Cascaded Switched Capacitor Multilevel Inverter Based On Improved Particle Swarm Optimization

Multilevel power conversion technology makes switched capacitor multilevel inverters（SCMLI）and cascaded multilevel inverters reliably applied in high power fields.Compared with the traditional multilevel inverter,SCMLI has the advantages of higher voltage gain and self-balancing of capacitor voltage;cascaded multilevel inverters have the advantages of easy expansion to high voltage levels and simpler modulation methods.In the modulation technology of multilevel inverters,selective harmonic elimination pulse-width modulation（SHEPWM）has the advantages of low switching loss and high output voltage quality,but the application of SHEPWM needs to solve a set of nonlinear transcendental equations,for which scholars at home and abroad also provide a variety of methods.The main research contents of the thesis are as follows:（1）By analyzing the existing SCMLI topology,in order to further increase the number of output levels,a cascaded switched capacitor multilevel inverter topology is proposed.The proposed topology is composed of SCMLI and traditional H-bridge inverter cascaded,including 2 voltage sources,14 switching devices and 2 capacitors can output up to 21 AC levels.The topology,working principle and cascading scheme of the proposed inverter circuit are analyzed.Finally,the parameters of the asymmetric cascaded switched capacitor multilevel inverter with a voltage ratio of 7 are analyzed.（2）Hybrid PWM and Nearest Level Control（NLC）control methods are used to analyze the output voltage quality,capacitor ripple and power distribution,compare the advantages and disadvantages of the two modulation methods,and then simulate verify.According to the characteristics of the cascaded switched capacitor multilevel inverter,SHEPWM is finally adopted,and the corresponding SHEPWM nonlinear transcendental equations are established for this purpose.（3）Analyze the existing solutions of SHEPWM nonlinear transcendental equations,aiming at the problem that the particle swarm optimization has poor global search ability and easy to fall into local optimum in the application when applied to the inverter’s SHEPWM.An improved PSO is proposed,improved PSO takes the traditional PSO as the main frame,the vertical crossover operator of genetic algorithm and elitism strategy are introduced in the search process to improve the global search performance,local search performance and retain excellent individuals of algorithm,thus improving the switching angle accuracy.The paper analyzes the topology,parameter design,modulation strategy and power distribution of the proposed inverter in detail.On the basis of theoretical analysis and simulation,a DSP-based cascaded switched capacitor multilevel inverter platform is built to verify the feasibility of the proposed topology and the effectiveness of the proposed algorithm in SHEPWM.