Research On Control Strategy Of Photovoltaic Power Station Participating In Power Grid Frequency Modulation

With the exhaustion of fossil energy,the development of renewable energy has gained a lot of attention.Photovoltaic(PV)power generation is widely distributed,environment-friendly and sustainable.However,the output power of PV system is affected by light intensity,temperature and other uncontrollable factors.Frequency of the system is greatly affected by the stochastic nature of solar power,which undoubtedly constrains the large-scale development of PV generation.In this paper,a grid-connected model of PV system is established.A fuzzy-control-based frequency regulation strategy is developed to adjust the output of PV system,in order to maintain the stability of frequency.Firstly,the simulation model of universal PV plant is introduced.By comparing mathematical models of different kinds of batteries,a model of the simplified version of lead-acid battery is established.The main components used in the PV grid-connected system include photovoltaic arrays and two-stage power conversion circuits.In order to maintain the output power with the maximum efficiency,this paper studies the general control strategy of PV system,and analyzes the characteristics of the photovoltaic array's output.The pre-stage DC / DC booster circuit use the maximum power point tracking control(MPPT)strategy,while the post-stage DC /AC inverter structure uses constant DC voltage constant reactive power control strategy to maximize the output and keep the DC bus voltage stable.To ensure that the PV system is able to stabilize the frequency,this paper introduced fuzzy-control-based active power control strategy with two two-dimensional fuzzy controllers,using average light intensity,light intensity gradient and the system frequency deviation as the detection values.The energy storage system changes its status of charge or discharge to replenish the system.This paper establishes the system model in Matlab/Simulink simulation software.The simulation cases are PV system model which is respectively connected with the micro-grid system and IEEE 9 node power system.The frequency regulation strategy in the micro-grid and large power grid can effectively regulate the frequency and the active power,proving its effectiveness and feasibility.The simulation results show that the frequency modulation strategy can quickly adjust the active power outputunder the condition of light intensity variation and system frequency fluctuation,so that the system frequency is maintained at 50 Hz.Finally,an engineering platform is built in a practical engineering project.,testing the performance of the proposed strategy on the distribution network system,proving the effectiveness of the algorithm in actual operation conditions.The proposed frequency modulation strategy is verified to reduce frequency fluctuations by fifty percent.