Research On Control And Capacity Optimization Of Hybrid Storage In Grid-Connected PV Station

With the rapid development of global economy, disposable energy is consumed quickly, which giving rise to worldwide energy crisis and environmental pollution. Distributed energy, especially the massive application of solar power, is the most effective ways to solve the current energy and environmental problems. Solar energy, with great randomness, intermittence and viability, affects the power distribution, output schedule and even operation safety.Using storage device at PV station side, so as to cooperate with PV station to connect to power grid, can solve the randomness and intermittence on a large scale. The smoothness of PV output, the promotion of absorption ability, stability and power quality of power grid is then achieved. Energy-style storage device is suitable for long-time response and power-style storage device is suitable for quick response. Only hybrid storage has the merits of the both. So, it is critical to research the control and optimization strategy of hybrid storage. This thesis is studied and discussed from the perspective of characteristics and model of each components in the grid-connected PV station, the control of inverter, control strategy of hybrid storage and capacity optimization of hybrid storage in large scale PV station.(1) The components and topology structure in grid-connected PV station is proposed, and the advantages and disadvantages of different hybrid storage access methods is analyzed. The characteristic of photovoltaic battery, lithium battery (Li) and supercapacitor (SC) is analyzed and modeled and the basic topology structure of Boost converter, Buck/Boost converter and inverter is also given.(2) The control object, principle and control block is analyzed, and power control, PI current control and phase-locked loop is designed. Its validity is proven through simulation. A SC voltage based control scheme is proposed, which decides the respective operation status of Li and SC and control the charge-recharge recycle precisely according to the voltage of SC and charge-recharge status. The target of prolong the service life of Li and rational utilization of storage device is achieved. Simulation has verified the feasibility of the control scheme, and the stabilization of transfer power is analyzed.(3) When it comes to the optimization of hybrid storage capacity in grid-connected PV station, neither statistics method nor HOMER software can solve the problem perfectly due to their drawbacks. So a comprehensive optimization scheme, which integrates HOMER and statistic method, is proposed. The rational optimization of hybrid storage capacity is based on two-stage. HOMER simulation figures out the power capacity and energy capacity of Li, completing the first-stage optimization. Chance constrained programming is then applied to the capacity of Li, suitable SC capacity is then allocated under certain confidence level through genetic algorithm, completing the second-stage optimization. Thus the storage optimization is achieved.(4) Environmental parameters, operating parameters and economic parameters is accessed from Internet database. Daily output power of PV is obtained from4.5kW PV panel and monitoring gateway of PV energy. Then, tens of typical transfer power reference of3MW PV station is deduced. HOMER can figure out the optimal solution from all the possible combinations under the precondition of lithium battery-only. Since the parameters of lithium battery is known, the power capacity and energy capacity of system can be calculated. Under different confidence level, chance constrained programming is solved by genetic algorithm, which allocates the respective power capacity and energy capacity of Li and SC. Capacity optimization is completed after choosing the optimal economic schedule. The influence of sensitivity variables, such as illumination intensity and Li lifespan, on the long time operation of PV station are analyzed at last.