Research On Several Key Technologies Of H-bridee Based Combinatorial Topology

Optimizing topology for equipment is an important and energetic research topic in the power electronics subject.Combinatorial topology is one of the most significant part in this research area.By implementing transformation and reconfiguration for the existing topologies,the performance of combinatorial topology gets improved and the defects of existing topologies are avoided.Even though the system complexity increases after topology combination,the advantages about combinatorial topology,such as excellent modular structure,power handling decentralization,performance improvement,highly redundant design and easy expansion,still make it possess high value for research and application.H-bridge is one of the most important basic unit in the combinatorial topology system.It has advantages of simple construction,strong universality and large potential on extension,which is able to implement the function of DC/AC or AC/DC conversion.This thesis chooses H-bridge as the entry point of combinatorial topology,focusing on some key points such as modulation strategy,system efficiency,stable operating condition,hardware design and so on.Some innovative opinions and application solutions are put forward related to combinatorial topology based on H-bridge.Cascade H-bridge(CHB)multilevel converter is a typical application of H-bridge in the combinatorial topology.First,the topology structure,operation principles and modulation strategies of CHB are introduced.Secondly,the application of H-bridge mode exchange strategy is analyzed in the CHB.However,the extra switching times may appear during the process of H-bridge mode exchange.The circumstances of H-bridge mode exchange are discussed and the root causes of the extra switching times are summarized.In order to solve this problem,an exchange strategy based on consistent switching sequence is put forward.This modified strategy can eliminate switching times caused by H-bridge mode exchange totally and improve system efficiency without impact on the system output.Finally,effect and feasibility of the proposed strategy is verified by experiment.Hybrid cascade multilevel converter is another important application of H-bridge in the combinatorial topology.T2C-HB is analyzed as an example of hybrid cascade multilevel converter.First,the topology structure,operation principles and switching sequence of T2C-HB under seven-level working mode is introduced.Secondly,mathematical expressions of stable working conditions are deduced based on sinusoidal pulse width modulation(SPWM).The results show that floating capacitor voltages are balanced only when the modulation index is less than 0.82 in any power factor load.Based on this results,hysteresis control and conduction path chosen method is utilized for capacitor voltage balance.In order to extend stable working conditions,Space-vector-modulation(SVM)is applied for this seven-level T2C-HB.A capacitor voltage regulation method based on cost function is put forward which can be used together with SVM to enlarge the conditions of capacitor voltage balance.Meanwhile,the efficiency of DC voltage is also improved.Based on the research about seven-level T2C-HB,other working mode of T2C-HB is also discussed.The advantages and disadvantages of five-level mode,seven-level mode and nine-level mode are summarized.In the aspect of dc voltage utilization,the maximum dc voltage utilization ratio is analyzed for five-level mode and seven-level mode.The improvements of dc voltage utilization ratio of five-level mode-and seven-level mode are calculated compared with two-level inverter.Finally,simulations and experimental results are presented to verify the conclusions illustrated above.In the field of DC/DC combinatorial topology,this thesis chooses Multiple Active Bridge(MAB)as a research object.A topology called Magnetic Coupling Multiple Active Bridge(MCMAB)is analyzed.First,the structure of MCMAB is introduced.MCMAB is able to reduce the port quantity in the secondary side of isolated transformer and increase system power density.Secondly,equivalent circuit model of MCMAB is introduced.The topology's operation principles and soft-switch conditions are analyzed.In addition,in order to solve the problem of capacitor voltage drift,a voltage regulation strategy based on inner phase angle shift is introduced.The relationship about inner phase angle and capacitor voltage is deduced in theory.This method brings a new conception for capacitor voltage balance,which has advantages of simple structure and good scalability.Finally,the feasibility of the MCMAB and capacitor voltage control strategy is verified by simulation and experimental results.In a word,several novel ideas and solutions about combinatorial topology based on H-bridge are provided in order to achieve some improvement on the performance and the practical implemention,which enriches the research work of combinatorial topology.In addition,some research results presented in this paper are easily extensible which are also suitable for combinatorial topologies composed of other basic units.