JP2014115201A - Power measurement device and power measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power measuring device and a power measuring method in which the calculation of phase difference between an AC voltage measured by using capacity coupling and an actual AC voltage is not required and which can suppress an increase in errors included in the measured AC power even if capacity formed between an electrode and a power line varies.SOLUTION: Input impedance of a voltage part 15 makes a cutoff frequency of a high frequency pass filter constituted of a first capacity formed by a power line 12a and a first electrode 13a1, a second capacity formed by a power line 12b and a second electrode 13b1, and the input impedance of the voltage part 15 have higher frequency than that of an AC voltage.

Description

  The present invention relates to a power measuring device and a power measuring method.

  As an apparatus for measuring the AC power supplied to the load via the power line based on the AC voltage applied to the power line and the AC current flowing through the power line, for example, the power described in Patent Document 1 There is a measuring device.

  In this power measurement device, as a preliminary preparation for measuring AC power, first, a voltage measurement probe having an electrode is used to form a capacitance between the electrode and the power line, and then applied to the power line by coupling the formed capacitance Measure the AC voltage that is being used. Next, the power measurement device directly connects a general cable to the power line, and measures the AC voltage applied to the power line. The power measuring device calculates a phase difference (phase shift) between the AC voltage measured via the voltage measurement probe and the AC voltage measured via a general cable, and stores the calculated phase shift. To complete the preparation.

  When the above preparation is completed, the power measurement device corrects the phase of the AC voltage measured via the voltage measurement probe by the stored phase shift (phase difference). Thereby, the power measuring device removes the phase shift from the AC voltage measured through the voltage measurement probe (the phase of the AC voltage measured through the voltage measurement probe and the AC voltage measured through a general cable). Match).

  The power measuring device measures the AC power supplied to the load via the power line based on the AC voltage from which the phase shift is removed and the AC current measured by the current measuring probe having the current sensor. .

JP 2006-343109 A

  The power measurement device described in Patent Document 1 described above corrects the calculated phase shift (phase difference) and the phase of the AC voltage measured via the voltage measurement probe. Therefore, in advance preparation, AC voltage measured via a voltage measurement probe (AC voltage measured using capacitive coupling), AC voltage measured via a general cable (actual AC voltage), It was necessary to calculate the phase difference.

  For example, if the relative position between the electrode of the voltage measurement probe and the power line changes, and the capacitance formed between the electrode and the power line becomes a different value from that calculated when the phase shift is calculated, the corrected AC voltage is The phase shift remains. For this reason, in the power measuring device described in Patent Document 1, if the capacitance formed between the electrode and the power line varies after storing the calculated phase shift, the error included in the measured AC power increases.

  The present invention has been made in view of the above circumstances, and does not require the calculation of the phase difference between the AC voltage measured using capacitive coupling and the actual AC voltage. An object of the present invention is to provide a power measuring device and a power measuring method capable of suppressing an increase in errors included in measured AC power even if the capacitance formed therebetween fluctuates.

  In order to achieve the above object, the first electrode of the power measuring apparatus according to the present invention makes it possible to obtain an AC voltage applied to one of the two-wire power lines by capacitively coupling with one of the power lines. . The second electrode makes it possible to acquire an AC voltage applied to the other of the two-wire power lines by capacitively coupling with the other power line. The voltage unit acquires the AC voltage applied to one power line via the first electrode, acquires the AC voltage applied to the other power line via the second electrode, and acquires the AC voltage The AC voltage applied to the two-wire power line is determined from the voltage difference. The current unit acquires an alternating current flowing through the two-wire power line. The power unit inputs the AC voltage obtained by the voltage unit and the AC current acquired by the current unit, and measures the AC power supplied to the load connected to the two-wire power line. The input impedance of the voltage unit includes a first capacitor formed by one power line and the first electrode, a second capacitor formed by the other power line and the second electrode, and an input impedance of the voltage unit. This is a value that makes the cutoff frequency of the high-pass filter higher than the frequency of the AC voltage.

  According to the present invention, it is not necessary to calculate the phase difference between the AC voltage measured using capacitive coupling and the actual AC voltage, and the capacitance formed between the electrode and the power line varies. However, it is possible to suppress an increase in errors included in the measured AC power.

It is a block diagram of the electric power measurement apparatus which concerns on embodiment of this invention. It is a figure which shows the circuit comprised from the capacity | capacitance formed with the electrode and the power line, and the input impedance of a voltage part. It is a figure which shows the frequency characteristic of the phase of the alternating voltage input into a voltage part.

  Hereinafter, a power measuring apparatus 11 according to an embodiment of the present invention will be described with reference to FIGS. The power measuring device 11 is connected to a single-phase two-wire power line based on an alternating voltage applied to the single-phase two-wire power line and an alternating current flowing through the single-phase two-wire power line. Measure the AC power supplied to the selected load.

  As shown in FIG. 1, the power measuring device 11 includes a voltage measuring probe 13a, 13b, a current transformer 14, a voltage unit 15, a current unit 16, A / D conversion units 17a, 17b, a 90 ° phase shifter. 18, a low pass filter (LPF) 19, a calculation control unit 20, and a communication unit 21.

  The voltage measurement probes 13a and 13b are probes for acquiring an AC voltage applied to the single-phase two-wire power line 12. Each of the voltage measuring probes 13a and 13b has, for example, an alligator clip.

  The voltage measurement probe 13a has the 1st electrode 13a1 comprised with the metal plate in one piece of an alligator clip.

  The voltage measurement probe 13a is arranged so that the power line 12a, which is one of the single-phase two-wire power lines 12, is sandwiched between alligator clips. With this arrangement, the first electrode 13a1 is capacitively coupled to the power line 12a, and an AC voltage applied to the power line 12a can be acquired. When the voltage measurement probe 13a having the first electrode 13a1 acquires the AC voltage applied to the power line 12a via the first electrode 13a1, the voltage measurement unit 13 generates a voltage signal indicating the amplitude corresponding to the acquired AC voltage. Output to.

  The voltage measurement probe 13b has a second electrode 13b1 made of a metal plate in one piece of the alligator clip.

  The voltage measurement probe 13b is arranged so that the power line 12b, which is the other of the single-phase two-wire power line 12, is sandwiched between alligator clips. With this arrangement, the second electrode 13b1 is capacitively coupled to the power line 12b, and an AC voltage applied to the power line 12b can be acquired. When the voltage measurement probe 13b having the second electrode 13b1 acquires the AC voltage applied to the power line 12b via the second electrode 13b1, the voltage signal indicating the amplitude corresponding to the acquired AC voltage is supplied to the voltage unit 15. Output to.

  The voltage unit 15 acquires the AC voltage applied to the power line 12a via the voltage measurement probe 13a, and acquires the AC voltage applied to the power line 12b via the voltage measurement probe 13b. And the voltage part 15 calculates | requires the alternating voltage applied to the single phase two-wire type power line 12 from the difference of the acquired alternating voltage.

  Specifically, the voltage unit 15 acquires the voltage signal output from the voltage measurement probe 13a and the voltage signal output from the voltage measurement probe 13b. Then, the voltage unit 15 amplifies each acquired voltage signal. Thereafter, the voltage unit 15 obtains a potential difference between the amplified voltage signals, and obtains an AC voltage applied to the single-phase two-wire power line 12.

  Then, the voltage unit 15 outputs the obtained AC voltage (AC voltage applied to the single-phase two-wire power line 12) to the A / D conversion unit 17a.

  Here, the value of the input impedance of the voltage unit 15 is determined in consideration of the capacitance formed by the first electrode 13a1 and the power line 12a and the variation of the capacitance formed by the second electrode 13b1 and the power line 12b. Yes. Specifically, the input impedance of the voltage unit 15 varies from the voltage unit 15 even if the capacitance formed by the first electrode 13a1 and the power line 12a and the capacitance formed by the second electrode 13b1 and the power line 12b vary. The phase of the output AC voltage is determined to be a value that maintains the phase advanced by 90 ° with respect to the phase of the actual AC voltage applied to the single-phase two-wire power line 12.

  The A / D conversion unit 17a samples the AC voltage output from the voltage unit 15 (AC voltage applied to the single-phase two-wire power line 12) and converts it into a digital value. Then, the A / D conversion unit 17a outputs an AC voltage indicated by a digital value to the 90 ° phase shifter 18.

  The 90 ° phase shifter 18 acquires the digital AC voltage output from the A / D converter 17a, delays the output timing of the AC voltage indicated by the acquired digital value by a predetermined time, and sends it to the LPF 19. Output.

  Specifically, the 90 ° phase shifter 18 corresponds to the 90 ° phase of the AC voltage applied to the single-phase two-wire power line 12 with respect to the output timing of the AC voltage indicated by the acquired digital value. Output to the LPF 19 with a delay of time. That is, the 90 ° phase shifter 18 delays the phase of the AC voltage indicated by the acquired digital value by 90 ° and outputs it to the LPF 19. Thereby, the 90 ° phase shifter 18 causes the phase of the AC voltage (hereinafter referred to as “acquired voltage”) output from the voltage unit 15 to be the actual AC voltage applied to the single-phase two-wire power line 12. To match the phase.

  Here, compared to the actual AC voltage applied to the single-phase two-wire power line 12, the phase of the acquired voltage is advanced by 90 ° because the voltage unit 15 uses capacitive coupling. Specifically, the AC voltage applied to the power lines 12a and 12b is acquired by using the charge and discharge of the capacitance formed between the electrode and the single-phase two-wire power line 12. .

  As described above, the 90 ° phase shifter 18 delays the phase of the acquisition voltage advanced by 90 ° compared to the actual AC voltage applied to the single-phase two-wire power line 12, thereby obtaining the acquisition voltage. And the phase of the actual AC voltage applied to the single-phase two-wire power line 12 are matched. Then, the 90 ° phase shifter 18 outputs to the LPF 19 a digital acquired voltage whose phase is delayed by 90 °.

  The LPF 19 acquires the acquired voltage (digital value) after phase correction from the 90 ° phase shifter 18 and removes high-frequency components (such as noise) from the acquired voltage. Then, the LPF 19 sequentially outputs the acquired voltage (digital value) from which the high frequency component has been removed to the arithmetic control unit 20.

  Here, the cutoff frequency of the LPF 19 is set in advance to be higher than the frequency of the acquired voltage after phase correction. Therefore, the LPF 19 can remove the high frequency component superimposed on the acquired voltage after phase correction, and output the acquired voltage from which the high frequency component has been removed to the arithmetic control unit 20.

  The current transformer 14 has, for example, an O-shaped clamp portion whose tip is configured to be openable and closable. The current transformer 14 is disposed on the outer periphery of the power line 12a by surrounding the power line 12a with a clamp portion. The current transformer 14 outputs a current signal indicating an amplitude corresponding to the alternating current flowing through the power line 12 a to the current unit 16.

  The current unit 16 acquires the current signal output from the current transformer 14, amplifies the acquired current signal, and sends the amplified current signal (corresponding to the alternating current flowing through the power line 12a) to the A / D conversion unit 17b. Output.

  The A / D conversion unit 17b samples the current signal output from the current unit 16 (corresponding to an alternating current flowing through the power line 12a, hereinafter referred to as “acquired current”) and converts it into a digital value. Then, the A / D conversion unit 17b sequentially outputs the current signal converted into the digital value to the arithmetic control unit 20.

  The arithmetic control unit 20 outputs the acquired voltage (digital value) after phase correction from which high-frequency components have been sequentially output from the LPF 19 and the acquired current (digital value) sequentially output from the A / D conversion unit 17b. get.

Then, the arithmetic control unit 20 substitutes the acquired voltage (digital value) for one cycle of the AC voltage applied to the single-phase two-wire power line 12 into the value V (n) shown in Equation 1 (n Indicates the order of acquisition of the digital values (in the first acquisition, n indicates 1). In addition, the arithmetic control unit 20 calculates the sampling number per cycle of the AC voltage applied to the single-phase two-wire power line 12 (the number calculated in advance from the sampling cycle of the A / D conversion unit 17a), Substitute for the value N in Equation 1. Then, the arithmetic control unit 20 calculates the value {V (n) ² } / N of Equation 1.

・・・式１

... Formula 1

The calculation control unit 20 obtains the value of {V (n) ² } / N by a set amount (for example, 32 periods of the AC voltage applied to the single-phase two-wire power line 12). Then, the arithmetic control unit 20 calculates the effective value V of the acquired voltage by calculating the sum of the calculated values (for example, for 32 periods) and calculating the square root of the calculated sum as shown in Equation 1. (The effective value V is obtained from the acquired AC voltage).

  In addition, the arithmetic control unit 20 obtains an acquired voltage (digital value) for one cycle of the AC voltage applied to the single-phase two-wire power line 12 and the AC applied to the single-phase two-wire power line 12. Substituting the acquired current (digital value) for one period of current into Equation 2, the product of the acquired voltage (digital value) and the acquired current (digital value) is a set amount (for example, 32 periods) Min) Then, as shown in Equation 2, the arithmetic control unit 20 calculates the sum of the calculated values (for example, for 32 cycles), and calculates a value obtained by dividing the calculated sum by the value N, thereby obtaining temporary power. Find P1.

・・・式２

... Formula 2

  Further, the arithmetic control unit 20 substitutes the effective value V of the acquired voltage and the temporary power P1 into Equation 3. In addition, the arithmetic control unit 20 determines in advance the effective value V1 of the actual AC voltage applied to the single-phase two-wire power line 12 (from the measured value of the AC voltage applied to the single-phase two-wire power line 12 in advance). The measured value P obtained by correcting the temporary power P1 is obtained by substituting the effective value V1) obtained and stored in the arithmetic control unit 20 into the expression 3.

・・・式３

... Formula 3

  That is, the arithmetic control unit 20 divides the effective value V1 of the actual AC voltage by the effective value V of the acquired voltage, and obtains the ratio of the effective value V of the acquired voltage to the effective value V1 of the actual AC voltage. . Thereafter, the arithmetic control unit 20 obtains the measured power P obtained by correcting the temporary power P1 by multiplying the temporary power P1 by the calculated difference ratio. Note that the effective value V1 of the actual AC voltage stored in the arithmetic control unit 20 is a value measured by, for example, a DMM (Digital Multi Meter).

  Further, when the calculation control unit 20 obtains the measured power P, it obtains the current time from an RTC (Real Time Clock) built in the calculation control unit 20, and associates the obtained current time with the obtained measured power P. For example, it is stored in a RAM (Random Access Memory) built in the arithmetic control unit 20.

  Note that, due to the influence of the current transformer 14, the arithmetic control unit 20 advances the phase of the acquired current acquired by the A / D converter 17b with respect to the phase of the acquired voltage acquired by the A / D converter 17a. If the time corresponding to the advance is stored in the RAM in advance, the following processing is performed. That is, the arithmetic control unit 20 temporarily holds the acquired voltages sequentially output from the A / D conversion unit 17a for the stored time. Then, the arithmetic control unit 20 obtains a temporary power P1 by obtaining the product of the temporarily acquired acquisition voltage (digital value) and the acquisition current (digital value).

  The communication unit 21 is, for example, a communication interface. The communication unit 21 is, for example, a communication driver such as RS-485 or RS-232C, or a USB (Universal Serial Bus) interface.

  When the communication unit 21 receives a power transmission command from, for example, an external device via the communication line 22, the communication unit 21 acquires the measured power P from the RAM of the arithmetic control unit 20, and transmits the acquired measured power P to the external device. Send. In addition, when the communication unit 21 receives the effective value V1 of the actual AC voltage from, for example, an external device via the communication line 22, the communication unit 21 outputs the received effective value V1 to the arithmetic control unit 20. When the arithmetic control unit 20 receives the effective value V1, the arithmetic control unit 20 stores the received effective value V1 in the RAM.

  In the power measuring apparatus 11 described above, the capacitor Cin1 formed by the first electrode 13a1 and the power line 12a, the input impedance Rin of the voltage unit 15, the capacitor Cin2 formed by the second electrode 13b1 and the power line 12b, and single phase 2 A circuit is formed from the linear power line 12. An equivalent circuit of this circuit is as shown in FIG. The power source that outputs the AC voltage V shown in FIG. 2A equivalently shows the actual AC voltage V applied to the single-phase two-wire power line 12.

  Here, when the relative position of the first electrode 13a1 and the power line 12a changes, the capacitance Cin1 changes. Further, when the relative position between the second electrode 13b1 and the power line 12b changes, the capacitance Cin2 changes.

  However, in the power measuring device 11, the value of the input impedance Rin of the voltage unit 15 is determined in consideration of fluctuations in the capacitance Cin1 and the capacitance Cin2. Therefore, even if the capacitance Cin1 and the capacitance Cin2 fluctuate, the power measuring device 11 changes the phase of the acquired voltage to 90 ° with respect to the phase of the actual AC voltage applied to the single-phase two-wire power line 12. It can be kept in an advanced state.

  Thereby, even if the capacity | capacitance Cin1 and the capacity | capacitance Cin2 fluctuate, the electric power measurement apparatus 11 can suppress the increase in the error contained in the measurement electric power P calculated | required by the calculation control part 20. FIG.

  The reason for this will be described using the equivalent circuit shown in FIG. First, the above-described equivalent circuit shown in FIG. 2A can be transformed into the equivalent circuit shown in FIG. This deformation can be performed from the following relationship.

  That is, as shown in the equivalent circuit of FIG. 2A, the AC voltage applied to the capacitor Cin1 is the voltage Vc1, the AC voltage applied to the input impedance Rin of the voltage unit 15 is the voltage Vr, and the capacitor Assuming that the AC voltage applied to Cin2 is the voltage Vc2, the AC voltage V applied to the single-phase two-wire power line 12 is the sum of the voltage Vc1, the voltage Vr, and the voltage Vc2. Therefore, AC voltage V = voltage Vc1 + voltage Vr + voltage Vc2.

  Here, when the alternating current flowing through the equivalent circuit shown in FIG. 2A is the current ia and the angular frequency of the actual alternating voltage V applied to the single-phase two-wire power line 12 is ω, the alternating voltage V = ia / jωCin1 + Rin × ia + ia / jωCin2 (j represents a complex number).

  When this equation is modified, the AC voltage V = −j × ia (1 / ωCin1 + 1 / ωCin2) + Rin × ia. Therefore, V / ia = −j × (1 / ωCin1 + 1 / ωCin2) + Rin. V / ia represents the input impedance Zina of the equivalent circuit shown in FIG. Therefore, the input impedance Zina of the equivalent circuit shown in FIG. 2A can be expressed as Zina = −j × (1 / ωCin1 + 1 / ωCin2) + Rin. Therefore, the equivalent circuit shown in FIG. 2A can be transformed into the equivalent circuit shown in FIG.

  Here, assuming that the capacitance Cin is a series capacitance when the capacitance Cin1 and the capacitance Cin2 of the equivalent circuit shown in FIG. 2B are connected in series, 1 / Cin = 1 / Cin1 + 1 / Cin2. By transforming this equation, Cin = (Cin1 × Cin2) / (Cin1 + Cin2). Therefore, the equivalent circuit shown in FIG. 2B can be transformed into the equivalent circuit shown in FIG.

  In this way, the equivalent circuit shown in FIG. 2A, in other words, the capacitor Cin1 formed by the first electrode 13a1 and the power line 12a, the input impedance Rin of the voltage unit 15, the second electrode 13b1 and the power line 12b The circuit formed by the capacitor Cin2 formed by (1) and the single-phase two-wire power line 12 is equivalent to the circuit shown in FIG.

  Further, as shown in the equivalent circuit of FIG. 2C, a high-pass filter is configured from the capacitor Cin and the input impedance Rin of the voltage unit 15.

  The cut-off frequency f of this high-pass filter is represented by 1 / (2 × π × Cin × Rin).

  Here, the capacitance Cin of the equivalent circuit shown in FIG. 2C is (capacitance Cin1 × capacitance Cin2) / (capacitance Cin1 + capacitance Cin2). The capacitor Cin1 is a capacitor formed between the first electrode 13a1 and the power line 12a. The capacitor Cin2 is a capacitor formed between the second electrode 13b1 and the power line 12b. Therefore, the capacitor Cin has, for example, the shape of the power lines 12a and 12b in addition to the change in the relative position between the first electrode 13a1 and the power line 12a and the change in the relative position between the second electrode 13b1 and the power line 12b. The value also changes depending on the material of the insulator used in the power lines 12a and 12b, the thickness of the insulator, changes in temperature, and changes in humidity.

  Assuming that the above-mentioned capacitance Cin varies, for example, between 10 pF and 100 pF, and assuming that the input impedance of the voltage unit 15 is determined to be, for example, 500 kΩ, the cutoff frequency f of the high-pass filter is About 159 kHz (Cin = 10 pF), about 32 kHz (Cin = 50 pF), and about 16 kHz (Cin = 100 pF).

  At this time, the phase of the acquired voltage (the AC voltage output from the voltage unit 15) with respect to the phase of the actual AC voltage V applied to the single-phase two-wire power line 12 is as shown in FIG.

  As shown in FIG. 3, for example, when the frequency of the actual AC voltage V applied to the single-phase two-wire power line 12 is 50 Hz, the capacitance Cin (capacitance Cin1 and capacitance Cin2) varies at the frequency of 50 Hz. Even so, the phase of the acquired voltage can be maintained at a state advanced by 90 ° with respect to the phase of the actual AC voltage V applied to the single-phase two-wire power line 12.

  This is because the input impedance Rin of the voltage unit 15 is such that the cutoff frequency f of the high-pass filter is higher than the frequency of the actual AC voltage V applied to the single-phase two-wire power line 12. By determining the value, even if the capacitance Cin1 and the capacitance Cin2 change, the advance of the voltage signal output from the voltage measurement probes 13a and 13b is maintained at 90 ° with respect to the phase of the actual AC voltage. Because you can.

  As a result, the power measuring apparatus 11 of the present embodiment applies the phase of the acquired voltage input to the 90 ° phase shifter 18 to the single-phase two-wire power line 12 even if the capacitance Cin1 and the capacitance Cin2 vary. It is possible to maintain a state advanced by 90 ° with respect to the phase of the actual AC voltage being applied. Therefore, the power measurement apparatus 11 of the present embodiment uses the phase of the acquired voltage after phase correction output from the 90 ° phase shifter 18 to the actual AC voltage applied to the single-phase two-wire power line 12. The phase can be matched. Therefore, according to the power measurement device 11 of the present embodiment, even if the capacitance Cin1 and the capacitance Cin2 vary, it is possible to suppress an increase in error included in the measured power P obtained by the arithmetic control unit 20.

  Furthermore, as described above, the power measurement device 11 according to the present embodiment sets the phase of the acquired voltage input to the 90 ° phase shifter 18 to the actual AC voltage applied to the single-phase two-wire power line 12. It can be maintained in a state advanced by 90 ° with respect to the phase. Therefore, according to the power measurement device 11 of the present embodiment, it is not necessary to calculate the phase difference between the AC voltage measured using capacitive coupling and the actual AC voltage.

  In particular, according to the power measurement device 11 of the present embodiment, even when the capacitance values of the capacitors Cin1 and Cin2 change and become maximum (in this embodiment, the value of the capacitor Cin becomes 100 pF). However, the input impedance Rin of the voltage unit 15 is set so that the cut-off frequency f of the high-pass filter is higher than the frequency of the actual AC voltage V applied to the single-phase two-wire power line 12. The value has been determined.

  Therefore, the power measurement device 11 of the present embodiment uses the single-phase two-wire power line to change the phase of the acquired voltage input to the 90 ° phase shifter 18 even when the fluctuations in the capacitance Cin1 and the capacitance Cin2 become maximum. 12 can be maintained at a state advanced by 90 ° with respect to the phase of the actual AC voltage applied to 12. Therefore, according to the power measurement device 11 of the present embodiment, even when the fluctuations of the capacitance Cin1 and the capacitance Cin2 are maximized, it is possible to suppress an increase in error included in the measured power P obtained by the arithmetic control unit 20. is there.

  Note that, as described above, in the power measurement device 11 of the present embodiment, the cutoff frequency f of the high-pass filter is higher than the frequency of the actual AC voltage V applied to the single-phase two-wire power line 12. high. For this reason, the voltage signal output from the voltage measurement probe 13 a and the voltage signal output from the voltage measurement probe 13 b are attenuated by the high-pass filter and input to the voltage unit 15.

  However, the voltage unit 15 amplifies the voltage signal output from the voltage measurement probe 13a and the voltage signal output from the voltage measurement probe 13b, and obtains a potential difference between the amplified voltage signals, thereby obtaining a single-phase two-wire. The AC voltage applied to the power line 12 of the equation is obtained. Therefore, even if the voltage signal output from the voltage measurement probe 13a and the voltage signal output from the voltage measurement probe 13b are attenuated by the high-pass filter, the power measurement device 11 is applied to the single-phase two-wire power line 12. AC voltage can be obtained.

  Further, according to the power measuring apparatus 11 of the present embodiment, the LPF 19 is provided in the previous stage of the arithmetic control unit 20. Here, as described above, the voltage unit 15 amplifies both the voltage signal output from the voltage measurement probe 13a and the voltage signal output from the voltage measurement probe 13b, and from the amplified signal, a single-phase two-wire system is used. AC voltage (acquired voltage) applied to the power line 12 is obtained. Therefore, the acquired high-frequency component (noise or the like) is superimposed on the acquired voltage obtained by the voltage unit 15. However, the cut-off frequency of the LPF 19 is higher than the frequency of the acquired voltage. For this reason, the LPF 19 can remove the superimposed high-frequency component and sequentially output the acquired voltage from which the high-frequency component has been removed to the arithmetic control unit 20. Therefore, the arithmetic control unit 20 can obtain the measured power P from the acquired voltage in which the influence of the superimposed high frequency component is suppressed. Therefore, according to the power measurement device 11 of the present embodiment, it is possible to suppress an increase in error included in the measured power P obtained by the arithmetic control unit 20.

  Further, according to the power measuring apparatus 11 of the present embodiment, the arithmetic control unit 20 divides the effective value V1 of the actual AC voltage by the effective value V of the acquired voltage to obtain the effective value V1 of the actual AC voltage. The ratio of the effective value V difference of the acquired voltage with respect to is obtained. After that, the arithmetic control unit 20 calculates the measured power P by correcting the temporary power P1 by multiplying the temporary power P1 by the calculated difference ratio. Therefore, the obtained measured power P shows a value close to the actual AC power supplied to the load connected to the single-phase two-wire power line 12. Therefore, according to the power measurement device 11 of the present embodiment, it is possible to suppress an increase in error included in the measured power P obtained by the arithmetic control unit 20.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and applications are possible.

  The arithmetic control unit 20 may realize the functions of the 90 ° phase shifter 18 and the LPF 19 by realizing the 90 ° phase shifter 18 and the LPF 19 included in the power measuring device 11 of the above-described embodiment with software.

  In addition, since the power measuring apparatus 11 of the above-described embodiment has predicted that the capacitance Cin varies between, for example, 10 pF to 100 pF, the input impedance Rin of the voltage unit 15 is determined to be, for example, 500 kΩ. It is not limited to. That is, for example, when the capacitance Cin is expected to vary between 10 pF and 100 pF, the input impedance Rin of the voltage unit 15 may be determined to be, for example, 250 kΩ. In this case, the cutoff frequency f of the high-pass filter is about 318 kHz (Cin = 10 pF), about 64 kHz (Cin = 50 pF), and about 32 kHz (Cin = 100 pF). Therefore, when the frequency of the actual AC voltage V applied to the single-phase two-wire power line 12 is 50 Hz, the cutoff frequency f of the high-pass filter is applied to the single-phase two-wire power line 12. The frequency is higher than the frequency of the actual AC voltage V.

  Further, when the capacitance Cin is expected to vary, for example, between 100 pF and 500 pF, the input impedance Rin of the voltage unit 15 may be determined to be, for example, 500 kΩ. In this case, the cutoff frequency f of the high-pass filter is about 32 kHz (Cin = 100 pF), about 12.8 kHz (Cin = 250 pF), and about 6.4 kHz (Cin = 500 pF). Therefore, when the frequency of the actual AC voltage V applied to the single-phase two-wire power line 12 is 50 Hz, the cutoff frequency f of the high-pass filter is applied to the single-phase two-wire power line 12. The frequency is higher than the frequency of the actual AC voltage V.

  Even if the frequency of the actual AC voltage V applied to the single-phase two-wire power line 12 is, for example, 100 Hz, the cutoff frequency f of the high-pass filter is 100 Hz as described above. The input impedance Rin of the voltage unit 15 may be determined in consideration of the variation of the capacitance Cin so as to indicate a frequency higher than the frequency.

  Various embodiments and modifications can be made to the present invention without departing from the broad spirit and scope of the present invention. Further, the above-described embodiment is for explaining the present invention, and does not limit the scope of the present invention. In other words, the scope of the present invention is indicated by the scope of claims, not the embodiment described above. Various modifications within the scope of the claims and within the scope of the equivalent invention are considered to be within the scope of the present invention.

DESCRIPTION OF SYMBOLS 11 Power measuring apparatus, 12 Single-phase two-wire type power line, 12a, 12b Power line, 13a, 13b Voltage measuring probe, 14 Current transformer, 15 Voltage part, 16 Current part, 17a, 17b A / D conversion part, 18 90 degrees Phaser, 19 LPF, 20 arithmetic control unit, 21 communication unit, 22 communication line

Claims (6)

A first electrode that makes it possible to obtain an AC voltage applied to one of the two-wire power lines by capacitively coupling the one power line;
A second electrode that makes it possible to obtain an AC voltage applied to the other of the two-wire power lines by capacitively coupling the other power line;
AC voltage applied to the one power line via the first electrode and AC voltage applied to the other power line via the second electrode to acquire the AC voltage A voltage unit for obtaining an AC voltage applied to the two-wire power line from the voltage difference;
A current section for acquiring an alternating current flowing in the two-wire power line;
A power unit that measures the AC power supplied to the load connected to the two-wire power line by inputting the AC voltage obtained by the voltage unit and the AC current acquired by the current unit. And
The input impedance of the voltage unit includes a first capacitor formed by the one power line and the first electrode, a second capacitor formed by the other power line and the second electrode, and an input impedance of the voltage unit. And a cutoff frequency of a high-pass filter composed of: a value that is higher than the frequency of the AC voltage,
Power measuring device. The input impedance of the voltage unit is a frequency that is higher than the frequency of the AC voltage when the cutoff frequency of the high-pass filter when the capacitance values of the first capacitor and the second capacitor are maximized is changed. Is the value to
The power measuring device according to claim 1. The voltage unit includes an AC voltage applied to the one power line acquired via the first electrode, and an AC voltage applied to the other power line acquired via the second electrode. Amplifying and obtaining the AC voltage applied to the two-wire power line from the difference between the amplified AC voltages;
The power measuring device according to claim 1 or 2. A low-pass filter having a cut-off frequency higher than the frequency of the input AC voltage, to which the AC voltage obtained by the voltage unit is input, the input AC voltage is filtered and output to the power unit Comprising
The power measuring device according to any one of claims 1 to 3. The power unit is
From the input AC voltage and the AC current acquired by the current unit, a temporary power acquisition unit for obtaining temporary power;
An input effective value acquisition unit that calculates an effective value of the AC voltage applied to the two-wire power line from the input AC voltage;
An actual measured value acquisition unit for acquiring an effective value of the alternating voltage obtained from an actual measured value of the alternating voltage applied to the two-wire power line;
The effective value obtained by the measured effective value acquisition unit is divided by the effective value obtained by the input effective value acquisition unit, and the divided value is multiplied by the temporary power obtained by the temporary power acquisition unit. A power measuring unit for obtaining AC power supplied to a load connected to the two-wire power line;
The power measuring device according to claim 4 provided with. A power measurement method for a power measurement device, comprising:
A first capacitor formed by a first electrode capable of obtaining an AC voltage applied to one of the two-wire power lines by capacitive coupling with the one power line, and the one power line; A second capacitor formed by a second electrode that allows the AC voltage applied to the other of the linear power lines to be obtained by capacitive coupling with the other power line, and the other power line; and an input In the voltage unit having the input impedance with a value that makes the cut-off frequency of the high-pass filter composed of impedance higher than the frequency of the AC voltage, the power measuring device passes through the first electrode. An AC voltage applied to the one power line is acquired, and an AC voltage applied to the other power line via the second electrode is acquired. From the difference between the acquired AC voltages, the 2 A voltage determining the AC voltage applied to the equation of the power line,
A current step in which the power measuring device acquires an alternating current flowing through the two-wire power line in a current section;
The power measuring device inputs an AC voltage obtained by the voltage unit and an AC current acquired by the current unit, and is supplied to a load connected to the two-wire power line A power step for measuring power; and
A power measurement method including:

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