Research On Three Phase Active Power Filter Harmonic Detection Method And Grid Connected Technology

With the depletion of fossil energy and increasingly serious environmental pollution problems,renewable energy access to the grid has become the world’s demands.However,the renewable energy in the network side and the nonlinear device in the user side seriously reduce the power quality.Active power filter is a kind of high efficiency harmonic control device.First of all,based on the brief description of the basic concepts of harmonic and reactive power,the relationship between the two and preventive measures,based on the research of active power filter,and then from the two perspectives of theory and industrial application,the research status and development trend are summarized.Secondly,based on the grid synchronization process,this dissertation discussed two grid synchronization methods from Phase locked loop and Frequency locked loop in two aspects:firstly,the two phase locked loop methods of DFF-PLL and SAI-PLL are compared and a double frequency phase locked loop method based on SAI is presented.Through simulation and experiment,the applicability of this method in unbalanced and distorted grid is verified;secondly,based on the theoretical research of SOGI-FLL,it makes a self-tuning filter and a SOGI be cascade connection,presenting a dual self-tuning SOGI frequency locked loop synchronization method.The influence of harmonic pollution is reduced.At the same time,the first order high pass filter and the differential node are introduced to effectively suppress the fluctuation of DC component to FLL.Once more,based on the harmonic generation of current signal,respectively,in-depth study of the traditional i_p-i_q method and MSOGI harmonic detection method in detecting delay caused by the parameter design of digital low pass filter in i_p-i_q method,resulting in adverse effects on the accuracy and real-time performance.And when the capacity of the harmonic compensation is greater than APF’s capacity,the flexibility of its use is reduced.Harmonic detection method of MSOGI just can extract the specified harmonic current by connecting the harmonic detection module in parallel with different frequencies combined with positive and negative sequence separation module.But when the harmonic number is more,the system structure becomes complex.In this dissertation,a method of harmonic current detection based on ROR is proposed by reducing the order of SOGI.Based on the frequency selection characteristics of ROR structure,the specified harmonics can be extracted and separated without the positive and negative sequence separation module.Finally,the PI+PR control strategy is adopted to control the fundamental and specified harmonic current components.Based on the theoretical and simulation analysis,the feasibility and effectiveness of the project is verified by the experiment of APF.