A Variable Step Maximum Power Point Tracking Method Using Differential Equation Solution

Solar power is considered as a kind of "clean power". The problems of using solar power include varying weather condition brings different power output of the photovoltaic cells, which may cause a serious waste of solar power. For solving this problem, a maximum power point tracking (MPPT) strategy is required to make Solar cells keep giving maximum power under different environment condition. In this paper, a variable step MPPT method is proposed for faster and more precise tracking process, based on an applicable solar cell model. The new MPPT method gives a second order convergence speed, compared with the traditional MPPT methods, which always behave as one order convergence. According to the applicable solar cell model, a series of differential equations are established to describe the MPPT process, and the maximum power point is present as the solution of those equations. Using a Newton iterative method can not only get the solution of the equations, but also set up ever search step of the tracking process. A matlab-simulink model was established as a two stage PV system including a DC/DC regulator and a load converter to analysis the performance of the proposed MPPT strategy. Simulation result in the last part proved that this MPPT method is practical with a better performance than the traditional strategies.