Research On The Topology Analysis And Control Strategy For Hybrid AC/DC Microgrid With PV And Battery

Developing renewable energy sources has become a global energy strategy, and microgrid is the most effective way to improve the flexibility and controllability of renewable energy. With the rapid development of the smart grid and digital society, a single AC or DC microgrid has exposed shortcomings on control and energy efficiency. Therefore, hybrid AC/DC micro-grid has emerged and attracted extensive attentions and studies at home and abroad.Firstly, the topologies of hybrid AC/DC microgrid are analyzed, and the grid structure planning principles and processes of hybrid AC/DC microgrid are summarized and proposed in this paper. The grid structure of hybrid AC/DC microgrid is classified into four typical structures whose advantages, disadvantages and applicabilities are discussed. Then, the grid structure evaluation indices of hybrid AC/DC microgrid are summarized and proposed which can evaluate the reliability, economy and safety of the designed structure. For the structure design of the demonstration project, the voltage level, the bus structure and the grounding of hybrid AC/DC microgrid are designed on the basis of extensive research. Meanwhile, the economic evaluation of the voltage level of DC subsystem and the safety evaluation of the grounding of DC subsystem are provided.Secondly, the simulation models of photovoltaic cell and energy storage battery are established. The simulation results are presented to verify its characteristics. According to the different control purposes of photovoltaic power generation in AC and DC side and energy storage battery charge-discharge control, the adaptive control strategies are studied. In order to solve the problem of large source-to-load ratio of DC side in demonstration projects, and improve the utilization of PV, the coordinated control strategy for hybrid AC/DC microgrid with PV and battery is proposed. In grid-connected operation, voltage of DC bus is controlled by battery, and the P/Q control strategy is used in the bi-directional AC/DC converter which transforms the surplus PV power from DC side to AC side. In islanded operation, voltage of DC bus is also controlled by battery, and the V/f control strategy is used in the bi-directional AC/DC converter which controls the voltage and frequency stability of AC bus based on battery. The PCC is set to send out switching signal in this paper. In order to achieve the switch between different control strategies, just the outer ring of bi-directional AC/DC converter is changed.Finally, the simulation model of hybrid AC/DC microgrid with PV and battery in PSCAD/EMTDC is established. The simulation results are presented to verify the validity of the coordinated control strategy for hybrid AC/DC microgrid with PV and battery.