| With the development of new energy,distributed generation and microgeneration equipment are required to be able to access microgrids flexibly and efficiently.At the same time,loads of microgrids tends to have more frequency converters.Microgrids gradually form three patterns,namely,AC microgrids,DC microgrids and AC and DC hybrid microgrids.Photovoltaic power generation and chemical energy storage equipment used to balance the renewably energy output can be connected to the grid directly in the form of DC.Thus,the AC/DC conversion is not needed,resulting higher power generation efficiency and simpler grid connection effort.The wide voltage range of DC/DC conversion can also benefit the echelon utilization of batteries.Meanwhile,the DC power supply for frequency variation loads can eliminate the rectification part in the frequency converter,improving the power consumption efficiency and reducing the cost.Bidirectional DC/DC converters can realize voltage conversion and bidirectional energy flow simultaneously.They can be used as the conversion equipment of photovoltaic power generation in DC microgrids and the charging/discharging equipment to connect the energy storage batteries.This thesis analyzed the characteristics of several basic bidirectional DC/DC converter topologies and studied their working principle,advantages and disadvantages.In order to solve the problem that the current through components in high-power single-phase bidirectional Buck-Boost converters is relatively large and high current quality control is relatively difficult,the topology,operation principle and control method of the three-phase interleaved bidirectional Buck-Boost DC/DC converter are studied in detail.The working states and control characteristics are analyzed through the mathematical model and the power loss model of system components is built and simulated.Based on the traditional control strategy of voltage outer loop and current inner loop control,the control strategy of outer loop voltage control and inner loop three-phase inductance current independent control is proposed.The output voltage can be stabilized and the three-phase inductance currents can be balanced while the total current is stabilized.This can reduce the current circulation within three phases,improve the working efficiency and prolong the lifetime of the equipment.In order to design and manufacture a 60 k W non-isolated bidirectional DC/DC converter,the main circuit parameters including the selection of power switches,inductance and DC bus capacitor are designed in this thesis.The control circuit of the converter is analyzed in detail,including the control circuit power supply,DC voltage and current sampling and conditioning circuit,IGBT drive,overvoltage and overcurrent protection circuit,etc.The module structure and heat dissipation structure of the power circuit are also analyzed and designed.The software architecture of the converter control system is designed and programmed,and the programming methods of several main functionalities such as A/D sampling,PWM interrupt control and fault interrupt control are described in detail.Based on the research and design of three-phase interleaved bidirectional Buck-Boost DC/DC converter,a 60 k W experimental prototype is manufactured and tested.The tested equipment is used to charge and discharge the energy storage battery pack.The problems during the debugging process are analyzed in detail and the methods and strategies proposed in the thesis are verified.The expected effect of engineering application is achieved through refinement. |
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