Sliding-mode control based on index control law for MPPT in photovoltaic systems

A novel maximum power point tracking method based on sliding mode control and average state model of PV generation systems is developed. This method consists of two parts: term of constant control and term of index control. It is different from the conventional sliding mode control which uses a constant speed control law. The developed method uses a controllable sliding mode switching function which can automatically adjust the approaching speed, so as to enable the photovoltaic system to achieve fast dynamic response and stable output power. System simulations using MATLAB are performed. Compared with conventional methods, simulation results show that maximum power point tracking times for the novel method both in start-up phase and in cases of environmental changes can be shorten by more than 50%. A experimental platform of 150W PV system has been established to conduct tests. Experimental results show that the maximum power point tracking times both in start-up phase and in load stepping phase including the illumination change phase, can be significantly decreased. These results indicate that the developed method owns better dynamic response than constant speed control law. It can be used in photovoltaic generation system.