Research On Harmonic Protection And Broadband Harmonic Detection Algorithm Based On ANN And APFFT

With the development trend of power electronics in the power system,the harmonic/resonance problem has undergone profound changes and has become an important factor affecting the safe and reliable operation of the power grid.Harmonics will cause distortion of voltage waveforms,cause resonance phenomena,reduce power quality,and adversely affect electrical equipment,automatic devices,measuring instruments,and communication systems.It is considered a public hazard to the power grid.This dissertation focuses on broadband harmonic detection algorithms and harmonic protection.The main research contents are as follows:(1)In order to analyze the advantages and disadvantages of the performance of the harmonic detection algorithms based on Artificial Neural Network(ANN)and All Phase Fast Fourier Transform(All Phase FFT,APFFT),their harmonic detection is explained separately Principles,and perform simulation tests on broadband harmonic signals.Theoretical analysis and simulation results show that the ANN-based harmonic detection algorithm has high frequency resolution and small amplitude detection error,but the phase detection performance is poor,and the neural network initialization has no reliable basis;APFFT has phase invariance,harmonic phase The detection accuracy is high,but there is the problem of spectrum leakage,and the frequency and amplitude detection ability is poor.(2)In order to retain the advantages of the two algorithms of ANN and APFFT and make up for their shortcomings,a combination optimization algorithm for broadband harmonic detection based on ANN and APFFT is proposed.The combined algorithm uses APFFT to preprocess the harmonic signals to obtain accurate harmonic phase information and spectral peak diagrams,which provides a basis for the initialization of the neural network,avoids the contingency caused by the selection of network structure,and reduces neural network training.The required number of iterations speeds up the convergence speed;and the ANN training process can make up for the spectrum leakage problem of APFFT,so as to obtain the frequency and amplitude information of all harmonic components in the harmonics.The simulation test of 0～2500Hz broadband harmonic signal proves that the combined optimization algorithm has the advantages of high accuracy,strong anti-interference ability,fast convergence speed and suitable for broadband harmonic detection.(3)Harmonic components will cause additional losses and shorten the service life of the transformer.Overvoltage and overcurrent generated by resonance will damage the capacitor.In order to ensure the safe and stable operation of the transformer and capacitor in the power grid,transformer harmonic protection and capacitor Harmonic protection.The judgment basis for transformer harmonic protection includes: harmonic voltage distortion rate and hot spot temperature;as the judgment basis for capacitor harmonic protection: harmonic overcurrent,harmonic voltage distortion rate and single harmonic Current.(4)In order to combine the harmonic detection with the harmonic protection of transformers and capacitors,the programming and simulation of harmonic analysis software is realized in Lab VIEW virtual instrument development software.The main functions of the software are: detecting harmonic signals,accurately obtaining the frequency,amplitude and phase information of each harmonic component;judging the safety and stability of transformers and capacitors,if the harmonic parameters exceed the specified limits,timely Send out alarm information;generate harmonic analysis report and harmonic over-limit alarm information report.The use of modularization to realize the programming of the software,and debugging and simulation on the Lab VIEW platform proves the validity and reliability of the software.