JP2007139434A - Method and device for estimating high-voltage capacitor current - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for estimating high-voltage capacitor current capable of estimating current of a high-voltage capacitor safely and accurately. <P>SOLUTION: The voltage of the high-voltage capacitor of three-phase high-voltage power distribution system is measured at a predetermined sampling period; the measured voltage waveform for one cycle of the voltage of the measured high-voltage capacitor is Fourier-transformed; differentiation is performed for every order of each harmonic included in the measured voltage waveform; then inverse Fourier transformation is performed; and the capacity of the high-voltage capacitor is multiplied to estimate the current of the high-voltage capacitor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high voltage capacitor current estimation method and apparatus for estimating the current of a high voltage capacitor such as a power factor correction capacitor connected to a three-phase high voltage distribution system.

  Generally, many high-voltage capacitors such as a power factor improving capacitor are scattered in a three-phase high-voltage distribution system, and these constitute an LRC closed circuit together with a distribution line impedance. When a rectifier load is present in the vicinity of the LRC closed circuit and periodic transient fluctuation occurs due to commutation of the rectifier or the like, vibration due to the natural frequency of the LRC closed circuit is induced. As a result, overcurrent flows through the high-voltage capacitor, causing electromagnetic noise, overheating, and the like. Therefore, when electromagnetic noise or overheating occurs, it is necessary to measure the current of the high-voltage capacitor in order to grasp the actual situation.

The current of the high-voltage capacitor is directly measured by a high-voltage current transformer. For example, a current transformer is inserted into one of the power factor improving capacitors (SC) installed in the substation equipment of the customer, and the charging current is measured. There is one in which the strength is obtained and a rectifier load that generates a harmonic wave that becomes an obstacle in the distribution system is identified with high accuracy and reliability in a short time (for example, see Patent Document 1).
JP-A-5-64372

  However, in order to measure the current of the high-voltage capacitor directly with a current transformer for high-voltage measurement, a current transformer is inserted into one of the power factor improving capacitors installed in the customer's substation equipment. Therefore, it is necessary to pay sufficient attention to safety because it is a high-pressure hot-wire operation. In addition, it is difficult to install a high-voltage current transformer in a narrow cubicle.

  An object of the present invention is to provide a high voltage capacitor current estimation method and apparatus capable of estimating the current of a high voltage capacitor safely and accurately.

  The high voltage capacitor current estimation method according to the invention of claim 1 measures the voltage of the high voltage capacitor of the three-phase high voltage distribution system, Fourier transforms the measured voltage waveform of one cycle of the measured voltage of the high voltage capacitor, and measures the measured voltage waveform. Is differentiated for each order of each harmonic included in the signal, and then subjected to inverse Fourier transform and multiplied by the capacity of the high-voltage capacitor to estimate the current of the high-voltage capacitor.

  The method for estimating the high-voltage capacitor current according to the invention of claim 2 measures the voltage between two lines connected to the high-voltage capacitor of a three-phase high-voltage distribution system, and suppresses measurement noise from the difference voltage between the two measured line voltages. The voltage of the obtained high voltage capacitor is obtained, and the measured voltage waveform for one cycle of the obtained voltage of the high voltage capacitor is subjected to Fourier transform, and after differentiation for each order of each harmonic included in the measured voltage waveform, inverse Fourier transform is performed, The current of the high voltage capacitor is estimated by multiplying the capacity of the high voltage capacitor.

  According to a third aspect of the present invention, there is provided a method for estimating a high-voltage capacitor current by measuring a voltage of a high-voltage capacitor of a three-phase high-voltage distribution system at a predetermined sampling period, and a sampling value at a certain sampling time and one sampling before or after the sampling time A differential value of the measured voltage is obtained by approximating the difference with the difference from the sampling value, and a current of the high voltage capacitor is estimated by multiplying the obtained differential value by the capacity of the high voltage capacitor.

  The method of estimating the high voltage capacitor current according to the invention of claim 4 measures the voltage between two lines connected to a high voltage capacitor of a three-phase high voltage distribution system, and suppresses measurement noise from the difference voltage between the two measured line voltages. The voltage of the high-voltage capacitor is measured at a predetermined sampling period, and the differential value of the measured voltage is obtained by approximating the difference by the difference between the sampling value at a certain sampling time and the sampling value before or after the sampling at one sampling time. The differential value is multiplied by the capacity of the high voltage capacitor to estimate the current of the high voltage capacitor.

  According to a fifth aspect of the present invention, there is provided a method for estimating a high-voltage capacitor current according to the third or fourth aspect, wherein the harmonic component having the highest content is corrected with respect to the high-voltage capacitor current estimated by the difference approximation. It is characterized in that the error with respect to frequency is corrected by a coefficient.

  A high voltage capacitor current estimation apparatus according to the invention of claim 6 is obtained by an A / D converter for A / D converting the voltage of a high voltage capacitor of a three-phase high voltage distribution system at a predetermined sampling period, and an A / D converter. Obtained by a Fourier transform means for performing Fourier transform on the measured voltage waveform for one cycle of the voltage of the high-voltage capacitor, a differential operation means for performing differentiation for each order of each harmonic included in the measured voltage waveform, and a differential operation means. The inverse Fourier transform means for obtaining a differentiated measurement voltage waveform by inverse Fourier transform of the calculation result, and the current of the high voltage capacitor is obtained by multiplying the differentiated measurement voltage waveform obtained by the inverse Fourier transform means by the capacity of the high voltage capacitor. And a current calculation means.

  A high voltage capacitor current estimating apparatus according to the invention of claim 7 is obtained by an A / D converter for A / D converting the voltage of a high voltage capacitor of a three-phase high voltage distribution system at a predetermined sampling period, and an A / D converter. Voltage differential value calculating means for obtaining a differential value of a measured voltage by approximating a difference by a difference between a sampling value at a certain sampling time of the voltage of the high voltage capacitor and a sampling value before or after one sampling at the sampling time, and a voltage differential value Current calculation means for obtaining the current of the high voltage capacitor by multiplying the differential value of the measured voltage obtained by the calculation means by the capacity of the high voltage capacitor.

  According to the present invention, instead of directly measuring the current of the high voltage capacitor, the current waveform is estimated and calculated from the voltage waveform of the high voltage capacitor measured by a watt hour meter or the like. Safety is ensured by eliminating the need for high-pressure hot-wire work to insert the flow device. Further, since the voltage difference between the two line voltages is used as the voltage used for current estimation, measurement noise can be suppressed and the current of the high-voltage capacitor can be estimated with high accuracy.

(First embodiment)
First, the principle of obtaining the current of the high voltage capacitor according to the present invention will be described. Rather than directly measuring the current of a high-voltage capacitor by installing a current transformer, the current waveform is estimated and calculated from the voltage waveform of the high-voltage capacitor. For example, the V-phase current iv of the three-phase high-voltage capacitor is expressed by the following equation (1) when the V-phase voltage vv and the high-voltage capacitor capacity is C. A V-phase current iv is obtained by measuring with a transformer, differentiating with time t and multiplying by the high-voltage capacitor capacity C. The U-phase current and the W-phase current are obtained in the same manner. However, in the case of three-phase equilibrium, the U-phase current and the W-phase current have the same magnitude as the V-phase current iv, and the phases are shifted by 120 ° and 240 ° Current.

  FIG. 1 is a flowchart showing the steps of a high-voltage capacitor current estimation method according to the first embodiment of the present invention. First, the voltage of the high-voltage capacitor of the three-phase high-voltage distribution system is measured at a predetermined sampling period (S1). For example, the V-phase voltage vv of a three-phase high-voltage capacitor is measured at a predetermined sampling period. Thereby, time-series data of the V-phase voltage vv is obtained for each predetermined sampling period.

Then, the measured voltage waveform for one cycle of the measured voltage of the high voltage capacitor is subjected to Fourier transform (S2). That is, the voltage waveform data of the V-phase voltage vv (t) of the three-phase high-voltage capacitor is converted into a Fourier series of equation (2) by Fourier conversion. Thereby, each harmonic contained in the measurement voltage waveform is obtained for each order. In the equation (2), N is the sampling number / cycle, n is the harmonic order, ω ₀ is the commercial frequency, and v _{r, n} and v _{i, n} are the coefficients of cos and sin.

Next, differentiation is performed at time t for each order of each harmonic included in the measured voltage waveform of the V-phase voltage vv (t) of the three-phase high-voltage capacitor (S3). That is, both sides of equation (2) are differentiated by time t to obtain equation (3).

  Here, Vr, n and Vi, n in the equation (3) are regarded as coefficients of a new Fourier series, and waveform synthesis is performed by inverse Fourier transform (S4).

  A high voltage capacitor current is obtained by multiplying the differential value of the V phase voltage vv (t) of the three-phase high voltage capacitor synthesized by inverse Fourier transform and the high voltage capacitor capacity C (S5).

  According to the first embodiment, since the current waveform is estimated and calculated from the voltage waveform of the high voltage capacitor instead of directly measuring the current of the high voltage capacitor, a current transformer is inserted into the connection line of the high voltage capacitor. High-pressure hot-wire work is not required, ensuring safety. In the first embodiment, since the number of samplings is determined according to the sampling theorem corresponding to the harmonics included in the voltage waveform of the high-voltage capacitor, no error against frequency occurs. In addition, it requires discrete Fourier transform / inverse Fourier transform (DFT / IDFT), which increases the amount of computation, but increases the computation speed of arithmetic processing devices such as personal computers and the application of high-speed Fourier transform / inverse Fourier transform (FFT / IFFT). If this is taken into consideration, the burden is not heavy, and if it is an off-line process, there is no restriction on the computation time.

(Second Embodiment)
FIG. 2 is a flowchart showing the steps of the high voltage capacitor current estimation method according to the second embodiment of the present invention. In the second embodiment, step S0 is added to the first embodiment shown in FIG. 1, and the voltage of the high voltage capacitor in which measurement noise is suppressed in step S1 ′ is set at a predetermined sampling period. It is to be measured. Steps indicating the same processing contents as those in FIG.

  First, two line voltages to which a high-voltage capacitor of a three-phase high-voltage distribution system is connected are measured (S0). As the two line voltages, two line voltages obtained by a watt hour meter are used. FIG. 3 is a measurement circuit diagram of two line voltages vuv and vvw of the three-phase uvw of the three-phase high-voltage distribution line 12 by the instrument transformer 11. The line voltages vuv and vvw are measured using the v phase of the three phases uvw as a reference (grounded).

Then, the voltage of the high voltage capacitor that suppresses the measurement noise is obtained from the difference voltage (vvw−vuv) between the two measured line voltages vuv and vvw, and is measured by sampling at a predetermined sampling period (S1 ′). Here, since the measurement noise often has the same amount of property at the same time between the two line voltages vuv and vvw, the measurement noise is suppressed for the difference voltage (vvw−vuv) between the two line voltages vuv and vvw. Voltage. Therefore, the voltage used for current estimation uses the V-phase voltage vv shown in the equation (4) in which measurement noise is suppressed. However, the zero phase voltage is assumed to be zero.

  In step S0, two line voltages to which the high-voltage capacitors of the three-phase high-voltage distribution system are connected are measured at a predetermined sampling period, and the voltage of the high-voltage capacitor in which measurement noise is suppressed is obtained in step S1 ′. Also good.

  Next, as in the first embodiment, the measured voltage waveform for one cycle of the measured voltage of the high-voltage capacitor is Fourier-transformed (S2), and the V-phase voltage vv (t) of the three-phase high-voltage capacitor is measured. Differentiation is performed at time t for each harmonic order included in the voltage waveform (S3), waveform synthesis is performed by inverse Fourier transform (S4), and high voltage capacitor capacity C is multiplied to obtain a high voltage capacitor current (S5).

  FIG. 4 is a characteristic diagram showing a comparison between the high-voltage capacitor current measured using a current transformer and the high-voltage capacitor current estimated by the Fourier transform of the second embodiment, and FIG. FIG. 4 (a2) is a frequency spectrum diagram of the actually measured high voltage capacitor current, FIG. 4 (b1) is a waveform diagram of the Fourier transform estimated high voltage capacitor current according to the second embodiment, and FIG. 4 (b2). These are frequency spectrum diagrams of Fourier transform estimated high-voltage capacitor current according to the second embodiment.

  When comparing FIG. 4 (a2) and FIG. 4 (b2), the harmonic component with the highest content rate matches at 5 [kHz], and the content rate is the Fourier transform estimated high-voltage capacitor according to the second embodiment. Although the current is slightly smaller than the actually measured high-voltage capacitor current, they are almost the same.

  According to the second embodiment, in addition to the effects of the first embodiment, the measurement noise is suppressed because the difference voltage (vvw−vuv) between the two line voltages vuv and vvw is used as the voltage used for current estimation. It is possible to accurately estimate the current of the high-voltage capacitor.

(Third embodiment)
FIG. 5 is a flowchart showing the steps of the high-voltage capacitor current estimation method according to the third embodiment of the present invention. In this third embodiment, instead of the discrete Fourier transform / inverse Fourier transform of the first embodiment or the second embodiment, a difference approximation with a difference between two time-series sampling values is performed. The differential value of the voltage is obtained. This difference approximation method has a simple algorithm and is capable of high-speed calculation. However, since the error increases in proportion to the frequency, when the error cannot be ignored, the error is corrected.

  In FIG. 5, first, the voltage of the high-voltage capacitor of the three-phase high-voltage distribution system is measured at a predetermined sampling period (S11). For example, the V-phase voltage vv of a three-phase high-voltage capacitor is measured at a predetermined sampling period. Thereby, time-series data of the V-phase voltage vv is obtained for each predetermined sampling period.

Then, as shown in the equation (5), the difference approximation is performed by the difference between the sampling value vv, k at a certain sampling time k and the sampling value vv, k-1 one sampling before the sampling time k (k-1). Then, the differential value of the measured voltage is obtained (S12), and the obtained differential value is multiplied by the capacity C of the high voltage capacitor to estimate the current iv, k of the high voltage capacitor at the time of sampling k (S13).

  Since G on the right side of the equation (5) is constant, the calculation at each time step (sampling point) k is only a difference, so the amount of calculation is very small compared to the Fourier transform. Therefore, the current effective value of the high-voltage capacitor can be calculated as densely as 1 sampling / cycle during online measurement, and high-speed calculation is possible.

  In the above description, the case where the difference approximation is performed by the difference between the sampling value vv, k at a certain sampling time point k and the sampling value vv, k-1 one sampling before the sampling time point k (k−1) has been described. The difference approximation may be performed by the difference between the sampling value vv, k at a certain sampling time k and the sampling value vv, k + 1 after one sampling (k + 1) at that sampling time k.

Next, the error with respect to frequency due to the difference approximation is examined. Assuming that the V-phase voltage vv is a sine wave having a peak value 1, Equation (5) is expressed by Equation (6).

On the other hand, a theoretical value that does not depend on the difference approximation is expressed by equation (7).

Accordingly, the absolute value error ε (f) between the difference approximation and the theoretical value is expressed by equation (8).

Table 1 shows the frequency characteristic of the absolute value error ε (f) when Δt = 39.0625 [μs] in the equation (8).

  From Table 1, it can be seen from the nature of the low-pass filter that the difference approximation has, correction is necessary because the error increases at high frequencies. However, since Fourier transform, which takes a long calculation time during measurement, is difficult, the current effective value of the high-voltage capacitor is corrected off-line at least with the correction coefficient of the harmonic component having the highest content rate after the measurement is completed. In addition, even if it does not correct | amend the frequency of all the harmonic components, the correction | amendment by the correction coefficient of only the harmonic component with the highest content rate is practically enough.

  Further, as a method of difference approximation, a method of approximating a section by a linear expression using two points of data has been described. However, the present invention is not limited to this, and a method of approximating a section by a quadratic expression using three points of data or four points It is also possible to apply a section approximation method using multipoint data, such as a section approximation method using data and a cubic equation.

  According to the third embodiment, as in the first embodiment, since the current of the high-voltage capacitor is not directly measured but is obtained by estimating and calculating the current waveform from the voltage waveform of the high-voltage capacitor. This eliminates the need for high-voltage hot-wire work that inserts a current transformer into the connection line, ensuring safety. In addition, since the differential value is obtained by differential approximation rather than Fourier transform, the algorithm is simple and high-speed calculation is possible. Although the error increases in proportion to the frequency, there is no practical problem because the effective current value of the high-voltage capacitor is corrected by the correction coefficient.

(Fourth embodiment)
FIG. 6 is a flowchart showing the steps of the high-voltage capacitor current estimation method according to the fourth embodiment of the present invention. In the fourth embodiment, step S10 is added to the third embodiment shown in FIG. 5, and the voltage of the high voltage capacitor in which the measurement noise is suppressed in step S11 ′ is set at a predetermined sampling period. It is to be measured. Steps indicating the same processing contents as those in FIG. 5 are denoted by the same reference numerals (S12, S13), and redundant description is omitted.

  First, two line voltages to which a high-voltage capacitor of a three-phase high-voltage distribution system is connected are measured (S0). As the two line voltages, two line voltages vuv and vvw obtained by a watt hour meter are used. The voltage of the high voltage capacitor in which measurement noise is suppressed is obtained from the difference voltage (vvw−vuv) between the two measured line voltages vuv and vvw, and is measured by sampling at a predetermined sampling period (S11 ′). That is, as the voltage used for current estimation, the V-phase voltage vv shown in Equation (4) with suppressed measurement noise is used.

  In step S0, two line voltages to which the high-voltage capacitors of the three-phase high-voltage distribution system are connected are measured at a predetermined sampling period, and the voltage of the high-voltage capacitor in which measurement noise is suppressed is obtained in step S1 ′. Also good.

  Next, as in the third embodiment, a difference is obtained by the difference between the sampling value vv, k at a certain sampling time k and the sampling value vv, k-1 one sampling before the sampling time k (k−1). A differential value of the measured voltage is obtained by approximation (S12), and the obtained differential value is multiplied by the capacitance C of the high-voltage capacitor to estimate the current iv, k of the high-voltage capacitor at the time point of sampling k (S13). In this case, the difference approximation may be performed by the difference between the sampling value vv, k at a certain sampling time k and the sampling value vv, k + 1 after one sampling (k + 1) at that sampling time k.

  Further, the method is not limited to the method of approximating a section with a linear expression using two points of data, the method of approximating a section with a quadratic expression using three points of data, the method of approximating a section with a cubic expression using four points of data, etc. It is also possible to apply an interval approximation method using multipoint data.

  FIG. 7 is a characteristic diagram showing a comparison between the high-voltage capacitor current measured using the current transformer and the high-voltage capacitor current estimated by the difference approximation of the fourth embodiment, and FIG. FIG. 7 (a2) is a frequency spectrum diagram of the actually measured high-voltage capacitor current, FIG. 7 (b1) is a waveform diagram of the differential approximation estimated high-voltage capacitor current according to the fourth embodiment, and FIG. 7 (b2). These are the frequency spectrum figures of the difference approximate estimation high voltage capacitor current by a 4th embodiment.

  When comparing FIG. 7 (a2) and FIG. 7 (b2), the harmonic component with the highest content rate matches at 5 [kHz], and the content rate is the difference approximation estimated high-voltage capacitor according to the fourth embodiment. The current is smaller than the measured high voltage capacitor current. Therefore, as in the case of the third embodiment, at least the effective current value of the high-voltage capacitor is corrected with the correction coefficient of the harmonic component having the highest content rate.

  According to the fourth embodiment, in addition to the effects of the third embodiment, the measurement noise is suppressed because the difference voltage (vvw−vuv) between the two line voltages vuv and vvw is used as the voltage used for current estimation. It is possible to accurately estimate the current of the high-voltage capacitor.

(Fifth embodiment)
FIG. 8 is a block diagram showing an example of a high-voltage capacitor current estimating apparatus according to the fifth embodiment of the present invention. The fifth embodiment shows an example of a high-voltage capacitor current estimation device for realizing the high-voltage capacitor current estimation method of the first embodiment or the second embodiment.

  In FIG. 8, the voltage of the high-voltage capacitor of the three-phase high-voltage distribution system, for example, the V-phase voltage vv of the three-phase high-voltage capacitor is detected by the instrument transformer 11 and input to the A / D converter 13. The A / D converter 13 converts the high voltage capacitor voltage of the analog signal detected by the voltage detector 11 at a predetermined sampling period into a digital signal and stores it in the storage device 14. Thereby, time-series data of the V-phase voltage vv is obtained for each predetermined sampling period.

  The Fourier transform means 16 of the arithmetic processing unit 15 Fourier transforms the measured voltage waveform for one cycle in the time-series data of the V-phase voltage vv stored in the storage device 14. The voltage waveform data of the V-phase voltage vv (t) of the three-phase high-voltage capacitor is converted by the Fourier transform means 16 into the Fourier series of the above-described equation (2). Thereby, each harmonic contained in the measurement voltage waveform is obtained for each order.

  The differential calculation means 17 performs differentiation at time t for each order of each harmonic included in the measured voltage waveform of the V-phase voltage vv (t) of the three-phase high-voltage capacitor obtained by the Fourier transform means 16. The calculation result obtained by the differential calculation means 17 is input to the inverse Fourier transform means 18, and the inverse Fourier transform means 18 performs inverse Fourier transform on the calculation result obtained by the differentiation calculation means 17 to obtain a differentiated measurement voltage waveform. Ask.

  The differential value of the V-phase voltage vv (t) of the three-phase high-voltage capacitor synthesized by inverse Fourier transform is input to the current calculation means 19, and the high-voltage capacitor capacitance C is added to the differential value of the V-phase voltage vv (t) of the high-voltage capacitor. Is multiplied to obtain the high voltage capacitor current. The high-voltage capacitor current calculated by the current calculation means 19 is output to the output device 20 as an estimated current value.

  Here, in the fifth embodiment, as in the first embodiment, the number of samples is determined according to the sampling theorem corresponding to the harmonics included in the voltage waveform of the high-voltage capacitor. Does not occur. In addition, it requires discrete Fourier transform / inverse Fourier transform (DFT / IDFT), which increases the amount of computation, but increases the computation speed of arithmetic processing devices such as personal computers and the application of high-speed Fourier transform / inverse Fourier transform (FFT / IFFT). If this is taken into consideration, the burden is not heavy, and if it is an off-line process, there is no restriction on the computation time.

  Further, as in the second embodiment, the voltage of the high-voltage capacitor that suppresses the measurement noise may be obtained from the instrument transformer 11. That is, as shown in FIG. 3, the line voltages vuv and vvw are measured using the v phase of the three phase uvw of the three-phase high-voltage distribution 12 as a reference (grounded). Then, the voltage of the high voltage capacitor that suppresses the measurement noise is obtained from the difference voltage (vvw−vuv) between the two measured line voltages vuv and vvw, and is sampled by the A / D converter 13 at a predetermined sampling period.

  According to the fifth embodiment, the same effect as in the first embodiment and the second embodiment can be obtained. That is, instead of directly measuring the current of the high-voltage capacitor, the current waveform is estimated and calculated from the voltage waveform of the high-voltage capacitor, which eliminates the need for high-voltage hot-wire work that inserts a current transformer into the connection line of the high-voltage capacitor. Sex is secured. Further, when the voltage difference (vvw−vuv) between the two line voltages vuv and vvw is used as the voltage used for current estimation, the measurement noise can be suppressed, so that the current of the high voltage capacitor can be estimated with high accuracy.

(Sixth embodiment)
FIG. 9 is a block diagram showing an example of a high-voltage capacitor current estimation apparatus according to the sixth embodiment of the present invention, and FIG. 10 shows another example of the high-voltage capacitor current estimation apparatus according to the sixth embodiment of the present invention. FIG. The sixth embodiment shows an example of a high-voltage capacitor current estimation device for realizing the high-voltage capacitor current estimation method of the third embodiment or the fourth embodiment.

  In FIG. 9, the voltage of the high-voltage capacitor of the three-phase high-voltage distribution system, for example, the V-phase voltage vv of the three-phase high-voltage capacitor is detected by the instrument transformer 11 and input to the A / D converter 13. The A / D converter 13 converts the high voltage capacitor voltage of the analog signal detected by the voltage detector 11 at a predetermined sampling period into a digital signal and stores it in the storage device 14. Thereby, time-series data of the V-phase voltage vv is obtained for each predetermined sampling period.

  The voltage differential value calculation means 21 of the arithmetic processing unit 15 includes the sampling value vv, k at a certain sampling time point k of the time series data stored in the storage device 14 and (k-1) one sampling before the sampling time point k. The differential value of the measured voltage is obtained by approximating the difference with the sampling value vv, k-1 (or the sampling value vv, k + 1 after one sampling (k + 1) of the sampling time point k).

  The differential value of the measured voltage obtained by the voltage differential value calculating means 21 is input to the current calculating means 19, and the high voltage capacitor current iv, k is obtained by multiplying the differential value of the measured voltage by the capacitance C of the high voltage capacitor. Then, the high-voltage capacitor current calculated by the current calculation means 19 is output to the output device 20 as a current estimated value.

  Here, as described above, in the case of difference approximation, an error with respect to frequency occurs. Therefore, as shown in FIG. 10, the anti-frequency error correction means 22 is provided to make the current effective value of the high-voltage capacitor at least the highest in content. Correction is performed with the correction coefficient of the harmonic component. In this case, it is practically sufficient to correct only the harmonic component having the highest content rate without correcting the frequencies of all the harmonic components.

  Further, as in the fourth embodiment, the voltage of the high-voltage capacitor that suppresses the measurement noise may be obtained from the instrument transformer 11. In this case, as shown in FIG. 3, the line voltages vuv and vvw are measured using the v phase of the three phase uvw of the three-phase high-voltage distribution 12 as a reference (grounded). Then, the voltage of the high voltage capacitor that suppresses the measurement noise is obtained from the difference voltage (vvw−vuv) between the two measured line voltages vuv and vvw, and is sampled by the A / D converter 13 at a predetermined sampling period.

  According to the sixth embodiment, the same effects as in the fourth and fifth embodiments can be obtained. That is, instead of directly measuring the current of the high-voltage capacitor, the current waveform is estimated and calculated from the voltage waveform of the high-voltage capacitor, which eliminates the need for high-voltage hot-wire work that inserts a current transformer into the connection line of the high-voltage capacitor. Sex is secured. In addition, since the differential value is obtained by differential approximation rather than Fourier transform, the algorithm is simple and high-speed calculation is possible. Although the error increases in proportion to the frequency, there is no practical problem because the effective current value of the high-voltage capacitor is corrected by the correction coefficient. Further, when a voltage difference (vvw−vuv) between two line voltages vuv and vvw is used as a voltage used for current estimation, measurement noise can be suppressed, so that the current of the high voltage capacitor can be estimated with high accuracy.

The flowchart which shows the process of the high voltage | pressure capacitor | condenser current estimation method concerning the 1st Embodiment of this invention. The flowchart which shows the process of the high voltage | pressure capacitor | condenser current estimation method concerning the 2nd Embodiment of this invention. FIG. 3 is a measurement circuit diagram of two line voltages vuv and vvw of a three-phase uvw. The characteristic view which contrasted and showed the high voltage capacitor current measured using the current transformer, and the high voltage capacitor current estimated by the Fourier transform of 2nd Embodiment. The flowchart which shows the process of the high voltage | pressure capacitor | condenser current estimation method concerning the 3rd Embodiment of this invention. The flowchart which shows the process of the high voltage | pressure capacitor | condenser current estimation method concerning the 4th Embodiment of this invention. The characteristic view which contrasted and showed the high voltage capacitor current measured using the current transformer and the high voltage capacitor current estimated by the difference approximation of 6th Embodiment. The block block diagram which shows an example of the high voltage | pressure capacitor current estimation apparatus concerning the 5th Embodiment of this invention. The block block diagram which shows an example of the high voltage | pressure capacitor current estimation apparatus concerning the 6th Embodiment of this invention. The block block diagram of the other example of the high voltage | pressure capacitor current estimation apparatus concerning the 6th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Instrument transformer, 12 ... Three-phase high voltage distribution line, 13 ... A / D converter, 14 ... Memory | storage device, 15 ... Arithmetic processing device, 16 ... Fourier transform means, 17 ... Differential operation means, 18 ... Reverse Fourier Conversion means, 19 ... current calculation means, 20 ... output device, 21 ... voltage differential value calculation means, 22 ... anti-frequency error correction means

Claims (7)

The voltage of the high-voltage capacitor of the three-phase high-voltage distribution system was measured, the measured voltage waveform for one cycle of the measured voltage of the high-voltage capacitor was Fourier transformed, and differentiation was performed for each order of each harmonic contained in the measured voltage waveform. A method for estimating a high voltage capacitor current, comprising performing inverse Fourier transform later and multiplying the capacity of the high voltage capacitor to estimate a current of the high voltage capacitor. Measure the voltage between the two lines connected to the high-voltage capacitor of the three-phase high-voltage distribution system, find the voltage of the high-voltage capacitor that suppresses the measurement noise from the difference voltage of the two measured line voltages, and calculate the voltage of the high-voltage capacitor The measured voltage waveform for one cycle is Fourier transformed, differentiated for each harmonic order contained in the measured voltage waveform, then inverse Fourier transformed, and multiplied by the capacity of the high voltage capacitor to estimate the current of the high voltage capacitor A method for estimating a high-voltage capacitor current. The voltage of the high-voltage capacitor of the three-phase high-voltage distribution system is measured at a predetermined sampling cycle, and the measured voltage is differentiated by approximating the difference by the difference between the sampling value at a certain sampling time and the sampling value one sampling before or after that sampling time. A method for estimating a high voltage capacitor current, comprising: obtaining a value and multiplying the obtained differential value by a capacity of the high voltage capacitor to estimate a current of the high voltage capacitor. Measure the voltage between two lines to which the high-voltage capacitor of the three-phase high-voltage distribution system is connected, measure the voltage of the high-voltage capacitor that suppresses measurement noise from the measured voltage difference between the two line voltages, at a predetermined sampling period, A differential value of the measured voltage is obtained by approximating the difference between the sampling value at a certain sampling time and the sampling value one sampling before or after that sampling time, and the obtained differential value is multiplied by the capacity of the high voltage capacitor. A method for estimating the current of a high-voltage capacitor, characterized in that the current is estimated. 5. The high-voltage capacitor current estimation according to claim 3, wherein the error with respect to the frequency is corrected with a correction coefficient of a harmonic component having the highest content ratio with respect to the current of the high-voltage capacitor estimated by the difference approximation. Method. An A / D converter that A / D converts the voltage of the high-voltage capacitor of the three-phase high-voltage distribution system at a predetermined sampling period, and a measured voltage waveform for one cycle of the voltage of the high-voltage capacitor obtained by the A / D converter Fourier transform means for performing Fourier transform, differential operation means for differentiating each order of each harmonic included in the measured voltage waveform, and inverse measurement result obtained by performing inverse Fourier transform on the operation result obtained by the differential operation means, A high voltage capacitor comprising: an inverse Fourier transform means to be obtained; and a current calculation means for obtaining a current of the high voltage capacitor by multiplying the differentiated measurement voltage waveform obtained by the inverse Fourier transform means by the capacity of the high voltage capacitor. Current estimation device. An A / D converter that A / D converts the voltage of the high-voltage capacitor of the three-phase high-voltage distribution system at a predetermined sampling period, a sampling value at a sampling time when the voltage of the high-voltage capacitor obtained by the A / D converter is A voltage differential value calculating means for obtaining a differential value of the measured voltage by approximating the difference with the sampling value one sampling before or after the sampling time, and a differential value of the high voltage capacitor obtained by the voltage differential value calculating means. A high voltage capacitor current estimation device comprising: current calculation means for multiplying a capacity to obtain a current of a high voltage capacitor.

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