Novel variable step-size maximum power point tracking control strategy for PV systems based on contingence angles

Most of the variable step-size algorithms for the photovoltaic (PV) generation system use the derivative values of power versus voltage (P´(u)) as the basic step-size reference. However, due to the fact that the mathematical properties of P´(u) are nonlinear and different on both sides of the maximum power point (MPP), some essential parameters, such as the maximal step-size, scaling factor and other key indexes, are difficult to estimate accurately. In order to overcome these defects, a novel variable step-size MPP tracking (MPPT) algorithm dependent on the contingence angle of the P-U curve is proposed in this paper. First, it calculates the arctangent of P´(u) and gets its normalization with cosine function, so that the tracking properties on both sides of MPP will be normalized, and the debugging process of a proper maximum step size will become much easier than that of traditional method. Afterwards, it builds up one reasonable mathematical model to get one more suitable scaling factor with excellent convergence capability dependent of the maximum step-size. This scaling factor may maintain a bigger step-size when far away from MPP and decrease step-size rapidly around MPP, so a more rapid tracking speed and a much higher accuracy can be made simultaneously. At last, the convergence criterion of new method is proved with D´Alembert theorem, and the accurate choice of the maximal step-size for tracking the MPPT has been made carefully in theory. Comprehensive experiments verify with relevant simulation investigations and theoretical analysis, which demonstrates the new method has much quicker tracking speed and higher tracking efficiency. It could find great potential applications in the PV engineering for its easy determination of maximal step-size and practical implementation.