Power conversion device and abnormality detection method

Abstract

Power conversion device (4) comprising: a power converter for converting a first power into a second power; a first current measuring unit for measuring a first current value representing a current value of the first power; a second current measuring unit for measuring a second current value representing a current value of the second power; and a control unit (18) for detecting an abnormality of the first current measuring unit based on the first current value and the second current value, wherein the control unit (18) determines that the first current measuring unit is abnormal when the first current value is less than a first threshold value and the second current value is greater than a second threshold value.

Description

Field of InterestThe present invention relates to a power conversion device that converts an input power into a desired power and outputs the power, and an abnormality detection method.BackgroundConventionally, a power conversion device is known that converts an input power into a desired power and outputs the converted power to a load. For example, a power conversion device described in Patent Literature 1 installed in a railway vehicle converts a direct current power input from a overhead wire into an alternating current power after amplifying the direct current power to a desired voltage, isolates the alternating current power by using a transformer, converts the alternating current power into a direct current power, and then outputs the direct current power to a load. The power conversion device described in Patent Literature 1 detects an overcurrent caused by a load short circuit or the like by a measurement instrument that measures a current value of a DC power output to a load; however, the power conversion device cannot detect the overcurrent when the measurement instrument malfunctions. Therefore, when a malfunction of the measuring instrument is detected, the power conversion device described in Patent Literature 1 stops its power conversion operation to protect internal circuits of the power conversion device from an overcurrent that cannot be detected when generated.Citation ListPatent LiteratureJP 2015-139 264 AJP 2008-109 846 AJP 2016-10 180 AUS 2017 / 0 158 057 A1SummaryTechnical ProblemHowever, in the above-described conventional method, the power conversion device cannot detect an abnormality of the measurement instrument that measures a current value of a power input to the power conversion device. The power conversion device has a problem in a case where the measurement instrument that measures an input current value is in an abnormal state that it is unable to detect an over-current of the input power and protect the internal circuits of the power conversion device.The present invention has been achieved in view of the above problems, and an object of the present invention is to provide a power conversion device that can detect abnormality of a measurement instrument that measures an input current value.Solution of the ProblemIn order to solve the above-described problem and achieve the object, a power conversion device of the present invention includes a power converter for converting a first power into a second power, a first current measurement unit for measuring a first current value representing a current value of the first power, a second current measurement unit for measuring a second current value representing a current value of the second power, and a control unit for detecting an abnormality of the first current measurement unit based on the first current value and the second current value.Advantageous Effects of the InventionAccording to the present invention, the power conversion device has an effect where it is possible to detect abnormality of a measurement instrument that measures an input current value.Brief Description of the DrawingsFIG. 1 is a diagram illustrating a configuration example of a power conversion device. FIG. 2 is a diagram illustrating a configuration example of a control unit. FIG. 3 is a flowchart illustrating an operation where the control unit detects abnormality of an input current sensor. FIG. 4 is a diagram illustrating an example of a case where a processing circuit included in the power conversion device is constituted by a processor and a memory. FIG. 5 is a diagram illustrating an example of a case where a processing circuit included in the power conversion device is constituted by dedicated hardware. FIG. 6 is a diagram illustrating a configuration example of a power conversion device to which a DC power is supplied.DESCRIPTION OF THE EMBODIMENTSA power conversion device and an abnormality detection method according to embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments.Embodiment.FIG. 1 is a diagram illustrating a configuration example of a power conversion device 4 according to an embodiment of the present invention. While an example where the power conversion device 4 is mounted in a railroad vehicle (not illustrated) will be described below, it is merely an example, and the power conversion device 4 may be installed in a vehicle other than a railroad vehicle. The power conversion device 4 is connected to a overhead wire voltage sensor 2, a main transformer 3, a load 5, and a display device 6. The overhead wire voltage sensor 2, the main transformer 3, the load 5, and the display device 6 are also installed in the railway vehicle. An AC overhead wire 1 supplies an AC power supplied from a substation (not illustrated) to the main transformer 3. The main transformer 3 converts a overhead wire voltage of the AC power supplied from the AC overhead wire 1 into a voltage at a level at which the voltage can be used by the power conversion device 4. A first AC power representing an AC power voltage-converted in the main transformer 3 is input to the power conversion device 4 as input power.The power conversion device 4 outputs a second alternating current power representing three-phase alternating current power converted from a direct current power to an inverter 16 described later to the load 5 as an output power. That is, the power conversion device 4 converts the first AC power input thereto into a second AC power and outputs the second AC power. The load 5 is an electric device installed in the railway vehicle. The load 5 is, for example, an engine, an air conditioner, or a compressor. When a control unit 18 of the power conversion device 4 described later has detected abnormality of an input current sensor 12, the display device 6 displays that the input current sensor 12 is abnormal under control of the control unit 18. The display device 6 is, for example, a monitor installed in an operator's cab of the railway vehicle.The configuration of the power conversion device 4 will be described. The power conversion device 4 includes a filter reactor 11, the input current sensor 12, a converter 13, a DC voltage sensor 14, a filter capacitor 15, the inverter 16, an output current sensor 17, and the control unit 18.The filter reactor 11 constitutes a filter circuit together with the filter capacitor 15 and reduces a rapid current change in the first AC power. The input current sensor 12 is a measurement instrument that measures a first current value representing a current value of the first AC power input from the main transformer 3 to the power conversion device 4. The input current sensor 12 represents a first current measurement unit. The converter 13 converts the first AC power input from the main transformer 3 to the power conversion device 4 into a DC power. The configuration of the converter 13 may be a general one and is not limited to any specific configuration. The DC voltage sensor 14 is a measurement instrument that measures a DC voltage value of the DC power output from the converter 13. The filter capacitor 15 removes harmonic components generated in power conversion processing performed by the converter 13 and the inverter 16 from the DC power. Further, the filter capacitor 15 is charged by the DC power output from the converter 13.The inverter 16 converts a direct current power, which is output from the converter 13 and with which the filter capacitor 15 is charged, into the second alternating current power. The configuration of the inverter 16 may be a general one, and is not limited to any specific configuration. Here, it is assumed that the second AC power output from the inverter 16 is a three-phase AC power. The output current sensor 17 is a measurement instrument that measures a second current value representing a current value of the second AC power of each phase output from the inverter 16. The output current sensor 17 represents a second current measuring unit. It is assumed that the converter 13 and the inverter 16 together constitute a power converter. The control unit 18 controls operations of the converter 13 and the inverter 16 constituting the power converter. The control unit 18 also detects abnormality of the input current sensor 12 based on the first current value representing a measurement result of the input current sensor 12 and the second current value representing a measurement result of the output current sensor 17. In the power conversion device 4, configurations different from the configuration of the control unit 18 are identical to configurations used in a general power conversion device.The configuration of the control unit 18 will be described. FIG. 2 is a diagram illustrating a configuration example of the control unit 18 according to the present embodiment. The control unit 18 includes an A / D (Analog / Digital) conversion unit 21 and a control calculation unit 22.The A / D conversion unit 21 converts a measured value obtained by measurement from each sensor from an analog value to a digital value. Specifically, the A / D conversion unit 21 converts each of the measured values, which are an overhead line voltage value measured by the overhead line wire voltage sensor 2, an input current value measured by the input current sensor 12, a DC voltage value measured by the DC voltage sensor 14, and an output current value measured by the output current sensor 17, from an analog value to a digital value. While the output current value is represented by a single line in FIG. 2, in practice, output current values for three phases are input to the A / D conversion unit 21 as illustrated in FIG. 1. In practice, similarly to the output current value output from the A / D conversion unit 21 to the control calculation unit 22, output current values for three phases are output from the A / D conversion unit 21.The control calculation unit 22 acquires each measured value converted into a digital value by the A / D conversion unit 21, and controls operations of the power conversion device 4 based on each measured value. The control calculation unit 22 includes a power conversion control unit 23, an abnormality detection unit 24, and a transmission control unit 25.The power conversion control unit 23 controls operations of the converter 13 and the inverter 16 using the overhead wire voltage value, the input current value, the direct current value, and the output current value obtained from the A / D conversion unit 21. The power conversion control unit 23 monitors the state of the alternating current power supplied from the alternating current overhead wire 1, and specifically, the phase and amplitude of an alternating current voltage using the overhead wire voltage value, and uses the monitored state to control the converter 13 and the inverter 16. The power conversion control unit 23 may calculate the target current value of the input current value based on the DC current value and the output current value. The power conversion control unit 23 controls the operation of the converter 13 in such a manner that the input current value becomes the target current value. The method of controlling the converter 13 and the inverter 16 by the power conversion control unit 23 may be a general one, and is not limited to a specific method. In a case where the converter 13 and the inverter 16 each include, for example, a switching element, the power conversion control unit 23 controls the operation of the switching element included by both the converter 13 and the inverter 16.The abnormality detection unit 24 detects an abnormality of the input current sensor 12 based on the input current value and the output current value obtained from the A / D conversion unit 21. Detailed operations of the abnormality detection unit 24 will be described later.When abnormality of the input current sensor 12 is detected in the abnormality detection unit 24, the transmission control unit 25 notifies the display device 6 that the input current sensor 12 is abnormal. The transmission control unit 25 makes the display device 6 display that the input current sensor 12 is abnormal.Next, an operation of the power conversion device 4 in which the control unit 18 detects an abnormality of the input current sensor 12 will be described. FIG. 3 is a flowchart illustrating an operation mode where the control unit 18 according to the present embodiment detects an abnormality of the input current sensor 12. As for a first threshold value used in a determination process in the operation mode illustrated in FIG. 3, it is allowed that the abnormality detection unit 24 receives a parameter from a user in advance or calculates the parameter during the operation. Regarding a second threshold, the abnormality detection unit 24 receives a parameter from a user in advance. Details of the first and second threshold values will be described in detail later.First, the abnormality detection unit 24 in the control unit 18 determines whether the converter 13 and the inverter 16 are operating (step S 1). Generally, when the converter 13 and the inverter 16 are operating, a control signal from the power conversion control unit 23 is input to the converter 13 and the inverter 16. The abnormality detection unit 24 may determine whether the converter 13 and the converter 16 are operating based on the presence of the control signal from the power conversion control unit 23 to the converter 13 and the converter 16. Further, the abnormality detection unit 24 may determine whether the inverter 13 and the inverter 16 are operating based on the contents of an operation instruction output from an operator's cab (not illustrated) in a railroad vehicle to the control unit 18. When the converter 13 and the inverter 16 are not operating (NO in step S 1), the abnormality detection unit 24 returns to the process in step S 1. When the converter 13 and the inverter 16 are operating (YES in step S 1), the abnormality detection unit 24 checks an output current value obtained from the A / D conversion unit 21 (step S 2).The abnormality detection unit 24 determines whether the obtained output current value exceeds the set second threshold value (step S 3). The second threshold value represents a value for determining whether the second AC power is output from the inverter 16 to the load 5. The second threshold value represents a fixed value larger than "0" and is set in advance by a user or the like. For example, the user sets the second threshold value based on the measurement accuracy of the output current sensor 17 while considering measurement errors or the like. The abnormality detection unit 24 compares each of the obtained output current values for three phases and the second threshold value with each other. When there is no output current value exceeding the second threshold value (NO in step S 3), the abnormality detection unit 24 returns to the process in step S 2. If there is NO in step S 3, this means that the second AC power is not output to the load 5. Therefore, the load 5 is not in operation. When there are one or more output current values exceeding the second threshold (YES in step S 3), the abnormality detection unit 24 checks an input current value obtained from the A / D conversion unit 21 (step S 4).The abnormality detection unit 24 determines whether the acquired input current value is less than the set first threshold value (step S 5). The first threshold value is a value for determining whether the first AC power is input from the main transformer 3 to the converter 13. The first threshold value may be a fixed value set in advance by a user or the like, or may be a calculated value set by the abnormality detection unit 24 based on calculation. The abnormality detection unit 24 calculates a value proportional to the magnitude of the output current value or a target current value calculated in the power conversion control unit 23 based on the output current value or the target current value, and sets the calculated value as the first threshold value. Accordingly, the abnormality detection unit 24 may set the first threshold value according to the magnitude of the output current value, so that it is possible to improve the determination accuracy in step S 5 as compared with a case where the first threshold value is a fixed value. When the first threshold value is calculated, the abnormality detection unit 24 may use the latest output current value or the target current value based on the latest output current value. Further, since the control unit 18 repeats the operation in the flowchart illustrated in FIG. 3, the abnormality detection unit 24 may use the output current value or the target current value obtained by the previous operation when calculating the first threshold value. In a case where the input current value becomes a certain constant value when the input current sensor 12 is abnormal, setting the first threshold value to a fixed value may reduce the processing load of the abnormality detection unit 24 compared to a case where the first threshold value is a calculated value.When the input current value is equal to or larger than the first threshold (NO in step S 5), the abnormality detection unit 24 returns to the process in step S 1. If NO in step S5, the input current sensor 12 is in a normal state. When the input current value is less than the first threshold value (YES in step S 5), the abnormality detection unit 24 determines that the input current sensor 12 is abnormal (step S 6). Upon detection of abnormality of the input current sensor 12, the abnormality detection unit 24 notifies the power conversion control unit 23 and the transmission control unit 25 that the input current sensor 12 is abnormal.When the abnormality detection unit 24 detects an abnormality of the input current sensor 12, the power conversion control unit 23 receives a notification from the abnormality detection unit 24, and stops operation of the converter 13 and the inverter 16 (step S 7). When the abnormality detection unit 24 detects an abnormality of the input current sensor 12, the transmission control unit 25 receives the notification from the abnormality detection unit 24, and notifies the display device 6 connected to the power conversion device 4 that the input current sensor 12 is abnormal. The transmission control unit 25 makes the display device 6 display that the input current sensor 12 is abnormal (step S 8). The contents displayed on the display device 6 may be a message indicating that the input current sensor 12 is abnormal or an error code.A user can recognize that the cause of stopping the operation of the converter 13 and the inverter 16 is an abnormality of the input current sensor 12 by confirming the displayed content on the display device 6. The control unit 18 repeats the process in the flowchart illustrated in FIG. 3.A hardware configuration of the power conversion device 4 will be described next. As described above, in the power conversion device 4, configurations different from the configuration of the control unit 18 are identical to configurations used in a general power conversion device. The control unit 18 is realized by a processing circuit. That is, the power conversion device 4 includes a processing circuit that can detect abnormality of the input current sensor 12. The processing circuit may be a processor that executes a program stored in a memory and the memory, or may be dedicated hardware.FIG. 4 is a diagram illustrating an example of a case where a processing circuit included in the power conversion device 4 according to the present embodiment is constituted by a processor and a memory. In a case where the processing circuit is constituted by a processor 91 and a memory 92, functions of the processing circuit of the power conversion device 4 are realized by software, firmware, or a combination of software and firmware. The software or the firmware is described as a program and is stored in the memory 92. The processing circuit realizes the functions thereof by reading and executing the program stored in the memory 92 by the processor 91. That is, the processing circuit includes the memory 92 storing therein a program that causes detection of an abnormality of the input current sensor 12 to be thus performed. Further, such programs can be regarded as elements that make a computer perform the procedures and a method of the power conversion device 4.The processor 91 may be a device such as a CPU (Central Processing Unit), a processing device, an arithmetic device, a microprocessor, a microcomputer, or a DSP (Digital Signal Processor). The memory 92 corresponds to, for example, a nonvolatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), and an EEPROM ®( electronic EPROM), or a device such as a magnetic disk, a flexible disk, an optical disk, a CD, a minidisk, and a DVD (Digital Versatile Disk).FIG. 5 is a diagram illustrating an example of a case where a processing circuit included in the power conversion device 4 according to the present embodiment is constituted by dedicated hardware. When the processing circuit is constituted by dedicated hardware, a processing circuit 93 illustrated in FIG. 5 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination of these elements. Each of the functions of the power conversion device 4 may be realized by the processing circuit 93 for each function, or these functions may be realized collectively by the processing circuit 93.As for the respective functions of the power conversion device 4, it is possible to configure that some parts of the functions are realized by dedicated hardware and other parts thereof are realized by software or firmware. In this way, the processing circuit can realize any function described above by dedicated hardware, software, firmware, or a combination of these elements.Normally, the control unit 18 performs control in such a manner that an input current value becomes a target current value. Therefore, the control unit 18 increases the target current value in a case where an abnormality occurs in the input current sensor 12 and the input current value is smaller than the target current value to increase the input current value, so that it becomes possible to generate an input overcurrent. According to the present embodiment, as described above, in the power conversion device 4, when an output current value of an AC power output from the inverter 16 is larger than the second threshold value and an input current value of an AC power input to the converter 13 is smaller than the first threshold value, the control unit 18 determines that the input current sensor 12 that has measured the input current value is abnormal. Upon detection of abnormality of the input current sensor 12, the control unit 18 stops operation of the converter 13 and the converter 16 because the control unit 18 cannot accurately control the converter 13 and the converter 16. Accordingly, in the power conversion device 4 according to the present embodiment, it is possible to prevent input overcurrent from being input to the converter 13, thereby protecting internal parts of the power conversion device 4. Further, the control unit 18 makes the display device 6 display that the input current sensor 12 is abnormal. A user confirming the contents of the display device 6 can recognize the cause of stopping the operations of the inverter 13 and the inverter 16.While in the present embodiment, a case where an AC power is supplied to a railway vehicle from the AC overhead wire 1 has been described, this case is merely an example, and the application of the present invention is not limited thereto. The present invention can also be applied to a case where a DC power is supplied from a DC overhead wire to a railroad vehicle, for example. FIG. 6 is a diagram illustrating a configuration example of a power conversion device 4 aaccording to the present embodiment to which direct current power is supplied. The power conversion device 4 ais the power conversion device 4 illustrated in FIG. 1, in which the input current sensor 12, the converter 13, the DC voltage sensor 14, and the control unit 18 have been omitted, and an input current sensor 12 aand a control unit 18 ahave been added. In the power conversion device 4 a, the input current sensor 12 ameasures a current value of a direct current power supplied from a direct current overhead wire 1 a, i.e., a direct current value, as an input current value. The control unit 18 adetects abnormality of the input current sensor 12 abased on the first current value, which is a measurement result of the input current sensor 12 a, and the second current value, which is a measurement result of the output current sensor 17. The contents of the processing performed by the control unit 18 aare similar to the contents of the processing performed by the control unit 18, and thus descriptions of detailed configurations and operations of the control unit 18 aare omitted. The DC power input to the power conversion device 4 amay be DC power after the voltage of the DC power supplied from the DC overhead wire 1 ais converted. The power conversion device 4 aconverts its DC power input into an AC power and outputs the AC power. That is, the present invention can be applied to a power conversion device that converts a first power input thereto into a second power and outputs the second power. The first power could be the first AC power described above or a DC power. The second power is the above-described second AC power. The power conversion device may detect abnormality of an input current sensor that measures an input current value, that is, a direct current value, using an output current value and the input current value.The configurations described in the above embodiment are merely examples of the content of the present invention. The configurations may be combined with other well-known methods, and a part of each of the configurations may be omitted or modified without departing from the scope of the present invention.List of reference characters1 AC overhead wire, 1 a DC overhead wire, 2 overhead wire voltage sensor, 3 main transformer, 4, 4 apower conversion device, 5 load, 6 display device, 11 filter reactor, 12, 12 ainput current sensor, 13 converter, 14 DC voltage sensor, 15 filter capacitor, 16 inverter, 17 output current sensor, 18, 18 acontrol unit, 21 A / D conversion unit, 22 control calculation unit, 23 power conversion control unit, 24 abnormality detection unit, 25 transmission control unit.

Claims

A power conversion device (4) comprising: a power converter for converting a first power into a second power; a first current measurement unit for measuring a first current value representing a current value of the first power; a second current measurement unit for measuring a second current value representing a current value of the second power; and a control unit (18) for detecting an abnormality of the first current measurement unit based on the first current value and the second current value, wherein the control unit (18) determines that the first current measurement unit is abnormal when the first current value is less than a first threshold value and the second current value is greater than a second threshold value.The power conversion device (4) according to claim 1, wherein the first power is a first AC power and the second power is a second AC power, the power converter comprising a converter (13) for converting the first AC power into a DC power, and an inverter (16) for converting the DC power into the second AC power, and the control unit (18) stops operations of the converter and the inverter (13) when an abnormality of the first current measurement unit is detected.The power conversion device (4) according to claim 1 or 2, wherein the control unit (18) calculates the first threshold value based on the second current value.The power conversion device (4) according to claim 1 or 2, wherein the first threshold value is a fixed value.The power conversion device (4) according to any one of claims 1 to 4, wherein the control unit (18) makes a display device (6) connected to the power conversion device (4) display that the first current measurement unit is abnormal when an abnormality of the first current measurement unit is detected.An abnormality detection method comprising: a power conversion step of converting a first power to a second power by a power converter; a first current measurement step of measuring a first current value representing a current value of the first power by a first current measurement unit; a second current measurement step of measuring a second current value representing a current value of the second power by a second current measurement unit; and an abnormality detection step of detecting an abnormality of the first current measurement unit based on the first current value and the second current value by a control unit (18), wherein in the abnormality detection step, the control unit (18) determines that the first current measurement unit is abnormal when the first current value is less than a first threshold value and the second current value is greater than a second threshold value.The abnormality detection method according to claim 6, wherein in a case where the first power is a first AC power and the second power is a second AC power, the power converter includes a converter (13) and an inverter (16), in the power conversion step, the converter (13) converts the first AC power into a DC power and the inverter (16) converts the DC power into the second AC power, and the abnormality detection method further includes a control step of stopping operations of the converter (13) and the inverter (16) when the control unit (18) has detected an abnormality of the first current measurement unit in the abnormality detection step.The abnormality detection method according to claim 6 or 7, wherein in the abnormality detection step, the control unit (18) calculates the first threshold value based on the second current value.The abnormality detection method according to claim 6 or 7, wherein the first threshold value is a fixed value.The abnormality detection method according to any one of claims 6 to 9, comprising a display step in which the control unit (18) makes a display device (6) display that the first current measurement unit is abnormal when the first current measurement unit is determined to be abnormal.

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