| Recent years,with the rapidly development of renewable energy resources,those problems caused by the traditional power generation technology,such as energy shortage,environmental pollution and the emission of greenhouse gas,had been effectively improved.Compared with the traditional power generation,those renewable energy such as solar energy and wind energy usually are determined by the environmental factors,thus with a poor stability and robustness.At the meantime,the structure of modern power grid also has been obviously changed with the connection of quantity nonlinear loads.In order to resolve the stability problem resulted by the connection of renewable energy and nonlinear loads,the modern power grid paralleled with energy storage systems was proposed on time.Thus,it’s a focused theme in nowadays research how to connect the energy storage systems with modern grid effectively and guarantee the operational stability.Dual-active-bridge(DAB)converter is the most wildly used in the current bidirectional DC-DC applications,with the advantages such as simple control strategy,wide soft switching range,high power density and so on.With various control strategies,how to make an optimal strategy in different conditions is also need to be studied.Moreover,the application of high frequency transformer also introduce the potential risk of magnetic saturation.Meanwhile,connected with the AC micro-grid,the energy storage system needs a complex algorithm and topology to realize soft switching in the inverter.Aiming to resolve above problems,this thesis thoroughly studied different control strategies of DAB converter,and proposed a prediction method of DC bias in DAB converter.What’s more,based on the above analysis of control strategies,this thesis proposed an inverter topology,which can be thoroughly operated under soft switching condition.At last,all the above analyses and proposed strategies were verified by the simulation and experiment results.First,this thesis made a summary about different optimal strategies of DAB converter,and analyzed several methodologies on how to analyze the strategies under various conditions.Different optimal control methods had been concluded for different targets such as minimum current stress,minimum reactive power,and wildest soft switching range.The transient responsible performance for DC-bias in high frequency transformer,dead time effect,surge current,and dynamic response were concluded in this thesis.Moreover,those various extended topologies based on dual-active-bridge were analyzed.The development of DAB converter in the future and the research direction were introduced at last.And then,the reason and related calculation about the DC-bias in high frequency transformer were analyzed in detail,and the prediction for the DC-bias caused by unmatched drive signals and inconsistency of devices was proposed.By this way,the high frequency transformer won’t be saturated if the permitted value always has a large scale than the maximum DC-bias.Compared to other active method to keep magnetic balance,the proposed method don’t require special topological design,conducting to lower expense and smaller volume.At last,based on the above research on control strategies,this thesis proposed an inverter topology,which could be operated under thorough soft switching condition.Cascading a switch with the capacitor on DC-link between DAB converter and inverter,the DC-link voltage could be got as 0V during the inner phase shift of the shoot-through phase-shift controlled DAB converter,and the zero-voltage-switching condition of inverter can be realized.The detailed topology and control strategy of proposed inverter were analyzed in this thesis and the validity of the proposed above were verified by simulation and experiment. |
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