Research On Frequency Control Strategy Of Large-scale Grid-connected Photovoltaic Generation

With the increasing of fossil energy consumption, every country faces more and more serious energy crisis. The key to resolve the crisis is to decrease the fossil energy consuming during industrial production. The renewable energy source, represented by photovoltaic (PV), is drawing people’s attention because it does not need any fossil energy and it is environmental friendly during power generation. Recently, with the rapid growth of PV industry, more and more large scale concentrated grid-connected PV stations arise. When the PV stations connect to the grid, the stations would bring tremendous impact on the grid frequency because of the large power proportion of these stations to the grid. This thesis has systematically studied the key technologies of large scale PV stations grid-connecting which focusing on the frequency fluctuation and frequency control strategy. Also, the model of large scale PV station grid-connecting is also proposed.Based on the analysis of key technology of PV station grid-connecting, the thesis put forward the moving cloud model under climate conditions. The model simulates the active power output fluctuation of PV array caused by the movement of shadow and the fluctuation curves of power output and frequency could be obtained by the model. According to amplitude, the fluctuation could be classified into two types, namely sharp severe fluctuation and slight concentrated fluctuation respectively, and the active power frequency modulation strategies of the two types of fluctuation are proposed. For the former, the feedback frequency active power frequency modulation strategy is put forward and its innovation lies in the regulating PV power point tracking control algorithm. In the algorithm, the reserve capacity of PV array is set and the PV power output could be regulated by power point tracking the fluctuation of frequency to lower the PV array active power sharp fluctuation. For the latter, the storage system active power frequency modulation strategy is proposed. The super capacitor (SC) is selected as the storage equipment and its topology structure is designed specially. The active power difference between two adjacent sampling points of DC-bus power fluctuation curve is chosen as the input of control part. The output of SC is controlled to decrease the slight concentrated fluctuation of PV array output.To verify the effectiveness of proposed control strategies, the grid-connected PV array and active power frequency modulation strategy are modelled based on MATLAB-Simulink platform and the curve of PV active power output fluctuation with moving shadow and the curve of PV power output after using power frequency modulation strategy are obtained. The comparison result indicates that the strategy could decrease the fluctuation of PV array active power output and it could also meet the demand of stabilizing the frequency when large scale PV stations are introduced in the grid.