On Novel Topology And Modulation Strategy For Multilevel DC-link Inverter

Multilevel DC-link inverter has drawn tremendous interest in multilevel converter areas, and moreand more been widely used in new energy power generation and motor drive, mainly due to high outputquality, low switching frequency, easy modularity and flexible control. However, the existing MLDCLinverter has the disadvantages that the topologies and modulation method of MLDCL inverter are toocomplicated, and their DC unit is difficult to boost, which would affect the system performance.This dissertation focuses on the structure and modulation method of MLDCL inverter topologies.The main contents and innovation of this dissertation are as follows:The design method of MLDCL inverter circuit topology is discussed. Then, a novel HybridMLDCL inverter is presented, which has the advantages of high quality waveform and less devices.This dissertation analyzes the causes in solving nonlinear transcendental equations existingSHEPWM by the Newton-Raphson algorithm. Then, the selection methods for initial values and thecalculation method of Newton downhill method with the advantage of wider convergence range forcalculating the SHEPWM equations are designed. And an improved Levenberg-Marquardt iterativealgorithm is presented, which avoiding the disadvantage of singular or pathological in Newton downhillmethod, by forcing matrix positive definite. A novel PSO method is designed for solving SHEPWMequations to overcome the difficulty of matrix inversion and initial selection in numerical method.For the output power of DC units are unequal with each other in the MLDCL inverter, a method ofSHEPWM based on power balance control is designed. It achieves the result of wide range of powerbalance in half period, by adjusting the control angle of DC unit.In order to overcome the shortcoming of SHEPWM based on power balance control, a new SPWMmethod based on power balance control is described. The proposed method can self-adjust to achievebalance charge control without a complex circuit or calculation.To resolve the problems of DC unit unable to boost, an improved MLDCL inverter based Z-sourceis proposed. Additionally, a SPWM method with high reliability, high gain, continuous current isdesigned.