Research On Control Of Energy Storage Used For Microgrid With Photovoltaic Generation

With the support of policy and development of technology, renewable energy develops quickly, especially wind power generation and photovoltaic generation (PV). Distributed generation and microgrid are important ways of renewable energy application. Distributed generation, especially microgrid, can avoid some negative effects of grid-connected large-scale renewable energy generation to power grid, at the same time, plays an positive role in improving power supply reliability and power quality, and so on. Mcrogrid has many advantages, such as independently controllable, flexible work mode and efficiently adjusting distributed renewable energy generation, and so forth. Therefore, application of distributed renewable energy generation and microgrid, which show efficient utilization of renewable energy generation, reveals great practical significance.Microgrid may contain intermittent and random renewable energy generation, therefore, microgrid shows power fluctuation when works on grid-connected and isolated grid. When microgrid is connecting sensitive load, and power grid is working abnormally, continuous power was to ensure supplying to sensitive load. Furthermore, when microgrid is working on isolated grid mode, microsource needs to support of reference voltage source. The problems above have different performance, but the solution depends on balance control of power. And energy storage technology is an important way of power balance and keeping normal work of microgrid. The application of energy storage needs to solve some key technology problems, such as economic energy storage capability configuration in relation to economic operation of microgrid, control strategy of restraining power fluctuation, control strategy of energy storage as voltage source support when microgrid is working on isolated grid mode, and control strategy of energy storage as fulcrum of dual mode transfer control of grid-connected, and so on. The paper is mainly about research of these key technology problems.Firstly, the paper analyzed energy storage configuration scheme in microgrid with photovoltaic generation. According to power exchange relationship of microgrid and power grid, it got relational expression of restraining power fluctuation, stabilizing power exchange of microgrid and power grid. Based on ideal of controllable power exchange of microgrid and power grid, it proposed a method of energy storage capability configuration, considering PV prediction error and load short-term prediction error. By distribution characteristics researches of PV and load short-term prediction error, it got that energy storage power configuration accords with normal distribution. According to nature of normal distribution variance, it showed that centralized energy storage configuration was more economic than dispersed one. Interval of energy storage power configuration in microgrid at confidence level was calculated by interval estimation. And then, according to stochastic process theory and relationship between power and capability, reference interval of energy storage capability configuration was gained. The proposed method was applied in capability configuration of practical energy storage system. And configurated energy storage system used in microgrid with PV for restraining power fluctuation.On the basis of research of energy storage capability configuration in microgrid, the paper designed microgrid system with PV and energy storage called as stability controller in microgrid, and optimized main circuit parameters of stability controller. Based on analysis of the influence of internal resistance to discharge characteristic of Li-on battery, a topology and control strategy of energy storage constituted by Li-on batteries replaced from electric vehicle was proposed. Energy storage capability of stability controller was configurated by the method described in the paper. After design of main circuit, the work was accomplished, including design of signal sampling and processing and control system of stability controller, and design of monitoring center of microgrid.According to functions of microgrid working on grid-connected and isolated grid, PQ decoupling control strategy of grid-connected mode and V-f control strategy of isolated grid mode and control strategy of dual mode transfer were analyzed, and control strategy of stability controller based on given sine table reference was proposed. Furthermore, the proposed control strategy could renew reference modulation wave in the control way of PQ decoupling or V-f, and seamlessly transfer to another working mode according with current status of reference modulation wave when dual mode transfer control is needed. The efficiency of three operating modes above has already been verified by Matlab. The proposed control strategy was applied in stability controller of microgrid, and was validated by experiment results in practice.Stability controller parallel works with PV when microgrid works on isolated grid mode. The paper analyzed voltage fluctuation of equivalent connecting reactance of stability controller which was arose by sudden change power of PV and load. And the relationship between output/input powers of stability controller and voltage fluctuation was provided. With amplitude constraint of reference voltage of connecting points for PV, the power supplied by stability controller for keeping voltage of points of common connection was analyzed. Meanwhile, influencing factor of dynamic response was analyzed when voltage of points of common connection was being adjusted by stability controller, and the solutions of reducing influence of dynamic response was put forward. The analysis conclusion has some certain reference meaning for design of stability controller equivalent connecting reactance and increasing capability of PV in microgrid.