Study On Harmonics Elimination In A Inverter Based On Improved PSO

Energy crisis and environmental problems of the world have attracted people’s attention, solar energy is clean energy which is an alternative to traditional energy sources and has been widely used in photovoltaic power generation. In the photovoltaic power generation, inverter and some power electronic devices and equipment will produce harmonics and reduce power quality in the course of operation. Through the study of the inverter control strategy makes transmission more stable power, reduce harmonics injected when photovoltaic delivery to the grid.The existence traditional controls of inverter have the problem of low utilization in DC voltage and are influenced by the maximum of switching frequency. In this paper, according to the Selective Harmonics Elimination and Pulse Width Modulation technology for cascade inverter to solve the problem of switching angles conducted in-depth research, mainly to do the work in the following aspects:Firstly, the research background of this treatise is summarized, analysis the issues related to power quality and potential harm that may cause by harmonic in the grid, describes the significance of the problem studied in this treatise.Secondly, Studied the topologies of multiple inverters, several kinds of structures were compared, summed up the advantages and disadvantages, finally choosing cascaded Inverter as research subjects. And by analyzing the control technology which now commonly used to compare the advantages and disadvantages as well as for occasions, using SHEPWM to control the inverter.Thirdly, according the theory of Fourier series and the basic principles of PWM to establish the SHEPWM nonlinear equations of cascaded inverter. This treatise has analyzed the Newton iterative method, homology algorithm, Walsh, genetic algorithm, respectively, using them to build equations to solve, but these algorithms have their own shortcomings, leading to unsatisfactory results. In order to solve nonlinear equations accurately, and to get accurate inverter switching angle, the paper by increasing symbolic function of inertia weight parameter in particle swarm algorithm, and changing position of the random number in the speed update equation. The improved particle swarm algorithm can avoid "premature" or fall into local optimal solution, so it could get a more accurate solution set. In simulations and experiments, the result of improved PSO and standard PSO and genetic algorithm are compared to verify that by using improved PSO the content of selected low-order harmonics approach zero. The THD of output voltage decreased dramatically in the inverter.Fourthly, In order to achieve improved particle swarm optimization algorithm for inverter output waveform, designed the main circuit, current and voltage measurement module, display hardware and software design of the module, the main circuit of the test, the results show that the feasibility of this algorithm.Simulation results show the improved particle swarm algorithm is feasible and effective SHEPWM equations, determined to achieve a precise inverter switching angle, reduced the inverter output voltage total harmonic content. The algorithm has practical value in optimizing control of photovoltaic grid connected inverter.