JP7330069B2 - Watt-hour meter and electrical equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a watt-hour meter and an electrical device equipped with a switch that opens and closes an electric circuit between a power source and a load.

Conventionally, there is known a watt-hour meter equipped with a switch that opens and closes an electric circuit between a power source and a load. have. Patent Document 1 discloses a watt-hour meter that detects the voltage of an electric circuit at a position on the load side of a switch, and determines whether or not the switching operation of the switch is normally performed based on the detected voltage. disclosed.

JP-A-2003-043076

However, due to the voltage drop due to the contact resistance, which is the resistance of the contacts in the switch, the voltage at the position closer to the load than the switch becomes lower than the voltage at the position closer to the power source than the switch. Therefore, the watt-hour meter described in Patent Document 1 may not be able to accurately measure the voltage supplied from the power supply due to the voltage drop described above.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a watt-hour meter capable of accurately measuring a voltage supplied from a power supply.

In order to solve the above-described problems and achieve the object, the watt hour meter of the present invention includes a switch, a current detector, a voltage detector, a contact resistance estimator, and a state value calculator. . A switch opens and closes an electric circuit between a power source and a load. The current detector detects a current flowing through the electric circuit. The voltage detection unit detects the voltage on the load side of the switch in the electric circuit. The contact resistance estimator calculates an estimated contact resistance of the switch based on the effective value of the current detected by the current detector. The state value calculator estimates the voltage drop due to the contact resistance based on the estimated value and the effective value of the current, and based on the estimated result, calculates the voltage effective value, which is the effective value of the voltage detected by the voltage detector. A correction process for correction is performed, and the electric energy is calculated using the corrected effective voltage value.

ADVANTAGE OF THE INVENTION According to this invention, it is effective in the ability to measure the voltage supplied from a power supply accurately.

1 is a diagram showing an example of a configuration of a watt hour meter according to a first embodiment of the present invention; FIG. 3 is a flow chart showing an example of a processing procedure by the computing unit of the watt-hour meter according to the first embodiment; 4 is a flowchart showing an example of an abnormality processing procedure by the abnormality detection unit of the watt-hour meter according to the first embodiment; FIG. 2 is a diagram showing an example of a hardware configuration of a control unit of the watt-hour meter according to the first embodiment; FIG.

EMBODIMENT OF THE INVENTION Below, the watt-hour meter and electric equipment concerning embodiment of this invention are demonstrated in detail based on drawing. In addition, this invention is not limited by this embodiment.

Embodiment 1.
FIG. 1 is a diagram showing an example of a configuration of a watt-hour meter according to Embodiment 1 of the present invention. A power meter 100 shown in FIG. 1 is connected between a power supply (not shown) and a load (not shown), and measures the amount of AC power supplied from the power supply to the load via a single-phase three-wire circuit. do. The watt-hour meter 100 electrically connects the load to the power source by closing the single-phase three-wire electric circuit, and disconnects the power from the load by opening the single-phase three-wire electric circuit. Cut off electrically. The watt-hour meter 100 is an electronic watt-hour meter called a smart meter, but it may be a watt-hour meter other than a smart meter.

The watt-hour meter 100 shown in FIG. , 12 and voltage detectors 13 and 14 . The watt-hour meter 100 also includes a display unit 15 , a communication unit 16 , a control unit 17 , and a temperature detection unit 18 .

The power supply terminals 1S, 2S, and 3S are connected to the power supply via single-phase three-wire conductive wires. The load-side terminals 1L, 2L, and 3L are connected to loads via single-phase three-wire conductive wires. Conductive wires 3, 4, 5 form a single-phase three-wire electric circuit together with single-phase three-wire conductive wires connected to power supply terminals 1S, 2S, 3S and load terminals 1L, 2L, 3L, respectively. do.

Specifically, the conductive wire 3 constitutes an electric path between the power supply side terminal 1S and the load side terminal 1L. The conductive wire 4 constitutes an electric path between the power supply side terminal 2S and the load side terminal 2L. The conductive wire 5 constitutes an electric path between the power supply side terminal 3S and the load side terminal 3L.

Each switch 6, 7 opens and closes an electric circuit between a power source (not shown) and a load (not shown). Specifically, the switch 6 is provided between the conductive wires 3 a and 3 b that constitute the conductive wire 3 . The conductive wire 3a connects the power supply side terminal 1S and the terminal of the switch 6 on the power supply side terminal 1S side, and the conductive wire 3b connects the load side terminal 1L side terminal of the switch 6 and the load side terminal 1L. do. The switch 6 electrically connects and disconnects the conductive wire 3a and the conductive wire 3b.

The switch 7 is provided between the conductive wires 5 a and 5 b that constitute the conductive wire 5 . The conductive wire 5a connects the power supply side terminal 3S and the terminal of the switch 7 on the side of the power supply side terminal 3S. The conductive wire 5b connects the load-side terminal 3L-side terminal of the switch 7 and the load-side terminal 3L. The switch 7 electrically connects and disconnects the conductive wire 5a and the conductive wire 5b.

The switches 6 and 7 are relays having electromagnetic coils and contacts, such as latching relays. It should be noted that the switches 6 and 7 are not limited to relays having electromagnetic coils as long as they have contact points. Also, the switches 6 and 7 may be integrally configured by one relay having two circuits.

A current detection unit 11 detects a current i1 flowing through the conductive wire 3 . The current detection unit 11 includes, for example, a current transformer that converts the current i1 flowing through the conductive wire 3 into a current signal that is a current signal smaller than the current i1, and a current signal output from the current transformer that converts the current signal into a voltage. and a conversion circuit that converts the signal into a voltage signal.

The current detection section 12 detects the current i2 flowing through the conductive wire 5 . The current detection unit 12 includes, for example, a current transformer that converts the current i2 flowing through the conductive wire 5 into a current signal that is a current signal smaller than the current i2, and a current signal output from the current transformer that converts the current signal into a voltage. and a conversion circuit that converts the signal into a voltage signal.

The voltage detection unit 13 detects the voltage on the load side terminal 1L side of the switch 6 in the conductive wire 3 . Specifically, the voltage detection unit 13 is connected to the conductive wire 3b and the conductive wire 4 connected to the load-side terminal 1L side terminal of the switch 6, and detects the voltage between the conductive wire 3b and the conductive wire 4. Detect v1. The voltage detection unit 13 includes, for example, a transformer that converts the voltage v1 between the conductive line 3b and the conductive line 4 into a voltage signal that is a signal with a voltage lower than the voltage v1.

The voltage detection unit 14 detects the voltage on the power supply side terminal 3S side of the switch 7 in the conductive wire 5 . Specifically, the voltage detection unit 14 is connected to the conductive wire 5a and the conductive wire 4 connected to the terminal on the power supply side terminal 3S side of the switch 7, and detects the voltage between the conductive wire 5a and the conductive wire 4. Detect v2. The voltage detection unit 14 includes, for example, a transformer that converts the voltage v2 between the conductive lines 5a and 4 into a voltage signal that is a signal with a voltage lower than the voltage v2.

The display unit 15 displays the power amount measured by the control unit 17 . The display unit 15 is, for example, a liquid crystal display, an OEL (Organic Electro-Luminescence) display, or a display having a display element such as electronic paper.

The communication unit 16 is a communication interface that exchanges information with an external device wirelessly or by wire. The control unit 17 transmits and receives data to and from an external device via the communication unit 16 . For example, the control unit 17 can cause the communication unit 16 to transmit measurement data including data indicating the measured power amount to the external device.

The control unit 17 includes a switch control unit 20 , AD (Analog-to-Digital) converters 21 , 22 , 23 , 24 and a calculation unit 25 . The switch controller 20 controls the switches 6 and 7 by outputting an open command or a close command to the switches 6 and 7 .

For example, when the electric circuit between the power source and the load is to be closed from an open state, the control unit 17 outputs a close command to the switches 6 and 7 to close the switches 6 and 7 from an open state. state. Further, when opening the electric circuit from the closed state, the control unit 17 outputs an open command to the switches 6 and 7 to open the switches 6 and 7 from the closed state.

The AD converter 21 converts the voltage signal output from the current detector 11 into a digital signal. The digital signal converted by the AD converter 21 contains data indicating the instantaneous value of the current i1 flowing through the conductive line 3. FIG. The AD converter 22 converts the voltage signal output from the current detector 12 into a digital signal. The digital signal converted by the AD converter 22 contains data indicating the instantaneous value of the current i2 flowing through the conductive line 5. FIG.

The AD converter 23 converts the voltage signal output from the voltage detection section 13 into a digital signal. The digital signal converted by the AD converter 23 contains data indicating the instantaneous value of the voltage v1 between the conductive lines 3b and 4. FIG. The AD converter 24 converts the voltage signal output from the voltage detection section 14 into a digital signal. The digital signal converted by the AD converter 24 contains data indicating the instantaneous value of the voltage v2 between the conductive lines 5a and 4. FIG.

The calculator 25 includes a state value calculator 31 , a contact resistance estimator 32 , a state determiner 33 , a resistance function setter 34 , and an abnormality detector 35 . State value calculation unit 31 calculates current effective value I1, current effective value I2, voltage effective value V1, voltage effective value V2, active power value based on data included in digital signals output from AD converters 21 to 24. P1, active power value P2, power factor λ1, power factor λ2, power amount W1, power amount W2, and the like are measured.

The current effective value I1 is the effective value of the current i1 flowing through the conductive line 3, and the current effective value I2 is the effective value of the current i2 flowing through the conductive line 5. The voltage effective value V1 is the effective value of the voltage v1 between the conductive lines 3b and 4, and the voltage effective value V2 is the effective value of the voltage v2 between the conductive lines 5a and 4.

The active power value P1 is the value of active power supplied from the power supply between the power supply terminals 1S and 2S, and the active power value P2 is the value of active power supplied from the power supply between the power supply terminals 2S and 3S. be. The power factor λ1 is the power factor value of the power supplied between the power supply terminals 1S and 2S, and the power factor λ2 is the power factor value of the power supplied between the power supply terminals 2S and 3S. The electric energy W1 is a value obtained by integrating the active power supplied from the power supply between the power supply terminals 1S and 2S over time. It is the integrated value. Arithmetic unit 25 calculates active power value P1 from current effective value I1, voltage effective value V1, and power factor λ1, and calculates electric energy W1 from active power value P1. Further, the calculation unit 25 calculates an active power value P2 from the current effective value I2, the voltage effective value V2, and the power factor λ2, and calculates the power amount W2 from the active power value P2.

The state value calculator 31 calculates the current effective value I1 based on the data indicating the instantaneous value of the current i1 output from the AD converter 21 . The state value calculator 31 calculates the current effective value I2 based on the data indicating the instantaneous value of the current i2 output from the AD converter 22 . In the following, for convenience of explanation, the current effective value I1 is referred to as the actually measured current value Im.

The state value calculator 31 calculates the actual voltage value Vm, which is the effective value of the voltage v1, based on the data indicating the instantaneous value of the voltage v1 output from the AD converter 23 . Further, the state value calculation unit 31 performs a correction process of adding the effective value of the voltage applied to the contact resistance of the switch 6 to the measured voltage value Vm. Vf is obtained as voltage effective value V1. The state value calculator 31 calculates the voltage effective value V2 based on the data indicating the instantaneous value of the voltage v2 output from the AD converter 24 .

Here, correction of the measured voltage value Vm by the state value calculation unit 31 will be specifically described. The state value calculator 31 corrects the actually measured voltage value Vm based on the estimated resistance value R calculated by the contact resistance estimator 32 to obtain a corrected voltage value Vf as the effective voltage value V1. The estimated resistance value R is an estimated value of the contact resistance, which is the resistance of the contacts in the switch 6 .

The contact resistance estimator 32 can calculate the estimated resistance value R, for example, by calculating the following equation (1) representing a resistance function for predicting a change in the estimated resistance value R of the switch 6 . In the following formula (1), "R(n)" is the estimated resistance value R calculated this time, "R(n-1)" is the estimated resistance value R calculated last time, and "α" is the degree of deterioration of the contact resistance due to the energy applied to the contacts of the switch 6; Further, in the following formula (1), "Im(n)" is the measured current value Im calculated this time. Note that n is an integer of 2 or more. When the following formula (1) is calculated first, "R(n-1)" is not calculated, so "Ra" is used as "R(n-1)". "Ra" is the initial value of the estimated resistance value R;
R(n)=R(n−1)+α×R(n−1)×Im(n) ² (1)

The resistance function shown in the above equation (1) is a function relating to the resistance value of the contact resistance of the switch 6 with respect to the measured current value Im(n), and is created by the designer of the watt-hour meter 100, for example. For example, the designer of the watt-hour meter 100 measures the initial value of the contact resistance of the switch 6, and measures the contact resistance of the switch 6 in a state where the switch 6 is closed and current is passed through the conductor 3. A resistance value of the contact resistance is calculated by sampling the voltage across the terminals, and a resistance function is created using the calculated resistance value of the contact resistance. Although the resistance function shown in the above formula (1) is a recurrence formula, the resistance function used by the contact resistance estimator 32 is not limited to the above formula (1).

The resistance function used by the contact resistance estimator 32 is, for example, as shown in the following formula (2), depending on the function indicating the change in the resistance value of the contact resistance due to the energization of the contacts in the switch 6 and the number of times the switch 6 is opened and closed. It may be a function obtained by synthesizing functions indicating changes in the resistance value of the contact resistance. In the following formula (2), "N" is the number of times the switch 6 is opened and closed, and "β" is a coefficient. The designer of the watt-hour meter 100 calculates the resistance value of the contact resistance by sampling the voltage across the contact resistance while repeatedly opening and closing the switch 6, and uses the calculated resistance value of the contact resistance to calculate the following formula (2 ) can be obtained. Note that when the following formula (2) is calculated first, "R(n-1)" is not calculated, so "Ra" is used as "R(n-1)".
R(n)=R(n−1)+α×R(n−1)×Im(n) ² +β×N (2)

The initial value Ra of the estimated resistance value R described above is determined, for example, by calculating the following equation (3) in the measurement inspection process of the watt-hour meter 100 . In the following formula (3), "V_in" is an input voltage value that is the effective value of the voltage applied between the power supply terminals 1S and 2S by a manufacturing device (not shown), and "I_in" is a manufacturing device (not shown). It is an input current value that is the effective value of the current that flows between the power supply terminals 1S and 2S by the device.
Ra=(V_in−Vm)/I_in (3)

The input voltage value V_in and the input current value I_in in the above equation (3) are notified to watt hour meter 100 by wire or wirelessly from a manufacturing device (not shown) used in the manufacturing process of watt hour meter 100 . The contact resistance estimator 32 of the watt-hour meter 100 acquires the input voltage value V_in and the input current value I_in notified from the manufacturing device (not shown), and calculates the estimated resistance value R , the initial value Ra is calculated.

The measured voltage value Vm in the above equation (3) is calculated by the state value calculator 31 . The contact resistance estimator 32 calculates the initial value Ra by calculating the above equation (3) based on the input voltage value V_in and the input current value I_in notified from the manufacturing apparatus and the calculated actually measured voltage value Vm. Note that the initial value Ra may be calculated by the manufacturing apparatus and notified from the manufacturing apparatus to the watt-hour meter 100 by wire or wirelessly. In this case, the contact resistance estimator 32 of the watt-hour meter 100 acquires the initial value Ra from a manufacturing device (not shown). The input current value I_in can also be calculated by the state value calculator 31 .

The state value calculator 31 corrects the measured voltage value Vm using the estimated resistance value R calculated by the contact resistance estimator 32 to calculate a corrected voltage value Vf. Hereinafter, the actual voltage value Vm actually measured this time is referred to as “actual voltage value Vm(n)” by the state value calculation unit 31, and the actual voltage value Vm actually measured last time is referred to as “actual voltage value Vm(n−1 )”. Further, the corrected voltage value Vf obtained by correcting the measured voltage value Vm(n) by the state value calculator 31 is referred to as "corrected voltage value Vf(n)". Also, the corrected voltage value Vf obtained by correcting the measured voltage value Vm(n-1) by the state value calculator 31 is referred to as "corrected voltage value Vf(n-1)".

The state value calculator 31 corrects the actually measured voltage value Vm by, for example, calculating the following formula (4) to calculate the corrected voltage value Vf. That is, the state value calculation unit 31 estimates the voltage drop due to the contact resistance of the switch 6 based on the estimated resistance value R(n) and the measured current value Im(n), and based on the estimated result, the measured voltage value Correction processing for correcting Vm(n) is performed to calculate a corrected voltage value Vf(n).
Vf(n)=Vm(n)+R(n)×Im(n) (4)

By comparing the amount of change in the corrected voltage value Vf and the amount of change in the measured voltage value Vm, the state determination unit 33 determines the effective value of the voltage actually supplied from the power supply to the power supply-side terminal 1S and the corrected voltage value Vf. is not too far off. In other words, the state determination section 33 determines whether or not the resistance function used by the contact resistance estimation section 32 is appropriate.

For example, the state determination unit 33 compares the amount of change in the corrected voltage value Vf and the amount of change in the measured voltage value Vm by calculating the following equation (5). In the following equation (5), "Vd" is the difference between the amount of change in the corrected voltage value Vf and the amount of change in the actually measured voltage value Vm, and may be hereinafter referred to as the "difference in amount of change Vd". In addition, the following formula (5) can be expressed as shown in the following formulas (4) to (6).
Vd=|(Vf(n)-Vf(n-1))-(Vm(n)-Vm(n-1))|
... (5)
Vd=|Im(n)×R(n)−Im(n−1)×R(n−1)| (6)

When the ratio of the change amount difference Vd to the corrected voltage value Vf(n) or the ratio of the change amount difference Vd to the measured voltage value Vm(n) is equal to or greater than the threshold value Rth1, the resistance function used in the contact resistance estimator 32 is not appropriate. there is a possibility. Therefore, the state determination unit 33 determines that the resistance function used in the contact resistance estimation unit 32 is not appropriate when the following formula (7) or the following formula (8) is satisfied.
Vd/Vm(n)>Rth1 (7)
Vd/Vf(n)>Rth1 (8)

In the above formulas (7) and (8), the threshold Rth1 is, for example, 0.01. If the permissible limit of the measurement error in the watt-hour meter 100 is defined as 2%, by setting Rth1=0.01, it is possible to set the threshold value Rth1 with a margin to the permissible limit. The JIS standard "JIS C1271" specifies that the allowable limit of measurement error in smart meters is 2%.

Here, the state determination unit 33 determines that the resistance function used in the contact resistance estimation unit 32 is It may be judged as inappropriate. Therefore, the state determination unit 33 uses time-series data of each of the measured voltage value Vm and the corrected voltage value Vf calculated by the state value calculation unit 31 to determine the voltage drop curve of the measured voltage value Vm and the corrected voltage value Vf. , respectively. Note that the voltage drop curve of the measured voltage value Vm is a curve showing the temporal change of the measured voltage value Vm, and the voltage fluctuation curve of the corrected voltage value Vf is a curve showing the temporal change of the corrected voltage value Vf.

The state determination unit 33 determines the predicted amount of change in the corrected voltage value Vf and the predicted amount of change in the measured voltage value Vm from the voltage drop curve of the measured voltage value Vm and the voltage fluctuation curve of the corrected voltage value Vf. do. The state determination unit 33 calculates the difference Vd^ between the predicted amount of change in the corrected voltage value Vf and the predicted amount of change in the measured voltage value Vm, and determines the difference between the calculated difference Vd^ and the above-described difference in amount of change Vd. compare. The state determining unit 33 determines the resistance used in the contact resistance estimating unit 32 when the above equations (7) and (8) are satisfied and the difference between the difference Vd^ and the change amount difference Vd is equal to or greater than the threshold value Rth2. It can be determined that the function is not suitable.

The resistance function setting unit 34 changes the resistance function used in the contact resistance estimating unit 32 when the state determining unit 33 determines that the resistance function used in the contact resistance estimating unit 32 is not appropriate. For example, the resistance function setting unit 34 corrects at least one parameter of the slope and offset of the resistance function used in the contact resistance estimating unit 32, so that the contact resistance estimating unit 32 uses the resistance function with the corrected parameters. generated as a function of resistance

The resistance function setting section 34 sets the corrected resistance function in the contact resistance estimation section 32 . Thereby, the contact resistance estimating section 32 can calculate the estimated resistance value R using the new resistance function corrected by the resistance function setting section 34 .

Further, the resistance function setting unit 34, for example, among the plurality of types of resistance functions, the resistance function closest to the voltage drop curve of the measured voltage value Vm calculated by the state value calculation unit 31 is newly set by the contact resistance estimation unit 32. can be the resistance function used. These multiple types of resistance functions are, for example, the initial value Ra of the contact resistance of the switch 6 and the amount of change in the contact resistance due to the energy applied to the contact of the switch 6 over time in the energized state of the switch 6. It is a function obtained by measuring in advance under different conditions.

The abnormality detection unit 35 shown in FIG. 1 determines whether or not the opening/closing operation of the switch 6 is normal when the switch control unit 20 performs control to switch the switching state of the switch 6 . For example, when the switch control unit 20 performs control to switch the switch 6 from the closed state to the open state, the abnormality detection unit 35 is set in advance to the measured voltage value Vm calculated by the state value calculation unit 31. It is determined whether or not the threshold value Vth1 or less is reached. When the abnormality detection unit 35 determines that the measured voltage value Vm has become equal to or less than the threshold value Vth1, it determines that the opening/closing operation of the switch 6 is normal. It is determined that the opening/closing operation of the switch 6 is abnormal. Note that the abnormality detection unit 35 detects whether the voltage v1 detected by the voltage detection unit 13 is not equal to or lower than a preset value and continues for a preset time or longer. It can also be determined that the operation is abnormal.

Further, when the switch control unit 20 performs control to switch the switch 6 from the open state to the closed state, the abnormality detection unit 35 is set in advance to the measured voltage value Vm calculated by the state value calculation unit 31. It is determined whether or not the threshold value Vth2 is exceeded. When the abnormality detection unit 35 determines that the measured voltage value Vm is equal to or greater than the threshold value Vth2, it determines that the opening/closing operation of the switch 6 is normal. It is determined that the opening/closing operation of the switch 6 is abnormal. Note that the abnormality detection unit 35 determines that the opening/closing operation of the switch 6 is abnormal when the voltage v1 detected by the voltage detection unit 13 continues to be equal to or higher than a preset value for a preset time or longer. It can also be determined that

Abnormality detection unit 35 detects an abnormality in the internal temperature of watt-hour meter 100 based on the data indicating the internal temperature of watt-hour meter 100 that is output from temperature detection unit 18 that detects the internal temperature of watt-hour meter 100 . be able to.

Further, based on the internal temperature of the watt-hour meter 100 detected by the temperature detection unit 18 and the measured voltage value Vm calculated by the state value calculation unit 31, the abnormality detection unit 35 detects the screw provided in the power supply terminal 1S. Abnormalities such as looseness can be detected. For example, the abnormality detection unit 35 detects the difference between the measured voltage value Vm predicted based on the internal temperature of the power meter 100 detected by the temperature detection unit 18 and the actual voltage value Vm calculated by the state value calculation unit 31. is equal to or greater than the threshold value Dth, it can be determined that there is an abnormality such as loose screws provided in the power supply side terminal 1S.

Further, when the abnormality detection unit 35 detects the above-described abnormality, the abnormality detection unit 35 causes the communication unit 16 to transmit information indicating the detected abnormality to an external device, or causes the display unit 15 to display information indicating the detected abnormality. can be done. As a result, the administrator who manages the watt hour meter 100 can detect an abnormality in the watt hour meter 100 at an early stage, and appropriately selects the timing for inspecting the watt hour meter 100 or replacing the watt hour meter 100. can be judged.

In the example described above, the voltage detection unit 14 detects the voltage on the power supply side terminal 3S side of the switch 7 in the conductive line 5 as the voltage supplied from the power supply, but the voltage on the load side terminal 3L side of the switch 7 is detected. It may be configured to detect. In this case, the calculation unit 25 calculates the voltage drop due to the contact resistance of the switch 7 by a process similar to the process of correcting the effective value of the voltage v1 detected by the voltage detection unit 13, and based on the calculated result, , corrects the effective value of the voltage v2 detected by the voltage detector . Based on the effective value of the voltage v2 or the value of the voltage v2 detected by the voltage detection unit 14, the abnormality detection unit 35 performs the same processing as in the case of the measured voltage value Vm to detect whether the switching operation of the switch 7 is abnormal. It is possible to determine whether In the watt-hour meter 100 shown in FIG. 1, since the voltage detection unit 14 detects the voltage on the power supply side terminal 3S side of the switch 7, there is no need to perform the above-described correction processing. The processing load is reduced compared to the case of detecting the voltage on the power supply side terminal 3S side of 7.

FIG. 2 is a flowchart showing an example of a processing procedure by the computing unit of the watt-hour meter according to the first embodiment, which is repeatedly executed by the computing unit 25 of the watt-hour meter 100 . As shown in FIG. 2, the calculation unit 25 determines whether or not the initialization has been completed (step S10). The initial setting in step S10 is, for example, the setting performed in the measurement inspection process of the watt-hour meter 100 .

Next, when determining that the initial setting has not been completed (step S10: No), the calculation unit 25 determines whether or not there is an initial setting request from the manufacturing apparatus (step S11). When determining that there is an initial setting request (step S11: Yes), the computing unit 25 acquires the initial value Ra of the contact resistance and multiple types of resistance functions from the manufacturing apparatus (step S12), One resistance function is selected from the functions (step S13).

In step S13, the calculation unit 25 selects a preset resistance function from among the plurality of types of resistance functions. The calculation unit 25 sets the initial value Ra of the contact resistance obtained in step S12 to the initial value Ra of the contact resistance in the resistance function selected in step S13.

When the processing of step S13 is completed, when it is determined that the initial setting is completed (step S10: Yes), or when it is determined that there is no initial setting request (step S11: No), the calculation unit 25 calculates the resistance function as is used to calculate an estimated resistance value R(n) (step S14), and a correction voltage value Vf(n) is calculated (step S15). For example, the calculation unit 25 calculates the estimated resistance value R(n) by calculating the above equation (1), and calculates the correction voltage value Vf(n) by calculating the above equation (4). When the previously calculated estimated resistance value R does not exist in the calculation of the above equation (1), the calculation unit 25 uses the initial value Ra as the estimated resistance value R(n−1).

Next, the calculation unit 25 calculates a change amount difference Vd, which is the difference between the change amount of the corrected voltage value Vf(n) and the change amount of the actually measured voltage value Vm(n) (step S16). Then, the calculation unit 25 determines whether Vd/Vm(n)>Rth1 or Vd/Vf(n)>Rth1 (step S17).

When determining that Vd/Vm(n)>Rth1 or Vd/Vf(n)>Rth1 (step S17: Yes), the calculation unit 25 corrects the resistance function or creates a new value from a plurality of types of resistance functions. A resistance function is selected (step S18). When the processing of step S18 is completed, or when it is determined that Vd/Vm(n)>Rth1 and Vd/Vf(n)>Rth1 are not satisfied (step S17: No), the calculation unit 25 performs the processing shown in FIG. exit.

FIG. 3 is a flowchart showing an example of an abnormality processing procedure by the abnormality detection unit of the watt-hour meter according to the first embodiment, which is repeatedly executed by the abnormality detection unit 35 of the watt-hour meter 100 . As shown in FIG. 3, the abnormality detection unit 35 acquires information indicating the internal temperature from the temperature detection unit 18 (step S20), and acquires information indicating the measured voltage value Vm from the state value calculation unit 31 (step S21). ). Then, the abnormality detection unit 35 determines whether there is an abnormality based on the internal temperature and the measured voltage value Vm (step S22).

In step S22, the abnormality detection unit 35 detects, for example, the difference ΔVm between the actual voltage value Vm predicted based on the internal temperature detected by the temperature detection unit 18 and the actual voltage value Vm calculated by the state value calculation unit 31. is greater than or equal to the threshold value Dth. When the difference ΔVm is equal to or greater than the threshold value Dth, the abnormality detection unit 35 determines that there is an abnormality such as loosening of a screw provided in the power supply terminal 1S.

If the abnormality detection unit 35 determines that there is an abnormality in step S22 (step S23: Yes), it notifies of the abnormality (step S24). In step S<b>23 , the abnormality detection unit 35 causes the communication unit 16 to transmit information indicating the detected abnormality to an external device, or causes the display unit 15 to display information indicating the detected abnormality. When the process of step S24 ends, or when it is determined that there is no abnormality in step S23 (step S23: No), the process shown in FIG. 3 ends.

4 is a diagram illustrating an example of a hardware configuration of a control unit of the watt-hour meter according to the first embodiment; FIG. As shown in FIG. 4 , the control unit 17 of the electricity meter 100 includes a computer having a processor 101 , a memory 102 and an interface circuit 103 . Processor 101 , memory 102 , and interface circuit 103 can transmit and receive data to and from each other via bus 104 , for example.

The AD converters 21-24 are realized by the interface circuit 103. FIG. Processor 101 performs the functions of switch control unit 20 and arithmetic unit 25 by reading and executing programs stored in memory 102 . The processor 101 is an example of a processing circuit, for example, and includes one or more of a CPU (Central Processing Unit), a DSP (Digital Signal Processor), and a system LSI (Large Scale Integration).

The memory 102 includes one or more of RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Registered Trademark) (Electrically Erasable Programmable Read Only Memory). include. The memory 102 also includes a recording medium in which a computer-readable program is recorded. Such recording media include one or more of nonvolatile or volatile semiconductor memories, magnetic disks, flexible memories, optical disks, compact disks, and DVDs (Digital Versatile Disks). The switch controller 20 and the calculator 25 may include integrated circuits such as ASIC (Application Specific Integrated Circuit) and FPGA (Field Programmable Gate Array).

In the example described above, the watt-hour meter 100 is a watt-hour meter that measures the amount of electric power supplied to the single-phase three-wire electric circuit. It can also be applied to electricity meters. In this case, the power meter 100 is not provided with the switch 7 . The watt-hour meter 100 can also be applied to a watt-hour meter that measures the amount of electric power supplied to a 3-phase 3-wire electric circuit or a 3-phase 4-wire electric circuit. In this case, the watt-hour meter 100 is an electric circuit in which three or more switches are provided in parallel on three or more electric circuits, and the voltage is measured on the load side of at least one of the three or more electric circuits. Correct the measured voltage. As described above, the watt hour meter 100 is an example of an electric device, and the configuration described above can be provided in an electric device other than the watt hour meter.

As described above, the watt-hour meter 100 according to the first embodiment includes the switch 6 , the current detector 11 , the voltage detector 13 , the contact resistance estimator 32 , and the state value calculator 31 . The switch 6 opens and closes the electric circuit between the power supply and the load. The current detection unit 11 detects current flowing through the electric circuit. The voltage detection unit 13 detects the voltage on the load side of the switch 6 in the electric circuit. The contact resistance estimation unit 32 calculates an estimated resistance value R, which is an estimated value of the contact resistance of the switch 6, based on the effective value of the current in the electric circuit detected by the current detection unit 11. FIG. The state value calculation unit 31 estimates the voltage drop due to the contact resistance of the switch 6 based on the measured current value Im, which is the effective value of the electric circuit current detected by the current detection unit 11, and the estimated resistance value R. Based on the results obtained, correction processing for correcting the actually measured voltage value Vm is performed to calculate the corrected voltage value Vf. The state value calculator 31 calculates the power amount W1 based on the corrected voltage value Vf. Accordingly, it is possible to accurately measure the voltage supplied from the power supply.

Further, the contact resistance estimator 32 calculates the estimated resistance value R using a function relating to the resistance value of the contact resistance with respect to the current effective value I1 and including a preset initial value Ra of the contact resistance as a parameter. . This makes it possible to measure the voltage supplied from the power supply with higher accuracy.

The watt-hour meter 100 also includes a state determination section 33 and a resistance function setting section 34 . The state determination unit 33 calculates a change amount difference that is a difference between the change amount of the measured voltage value Vm and the change amount of the corrected voltage value Vf, and calculates a first value or a ratio of the change amount difference to the measured voltage value Vm. It is determined whether or not the second value, which is the ratio of the change amount difference to the corrected voltage value Vf, is equal to or greater than the threshold value Rth1. The resistance function setting unit 34 sets a function and a parameter of the function used by the contact resistance estimating unit 32 to estimate the contact resistance when the state determining unit 33 determines that the first value or the second value is larger than the threshold value Rth1. change at least one of This makes it possible to measure the voltage supplied from the power supply with higher accuracy.

The watt-hour meter 100 also includes a temperature detection section 18 and an abnormality detection section 35 . Temperature detection unit 18 detects the internal temperature of power meter 100 . Abnormality detection unit 35 detects the presence or absence of an abnormality based on the internal temperature of watt-hour meter 100 detected by temperature detection unit 18 and measured voltage value Vm, and notifies the result of the detection. As a result, for example, the administrator of the watt-hour meter 100 can grasp whether or not the voltage supplied from the power supply is being measured in a state where an abnormality has occurred, and can check the watt-hour meter 100 or check the power supply. The timing for replacing the weighing scale 100 can be appropriately determined.

The configuration shown in the above embodiment shows an example of the content of the present invention, and it is possible to combine it with another known technology, and one configuration can be used without departing from the scope of the present invention. It is also possible to omit or change the part.

1L, 2L, 3L load side terminals 1S, 2S, 3S power supply side terminals 3, 3a, 3b, 4, 5, 5a, 5b conducting wires 6, 7 switches 11, 12 current detectors 13, 14 voltage detection unit, 15 display unit, 16 communication unit, 17 control unit, 18 temperature detection unit, 20 switch control unit, 21 to 24 AD converter, 25 operation unit, 31 state value calculation unit, 32 contact resistance estimation unit, 33 state determination unit, 34 resistance function setting unit, 35 abnormality detection unit, 100 electricity meter.

Claims (5)

A switch that opens and closes the electric circuit between the power supply and the load;
a current detection unit that detects a current flowing through the electric circuit;
a voltage detection unit that detects the voltage on the load side of the switch in the electric circuit;
a contact resistance estimation unit that calculates an estimated value of the contact resistance of the switch based on the effective value of the current detected by the current detection unit;
estimating the voltage drop due to the contact resistance based on the estimated value and the effective value of the current, and correcting the voltage effective value, which is the effective value of the voltage detected by the voltage detection unit, based on the estimated result; and a state value calculation unit that performs a correction process for correcting the voltage and calculates the electric energy using the corrected effective voltage value. The contact resistance estimator,
2. The estimated value is calculated using a function relating to the resistance value of the contact resistance with respect to the effective value of the current and including a preset initial value of the contact resistance as a parameter. watt-hour meter described in . calculating a change amount difference, which is a difference between a first change amount that is a change amount of the voltage effective value before the correction process and a second change amount that is a change amount of the voltage effective value after the correction process, and performing the correction process; Determining whether a first value that is the ratio of the change amount difference to the previous voltage effective value or a second value that is the ratio of the change amount difference to the voltage effective value after the correction process is equal to or greater than a threshold. a state determination unit to
changing at least one of the function and parameters of the function used in the contact resistance estimating unit when the state determining unit determines that the first value or the second value is greater than the threshold value 3. The watt-hour meter according to claim 2, further comprising a resistance function setting unit for setting the resistance function. a temperature detection unit that detects the internal temperature of the power meter;
an abnormality detection unit that detects the presence or absence of an abnormality based on the internal temperature detected by the temperature detection unit and the voltage effective value before correction processing, and notifies the result of detection. The electricity meter according to any one of claims 1 to 3. A switch that opens and closes the electric circuit between the power supply and the load;
a current detection unit that detects a current flowing through the electric circuit;
a voltage detection unit that detects the voltage on the load side of the switch in the electric circuit;
a contact resistance estimation unit that calculates an estimated value of the contact resistance of the switch based on the effective value of the current detected by the current detection unit;
estimating the voltage drop due to the contact resistance based on the estimated value and the effective value of the current, and correcting the voltage effective value, which is the effective value of the voltage detected by the voltage detection unit, based on the estimated result; and a state value calculation unit that performs a correction process to calculate the power amount using the corrected voltage effective value.

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