Improvement and implementation of a new modulation technique for grid connected multilevel converters

Due to its nature of easier controllability, two level converters, which are the most basic type of converters in power electronics, are generally the first choice of use. In order to lower the THD generated by these converters, their switching frequency is increased. As a result, system efficiency decreases. By immigrating to multi-level converters, it is possible to increase the efficiency of a grid connected system without increasing THD. Despite the advantages introduced by these converters, system complexity is increased due to the fact that the number of power electronics elements to be controlled is increased. Additionally, provided that the neutral point balance is not considered, system reliability becomes degraded inevitably. In this thesis, mathematical method of a new generalized space vector modulation calculation algorithm is proposed for two or higher level converters by utilizing conventional two level space vector modulation. In this proposed method, system design simplification of a multi-level converter is achieved by making the design at the degree of a two level converter without increasing the utilization of system resources. To replace conventionally utilized two level topologies, a grid connected three level converter design and implementation has been realized in order to demonstrate the fact that with the application of simplified space vector modulation, even three or higher level converters that have not become widespread, due to their complex nature of controllability, could be controlled easily. Before the design of three level converter was realized, a two level converter had been built so that it could have been possible to illustrate hardware and software differences between the two level converter itself and the three level converter. When compared in terms of hardware structure, design resources that will be spent to realize a three level converter will not be more than that of a two level converter Software developed for the two level converter spends 88-90 μs during one switching period (125 μs) whilst software developed for the two level converter spends 98-100 μs during one switching period (125 μs). It is possible to see that the proposed new generalized space vector modulation calculation algorithm for two or higher level converters by utilizing conventional two level space vector modulation in this thesis spends only 10 μs more during one switching period when compared with the software developed for the two level converter with conventional space vector control scheme. The time spent for neutral point balancing algorithm is inclusive to the aforementioned time difference.