KR101035702B1 - Apparatus and method for measuring the power quality - Google Patents

Abstract

PURPOSE: An apparatus and a method for measuring the quality of power is provided to reduce the number of operations required for decomposing harmonic wave components by implementing fast Fourier transform with respect to a standard waveform signal. CONSTITUTION: A detecting unit(110) receives voltage waveform signals and current waveform signals from an electric power system by a pre-set time interval. Samples are obtained from the voltage waveform signals and the current waveform signals. A signal converting unit(120) converts the samples into digital signals. An operating unit(130) overlaps the voltage waveform signals by one interval or a half interval. A voltage standard waveform signal and a current standard waveform signal are generated. Fast Fourier transform is implemented with respect to the voltage standard waveform signal and the current standard waveform signal.

Description

[0001] Apparatus and method for measuring power quality [0002]

The present invention relates to an apparatus and method for measuring power quality.

As the industrial equipment becomes larger, there is a case where a large amount of harmonics or flickers are generated. Therefore, in the case of a consumer using an electric device having a sensitive characteristic due to a momentary drop in voltage, There are frequent phenomena related to electric quality such as stopping of operation.

Currently, in Korea, electrical quality standards are established and amended based on the standards of the International Electrotechnical Commission (IEC). According to the IEC standard, measurements for electrical quality assessment should be made at the customer acceptance point (PCC). In this case, the electric power company must build a Power Quality Monitoring System (PQMS) at all the customer's entrance points in order to manage the electricity quality, and it is necessary to have very expensive equipments considering the operation speed and precision to acquire data suited to the related standard . Therefore, it is difficult to constantly monitor using PQMS in electric power companies because of high cost of installation and many places to be managed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and method for measuring power quality that can reduce the burden on a device and reduce manufacturing costs by reducing voltage and current waveform information for harmonic measurement and analysis.

According to an aspect of the present invention, there is provided a power quality measuring apparatus.

The power quality measuring apparatus includes a detector for obtaining a voltage waveform signal and a current waveform signal at predetermined time intervals in a power system and sampling the sampled voltage waveform signal and the current waveform signal at a predetermined sampling period, A voltage representative waveform signal and a current representative waveform signal are generated by superimposing each of the voltage waveform signal and the current waveform signal converted into the digital signal in one cycle or half period and an average value of each of the superimposed voltage waveform signal and current waveform signal, The voltage representative waveform signal and the current representative waveform signal are subjected to high-speed Fourier transform to decompose harmonics of the fundamental wave and the order, and the overall harmonic distortion factor of each voltage and current is calculated by using the fundamental wave signal and the harmonic signals of each order And compares it with a predetermined harmonic distortion factor reference value And a communication unit for transmitting the calculation unit and the total harmonic distortion factor of voltage and current to the outside.

According to another aspect of the present invention, there is provided a method for measuring power quality.

The power quality measuring method includes the steps of acquiring a voltage waveform signal and a current waveform signal at predetermined time intervals in a power system, sampling each of the acquired voltage waveform signal and current waveform signal at a predetermined cycle, Generating a voltage representative waveform signal and a current representative waveform signal by superimposing each of the current waveform signals on one cycle or a half cycle and an average value of each of the superposed voltage waveform signal and current waveform signal; Calculating the ratio of the effective value of the fundamental wave and the effective value of the total harmonic from each of the voltage representative waveform signal and the current representative waveform signal to calculate the total harmonic distortion factor, .

The apparatus for measuring power quality according to an embodiment of the present invention can reduce the number of operations for decomposing harmonic components by performing fast Fourier transform on a representative waveform signal. Further, the power quality measuring apparatus can reduce and store the amount of harmonic data for each order. In addition, the power quality measurement device can reduce the amount of transmitted data and reduce the network load by transmitting only the total harmonic distortion factor to the server for monitoring the power system.

1 is a diagram illustrating a power quality monitoring system in accordance with an embodiment of the present invention.
FIG. 2 illustrates a power quality measurement apparatus according to an embodiment of the present invention. Referring to FIG.
3 to 5 are views for explaining the operation of the power quality measuring apparatus of FIG.
6 is a flowchart illustrating a power quality measurement method according to an embodiment of the present invention.

While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and similarities. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In addition, numerals (e.g., first, second, etc.) used in the description of the present invention are merely an identifier for distinguishing one component from another.

Also, in this specification, when an element is referred to as being "connected" or "connected" with another element, the element may be directly connected or directly connected to the other element, It should be understood that, unless an opposite description is present, it may be connected or connected via another element in the middle.

Hereinafter, a power quality monitoring system according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a power quality monitoring system in accordance with an embodiment of the present invention.

Referring to FIG. 1, the power quality monitoring system includes a power quality measuring apparatus 100 and a server 200.

The power quality measuring device 100 is connected to the VCT (power transformer, current transformer) of the power system 10. Specifically, the power quality measuring apparatus 100 acquires the voltage waveform signal and the current waveform signal from the three voltage transformers (PT) and three current transformers (CT) provided in the VCT (transformer, current transformer). The power quality measuring apparatus 100 samples each of the acquired voltage waveform signal and current waveform signal at a predetermined sampling period. The power quality measuring apparatus 100 converts an analog signal of each of the sampled voltage waveform signal and the current waveform signal into a digital signal. The power quality measuring apparatus 100 generates a voltage representative waveform signal and a current representative waveform signal by superimposing each of the converted voltage waveform signal and the current waveform signal on a cycle-by-cycle basis.

Here, each of the voltage representative waveform signal and the current representative waveform signal is generated as an average value of the waveform signals superimposed in one cycle. The power quality measuring apparatus 100 performs fast Fourier transform on the voltage representative waveform signal and the current representative waveform signal to decompose fundamental waves and harmonics of respective orders. Here, the fast Fourier transform is a method of performing high-speed conversion in the frequency domain due to the Fourier theorem, in which one signal can be represented by the sum of a number of signals (sinusoidal waves). For example, the power quality measuring apparatus 100 performs fast Fourier transform on a voltage representative waveform signal to decompose a voltage fundamental wave and voltage harmonics of each order. Further, the power quality measuring apparatus 100 performs fast Fourier transform on the current representative waveform signal to decompose the current fundamental wave and the current harmonic of each order.

The power quality measuring apparatus 100 calculates the ratio of the effective value of the fundamental wave decomposed from the voltage representative waveform signal and the current representative waveform signal to the effective value of the total harmonics to calculate a total harmonic distortion (THD).

The power quality measuring apparatus 100 transmits the calculated total harmonic distortion factor to the server 200.

The server 200 receives the result of the overall harmonic distortion factor from the power quality measuring apparatus 100. [ The server 200 may store the resultant of the total harmonic distortion factor. To this end, the server 200 may further include a database for storing the results of the total harmonic distortion.

FIG. 2 illustrates a power quality measurement apparatus according to an embodiment of the present invention. Referring to FIG. FIGS. 3 to 5 are views illustrating an exemplary operation of the power quality measuring apparatus of FIG. 2. FIG.

2, a power quality measuring apparatus 100 according to an embodiment of the present invention includes a detecting unit 110, a signal converting unit 120, a calculating unit 130, a display unit 140, a warning unit 150, A storage unit 160 and a communication unit 170.

(n은 7 이상의 자연수) 주기로 취득된 전압 파형 신호 및 전류 파형 신호를 샘플링할 수 있다. 이때, 검출부(110)에서 전압 파형 신호 및 전류 파형 신호를 샘플링하는 주기를 샘플링 주기라고 한다.The detection unit 110 acquires continuous voltage waveform signals and current waveform signals at a predetermined time interval in the power system 10 and samples them at a predetermined sampling period. For example, the detection unit 110 may detect

(n is a natural number equal to or larger than 7) cycle of the voltage waveform signal and the current waveform signal. At this time, a period for sampling the voltage waveform signal and the current waveform signal in the detection unit 110 is referred to as a sampling period.

In general, for harmonic component decomposition in the frequency domain, a sampling period of at least 128 cycles or 256 cycles is required. Accordingly, the present specification assumes that the sampling period is 128 cycles or more. However, the sampling period is not limited to 128 cycles or more but may be less than 128 cycles. The detection unit 110 transmits the sampled voltage waveform signal and the current waveform signal to the signal conversion unit 120 according to a designated sampling period.

The signal converting unit 120 converts the analog signals of the sampled voltage waveform signal and the current waveform signal into digital signals. To this end, the signal converting unit 120 may include a low-pass filter for passing a signal having a low frequency, an amplifier for amplifying the signal, and an analog / digital converter for converting the analog signal into a digital signal.

The arithmetic unit 130 superimposes the voltage waveform signal and the current waveform signal converted into the digital signal to generate a voltage representative waveform signal and a current representative waveform signal. The operation unit 130 superimposes the sampled voltage waveform signal and the current waveform signal in the same manner as the first sampling waveform 310, the second sampling waveform 320 and the third sampling waveform 330 shown in FIG. To sum the values of the same sampling period. The sampling waveforms shown in Figure 3 are illustratively shown to facilitate the superposition of the sampled signals converted into digital signals. Accordingly, the overlapping of the signals performed by the operation unit 130 is not limited to those shown in FIG.

The arithmetic unit 130 divides the waveform into the number of times by the predetermined period to obtain an average value, and generates a voltage representative waveform signal and a current representative waveform signal of one cycle as shown in the representative waveform 400 shown in FIG. The representative waveform 400 shown in FIG. 4 is illustratively illustrated to easily describe the voltage representative waveform signal and the current representative waveform signal generated by the calculation unit 130. Accordingly, the voltage representative waveform signal and the current representative waveform signal generated by the calculation unit 130 are not limited to those shown in Fig.

The calculating unit 130 performs fast Fourier transform on the voltage representative waveform signal and the current representative waveform signal to calculate the fundamental wave 500 and the harmonic waves 510, 520, 530, and 540 shown in FIG. 5 from the voltage representative waveform signal and the current representative waveform signal, respectively Disassemble. For example, the operation unit 130 performs fast Fourier transform on the voltage representative waveform signal to decompose the voltage fundamental wave and voltage harmonics of each order. The calculating unit 130 performs fast Fourier transform on the current representative waveform signal to decompose the current fundamental wave and the current harmonic of each order. The fundamental wave 500 and the harmonic waves 510, 520, 530 and 540 shown in FIG. 5 are illustratively illustrated to facilitate the fast Fourier transform of the operation unit 130. Accordingly, the fast Fourier transform performed by the arithmetic operation unit 130 is not limited to FIG.

The calculating unit 130 calculates the ratio of the effective value of the voltage fundamental wave decomposed from the voltage representative waveform signal to the effective value of the total voltage harmonic to calculate the total harmonic distortion factor of the voltage. The calculating unit 130 calculates the ratio of the effective value of the current fundamental wave decomposed from the current representative waveform signal to the effective value of the total current harmonic to calculate the total harmonic distortion factor of the current. The overall harmonic distortion factor evaluates the voltage and current harmonics in the power system 10 to the degree of distortion of the waveform. Where the total harmonic distortion factor is the ratio of the sum of the rms values of all the harmonic components up to the measurement order for the rms value of the fundamental component. That is, the total harmonic distortion factor can be expressed by the following equation (1).

Where Q is the current or voltage, Q1 is the effective value of the fundamental component, h is the harmonic order, and Qh is the rms value of the h-th harmonic.

The calculating unit 130 compares the total harmonic distortion factor of the voltage and the current with the harmonic distortion factor reference value set for the power quality management of the power system 10. [ Here, the harmonic distortion factor reference value can be set to about 5%. The operation unit 130 detects an abnormal occurrence of the power system 10 when the result of the comparison indicates that the harmonic distortion factor exceeds the harmonic distortion factor reference value. At this time, when the total harmonic distortion factor exceeds the harmonic distortion factor reference value, the operation unit 130 transmits a warning signal to the warning unit 150 so that the harmonic components of the voltage and the current can be checked according to the order.

The warning unit 150 receives an alarm signal from the operation unit 130 to alert the power system 10 of an abnormality. The warning unit 150 may warn the harmonic components of the voltage and the current by the order of the order.

The display unit 140 receives and displays the total harmonic distortion factor of each of the voltage and the current from the calculation unit 130. For example, the display unit 140 displays the total harmonic distortion factor as an image. For this, the display unit 140 may include a display device for displaying the total harmonic distortion factor of each of the voltage and the current, and a driver for driving the display device.

The storage unit 160 stores the total harmonic distortion factor of the voltage and the current for backup. In addition, the storage unit 160 stores the harmonic distortion factor reference value set for the power quality management of the power system 10. The storage unit 160 may provide the harmonic distortion factor reference value to the operation unit 130 at the request of the operation unit 130.

The communication unit 170 transmits the overall harmonic distortion factor of the voltage and the current and the warning signal. The communication unit 170 may include an Ethernet driver, an RS422 driver, and a connection port for communication with the outside. Here, the communication unit 170 transmits only the resultant value of the total harmonic distortion factor or the warning signal to the outside, thereby significantly reducing the amount of transmitted data than when transmitting the voltage representative waveform signal and the current representative waveform signal.

The power quality measuring apparatus 100 according to an exemplary embodiment of the present invention adds a continuous waveform and calculates a value obtained by fast Fourier transforming an average waveform divided by a period of a sum. The calculated value is not different from the value obtained by the harmonic measurement standard of IEC61000-4-30 of the International Electrotechnical Commission (IEC) - the value obtained by fast Fourier transforming each waveform of the voltage and current according to the cycle . An examination of the error between the calculated value and the merged value will be described with reference to Tables 1 to 3 below.

Table 1 shows experimental values obtained by measuring the magnitude of the fundamental wave by performing fast Fourier transform on the waveform signal of the first cycle according to the harmonic measurement standard of IEC61000-4-30 of the International Electrotechnical Commission.

Table 1 shows the fundamental wave magnitudes of about 220 calculated by using the periodic sampling value, sine component and cosine component of the first cycle according to the harmonic measurement standard of IEC61000-4-30.

Table 2 shows experimental values of fundamental wave size measured by high-speed Fourier transform of the waveform signal of the second cycle according to the harmonic measurement standard of IEC61000-4-30 of the International Electrotechnical Commission.

Table 2 shows the fundamental wave size of about 200 calculated by using the periodic sampling value, sine component and cosine component of the second cycle according to the harmonic measurement standard of IEC61000-4-30.

Here, the value obtained by combining the fundamental wave size of the first cycle and the fundamental wave size of the second cycle is calculated as 210.139.

Table 3 shows experimental values obtained by summing up the continuous waveforms of the first cycle and the second cycle, and measuring the size of the fundamental wave by Fourier-transforming the average waveform created in one cycle.

Table 3 shows the fundamental wave size of 210.141 calculated using the sampling value, sine component, and cosine component of the average waveform.

The results of Tables 1 to 3 indicate that there is no error in the values obtained by combining the respective waveforms according to the harmonic measurement standard of IEC61000-4-30 and the average value of the continuous waveforms according to the embodiment of the present invention Able to know.

According to IEC61000-4-30 harmonics measurement standard, the parts requiring long-term measurement and evaluation, such as power system (10), in which harmonic variation is not significant, are required to use values of 10 minutes or 2 hours. If the 10-minute value (600 seconds) is evaluated, 3,000 (= 600 / 0.2) values obtained by continuously performing the fast Fourier transform every 12 cycles (0.2 seconds) are calculated. The power quality measuring apparatus according to an embodiment of the present invention continuously generates a mean waveform by dividing a cycle by a period added by 10 minutes, and performs one FFT to calculate the same result as calculated by the IEC standard .

A conventional system for measuring and monitoring harmonics samples voltage waveforms and current waveforms every 0.2 seconds and performs fast Fourier transforms to evaluate harmonic characteristics. For example, when evaluating the 10-minute long-term measurement value of 3-phase power, the amount of data to be processed is 3,000 high-speed Fourier transforms and stores the result of 3,000 times and calculates the harmonic characteristic of 10 minutes.

On the other hand, the power quality monitoring system according to an embodiment of the present invention calculates a waveform of one cycle of 10 minutes and performs a fast Fourier transform on the waveform to reduce the number of operations from 3000 to 1. In addition, the power quality measuring device can reduce 18300 [3000.times.61 (each wave result value)] pieces of data to one piece of data when storing the harmonic order value. That is, the power quality measuring device can reduce the amount of data to be transmitted to the server by about 18300 times or more for monitoring the power system.

In addition, the power quality measuring apparatus can obtain the same result as the conventional method of measuring the magnitude of the fundamental wave by the fast Fourier transform by merging the waveforms acquired during the measurement period.

6 is a flowchart illustrating a power quality measurement method according to an embodiment of the present invention. Each step performed below is performed by each internal component of the power quality measuring device, but will be collectively referred to as a power quality measuring device for ease of understanding and explanation.

In step S10, the power quality measuring apparatus acquires each of the voltage waveform signal and the current waveform signal of the power system connected to the power quality measuring apparatus at predetermined time intervals, and samples each of the acquired voltage waveform signal and current waveform signal at a predetermined sampling period . Since these are the same as those described above, an overlapping description thereof will be omitted.

In step S20, the power quality measuring apparatus superimposes the sampled voltage waveform signal and the sampled current waveform signal in one cycle over a measurement period to generate a voltage representative waveform signal and a current representative waveform signal. For example, the power quality measuring apparatus can generate a voltage representative waveform signal and a current representative waveform signal by superimposing the sampled voltage waveform signal and the current waveform signal in one cycle and calculating an average value thereof.

In step S30, the power quality measuring apparatus performs fast Fourier transform on the generated voltage representative waveform signal and current representative waveform signal, respectively. The fundamental wave and the harmonic of each order are decomposed from the voltage representative waveform signal and the current representative waveform signal, respectively.

In step S40, the power quality measuring apparatus calculates the ratio of the effective value of the fundamental wave to the effective value of the total harmonic to calculate the total harmonic distortion factor of the voltage. Here, the power quality measuring apparatus calculates the ratio of the effective value of the voltage fundamental wave decomposed from the voltage representative waveform signal to the effective value of the total voltage harmonic to calculate the total harmonic distortion factor of the voltage. Also, the ratio of the effective value of the current fundamental wave decomposed from the current representative waveform signal to the effective value of the total current harmonic is calculated to calculate the total harmonic distortion factor of the current.

Next, the total harmonic distortion factor is calculated and compared with the harmonic distortion factor reference value set for managing the power quality of the power system. Next, a warning signal is generated when the result of the comparison indicates that the harmonic distortion factor exceeds the harmonic distortion factor reference value. Next, a warning signal is received and a warning sound or a warning indication is generated to warn the occurrence of an abnormality in the power system.

In step S50, the power quality measuring apparatus transmits the total harmonic distortion factor of the voltage and the total harmonic distortion factor of the current to the outside. In addition, the power quality measuring device can also transmit a warning signal to the outside.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It will be understood that the invention may be varied and varied without departing from the scope of the invention.

100: Power quality measuring apparatus 110:
120: signal conversion unit 130:
140: Display part 150: Warning part
160: storage unit 170: communication unit
200: Server

Claims (13)

An apparatus for measuring the quality of a power system,
A detector that acquires the voltage waveform signal and the current waveform signal at predetermined time intervals in the power system and samples the waveform waveform signal and the current waveform signal at a predetermined sampling period;
A signal converter for converting the sampled voltage waveform signal and the sampled current waveform signal from an analog signal to a digital signal;
The voltage waveform signal and the current waveform signal converted into the digital signal are superimposed one cycle or a half cycle and a voltage representative waveform signal and a current representative waveform signal are generated with an average value of each of the voltage waveform signal and the current waveform signal superimposed , The voltage representative waveform signal, and the current representative waveform signal, respectively, to decompose the fundamental wave and the harmonic wave according to the order. Using the fundamental wave signal and the harmonic signals of the respective orders, An arithmetic unit for calculating a distortion factor and comparing the distortion factor with a preset reference value of harmonic distortion factor; And
And a communication unit for transmitting the total harmonic distortion factor of each of the voltage and the current to the outside.
The method according to claim 1,
Wherein the operation unit generates a warning signal when the total harmonic distortion rate exceeds the harmonic distortion factor reference value.
The method according to claim 1,
Wherein the harmonic distortion factor reference value is a preset value assuming an abnormality of the power system and is set as a ratio of the whole harmonic component to the fundamental wave.
3. The method of claim 2,
Further comprising a warning unit for receiving the warning signal from the operation unit and warning the occurrence of an abnormality in the power system.
delete delete The method according to claim 1,
The detector may be used in one cycle

(Where n is a natural number equal to or larger than 7) sampling periods of the acquired voltage waveform and current waveform, respectively.
A method for measuring a power quality of a power system,
(a) acquiring a voltage waveform signal and a current waveform signal at predetermined time intervals in a power system;
(b) sampling each of the acquired voltage waveform signal and current waveform signal at a predetermined cycle;
(c) superimposing the sampled voltage waveform signal and the sampled current waveform signal in one cycle or half period, and outputting a voltage representative waveform signal and a current representative signal as an average value of the voltage waveform signal and the current waveform signal superimposed, Generating a waveform signal;
(d) subjecting the voltage representative waveform signal and the current representative waveform signal to fast Fourier transform and analyzing;
(e) calculating an effective harmonic distortion factor by calculating an effective value ratio between the effective value of the fundamental wave and the total harmonic from the voltage representative waveform signal and the current representative waveform signal, respectively; And
(f) transmitting the total harmonic distortion factor to the outside.
delete delete 9. The method of claim 8,
After the step (e)
(e-1) comparing the total harmonic distortion factor with a harmonic distortion factor reference value set for quality control of the power system.
12. The method of claim 11,
After the step (e-1)
(e-2) generating a warning signal when the total harmonic distortion factor exceeds the harmonic distortion factor reference value.
13. The method of claim 12,
After the step (e-1)
(e-3) receiving the warning signal and warning the occurrence of an abnormality in the power system through at least one of a warning sound and a warning indication.

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