Research Of The Reactive Power Voltage Optimization In Large-Scale PV Plant

As the penetration of photovoltaic power generation increases rapidly in recent years, the voltge and reactive power problems between photovoltaic power generation and the grid is increasingly outstanding. Large-scale photovoltaic plants should have the ability to regulate the voltage and reactive power independently, and if necessary it shoud participate in reactive power regulation of the power system. On the other hand, with the photovoltaic plants developing to a larger scale, the voltge and reactive power problems in the photovoltaic power plant is gradually emerging. So in order to ensure the photovoltaic power plants operate safely and stably, it is necessary and meaningful to study the mechanism and influencing factors of voltage fluctuation in the photovoltaic plants and catch up reactive voltage optimal control strategy of large-scale photovoltaic plants.With the research object of large-scale photovoltaic plants connected to the infinity power grid, this dissertation establishes a model of steady state operation of photovoltaic power plants considering the impedance of collector lines?box-type transformers?the main transformer and high voltage transmission Line. Then on this basis, voltage of POI and nodes inside the station is studyed. The fluctuation range and developing trend of voltage at POI and AC side of inverters is analysised through simulation.On the basis of equivalent model, the reactive power optimization model is established where optimization target are that the voltage of POI is most closed to the rated value?the difference of internal voltage and active power loss is minimum. Then immune particle swarm optimization is used to solve the optimization model. In order to improve the algorithm's search ability, hamming distance is used to calculate concentration of particles and elitism is introduced. As illumination is changing at any time, this results in the optimization model has different solution at different times.The illumination curve illumination curve is segmentated according the time cost of optimization model caculation and the maximum operating frequency of transformer tap. In this way, the dynamic optimization problem is transformed to static optimizations, ensuring the voltage of photovoltaic plant regulated dymanically.A fast optimization control strategy is proposed to deal with the situation when the illumination changes severely. In this strategy, a PI controller is used in the voltage regulating process to maintain the voltage at POI equals to reference. In order to optimize the internal voltage using the reactive power of PV generator units, sensitivity analysis method is used to get analytic function formula of the reactive power optimization model. In this optimization model, the target is to average the internal voltage of the station, constraint conditions are that the reactive power demand of the POI must be satisfied and the inverters can't run out of their rated capacity.As the analytic function formula of the optimization target is known, the optimization model can be solved with less time. This guarantees the control strategy achieves a high dynamic performance when the llumination changes severely.