Power meter, current correction method, and power opening / closing module

Abstract

A power meter for measuring AC power supplied through an electric path connecting an AC power supply and a load, comprising: a current measurement unit for measuring an AC current flowing through the electric path; a voltage measurement unit for measuring an AC voltage applied to the electric path; a current correction value calculation unit for calculating a correction value for correcting the current measurement value; a current computation unit for correcting the current measurement value on the basis of the correction value and calculating an AC current value flowing through the electric path; a voltage computation unit for calculating an AC voltage value applied to the electric path on the basis of the voltage measurement value; and a power calculation unit for calculating an AC power value supplied through the electric path on the basis of the AC voltage value and the AC current value. The current correction value calculation unit estimates the effective value of the current measurement value by averaging the peak values of waveforms of the current measurement value, and calculates the correction value by comparing the effective value of the estimated current measurement value with the effective value of a reference value of the AC current flowing through the electric path.

Description

Power meter, current correction method, and power switching module

[0001] The present invention relates to a power meter, a current correction method, and a power switching module.

[0002] Recently, the specified measurement system has permitted the use of meters that do not have specifications that require certification under the Measurement Act as special meters. Under this specified measurement system, businesses that have submitted prior notification can measure using meters with appropriate accuracy. In this case, the accuracy is assumed to be a power factor of 1, and accuracy can be guaranteed at a specified power consumption, eliminating the need for the conventional high-precision power measurement function.

[0003] Conventionally, when measuring the amount of electric power, the voltage of a distribution line connected to an AC power system and the current flowing through the distribution line are each converted to analog to digital, and the amount of electric power is calculated using software installed in a microcomputer. Furthermore, while it is sufficient to guarantee a measurement accuracy of about ±2% within a voltage range of ±10% of the rated voltage for the input voltage, the input current has a wide range from 0.5 A to the rated value (e.g., 16 A), and the accuracy is significantly affected by variations in the current detection circuit and current detection sensor (e.g., Hall element). Therefore, a method of correcting the slope (gain correction) of the detected value has been used (see, for example, Patent Document 1).

[0004] However, when making corrections while still using the original AC power supply, it is necessary to use the effective current value to convert the AC current to DC, but for reasons such as the need to perform square root calculations, it is necessary to use a high-performance microcomputer.

[0005] JP 2023-28478 A

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide a wattmeter with a small processing load for calculating power.

[0007] In order to solve the above problems, the present invention provides a wattmeter that is provided in an electric circuit connecting an AC power source and a load, and that measures AC power supplied from the AC power source to the load through the electric circuit, the wattmeter comprising: a current measuring unit that measures the AC current flowing through the electric circuit; a voltage measuring unit that measures the AC voltage applied to the electric circuit; a current correction value calculating unit that calculates a correction value for correcting a measured current value output from the current measuring unit; a current calculating unit that corrects the measured current value output from the current measuring unit based on the correction value and calculates a value of an AC current flowing through the electric circuit; a voltage calculating unit that calculates a value of an AC voltage applied to the electric circuit based on a measured voltage value output from the voltage measuring unit; and a power calculating unit that calculates a value of AC power supplied through the electric circuit based on the AC voltage value calculated by the voltage calculating unit and the AC current value calculated by the current calculating unit, The current correction value calculation unit is characterized in that it averages peak values ​​of the waveform of the current measurement value to estimate the effective value of the current measurement value, and calculates the correction value by comparing the estimated effective value of the current measurement value with the effective value of a reference value of the AC current flowing through the electrical circuit.

[0008] According to this method, the peak values ​​of the waveform of the measured current are averaged to estimate the effective value of the measured current, so the processing load when estimating the effective value is smaller than when performing a calculation that requires a large processing load, such as calculating the square root, and therefore it is possible to provide a wattmeter with a low processing load for power calculation.

[0009] In the present invention, the current measurement value may be a voltage value indicating the AC current.

[0010] According to this, by using a voltage value indicating an AC current as the current measurement value, data with high resolution can be processed, and therefore, highly accurate power calculation is possible.

[0011] In the present invention, the reference value may be a measurement value of the AC current flowing through the electrical path that is more accurate than the current measurement unit.

[0012] According to this, the correction value for the measured current value can be calculated with high accuracy based on the reference value with high accuracy from the current measuring unit, and therefore, it is possible to calculate the power with high accuracy.

[0013] In the present invention, the reference value may be a command value of the AC current flowing through the electrical path by the load.

[0014] This allows the correction value to be calculated accurately based on a preset reference value as a command value for the AC current flowing through the electrical circuit due to the load, thereby enabling highly accurate power calculation. In addition, since there is no need to transfer the reference value to the current correction value calculation unit from an external source, unnecessary communication means can be omitted.

[0015] The present invention provides a current correction method for correcting a measured value of an AC current flowing through an electric circuit connecting an AC power source and a load, the method being used to calculate AC power supplied through the electric circuit, the method comprising the steps of: measuring the AC current to obtain the measured value; averaging peak values ​​of the waveform of the measured value to estimate an effective value of the measured value; and comparing the estimated effective value with the effective value of a reference value of the AC current to calculate a correction value for correcting the measured value.

[0016] This method estimates the effective value of the measured AC current by averaging the peak values ​​of the measured AC current waveform, which reduces the processing load when estimating the effective value compared to when performing a calculation with a large processing load, such as calculating the square root, and therefore reduces the processing load when calculating AC power.

[0017] In the present invention, the measurement value may be a voltage value indicating the AC current.

[0018] According to this, by converting the measured value of AC current into a voltage value indicating AC current, data with high resolution can be processed, and therefore, power can be calculated with high accuracy.

[0019] In the present invention, the reference value may be a measurement value of the AC current flowing through the electrical path that is more accurate than the measurement value.

[0020] According to this, the correction value for the measured current value can be calculated with high accuracy based on the reference value with high accuracy from the current measuring unit, and therefore, it is possible to calculate the power with high accuracy.

[0021] In the present invention, the reference value may be a command value of the AC current flowing through the electrical path by the load.

[0022] This allows the correction value to be calculated accurately based on a preset reference value as a command value for the AC current flowing through the electrical circuit due to the load, thereby enabling highly accurate power calculation. In addition, since there is no need to transfer the reference value to the current correction value calculation unit from an external source, unnecessary communication means can be omitted.

[0023] The present invention also provides an electric power switching module that switches an electric circuit connecting an AC power source and an electric vehicle, the module comprising: a power switching unit that switches 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 a switching instruction signal that instructs the power switching unit 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 power measurement unit has: a current measurement unit that measures an AC current flowing through the electric circuit; a voltage measurement unit that measures an AC voltage applied to the electric circuit; a current correction value calculation unit that calculates a correction value to correct a measured current value output from the current measurement unit; a current calculation unit that corrects the measured current value output from the current measurement unit based on the correction value and calculates an AC current value flowing through the electric circuit; a voltage calculation unit that calculates an AC voltage value applied to the electric circuit based on the measured voltage value output from the voltage measurement unit; and a power calculation unit that calculates an AC power value supplied through the electric circuit based on the AC voltage value calculated by the voltage calculation unit and the AC current value calculated by the current calculation unit. The current correction value calculation unit is characterized in that it averages peak values ​​of the waveform of the current measurement value to estimate the effective value of the current measurement value, and calculates the correction value by comparing the estimated effective value of the current measurement value with the effective value of a reference value of the AC current flowing through the electrical circuit.

[0024] According to this method, the peak values ​​of the waveform of the measured current are averaged to estimate the effective value of the measured current, so the processing load when estimating the effective value is smaller than when performing a calculation that requires a large processing load, such as calculating the square root. Furthermore, the memory area (ROM, RAM, etc.) required to store the calculation functions required for the square root calculation can be reduced. Therefore, it is possible to provide a power switching module that has a low processing load for power calculation and does not use unnecessary memory area.

[0025] According to the present invention, it is possible to provide a power meter that has a small processing load for power calculation and does not use unnecessary storage areas.

[0026] Fig. 1 is a diagram showing a schematic configuration of a wattmeter according to an embodiment of the present invention, Fig. 2 is a flowchart showing a current correction method according to an embodiment of the present invention, and Fig. 3 is a diagram showing the overall configuration of a charging system including a power switching module according to an embodiment of the present invention.

[0027] [Application Example] Application examples of the present invention will be described below with reference to the drawings. Fig. 1 shows a watt-hour meter 100 to which the present invention is applied.

[0028] The electricity meter 100 includes a current detection unit 11, a voltage detection unit 12, a current AD conversion unit 13, a voltage AD conversion unit 14, a current correction calculation unit 15, a current calculation unit 16, a voltage calculation unit 17, a power calculation unit 18, and a communication unit 19.

[0029] The watt-hour meter 100 is a device that is arranged, for example, on an electrical path PL1 that supplies AC power from an AC power source 120 to a load 130, and measures the power or amount of power supplied from the AC power source 120 to the load 130.

[0030] The current detection unit 11 includes a current sensor that detects the current in the electric circuit PL1 and outputs a value indicating the current in the electric circuit PL1 as an analog value. Here, the value indicating the current in the electric circuit PL1 is output as a voltage value. The current AD conversion unit 13 converts the value indicating the current in the electric circuit PL1 input from the current detection unit 11 into a digital value (referred to as a current measurement value).

[0031] The current correction calculation unit 15 calculates a gain correction value used in the current calculation unit 16. The processing of the current correction calculation unit 15 will be described with reference to the flowchart shown in FIG. 2 . First, an AC current is applied to the load 130 from the AC power source 120 via the watt-hour meter 100 (step S1). The current correction calculation unit 15 acquires a current measurement value from the current AD conversion unit 13 (step S2). The current correction calculation unit 15 then extracts peak points (peak values) from the waveform of the acquired current measurement value and calculates the average value of the extracted peak points (step S3). Based on the average value of the peak points of the current measurement value, the current correction calculation unit 15 estimates the effective value of the current input to the watt-hour meter 100. The estimated effective value of the current is compared with the true value of the current input to the watt-hour meter 100, which is input from the adjustment equipment 110, to calculate a gain correction value (step S4). The gain correction value and the adjustment value correspond to the correction value in this invention. The calculated gain correction value is then set as a current adjustment value used in the current calculation unit 16 (step S5), which will be described later.

[0032] The current calculation unit 16 calculates the current value to be input to the watt-hour meter 100 from the current measurement value input from the current AD conversion unit 13 using the gain correction value set as the adjustment value.

[0033] The voltage detection unit 12 outputs a value indicating the voltage of the electric line PL1 as an analog value. The voltage AD conversion unit 14 converts the value indicating the voltage of the electric line PL1 input from the voltage detection unit 12 into a digital value (referred to as a voltage measurement value).

[0034] The voltage calculation unit 17 calculates the voltage value to be input to the load from the voltage measurement value input from the voltage AD conversion unit 14 .

[0035] The power calculation unit 18 calculates the power input to the watt-hour meter 100 and the amount of power obtained by integrating this power over a predetermined period of time based on the current value and voltage value.

[0036] By calculating the gain correction value by the method described for the current correction calculation unit 15, the processing load when calculating the gain correction value can be reduced compared to when calculating the effective value by calculating the square root, thereby reducing the processing load when calculating the power.

[0037] [Example 1] The following describes in more detail a watt-hour meter 100 according to Example 1 of the present invention, with reference to the drawings. However, the configurations of the device and system described in this example should be modified as appropriate depending on various conditions. In other words, the scope of the present invention is not intended to be limited to the following example.

[0038] FIG. 1 shows a functional block diagram of a watthour meter 100. The watthour meter 100 includes a current detection unit 11, a voltage detection unit 12, a current AD conversion unit 13, a voltage AD conversion unit 14, a current correction calculation unit 15, a current calculation unit 16, a voltage calculation unit 17, a power calculation unit 18, and a communication unit 19. The current correction calculation unit 15, the current calculation unit 16, the voltage calculation unit 17, and the power calculation unit 18 are functional units realized by a watthour meter control unit 10, which includes a processor such as an MPU, executing a predetermined program. The watthour meter 10 can calculate power and energy and corresponds to a wattmeter of the present invention. The current detection unit 11 and the current AD conversion unit 13 correspond to a current measurement unit of the present invention, and the voltage detection unit 12 and the voltage AD conversion unit 14 correspond to a voltage measurement unit of the present invention. The current correction calculation unit 15 corresponds to a current correction value calculation unit of the present invention, and the current calculation unit 16 and the voltage calculation unit 17 correspond to a current calculation unit and a voltage calculation unit of the present invention. The power calculation unit 18 corresponds to the power calculation unit of the present invention.

[0039] 1 also shows an adjustment facility 110 in addition to the watt-hour meter 100. The adjustment facility 110 is used to set an adjustment value used for controlling the load 130 and correcting the current when the watt-hour meter 100 is manufactured.

[0040] The current detection unit 11 includes a current sensor that detects the current in the electric circuit PL1 and outputs a value indicating the current in the electric circuit PL1 as an analog value. Here, the value indicating the current in the electric circuit PL1 is output as a voltage value. The current AD conversion unit 13 converts the value indicating the current in the electric circuit PL1 input from the current detection unit 11 into a digital value. The digital value indicating the current in the electric circuit PL1 output from the current AD conversion unit 13 is called a current measurement value. By using a voltage value as the value indicating the current in the electric circuit PL1, high-resolution data can be processed, enabling highly accurate power calculation.

[0041] The current correction calculation unit 15 calculates a gain correction value used in the current calculation unit 16. FIG. 2 shows a flowchart illustrating a method for setting the gain correction value, which will be described together with the function of the current correction calculation unit 15. The gain correction value is set based on instructions from the adjustment facility 110. First, an AC current is applied to the load 130 from the AC power source 120 via the watt-hour meter 100 (step S1). The current correction calculation unit 15 acquires a current measurement value from the current AD conversion unit 13 (step S2). The current correction calculation unit 15 then extracts peak points from the waveform of the acquired current measurement value and calculates an average value of the extracted peak points (step S3). Based on the average value of the peak points of the current measurement value calculated in this manner, the current correction calculation unit 15 estimates the effective value of the current input to the watt-hour meter 100, and compares this estimated effective value with the true value of the current input to the watt-hour meter 100, input from the adjustment facility 110, to calculate a gain correction value (step S4). In this way, the effective value of the current input to the watthour meter 100 is estimated based on the average value of the peak points of the current measurement values, and the gain correction value is calculated using the estimated effective value. This reduces the processing load when calculating the gain correction value compared to when the effective value is calculated by calculating the square root. The calculated gain correction value is then set as a current adjustment value used in the current calculation unit 16 (described later) (step S5). That is, the gain correction value is stored in a predetermined area of ​​the storage unit.

[0042] The current calculation unit 16 calculates the current value to be input to the watthour meter 100 from the current measurement value input from the current AD conversion unit 13. In the process of calculating the current to be input to the watthour meter 100, the current calculation unit 16 performs correction using the gain correction value calculated by the current correction calculation unit 15 and set as an adjustment value.

[0043] The voltage detection unit 12 outputs a value indicating the voltage of the electric line PL1 as an analog value. The voltage AD conversion unit 14 converts the value indicating the voltage of the electric line PL1 input from the voltage detection unit 12 into a digital value. The digital value indicating the voltage of the electric line PL1 output from the voltage AD conversion unit 14 is called a voltage measurement value.

[0044] The voltage calculation unit 17 calculates the voltage value to be input to the load from the voltage measurement value input from the voltage AD conversion unit 14 .

[0045] The power calculation unit 18 calculates the power input to the power meter 100 and the amount of power accumulated over a specified period of time based on the current value and voltage value input to the power meter 100 calculated by the current calculation unit 16 and the voltage calculation unit 17.

[0046] The adjustment equipment 110 has a function of measuring the current value input to the watt-hour meter 100. The adjustment equipment 110 is capable of measuring current with higher accuracy than the current detection unit 11 of the watt-hour meter 100. For this reason, the current value measured by the adjustment equipment 110 is referred to as the true value. The adjustment equipment 110 also transmits to the watt-hour meter 100 the true value of the current value input to the watt-hour meter 100, and also transmits an instruction to perform a correction during current calculation. The adjustment equipment 110 is independent from the watt-hour meter 100, and is connected to and used by the watt-hour meter 100 only during manufacturing inspection of the watt-hour meter 100. The location and method of measuring the current value supplied to the watt-hour meter 100 in the adjustment equipment 110 are not limited.

[0047] The communication unit 19 is an interface that performs communication such as transmitting power or the amount of power to a device or system provided outside the watt-hour meter 100 according to a predetermined communication method.

[0048] Such a watthour meter 100 can realize a current correction method that can reduce the processing load and perform accurate current calculations without using unnecessary storage areas.

[0049] [Modification] In the first embodiment described above, the adjustment equipment 110 measures the current flowing through the electric circuit PL1 with higher accuracy than the current detection unit 11 and the current AD conversion unit 13 and provides the current as a reference value (true value) to the current correction calculation unit 15. However, as shown in FIG. 1 , the adjustment equipment 110 may also utilize a function for controlling the load 130. That is, the same effect can be achieved by having the adjustment equipment 110 control the load 130 so that the current value consumed by the load 130 becomes a preset reference value (command value). In this case, the adjustment equipment 110 adjusts the current value flowing through the load 130 with higher accuracy than the current detection unit 11 and the current AD conversion unit 13. The processing in the current correction calculation unit 15 is similar, but when calculating the gain correction value, a preset current value (command value) is used as the true value of the current input to the watthour meter 100, rather than the current value measured by the adjustment equipment 110. For example, the true value is set to 16 A in advance, and the adjustment equipment 110 adjusts the current value consumed by the load 130 to 16 A with high precision, and transmits a correction instruction when calculating the current. In this way, a current correction method that allows for accurate current calculation can be realized, and the function of transmitting the true current value from outside to the watt-hour meter 100 can be omitted.

[0050] 3 shows a charging system 300 including a power switching module 200 equipped with the watt-hour meter 100 according to Example 1. Charging system 300 includes an EV charging outlet 220, a power switching module 200 that opens and closes an electrical circuit PL2 that charges a storage battery of an EV (Electric Vehicle) 230 connected via EV charging outlet 220 using power supplied from an AC power source 210, and a charging management system 250 that is connected to power switching module 200 via a network NT1.

[0051] 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 opens and closes an electric circuit PL2 that connects the AC power source 210 and the EV charging outlet 220. The power measurement unit 22 measures the power supplied to the EV 230 through the electric circuit PL2. The communication unit 23 is an interface that transmits and receives information between the power switching module 200 and an external device using a predetermined communication method. The control unit 24 performs overall control of the relay 21, the power measurement unit 22, and the communication unit 23. The relay 21 corresponds to the power switching unit of the present invention.

[0052] The power measuring unit 22 includes the current detecting unit 11, the voltage detecting unit 12, the current AD converting unit 13, the voltage AD converting unit 14, the current correction calculating unit 15, the current calculating unit 16, the voltage calculating unit 17, and the power calculating unit 18 of the watthour meter 100 according to the first embodiment, and the control unit 24 includes a processor such as an MPU and a memory, and also functions as the watthour meter control unit 10. The communication unit 23 functions as the communication unit 19 of the watthour meter 100 according to the first embodiment. The control unit 24 may operate in cooperation with an independently provided watthour meter control unit 10.

[0053] The following describes an example of operation of the above-described charging system 300. The charging management system 250 is, for example, a computer device such as a plurality of servers arranged on a cloud.

[0054] The charging management system 250 monitors and controls the power switching module 200 connected via the network NT1 via the target EV charging outlet 220.

[0055] Power switching module 200 is housed as a module in the housing of, for example, a pole or box that is charging equipment 260 provided with EV charging outlet 220. Relay 21 and power measurement unit 22 are arranged on electric circuit PL2 that connects AC power source 210 and EV charging outlet 220 and supplies AC power supplied from AC power source 210 to EV 230 via EV charging outlet 220. Relay 21 opens and closes electric circuit PL2 in response to an instruction from control unit 24 based on an opening / closing instruction signal received from charging management system 250 via communication unit 23, thereby charging the storage battery of EV 230. Power measurement unit 22 measures the power or amount of power supplied from AC power source 210 to EV 230 via EV charging outlet 220. Charging management system 250 monitors and controls the operation of power switching module 200 based on necessary information transmitted from communication unit 23.

[0056] In such a charging system 300, the current input to the power switching module 200 can be corrected without increasing the processing load, so that a power switching module 200 can be provided that can accurately measure power or amount of power without increasing the processing load.

[0057] 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 wattmeter (100) is provided in an electric circuit (PL1) connecting an AC power source (120) and a load (130), and measures AC power supplied from the AC power source (120) to the load (130) through the electric circuit (PL1), comprising: a current measurement unit (11, 13) that measures an AC current flowing through the electric circuit (PL1); a voltage measurement unit (12, 14) that measures an AC voltage applied to the electric circuit (PL1); a current correction value calculation unit (15) that calculates a correction value for correcting a current measurement value output from the current measurement unit (11, 13); a current calculation unit (16) that corrects the current measurement value output from the current measurement unit (11, 13) based on the correction value and calculates an AC current value flowing through the electric circuit (PL1); and a voltage calculation unit (17) that calculates an AC voltage value applied to the electric circuit based on a voltage measurement value output from the voltage measurement unit. and a power calculation unit (18) that calculates an AC power value supplied through the electric circuit (PL1) based on the AC voltage value calculated by the voltage calculation unit (17) and the AC current value calculated by the current calculation unit (16), wherein the current correction value calculation unit (15) averages peak values ​​of the waveforms of the current measurement values ​​to estimate an effective value of the current measurement values, and calculates the correction value by comparing the estimated effective value of the current measurement values ​​with an effective value of a reference value of the AC current flowing through the electric circuit (PL1). <Supplementary Note 2> The wattmeter (100) according to Supplementary Note 1, wherein the current measurement values ​​are voltage values ​​indicating the AC current. <Supplementary Note 3> The wattmeter (100) according to Supplementary Note 1 or 2, wherein the reference value is a measurement value of the AC current flowing through the electric circuit (PL1) that is more accurate than that of the current measurement units (11, 13). <Supplementary Note 4> The wattmeter (100) according to Supplementary Note 1 or 2, characterized in that the reference value is a command value of the AC current flowing through the electric line (PL1) by the load (130).<Supplementary Note 5> A current correction method for correcting a measurement value of an AC current flowing through an electric circuit (PL1) connecting an AC power source (120) and a load (110), the current correction method comprising the steps of: measuring the AC current to obtain the measurement value; averaging peak values ​​of the waveform of the measurement value to estimate an effective value of the measurement value; and comparing the estimated effective value with an effective value of a reference value of the AC current to calculate a correction value for correcting the measurement value. <Supplementary Note 6> The current correction method according to Supplementary Note 5, wherein the measurement value is a voltage value indicating the AC current. <Supplementary Note 7> The current correction method according to Supplementary Note 5 or 6, wherein the reference value is a measurement value of the AC current flowing through the electric circuit (PL1) that is more accurate than the measurement value. <Supplementary Note 8> The current correction method according to Supplementary Note 5 or 6, wherein the reference value is a command value of the AC current flowing through the electric line (PL1) by the load (130).<Supplementary Note 9> A power switching module (200) that opens and closes an electric circuit (PL2) connecting an AC power source (210) and an electric vehicle (230), comprising: a power switching unit (21) that opens and closes the electric circuit (PL2); a power measurement unit (22) that measures an amount of power supplied to the electric vehicle (230) through the electric circuit (PL2); a communication unit (23) that receives an opening and closing instruction signal that instructs the power switching unit (21) to open or close the electric circuit (PL2) and transmits the amount of power measured by the power measurement unit (22); and a control unit (24), wherein the power measurement unit (22) comprises: current measurement units (11, 13) that measure an AC current flowing through the electric circuit (PL2); and voltage measurement units (12, 14) that measure an AC voltage applied to the electric circuit (PL2), a current calculation unit (16) that corrects the current measurement values ​​output from the current measurement units (11, 13) based on the correction value and calculates the AC current value flowing through the electric circuit (PL2); a voltage calculation unit (17) that calculates the AC voltage value applied to the electric circuit (PL2) based on the current measurement values ​​output from the voltage measurement units (12, 14); and a power calculation unit (18) that calculates the AC power value supplied through the electric circuit (PL2) based on the AC voltage value calculated by the voltage calculation unit (17) and the AC current value calculated by the current calculation unit (16), The current correction value calculation unit (15) calculates the correction value by averaging peak values ​​of the waveform of the current measurement value, estimating the effective value of the current measurement value, and comparing the estimated effective value of the current measurement value with the effective value of a reference value of the AC current flowing through the electrical circuit.

[0058] 11: Current detection unit 12: Voltage detection unit 13: Current AD conversion unit 14: Voltage AD conversion unit 15: Current correction value calculation unit 16: Current calculation unit 17: Voltage calculation unit 18: Power calculation unit 100: Power meter 120: AC power supply 130: Load PL1: Electric circuit

Claims

1. A wattmeter that is provided in an electric circuit connecting an AC power source and a load, and measures AC power supplied from the AC power source to the load through the electric circuit, comprising: a current measuring unit that measures the AC current flowing through the electric circuit; a voltage measuring unit that measures the AC voltage applied to the electric circuit; a current correction value calculating unit that calculates a correction value for correcting the current measurement value output from the current measuring unit; a current calculating unit that corrects the current measurement value output from the current measuring unit based on the correction value and calculates the AC current value flowing through the electric circuit; a voltage calculating unit that calculates the AC voltage value applied to the electric circuit based on the voltage measurement value output from the voltage measuring unit; and a power calculating unit that calculates the AC power value supplied through the electric circuit based on the AC voltage value calculated by the voltage calculating unit and the AC current value calculated by the current calculating unit, the current correction value calculation unit estimates an effective value of the measured current value by averaging peak values ​​of a waveform of the measured current value, and calculates the correction value by comparing the estimated effective value of the measured current value with an effective value of a reference value of the AC current flowing through the electric circuit.

2. The wattmeter according to claim 1, wherein the current measurement value is a voltage value indicative of the AC current.

3. A power meter as claimed in claim 1 or 2, characterized in that the reference value is a measurement value of the AC current flowing through the electrical circuit that is more accurate than that of the current measuring unit.

4. A wattmeter according to claim 1 or 2, characterized in that the reference value is a command value of the AC current flowing through the electrical circuit by the load.

5. A current correction method for correcting a measurement value of an AC current flowing through an electric circuit connecting an AC power source and a load and used for calculating AC power supplied through the electric circuit, comprising: a step of measuring the AC current to obtain the measurement value; a step of averaging peak values ​​of a waveform of the measurement value to estimate an effective value of the measurement value; and a step of comparing the estimated effective value with the effective value of a reference value of the AC current to calculate a correction value for correcting the measurement value.

6. The current correction method according to claim 5, wherein the measured value is a voltage value indicating the AC current.

7. A current correction method according to claim 5 or 6, characterized in that the reference value is a measurement value of the AC current flowing through the electrical circuit that is more accurate than the measurement value.

8. A current correction method according to claim 5 or 6, characterized in that the reference value is a command value of the AC current flowing through the circuit by the load.

9. An electric power switching module that opens and closes an electric circuit connecting an AC power source and an electric vehicle, comprising: a power switching unit that opens and closes the electric circuit; a power measuring unit that measures an amount of electric power supplied to the electric vehicle through the electric circuit; a communication unit that receives an opening and closing instruction signal that instructs the power switching unit to open or close the electric circuit and transmits the amount of electric power measured by the power measuring unit; and a control unit, wherein the power measuring unit has: a current measuring unit that measures an AC current flowing through the electric circuit; a voltage measuring unit that measures an AC voltage applied to the electric circuit; a current correction value calculation unit that calculates a correction value for correcting a current measurement value output from the current measuring unit; a current calculation unit that corrects the current measurement value output from the current measuring unit based on the correction value and calculates an AC current value flowing through the electric circuit; a voltage calculation unit that calculates an AC voltage value applied to the electric circuit based on a voltage measurement value output from the voltage measurement unit; and a power calculation unit that calculates an AC power value supplied through the electric circuit based on the AC voltage value calculated by the voltage calculation unit and the AC current value calculated by the current calculation unit. The current correction value calculation unit calculates the correction value by averaging peak values ​​of the waveform of the current measurement value, estimating an effective value of the current measurement value, and comparing the estimated effective value of the current measurement value with an effective value of a reference value of the AC current flowing through the electric circuit.

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