Modeling And Array Mismatch Of Solar Cell-supercapacitor Device Under Partial Shading

Solar energy as one of the renewable energy,have been large-scale promotion and application because of its abundant reserves,easy access,low installation cost and other characteristics of.However,the operating environment of the existing photovoltaic power generation system is complex,especially the photovoltaic system in residential areas,which is easy to generate partial shading by buildings or the self-shielding between arrays.As a result,the current difference between photovoltaic modules will lead to array mismatch,and its power output characteristics will also produce multiple peaks,which also poses a threat to the stable operation of power system.Therefore,how to solve the problem of multi-peak photovoltaic array under partial shading becomes an important premise for photovoltaic power grid connection.Solar cell-supercapacitor device is a new structure proposed by scholars in recent years.By integrating photovoltaic modules and supercapacitor,the monomer control of each photovoltaic module can be achieved without considering the energy storage balance.Meanwhile,the dynamic reconstruction of photovoltaic array is also an effective way to solve the shadow problem.Therefore,it is of great significance to study the mathematical model,output characteristics,operation strategy and topological reconfiguration method based on solar cell-supercapactor for solving the problem of multi-peak power of photovoltaic arrays caused by partial shading.Firstly,the paper provides the structure and equivalent circuit of the solar cell-supercapacitor device(SCSD),and provides a mathematical model of SCSD.On this basis,the conventional photovoltaic array and SCSD array under uniform illumination and partial shading are modeled and their output characteristics are compared.Finally,the simulation results show that the array composed of solar cell and supercapacitor has higher output power under uniform illumination.In partial shading,the solar cell-supercapacitor have stronger shadow adaptability than conventional photovoltaic arrays.Secondly,the grid connection system of solar cell-supercapacitor is constructed by using the dual function of solar cell-supercapacitor.Aiming at the partial shading problem,a multi-objective hierarchical optimal charge and discharge control strategy is proposed.The optimal discharge current reference value of the control loop is obtained by using the multi-objective optimization of the upper layer,and the supercapacitor in SCSD can be charged and discharged eventually.Considering the constraints of the super capacitor charge and discharge power,charged state and system power balance,an optimization model is established with the goals of smooth photovoltaic output volatility,minimum system loss and keep the super capacitor charge and discharge capacity quickly.Through the weighted sum method,the upper optimization model is established,and the analytic hierarchy process is used to obtain the optimal reference value of the charge and discharge current of the supercapacitor,which is used as the input of the control model of the lower layer.The PI control method with current feedback is adopted for the lower layer control.Finally,the simulation verifies that the proposed method can completely solve the multi-peak problem in light shadow.In the case of severe shadow and multi-layer shadow,the number of multi-peak values can be reduced,the global maximum power can be increased,and the system loss can be reduced.The single control of each SCSD can be realized,effectively avoiding the problem of unbalanced SOC of energy storage batteries.Finally,an array reconfiguration method based on solar cell-supercapacitor is proposed to solve the problem of power multi-peak value in the case of severe shadow and multi-layer shadow,as well as the limitations of under-compensation and over-compensation when traditional local reconfiguration method solves partial shading problem.Considering the constraints of power fluctuation,energy storage charging and discharging power and SOC,an optimization model is established with the goals of the maximum output power of photovoltaic array and the minimum number of reconfigured switches,solves the model by the improved particle swarm optimization algorithm.Through the example simulation analysis of the partial shading using traditional reconfiguration methods and thesis SCSD array output characteristic of the proposed method,the proposed method is verified not only effectively solve the traditional local reconfiguration method under compensation and over compensation,reduce the number of switch actions,further solve the severe shadow and multilayer shadow SCSD array multi-peak output power questions.