Research On System Architectures And The Key Technologies Of Power Interfaces For DC Distributed Power System In Buildings

Nowadays,the electric energy consumption of the buildings has taken more than one third part of the total electric energy consumption of all over the world,so it is indispensable to research the energy saving technology for buildings and to develop the green buildings.What's more,the solar energy,which is a clean energy with abundant reserves,is one of the most important energy for the power systems of green buildings.Therefore,the DC distributed power system with photovoltaic power has become an important trend for the power systems in green buildings.The study of the DC distributed power system is also quite meaningful for promoting and popularizing the technologies of DC power.This thesis takes the DC distributed power system with photovoltaic power in buildings as the research object.For different architectures of the DC power system,the energy efficiency is analyzed and compared and the key technologies of the main power interfaces are studied,such as the efficient topologies and the reasonable control strategies etc.,which can lay a certain foundation for establishing the testing system of the DC distributed power system with photovoltaic power in green buildings.The following are the major contents of this thesis.1.Based on the calculation method by analyzing the paths of the input and output energy,the efficiency of different architectures of the power system in buildings are analyzed.That is,the efficiency of the architecture of the conventional DC system with fixed bus voltage,the architecture of the DC system with battery bus,the architecture of the DC system with photovoltaic bus and the architecture of the traditional AC system are analyzed and compared.The results show that for the energy utilizing of the solar and battery energy,the architecture of the DC system with battery bus and that with photovoltaic bus are better than the conventional DC system with fixed bus voltage,the architecture of the traditional AC architecture shows a comparatively worst result.The proposed analysis and calculation method can be used for evaluating the architecture of the power system in buildings.2.In the research of the photovoltaic interfaces,for the conventional DC system with fixed bus voltage(350~400V),the two-switch Buck-boost converter with coupled inductor is studied,which is used for the photovoltaic cells of centralized application;the Current-Fed Half Bridge converter is studied,which is used for the photovoltaic cells of modular application.For the two-switch Buck-boost converter with coupled inductor,an asynchronous modulation method which can improve the efficiency is proposed as well as the control strategy that can fulfill the requirements of photovoltaic interface.For the Current-Fed Half Bridge converter,an optimized design method which is considered with the efficiency,the power density and the power envelopes of photovoltaic cells is proposed.The proposed control strategy for the Current-Fed Half Bridge converter not only can fulfill the requirements of photovoltaic interface,but also can solve the problem for soft-start and controlling the output voltage on light load conditions.The experimental studies are implemented for the above two converters,which verifies that the proposed control strategies are corrected.Based on the aforementioned work,the two-switch Buck-boost converter with coupled inductor is taken as an example to discuss the parameter design method and the control strategy for the architecture of DC system with float bus voltage(which is mainly referred to the DC system with battery bus,260~400V),the differences on this converter between the two DC architectures are analyzed.The results show that the parameters of the converter for the two architectures have a certain difference,but they can be applied with a similar control strategy.3.In the research of the energy storage interface,the Bi-directional Current-Fed Half Bridge converter is studied,which is used for the energy storage interface with only the battery;a new Multi-Ports converter derived from the Bi-directional Current-Fed Half bridge converter is studied,which is used for the energy storage interface with both the battery and the super-capacitor;the power relationship,the soft switching conditions(ZVS conditions)and the control strategy are analyzed.The control strategies are also proposed,which can realized ZVS conditions with matching the voltage of two sides of the transformer in the above converters,and can fulfill the requirements of energy management for single or mixed storage devices respectively.For the application of modular energy storage converter,a Current-Fed Half Bridge converter with two transformers is studied.When make the output of the two circuits with transformer series,the converter can be applied to the DC power system with the bus voltage up to 600 V.The experimental studies are also implemented for the above converters.4.In the research of the grid interface,based on the research of the full bridge converter for grid interface,a Bi-directional AC/DC converter with two stages,that is,the Full Bridge circuit cascaded with the Dual Active Bridge circuit is studied for the architecture of DC system with float bus voltage(260~400V).The operation and the control strategy of the two stages are analyzed.For the Dual Active Bridge stage,the power relationship and the ZVS conditions are analyzed,then a coordinated control strategy is proposed for the converter with two stages.The simulation and experiment results show that the bi-directional AC/DC converter with two stages can make power transferred from the AC grid to the DC system in two directions.By detecting the power conditions,the proposed control strategy can change the mid-bus voltage to change the operation conditions of the two stages,which can be helpful for improving the efficiency.The studies obtained in this thesis,that is the efficiency analysis method for different architectures of power system,the main topologies and the control strategies combined with multi-functions for different power interfaces,can be a certain reference for the studies of the DC distributed system which can use the photovoltaic power,the storage power and AC grid power reasonably and efficiently in buildings,and for the studies of the main power interfaces which apply to different architectures of DC system.The studies in this thesis also can lay a certain foundation for establishing the testing system of the DC distributed power system,and the research of the DC distributed power system in buildings.