TWI408860B - Harmonic analysis system and method based on orthogonal frequency multiplex transmission - Google Patents

Abstract

The present invention relates to a system and method of harmonic waves analysis based on orthogonal frequency multiplexing transmission, which installs signal acquiring unit on the user end of power transmission system. At least a series of voltage signals can be analyzed is converted from the power signals that are acquired from the output of power transmission system. The voltage signals are separated into a plurality sections by the first data analysis unit, and each section processed by the Fourier transform. The characteristics of fundamental wave and harmonics wave of each voltage signal are analyzed. Then the analyzed information of power status of each user is acquired. The reverse discrete wavelet transformation of analyzed information or voltage signal are utilized by the first data processing unit, and modulate the analyzed information or voltage signals to the information signals that can be transmitted. After these information signals transmitted to the monitor end of power transmission system that can be used as the evidence of electrical harmonic compensation.

Description

Harmonic analysis system and method based on orthogonal frequency multiplex transmission

The invention relates to a harmonic analysis system and method based on orthogonal frequency multiplex transmission, in particular to detecting and analyzing harmonic components in a power transmission system, and reporting the analysis result to the power transmission system. The monitoring terminal serves as the basis for harmonic compensation.

Due to the rapid development of the industry, power companies and subscribers (especially semiconductor manufacturers or precision processing plants) have stricter requirements on the quality of power supply, and all hope to obtain the best power transmission efficiency to improve the operation of working equipment. Efficiency, therefore, how to improve the quality of power supply has become a challenge and problem that power companies and their users are eager to overcome.

In semiconductors or precision processing plants, switching between high-frequency transients and high-frequency power electronic switches caused by non-linear loads is an important cause of harmonic loss and power factor degradation, resulting in poor power supply quality. The general harmonic refers to the waveform component of the voltage and current in addition to the fundamental wave, and the waveform component of other frequencies. In the power transmission system (ie, the power supply network of the power company is 60 Hz), the main source of harmonics is 3 harmonics. Odd harmonics such as wave (180 Hz) and 5th harmonic (300 Hz). Harmonic distortion is caused by nonlinear devices in power transmission systems, and non-linear devices refer to power electronic conversion devices (such as rectifiers, transformers, converters, etc.). In recent years, nonlinear loads have been widely used in power transmission systems, and they are also the main cause of harmonic generation. The influence caused by harmonics will cause the power distribution system to resonate in parallel, which may cause overload of the power equipment or affect the normal operation of the working equipment. In the definition of traditional virtual power and power factor, the system that suffers from harmonic pollution cannot be completely described. Therefore, it will cause the problem of virtual power compensation, which will cause the malfunction of the capacitor to be improved. In addition, due to the influence of current harmonic components, The current in the conductor is redistributed, and excessive harmonic current in the cable will cause overheating, which will cause the insulation layer in the cable to be deteriorated by heat and shorten the service life of the cable; other protection devices such as electric shovel and circuit breaker will be harmonized. Wave distortion causes malfunction.

Currently known power harmonic detection methods are mostly implemented by harmonic measurement instrument with analysis software, and the time domain waveform identification technology or frequency domain waveform identification technology is used to identify the magnitude and nonlinear characteristics of harmonics. And harmonic load types. In terms of time domain waveform identification technology, the distortion time domain waveform contains basic waves and various harmonic components. If the sawtooth phenomenon is more obvious, it means that the harmonic interference is larger. In addition, in the frequency domain waveform identification technology, most of them are analyzed by fast Fourier transform (FFT). First, the power harmonics are converted from the time domain to the frequency domain, and then the frequency domain pattern is used to determine the harmonic interference events. The detection process cannot simplify the calculation steps, so that the memory space cannot be effectively saved. In addition, it cannot directly analyze the time-varying and non-time-varying harmonic components, and because it does not have an elasticized filter array to directly analyze the architecture, it will be generated. Inter-harmonic problems, or high complexity calculation problems, the practical structure does have the need for further improvement.

A first object of the present invention is to provide a harmonic analysis system and method based on orthogonal frequency multiplexing transmission, which mainly analyzes and detects high-order harmonic components in a voltage signal of a power transmission system by short-time Fourier transform, and Report the analysis results to the monitoring unit of the power transmission system as the design basis for harmonic compensation, thereby avoiding the huge impact on the power and load equipment caused by harmonics, so as to reduce the unnecessary meaning caused by the power transmission process. Loss of power and power pollution, and can improve the quality of power supply, thereby improving the performance of the load equipment.

In order to achieve the above-mentioned effects, the technical means adopted by the present invention comprises a signal acquisition unit disposed on a user end of a power transmission system, a first data analysis unit and a first data processing unit, and the signal acquisition unit is disposed at The user terminal of the power transmission system is configured to capture the power signal output by the power transmission system and convert the output into at least one string of voltage signals for analysis, and the first data analysis unit divides the voltage signals into a plurality of regions. Segments, and each segment performs Fourier transform to analyze the frequency domain characteristics of the fundamental waves and harmonics in each voltage signal, thereby obtaining analysis information of the power state of the user terminal, and the first data processing unit uses Perform inverse discrete wavelet transform on the analysis information or the voltage signal, so that the analysis information or the voltage signal is modulated into a data signal that can be transmitted, and then the data signal is transmitted to the monitoring end of the power transmission system, and can be used as a power harmonic The basis of wave compensation.

The second object of the present invention is to transform the detected voltage signal into an OFDM communication protocol data signal by inverse discrete wavelet transform, and then perform harmonic analysis by Orthogonal Frequency Division Multiplexing (OFDM). The data signal is reported to the monitoring unit of the power transmission system as a design basis for harmonic compensation, thereby reducing the erection and maintenance cost of the signal transmission.

In order to achieve the above effects, the technical means adopted by the present invention is a power line communication module using an (OFDM) communication protocol, the power line communication module including a data signal transmitted by at least one power supply network of the power transmission system. a transmitting unit, and a receiving unit that receives the data signal by the power supply network.

one. Technical concept and characteristics of the present invention

Please refer to the first and second figures. The present invention is mainly applied to the power harmonic detection and analysis of the power transmission system (10), and corresponding compensation measures can be performed according to the analysis results. In addition, the present invention uses short-time Fourier Transform (STFT) to analyze power harmonics, which is characterized by good localization characteristics in the frequency domain, which can be used to analyze and detect higher harmonics in voltage signals. The composition and analysis results can be provided for harmonic compensation design. And the inverse discrete wavelet transform is used to modulate the detected voltage signal into the data signal of the power line communication module of the (OFDM) communication protocol, and then transmitted to the monitoring terminal (12) of the power company through the power supply network (13), and The analyzed data signal can be replied to obtain the power supply status information of the user terminal (11).

The invention mainly analyzes and detects high-order harmonic components in the voltage signal of the power transmission system (10) by short-time Fourier transform, and can report the analysis result to the monitoring unit of the power transmission system (10) to do The basis for harmonic compensation design, in order to avoid the huge impact on the power and load equipment caused by harmonics, to reduce the unnecessary wear and power pollution caused by power transmission, and to improve the quality of power supply, and then Improve the operating efficiency of the load device; at the same time, the harmonic analysis information can be reported to the monitoring unit of the power transmission system (10) through the power line communication module of the OFDM communication protocol, as the basis for the harmonic compensation design, thereby reducing the signal transmission. Erection and maintenance costs.

two. Basic technical features of the invention

Please refer to the first and second figures. In order to achieve the above functions, the basic technical features of the present invention include a signal extraction unit (20) disposed on the user terminal (11) of a power transmission system (10). The first data analysis unit (30) and a first data processing unit (40). The signal acquisition unit (20) is disposed on the user end (11) of the power transmission system (10) for capturing the power signal output by the power transmission system (10) and converting the output into at least one string for analysis. a voltage signal, and the first data analysis unit (30) divides each voltage signal into a plurality of segments, and performs Fourier transform on each segment to perform frequency domain on the fundamental waves and harmonics in each voltage signal. Characteristic analysis, and then obtain analysis information of the power state of the user terminal (11).

The first data analysis unit (30) determines the required segment length according to a window function to perform Fourier transform on each segment. The first data processing unit (40) is configured to perform inverse discrete wavelet transform on the analysis information or the voltage signal, so that the analysis information or the voltage signal is modulated into a data signal that can be transmitted, and then the data signal is transmitted to the power. The monitoring terminal (12) of the transmission system (10) can be used as a basis for power harmonic compensation.

Participation. Specific implementation of the technical features of the present invention

Referring to the first and second figures, the power transmission system (10) of the present invention may be the power supply network (13) of the power company, and the monitoring terminal (12) refers to the monitoring center of the power company with built-in computer equipment. Or monitor the computer room. In a more specific embodiment, the monitoring terminal (12) is configured to include a second data processing unit (51) and a second data analysis unit (50), and the second data processing unit (51) is configured to execute the data signal Discrete wavelet transform (DWT) for demodulating the data signal, and second data analyzing unit (50) for performing short-time Fourier transform on the demodulated data signal to convert the fundamental wave in the data signal The harmonics are analyzed in the frequency domain to obtain the analysis information, so that the analysis information can be interpreted and processed. The specific embodiment of the signal extraction unit (20) is a digital electric meter capable of outputting a digital voltage signal. The hardware structure of the first data analysis unit (30) may be a computer having a software module for performing short-time Fourier transform, and a hardware architecture for performing short-time Fourier transform. A digital filter array is implemented. In addition, the second data analysis unit (50) can be constructed in the above computer, and the computer has a software module for performing short-time inverse discrete wavelet transform.

Please refer to the first and second figures to report the harmonic analysis information to the monitoring unit of the power transmission system (10) as the basis for the harmonic compensation design, so as to reduce the erection and maintenance cost of the signal transmission. In a more specific embodiment, the first data processing unit further includes a power line communication module (41) using an Orthogonal Frequency Division Multiplexing (OFDM) protocol, and the power line communication module (41) A transmitting unit (410) for transmitting data signals by at least one power supply network (13) of the power transmission system (10), and a receiving unit for receiving data signals by the power supply network (13) (411).

Hey. Operation of the specific implementation of the present invention

The invention uses short-time Fourier transform (STFT) application in the analysis of power harmonics, can be realized by digital signal technology, and is measured and analyzed by the actual power transmission system (10). In language processing, the voltage signal is considered to be fixed in a short period, which can be written as: x _p ( m ) = x ( m ) w ( n - m ) (9) w ( m ) is a length For a finite length windowing function of L, p is the number of segments and m = 0, 1, 2, ... L -1. To generate the short-term Fourier transform, we use the definition of Fourier transform, and each section takes a discrete Fourier transform, as follows:

Set (10) where ω = ω _i , i =0, 1, 2, ... N -1. Rewrite (10) as: Setting h ( n ) is the filter function. Therefore, (11) can be rewritten as Then we can define h _i ( n )

Using (13) we obtain x _i (n) from the i-th item complex bandpass filters h _i (n) is directly outputted, the center frequency of the filter is defined as the following equation :: f _i = f _{s i} / N , i =0,1,2,... N -1, f _s : sampling frequency (14) The bandwidth is defined as the following formula: 2 B =4 f _s / L (15)

B is the width of the cutoff frequency to the center frequency. Therefore, we can use (11), (14) and (15) to determine the implementation of the filter array specifications.

Please refer to the third figure, which is a schematic diagram of the frequency response of the numerical simulation short-time Fourier transform to analyze the single-phase voltage waveform of a three-phase power supply system with high-frequency harmonics and irregular distortion. The fourth graph is a short-time Fourier transform to achieve the spectral distribution of the equivalent filter. From the analysis of the fourth graph, it can be seen that the short-time Fourier transform can directly analyze the time-varying and non-time-varying harmonic components. And because its flexible filter array directly analyzes the architecture, there is no harmonic problem between general harmonic analysis theory or high complexity calculation.

The frequency response of the short-time Fourier transform is:

Short-time complex leaf transformation realizes the equivalent filter spectrum distribution map (basic wave, fifth harmonic, seventh harmonic and thirteenth harmonic) continuous wavelet transform (CWT) is a recursive function. The wavelet equation Ψ _{a , b} ( t ) is defined as the following formula:

a : multiple coefficient, b : displacement coefficient continuous wavelet transform coefficient C ( a , b ) is defined as the following formula:

C ( a , b )=∫ f ( t ) Ψ ^* _{a , b} ( t ) dt (17)

f ( t ): voltage signal. In equation (17), both a and b are real or continuous. Its discrete form is as follows:

n : discrete time domain indicator, m : discrete time domain multiple indicator.

(18) is rewritten as follows:

The implementation architecture of Discrete Wavelet Transform (DWT) is called subband filtering or offset tree filtering. By replacing a ₀ with 2, equation (19) can be rewritten as follows:

The filters used for subband filtering are defined as follows:

g [ n ], g ^' [ n ]: Qualcomm decomposition and reconstruction quadrature mirror filters.

h [ n ], h ^' [ n ]: low-pass decomposition and reconstruction quadrature mirror filters.

In equation (20), the wavelet and filter functions are related as follows:

The first level is analysis or decomposition, and its function is shown in (22).

The following is a schematic diagram of the process for its decomposition architecture:

Let C ^j = Aj and d ^j = Dj . The frequency ranges of Aj and Dj are based on the above illustration, with a sampling frequency of 15,360 Hz, six decomposition layers, and the use of the db 10 wavelet function. The fundamental wave (60 Hz) and third harmonic (180 Hz) analysis STFT filter frequency response diagram (as shown in the first figure, the point 2).

Please refer to the fifth figure, which is the filter frequency response diagram of the first data processing unit (40) before the transmitting end (user end) (as shown in the first figure). The sixth diagram is a schematic diagram of the sum frequency response of the digital meter before the transmitting end. It can be seen from the sixth figure that this method can ensure the spectral integrity of the information during transmission (as shown in the first figure). ). The seventh picture is a power line signal waveform simulation diagram to verify that the system can be successfully operated (as in the first point of the capture point 1), and when the measurement points 1 to 5 are used, the simulation is used. The tool Matlab software sets the basic wave to 60 Hz, the third harmonic to 180 Hz, and the sampling frequency to 15360 Hz. Please refer to the eighth to thirteenth drawings, which are schematic diagrams of the spectrum amplitudes of the positions 1 to 5 of the capture point as shown in the first figure, and the spectral amplitudes of the random noise extraction points 1 to 5 are different. Because the signal processing is not normalized, but the spectrum position and amplitude comparison can be seen that this concept is feasible and the original data can be restored. When the measurement points 1~5 are used, the simulation tool Matlab software is used. The fundamental wave is set to 60 Hz, the third harmonic is set to 180 Hz, and the sampling frequency is 15360 Hz.

Conclusion

Therefore, by the above technical features, the present invention does have the following features:

1. The present invention can indeed use short-time Fourier transform to analyze and detect higher harmonic components in the voltage signal of the power transmission system, and can report the analysis result to the power transmission. The monitoring unit of the transmission system is used as the design basis for harmonic compensation, thereby avoiding the huge impact on the power and load equipment caused by harmonics, so as to reduce the unnecessary wear and power pollution caused by the power transmission process, and It can improve the supply quality of power, and thus improve the running performance of load equipment.

2. The present invention can indeed use the inverse discrete wavelet transform to convert the detected voltage signal into the data signal of the OFDM protocol, and then the power line communication module (OFDM) returns the data signal of the harmonic analysis to the power transmission system. The monitoring unit is used as the basis for harmonic compensation design to reduce the cost of erection and maintenance of signal transmission.

The above is only one of the possible embodiments of the present invention, and is not intended to limit the scope of the patents of the present invention, and the equivalents of other variations of the contents, the features and the spirit of the following claims. All should be included in the scope of the patent of the present invention. The method and the mechanism of the invention, in addition to the above advantages, are deeply utilized by the industry, can effectively improve the lack of use, and are specifically defined in the scope of the patent application, are not found in the same kind of articles, and therefore have practicality. And progress, has met the requirements of the invention patent, and filed an application according to law. I would like to ask the bureau to approve the patent in accordance with the law to protect the legitimate rights and interests of the applicant.

(10)‧‧‧Power transmission system

(11) ‧‧‧Client

(12) ‧‧‧Monitor

(13)‧‧‧Power supply network

(20) ‧‧‧Signal capture unit

(30) ‧‧‧First Data Analysis Unit

(40) ‧‧‧First Data Processing Unit

(41)‧‧‧Power Line Communication Module

(410)‧‧‧Send unit

(411)‧‧‧ Receiving unit

(50) ‧‧‧Second data analysis unit

(51) ‧‧‧Second data processing unit

The first figure is a schematic diagram of the implementation of the basic architecture of the present invention.

The second figure is a schematic diagram of the operational implementation of the present invention.

The third figure is a schematic diagram of the frequency response of the present invention via short-time Fourier transform.

The fourth figure is a schematic diagram of the spectrum distribution of the equivalent filter implemented by the short-time Fourier transform of the present invention.

The fifth figure is a schematic diagram of the filter frequency response of the present invention at point 3.

The sixth figure is a schematic diagram of the frequency response of the present invention at the capture point 4.

The seventh figure is a schematic diagram of the frequency response of the fundamental wave and the third harmonic of the point 1 of the present invention.

The eighth figure is a schematic diagram of the simulation of the power signal waveform of the present invention at point 1.

The ninth figure is a schematic diagram of spectrum analysis of the output of the digital electric meter of the present invention.

The tenth figure is a schematic diagram of the comparison between the fundamental wave and the harmonic of the capture point 2 of the present invention.

The eleventh figure is a schematic diagram of the comparison between the fundamental wave and the harmonic of the capture point 3 of the present invention.

The twelfth figure is a schematic diagram of the comparison between the fundamental wave and the harmonic of the capture point 4 of the present invention.

The thirteenth diagram is a schematic diagram of the frequency response of the present invention at the extraction point 5.

(10). . . Power transmission system

(12). . . Monitor side

(13). . . Power supply network

(20). . . Signal acquisition unit

(30). . . First data analysis unit

(40). . . First data processing unit

(41). . . Power line communication module

(410). . . Sending unit

(411). . . Receiving unit

(50). . . Second data analysis unit

(51). . . Second data processing unit

Claims (9)

A harmonic analysis system based on orthogonal frequency multiplex transmission, comprising: a signal extraction unit disposed on a user end of a power transmission system for capturing a power signal output by the power transmission system, and The conversion output is at least one string of voltage signals for analysis; a first data analysis unit that divides each voltage signal into a plurality of segments, and performs Fourier transform on each of the segments to be in the voltage signal The fundamental wave and the harmonic are analyzed in the frequency domain to obtain analysis information of the power state of the user end; and a first data processing unit is configured to perform inverse discrete wavelet transform on the analysis information or the voltage signal, The analysis information or the voltage signal is modulated into a data signal for transmission, and the data signal is transmitted to the monitoring end of the power transmission system as a basis for power harmonic compensation. The harmonic analysis system based on orthogonal frequency multiplexing transmission according to Item 1 of the present invention, wherein the monitoring terminal includes: a second data processing unit configured to perform discrete wavelet transform on the data signal, Performing demodulation processing on the data signal; and a second data analyzing unit, configured to perform short-time Fourier transform on the demodulated data signal to perform frequency domain of the fundamental wave and harmonic in the data signal Analysis of the characteristics, and then obtain the analysis information. The harmonic analysis system based on orthogonal frequency multiplexing transmission according to Item 1, wherein the hardware architecture for performing short-time Fourier transform on the first data analysis unit and the second data analysis unit is digital Filter array. The harmonic analysis system based on orthogonal frequency multiplexing transmission according to Item 1 of the claim, wherein the signal acquisition unit is a digital electricity meter capable of outputting the digital voltage signal. The harmonic analysis system based on the orthogonal frequency multiplexing transmission described in claim 1, wherein the first data processing unit further comprises a power line communication module using an Orthogonal Frequency Division Multiplexing (OFDM) protocol. The power line communication module includes a transmitting unit that transmits the data signal through at least one power supply network of the power transmission system, and a receiving unit that receives the data signal by using the power supply network. A harmonic analysis method based on orthogonal frequency multiplex transmission, comprising: providing a harmonic analysis system based on orthogonal frequency multiplexing transmission according to claim 1; and a power signal flowing through the signal extraction unit The conversion output is at least one string of voltage signals for analysis; the first data analysis unit divides each of the voltage signals into a plurality of segments, and performs Fourier transform on each segment to basicize the voltage signal Wave and harmonics are analyzed in the frequency domain to obtain analysis information of the power state of the user end; the first data processing unit performs inverse discrete wavelet transform on the analysis information, so that the analysis information or the voltage signal is Modulated into a data signal for transmission; and the signal transmission module transmits the data signal to the monitoring end of the power transmission system, thereby serving as a basis for power harmonic compensation. Harmonic analysis method based on orthogonal frequency multiplex transmission as described in Item 6 of the claim The method includes: a second data processing unit configured to perform discrete wavelet transform on the data signal to perform demodulation processing on the data signal; and a second data analysis unit, The short-time Fourier transform is performed on the data signal after the demodulation process, so that the fundamental wave and the harmonic in the data signal are analyzed in the frequency domain to obtain the analysis information. The method for harmonic analysis based on orthogonal frequency multiplexing transmission according to Item 6 of the claim, wherein the first data processing unit further comprises a power line communication module using an Orthogonal Frequency Division Multiplexing (OFDM) protocol. The power line communication module includes a transmitting unit that transmits the data signal through at least one power supply network of the power transmission system, and a receiving unit that receives the data signal by using the power supply network. The method for harmonic analysis based on orthogonal frequency multiplexing transmission according to Item 6 of the claim, wherein the first data analysis unit determines a length of the required segment according to a window function, for each of the The segment performs a Fourier transform.