Power switchgear, power switching system, power switching module, and method for protecting power switchgear

Abstract

This power switchgear monitors the temperature of a relay for interrupting a power supply to a load, to determine whether or not to interrupt the power supply, the power switchgear comprising: a relay including a drive coil; a temperature calculation unit for calculating the temperature of the drive coil on the basis of a relational expression between the temperature and the resistance value of a resistance that changes as a result of a temperature change, for a case in which the drive coil included in the relay is regarded as a resistor; a reference temperature acquisition unit for measuring a reference temperature, which is the ambient temperature of the drive coil at a predetermined time point; a reference resistance value acquisition unit for calculating a reference resistance value, which is the resistance value of the resistance at a predetermined time point; and a determination unit for determining whether or not to interrupt the power supply on the basis of the temperature of the drive coil calculated by the temperature calculation unit. The temperature calculation unit calculates the temperature of the drive coil on the basis of the relational expression calibrated on the basis of the reference temperature and the reference resistance value.

Description

Power switch, power switch system, power switch module, and power switch protection method

[0001] The present invention relates to a power switch, a power switch system, a power switch module, and a method for protecting a power switch.

[0002] Conventionally, there have been proposed devices that monitor the temperature rise of an electrical appliance such as a relay and determine whether to stop its operation depending on whether an abnormality has occurred. For example, in Patent Document 1, a temperature measurement module is provided that measures the temperature of the electrical appliance, and whether an abnormality has occurred in the electrical appliance is determined based on the temperature measurement result and the current measurement result.

[0003] However, when detecting an abnormal rise in ambient temperature and stopping operation, it is difficult to accurately know the temperature of the switch components of the electrical appliance, such as a relay, so it was necessary to measure the ambient temperature using other sensors, etc., and determine whether to stop operation within a certain safe tolerance range. Furthermore, after stopping operation of an electrical appliance due to an abnormal rise in ambient temperature, it was difficult to remotely determine whether the abnormal temperature rise had been resolved and operation could be restored, so work had to be done directly on site.

[0004] Japanese Patent Application Laid-Open No. 2022-68855

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a technology for accurately calculating the temperature of a drive coil of a relay and performing appropriate protection based on the accurate temperature.

[0006] In order to solve the above problem, the present invention provides a power switch that monitors the temperature of a relay that cuts off power supply to a load and determines whether to cut off the power supply, comprising: the relay including a drive coil; a temperature calculation unit that calculates the temperature of the drive coil based on a relational equation between the resistance value of the resistor that changes with temperature when the drive coil included in the relay is considered to be a resistor and the temperature; a reference temperature acquisition unit that measures a reference temperature which is the ambient temperature of the drive coil at a predetermined point in time; a reference resistance value acquisition unit that calculates a reference resistance value which is the resistance value of the resistor at the predetermined point in time; and a determination unit that determines whether to cut off the power supply based on the temperature of the drive coil calculated by the temperature calculation unit, wherein the temperature calculation unit calculates the temperature of the drive coil based on the relational equation calibrated based on the reference temperature and the reference resistance value.

[0007] With this, even if there is variation in the resistance value of the drive coil at a specific temperature, the relationship between the resistance value of the drive coil, which changes with temperature, and the temperature is calibrated based on the reference temperature and reference resistance value, and the temperature of the drive coil is calculated accurately based on the calibrated relationship, so that appropriate protection can be provided based on the accurate temperature.

[0008] In the present invention, the predetermined time point may be a predetermined period immediately after the relay is turned on.

[0009] According to this, the relational expression is calibrated each time the relay is repeatedly turned on, and the accuracy of the temperature calculation is improved.

[0010] The present invention also provides a power switching system including: the power switch; and a communication unit that transmits information relating to the determination result in the determination unit to an external device connected via a network.

[0011] The present invention also provides a method for protecting a power switch that monitors the temperature of a relay that cuts off power supply to a load and determines whether to cut off the power supply, the method including the steps of: measuring a reference temperature, which is the ambient temperature of a drive coil included in the relay at a predetermined time point; calculating a reference resistance value, which is the resistance value of the resistor at the predetermined time point, assuming that the drive coil is a resistor; calibrating a relational expression between the resistance value of the resistor that changes with temperature and the temperature based on the reference temperature and the reference resistance value, and calculating the temperature of the drive coil using the calibrated relational expression; and determining whether to cut off the power supply based on the temperature of the drive coil calculated in the temperature calculation step.

[0012] With this, even if there is variation in the resistance value of the drive coil at a specific temperature, the relationship between the resistance value of the drive coil, which changes with temperature, and the temperature is calibrated based on the reference temperature and reference resistance value, and the temperature of the drive coil is calculated accurately based on the calibrated relationship, so that appropriate protection can be provided based on the accurate temperature.

[0013] In the present invention, the predetermined period may be a predetermined period immediately after the relay is turned on.

[0014] According to this, the relational expression is calibrated each time the relay is repeatedly turned on, and the accuracy of the temperature calculation is improved.

[0015] The present invention also provides an electric power switching module that opens and closes an electric circuit connecting an AC power source and an electric vehicle, the module comprising: a relay that opens and closes the electric circuit; a power measurement unit that measures an amount of electric power supplied to the electric vehicle through the electric circuit; a communication unit that receives an opening / closing instruction signal that instructs the relay to open or close the electric circuit and transmits the amount of electric power measured by the power measurement unit; and a control unit, wherein the relay includes a drive coil; and when the drive coil included in the relay is considered to be a resistor, a temperature calculation unit that calculates a temperature of the drive coil based on a relational equation between a resistance value of the resistor that changes with temperature and the temperature; a reference temperature acquisition unit that measures a reference temperature that is an ambient temperature of the drive coil at a predetermined time point; a reference resistance value acquisition unit that calculates a reference resistance value that is the resistance value of the resistor at the predetermined time point; and a determination unit that determines whether or not to open the electric circuit based on the temperature of the drive coil calculated by the temperature calculation unit, wherein the temperature calculation unit calculates the temperature of the drive coil based on the relational equation calibrated based on the reference temperature and the reference resistance value.

[0016] According to this, even if there is variation in the resistance value of the drive coil at a specific temperature in the power switching module, the relationship between the resistance value of the drive coil, which changes with temperature, and the temperature is calibrated based on the reference temperature and reference resistance value, and the temperature of the drive coil is accurately calculated based on the calibrated relationship, so that appropriate protection can be performed based on the accurate temperature.

[0017] According to the present invention, the temperature of the drive coil of the relay can be calculated with high accuracy, and appropriate protection can be performed based on the accurate temperature.

[0018] Fig. 1 is a diagram showing an outline of the overall configuration of a power switching system according to a first embodiment of the present invention. Fig. 2 is a circuit diagram including a drive coil of a relay according to the first embodiment of the present invention. Fig. 3 is a flowchart showing a method for protecting a relay according to the first embodiment of the present invention. Figs. 4(A) and 4(B) are diagrams for explaining the effects of the first embodiment of the present invention in comparison with a conventional example.

[0019] 1 , a charging system 300 includes a power switching module 200 that switches an electric circuit PL that charges a storage battery of an EV (electric vehicle) 230 connected via an EV charging outlet 220 with electric power supplied from an AC power source 210, and a charging management system 250.

[0020] The relay 21 includes a drive coil 21 a and opens and closes an electrical circuit PL that is connected to the EV 230 via an AC power supply 210 and an EV charging outlet 220 .

[0021] The power switching module 200 mainly includes a relay 21, a power measurement unit 22, a communication unit 23, and a control unit 24. The relay 21 has a drive coil 21a and opens and closes an electric circuit PL connected to the EV 230 via an AC power supply 210 and an EV charging outlet 220. The power measurement unit 22 measures the electric power supplied to the EV 230 through the electric circuit PL. The communication unit 23 is connected to the charging management system 250 via a network NT1, and is an interface that transmits and receives information between the charging management system 250 and the power switching module 200.

[0022] The power switching module 200 monitors the temperature of the relay 21 and determines whether or not to cut off the power supply from the AC power source 210 to the EV 230 through the electrical path PL via the EV charging outlet 220 .

[0023] Fig. 2 is a circuit diagram showing a schematic configuration of the relay 21. The relay 21 cuts off the power supply via the EV charging outlet 220 when a temperature rise exceeding a predetermined threshold is detected. As shown in Fig. 2, the relay 21 has a drive coil 21a and a switching unit 21b. The drive coil 21a is a component that constitutes the relay 21 and is formed mainly from copper wire. If the drive coil 21a is considered to be a resistor in an electric circuit, its resistance value changes with temperature changes.

[0024] When the drive coil 21 a is regarded as a resistor, the resistance value RL changes in response to changes in temperature. This is utilized to detect temperature changes based on the resistance value of the drive coil 21 a. Then, upon detecting an abnormal temperature rise, the power switching module 200 determines whether to stop the power supply via the EV charging outlet 220.

[0025] The control unit 24 functions as a reference temperature acquisition unit 24a, a reference resistance value acquisition unit 24b, a temperature calculation unit 24c, a determination unit 24d, and an operation recovery determination unit 24e.

[0026] The reference temperature acquisition unit 24a acquires a reference temperature used for temperature calculation in the temperature calculation unit 24c, as will be described in detail later.

[0027] The reference resistance value acquiring unit 24b acquires a reference resistance value used for temperature calculation in the temperature calculating unit 24c, as will be described in detail later.

[0028] The temperature calculation unit 24c calculates the resistance value RL of the drive coil 21a included in the relay 21, which changes with temperature when the drive coil 21a is regarded as a resistor, and calculates the temperature of the drive coil 21a based on a relational expression that defines the relationship between the resistance value and temperature. This relational expression is calibrated based on the reference temperature and reference resistance value described above. For example, the reference temperature and reference resistance value can be averages for 60 seconds immediately after the relay is turned on. This calibrates the relational expression each time the relay 21 is turned on, allowing the temperature of the drive coil 21a, which is regarded as a resistor, to be calculated with high accuracy, thereby enabling appropriate protection to be performed based on the accurate temperature.

[0029] [First Embodiment] A charging system 100 including a power switching module 200 according to a first embodiment of the present invention will be described in more detail below with reference to the accompanying drawings. However, the configurations of the device and system described in this embodiment may be modified as appropriate depending on various conditions. In other words, the scope of the present invention is not limited to the following embodiment.

[0030] As shown in FIG. 1 , charging system 300 according to this embodiment includes a power switching module 200 that opens and closes an electric circuit PL that charges a storage battery of an EV (Electric Vehicle) 230 connected via an EV charging outlet 220 with power supplied from an AC power source 210, and a charging management system 250. Charging management system 250 is, for example, a computer device such as a plurality of servers arranged on a cloud. Charging system 300 corresponds to the power switching system of the present invention. Furthermore, power switching module 200 corresponds to the power switch of the present invention. Furthermore, charging management system 250 corresponds to the management system of the present invention. Furthermore, AC power source 210 corresponds to the AC power source of the present invention.

[0031] The charging management system 250 monitors and controls the charging of the power switching module 200 connected via the network NT1 through the target EV charging outlet 220.

[0032] The power switching module 200 is housed as a module in the housing of a pole or box that is the charging equipment 260 on which the EV charging outlet 220 is provided, for example.

[0033] The power switching module 200 mainly includes a relay 21, a power measurement unit 22, a communication unit 23, and a control unit 24. The relay 21 has a drive coil 21a and opens and closes an electric circuit PL connected to the EV 230 via an AC power supply 210 and an EV charging outlet 220. The power measurement unit 22 measures the power supplied to the EV 230 through the electric circuit PL.

[0034] The communication unit 23 is connected to the charge management system 250 via the network NT1 and is an interface for transmitting and receiving information between the charge management system 250 and the power switching module 200. As a communication method between the power switching module 200 and the charge management system 250, for example, a wireless communication method can be adopted, but the communication method is not limited to this. Necessary information is transmitted from the communication unit 23 to the charge management system 250 via the network NT1. The charge management system 250 transmits an instruction (opening / closing instruction signal) to the power switching module 200 to cause the relay 21 to close or open the electric circuit PL, and based on this, the power switching module 200 closes or opens the relay 21. The control unit 24 includes a processor such as an MPU and a memory.

[0035] The power switching module 200 monitors the temperature of the relay 21 and determines whether or not to cut off the power supply from the AC power source 210 to the EV 230 through the electrical path PL via the EV charging outlet 220 .

[0036] Fig. 2 is a circuit diagram showing a schematic configuration of the relay 21. The relay 21 cuts off the power supply via the EV charging outlet 220 when a temperature rise exceeding a predetermined threshold is detected. As shown in Fig. 2, the relay 21 has a drive coil 21a and a switching unit 21b. The drive coil 21a is a component that constitutes the relay 21 and is formed mainly from copper wire. If the drive coil 21a is considered to be a resistor in an electric circuit, its resistance value changes with temperature changes.

[0037] When the drive coil 21 a is regarded as a resistor, the resistance value RL changes in response to changes in temperature. This is utilized to detect temperature changes based on the resistance value of the drive coil 21 a. Then, upon detecting an abnormal temperature rise, the power switching module 200 determines whether to stop the power supply via the EV charging outlet 220.

[0038] Switching unit 21b switches the power supply via EV charging outlet 220 between an on state and an off state.

[0039] The control unit 24 functions as a reference temperature acquisition unit 24a, a reference resistance value acquisition unit 24b, a temperature calculation unit 24c, a determination unit 24d, and an operation recovery determination unit 24e.

[0040] The reference temperature acquisition unit 24a acquires a reference temperature used for temperature calculation in the temperature calculation unit 24c, as will be described in detail later.

[0041] The reference resistance value acquiring unit 24b acquires a reference resistance value used for temperature calculation in the temperature calculating unit 24c, as will be described in detail later.

[0042] When the drive coil 21a included in the relay 21 is regarded as a resistor, the temperature calculation unit 24c calculates the resistance value RL of the drive coil 21a, which changes with temperature changes, and calculates the temperature of the drive coil 21a.

[0043] Based on the temperature of drive coil 21 a calculated by temperature calculation unit 24 c, determination unit 24 d determines whether to cut off the power supply via EV charging outlet 220. Information related to the determination result is transmitted to charge management system 250 via communication unit 23.

[0044] As shown in FIG. 4(B) , when determination unit 24d detects a temperature rise exceeding the danger temperature threshold (100°C), operation recovery determination unit 24e determines that an abnormality has occurred and cuts off the power supply via EV charging outlet 220. After that, when time passes and relay 21 is naturally cooled and the temperature of drive coil 21a becomes less than the safety temperature threshold (60°C), operation of relay 21 is restored.

[0045] The power switching module 200 according to this embodiment calculates the temperature of the drive coil 21a included in the relay 21 using the configuration described above, thereby detecting whether the relay 21 is abnormally hot, and if the relay 21 is in an abnormally high temperature state, cutting off the power supply via the EV charging outlet 220.

[0046] A method for calculating the temperature of the drive coil 21a will be described below. The upper limit temperature of the relay 21 depends on the temperature of the drive coil 21a, which is generally made of copper wire.

[0047] The temperature rise of copper windings such as coils can be calculated by the resistance method using the following equation (1).

[0048] Here, t: coil temperature before the test (°C), T: coil temperature after the test (°C), Rt: coil resistance at temperature t (Ω), RT: coil resistance at temperature T (Ω), and 234.5: copper constant.

[0049] For example, in the case of a relay 21 in which the resistance value of the drive coil 21a is 47 Ω at 23° C., when the temperature of the drive coil 21a changes, the resistance value RT after the temperature change (120° C., −5° C.) is calculated using the following formulas (2) and (3), respectively. Note that 120° C. is a typical maximum rated temperature of the relay 21, and −5° C. is the minimum operating temperature of the relay 21.

[0050] Fig. 2 shows an electric circuit using a resistor Rx used to calculate the temperature of the drive coil 21a when the relay 21 is in operation. In the electric circuit diagram around the relay 21 shown in Fig. 2, the drive coil 21a of the relay 21 can be regarded as a resistor (resistance value RL) except during transient periods. The resistance value RL can be calculated using the following equation (4). Here, Rx is a specified value, and V １ , V ＲＬ , V ＣＥ１ The voltage value can be obtained by using an A / D converter, so by equation (4), R Ｌ You can get the value of I １ is the current flowing through the resistor when the drive coil 21a is regarded as a resistor. １ is the voltage across the relay 21. ＲＬ is the current flowing through the resistor when the drive coil 21a is regarded as a resistor. ＲＸ is the voltage across the resistor Rx used to calculate the temperature of the drive coil 21a during operation. ＣＥ１ is the voltage between ground and point B (transistor 25).

[0051] In formula (1), RT = R ＬTherefore, the temperature of the drive coil 21a when the resistance value is RL is expressed by the following equation (5) by modifying equation (1).

[0052] For example, if the resistance value of the drive coil 21a of the relay 21 described above is 62.5Ω at 23° C., the temperature T of the drive coil 21a is In this way, it is possible to determine whether it is safe or dangerous by specifying the temperature of the drive coil 21a.

[0053] For example, when V1=5V, the voltage at point A Va=1.1V, the voltage at point B Vb=0.05V, and Rx=22Ω, Therefore, the temperature of the drive coil 21a is It can be calculated as follows.

[0054] Although it is possible to measure the temperature using the method described above, the resistance value of the drive coil 21a when the relay 21 is driven is as shown in the table below. At 23° C., the resistance varies in the range of 61 Ω to 68 Ω. Because there is variation in the resistance value at 23° C., the resistance value also varies when the temperature rises.

[0055] For example, if you want to stop the relay at 100°C, and you create an algorithm that detects it at 81.19 Ω based on the typical value, if the resistance value is the minimum value of the variation, the temperature will be 137°C, if the typical value of the variation is 100°C, and if the maximum value of the variation is 70°C, this will be problematic in practical use. Therefore, measurements are taken every time the relay 21 is turned on, and calibration is performed for the temperature measurement formula each time. The processing procedure for the relay protection method in this case is shown in Figure 3.

[0056] That is, Here, t (ambient): ambient temperature (°C) immediately after the relay 21 is activated, Rt: drive coil resistance (Ω) at the ambient temperature immediately after the relay is activated, T: current drive coil temperature (°C) after the relay is activated (after calibration is completed), RT: current drive coil resistance (Ω) after the relay is activated (after calibration is completed), and 234.5: copper constant.

[0057] First, when the relay 21 is turned on, t (ambient) and Rt in equation (8) are recorded. Here, the average value over 60 seconds is recorded (steps S1 and S2). Here, equation (8) corresponds to the relational expression of the present invention, and t (ambient) and Rt correspond to the reference temperature and reference resistance value of the present invention, respectively. Here, the time after the relay 21 is turned on corresponds to the predetermined time point of the present invention, and 60 seconds corresponds to the predetermined period of the present invention. t (ambient) may be, but is not limited to, the temperature around the drive coil 21a, for example, the temperature of the MCU, measured by a temperature sensor.

[0058] Then, RT in equation (8) is monitored (step S3), and the current temperature of the drive coil 21a is calculated from equation (8) (step S4). Then, it is determined whether the temperature of the drive coil 21a exceeds a dangerous temperature threshold (100°C) (step S5). If the temperature exceeds the dangerous temperature threshold (100°C), an abnormality is detected, and the relay 21 is opened, cutting off the power supply via the EV charging outlet 220 (step S6). If the temperature of the drive coil 21a does not exceed the dangerous temperature threshold (100°C), the process returns to step S3. In this way, calibration is performed at t (ambient) to measure the resistance value of the drive coil 21a immediately after the relay is turned on. By setting Rt separately from the ambient temperature, it is not necessary to consider the resistance variation of the drive coil 21a of the relay 21. Here, step S4 corresponds to the temperature calculation step of the present invention.

[0059] This allows accurate temperature measurement near the heat source inside the power switching module. The threshold temperature used to determine whether to shut down the module due to temperature protection or automatically restart the module when the temperature returns to normal based on the measured temperature information does not require a margin for measurement error compared to other methods, improving user convenience.

[0060] FIG. 4 is a graph illustrating temperature protection using the method of this embodiment and other methods, in which the relay 21 is stopped when the temperature rises and reaches a dangerous temperature threshold, and then restored when the temperature cools down and reaches a safe temperature threshold. FIG. 4A shows an example of the other method. When the relay 21 is stopped when the dangerous temperature threshold (100°C) is reached, because 100°C is not accurately known, a margin must be provided, for example, to stop the relay 21 when the temperature reaches 90°C, resulting in increased usage restrictions. In contrast, FIG. 4B shows an example of the method of this embodiment. Because the temperature of the relay 21 can be measured more accurately, the relay 21 is stopped when the dangerous temperature threshold (100°C) is reached, and then restored when the temperature cools down and reaches the safe temperature threshold (60°C). As a result, the range of usage restrictions is narrower than with other methods, improving user convenience.

[0061] In charging system 300 according to the first embodiment, temperature calculation unit 24c and determination unit 24d provided inside power switching module 200 calculate the temperature of drive coil 21a included in relay 21 and determine whether to cut off power supply via EV charging outlet 220. However, charging management system 250, which is an external device, may be provided with components corresponding to a reference temperature acquisition unit, a reference resistance value acquisition unit, a temperature calculation unit, a determination unit, and an operation recovery determination unit. Control unit 24 of power switching module 200 acquires data related to a change in resistance value from drive coil 21a included in relay 21, and transmits the data to charging management system 250 via communication unit 23.

[0062] In this case, a temperature calculation unit calculates the temperature of drive coil 21 a based on a relational expression formed by the reference temperature and reference resistance value acquired by a reference temperature acquisition unit and a reference resistance value acquisition unit, both of which are provided in charge management system 250, and a determination unit determines whether to cut off power supply via EV charging outlet 220 based on the calculated temperature. An operation recovery determination unit may also be provided in charge management system 250.

[0063] In the following, the constituent elements of the present disclosure will be described with the reference numerals in the drawings so that the constituent elements of the present disclosure can be compared with the configurations of the examples. <Supplementary Note 1> A power switch (200) that monitors the temperature of a relay (21) that cuts off power supply to a load (230) and determines whether to cut off the power supply, comprising: the relay (21) including a drive coil (21a); ​​a temperature calculation unit (24c) that calculates the temperature of the drive coil (21a) based on a relational expression between the temperature and a resistance value of the resistor that changes with temperature when the drive coil (21a) included in the relay (21) is considered to be a resistor; a reference temperature acquisition unit (24a) that measures a reference temperature that is an ambient temperature of the drive coil (21a) at a predetermined time point; a reference resistance value acquisition unit (24b) that calculates a reference resistance value that is the resistance value of the resistor at the predetermined time point; and a determination unit (24d) that determines whether to cut off the power supply based on the temperature of the drive coil (21a) calculated by the temperature calculation unit (24c). The power switch (200) is characterized in that the temperature calculation unit (24c) calculates the temperature of the drive coil (21a) based on the relational expression calibrated based on the reference temperature and the reference resistance value. <Supplementary Note 2> The power switch (200) according to Supplementary Note 1, wherein the predetermined time point is a predetermined period immediately after the relay (21) is turned on. <Supplementary Note 3> A power switch system (300) comprising: the power switch (200) according to Supplementary Note 1 or 2; and a communication unit (23) that transmits information related to the determination result in the determination unit (24d) to an external device connected via a network.<Supplementary Note 4> A method for protecting a power switch (200) that monitors the temperature of a relay (21) that cuts off power supply to a load (230) and determines whether to cut off the power supply, the method comprising: a step (S1) of measuring a reference temperature that is an ambient temperature of a drive coil (21 a) included in the relay (21) at a predetermined time point; a step (S2) of calculating a reference resistance value that is a resistance value of the resistor at the predetermined time point when the drive coil (21 a) is considered to be a resistor; a temperature calculation step (steps S3, S4) of calibrating a relational expression between the resistance value of the resistor that changes with temperature and the temperature based on the reference temperature and the reference resistance value, and calculating the temperature of the drive coil using the calibrated relational expression; and a step (S5) of determining whether to cut off the power supply based on the temperature of the drive coil calculated in the temperature calculation step. <Supplementary Note 5> The method for protecting a power switch (200) according to Supplementary Note 4, wherein the predetermined period is a predetermined period immediately after the relay (21) is turned on.<Supplementary Note 6> An electric power switching module (200) that opens and closes an electric line (PL) connecting an AC power source (210) and an electric vehicle (230), comprising: a relay (21) that opens and closes the electric line (PL); a power measurement unit (22) that measures an amount of electric power supplied to the electric vehicle (230) through the electric line (PL); a communication unit (23) that receives an opening / closing instruction signal that instructs the relay (21) to open or close the electric line (PL) and transmits the amount of electric power measured by the power measurement unit (22); and a control unit (24), wherein the relay (21) includes a drive coil (21 a), and a temperature calculation unit (24c) that calculates a temperature of the drive coil (21 a) based on a relational expression between a resistance value of the resistor that changes with temperature when the drive coil (21 a) included in the relay (21) is considered as a resistor and a temperature a reference temperature acquisition unit (24a) that measures a reference temperature, which is the ambient temperature of the drive coil (21a) at a predetermined time; a reference resistance value acquisition unit (24b) that calculates a reference resistance value, which is the resistance value of the resistor at the predetermined time; and a judgment unit (24d) that judges whether or not to open the electric circuit (PL) based on the temperature of the drive coil (21a) calculated by the temperature calculation unit (24c), wherein the temperature calculation unit (24c) calculates the temperature of the drive coil (21d) based on the relational expression calibrated based on the reference temperature and the reference resistance value.

[0064] 21: Relay 21a: Drive coil 24a: Reference temperature acquisition unit 24b: Reference resistance value acquisition unit 24c: Temperature calculation unit 24c 24d: Determination unit 200: Power switching module 230: Electric vehicle

Claims

1. A power switch that monitors the temperature of a relay that cuts off the supply of power to a load and determines whether to cut off the power supply, comprising: the relay including a drive coil; a temperature calculation unit that calculates the temperature of the drive coil based on a relational equation between the resistance value of the resistor that changes with temperature when the drive coil included in the relay is considered to be a resistor and the temperature; a reference temperature acquisition unit that measures a reference temperature which is the ambient temperature of the drive coil at a predetermined point in time; a reference resistance value acquisition unit that calculates a reference resistance value which is the resistance value of the resistor at the predetermined point in time; and a judgment unit that judges whether to cut off the power supply based on the temperature of the drive coil calculated by the temperature calculation unit, wherein the temperature calculation unit calculates the temperature of the drive coil based on the relational equation calibrated based on the reference temperature and the reference resistance value.

2. The power switch according to claim 1, wherein the predetermined time point is a predetermined period immediately after the relay is turned on.

3. An electric power switching system comprising: an electric power switch according to claim 1 or 2; and a communication unit that transmits information relating to the judgment result in the judgment unit to an external device connected via a network.

4. A method for protecting a power switch that monitors the temperature of a relay that cuts off the power supply to a load and determines whether to cut off the power supply, comprising: a step of measuring a reference temperature, which is the ambient temperature of a drive coil included in the relay at a predetermined time point; a step of calculating a reference resistance value, which is the resistance value of the resistor at the predetermined time point when the drive coil is regarded as a resistor; a temperature calculation step of calibrating an equation relating the resistance value of the resistor that changes with temperature and the temperature based on the reference temperature and the reference resistance value, and calculating the temperature of the drive coil using the calibrated equation; and a step of determining whether to cut off the power supply based on the temperature of the drive coil calculated in the temperature calculation step.

5. The method for protecting a power switch according to claim 4, wherein the predetermined period is a predetermined period immediately after the relay is turned on.

6. An electric power switching module for opening and closing an electric circuit connecting an AC power source and an electric vehicle, comprising: a relay for opening and closing the electric circuit; a power measuring unit for measuring an amount of electric power supplied to the electric vehicle through the electric circuit; a communication unit for receiving an opening / closing instruction signal instructing the relay to open or close the electric circuit and transmitting the amount of electric power measured by the power measuring unit; and a control unit, wherein the relay includes a drive coil, and when the drive coil included in the relay is regarded as a resistor, a temperature calculation unit for calculating a temperature of the drive coil based on a relational equation between a resistance value of the resistor that changes with temperature change and the temperature, a reference temperature acquisition unit for measuring a reference temperature which is the ambient temperature of the drive coil at a predetermined point in time; a reference resistance value acquisition unit for calculating a reference resistance value which is the resistance value of the resistor at the predetermined point in time; and a judgment unit for judging whether or not to open the electric circuit based on the temperature of the drive coil calculated by the temperature calculation unit, wherein the temperature calculation unit calculates the temperature of the drive coil based on the relational equation calibrated based on the reference temperature and the reference resistance value.

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