Research On Power Stabilizing Control Of Grid-connected Photovoltaic System Based On Hybrid Energy Storage

With the decreasing of fossil fuel, development of renewable energy is swift. But the defects emerged. Among the renewable energy, solar energy has been used widely. Due to the influence of the intensity and time of the sunshine, the output power of PV generation is fluctuating. Therefore, there are still some problems in PV technology. In this paper, aiming at the power fluctuation caused by intensity of the sunshine and changing temperature, an energy storage-based grid-connected photovoltaic (PV) power generation system is proposed to overcome the grid-connected power fluctuation. On the basis of Maximum Power Point Tracking (MPPT) and grid-connected DC-AC conversion, a hybrid storage system which includes lead-acid batteries and super capacitors is employed to smooth the grid-injected power of PV.Firstly, this thesis focuses on the comprehensive control strategies in single-stage grid-connected PV system, and carries on a thorough research about the modeling of PV arrays, maximum power point tracking technology, the topology and modeling of the single-stage grid-connected PV system. This paper proposed a variable step MPPT strategy, and this strategy has more advantages when compared with fixed step MPPT algorithm:faster response speed, more accurate optimization process, and it can avoid the oscillation of the system caused by MPPT better, and so on. Aiming at the control strategy of PV grid-connected system, space vector pulse width modulation (SVPWM) is used to generate the trigger signals, the method has the advantages of low harmonic contents, high utilization rate of DC voltage. The paper ultimately determined the control strategy based on SVPWM in grid-connected PV system.Secondly, by comparing the advantages and disadvantages of various energy storage technologies, the hybrid storage system consisted of the batteries and super capacitors is chosen. The idea using the hybrid storage system as the storage of stand-alone PV system is proposed to optimize the charging and discharging process of batteries. The hybrid energy storage system has three kinds of connection modes, the paper uses an active type parallel scheme through power converters. In order to realize target that uses the energy storage system to stabilize the fluctuation of PV output power, and to improve the service life of the battery, a unified control design method of parallel controller and charging controller is adopted; Considering the effects of the independent PV system capacity and outside weather, the capacity of super capacitors and batteries is designed, and the optimum design method under different conditions is given; The control strategy for proposed hybrid storage system is verified by simulation and experiment.Finally, the idea that uses the hybrid storage system as the storage of grid-connected PV system is proposed, and the control strategy of mix energy storage system based on the bidirectional DC-DC converter is established. The bidirectional DC-DC converter is designed for different operating modes, in order to change the power flow, and to realize the power exchange of super capacitor and battery. The theme of this paper is chosen based on the10kW PV-hybrid storage generation demonstration project of CHINA EPRI SCIENCE&TECHNOLOGY CO. LTD. In the end, the parameters of composited equipments, control strategy and control system of the system are introduced. Through the practical application of engineering, the mix storage energy system suppressing the fluctuations of PV power is verified to be correct.