The Research On PV MPPT Algorithm Based On Thermal Voltage Model And Power Optimizer

With the development and consumption of non-renewable energy sources,a worldwide energy crisis is on the horizon,which,together with ecological and environmental problems,has stimulated the need for renewable energy in human society and sustainable development is being taken seriously.Solar energy,with its non-polluting,safe,widely distributed and cost-free characteristics,is considered an important way to solve the dilemma of energy scarcity.Distributed photovoltaic power generation systems have gained wide attention for their ability to track the maximum power of each photovoltaic cell by individually connecting a module-level power optimiser to each cell,avoiding power loss due to shading and greatly improving the efficiency of the power generation system.As a module-level device,the photovoltaic power optimiser has become a research hot because it combines the advantages of high efficiency and low cost.The equivalent circuit model of photovoltaic cell and a general four-parameter engineering model is reviewed at first.At the basis,an improved voltage model for the single diode model of photovoltaic cell,the thermal voltage dynamic model,is proposed and studied.Simulations in MATLAB/Simulink are conducted to analyse the P-U and I-U curves of PV cells under different environmental parameters.A comparison of the simulation results between the four-parameter model engineering model and the thermal voltage dynamic model verify the accuracy of the thermal voltage dynamic model.Then the reference voltage values V_ref at MPP for the thermal voltage dynamic model are estimated.Based on this,the simulation of the PV array under shading condition is carried out to analyse the multi-peak output characteristics of the PV array.To improve the efficiency of PV power generation,several common MPPT algorithms applied to PV cell engineering are investigated,together with the analysis of the advantages and disadvantages of each algorithm.Based on the thermal voltage dynamic model proposed previously,an improved perturbation observation method based on V_ref is presented.The improved algorithm can save tracking time and achieve fast response with good dynamic performance.Then the DC/DC circuit of the power optimiser is investigated.An improved dual inductor Boost circuit is studied on the basis of Boost as well as cascaded Boost circuits,and the system small signal is analyzed.The individual component parameters of this circuit are designed,followed by the analysis and design of the control section circuit.In addition,the design and operation flow of the overall software algorithm is given.Finally a prototype power optimiser is built and physical experiments are conducted.From the test results,the improved dual-inductor Boost circuit performs well,and the efficiency reaches more than 95%.The power optimizer can effectively track to the maximum power point and the tracking efficiency reaches99%,which verifies the correctness of the power optimizer design in this paper.