The Research On SHEPWM Strategy And Power Balance Control Scheme Of Multilevel Inverter

With the development of power electronics and power semiconductor devices,multilevel inverters have been extensive used in high voltage and high power applications,it can reduce the dv/dt and the voltage stress of switches,can get lower electromagnetic interference and higher power factor,it is also beneficial to the modular production.Therefore,it is very important to study the multilevel inverters.This paper takes the asymmetrical multilevel inverters as the object of study,and the main contents and innovations are as follows:The topology and working principle of three kinds of traditional multilevel inverters are introduced,and their advantages and disadvantages are discussed.Meanwhile,the control strategies of the four typical multilevel inverters are described,and the specific implementation and operating characteristics are addressed.In order to control the cascaded H bridge inverters with irregular DC sources,SHEPWM strategy is adopted.The characteristics of SHEPWM equations for multilevel inverters are analyzed theoretically,the traditional numerical method such as Newton Method,Homotopy Algorithm and Walsh Function Method and the intelligent algorithms such as Particle Swarm Algorithm and Genetic Algorithm for solving equations is discussed,and the characteristics and the advantages and disadvantages of the algorithms are analyzed.This paper puts forward a novel SHEPWM technique for the case of irregular DC voltage sources.Taking a seven-level inverter as an example,three cases of different voltage are selected,the established nonlinear equations are solved and the switch angle solution are got by using multiple population genetic algorithm.The switch angle trajectories under three cases are researched.For the solution trajectory bifurcation,two groups of solutions are discussed when modulation is between 0.65 to 0.85 and the different harmonic elimination effect between different solutions is contrasted.It provides a reference for the choice of harmonic elimination angle for different requirements.Simulation and experimental results confirm that the control technology is feasible and reliable.Furthermore,in this paper,a novel hybrid staircase-carrier modulation strategy is proposed for the hybrid seven-level inverter constituted by two H-bridge cells.With the strategy,the Phase Opposite Disposition carrier PWM modulation is performed on the low-voltage cell in the case of the high-voltage cell operating at the fundamental frequency,the quality of the output voltage is improved.On this basis,the relationship between the output voltage fundamental amplitude and the output active power of H-bridge cells is analyzed,a power balance control scheme of the novel hybrid modulati on strategy is proposed,thus,the occurrence of the phenomena of extremely uneven output power distribution between the high and low-voltage H-bridge cells in low amplitude modulation is avoided,the output power balance of H-bridge cells in full amplitude modulation is achieved.Simulation and experimental results verify the validity of the proposed strategy,and it provides a reference for the application in practical engineering.