An improvised algorithm for capacitor voltage balancing of symmetrically cascaded floating capacitor H-bridge inverter

摘要

Symmetric cascaded floating capacitor H-bridge converters where the voltages of each capacitor stage is half the previous stage have several advantages like improved reliability, single DC supply etc. These converters have gained popularity in recent past. Control of this type of converters needs a huge lookup table to generate the switching states which have to be extracted manually based on the demanded level, current direction and capacitor voltages using an iterative process. As the number of levels increase, entire look up table has to be redeveloped iteratively which makes scaling of these power converters difficult. This paper presents a detailed analysis of the capacitor balancing algorithm along with a novel control algorithm that can be scaled for any level converters of this genre. This algorithm can be realized with simple logic gates and does not need any look up table. Also more number of capacitor stages can be added later with little modification of the capacitor balancing algorithm. The controller is realized and experimentally verified on a three phase 5-level inverter and the results are compared with look up table based converter. The proposed control algorithm has several advantages like modular scalability, being non-iterative, ease of implementation etc.