Research On SHEPWM Technology Of Multi-level Inverters

The multi-level inverter is the core part of the medium and high voltage frequency conversion system.It has the advantages of high output voltage,high energy conversion efficiency and less electromagnetic interference.However,with the increasing demand for the efficiency of the inverter and the quality of the waveform,it is of great significance to reduce the harmonic generation.The harmonic caused by the high power inverter causes the power quality of the power grid to decrease.The active power filter(APF)has high cost to solve the harmonic problem.The specific harmonic elimination technique(SHEPWM)can be carried out simultaneously by the calculation of the inverter modulation wave and harmonic elimination,and the switching frequency is low and the efficiency is high,and the efficiency is high.This paper takes diode clamped and cascaded multilevel inverters as the research object,and discusses the application of specific harmonic elimination technology,and carries out theoretical and experimental analysis on it.In view of the shortcomings of the existing algorithms in the special harmonic elimination technology,this paper introduces an ant colony optimization algorithm with high precision and global convergence to solve the nonlinear harmonic elimination equations.For the diode clamped three-level inverter and the cascaded seven-level inverter,the phase voltage of the inverter is carried out by Fourier expansion and according to its waveform symmetry.A set of nonlinear equations is obtained by establishing single pole and step wave harmonic elimination models respectively.The equations can be accurately solved to get the switch angle to control the power switch,and the specified lower order harmonics can be eliminated when the amplitude of the fundamental wave is guaranteed.First,a SHEPWM controlled diode clamped three level inverter simulation model is built,and the results of the Newton-Raphson iterative method and the ant colony system are introduced.Compared with the analysis of the voltage waveform and spectrum analysis obtained by the different algorithms,it can be found that the ant colony optimization algorithm does not depend on the initial value and has global convergence,and can eliminate the specified low order harmonics under the condition of guaranteeing the fundamental amplitude of the fundamental wave,and there are two solutions of the switch angles,which provides a reference for the selection of feasible solutions in the actual application.Secondly,a SHEPWM controlled cascaded seven level inverter is built.By analyzing the spectrum of its output waveform,the low order harmonic is eliminated,which verifys the effectiveness of the ant colony optimization algorithm to solve the nonlinear harmonic elimination equations.Finally,after the experimental platform of three-level inverter is built and the software system is debuged,the feasibility of the ant colony optimization algorithm in SHEPWM technology is verified by the analysis of the experimental results.