| Along with the fast development of our national economy,and the electric power sector is stricter in regulating the quality of electric energy.Due to the tremendous increase of nonlinear loads in power grid,the voltage of power grid distorts and pollution of power quality appears,which seriously affects the normal work of electricity users,and has great harm on the safe operation of the power system.Influenced by the electricity environment,the phenomenon of harmonic pollution in the power grid is becoming increasingly frequent and the scope of the influence is more and more widespread.Therefore,the harmonic problem of the power grid is attracting more and more attention.The calculation of the eigenvalues of harmonic can provide important basis for the governance of harmonic.Moreover,the study of new harmonic detection method makes great sense to the control of harmonic pollution in power grid.First of all,this thesis briefly introduces the waveform distortion and the basic concept of harmonic in power system,expounds the detriment and cause of harmonic and discusses the current research process of harmonic detection algorithm and the future development direction.Based on the characteristics and shortcomings of various harmonic detection algorithms,the advantages and disadvantages of the application of various time-frequency algorithms are analyzed.Secondly,the principle and characteristics of S transform are introduced in brief.Aiming at the deficiencies of Improved S transform,the research emphasis of this article is pointed out.Through the introduction of the regulatory factors of adjusting parameter,adaptive Gauss window function is set up.On the basis of S transformation,a new time-frequency algorithm,Improved S transform,is proposed,and the concrete derivation process of the algorithm is given.Through the comparison of simulation experiment,the characteristics of Improved S transform are analyzed,and provides some theoretical basis for that the future application of this algorithm in harmonic measurement.In this thesis,a harmonic detection method based on improved S transform fast algorithm is introduced,taking reduce the actual computation as the basic point.And the characteristic frequency point of filtering the threshold value is set.The calculation accuracy is ensured while the calculated amount is reduced.The harmonic signals under different conditions are simulated and the test is carried out,so as to verify the feasibility of the simplified algorithm.At the same time,white noise is added to the signal,and a variety of harmonic signals are simulated and analyzed.Based on fast improved S transform algorithm proposed in this thesis,an embedded device with ADC + DSP architecture is built,the design of hardware and software design is proposed.In addition,the detailed introduction of data sampling module,processing module and other hardware parts is given.The software design scheme of harmonic detection module and the experiment process specific task program are elaborated.Finally,on the basis of actual test,the feasibility of the harmonic detection device is analyzed.The experimental results show that the overall design of this device is safe and reliable for the harmonic signal detection under different situations.The relative error of amplitude and time error mainly reach the standard.There is the practical reference value in harmonic time-frequency analysis research. |
