JP6757272B2 - Power measuring device, power measuring method and power measuring program - Google Patents

Description

The present invention relates to a power measurement technique for measuring power between single-phase, three-wire distribution lines.

Patent Document 1 discloses a power measuring device that measures the power of a single-phase three-wire main circuit in a distribution board or the like. This power measuring device flows through each distribution line with a voltage V11 between one distribution line and the neutral wire of the two distribution lines and a voltage V12 between the other distribution line and the neutral line. The currents I11 and I12 are measured, and the power calculated by the voltage V11 and the current I11 is added up with the power calculated by the voltage V12 and the current I12 to measure the power of the main circuit (Patent Document 1). Paragraph 0025).

Since the above-mentioned power measuring device measures voltage and current for each phase, it is possible to measure power with high accuracy.

Japanese Unexamined Patent Publication No. 2006-337193 (published on December 14, 2006)

However, the above-mentioned power measuring device requires two voltage detection transformers for detecting the voltages V11 and V12, respectively. Further, since two channels of the A / D converter for converting the secondary side voltage of the voltage detection transformer into a digital value are required, the price can be easily increased. Further, the voltage detection transformer is large and occupies a large area on the substrate. Therefore, the size of the board on which the power measuring instrument is mounted becomes large.

Further, another power measuring device measures the voltage V between the two distribution lines and the above-mentioned currents I1 and I2 flowing through the two distribution lines to measure the power. Specifically, this power measuring device sets the voltage V11 between one distribution line and the neutral wire and the voltage V12 between the other distribution line and the neutral wire to 1/2 * V, respectively. Assume. The single-phase three-wire system power is measured by adding up the first power obtained by multiplying the voltage V11 and the current I11 and the second power obtained by multiplying the voltage V12 and the current I12.

However, although this power measuring device assumes that V11 = V12, this assumption does not always hold. In particular, if there is a difference between the currents I11 and I12, the error in power measurement becomes large. This is because the values of the currents I11 and I12 are determined by the connection status of the loads of each phase, but the loads connected to each phase are not always balanced.

One aspect of the present invention is an electric power that can be reduced in cost and size, and has a small error in measurement accuracy even if there is a difference between the currents flowing through the two distribution lines in the single-phase three-wire main circuit. The purpose is to realize a measuring device.

In order to solve the above problems, the power measuring device according to one aspect of the present invention includes the first distribution wire, the second distribution wire, and the neutral wire constituting the single-phase three-wire. A voltage measuring circuit that measures the voltage between the second distribution line, a current measuring circuit that measures the first current flowing through the first distribution line, and a second current flowing through the second distribution line, and the single phase. It includes a power measurement processor that measures the power of three wires, and the power measurement processor uses preset resistance values of the neutral wire, the first distribution wire, and the second distribution wire from the assumed power supply voltage. The measured voltage is applied to the first load between the first distribution wire and the neutral wire so as to be a value obtained by subtracting the voltage drop, and the first load voltage and the second distribution. The second load voltage applied to the second load between the electric power and the neutral wire is divided into, and the product of the first load voltage and the measured first current and the second load voltage. The electric power is calculated by summing the product of the measured second current and the measured second current.

Further, in order to solve the above problem, the power measuring device according to another aspect of the present invention is the first of the first distribution wire, the second distribution wire and the neutral wire constituting the single-phase three-wire. A voltage measuring circuit that measures the voltage between the distribution line and the second distribution line, a current measuring circuit that measures the first current flowing through the first distribution line, and a second current flowing through the second distribution line. A power measuring processor for measuring the power of the single-phase three-wire is provided, and the power measuring processor adds the product of a positive half-cycle value of the instantaneous value of the voltage and the first current in a predetermined period. The active power is calculated by adding the averaged first active power, the product of the negative half-cycle value of the instantaneous value of the voltage and the second current, and the second active power averaged in the predetermined period. , Calculate the effective voltage of the positive half cycle or negative half cycle value of the instantaneous value of the voltage, and multiply the square of the difference between the first active power and the second active power by a preset resistance value. The value is obtained by dividing the value obtained by the square of the effective voltage, and the active power is added to the value to calculate the power.

According to any aspect of the present invention, it is possible to reduce the cost and size, and even if there is a difference between the currents flowing through the two distribution lines in the single-phase three-wire main circuit, an error in measurement accuracy can be obtained. It has the effect of being able to reduce it.

It is a block diagram which shows the structure of the electric power measurement system which concerns on Embodiments 1 to 3 of this invention. It is a block diagram which shows the structure of the power measuring device and a distribution board in the said power measuring system. (A) is a circuit diagram showing the configuration of the voltage detection circuit in the power measurement device, (b) is a circuit diagram showing the configuration of the first current detection circuit in the power measurement device, and (c) is the circuit diagram showing the configuration of the first current detection circuit in the power measurement device. It is a circuit diagram which shows the structure of the 2nd current detection circuit in a measuring apparatus. It is a circuit diagram which shows the equivalent circuit of the distribution system by the said distribution board. It is a waveform diagram which shows the change of voltage and current in the main circuit according to the operation state of the load connected to the branch circuit of the distribution board. It is a graph which shows the electric power error when two power supply voltages of the main circuit are equal, and (a) is calculated by the electric power error calculated by the electric power calculation method of the comparative example, and by the electric power calculation method of the electric power measuring apparatus. It is a graph showing the absolute error of the electric power, and (b) shows the electric power error calculated by the electric power calculation method of the comparative example and the relative error of the electric power calculated by the electric power calculation method of the electric power measuring device as a percentage. It is a graph. It is a graph which shows the electric power error when one of the two power supply voltages of the main circuit is large, (a) is the electric power error calculated by the electric power calculation method of the comparative example, and the electric power calculation method of the electric power measuring apparatus. It is a graph showing the absolute error of the electric power calculated by the above, and (b) is a percentage of the electric power error calculated by the electric power calculation method of the comparative example and the relative error of the electric power calculated by the electric power calculation method of the electric power measuring device. It is a graph shown by. It is a graph which shows the electric power error when the other of the two power supply voltages of the main circuit is large, (a) is the electric power error calculated by the electric power calculation method of the comparative example, and the electric power calculation method of the electric power measuring apparatus. It is a graph which shows the absolute error of the electric power calculated by, (b) is the electric power error calculated by the electric power calculation method of the comparative example, and the relative error of electric power calculated by the electric power calculation method of the said electric power measuring apparatus as a percentage It is a graph shown by. It is a graph which shows the electric power error measured by the electric power calculation method which concerns on the modification of Embodiment 1 and the electric power error calculated by the electric power calculation method of the comparative example. It is a figure which shows the screen which sets the resistance value of a distribution line by a user which concerns on Embodiment 2 of this invention. (A) is a diagram showing a screen for automatically setting a resistance value of a distribution line according to the second embodiment of the present invention, (b) is a diagram showing a screen for setting a calculated resistance value, and (c). Is a diagram showing a screen prompting a retry of calculation of the resistance value.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS. 1 to 9.

FIG. 1 is a block diagram showing a configuration of a power measurement system according to the present embodiment.

As shown in FIG. 1, the power measurement system includes a power measurement device 101, a distribution board 102, a photovoltaic power generation module 103, a storage battery 104, and the like, which are provided in a building 100 having a power demand such as a general house. It includes a power conditioner 105, a HEMS (Home Energy Management System) controller 106, a wireless LAN router 107, and a display terminal 108. Further, the power measurement system includes an Internet 200 and a cloud server 201 provided outside the area of the building 100. The power measurement system may include a public wireless network instead of the Internet 200.

The power measuring device 101 is a device that measures the power of the main circuit in the distribution board 102. Further, the power measuring device 101 notifies the HEMS controller 106 of the measured power as power information by wireless communication (IEEE 802.15.4). When a request for acquiring power information is received from the HEMS controller 106, the power information is transmitted in response to the request. Further, the power measuring device 101 is communicably connected to the power conditioner 105, and by communicating with the power conditioner 105, the state of the photovoltaic power generation module 103 and the storage battery 104 is acquired or controlled. it can. The power measuring device 101 will be described in detail later.

The distribution board 102 is a device that branches the AC power from the power conditioner 105 or the pole transformer 109 provided in the power system to various parts of the building 100, and has various breakers. The distribution board 102 will be described in detail later.

The storage battery 104 is a battery that stores the electric power output from the photovoltaic power generation module 103, and discharges the electric power as necessary to output the electric power to the power conditioner 105.

The power conditioner 105 controls the operating voltage of the photovoltaic power generation module 103 so that the generated power of the photovoltaic power generation module 103 is always maximized, and uses the DC power output from the photovoltaic power generation module 103 or the storage battery 104 as AC power. Is converted to and supplied to the distribution board 102. Further, the power conditioner 105 subtracts the power stored in the storage battery 104 and the power supplied to the load (not shown) connected to the distribution board 102 from the generated power, and causes the remaining surplus power to flow back to the power system. ..

The HEMS controller 106 is a device having functions such as aggregating energy (electric power) information of the building 100 and unifying the operation of various devices. The HEMS controller 106 stores the power information received from the power measuring device 101 in an internal storage device in order to collect the power information. Further, the HEMS controller 106 transmits power information to the display terminal 108 by performing wireless LAN communication with the display terminal 108 in the building 100 via the wireless LAN router 107. Further, the HEMS controller 106 uploads power information to the cloud server 201 via the Internet 200.

The display terminal 108 is a portable device such as a smartphone, a tablet terminal, or a laptop computer, which has a communication function of a wireless LAN or a public wireless network. Further, the display terminal 108 has a display panel 108a (display unit) for realizing the display function, and has a touch panel 108b for realizing the operation function. The display terminal 108 can be used inside and outside the building 100. When the display terminal 108 is used in the building 100, it communicates directly with the HEMS controller 106 via the wireless LAN router 107 or with the cloud server 201 by using the communication function of the wireless LAN. And display the power information. Further, when the display terminal 108 is used outside the building 100, it communicates with the cloud server 201 by using the communication function of the public wireless network to display the power information.

The wireless LAN router 107 is a broadband router that relays wireless LAN communication with wireless LAN devices such as a display terminal 108 existing in the building 100. Further, the wireless LAN router 107 is connected to the HEMS controller 106 via a LAN cable, and performs wired LAN communication with the HEMS controller 106. Further, the wireless LAN router 107 is connected to the Internet 200.

Subsequently, the details of the power measuring device 101 will be described. FIG. 2 is a block diagram showing the configurations of the power measuring device 101 and the distribution board 102. FIG. 3A is a circuit diagram showing the configuration of the voltage detection circuit 2 in the power measuring device 101. FIG. 3B is a circuit diagram showing the configuration of the first current detection circuit 3 in the power measuring device 101. FIG. 3C is a circuit diagram showing the configuration of the second current detection circuit 4 in the power measuring device 101. First, the distribution board 102 will be described.

As shown in FIG. 2, the distribution board 102 has a single-phase three-wire main circuit composed of two distribution lines L1 and L2 and a neutral wire N, and a branch circuit branched from the main circuit.

A main breaker 21 is provided in the main circuit.

The branch circuit is a circuit branched from two distribution lines L1 (first distribution line) and neutral line N in the main circuit, and two distribution lines L2 (second distribution line) and neutral line N in the main circuit. The branch breakers 22 and 23 are provided for each. Further, a clamp ammeter 24 is attached to the distribution line L1, and a clamp ammeter 25 is attached to the distribution line L2. The clamp ammeters 24 and 25 are current detectors including current transformers and the like, and detect currents flowing through the distribution lines L1 and L2, respectively.

The power measuring device 101 includes a power measuring unit 1, a voltage detecting circuit 2 (voltage measuring circuit), a first current detecting circuit 3 (current measuring circuit), a second current detecting circuit 4 (current measuring circuit), and wireless. It includes a communication module 5 and an antenna 6. The power measurement device 101 is configured by mounting a power measurement unit 1, a voltage detection circuit 2, a first current detection circuit 3, a second current detection circuit 4, a wireless communication module 5, and an antenna 6 on a substrate as electronic components. Has been done.

The voltage detection circuit 2 is connected to the distribution lines L1 and L2 of the distribution board 102 and detects the voltage V between the distribution lines L1 and L2. As an example, the voltage detection circuit 2 has a voltage detection transformer T and a resistor R1 as shown in FIG. 3A.

The distribution lines L1 and L2 are connected to both ends of the primary winding of the voltage detection transformer T. A resistor R1 is connected between both ends of the secondary winding of the voltage detection transformer T, and a voltage V is output to both ends of the resistor R1. The primary side of the voltage detection transformer T is electrically isolated from other electronic components on the substrate.

The first current detection circuit 3 is a circuit connected to the clamp ammeter 24 and detects the current I1 (first current) flowing through the distribution line L1. As shown in FIG. 3B, the first current detection circuit 3 has a resistor R2.

The second current detection circuit 4 is a circuit connected to the clamp ammeter 25 and detects the current I2 (second current) flowing through the distribution line L2. As shown in FIG. 3C, the second current detection circuit 4 has a resistor R3.

The wireless communication module 5 is a communication processing circuit for performing wireless communication with the HEMS controller 106 via the antenna 6.

The power measurement unit 1 is based on the voltage V detected by the voltage detection circuit 2, the current I1 detected by the first current detection circuit 3, and the current I2 detected by the second current detection circuit 4. Measure the power of the circuit. The power measurement unit 1 is composed of an IC (Integrated Circuit), and in order to measure power, an A / D converter 11 (indicated by “ADC” in FIG. 2) and a power measurement processor 12 are used. Have.

The A / D converter 11 is a circuit that converts the differential voltage output from each of the voltage detection circuit 2, the first current detection circuit 3, and the second current detection circuit 4 from an analog value to a digital value. It is assumed that the A / D converter 11 has at least three independent A / D converters.

The power measurement processor 12 is a processor that measures the power by calculating the power of the main circuit of the distribution board 102 based on the digital voltage V and the currents I1 and I2 output from the A / D converter 11. Is. In order to calculate the power of the main circuit, the power measurement processor 12 includes a controller 121, a program memory 122, a data memory 123, a resistance calculation unit 124, a power supply voltage calculation unit 125, a load voltage calculation unit 126, and the like. It has a power calculation unit 127.

The program memory 122 is a memory for storing a power measurement program that defines a procedure for measuring power, and is composed of a ROM (Read Only Memory). The data memory 123 is a memory provided for the controller 121 to store various types of data, and is composed of a RAM (Random Access Memory).

The controller 121 realizes the power measurement function according to the procedure of the program stored in the program memory 122.

The resistance calculation unit 124 calculates the resistance value R of the distribution line from the pole transformer 109 to the building 100. In each embodiment including the present embodiment, the resistance value R is calculated, but it may be set as a fixed value in advance or may be set manually. It is a feature of the present invention that the electric power is calculated in consideration of the voltage drop due to the resistance value R.

The power supply voltage calculation unit 125 calculates the power supply voltage E1 between the distribution line L1 and the neutral line N and the power supply voltage E2 between the neutral line N and the distribution line L2 in the pole transformer 109. In the present embodiment, the voltage in the pole transformer 109 is referred to as a power supply voltage. The power supply voltage calculation unit 125 calculates the power supply voltages E1 and E2 based on the measured voltages V, currents I1 and I2, and resistance value R.

The load voltage calculation unit 126 describes the load voltage V1 (first load voltage) between the distribution line L1 and the neutral line N and the load voltage between the neutral line N and the distribution line L2 in the distribution board 102. Calculate V2 (second load voltage). In the present embodiment, the voltage in the distribution board 102 is referred to as a load voltage. The load voltage is obtained by subtracting the voltage drop due to the resistors R of the distribution lines L1 and L2 from the power supply voltages E1 and E2. How much voltage drop there is is determined by the relationship between the resistors R of the distribution lines L1 and L2, the current I1 flowing through the distribution line L1, and the current I2 flowing through the distribution line L2. The current I1 depends on the load LD1 (first load) between the distribution line L1 and the neutral wire N. Similarly, the current I2 depends on the load LD2 (second load) between the neutral wire N and the distribution line L2.

The power calculation unit 127 calculates the power of the main circuit in the distribution board 102 based on the load voltages V1 and V2 and the currents I1 and I2.

The operation (power measurement method) of power measurement by the power measurement device 101 configured as described above will be described.

FIG. 4 is a circuit diagram showing an equivalent circuit of the distribution system by the distribution board 102. FIG. 5 is a waveform diagram showing changes in load voltages V1 and V2 and currents I1 and I2 in the main circuit according to the operating state of the load LD2 connected to the branch circuit of the distribution board 102.

As shown in FIG. 4, a power supply voltage E1 is applied as a main power source between the distribution line L1 and the neutral line N, and a power supply voltage E2 is applied as a main power source between the neutral line N and the distribution line L2. It has been applied. Further, a load LD1 is connected between the distribution line L1 and the neutral line N, and a load LD2 is connected between the neutral line N and the distribution line L2. A load voltage V1 is applied to the load LD1, and a load voltage V2 is applied to the load LD2.

Here, the resistance component of the distribution line from the pole transformer 109 to the building 100 is defined as the resistance R. Further, in the following description, R also represents the resistance value of the resistor R.

First, in the distribution system shown in FIG. 4, the current I1 flows from the AC power source that outputs the power supply voltage E1 to the neutral line N via the distribution line L1 and the load LD1 and returns to the AC power source. Further, the current I2 flows from the AC power source that outputs the power supply voltage E2 to the distribution line L2 via the neutral wire N and the load LD2, and returns to the AC power source.

On the neutral line N, the currents I1 and I2 flow in opposite directions. Therefore, when the currents I1 and I2 are equal to each other, the currents I1 and I2 cancel each other out, and no current flows through the neutral wire N. When the current I1 is larger than the current I2, the current flows in the direction (leftward) shown by the broken line in FIG. When the current I1 is smaller than the current I2, the current flows in the direction (rightward) shown by the alternate long and short dash line in FIG.

In any of the above cases, equations (1) and (2) hold.

V1 = E1- (2 * I1-I2) * R ... (1)
V2 = E2- (2 * I2-I1) * R ... (2)
The power supply voltages E1 and E2 are not always equal, but here, in order to proceed with the subsequent calculations, it is assumed that the power supply voltages E1 and E2 are equal. Later, a simulation result when the power supply voltages E1 and E are not equal will be described. Further, the power supply voltages E1 and E2 are collectively referred to as a power supply voltage E.

When both sides of the equations (1) and (2) are added together, it is expressed as the equation (3).

V1 + V2 = E1 + E2- (I1 + I2) * R
V = 2E- (I1 + I2) * R ... (3)
The voltage V in the formula (3) is the voltage between the distribution line L1 and the distribution line L2 in the distribution board 102, and is equal to the sum of the load voltages V1 and V2. In this embodiment, the load voltages V1 and V2 are not measured individually. Only the voltage V and the currents I1 and I2 are measured.

Here, the calculation of the resistance value R will be described. A device such as a dryer through which a large current flows instantaneously is connected to either the load LD1 or the load LD2. For example, a device in which a large current flows is connected to the load LD2, the voltage V in the state where the device is not turned on (power OFF state) is set to voltage Voff, and the voltage in the state where the device is turned on (power ON state). Let V be the voltage Von. Further, the currents I1 and I2 in the power-off state of the device are set to I1off and I2off, respectively, and the currents I1 and I2 in the power-on state of the device are set to I1on and I2on, respectively.

In the power-off state, the equation (3) is expressed as the equation (4), and in the power-on state, the equation (3) is expressed as the equation (5).

Voff = 2E- (I1off + I2off) * R ... (4)
Von = 2E- (I1on + I2on) * R ... (5)
Therefore, when both sides of both equations (4) and (5) are subtracted and arranged, the resistance value R is expressed as in equation (6).

Voff-Von = (I1on + I2on-I1off-I2off) * R
R = (Voff-Von) / (I1on + I2on-I1off-I2off)
… (6)
For example, when a dryer is used as the above device, as shown in FIG. 5, when the power is switched from the power off state to the power on state, a large current I2on flows instantaneously, and the load voltage V2 is changed from the load voltage V2off. The load voltage V2on drops, but the other load voltage V1 rises from the load voltage V1off to the load voltage V1on. As an example, when the power is off, V1off = 101.5V, V2off = 100.4V, I1off = 0.4A, and I2off = 0.8A. Further, in the power-on state, V1on = 101.9V, V2on = 99.6V, I1on = 0.4A, and I2on = 11.8A. The load voltages V1off, V2off, V1on, and V2on shown in FIG. 5 are actually measured values for demonstrating that the resistance value R can be obtained by the equation (6). What is actually measured in this embodiment is V1 + V2. Further, it is assumed that only the load LD2 changes during the measurement of V1 + V2, and the load LD1 does not change.

Since Voff = V1off + V2off and Von = V1on + V2on, substituting each of the above values into the equation (6), R can be obtained as follows.

R = (201.9-201.5) / (0.4 + 11.8-0.4-0.8)
= 0.4 / 11 = 0.0363636 [Ω]
Therefore, if the voltage V and the currents I1 and I2 in the power-off state and the power-on state are measured, the external distribution from the pole transformer 109 to the building 100 can be performed by performing the calculation of the equation (6) using these values. The resistance value R of the electric wire can be obtained. Since the resistance value R is considered to be proportional to the distance of the external distribution line from the pole transformer 109 to the building 100, the same resistance value R is used for each of the distribution lines L1 and L2 and the neutral line N as shown in FIG. Is considered to have. The resistance value R may be calculated by performing it only once in advance in the environment where the power measuring device 101 is actually installed. The resistance calculation unit 124 described above calculates the resistance value R by performing the calculation of the equation (6).

In the above example, the large current device is connected to the load LD2, but the large current device may be connected to the load LD1.

Next, a power calculation method considering the voltage drop will be described.

From the above equation (3), the power supply voltage E is expressed as the equation (7). The power supply voltage calculation unit 125 described above calculates the power supply voltage E by performing the calculation of the equation (7).

E = {V + (I1 + I2) * R} / 2 ... (7)
Further, since the power supply voltage E is obtained, the load voltages V1 and V2 can be calculated from the equations (1) and (2) as in the equations (8) and (9). The load voltage calculation unit 126 described above calculates the load voltages V1 and V2 by performing the calculations of the equations (8) and (9).

V1 = E- (2 * I1-I2) * R ... (8)
V2 = E- (2 * I2-I1) * R ... (9)
Then, by obtaining the load voltages V1 and V2, the power P can be calculated as shown in the equation (10).

P = V1 * I1 + V2 * I2 ... (10)
The power calculation unit 127 described above calculates the load voltages V1 and V2 and the power P by performing the calculation of the equation (10).

Subsequently, the error of the power measured by the power measuring unit 1 will be described. Here, the method of power measurement in the present embodiment is referred to as a voltage drop method because the voltage drop due to the resistance value R is taken into consideration. As a comparison, the error of the power measured by the simple method will be described. The simple method is a method of calculating the power P by simply assuming that 1/2 of the voltage V is the load voltage V1'and V2' as in the following equation. Even in this simple method, the equation (10) is used for the calculation of the electric power P.

V1'= V2'= V / 2 = (V1 + V2) / 2
First, the true power Pr is as follows. Note that V1 and V2 are true values. There are three measurables, V (= V1 + V2), I1 and I2, but these can be measured correctly.

Pr = V1 * I1 + V2 * I2
The electric power Ps obtained by the simple method is as follows.

Ps = V1'* I1 + V2'* I2
= V / 2 * (I1 + I2) = (V1 + V2) * (I1 + I2) / 2
Therefore, the error ERRs of the simple method are as follows.

ERRs = Ps-Pr
= V / 2 * (I1 + I2) -V1 * I1-V2 * I2
= -1 / 2 * (V1-V2) * (I1-I2) ... (11)
The power Pd obtained by the voltage drop method is as follows. Here, from equations (1), (2), and (7), it is assumed that E1 and E2 are both E having the same value.

V1'' = E- (2 * I1-I2) * R
= {V + (I1 + I2) * R} / 2- (2 * I1-I2) * R
= 1/2 * V + 3/2 * (I2-I1) * R
V2'' = E- (2 * I2-I1) * R
= {V + (I1 + I2) * R} / 2- (2 * I2-I1) * R
= 1/2 * V + 3/2 * (I1-I2) * R
Therefore, the power Pd measured by the voltage drop method is expressed by the equation (12) from the equation (10).

Pd = V1'' * I1 + V2'' * I2
= 1/2 * V * I1 + 3/2 * (I2-I1) * I1 * R
+ 1/2 * V * I2 + 3/2 * (I1-I2) * I2 * R
= 1/2 * V * (I1 + I2) -3/2 * (I1-I2) ² * R
… (12)
Therefore, the error ERRd of the power Pd measured by the voltage drop method is expressed by the equation (13).

ERRd = Pd-Pr
= 1/2 * V * (I1 + I2) -3/2 * (I1-I2) ² * R
-(V1 * I1 + V2 * I2)
= -3/2 * (I1-I2) ² * R
-1 / 2 * (V1-V2) * (I1-I2) ... (13)
Here, when the equation (2) is subtracted from the equation (1) for both sides, it is expressed as the equation (14).

V1-V2 = E1-E2-3 * (I1-I2) * R ... (14)
Substituting equations (14) into equations (11) and (13) and eliminating (V1-V2), the errors ERRs and ERRd are expressed as equations (15) and (16), respectively.

ERRs = -1 / 2 * {(E1-E2) -3 * (I1-I2) * R}
* (I1-I2)
= 3/2 * (I1-I2) ² * R
-1 / 2 * (E1-E2) * (I1-I2) ... (15)
ERRd = -3/2 * (I1-I2) ² * R-1 / 2 * {(E1-E2)
-3 * (I1-I2) * R} * (I1-I2)
= -1 / 2 * (E1-E2) * (I1-I2) ... (16)
Here, if ΔE≡E1-E2 (definition) and χ≡I1-I2 (definition), the error ERRs are represented by a quadratic function of χ as in Eq. (17), and the error ERRd is Eq. (18). It is represented by a linear function of χ as in.

ERRs = 3/2 * R * χ 2 -1 / 2 * ΔE * χ
= 3/2 * R * χ * {χ-1 / 3 * ΔE / R}… (17)
ERRd = -1 / 2 * ΔE * χ ... (18)
As can be seen from the equation (17), the error ERRs are 0 when χ = 0 or χ = 1/3 * ΔE / R. As can be seen from the equation (18), the error ERRd becomes 0 when χ = 0.

Subsequently, changes in errors ERRs and ERRd with respect to changes in current I2 will be described.

FIG. 6 is a graph showing a power error when the power supply voltages E1 and E2 are equal. FIG. 6A is a graph showing the error of the electric power calculated by the simple method and the absolute error of the electric power calculated by the voltage drop method. FIG. 6B is a graph showing the error of the electric power calculated by the simple method and the relative error of the electric power calculated by the voltage drop method as a percentage.

FIG. 7 is a graph showing a power error when the power supply voltage E1 is larger than the power supply voltage E2. FIG. 7A is a graph showing the error of the electric power calculated by the simple method and the absolute error of the electric power calculated by the voltage drop method. FIG. 7B is a graph showing the error of the electric power calculated by the simple method and the relative error of the electric power calculated by the voltage drop method as a percentage.

FIG. 8 is a graph showing a power error when the power supply voltage E2 is larger than the power supply voltage E1. FIG. 8A is a graph showing the error of the electric power calculated by the simple method and the absolute error of the electric power calculated by the voltage drop method. FIG. 8B is a graph showing the error of the electric power calculated by the simple method and the relative error of the electric power calculated by the voltage drop method as a percentage.

In the example shown in each (a) of FIGS. 6 to 8, the current I1 is fixed at 20 [A], and the current I2 is 0.1 [A] from -20.0 [A] to +20.0 [A]. The errors ERRs (= Ps-Pr) and ERRd (= Pd-Pr), which are the absolute errors when changed in steps, are compared. The example shown in each (b) of FIGS. 6 to 8 shows the relative error ((Ps-Pr) / Pr and (Pd-Pr) / under the same conditions as the example shown in each (a) of FIGS. 6 to 8. Pr) is being compared. In FIGS. 6 to 8 (a) and (b), the horizontal axis represents (I1-I2) [A].

As shown in FIG. 6A, when E1 = E2, the absolute error of the voltage drop method shows a linear equation with a slope of 0 and agrees with equation (18), and the absolute error of the simple method has a quadratic curve. Shown and consistent with equation (17). As shown in FIG. 6B, when E1 = E2, the relative error of the voltage drop method does not exceed the relative error of the simple method.

As shown in FIG. 7A, when E1> E2, the absolute error of the voltage drop method shows a linear equation having a negative slope and matches the equation (18), and the absolute error of the simple method is 2. The next curve is shown and is consistent with equation (17). As shown in FIG. 7B, when E1> E2, the relative error of the voltage drop method is in a part range (range of 0.0 <I1-I2 <15.0) than the relative error of the simple method. ), But otherwise it is below.

As shown in FIG. 8A, in E1 <E2, the absolute error of the voltage drop method shows a linear equation having a positive slope and matches the equation (18), and the absolute error of the simple method is 2. The next curve is shown and is consistent with equation (17). As shown in FIG. 8B, when E1 <E2, the relative error of the voltage drop method is in a part range (-15.0 <I1-I2 <0.0) from the relative error of the simple method. Although it may exceed in the range), it is below in other cases.

It should be noted that, as shown by equations (17) and (18), the absolute error of the simple method increases with the quadratic function of χ (≡I1-I2), whereas the voltage drop method The absolute error of is suppressed by the linear function of χ (≡I1-I2). Therefore, in some ranges, the relative error of the voltage drop method may be worse than that of the simple method, but it can be said that the voltage drop method can reduce the error compared to the simple method when judged comprehensively.

By the way, in the measurement of AC power, the power factor must be taken into consideration. The power measurement considering the power factor will be described below.

Here, it is assumed that the load voltages V1 and V2 are the effective voltages, and the currents I1 and I2 are the effective currents, respectively. Further, the phase difference of the current I1 with respect to the load voltage V1 is set to θ1, and the phase difference of the current I2 with respect to the load voltage V2 is set to θ2.

With reference to FIG. 4, the calculation formulas of the voltage drop considering the power factor are expressed as the formulas (19) and (20), respectively.

V1 = E1- (2 * I1 * cosθ1-I2 * cosθ2) * R
-(2 * I1 * sinθ1-I2 * sinθ2) * X ... (19)
V2 = E2- (2 * I2 * cosθ2-I1 * cosθ1) * R
-(2 * I2 * sinθ2-I1 * sinθ1) * X ... (20)
In equations (19) and (20), R represents the resistance value [Ω] of the distribution line from the pole transformer 109 to the building 100, and X represents the reactance [Ω] of the distribution line from the pole transformer 109 to the building 100. Represents.

The resistance value and reactance are proportional to the distribution length. However, the voltage drop due to reactance is slight and can be ignored. Then, V1 and V2 are expressed as equations (21) and (22), respectively.

V1 = E1- (2 * I1 * cosθ1-I2 * cosθ2) * R ... (21)
V2 = E2- (2 * I2 * cosθ2-I1 * cosθ1) * R ... (22)
When both sides of the equations (21) and (22) are added together, the voltage V is expressed as the equation (23).

V = V1 + V2
= E1 + E2- (I1 * cosθ1 + I2 * cosθ2) * R ... (23)
Further, when (22) is subtracted from the equation (21) for both sides, the value is expressed as the equation (24).

V1-V2 = E1-E2-3 * (I1 * cosθ1-I2 * cosθ2) * R
= ΔE-3 * (I1 * cosθ1-I2 * cosθ2) * R ... (24)
Let ΔE≡E1-E2.

Here, the electric powers P1 and P2 in consideration of the power factor are as follows.

P1 = V1 * I1 * cosθ1
P2 = V2 * I2 * cosθ2
Summing these up, the true power Pr is expressed as:

Pr = P1 + P2
= V1 * I1 * cosθ1 + V2 * I2 * cosθ2
In the simple method, as described above, it is assumed that V1'= V2'= V / 2 = (V1 + V2) / 2, so the power Ps is expressed by the equation (25).

Ps = P1'+ P2'
= V1'* I1 * cosθ1 + V2'* I2 * cosθ2
= 1/2 * (V1 + V2) * (I1 * cosθ1 + I2 * cosθ2) ... (25)
Therefore, the error ERRs are expressed by Eq. (26).

ERRs = Ps-Pr
= -1 / 2 * (V1-V2) * (I1 * cosθ1-I2 * cosθ2)
… (26)
On the other hand, in the voltage drop method, the load voltages V1 and V2 are assumed as follows.

V1'' = E- (2 * I1 * cosθ1-I2 * cosθ2) * R
= 1/2 * V + 3/2 * (I2 * cosθ2-I1 * cosθ1) * R
V2'' = E- (2 * I2 * cosθ2-I1 * cosθ1) * R
= 1/2 * V + 3/2 * (I1 * cosθ1-I2 * cosθ2) * R
Therefore, the power Pd is expressed by the equation (27).

Pd = V1'' * I1 * cosθ1 + V2'' * I2 * cosθ2
= 1/2 * (V1 + V2) * (I1 * cosθ1 + I2 * cosθ2)
-3/2 * (I1 * cosθ1-I2 * cosθ2) ² * R ... (27)
The first term in the equation (27) is the electric power Ps itself. The second term in the formula (27) is referred to as a correction term.

Correction term = -3/2 * (I1 * cosθ1-I2 * cosθ2) ² * R
Then, the power Pd is expressed by the following equation.

Pd = Ps + correction argument Thus, the error ERRd is expressed as in Eq. (28).

ERRd = Pd-Pr
= Ps + correction term-Pr = (Ps + correction term) -Pr
= ERRORs + correction argument
= -1 / 2 * (V1-V2)
* (I1 * cosθ1-I2 * cosθ2) + correction term ... (28)
Substituting equation (24) into (V1-V2) of equation (28), the error ERRd is expressed as in equation (29), and there is no correction term.

ERRd = -1 / 2 * {ΔE-3 * (I1 * cosθ1-I2 * cosθ2)
* R} * (I1 * cosθ1-I2 * cosθ2) + correction term = −1 / 2 * ΔE * (I1 * cosθ1-I2 * cosθ2)… (29)
Similarly, when equation (24) is substituted into equation (V1-V2) for equation (26), the error ERRs are expressed as in equation (30), and the error ERRd is subtracted from the correction argument.

ERRs = -1 / 2 * (ΔE-3 * (I1 * cosθ1-I2 * cosθ2))
* R) * (I1 * cosθ1-I2 * cosθ2)
= -1 / 2 * ΔE * (I1 * cosθ1-I2 * cosθ2)
+ 3/2 * (I1 * cosθ1-I2 * cosθ2) ² * R
= ERRd-correction term ... (30)
Therefore, if χ≡I1 * cosθ1-I2 * cosθ2, the errors ERRs and ERRd are expressed by the above equations (17) and (18), respectively.

According to the above calculation, since Pd = Ps + correction term, the power Pd obtained by the voltage drop method may be corrected by the amount of the correction term from the power Ps obtained by the simple method. Therefore, in the actual calculation, it is better to first obtain the power Ps by a simple method and then separately calculate and correct the correction term. In fact, it's easy to calculate with the simple method.

The correction term should be considered as follows. The correction argument is expressed by the following equation.

Correction term = -3/2 * (I1 * cosθ1-I2 * cosθ2) ² * R
Here, the correction term is expressed as follows by the following two equations.

I1 * cosθ1 = P1 / V1
I2 * cosθ2 = P2 / V2
Correction term = -3/2 * (P1 / V1-P2 / V2) ² * R
For the above resistance R, a separately calculated one or a set one is used. Further, for P1 / V1 and P2 / V2, those obtained by the simple method may be used. In the simple method, V1 and V2 may not be obtained correctly, but even if V1'is a value k times deviated from the true value, P1'is also deviated k times. Therefore, both when V1'and P1'are displaced and when V1'and P1'are not displaced, the values are equivalent as P1'/ V1'.

V1'= V2'= 1/2 * (V1 + V2)
Therefore, the correction argument is expressed as the following equation.

Correction term = -3/2 * ((P1'-P2') / V1') ² * R
= -3/2 * (P1'-P2') ² / V1' ² * R
P1 ', P2', V1 ' 2 is not OK to use those obtained by the simple method, respectively. A more detailed calculation method will be described later.

As described above, the power measuring device 101 according to the present embodiment calculates the power by the voltage drop method. The power measuring device 101 first calculates the power by the simple method, and further calculates and corrects the correction term to obtain the power by the voltage drop method. As a result, the error of the measured power is generally smaller than that of the current measurement by the simple method. Further, since the voltage V between the distribution lines L1 and L2 is measured, it is only necessary to provide one voltage detection transformer T and one A / D converter 11 for voltage detection. Therefore, the power measuring device 101 can be reduced in cost and size.

Subsequently, a modified example of the present embodiment will be described below with reference to FIG.

In the above-described embodiment, an example of calculating the power Pd by adding a correction term to the power Ps obtained by the simple method has been described. In this modification, a method of further reducing the amount of calculation in the calculation of the electric power Pd will be described.

Here, a measurement method of a general digital sampling wattmeter will be briefly described. In the digital sampling wattmeter, the active power P is calculated as follows.

The instantaneous voltage e (t) and the instantaneous current i (t) at time t are defined as follows.

e (t) = sqrt (2) * E * sin (ω * t)
i (t) = sqrt (2) * I * sin (ω * t-θ)
In the above equation, E is the effective voltage, I is the effective current, θ is the phase difference between the voltage and the current, ω is the angular velocity, and ω = 2 * PI * f and f are the frequencies of 50 Hz or 60 Hz.

The active power P can be calculated by the following equation.

_{k = N-1}
P = 1 / N * Σe (k) * i (k) * Δt
^{k = 0}
In the above equation, Δt is the sampling interval.

It is known that the electric power P calculated by the above equation is about the same as the active electric power of the following equation considering the power factor.

P = E * I * cosθ
The effective voltage can be calculated by the following formula.

_{k = N-1}
E = sqrt (1 / N * Σe (k) ^ 2 * Δt)
^{k = 0}
This modified example is basically the same as a general digital sampling wattmeter.

First, the power calculation unit 127 averages the product of the instantaneous voltage (instantaneous value) and the instantaneous current (instantaneous value) in order to calculate the electric power Ps which is the active power. Specifically, the power calculation unit 127 adds the instantaneous power obtained from the values of the instantaneous voltage and the instantaneous current obtained for each sampling cycle, and when 1 second elapses, 1 second (predetermined period). The active power can be obtained by averaging the number of sampling times.

In the simple method, only the power Ps (active power) needs to be obtained, but in the voltage drop method, the effective voltage (to be exact, the square of the effective voltage) also needs to be calculated in order to obtain the correction term.

This is because the correction term is expressed by the formula including I * cos θ as described above, and the power is expressed by the formula of P = V * I * cos θ. It can be expressed as I * cosθ = P / V. From this, in order to obtain the correction term, only P (active power) and V (effective voltage) need to be calculated. This eliminates the need to calculate I (effective current), so that the amount of calculation can be reduced.

Specifically, the A / D converter 11 samples the voltage V and the currents I1 and I2 a predetermined number of times per second. For example, sampling 3200 times per second. Further, the A / D converter 11 operates in the continuous mode. The continuous mode is an operation mode in which A / D conversion is continuously performed without interruption.

Here, the voltage detection circuit 2 detects the instantaneous voltage V (t) between the distribution lines L1 and L2. The first current detection circuit 3 detects the instantaneous current I1 (t) flowing through the distribution line L1. The second current detection circuit 4 detects the instantaneous current I2 (t) flowing through the distribution line L2.

The instantaneous voltage V (t), the instantaneous current I1 (t), and the instantaneous current I2 (t) converted into digital values by the A / D converter 11 are 16-bit signed integers (int16_t) and have positive and negative values. I take the.

The controller 121 executes an interrupt when one A / D conversion by the A / D converter 11 is completed. During the interrupt period, the sampling result by the A / D converter 11 is stored in the data memory 123. In the main routine, the power calculation unit 127 takes out the data of the instantaneous voltage V (t), the instantaneous current I1 (t), and the instantaneous current I2 (t) stored in the data memory 123, and stacks them. Perform a sum operation. First, the power calculation unit 127 sets the instantaneous voltage V (t) to the positive half-cycle instantaneous voltage V1 (t) between the distribution line L1 and the neutral wire N and the neutral wire N as follows. It is simply divided into two with a negative half-cycle instantaneous voltage V2 (t) between the distribution line L2 and the distribution line L2. The instantaneous voltages V1 (t) and V2 (t) are 180 degrees out of phase with each other, so their codes are inverted. The following sd16mem0 represents the data of the instantaneous voltage V (t). Further, the following sd16mem1 represents the data of the instantaneous current I1 (t), and the sd16mem2 represents the data of the instantaneous current I2 (t).

V1 (t) ← + 1/2 * sd16mem0
V2 (t) ← -1 / 2 * sd16mem0
The power calculation unit 127 performs the product-sum calculation of the instantaneous voltages V1 (t) and V2 (t) for obtaining the active power of the distribution lines L1 and L2 as follows. POWER_L1 and POWERL2 represent the result of the product-sum operation.

POWER_L1 ← POWER_L1 + (int32_t) V1 (t) * (int32_t) sd16mem1
POWER_L2 ← POWER_L2 + (int32_t) V2 (t) * (int32_t) sd16mem2
Further, the load voltage calculation unit 126 performs a product-sum calculation of the effective voltage Ve1 between the distribution line L1 and the neutral line N as follows. VOLT_L1 represents the result of the product-sum calculation of the effective voltage Ve1.

VOLT_L1 ← VOLT_L1 + (int32_t) V1 (t) * (int32_t) V1 (t)
Here, the effective voltage Ve2 between the neutral wire N and the distribution line L2 has the same value as the effective voltage Ve1 and can be omitted. As a result, the product-sum calculation of the effective voltage Ve2 becomes unnecessary, and the amount of calculation can be reduced.

Note that POWER_L1, POWER_L2, and VOLT_L1 are 64-bit signed integers (int64_t) so as not to overflow digits. The initial value is POWER_L1 = POWER_L2 = VOLT_L1 = 0. Further, the multiplication is performed by 32 bits.

Subsequently, the details of the power calculation performed by the power calculation unit 127 will be described.

The power calculation unit 127 calculates the power Ps (active power) and the correction term every second. If the sampling by the A / D converter 11 reaches 3200 times, one second has elapsed. Therefore, the power calculation unit 127 performs the following calculation every 3200 sampling times.

The lldiv function is a function that finds the quotient and the remainder at the same time (signed 64-bit integer version). The result is returned in the lldiv_t structure. The quotient is assigned to quat and the remainder is assigned to rem. The quotient and remainder are returned as signed 64-bit integers. Div_result1, div_result2, and div_result3 in the following operations are all lldiv_t structures. Further, V_COFF and I_COFF are coefficients of voltage and current, respectively, and need to be adjusted at the time of production. Further, P1 and P2 are active powers (first active power and second active power) for the most recent one second in the L1 phase and the L2 phase calculated by the simple method. Ve1 is the effective voltage for the last 1 second in the L1 phase calculated by the simple method. The electric power P1 and P2 and the voltage V2 are obtained in a double type, respectively.

div_result1 ← lldiv (POWER_L1,3200)
P1 ← div_result1. quat / (V_COFF * I_COFF)
POWER_L1 ← div_result1. rem
div_result2 ← lldiv (POWER_L2, 3200)
P2 ← div_result2. quat / (V_COFF * I_COFF)
POWER_L2 ← div_result2. rem
div_result3 ← lldiv (VOLT_L1,3200)
Ve1 ← sqrt (div_result3.quat) / V_COFF ... (31)
VOLT_L1 ← div_result 3. rem
The total power Ps (= P1 + P2) of P1 and P2 is the active power for the last 1 second calculated by the simple method.

The power calculation unit 127 further calculates a correction term. Applying the relationship of I1 * cosθ1 = P1 / V1 and I2 * cosθ2 = P2 / V1, the correction argument is expressed as in equation (32). For the resistance value R, the data stored in the data memory 123 is used.

Correction term = -3/2 * (I1 * cosθ1-I2 * cosθ2) ² * R
= -3/2 * (P1 / V1-P2 / V1) ² * R ... (32)
Will be.

Therefore, the total of the instantaneous powers of the distribution lines L1 and L2 is expressed by the equation (33).

Pd = Ps + correction term = P1 + P2-3 / 2 * (P1 / V1-P2 / V1) ² * R
= P1 + P2-3 / 2 * (P1-P2) ² * R / V1 ² ... (33)
The effective voltage Ve1 is calculated by the equation (31), but the effective voltage Ve1 is not required to obtain the correction term, and V1 ² (the square of the effective voltage Ve1) may be used instead. Therefore, the calculation of the sqrt (square root) of the equation (31) is not actually necessary and may be omitted. As a result, the amount of calculation can be reduced.

In order to further reduce the amount of calculation, the product-sum operation may be a 32-bit signed integer (int32_t) instead of a 64-bit signed integer (int64_t). However, if the multiplication is performed as it is, the digits will overflow, so the lower few bits of voltage and current are truncated for calculation.

For example, when calculating the active power, the lower 8 bits of the voltage are truncated and the lower 1 bit of the current is truncated. When calculating the effective voltage, the lower 5 bits of the voltage are truncated. As described above, the power calculation unit 127 divides the instantaneous voltage V (t) into the instantaneous voltage V1 (t) and the instantaneous voltage V2 (t), and each of them is as follows. Perform a product-sum operation.

V1 (t) ← + 1/2 * sd16mem0
V2 (t) ← -1 / 2 * sd16mem0
POWER_L1 ← POWER_L1 + (int32_t) (V1 (t) >> 8) * (int32_t) (sd16mem1 >> 1)
POWER_L2 ← POWER_L2 + (int32_t) (V2 (t) >> 8) * (int32_t) (sd16mem1 >> 1)
>> in the above operation represents a right shift operation.

Further, the load voltage calculation unit 126 performs a product-sum calculation of the effective voltage Ve1 between the distribution line L1 and the neutral line N as follows. The electric power P1 and P2 and the voltage V2 are obtained in a double type, respectively.

VOLT_L1 ← VOLT_L1 + (int32_t) (V1 (t) >> 5) * (int32_t) (V1 (t) >> 5)
The power calculation unit 127 performs the calculation every second as follows.

The independent function is a function that obtains the quotient and the remainder at the same time (signed 32-bit integer version). The result is returned in the ldiv_t structure. The quotient is assigned to quat and the remainder is assigned to rem. The quotient and remainder are returned as signed 32-bit integers. Div_result1, div_result2, and div_result3 in the following operations are all liv_t structures.

div_result1 ← ldiv (POWER_L1,3200)
P1 ← div_result1. quat / (V_COFF * I_COFF / 512)
POWER_L1 ← div_result1. rem
div_result2 ← ldiv (POWER_L2,3200)
P2 ← div_result2. quat / (V_COFF * I_COFF / 512)
POWER_L2 ← div_result2. rem
div_result3 ← ldiv (VOLT_L1, 3200)
Ve1 ← sqrt (div_result3.quat) / (V_COFF / 32)
VOLT_L1 ← div_result 3. rem
Of course, it is more accurate to calculate with a 64-bit signed integer, but even if it is calculated with a 32-bit signed integer, there is only a slight deterioration in accuracy, and there is no big difference. The error simulation results are shown below. FIG. 9 is a graph showing the simulation result.

In FIG. 9, power Ps (product-sum operation of 32-bit signed integers), power Ps (product-sum operation of 64-bit signed integers), power Pd (product-sum operation of 32-bit signed integers), and power Pd. The result of simulating the error for each of (the product-sum operation of 64-bit signed integers) under the condition that the power supply voltage E1 is larger than the power supply voltage E2 is shown.

As can be seen from the simulation results, even if the amount of calculation is reduced, there is no big difference between the case of calculating with a 32-bit signed integer and the case of calculating with a 64-bit signed integer. Further, the error of the power Pd measured by the voltage drop method is smaller than the error of the power Ps measured by the simple method. In this simulation, the calculation of the correction terms, P1 ', P2', V1 '2 is using those obtained in a simple method, respectively. Even if it is calculated in this way, since the absolute error of the voltage drop method shows a linear equation, it can be seen that it is in good agreement with the theoretically calculated equation (18).

As described above, according to the present embodiment, as shown in the equation (33), the voltage drop method is performed by first calculating the electric power by the simple method (Ps) and then calculating and correcting the correction term. Power (Pd) is obtained. As a result, as shown in FIG. 9, the power calculated by the voltage drop method can have an overall smaller error than the power calculated by the simple method. The amount of calculation required for the actual power calculation is also increased by about 1.5 times as compared with the case of obtaining by the simple method, but it is a sufficiently feasible method.

[Embodiment 2]
The second embodiment of the present invention will be described below with reference to FIGS. 2, 10 and 11. For convenience of explanation, the same reference numerals will be added to the components having the same functions as the components described in the first embodiment, and the description thereof will be omitted. This embodiment can also be applied to the first embodiment.

FIG. 10 is a diagram showing a screen in which the resistance value of the distribution line according to the second embodiment is set by the user. FIG. 11A is a diagram showing a screen for automatically setting the resistance value of the distribution line according to the third embodiment. FIG. 11B is a diagram showing a calculated resistance value setting screen. FIG. 11C is a diagram showing a screen for prompting a retry of calculation of the resistance value.

In the present embodiment, a user interface that can select whether to set the resistance value R by input by the user or automatically will be described.

First, the power measurement processor 12 calculates the resistance value R by the resistance calculation unit 124 as described above, but also accepts the user to set the resistance value R. The operation display interface unit 128 of the power measurement processor 12 causes the display panel 108a of the display terminal 108 to display a selection screen (not shown) for selecting user setting or automatic setting for setting the resistance value R.

When the user selects a user setting on the selection screen, the operation display interface unit 128 causes the resistance value setting screen 300 shown in FIG. 10 to be displayed on the display panel 108a. The resistance value setting screen 300 has a resistance value input box 301 and a setting button 302. When the user inputs the resistance value R into the resistance value input box 301 and presses the setting button 302, the operation display interface unit 128 passes the input resistance value R to the controller 121. The controller 121 stores the resistance value R in the data memory 123.

When the user selects automatic setting on the selection screen, the operation display interface unit 128 causes the display panel 108a to display the automatic setting instruction screen 400 (interface screen) shown in FIG. 11A. The automatic setting instruction screen 400 has a start button 401 for receiving an input instructing the start of calculation of the resistance value R, and includes an explanation such as turning on / off a large current device. When the user presses the start button 401, the operation display interface unit 128 notifies the controller 121 of the input start instruction. When the resistance calculation unit 124 receives a start instruction via the controller 121, the resistance calculation unit 124 calculates the resistance value R, stores it in the data memory 123, and passes it to the controller 121.

The operation display interface unit 128 causes the resistance value setting screen 500 (interface screen) shown in FIG. 11B to be displayed on the display panel 108a together with the resistance value R received from the controller 121. The resistance value setting screen 500 includes an explanation that the resistance value R has been successfully calculated and an explanation that prompts the setting of the calculated resistance value R. The controller 121 confirms the resistance value R when the user presses the OK button 501 on the resistance value setting screen 500, and erases the resistance value R of the data memory 123 when the user presses the cancel button 502 on the resistance value setting screen 500. To do.

Further, when the calculation of the resistance value R by the resistance value setting screen 500 is unsuccessful, the operation display interface unit 128 causes the display panel 108a to display the retry screen 600 shown in FIG. 11 (c). The retry screen 600 includes an explanation that the calculation of the resistance value R has failed and an explanation that prompts the retry of the calculation of the resistance value R. When the user presses the OK button 601 on the retry screen 600, the operation display interface unit 128 notifies the controller 121 of the input retry instruction. When the resistance calculation unit 124 receives a retry instruction via the controller 121, the resistance value R is calculated again, stored in the data memory 123, and passed to the controller 121.

As described above, in the present embodiment, the resistance value R can be selected to be set by either the user setting or the automatic setting. Therefore, if the resistance value R can be calculated from the length of the distribution line and the conductor resistance, it can be set directly. Further, when the resistance value R cannot be calculated, the necessary work (ON / OFF operation of the large current device) and the like can be accurately instructed to the user by automatically calculating the resistance value R. Further, since the screen for confirming the resistance value R is provided, the user can work while confirming the resistance value R.

[Example of realization by software]
The control block of the power measurement device 101 (particularly, the resistance calculation unit 124, the power supply voltage calculation unit 125, the load voltage calculation unit 126, the power calculation unit 127, and the operation display interface unit 128) is subjected to the power measurement program as described above. Alternatively, it may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like.

In the former case, the power measurement processor 12 that functions as a computer in the power measurement device 101 is an ALU that executes arithmetic processing based on the instructions of the power measurement program, and a program memory 122 in which the power measurement program is readable by the controller 121 ( It is equipped with a "recording medium"). Then, the power measurement processor 12 reads the power measurement program from the recording medium and executes it, thereby achieving the object of the present invention. The recording medium is a "non-temporary tangible medium" and is not limited to a semiconductor memory, and the power measurement program is an arbitrary transmission medium (communication network, broadcast wave, etc.) capable of transmitting the program. It may be supplied to the power measurement processor 12 via. It should be noted that one aspect of the present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the above program is embodied by electronic transmission.

[Summary]
The power measuring device according to the first aspect of the present invention is the first distribution line (distribution line L1), the second distribution line (distribution line L2), and the neutral line (N) constituting the single-phase three-wire. To the voltage measuring circuit (voltage detection circuit 2) that measures the voltage V between the 1 distribution wire and the 2nd distribution wire, the 1st current (current I1) flowing through the 1st distribution wire, and the 2nd distribution wire. A current measuring circuit (first current detecting circuit 3, second current detecting circuit 4) for measuring the flowing second current (current I2) and a power measuring processor (12) for measuring the power of the single-phase three-wire are provided. The power measuring processor is obtained by subtracting the voltage drop due to the preset resistance values of the neutral wire, the first distribution wire, and the second distribution wire from the assumed power supply voltage E. The measured voltage V is applied to the first load (voltage V1) between the first distribution wire and the neutral wire, and the second distribution wire and the neutral wire. It was divided into a second load voltage (voltage V2) applied to the second load between the two, and the product of the first load voltage and the measured first current was measured as the second load voltage. The power is calculated by summing the product with the second current.

According to the above configuration, as shown in the above equations (8) and (9), the first load voltage and the second load voltage are calculated by the voltage drop due to the resistance value. As a result, the error of the measured power is generally smaller than that of the current measurement by the simple method in which the voltage between the first distribution line and the second distribution line is simply halved. Further, since the voltage between the distribution lines is measured, it is only necessary to provide one voltage detection transformer and one A / D converter for voltage detection. Therefore, it is possible to reduce the cost and size of the power measuring device.

The power measuring device according to the second aspect of the present invention is the first distribution line (distribution line L1), the second distribution line (distribution line L2), and the neutral line (N) constituting the single-phase three-wire. To the voltage measuring circuit (voltage detection circuit 2) that measures the voltage V between the 1st distribution wire and the 2nd distribution wire, the 1st current (current I1) flowing through the 1st distribution wire, and the 2nd distribution wire. A current measuring circuit (first current detection circuit 3, second current detection circuit 4) for measuring the flowing second current (current I2) and a power measuring processor (12) for measuring the power of the single-phase three-wire are provided. In the power measurement processor, the product of the positive half-cycle value of the instantaneous value of the voltage V and the first current is added over a predetermined period and averaged to obtain the first active power and the instantaneous value of the voltage V. The active power is calculated by adding the product of the negative half-cycle value and the second current to the second active power obtained by averaging the product over the predetermined period, and the positive half-cycle or negative of the instantaneous value of the voltage V is calculated. The effective voltage of the half-cycle value of is calculated, and the value obtained by multiplying the square of the difference between the first active power and the second active power by a preset resistance value is divided by the square of the effective voltage. At the same time, the power is calculated by adding the active power to the value.

According to the above configuration, as shown in the above equation (33), it is effective for the value obtained by multiplying the square of the difference between the first active power and the second active power by the resistance value and dividing by the square of the effective voltage. The electric power is calculated by adding the electric power. As a result, the error of the measured power is generally smaller than that of the current measurement by the simple method in which the voltage between the first distribution line and the second distribution line is simply halved. Further, since the voltage between the distribution lines is measured, it is only necessary to provide one voltage detection transformer and one A / D converter for voltage detection. Therefore, it is possible to reduce the cost and size of the power measuring device. Further, since the number of calculation steps can be reduced, the load on the power measurement processor can be reduced and the trouble caused in real-time processing can be suppressed.

In the power measuring device according to the third aspect of the present invention, in the first or second aspect, the power measuring processor (12) is placed between the first distribution line and the neutral line (N) or the second distribution line. The resistance based on the voltage V, the first current, and the second current, respectively, in the state in which the load connected between the and the neutral wire is not turned on and the state in which the power is turned on. The value may be calculated and set.

According to the above configuration, the resistance value can be calculated automatically. As a result, the above-mentioned power calculation can be easily performed.

In the power measuring device according to the fourth aspect of the present invention, in the third aspect, the power measuring processor (12) receives an input instructing the start of calculation of the resistance value and displays the calculated resistance value. The screen may be displayed on the display unit.

According to the above configuration, the resistance value can be obtained at a desired time by instructing the user to automatically set the calculation of the resistance value. Therefore, a worker who installs electrical equipment can perform the work while checking the resistance value.

The power measurement method according to the fifth aspect of the present invention is the first distribution line (distribution line L1), the second distribution line (distribution line L2), and the neutral line (N) constituting the single-phase three-wire. The voltage V between the first distribution line and the second distribution line is measured, and the first current (current I1) flowing through the first distribution line and the second current (current I2) flowing through the second distribution line are measured. Then, the first current flowing through the first distribution line and the second current flowing through the second distribution line are measured, and from the assumed power supply voltage, the neutral wire, the first distribution line, and the second distribution line A first load in which the measured voltage V is applied to a first load between the first distribution wire and the neutral wire so as to be a value obtained by subtracting the voltage drop due to a preset resistance value. The load voltage and the second load voltage applied to the second load between the second distribution wire and the neutral wire are divided into the first load voltage and the measured first current. The power of the single-phase three-wire is calculated by summing the product and the product of the second load voltage and the measured second current.

According to the above method, the same effect as that of the power measuring device according to the first aspect is obtained.

The power measurement method according to the sixth aspect of the present invention is the first distribution wire (distribution wire L1), the second distribution wire (distribution wire L2), and the neutral wire (N) constituting the single-phase three-wire. The voltage V between the first distribution line and the second distribution line is measured, and the first current (current I1) flowing through the first distribution line and the second current (current I2) flowing through the second distribution line are measured. Then, the first current flowing through the first distribution line and the second current flowing through the second distribution line are measured, and the product of the positive half-cycle value of the instantaneous value of the voltage V and the first current is determined. By adding the first active power that is added and averaged over a period, and the second active power that is the product of the negative half-cycle value of the instantaneous value of the voltage V and the second current over a predetermined period. The active power is calculated, the effective voltage of the positive half cycle or the negative half cycle value of the instantaneous value of the voltage V is calculated, and the square of the difference between the first active power and the second active power is preset. The power of the single-phase three-wire is calculated by dividing the value obtained by multiplying the resistance value by the square of the effective voltage and adding the active power to the value.

According to the above method, the same effect as that of the power measuring device according to the second aspect is obtained.

The power measurement program according to the seventh aspect of the present invention may be realized by a computer. In this case, the power measurement program that causes the computer to execute the power measurement method of the fifth or sixth aspect, and the computer reading that records the power measurement program. Possible recording media also fall within the scope of the present invention.

[Additional notes]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

2 Voltage detection circuit (voltage measurement circuit)
3 First current detection circuit (current measurement circuit)
4 Second current detection circuit (current measurement circuit)
12 Power measurement processor 101 Power measurement device 108a Display panel (display unit)
121 Controller 124 Resistance calculation unit 125 Power supply voltage calculation unit 126 Load voltage calculation unit 127 Power calculation unit 128 Operation display Interface unit 400 Automatic setting instruction screen (interface screen)
500 Resistance value setting screen (interface screen)
E Power supply voltage I1 current (first current)
I2 current (second current)
L1 distribution line (1st distribution line)
L2 distribution line (second distribution line)
LD1 load (first load)
LD2 load (second load)
N Neutral wire R Resistance V Voltage V1, V2 Load voltage

Claims (7)

A voltage measuring circuit for measuring the voltage between the first distribution line and the second distribution line among the first distribution line, the second distribution line, and the neutral line constituting the single-phase three-wire system.
A current measuring circuit that measures the first current flowing through the first distribution line and the second current flowing through the second distribution line, and
It is equipped with a power measurement processor that measures the power of the single-phase three-wire system.
The power measurement processor
The value is obtained by subtracting the voltage drop due to the preset resistance values of the neutral wire, the first distribution line, and the second distribution line from the assumed power supply voltage.
The measured voltage
The first load voltage applied to the first load between the first distribution line and the neutral wire,
The second load voltage applied to the second load between the second distribution line and the neutral wire,
Divide into
The electric power is calculated by summing the product of the first load voltage and the measured first current and the product of the second load voltage and the measured second current. Power measuring device. A voltage measuring circuit for measuring the voltage between the first distribution line and the second distribution line among the first distribution line, the second distribution line, and the neutral line constituting the single-phase three-wire system.
A current measuring circuit that measures the first current flowing through the first distribution line and the second current flowing through the second distribution line, and
It is equipped with a power measurement processor that measures the power of the single-phase three-wire system.
The power measurement processor
The first active power obtained by adding and averaging the product of the positive half-cycle value of the instantaneous value of the voltage and the first current over a predetermined period, the negative half-cycle value of the instantaneous value of the voltage, and the first The active power is calculated by adding the product of the two currents to the second active power averaged over the predetermined period.
The effective voltage of the positive half cycle or negative half cycle value of the instantaneous value of the voltage is calculated.
A value obtained by multiplying the square of the difference between the first active power and the second active power by a preset resistance value is divided by the square of the effective voltage, and the active power is added to the value. A power measuring device, characterized in that the power is calculated accordingly. The power measurement processor is powered on when the load connected between the first distribution line and the neutral line or between the second distribution line and the neutral line is not turned on. The power measuring device according to claim 1 or 2, wherein the resistance value is calculated and set based on the voltage, the first current, and the second current, respectively, of the states. The power measurement according to claim 3, wherein the power measurement processor receives an input instructing the start of calculation of the resistance value, and displays an interface screen for displaying the calculated resistance value on the display unit. apparatus. Of the first distribution line, the second distribution line, and the neutral wire constituting the single-phase three-wire system, the voltage between the first distribution line and the second distribution line is measured.
The first current flowing through the first distribution line and the second current flowing through the second distribution line were measured.
The value is obtained by subtracting the voltage drop due to the preset resistance values of the neutral wire, the first distribution line, and the second distribution line from the assumed power supply voltage.
The measured voltage
The first load voltage applied to the first load between the first distribution line and the neutral wire,
The second load voltage applied to the second load between the second distribution line and the neutral wire,
Divide into
The power of the single-phase three-wire is calculated by summing the product of the first load voltage and the measured first current and the product of the second load voltage and the measured second current. A power measurement method characterized by this. Of the first distribution line, the second distribution line, and the neutral wire constituting the single-phase three-wire system, the voltage between the first distribution line and the second distribution line is measured.
The first current flowing through the first distribution line and the second current flowing through the second distribution line were measured.
The power supply voltage is calculated by adding the voltage drop due to the preset resistance value of the neutral wire, the first distribution line and the second distribution line to the voltage.
The first active power obtained by adding and averaging the product of the positive half-cycle value of the instantaneous value of the voltage and the first current over a predetermined period, the negative half-cycle value of the instantaneous value of the voltage, and the first The active power is calculated by adding the product of the two currents to the second active power averaged over the predetermined period.
The effective voltage of the positive half cycle or negative half cycle value of the instantaneous value of the voltage is calculated.
A value obtained by multiplying the square of the difference between the first active power and the second active power by a preset resistance value is divided by the square of the effective voltage, and the active power is added to the value. A power measurement method characterized by calculating the power of the single-phase three-wire system. A power measurement program for causing a computer to execute the power measurement method according to claim 5 or 6.

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