The New Modular Multi-level Inverter Design And Research

An inverter is a DC-AC power converting device, which is widely used in many fields such as new energy source power generation, AC electrical drive, UPS, frequency converter etc. Traditionally, the output PWM pulse wave of the inverter contains only 2 levels. Thus, a high common mode voltage as well as a high du/dt could be existed in the system, both of which will put a threat to the insulation of the motor windings. Besides, the design of the output filter is comparatively complicate due to the high THD (Total Harmonious Distortion). In order to find a solution to these questions, the multilevel inverter is introduced.The output PWM pulse wave of a multilevel inverter contains several levels. Thanks to its lower THD and common mode voltage, it can perfectly be applied to power electronics systems with high power capacity and has become one of the new focuses of research in power electronics.In the paper, we analyzed both the topology and the control schema of multilevel inverter. A new concept named "Multilevel Building Blocks" was put forward by means of expanding the existing concept of "Power Electronics Building Blocks". Then, two kinds of new topology were introduced based on this new concept. According to their features, we put forward a SHEPWM schema especially for these topologies. After software simulation and hardware experimentation, we came to the conclusion that these topologies can work efficiently once properly controlled and the SHEPWM schema for these topologies can control these circuits by eliminating several selected harmonies in their multilevel output waves. Comparing with several traditional multilevel topologies which produce the same output voltage levels, the circuits of new topologies is simpler and the system efficiency is higher.In detail, the principle and features of several existing multilevel topologies are analyzed. The so-called Symmetric Full Bridge (SFB) and Asymmetric Full Bridge (AFB) topologies and their combined N-phase topologies are introduced.The control methods of multilevel inverter such as multilevel carrier PWM, multilevel space vector PWM are also analyzed in the paper. A SHEPWM schema...