Research On GMPPT Algorithm And Inverter Control Strategy For PV Grid Connected System

In order to alleviate the impact of various traditional energy on climate change,clean energy,such as solar energy,has been widely developed and utilized.Photovoltaic grid connected power generation is one of the most common forms of solar energy use.This paper mainly studies several technical problems in the process of grid connected power generation.The traditional R_s and R_s-R_p photovoltaic module based on single diode is poor in temperature and low light conditions,and does not consider the composite loss of the diode.The proposed dual diode photovoltaic module can overcome these shortcomings,but the amount of calculation is great.A new type of dual diode PV module is presented in this paper.The parameter calculation equation is simplified,and the corresponding parameters of the model are calculated by the proposed iterative method and analysis method,which greatly reduces the computation and improves the computation speed.Then,based on the photovoltaic module,a photovoltaic array simulator that can reflect the local shadow state is established,which provides convenience for the follow-up research.Under the condition of local shadow,the P-V curve of the photovoltaic array becomes multi peak,and the traditional maximum power point tracking algorithm will fail.In this paper,a global maximum power point tracking algorithm is proposed based on the study of the output characteristic curve of the photovoltaic array.The algorithm presents a method to judge the illumination condition based on the voltage variation characteristic of the parallel diode in the photovoltaic module.In the uniform illumination conditions by the constant pressure and the look-up table method proposed to locate the maximum power point.Under the condition of partial shading,DC-DC converter working location to several nearby local peaks by the duty ratio formula,then comparing these local maximum power point to locate near the global maximum power point.Compared with the traditional algorithm it avoid the scanning process and greatly reduce the execution time.Then the perturbation observation method is used near the global maximum power point to achieve accurate positioning.In order to achieve grid connected control,the LCL three-phase inverter system is converted to d and q coordinate system,and a decoupling strategy of coupling quantity feedforward is proposed to realize the coupling problem of the inverter system in d and q coordinate system.Then the decoupled system uses a current double closed loop control strategy to complete the grid-connected.Finally,a PV inverter system with a rated power of10kW is built,and the corresponding algorithm is verified on the platform.The experimental results show that the system achieves synchronous control of grid voltage and grid current,and the THD of grid connected current meets the requirements of grid connection.