 are connected in parallel in the secondary circuit 12c. The collectors of each of the three phototransistors Tr5, Tr6, and Tr7 are connected to connection point X3. The emitters of each of the three phototransistors Tr5, Tr6, and Tr7 are connected to a common potential point. In this way, the three photocouplers PC11, PC12, and PC13 are connected in parallel in both the primary circuit 11c and the secondary circuit 12c.

[0167] Figure 10 is a waveform diagram illustrating the operation of the monitoring circuit in Figure 9. In Figure 10, (a) shows the three-phase AC voltage Vin, and (b) shows the pulse signal Vout under normal conditions. In Figure 10, the voltage originating from AC power supply L1 is shown by a solid line, the voltage originating from AC power supply L2 is shown by a dashed line, and the voltage originating from AC power supply L3 is shown by a dashed line.

[0168] Under normal conditions, when the voltage applied to all three AC power supplies L1, L2, and L3 is below the threshold Th3, the three photocouplers PC11, PC12, and PC13 remain in the OFF state, and the second connection point X3 becomes a value based on the voltage V1 and resistor R52. Therefore, a high level is output as the pulse signal Vout.

[0169] Under normal conditions, when the AC power supply L1 applies a voltage above the threshold Th3, both photocouplers PC12 and PC13 remain OFF, while photocoupler PC11 turns ON. As a result, the second connection point X3 becomes the potential of the common potential point, and a low level is output as a pulse signal Vout.

[0170] Similarly, when AC power supply L2 applies a voltage equal to or greater than the threshold Th3, both photocouplers PC11 and PC13 remain OFF, while photocoupler PC12 turns ON. Also, when AC power supply L3 applies a voltage equal to or greater than the threshold Th3, both photocouplers PC11 and PC12 remain OFF, while photocoupler PC13 turns ON. In these cases as well, the second connection point X3 becomes the potential of the common potential point, and a low level is output as the pulse signal Vout.

[0171] Thus, under normal conditions, when the three AC power supplies L1, L2, and L3 are sequentially subjected to a voltage above the threshold Th3, the three photocouplers PC11, PC12, and PC13 turn ON in sequence, changing the pulse signal Vout from a high level to a low level. As a result, under normal conditions, the frequency FR2 of the pulse signal Vout output to the secondary circuit 12c is three times the frequency FR1 of the AC voltage Vin.

[0172] Next, consider the case where the photocoupler PC13 fails and the phototransistor Tr7 remains OFF even when the AC power supply L3 applies a voltage above the threshold Th3. In this case, in Figure 10(b), only the low-level output (dashed rectangle) caused by the photocoupler PC13 changes to a high level, while the other outputs remain as shown in (b). Therefore, the frequency FR2 of the output pulse signal Vout becomes approximately twice the frequency FR1 of the AC voltage Vin.

[0173] Furthermore, if photocoupler PC12 fails and phototransistor Tr6 remains OFF even when AC power supply L2 applies a voltage above threshold Th3, the low-level output (dashed rectangle) caused by photocoupler PC12 in Figure 10(b) also changes to a high level, and only the low-level output caused by photocoupler PC11 is maintained. Therefore, the frequency FR2 of the output pulse signal Vout becomes equal to the frequency FR1 of the AC voltage Vin.

[0174] In this way, even if an element included in the monitoring circuit 10c fails, the monitoring circuit 10c can continue to monitor whether or not the power system 50a is experiencing a power outage, thereby improving the reliability of the monitoring circuit 10c.

[0175] In the above explanation, the photocouplers PC11, PC12, and PC13 are described as turning ON only when a positive voltage of a predetermined threshold Th3 or higher is applied. However, the three photocouplers PC11, PC12, and PC13 may also turn ON only when a negative voltage of a predetermined threshold Th4 or lower is applied. In this case as well, the monitoring circuit 10c outputs the same pulse signal Vout.

[0176] [3.4 Variations of polarity of the conversion section] In the monitoring circuit 10 of this embodiment, the light-emitting diode D12 of the first conversion unit PC1 and the light-emitting diode D22 of the second conversion unit PC2 are connected with opposite polarities. As a result, the first conversion unit PC1 turns ON with a positive polarity AC voltage Vin, and the second conversion unit PC2 turns ON with a negative polarity AC voltage Vin. If there are no faults in the first conversion unit PC1 and the second conversion unit PC2, a pulse signal Vout with a frequency twice that of the AC voltage Vin is output.

[0177] In contrast, the light-emitting diode D12 of the first conversion unit PC1 and the light-emitting diode D22 of the second conversion unit PC2 may be connected with the same polarity. For example, in Figure 2, the anode and cathode of the light-emitting diode D22 may be reversed. , Da The anode and cathode of the ion D21 may be reversed.

[0178] In this case, both the first converter PC1 and the second converter PC2 turn ON at an AC voltage Vin of a predetermined polarity (for example, positive polarity). If there are no faults in the first converter PC1 and the second converter PC2, a pulse signal Vout with the same frequency as the AC voltage Vin is output (a pulse signal Vout similar to that in Figure 3(c)). Furthermore, even if there is a fault in either the first converter PC1 or the second converter PC2, a pulse signal Vout with the same frequency as the AC voltage Vin is output, allowing monitoring of the power system 50 to continue.

[0179] [3.5 Other] In this embodiment, the monitoring circuit 10 outputs a high-level pulse signal Vout when either of the two photocouplers PC1 or PC2 is ON, and outputs a low-level pulse signal Vout when both of the two photocouplers PC1 or PC2 are OFF. However, the monitoring circuit 10 may also be configured to output a low-level pulse signal Vout when either of the two photocouplers PC1 or PC2 is ON, and output a high-level pulse signal Vout when both of the two photocouplers PC1 or PC2 are OFF, as in the modified monitoring circuit 10b.

[0180] Similarly, the modified monitoring circuits 10b and 10c may be configured to output a high-level pulse signal Vout when the conversion unit is ON, and a low-level pulse signal Vout when the conversion unit is OFF, just like monitoring circuit 10.

[0181] Multiple resistors R11, R12, R13, R21, R22, R23, R1, R2, R3, R31, R32, R33, R34, R41, R42, R43 provided in the primary circuits 11, 11a, 11b, and 11c, respectively, may be omitted as appropriate.

[0182] [Additional Note] Furthermore, at least some of the embodiments and various modifications described above may be combined in any way. Also, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims, and all modifications within the meaning and scope of equivalence to the claims are intended. [Explanation of symbols]

[0183] 1. Power Conversion System 10,10a,10b,10c monitoring circuit 11,11a,11b,11c Primary side circuit 12,12b,12c Secondary side circuit 13 Detection unit 14 Control Unit 15 Power line 20 Relay Circuits 21 contacts 22 coils 30 Power converter 40 DC power supply 50 Power system 50a power system 60 load 90 Monitoring circuit T1, T2 Input Terminals T31, T32, T33, T34 Input Terminals T91, T92 Input Terminals PC1 First conversion unit (photocoupler) PC2 Second Conversion Unit (Photocoupler) PC11 First conversion unit (photocoupler) PC12 Second Conversion Unit (Photocoupler) PC13 Third Conversion Unit (Photocoupler) PC91 Photocoupler PC92 Photocoupler CM1 First conversion unit (comparator) CM2 Second Conversion Unit (Comparator) D 1 Da Iord D 2 Da Iord D1 1 Da Iord D12 Light-emitting diode (first element) D2 1 Da Iord D22 Light-Emitting Diode (Second Element) D3 1 Da Iord D32 Light Emitting Diode D4 1 Da Iord D42 Light Emitting Diode D5 1 Da Iord D52 Light Emitting Diode D91 Light-Emitting Diode D92 Light-Emitting Diode A1 operational amplifier A2 Op-amp T11 Non-inverting input T12 Inverted Input T21 Inverted Input T22 Non-inverting input Tr1 Phototransistor Tr2 Phototransistor Tr3 transistor Tr4 transistor Tr5 Phototransistor Tr6 phototransistor Tr7 Phototransistor Tr91 Phototransistor Tr92 Phototransistor R1,R2,R3 resistance R11,R12 Resistor (1st resistor) R21,R22 Resistor (2nd resistor) R13, R23 Resistors R31, R32 Resistors (First Resistors) R33, R34 Resistors (Second Resistors) R41, R42, R43 Resistors R51,R52 resistance R91,R92 resistance X1 First connection point X2, X3 Second connection point Ic1 Output current of photocoupler PC1 Ic2 Photocoupler PC2 output current Current transfer rate of photocoupler PC1 CTR1 Current transfer rate of photocoupler PC2 CTR2 Vf1 is the forward voltage of the light-emitting diode D12. Vf2 is the forward voltage of the light-emitting diode D22. Rx1 is the sum of resistors R11 and R12. Rx2 is the sum of resistors R21 and R22. Th1 First Threshold Th2 Second Threshold Th3 threshold Th4 threshold Th91 1st threshold Th92 2nd threshold Z1 predetermined value Z2 Lower Limit V1 Voltage Vin AC voltage Vin1 (Normal AC voltage) Vin2 (AC voltage at low voltage) Vout pulse signal Vc1 Voltage F1 function PL Plot FR1 (frequency of AC voltage Vin) FR2 (frequency of pulse signal Vout) L1 AC power supply L2 AC power supply L3 AC power supply C9 Capacitance

Claims

1. A monitoring circuit for monitoring AC voltage, The primary side circuit to which the aforementioned AC voltage is input, A secondary circuit that outputs a pulse signal with a period corresponding to the AC voltage, Multiple conversion units that convert the AC voltage into the pulse signal, Detection unit, Equipped with, The plurality of conversion units include a first conversion unit and a second conversion unit, and are connected in parallel to each other in both the portion included in the primary circuit and the portion included in the secondary circuit. The first conversion unit is, A first element included in the primary circuit, which outputs when an AC voltage of positive polarity equal to or greater than a first threshold is applied, The secondary circuit includes a first transistor whose collector and emitter are energized by the output of the first element, Includes, The second conversion unit is, In the primary circuit, a second element is connected in parallel with the first element and outputs when the AC voltage with negative polarity below the second threshold is applied, In the secondary circuit, a second transistor is connected in parallel with the first transistor, and its collector and emitter are energized by the output of the second element, Includes, The aforementioned pulse signal is The first connection point where the emitters of the first transistor and the second transistor are connected to each other, The output is from the second connection point where the collectors of the first transistor and the second transistor are connected to each other, The detection unit detects that the first element or the second element is faulty when the frequency of the pulse signal is equal to the frequency of the AC voltage. monitoring circuit.

2. The primary side circuit is, One or more first resistors connected in series with the first element, One or more second resistors connected in series with the second element and connected in parallel with one or more of the first resistors, including, The monitoring circuit according to claim 1.

3. The primary circuit includes a plurality of first resistors and a plurality of second resistors, The first end of the first element is connected to the ungrounded wire of the primary circuit. The second end of the first element is connected to the ground wire of the primary circuit. The third end of the second element is connected to the ungrounded wire of the primary circuit. The fourth end of the second element is connected to the ground wire of the primary circuit. Multiple first resistors are connected in series, at least one to each of the first and second ends of the first element. Multiple of the second resistors are connected in series, at least one to each of the third and fourth terminals of the second element. The monitoring circuit according to claim 2.

4. The first element and the second element are each light-emitting diodes. The first transistor is a phototransistor in which the collector and emitter are energized by the light emitted from the first element. The second transistor is a phototransistor in which the collector and emitter are energized by the light emitted from the second element. A monitoring circuit according to any one of claims 1 to 3.

5. The first element and the second element are operational amplifiers, The first transistor is a transistor whose collector and emitter are energized by the output of the first element, The second transistor is a transistor whose collector and emitter are energized by the output of the second element. A monitoring circuit according to any one of claims 1 to 3.

6. The detection unit acquires the effective value of the AC voltage based on the duty cycle of the pulse signal. The monitoring circuit according to claim 1.

7. The detection unit determines that the power system providing the AC voltage is normal if the frequency of the pulse signal is one or two times the frequency of the AC voltage, and the effective value is equal to or greater than the lower limit that the AC voltage should maintain. The monitoring circuit according to claim 6.

8. The detection unit is If the pulse signal remains at a high or low level for a predetermined period longer than the period of the AC voltage, it is determined that the power system is experiencing a power outage. If the effective value is less than the lower limit, it is determined that the power system is in a low-voltage state. The monitoring circuit according to claim 7.

9. The system further comprises a control unit that controls a relay circuit for connecting and disconnecting the power system and the load, The control unit, When the detection unit determines that the power system is functioning normally, it controls the relay circuit to connect the power system and the load. When the detection unit determines that the power system is experiencing a power outage or is in a low-voltage state, it controls the relay circuit to disconnect the power system from the load. The monitoring circuit according to claim 8.

10. The monitoring circuit described in claim 9, The relay circuit and, A power converter that converts DC power supplied from a DC power source into AC power and supplies it to the power system or load, and converts AC power supplied from the power system into DC power and supplies it to the DC power source, Equipped with, The power conversion device is a power conversion system that, when the power system and the load are disconnected by the relay circuit, converts the DC power supplied from the DC power source into AC power and supplies it to the load.

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