| In recent years, the power electronic technology has got rapid development. The application of PWM inverter is also widely used in various electronic devices.It brings energy saving, high efficiency and also brings serious harmonic pollution at the same time. The low conversion efficiency of photovoltaic power generation system and the harmonic pollution affect the quality of the output voltage and current waveforms seriously. In order to further suppress the harmonic pollution and improve the quality of output waveform, various technical methods of harmonic suppression have appeared. This paper chooses voltage type PWM inverter as an example, a more in-depth research on the inverter and selective harmonic elimination technology was expanded on the basis of output voltage harmonic analysis.1.According to the principle of Fourier series theory and the PWM technology, the SPWM and PFPWM MATLAB simulation of Simulink model have established with sinusoidal PWM inverter and random frequency PWM inverter as the research objects.Through the modulation depth and the change of carrier ratio for qualitative and quantitative analysis, the harmonic distribution law of the SPWM Inverter and random frequency inverter is obtained, providing a basis for the inverter harmonic suppression.2.The mathematical model of single-phase, three-phase inverter output voltage waveform is established according to the principle of the selective harmonic elimination technique. The core of the selective harmonic elimination technology is to solve the switching angles and the equations for solving are nonlinear equations, which solving method generally choose Newton iterative algorithm. This method has a strong local convergence and the choice of initial value had a great influence on the process of solving.3.This paper presents a new method of ant colony algorithm to solve nonlinear equations. Many groups of data switching angles are obtained through programming calculation and the improvement. By comparison, proving that ant colony algorithm has characteristics of rapid convergence, and can realize accurate solution.The optimization strategy of specific harmonic is studied in order to get a higher quality sine wave. By the research and comparison of switch angle distribution rule, the method of omitting the narrow pulse can implement specific harmonic optimization.This method ensures the output voltage waveform, reducing the switching frequency and the loss.Finally, the combination technique of inverter is proposed through the characteristics of inverter. The technology is mainly multiply superposed of the inverter.The basic principle is to put two or more identical square wave superimposed according toacertain retardation, making theirlow-order harmonics have180degrees phase difference andoffset each other to obtain thestep wave which has less harmonic allowance. After a small low-pass filtering to obtain a sine wave output, so as to achieve the improvement of the output voltage waveform. |
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