Study On The Effect Of Harmonic And Voltage Fluctuation On The Electrical Energy Measurement

Electric energy is the main energy of the national economy and people's life,and plays a decisive role in the development of the country.Energy measurement data is related to tripartite economic interests including power generation,power supply and electricity.It is also an important basis for the calculation of many technical indicators.At present,with the extensive application of electrical equipment and power electronics technology,more and more non-linear load and new power supply is accessed to the grid,resulting in a large number of harmonic injection,and which may cause influence on the stability of the grid voltage.As most of the energy metering devices are designed based on power frequency,effects of harmonics and voltage fluctuations on the energy measurement have been negligible.Therefore,the following research work on the accurate measurement of electric energy under harmonic and voltage fluctuation conditions is carried out:First of all,as the typical new power supply,a model of distributed photovoltaic power generation system is established to analyze grid-connected characteristics.To analyze non-linear characteristics,models of transformer,single-phase series motor speed control device and AC arc furnace are established as ferromagnetic saturation,power electronic switch and arc furnace type of non-linear load respectively.Based on the harmonic and voltage fluctuation characteristics of different kinds of load model simulation,compared with static harmonic energy meter detection standard and voltage fluctuation immunity test standard,the harmonic and voltage fluctuation signal characterization for energy metering simulation experiment are summarized,combining the actual nonlinear load and the sampling waveform of distributed PV.Then,the basic structure and working principle of the electronic energy meter are analyzed.The analog energy meter model based on the time division multiplier is established,and the digital energy meter model based on the fast Fourier transform algorithm is established as well.In this paper,the error coefficients of the split multiplier in the harmonic modulation process,the error characteristics of the fast Fourier transform in the harmonic detection process,and the error principle of the instantaneous power integral window of the electronic energy meter under voltage fluctuation conditions is studied.The analog energy meter harmonic measurement improvement module based on the harmonic error coefficient,the digital energy meter harmonic improvement module based on the fast Fourier transform and the Hilbert yellow transform,and a voltage fluctuation metering improvement module based on an adaptive power integration window has been designed respectively.Finally,an improved energy metering model of analogue energy meter and digital energy meter is set up.The energy measurement simulation experiment is carried out with the summarized harmonic and voltage fluctuation characteristic signal as an input.Considering the fundamental signal with single harmonic as input signal,the square wave signal and the steep wave signal added,the validity of the improved model of analog and digital energy meter in harmonic condition is verified.Considering voltage fluctuation signal as an input,the validity of the electronic energy meter improvement model proposed in this paper is verified under the voltage fluctuation condition.