Overcurrent determination device and power conversion device

Abstract

This overcurrent determination device (1) comprises a high-pass filter (11) and an overcurrent determination unit (12). The high-pass filter (11) has a plurality of capacitors (C1, C2) that are electrically connected in parallel to each other, and receives the input of a current sensor signal which is an analog signal outputted by a current sensor that measures the value of an AC current inputted to a power conversion circuit (21) or the value of an AC current outputted from the power conversion circuit (21). The overcurrent determination unit (12) determines whether an overcurrent has occurred in the power conversion circuit (21) from a comparison between the output of the high-pass filter (11) and a threshold determined in accordance with the rate of change in the AC current when an overcurrent occurs in the power conversion circuit (21). Any capacitor (C1) among the plurality of capacitors (C1, C2) has temperature characteristics in which a variation amount of the capacitance of said capacitor according to temperature compensates for at least a portion of a variation amount of the capacitance of the other capacitor (C2) according to temperature.

Description

Overcurrent determination device and power conversion device

[0001] The present disclosure relates to an overcurrent determining device and a power conversion device.

[0002] Some power conversion devices, which are a type of electronic device, are equipped with an overcurrent determination device that determines whether an overcurrent is flowing in a power conversion circuit. An example of an overcurrent determination device is disclosed in Patent Document 1. The battery monitoring device disclosed in Patent Document 1 includes a differentiation circuit that determines the current change rate of a charge / discharge current, and a comparison means that outputs a signal in accordance with whether the current change rate of the charge / discharge current is greater than a preset threshold voltage.

[0003] International Publication No. 2016 / 185711

[0004] The differentiation circuit included in the battery monitoring device disclosed in Patent Document 1 includes a capacitor, a resistor, and an operational amplifier. When the temperature of the capacitor fluctuates, the capacitance fluctuates, which changes the characteristics of the differentiation circuit, such as the time constant. When the characteristics of the differentiation circuit change with temperature, it becomes difficult to accurately determine whether an overcurrent is flowing.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide an overcurrent determination device that can accurately determine whether or not an overcurrent is occurring, and a power conversion device that is equipped with an overcurrent determination device.

[0006] To achieve the above object, the overcurrent detection device of the present disclosure includes a high-pass filter and an overcurrent detection unit. The high-pass filter has a plurality of capacitors electrically connected in parallel to each other. A current sensor signal, which is an analog signal output by a current sensor that measures the value of the AC current input to or output from the power conversion circuit, is input to the high-pass filter. The overcurrent detection unit determines whether an overcurrent has occurred in the power conversion circuit by comparing the output of the high-pass filter, which indicates the rate of change of the AC current, with a threshold value determined according to the rate of change when an overcurrent occurs in the power conversion circuit. One of the plurality of capacitors has temperature characteristics such that a change in capacitance of that capacitor in response to a temperature change at least partially compensates for a change in capacitance of the other capacitors in response to a temperature change.

[0007] In the overcurrent detection device according to the present disclosure, one of the capacitors included in the high-pass filter has temperature characteristics such that the amount of capacitance change in response to temperature change of that capacitor compensates for at least a portion of the amount of capacitance change in response to temperature change of the other capacitors, thereby providing an overcurrent detection device that can accurately determine whether an overcurrent is occurring.

[0008] FIG. 1 is a block diagram of an overcurrent determination device and a power conversion device according to an embodiment; FIG. 2 is a diagram showing a hardware configuration of a control circuit provided in a power conversion device according to an embodiment; FIG. 3 is a diagram showing an example of a current sensor signal in an embodiment; FIG. 4 is a diagram showing an example of temperature characteristics of a capacitor provided in an overcurrent determination device according to an embodiment; FIG. 5 is a diagram showing a modified example of a high-pass filter provided in an overcurrent determination device according to an embodiment;

[0009] An overcurrent determination device and a power conversion device according to an embodiment of the present disclosure will now be described in detail with reference to the drawings, in which the same or equivalent parts are designated by the same reference numerals.

[0010] An example of an electronic device installed on a railway vehicle is a power conversion device that is installed on the railway vehicle, converts power supplied from a power source into power to be supplied to a load device, and supplies the converted power to the load device.

[0011] The power conversion device 101 shown in FIG. 1 includes a power conversion circuit 21 that converts input power into power to be supplied to an electric motor 91, which is an example of a load device, and outputs the converted power to the electric motor 91; a control circuit 22 that controls a plurality of switching elements of the power conversion circuit 21; a current sensor 23 that measures the value of the AC current input to the power conversion circuit 21 or the AC current output from the power conversion circuit 21, and outputs a current sensor signal S1 that indicates the value of the AC current; and an overcurrent determination device 1 that determines whether or not an overcurrent has occurred in the power conversion circuit 21, and outputs a determination result signal S2 that indicates the determination result.

[0012] As an example, the power conversion device 101 is mounted on a railway vehicle that uses a DC power feed system, converts DC power supplied from a power source into three-phase AC power for supply to the electric motor 91, and supplies the three-phase AC power to the electric motor 91. The electric motor 91 is, for example, a three-phase induction motor that rotates upon receiving a supply of three-phase AC power and generates propulsive force for the railway vehicle.

[0013] The power conversion circuit 21 is, for example, an inverter circuit that converts input DC power into three-phase AC power and supplies the three-phase AC power to the electric motor 91. The power conversion circuit 21 has a plurality of switching elements whose on / off states are controlled by the control circuit 22, such as IGBTs (Insulated Gate Bipolar Transistors), GTOs (Gate Turn-Off thyristors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and the like.

[0014] The control circuit 22 controls a plurality of switching elements included in the power conversion circuit 21 in response to a railway vehicle operation command obtained from a driver's cab (not shown) and a determination result signal S2 indicating the determination result of the overcurrent determination device 1. For example, the control circuit 22 controls each IGBT included in the power conversion circuit 21 by sending a PWM (Pulse Width Modulation) signal to each gate terminal of the IGBT.

[0015] The current sensor 23 uses a current transformer type sensor CT1 to measure the value of the AC current input to the power conversion circuit 21 or the AC current output from the power conversion circuit 21. In the example of FIG. 1 , the current sensor 23 measures the value of the AC current output from the power conversion circuit 21 using the sensor CT1 attached to one of the bus bars connecting the power conversion circuit 21 and the electric motor 91. The current sensor 23 outputs a current sensor signal S1, which is an analog signal indicating the measured value of the AC current output from the power conversion circuit 21, to the overcurrent determination device 1.

[0016] The overcurrent determination device 1 determines whether or not an overcurrent due to a short circuit, a ground fault, element damage, etc. is occurring in the power conversion circuit 21. The overcurrent determination device 1 includes a high-pass filter 11 that receives a current sensor signal S1 and functions as a differential circuit, an overcurrent determination unit 12 that determines whether or not an overcurrent is occurring in the power conversion circuit 21 by comparing the output of the high-pass filter 11 with a threshold value, and a resistor R1 that has one end connected to the high-pass filter 11 and the other end grounded.

[0017] A current sensor signal S1 is supplied from the current sensor 23 to an input terminal 11a of the high-pass filter 11. The input terminal 11a is electrically connected to one end of a resistor R1. An output terminal 11b of the high-pass filter 11 is electrically connected to the overcurrent determination unit 12.

[0018] 1, the high-pass filter 11 includes two capacitors, specifically, a first capacitor C1 and a second capacitor C2. The high-pass filter 11 includes an operational amplifier OP1 having a non-inverting input terminal grounded, the first capacitor C1 and the second capacitor C2 electrically connected to the inverting input terminal of the operational amplifier OP1 via a resistor R2 and electrically connected in parallel with each other, and a resistor R3 having one end electrically connected to the inverting input terminal of the operational amplifier OP1 and the other end electrically connected to the output terminal 11b of the operational amplifier OP1.

[0019] The high-pass filter 11 having the above configuration outputs a voltage signal indicating the rate of change of the AC current output by the power conversion circuit 21 to the overcurrent determination unit 12. In other words, the high-pass filter 11 operates as a differentiation circuit that outputs the result of time differentiation of the AC current output by the power conversion circuit 21.

[0020] The cutoff frequency of the high-pass filter 11 is determined according to the frequency of the AC current when an overcurrent occurs in the power conversion circuit 21. The capacitances of the first capacitor C1 and the second capacitor C2 and the resistance values ​​of the resistors R2 and R3 are determined to obtain the cutoff frequency determined as described above. As an example, if the frequency of the AC current output by the power conversion circuit 21 when power is supplied to the electric motor 91 in a state where no overcurrent occurs, in other words, during normal operation, is 60 Hz, the cutoff frequency is set to 120 Hz, which is twice the normal frequency.

[0021] The overcurrent determination unit 12 has a comparator CP1 that compares the value of the voltage applied from the constant voltage power supply VS1 with the value of the voltage signal output from the high-pass filter 11. The comparator CP1 outputs a determination result signal S2 to the control circuit 22. The determination result signal S2 is at an H (High) level if the value of the voltage signal output from the high-pass filter 11 is equal to or greater than the value of the voltage applied from the constant voltage power supply VS1, and is at an L level if the value of the voltage signal output from the high-pass filter 11 is less than the value of the voltage applied from the constant voltage power supply VS1.

[0022] The value of the voltage applied to the comparator CP1 by the constant voltage power supply VS1 is a threshold value used to determine whether an overcurrent has occurred. The threshold value is determined according to the possible values ​​of the rate of change of the AC current input to or output from the power conversion circuit 21 when an overcurrent occurs in the power conversion circuit 21.

[0023] As an example, the maximum frequency of the three-phase AC current supplied from the power conversion circuit 21 to the electric motor 91 is assumed to be 200 Hz. In this case, if the current sensor signal contains only components below 200 Hz, the power conversion circuit 21 can be considered to be normal. On the other hand, if the current sensor signal contains harmonic components that are not present in a normal state, such as frequency components above 400 Hz (twice the maximum value), the power conversion circuit 21 can be considered to be abnormal. Therefore, the cutoff frequency of the high-pass filter 11 is set to 400 Hz (twice the maximum value), and the threshold is set to a value lower than the output of the high-pass filter 11 when the current sensor signal contains frequency components above 400 Hz. As a result, when the current sensor signal contains harmonic components above 400 Hz, the output of the comparator CP1 becomes H level, making it possible to detect the occurrence of an overcurrent.

[0024] The hardware configuration of the control circuit 22 included in the power conversion device 101 having the above configuration is shown in Figure 2. The control circuit 22 includes a processor 81, a memory 82, and an interface 83. The processor 81, the memory 82, and the interface 83 are connected to one another via a bus 80. The functions of each part of the control circuit 22 are realized by software, firmware, which is software embedded in an electronic device, or a combination of software and firmware. The software is written as a program and stored in the memory 82. The processor 81 reads and executes the program stored in the memory 82, thereby realizing the functions of each part described above. In other words, the memory 82 stores programs for executing the processing of each part of the control circuit 22.

[0025] The memory 82 includes, for example, non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read-Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable and Programmable Read-Only Memory), magnetic disk, flexible disk, optical disk, compact disk, mini disk, DVD (Digital Versatile Disc), etc.

[0026] The control circuit 22 is connected to the power conversion circuit 21, the current sensor 23, and the overcurrent determination device 1 via an interface 83. The interface 83 has an interface module that complies with one or more standards depending on the connection destination.

[0027] The overcurrent determination process performed by the overcurrent determination device 1 having the above configuration will be described below. An example of a current sensor signal is shown in Fig. 3. In Fig. 3, the horizontal axis represents time, and the vertical axis represents the value of the current sensor signal. Time T1 is the time when an overcurrent occurs in the power conversion circuit 21. At time T1, the amplitude and frequency of the AC current flowing from the power conversion circuit 21 to the electric motor 91 increase.

[0028] Immediately after time T1, the rate of change of the AC current indicated by the current sensor signal increases. Therefore, the output of the high-pass filter 11, to which the current sensor signal shown in FIG. 3 is input, increases immediately after time T1. Immediately after time T1, when the output of the high-pass filter 11 exceeds the threshold, the output of the comparator CP1 in the overcurrent determination unit 12 becomes H level. When the output of the comparator CP1 becomes H level, i.e., when the determination result signal S2 becomes H level, the control circuit 22 turns off each switching element in the power conversion circuit 21. As a result, the power conversion circuit 21 stops operating.

[0029] When the power conversion device 101 having the above configuration is installed on a railway vehicle, a large current flows through the power conversion device 101, causing the components of the power conversion device 101 to become hot. When the temperatures of the first capacitor C1 and the second capacitor C2, which are components of the power conversion device 101, change, the capacitances of the first capacitor C1 and the second capacitor C2 fluctuate. As described above, the time constant of the high-pass filter 11 is determined by the capacitances of the first capacitor C1 and the second capacitor C2 and the resistance values ​​of the resistors R2 and R3. Therefore, when the power conversion device 101 operates and generates heat, the characteristics of the high-pass filter 11 may change.

[0030] Therefore, the high-pass filter 11 includes a plurality of capacitors, specifically a first capacitor C1 and a second capacitor C2, whose temperature characteristics cancel each other out. Specifically, the first capacitor C1 has a temperature characteristic such that the amount of change in capacitance of the first capacitor C1 in response to temperature change compensates for at least a portion of the amount of change in capacitance of the second capacitor C2 in response to temperature change.

[0031] An example of the temperature characteristics of the capacitance of the first capacitor C1 and the second capacitor C2 is shown in Fig. 4. In Fig. 4, the horizontal axis represents the element temperature (unit: °C), and the vertical axis represents the rate of change of capacitance (unit: %). In Fig. 4, the dashed-dotted line graph represents the temperature characteristics of the capacitance of the first capacitor C1, and the solid line graph represents the temperature characteristics of the capacitance of the second capacitor C2.

[0032] The rate of change in capacitance is calculated by dividing the difference between the capacitance at each temperature and the capacitance at the reference temperature, i.e., the amount of change, by the capacitance at the reference temperature. In the example of Fig. 4, the reference temperature is 20°C, and the capacitances of the first capacitor C1 and the second capacitor C2 at the reference temperature are the same.

[0033] 4, the capacitance of the first capacitor C1 at temperatures lower than the reference temperature is higher than the capacitance of the first capacitor C1 at the reference temperature, and the capacitance of the second capacitor C2 at temperatures lower than the reference temperature is lower than the capacitance of the second capacitor C2 at the reference temperature. In other words, at temperatures lower than the reference temperature, the rate of change in capacitance of the first capacitor C1 is positive, while the rate of change in capacitance of the second capacitor C2 is negative. As a result, at temperatures lower than the reference temperature, the fluctuations in capacitance of the first capacitor C1 and the second capacitor C2 cancel each other out, and the combined capacitance of the first capacitor C1 and the second capacitor C2 is approximately the same as at the reference temperature.

[0034] The capacitance of the first capacitor C1 at temperatures higher than the reference temperature is lower than the capacitance of the first capacitor C1 at the reference temperature, and the capacitance of the second capacitor C2 at temperatures higher than the reference temperature is higher than the capacitance of the second capacitor C2 at the reference temperature. In other words, at temperatures higher than the reference temperature, the rate of change in capacitance of the first capacitor C1 is negative, while the rate of change in capacitance of the second capacitor C2 is positive. As a result, at temperatures higher than the reference temperature, the fluctuations in capacitance of the first capacitor C1 and the second capacitor C2 cancel each other out, and the combined capacitance of the first capacitor C1 and the second capacitor C2 becomes approximately the same as at the reference temperature.

[0035] As described above, the combined capacitance of the first capacitor C1 and the second capacitor C2 can be regarded as constant regardless of temperature, which prevents the characteristics of the high-pass filter 11 from changing with temperature.

[0036] As described above, in the overcurrent detection device 1 according to the embodiment, the first capacitor C1 has temperature characteristics such that the amount of capacitance change in response to temperature change of the first capacitor C1 compensates for at least a portion of the amount of capacitance change in response to temperature change of the second capacitor C2. This allows the combined capacitance of the first capacitor C1 and the second capacitor C2 to be considered constant regardless of temperature. As a result, changes in the characteristics of the high-pass filter 11 due to temperature are suppressed. This provides an overcurrent detection device 1 that can accurately determine whether an overcurrent is occurring.

[0037] The overcurrent detection device 1 determines whether an overcurrent has occurred based on the rate of change of the current sensor signal, which is an analog signal, and is therefore able to detect the occurrence of an overcurrent more quickly than devices that perform A / D (Analog / Digital) conversion and then determine whether an overcurrent has occurred by comparing a digital value indicating the measured AC current value with a threshold value.

[0038] Because the overcurrent determination device 1 determines whether an overcurrent has occurred based on the rate of change of the current sensor signal, it can detect the occurrence of an overcurrent before the value indicated by the current sensor signal increases significantly due to the occurrence of an overcurrent. In other words, the overcurrent determination device 1 can detect the occurrence of an overcurrent more quickly than devices that determine the occurrence of an overcurrent by comparing the value indicated by the current sensor signal with a threshold value that is set to a value sufficiently larger than the current value that can be assumed under normal circumstances.

[0039] The present disclosure is not limited to the exemplary embodiments. The high-pass filter 11 may have any configuration as long as it can output the rate of change of an AC current. As an example, the high-pass filter 11 shown in FIG. 5 is a feedback high-pass filter including a capacitor C3 having one end connected to the input terminal 11a, capacitors C4 and C5 having one end connected to the capacitor C3, a resistor R4 having one end connected to the junction of the capacitors C3, C4, and C5 and the other end grounded, a resistor R5 having both ends connected to the other ends of the capacitors C4 and C5, and an operational amplifier OP2 having an inverting input terminal connected to the capacitor C4 and the resistor R5 and a non-inverting input terminal grounded. The other end of the capacitor C5 is connected to the resistor R4 and the output terminal of the operational amplifier OP2.

[0040] 5, the capacitors C4 and C5 correspond to the first capacitor and the second capacitor, respectively. In this case, the capacitors C4 and C5 only need to have temperature characteristics that cancel each other out.

[0041] As another example, the high-pass filter 11 shown in FIG. 5 may have a configuration in which at least one of the capacitors C3, C4, and C5 is replaced with the first capacitor C1 and the second capacitor C2 electrically connected in parallel to each other as shown in FIG. 1.

[0042] The power conversion device 101 may be mounted on a railway vehicle using a DC power supply as in the embodiment, or on a railway vehicle using an AC power supply. The power conversion device 102 shown in Fig. 6 is mounted on a railway vehicle using an AC power supply and receives AC power from a power source. The power conversion device 102 includes a transformer 24 that steps down the voltage of the supplied AC power, a power conversion circuit 21 that converts the AC power stepped down by the transformer 24 into three-phase AC power and outputs the three-phase AC power to an electric motor 91, a control circuit 22 that controls multiple switching elements included in the power conversion circuit 21, a current sensor 23 that measures the value of the AC current input to the power conversion circuit 21, and an overcurrent determination device 1 that determines whether an overcurrent has occurred in the power conversion circuit 21.

[0043] The power conversion circuit 21 includes, for example, a converter that converts AC power into DC power and outputs the DC power, and an inverter that converts the DC power output by the converter into three-phase AC power and supplies the three-phase AC power to the electric motor 91. The control circuit 22 controls the on / off of a plurality of switching elements included in the converter and the inverter.

[0044] In the example of FIG. 6 , the current sensor 23 measures the value of the AC current input to the power conversion circuit 21 using a sensor CT1 attached to a bus bar connecting the transformer 24 and the power conversion circuit 21.

[0045] 6 is similar in configuration and operation to the embodiment. The overcurrent determination device 1 included in the power conversion device 102 determines whether an overcurrent has occurred by comparing the rate of change of the AC current input to the power conversion circuit 21 with a threshold value.

[0046] In the above embodiment, the overcurrent discriminator 1 detects the occurrence of an overcurrent based on a sudden increase in the rate of change of the AC current, but it may also determine that an overcurrent has occurred when the rate of change of the AC current suddenly decreases. In this case, the overcurrent discriminator 1 may include an absolute value circuit that converts the output of the high-pass filter 11 into an absolute value and outputs the absolute value to the overcurrent discriminator 12.

[0047] The load devices to which the power conversion devices 101, 102 supply power are not limited to the electric motors 91, but may also be electronic devices mounted on railway vehicles, such as lighting equipment and air conditioning equipment. In this case, the overcurrent determination device 1 determines whether an overcurrent has occurred by comparing the rate of change of the AC current output from the power conversion circuit 21 of the power conversion devices 101, 102 to the load device or the AC current input to the power conversion circuit 21 with a threshold value.

[0048] The hardware configuration of the control circuit 22 included in the power conversion devices 101, 102 is not limited to the above example. As shown in Fig. 7 , the control circuit 22 may be realized by a processing circuit 84. The processing circuit 84 is connected to the power conversion circuit 21, the current sensor 23, and the overcurrent determination device 1 via an interface circuit 85.

[0049] When the processing circuitry 84 is dedicated hardware, the processing circuitry 84 includes, for example, a single circuit, a composite circuit, a processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. Each part of the control circuit 22 may be realized by an individual processing circuit 84 or may be realized by a common processing circuit 84.

[0050] Some of the functions of the control circuit 22 may be implemented by dedicated hardware, and other functions may be implemented by software or firmware. For example, some of the functions of the control circuit 22 may be implemented by a processing circuit 84 shown in Fig. 7, and other functions may be implemented by a processor 81 shown in Fig. 2 reading and executing a program stored in a memory 82.

[0051] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments are intended to illustrate the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of equivalent disclosures are considered to be within the scope of the present disclosure.

[0052] 1 Overcurrent determination device, 11 High-pass filter, 11a Input terminal, 11b Output terminal, 12 Overcurrent determination unit, 21 Power conversion circuit, 22 Control circuit, 23 Current sensor, 24 Transformer, 80 Bus, 81 Processor, 82 Memory, 83 Interface, 84 Processing circuit, 85 Interface circuit, 91 Electric motor, 101, 102 Power conversion device, C1 First capacitor, C2 Second capacitor, C3, C4, C5 Capacitors, CP1 Comparator, CT1 Sensor, OP1, OP2 Operational amplifier, R1, R2, R3, R4, R5 Resistor, S1 Current sensor signal, S2 Determination result signal, VS1 Constant voltage power supply.

Claims

1. An overcurrent detection device comprising: a high-pass filter having a plurality of capacitors electrically connected in parallel with each other, to which a current sensor signal, which is an analog signal output by a current sensor that measures the value of the AC current input to or output from the power conversion circuit, is input; and an overcurrent detection unit that determines whether an overcurrent has occurred in the power conversion circuit by comparing the output of the high-pass filter, which indicates the rate of change of the AC current, with a threshold value determined according to the rate of change when an overcurrent occurs in the power conversion circuit, wherein any one of the plurality of capacitors has temperature characteristics such that the amount of change in capacitance of that capacitor in response to temperature change compensates for at least a part of the amount of change in capacitance of the other capacitors in response to temperature change.

2. The overcurrent discriminator according to claim 1, wherein the high-pass filter has a first capacitor and a second capacitor, which are two of the capacitors electrically connected in parallel to each other; the capacitance of the first capacitor when the temperature is lower than a reference temperature is higher than the capacitance of the first capacitor at the reference temperature, and the capacitance of the second capacitor when the temperature is lower than the reference temperature is lower than the capacitance of the second capacitor at the reference temperature; the capacitance of the first capacitor when the temperature is higher than the reference temperature is lower than the capacitance of the first capacitor at the reference temperature, and the capacitance of the second capacitor when the temperature is higher than the reference temperature is higher than the capacitance of the second capacitor at the reference temperature.

3. The overcurrent detection device according to claim 2, wherein the high-pass filter comprises an operational amplifier, the first capacitor having one end connected to the inverting input terminal of the operational amplifier, and the second capacitor having one end connected to the other end of the first capacitor and the other end connected to the output terminal of the operational amplifier.

4. The overcurrent discriminating device according to claim 2, wherein the high-pass filter comprises an operational amplifier, and the first capacitor and the second capacitor connected to the inverting input terminal of the operational amplifier via a resistor and electrically connected in parallel with each other.

5. A power conversion device mounted on a railway vehicle, comprising: the overcurrent discrimination device according to any one of claims 1 to 4; a power conversion circuit that converts input power into power to be supplied to a load device and outputs the converted power to the load device; a current sensor that measures the value of the AC current input to the power conversion circuit or the AC current output from the power conversion circuit and outputs a current sensor signal which is an analog signal indicative of the measured value; and a control circuit that controls the on / off of a plurality of switching elements in the power conversion circuit, wherein the current sensor signal output by the current sensor is input to the high-pass filter provided in the overcurrent discrimination device, and the control circuit turns off each of the switching elements when it is determined that an overcurrent is occurring in the overcurrent discrimination section provided in the overcurrent discrimination device.

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