Translated Abstract
The facts including the extensive access of new energy and the growth of non-linear loads have brought new challenges to the tranditional grid structure based on alternating current. The concept of Energy Internet suits these changes and has been widely researched. The key equipement in this concept is called Power Router, which takes Solid State Transformer (SST) as the core. Dual Avtive Bridge (DAB) converter plays an important part in SST. In an SST composed of multiple DAB-containing sub-modules, the serial and parallel balance control as well as the power flow control is quite a crutial problem. Therefore, it is meaningful to improve the performnce of DAB by designing its control system properly.
To reach this goal, we need to establish an accurate DAB math model. This thesis begins with introducing DAB working principles under various sorts of modulation modes, using conventional analysis method as well as voltage current decomposition method, and derives the expressions of average transfer power. Then tranditional state space averaging method is applied to DAB modeling, which explains the limitation of this method. After that, the study of the various existing DAB math models, as well as the comparioson of their advantages and disadvantages, makes it clear that these models are hard to statisfy low-frequency accuracy, high-frequency accuracy and ease of use simultaneously. To get a math model that is more accurate and more easy to use, this thesis improves the generalized state space averaging method and proposes an odd-harmonics-approximation method for DAB. The accuracy of the new model is verified by MATLAB and PLECS software tools.
Based on the proposed DAB math model, this thesis designs its control system. Firstly, the modulation strategy satisfying the optimization conditions under both light and heavy load circumstances is determined. Then, the control strategy of PI controller is designed, and the parameters of the controller are further optimized according to the odd-harmonics-approximation math model and frequency domain analysis . Simulative and experimental results are given to verify the validity of the designed control system.
This thesis also introduces the 10kV-1MW SST produced by TBEA, including its modular topology structure, its control strategy based on voltage balance control among modules using DAB, and its layered control system architechture. The experimental waveforms of the whole machine is showed in this thesis. As an application of DAB control system design, this thesis proposes the redundancy fault-tolerant control strategy of SST, which has been applied in the SST prototype.
Translated Keyword
[Controlle system design, Dual active bridge, Mathematical modeling, Redundancy fault-tolerant control, Solid state transformer]
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