Research On Harmonic Detection And Suppression Of Microgrid Based On Wavelet Transform

As a flexible small power system with distributed generation,energy storage and load devices,microgrid can effectively improve energy utilization and reduce transmission loss.It is an effective method to deal with resource shortage at present.However,with the increasing application of nonlinear loads around the world,harmonic pollution has become an important problem affecting the normal operation of microgrid and loads.Therefore,it is very important to control harmonic pollution,and the suppression effect of harmonic pollution largely depends on the accurate and timely detection of harmonic.Therefore,the effective detection and suppression of harmonics in the design of microgrid has important research significance for the accurate evaluation and effective control of power quality problems.In order to solve the problems of modal aliasing and noise interference in the process of harmonic detection in microgrid,the synchronous extruded wavelet transform is applied to harmonic detection analysis,and an improved synchronous extruded wavelet transform harmonic detection method is proposed.This method combines the advantages of continuous wavelet transform and empirical mode decomposition,decomposes the total harmonic into fundamental component and each synchronous / supersynchronous harmonic component,and extracts the parameters of each component in combination with Hilbert transform.In order to improve the detection accuracy of instantaneous frequency and instantaneous amplitude,the instantaneous frequency estimation is improved to enhance the time-frequency aggregation and reconstruction accuracy of each component.The experimental results show that,compared with continuous wavelet transform and empirical mode decomposition,the proposed method can accurately extract each harmonic component to obtain a better time-frequency distribution,effectively suppress modal aliasing and noise interference,and improve the harmonic detection accuracy.Aiming at the problem of harmonic suppression of grid side converter of wind turbine generator under the condition of harmonic pollution in microgrid,a PI repetitive control compound controller with harmonic suppression function is designed.This method takes the doubly fed wind turbine as the research object,establishes the mathematical model of the harmonic system of the grid side converter,designs and values its parameters,improves the double closed-loop control system of the grid side converter,and designs a repetitive controller based on the internal model principle to suppress the harmonic of the system.The experimental results show that the proposed method can effectively improve the immunity of the harmonic suppression system,and achieve the optimal harmonic suppression effect with a simple and economical method.The simulation model is built by MATLAB / Simulink,and the improved harmonic detection and suppression scheme in microgrid is simulated and verified.The simulation results verify the effectiveness of the improved synchronous extrusion wavelet transform harmonic detection method proposed in this paper,and also verify that the PI repetitive control composite controller designed in this paper has good harmonic suppression ability.