Research On Design And Simulation Of PV Charging Station With Energy Storage

With the rapid development of the industry in the world, conflict among the society economy, the environment and the energy is increasingly prominent, has became a key factor restricting the sustainable development of human society. Photovoltaic power generation and electric vehicles are obvious regenerate with environment and economic benefits, as a reason of a substantial increase on the technology advances in energy storage, intelligent level of power grid and ownership level of electric vehicles in the future, the research and construction of a new(PV-storage) type electric vehicle charging station is of vital significance.In this paper, a new type PV charging station with energy storage has been researched mainly on the structural design and simulation analysis, including the basic parts of charging stations, the structure and control of DC/DC and AC/DC converters, the design and coordination control of PV Charging Station and improved droop control, details as follows:Firstly, photovoltaic systems, Li FePO4 battery and flywheel energy storage systems are introduced with their mathematical principle analyzed and simulation modeling carried out. Where perturbation observation is used to MPPT control of PV, two methods called Thevenin and exponential curve mechanism are compared for modeling of LiFePO4 battery, two modes of operation, free power store-consume and idle charge-discharge, are set for the flywheel control, all of which can achieve desired effects.Secondly, the topologies, mathematical models and control strategies of DC/DC and AC/DC converters are recommended. As for DC/DC, the control strategies of constant current charge in stage and limited current discharge have been designed refer to the battery charge and discharge strategies; constant voltage control strategy called CVC has been designed to achieve stable control of the voltage output of PV converter. As for AC/DC, three control strategies of PQ control, U/f control and Droop control are described and simulated for the inverter operating mode.Thirdly, after designing the basic structure of an electric vehicle charging station with PV power and energy storage, the functions of each parts in it have been introduced. The flywheel and battery energy storage are presented to the systems as a form of hybrid energy storage, when the bus voltage is support by the energy storage, flywheel smooth high-frequency power fluctuation and some low-frequency power, battery maintain the voltage of DC bus smooth stable by balancing system power in baseline. A hierarchical coordination control based on the DC bus voltage of 5 layers is designed to achieve optimal operation of the charging station, a central control structure for it is also introduced. A simulation systems of the charging station is built to verify in different conditions.At last, in the situation of this type EV charging station connected into the power micro grid as a DG, a power coupling based on SOC improved droop control is designed, which can improve power allocation within charging stations and other DG according to the SOC change of the charging station, when in a lonely island mode; switching in micro grid on-grid and off-grid dual modes, smooth transition can be realized combined with the corresponding change of on-grid power output under PQ control and pre-synchronization of droop control. Quasi PR control is used to track the reference signal fast and no errors for voltage inside controller. And a simulation comparison has been carried out.