Research On Operation Control Strategy Of Photovoltaic Grid-connected Power Generation System

Economic development and social progress have caused a large amount of traditional energy to be consumed,followed by environmental degradation.At present,countries around the world have set out to build micro-grid systems consisting of renewable energy such as wind and light to solve the problems of resource exhaustion and environmental pollution.In this thesis,the photovoltaic grid-connected power generation system is the main research object,and the control objectives are divided into normal operating conditions and fault operating conditions to study the control strategies.Firstly,this thesis analyzes the development of the photovoltaic industry at home and abroad.The two-stage photovoltaic grid-connected power generation system is used as the topological structure,the working principle is studied,and a mathematical model is established.Matlab is used to build a simulation model to get the output characteristic curve.Under normal operating conditions of the power grid,in order to ensure the stability of the output of the photovoltaic system,an MPPT method based on model predictive control is proposed.This method can quickly track the maximum power point and ensure the maximum utilization of solar energy resources.At the same time,the accuracy of tracking can be guaranteed when the external environmental conditions change suddenly.For photovoltaic grid-connected inverters,a double closed-loop control value strategy based on the directional vector of the grid voltage is used to achieve power decoupling while ensuring that the unit power factor is grid-connected.Under the fault condition of power grid voltage sag,the method of grid voltage sag detection is first studied.A voltage-sag detection method based on a single-synchronous coordinate system phase-locked loop is used under symmetric faults.Under asymmetrical faults,a method for detecting the depth of power grid voltage drop based on an improved Second Order Generalized Integrator-Phase Locked Loop(SOGI-PLL)is adopted.The improved SOGI structure can not only eliminate the influence of negative sequence component fluctuations,but also eliminate the DC offset and harmonic component detection of the voltage drop depth of the power grid.In the case of symmetrical faults,the inverter adopts a reactive power priority control method,which injects a certain amount of reactive power into the power grid according to the depth of the power grid industry’s drop.In asymmetrical faults,the elimination of negative sequence components is the main control target.The inverter uses a dual-loop control structure based on the PR controller.Finally,a simulation model was built in Matlab / Simulink to verify the correctness and validity of the proposed theory.