Research On SHEPWM Of Five-Level Inverter Based On Improved Imperialist Competitive Algorithm

The multilevel converters have been widely applied in high-voltage and highpower applications due to their advantages of effectively improving the quality of output voltage waveform,large output capacity,and high inverting efficiency.This paper took NPC/H-Bridge five-level inverter as the research object,analyzed its topology and several applicable modulation strategies and studied the SHEPWM strategy which has the advantages of low switching frequency and high DC side voltage utilization.And the common mode voltage suppression problem of NPC/H-Bridge fivelevel inverter also has been studied based on SHEPWM strategy.The key challenge for SHEPWM technique is to solve the nonlinear equations containing trigonometric functions to obtain the right switching angles.A lot of contributions have been made to address this issue in recent years.Several numerical algorithms has been used to solve the SHEPWM equations,but they all need to be given initial values.The intelligent algorithms also are used to solve the SHEPWM equations.SHEPWM strategies based on particle swarm optimization algorithm and genetic algorithm has been studied,but these two algorithm has its own insufficients.In this paper,the imperialist competitive algorithm which has better performance than conventional genetic algorithm and particle swarm optimization algorithm was applied to solve SHEPWM equations,but the algorithm still has the disadvantages of premature and insufficient precision.Based on this,two improved imperialist competitve algorithms which are associated with differential evolution algorithm and particle swarm optimization algorithm respectively have been proposed.These two proposed algorithms both could improve the convergence rate and accuracy of the solutions.Processed the calculation results,and drawn the figures of the solutions when modulation index equals 0 to 1.15.The characteristics of the quarter-wave symmetry and half-wave symmetry SHEPWM solutions of the waveform have been analyzed.The generation of common mode voltage of multilevel inverter and the association between SHEPWM strategy and SVPWM strategy have been analysed.One modulation strategy to suppress CMV which based on redundant vector has been introduced.In addition,since the composition of the common mode voltage is closely related to the triple harmonics,and the SHEPWM strategy could eliminates the specified harmonics of output voltage,it is considered to suppress the common mode voltage by eliminating the triple harmonics.The NPC/H-Bridge five-level inverter model was built by Matlab/Simulink software to verify the effectiveness of the proposed algorithms,and the hardware-inloop experiments were carried out by using the RT-LAB experimental platform and the controller based on DSP and FPGA.The correctness and effectiveness of the proposed algorithms are verified and evaluated by the simulation and experimental results.