Research On Key Technologies Of Power Quality Parameter Detection Based On Wide Area Synchronized Measurement

With the development of the society,the improvement of the industrial level and the wide use of nonlinear load and the renewable energy,pollution of power quality becomes severe problems and even exceeds the allowable range.High-quality power is the prerequisite to guarantee the safe and stable operation of the power grid and electrical equipment and also improvement of daily life of residents.In order to improve the power quality,it is important to analyze and study the power quality issue systematically,find out the reasons of the power quality problem and utilize targeted solutions.Therefore,it is crucial to use the approach of synchronous measurement to analyze the power quality issues.Traditional power quality analysis is based on a single point of local measurement.The measurement data lacks of uniform and accurate time index.Thus the measurement data are only effective in a local system and time,which makes it difficult to be used for large area state estimation for power system safe and stable operation.The wide-area measurement system is new power grid monitoring system based synchronized phasor measurement,which aims to power system dynamic detection,analysis and control.Combining the idea of wide area measurement system and the power quality measurement and realizing the wide area synchronized power quality measurement,we can not only obtain the all kinds of information of power in distribution system through the power quality measurement,but also systematically keep track of the running state of the entire network from multipoint synchronized measurement in wide area measurement system,which can realize the real-time monitoring and state prediction under the condition of power grid failure and provide theory guide to improve system stability and optimize the power grid operation.Due to the demand of wide area synchronized power quality parameter analysis,this dissertation studies the synchronous sampling method,phasor measurement algorithm,voltage flicker measurement algorithm and harmonic measurement algorithm.Furthermore,DSP + ARM based wide area synchronized power quality measurement system is developed.The main research work is as follows:1)To address the requirement of power system synchronized measurement,the GPS(Global Position System)clock timing based self-adaptive sampling method is proposed.Using the high-precision pulse per second signal provided by GPS to trigger the ADC conversion,the synchronous sampling is realized.To compensate for the sampling time error caused by the division remainder between the desirable sampling rate and the oscillator frequency,a variable sampling interval control method is presented to approach the ideal sampling rate.The frequency of the onboard oscillator is monitored in real-time using the PPS timing reference from GPS.The sampling control is adaptively adjusted each second according to the latest estimated oscillator frequency,which suppresses the remainder error cause by oscillator frequency drift and improves the immunity and stability of the synchronous sampling method.2)In order to realize fast and accurate power system phasor measurement,a single phase quasi-positive sequence recursive discrete Fourier transfer(DFT)based phasor measurement algorithm is proposed.Using the recursive formula to simplify the DFT calculation and the system frequency is obtained by least squares estimation based angle fitting.According to the frequency estimation result,original sampling data is resampled and the frequency is iteratively estimated to increase the accuracy of frequency measurement.The quasi-positive sequence method is proposed to increase the single phase angle and amplitude measurement accuracy under the off-nominal condition.The algorithm does not use special window function for signal truncation.Results of the simulation indicate that under the conditions of white noise,harmonic or flicker existing,drastic deviation of the fundamental frequency and non-stationary input signal,a low computational effort is needed to obtain the accurate phasor measurement result,which is suitable for fast high-precision power system phasor measurement.3)The key factors relevant to the FFT-based harmonic analysis accuracy are analyzed.To suppress the spectral leakage and the picket-fence effects,the Kaiser self-convolution window of high performance is proposed.As the traditional FFT algorithm has the constraint of single frequency domain feature and is not suitable for the distorted harmonic analysis,IIR type filter is first used for signal decomposition and then Teager-Kaiser energy operator is used for fast detection of instability onset time of the distorted harmonic signal.The stability interval of each harmonic component is obtained and then the FFT-based method is applied to each stable signal.With theoretical results on frequency characteristics of the adaptive Kaiser self-convolution window(AKSCW),the FFT-based harmonic analysis algorithm based on the window is proposed.By utilizing the least-square polynomial fitting method,the polynomial interpolation for discrete frequency spectrum and the calculation of harmonic parameters are derived.Simulation results verify the effectiveness and accuracy of the AKSCW based harmonic measurement method on the conditions of distorted harmonic,week harmonic components and white noise interferences.4)To achieve fast and accurate voltage flickers measurement and analysis,a new voltage flicker measurement algorithm using fast S-transform is formulated and realized.Based on discrete implementation steps of S-transform and its time-frequency analysis ability,the fast S-transform algorithm is proposed based on maxima detection and energy threshold judgment of spectrum.Follwing the International Electrotechnical Commission(IEC)recommended flicker measurement block diagram and the principle of IEC flicker measurement,a novel flicker measurement method based on fast S-transform is built.The Teager energy operator is used to realize flicker signal envelope extraction.The fast S-transform is utilized for time-frequency analysis of flicker envelope signal.From the S matrix,the flicker value is calculated by averaging the value of amplitude curves.The starting and end time of each flicker component is gained through the inflection point by calculating the derivation of each amplitude curve.Simulation results show that this method has a high flicker measurement accuracy and can realize accurate detection of the start,end and duration time of flicker.5)Based on the DSP+ARM platform,a wide area synchronized power quality parameter measurement system is designed.The overall structure of the system and hardware design is given.Taking the phasor measurement as an example,the algorithm implementation and workflow of the system are discussed in details.The system is tested and the error is analyzed.The test steps,results and error analysis are given.The results and error analysis show that the accuracy of the phasor measurement meets the standard requirement,demonstrating the ability to achieve high accuracy of synchronized phasor measurement.