KR101626318B1 - Power signal blackbox system using dct techniques - Google Patents

Abstract

The present invention relates to an electric signal black box system using discrete cosine transform (DCT) technology. The present invention comprises: an electric signal acquiring unit for acquiring electric signals; an AD converter for converting the analog electric signals received by the electric signal acquiring unit to digital signals; an electric signal compressing unit for compressing the electric signals inputted by the AD converter by using DCT; a storing unit for storing the electric signal compressing data compressed by the electric signal compressing unit; and an electric signal restoring unit for restoring the electric signal compressing data stored in the storing unit by using inverse DCT. The purpose of the present invention is to provide the electric signal black box system using a compressing technology of storing converted coefficients to make an error range between the original signal and restored signal lower than 5%.

Description

TECHNICAL FIELD [0001] The present invention relates to a power signal black box system using a DCT (Discrete Cosine Transform)

The present invention relates to a power signal black box system, and more particularly, to a power signal black box system using a DCT technique capable of power quality analysis by compressing a power signal using the DCT-2 technique, Black box system.

Recently, the increase of the nonlinear load and the time varying load in the power system, the increase of the distributed power source due to the smart grid, and the power generation using renewable energy have been linked to the existing power system, Are increasing.

In the past, the term power quality was used only to describe voltage, current, and frequency variations in power systems, and most electrical appliances were able to operate well over a relatively wide range of variations. However, there are many cases in which sensitive scientific equipment, communication equipment, and medical equipment that are becoming increasingly advanced and refined require higher quality of electric power. However, it is not necessary to upgrade the quality of all the power according to the requirements of these advanced devices. Supplying high-quality power to a place where high-quality power is not required is expensive, so it is only necessary to supply high-quality power to the place where it is needed, and power supply of a general electric appliance is usually required. Moreover, the damage caused by the power quality problem is increasing year by year, but the survey and application technology in Korea is still insufficient.

Therefore, there is a need to monitor and analyze power quality at specific time and place through constant monitoring of power signal. For this purpose, it is necessary to continuously store the power signal. In order to store a large amount of data, it is advantageous to compress and store the signal.

Korean Patent Publication No. 10-2008-0094489 (published on October 23, 2008) Korean Patent Publication No. 10-2011-0100855 (published September 15, 2011).

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and apparatus for transforming a power signal using a DCT-2 technique with excellent compression performance, And a compression scheme for cutting and storing the transformed coefficients so that the error range from the original signal is within 5% when the compressed and stored coefficients are restored through inverse transform.

According to an aspect of the present invention, there is provided a power signal black box system using a DCT technique, including: a power signal obtaining unit for obtaining a power signal; an analog-to-digital converter An analog-to-digital converter (ADC), a power signal compressor for compressing the power signal input from the analog-to-digital converter using discrete cosine transform (DCT) And a power signal restoring unit for restoring the power signal compressed data stored in the storage unit using an inverse discrete cosine transform (IDCT).

As described above, according to the power signal black box system using the DCT technique according to the present invention, the power signal is efficiently compressed using the DCT-2 having the energy condensation characteristic and is stored by time zone, , It is possible to restore the original signal with only the necessary data with an error rate of 5% or less, and it is possible to perform time-based error detection, which is efficient in analyzing the power quality of the actual power signal.

1 is a block diagram schematically showing the overall configuration of a power signal black box system according to an embodiment of the present invention.
2 is a flowchart illustrating a process of compressing a power signal using a DCT.
3 is a graph showing compression and restoration simulation results for a combined power signal.
4 is a graph showing compression and restoration simulation results for instantaneous power failure.
5 is a graph showing compression and restoration simulation results for instantaneous voltage drop.
6 is a graph showing compression and restoration simulation results for instantaneous voltage drop.
7 illustrates a text file in which power signal compressed data is stored.
8 is a flowchart illustrating a process of restoring the power signal using the IDCT.
9 shows a display screen of the real-time monitoring module.
10 shows DCT coefficients and position information files stored in the storage unit.
11 shows a display screen of the mailing module.
12 shows a display screen of the power signal black box module.
13 shows a display screen of the power signal black box module when an abnormal signal is detected.

Hereinafter, a power signal black box system using the DCT technique of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram schematically showing the overall configuration of a power signal black box system according to an embodiment of the present invention.

Referring to FIG. 1, a power signal black box system according to an embodiment of the present invention includes a power signal obtaining unit 100 for obtaining a power signal, an analog power signal obtained in the power signal obtaining unit 100, An analog-to-digital converter (ADC) 200 for converting a power signal to a power signal, a power signal compressing unit 300 for compressing a power signal using discrete cosine transform (DCT) And a power signal restoring unit 500 for restoring the power signal compressed data stored in the storage unit 400 by using the IDCT. A power signal compressing unit 300, a storage unit 400, and a power signal restoring unit 500 (not shown) for detecting an abnormal signal in the restored power signal restored data by the power signal restoring unit 500. [ A display unit 700 for displaying data of the abnormal signal detector 600, and a power unit 800 as a basic power source for operating the respective components.

The power signal acquisition unit 100 acquires a power signal using a PT (Potential Transformer) and converts the obtained power signal into a signal of a range that can be recognized by the analog-to-digital converter 200 , And a DC offset voltage is added through the OP-AMP adder so as not to have a negative value. Specifically, in the power signal acquisition unit 100 of the present invention, the transformer is an apparatus for acquiring a power signal, and has an output signal of -1.5 V to +1.5 V with a commercial voltage of 220 V as an input signal, and the OP-AMP adder A signal of -1.5 V to +1.5 V that has passed through the transformer is offset to a voltage of 0 to 3 V to produce a signal within a range that can be recognized by the analog-to-digital converter 200 and the power signal compression unit 300.

An analog-to-digital converter (ADC) 200 converts the analog power signal obtained by the power signal obtaining unit 100 into a digital signal.

The power signal compressing unit 300 compresses the power signal using the DCT. In one embodiment of the present invention, the power signal compression unit 300 may be a DSP board or the like.

First, DCT (Discrete Cosine Transform), which is a power signal compression technique used in the power signal compressing unit 300 of the present invention, will be described using DCT as a discrete cosine function, . It is used for JPEG, which is a compression method of color still images, and MPEG, which is a compressed file of color moving images, and is also useful for extracting frequency components from time domain data. When there is any arbitrary signal, if it is a Fourier transform that expresses it as a sum of sine or cosine, it is DCT to express it as a sum of cosines only. The coefficient of each cosine function is called a DCT coefficient, and this coefficient represents the frequency component of the time domain data. Knowing the DCT coefficients can inversely calculate the original data array. The inverse discrete cosine transform (IDCT) is used to obtain the original data array using the DCT coefficients. When DCT is applied to n pieces of data, n DCT coefficients are outputted. However, the DCT coefficients are scattered in a specific band. Even if IDCT is performed by ignoring large values, that is, small values, among these coefficients, there is not much difference from the original data. Therefore, it is possible to restore the original signal by using only a small number of coefficient data.

DCT can be classified into four types. The most widely used transformed DCT algorithm is type-II DCT. In fact, digital TV also uses type-II DCT for data transmission and reception. The type-II DCT is often called "DCT" because it is most commonly used. DCT coefficients are the most widely used and most widely used image processing or signal processing methods because their information is distributed in a specific band and computation is much simpler. One of the reasons why DCT became so widely known is that DCT uses real numbers only from start to finish during computation, unlike fast Fourier transforms that use complex numbers.

In addition, DCT-2 is more efficient than DFT (discrete Fourier transform) in data compression applications due to energy compaction characteristics. In data compression, DCT-2 has a better advantage in data compression than DCT-2, so DCT-2 is used to compress a power signal.

The related equation of DCT-2 for signal compression is as follows.

[Equation 1] DCT-related equation

: 입력, N :

의 데이터 개수 )(

: Input, N:

Of data)

[Equation 2] IDCT-related expression

의 데이터 개수 )(N:

Of data)

는 DCT-2의 가중함수로서 식은 다음과 같다.here,

Is the weighting function of DCT-2.

&Quot; (3) "

Next, FIG. 2 is a flowchart illustrating a process of the power signal compressing unit 300 compressing the power signal using the DCT. Referring to FIG. 2, the process of compressing the power signal will be described below. When the power signal is transmitted through the ADC 200, the power signal compressing unit 300 samples the power signal first (S201). In one embodiment of the present invention, the sampling frequency is set to 7680 Hz so that the sampling frequency is 128 data per one cycle, according to IEEE std 1159. Since the sampled data accumulates over time, it must be truncated on a specific time basis and then operated on. The sampled and windowed data is subjected to a DCT operation (S202). Thereafter, the DCT coefficients are arranged in descending order according to their sizes (S203), and coefficients having a larger value among the DCT coefficients are sequentially selected (S204), and the position information of the coefficients is stored. The specific operation of steps S203 to S205 will be described in more detail with reference to Figs. 3 to 6 below.

If the power quality problem is classified according to the IEC standard, it can be largely divided into an event and a variation. An event refers to a case where a voltage or current waveform of a power signal causes a large variation in a short time, and there is a phenomenon such as a short interruption, a voltage sag, and a voltage swell. Variation, on the other hand, refers to the case where a voltage or current waveform changes continuously over a relatively long period of time, such as harmonics, voltage flicker, and the like.

Approximately 95% of the power quality problems occur in the customers after the water supply point, and about 80% of the losses are caused by the instantaneous power failure, the instantaneous voltage drop, and the instantaneous voltage rise occurring in the power company. In the embodiment, this problem is simulated. All simulations are performed by IEEE std. 1159, and the window length was 12 cycles. Therefore, the sampling frequency is 7680 Hz and the number of data for 12 cycles is 1,536.

1. Synthetic signal

3 is a graph showing compression and restoration simulation results for a combined power signal.

3A is a signal obtained by synthesizing only odd harmonics up to 31 th in accordance with IEC 61000-3-6 standard of Table 1.

Harmonic size according to IEC 61000-3-6 standard Odd harmonics
(Multiples of non-3) Odd harmonics
(Multiples of 3) Even harmonics Harmonic
Order (H) Harmonic
Voltage Distortion Rate (%) Harmonic
Order (H) Harmonic
Voltage Distortion Rate (%) Harmonic
Order (H) Harmonic
Voltage Distortion Rate (%) 5 6 3 5 2 2 7 5 9 1.5 4 One 11 3.5 15 0.4 6 0.5 13 3 21 0.3 8 0.5

0.2

A simple expression for the composite signal is shown in Equation 4 below.

&Quot; (4) "

는 각고조파 크기,

는 기본 주파수,

는 위상이다.here,

Is the magnitude of each harmonic,

The fundamental frequency,

Is the phase.

In one embodiment of the present invention, the total sampling number is 1536, the sampling frequency is 7680 Hz, and the sampling number per one cycle is 128 (step S201). Observation time was measured by IEEE std. 1159, respectively. FIG. 3B is a DCT coefficient waveform of the synthesized signal (step S202), and FIG. 3C is a waveform obtained by sorting the absolute values of the coefficient magnitudes by data size in descending order (step S203). FIG. 3D is a waveform in which only 300 pieces of large data among 1536 pieces of data are left (Step S204). This is the process of compressing the power signal. FIG. 3E is a DCT coefficient waveform obtained by rearranging 300 compressed data to the original position, and FIG. 3F is a signal restored using IDCT. The error between the synthesized signal of FIG. 3A and the restored signal of FIG. 3F is shown in FIG. 3G. As a result of the simulation, the error rate is within 5%, and the compression ratio (see Equation 5) when compressed to 300 out of 1,536 is 80.47%.

&Quot; (5) "

2. Momentary power failure

4 is a graph showing compression and restoration simulation results for instantaneous power failure.

When the instantaneous power failure (for 6 cycles) is implemented as an input waveform, the signal of FIG. 4A is implemented (step S201). 4B is a DCT coefficient waveform of the synthesized signal (step S202), and FIG. 4C is a waveform obtained by sorting the absolute values of the coefficient magnitudes by data size in descending order (step S203). FIG. 4D shows a waveform leaving only 300 data (step S204). Figure 4e is a rearranged DCT coefficient waveform and Figure 4f is a reconstructed signal. Fig. 4g is for confirming the error rate (within 5%). The compression rate when compressed to 300 out of 1536 total data is 80.47%.

3. Instantaneous voltage drop

5 is a graph showing compression and restoration simulation results for instantaneous voltage drop.

When the instantaneous voltage drop (0.4 pu during 6 cycles) is implemented as an input waveform, the signal of Fig. 5A is implemented (step S201). FIG. 5B is a DCT coefficient waveform of the synthesized signal (step S202), and FIG. 5C is a waveform obtained by sorting the absolute values of the coefficient magnitudes by data size in descending order (step S203). 5D shows waveforms of only 300 data (step S204). FIG. 5E is a rearranged DCT coefficient waveform and FIG. 5F is a reconstructed signal. Fig. 5g is for confirming the error rate (within 5%). The compression rate when compressed to 300 out of 1536 total data is 80.47%.

4. Instantaneous voltage rise

6 is a graph showing compression and restoration simulation results for instantaneous voltage drop.

When the instantaneous voltage rise (1.4 pu for 6 cycles) is implemented as an input waveform, the signal of Fig. 6A is implemented (step S201). FIG. 6B is a DCT coefficient waveform of the synthesized signal (step S202), and FIG. 6C is a waveform obtained by sorting the absolute values of the coefficient magnitudes by data size in descending order (step S203). 6D shows waveforms of only 300 pieces of data (step S204). 6E is a rearranged DCT coefficient waveform and FIG. 6F is a reconstructed signal. Fig. 6g is to confirm the error rate (within 5%). The compression rate when compressed to 300 out of 1536 total data is 80.47%.

As described above, simulation results show that the error rate of the input signal and the restored signal for the composite signal, the instantaneous power failure, the instantaneous voltage drop, and the instantaneous voltage rise is within 5% when the number of DCT coefficients is 300, Is 80.47%. Therefore, at least 300 data must be used to analyze power quality. Accordingly, in one embodiment of the present invention, when implementing the power signal compression scheme, it is desirable to design and implement the DCT coefficient to take 300 DCT coefficients.

Next, the storage unit 400 receives the compressed power signal compressed data from the power signal compressing unit 300, and stores the compressed data in the form of a text file or the like in a time zone. The storage unit 400 may be connected to the power signal compressing unit 300 through the RS-232 serial communication to transmit the power signal compression data .

7 illustrates a text file in which power signal compressed data is stored. 7, the first column indicates the DCT coefficient value, and the second column indicates the position information of the coefficient value.

The power signal restoring unit 500 rearranges the DCT coefficients of the power signal compressed data stored in the form of a text file or the like in the storage unit 400, restores the final power signal using the IDCT operation, Monitor, etc., so that the user can monitor it. In one embodiment of the present invention, the power signal restoring unit 500 can use a LabVIEW program.

FIG. 8 is a flowchart illustrating a process in which the power signal restoring unit 500 restores the power signal using the IDCT. Referring to FIG. 8, the power signal restoring process will be described below. After the power signal is compressed through the power signal compressing unit 300, the power signal restoring unit 300 rearranges the compressed coefficient in step S204 to its original position (S801). In this case, as described above, it is desirable to design and implement the DCT coefficient of 300 to obtain the error rate of the input signal and the restored signal within 5% and the compression rate of 80 or more. In step S802, zero-padding is performed to add M 0s to the time series so that N + M is 2n in the time series function where the number of data is N (<2n, n is a natural number). Finally, the power signal restoring unit 500 restores the power signal using the IDCT (S803). The specific operation of steps S801 to S803 is as specifically illustrated in Figs. 3 to 6 above.

The abnormal signal detector 600 detects and alarms an event when an abnormal signal is detected. In an embodiment of the present invention, an average of the magnitude of the IDCT signal is calculated to detect a voltage drop of 5% and a voltage rise of 5%. At this time, the voltage drop and voltage rising rate of the abnormal signal detection may be configured by the user.

The display unit 700 receives the power signal compressed by the power signal compressing unit 300, the data stored in the storage unit 400, the power signal restored by the power signal restoring unit 500, Events, and the like. In the power signal restoring unit 500 according to an embodiment of the present invention, the display part can be broadly divided into a real time monitoring module 510 and a power signal black box module 520.

First, the real-time monitoring module 510 stores the compressed power signal compressed data in the power signal compressing unit 300 at a predetermined time (for example, one minute) and stores the compressed power signal in the form of a text file in the storage unit 400, The restoration unit 500 can monitor the restored power signal restoration data through the IDCT calculation in real time. The real-time monitoring module 510 may automatically send an e-mail to a person in charge when an event is detected through the abnormal signal detector 600.

FIG. 9 shows a display screen of the real-time monitoring module 710, and FIG. 10 shows DCT coefficients and position information files stored in the storage unit. Referring to FIG. 9, (1) is a graph showing the power signal compressed data after the DCT operation in real time in the power signal compressing unit 300. The data in FIG. 9 (1) is a graph that is output at intervals of 1 second, and the compressed data is piled up and stored in the form of a text file in the storage unit 400 as shown in FIG. 10 every minute. The text file stores DCT coefficients and location information. (2) indicates a signal obtained by restoring the compressed data by IDCT in the power signal restoring unit 500. And (3) represents an event detector through the abnormal signal detector 600. When the event detector is turned on, the LED lights when an abnormal signal is input. ④ indicates alarm mail service. If an abnormal signal is detected through the abnormal signal detector 600 while the event detector is turned on and the alarm mail service is also turned on, a message is sent via the email of the person in charge.

11 shows a display screen of the mailing module. 11A shows a mailing option. When you send mail, you can specify the recipient, and you can set the title and content of the email. 11B, the real-time monitoring module 710 alerts the user by turning on the LED when an abnormal signal is detected through the abnormal signal detector 600 while the event detector and the alarm mail service are turned on, . 11C is a screen showing an e-mail sent after detecting an abnormal signal.

Next, the power signal black box module 720 retrieves one of the text files stored in the storage unit 400, restores the signal through the power signal restoring unit 500, and outputs a graph. In this case, it is also possible to easily detect an abnormal signal through the abnormal signal detecting unit 600 and to check which part has generated an abnormal signal.

FIG. 12 shows a display screen of the power signal black box module 720, and FIG. 13 shows a display screen of the power signal black box module 720 when an abnormal signal is detected. 12, the filed data after the DCT compression operation in the power signal compressing unit 300 is stored in the storage unit 400 every predetermined time (for example, one minute) as shown in FIG. 10, and the power signal black box module The power signal restoring unit 500 restores the original signal as shown in FIG. That is, the data compressed by the power signal compressing unit 300 includes the DCT coefficient and the position information, and after the IDCT operation is performed in the power signal restoring unit 500, the data is finally restored. When an abnormal signal is detected in the original signal through the abnormal signal detector 600, it is possible to check which part has an abnormal signal through the event detector as shown in FIG.

The power supply unit 800 is a basic power supply for operating the OP-AMP of the power signal acquisition unit 100, the DSP board of the power signal compression unit 300, and the like. In the embodiment of the present invention, + 12V , -12V Two DC voltage sources and a 5V DC voltage source for operating the DSP board.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention.

100: power signal acquisition unit
200: Analog to Digital Converter
300: power signal compression unit
400:
500: Power signal restoration unit
600:

Claims (6)

A power signal obtaining unit for obtaining a power signal,
An analog-to-digital converter (ADC) for converting the analog power signal obtained by the power signal obtaining unit into a digital signal,
A power signal compression unit for compressing the power signal input from the analog-to-digital converter using a discrete cosine transform (DCT)
A storage unit for storing compressed power signal data compressed by the power signal compressing unit;
And a power signal restoring unit for restoring the power signal compressed data stored in the storage unit using an inverse discrete cosine transform (IDCT)
The power-
Sampling the power signal,
Performing a DCT operation on the sampled power signal,
Arranging the DCT coefficients in descending order of magnitude; and
Performing a step of selecting 300 coefficients in order having a larger value among the DCT coefficients,
Wherein the power signal restoring unit comprises:
The power signal is compressed through the power signal compressing unit, and then the reassigned 300 coefficients are rearranged to their original positions,
Performing zero filling; and
And performing an IDCT operation on the power signal compressed data. The method according to claim 1,
An abnormal signal detector for detecting an abnormal signal in the power signal restored data restored by the power signal restorer;
A display unit for displaying data of the power signal compression unit, the storage unit, the power signal restoration unit, and the abnormal signal detection unit,
Further comprising a power supply that is a basic power source for operating each component. delete The method according to claim 1 or 2,
Wherein,
And the power signal compressed data is stored for each time slot. delete The method according to claim 2,
Wherein the abnormality signal detecting unit comprises:
And detects an abnormal signal when the voltage drop rate or the voltage increase rate of the IDCT-calculated power signal recovery data size average exceeds a predetermined ratio.

Images