A method for MPPT control while searching for parameters corresponding to weather conditions for PV generation systems

A method for a maximum power point tracking (MPPT) control while searching for optimal parameters corresponding to weather conditions is described in this paper. The conventional method has problems that it becomes impossible to acquire the generating power at the maximum power point in low solar radiation (irradiation) states. It was found experimentally that the maximum output power and the optimal current which gives this maximum had a linear relation in low irradiation states. The linearity is maintained in low irradiation states because the surface temperature of solar arrays is seldom changed. On the other hand, as the surface temperature changes in high irradiation states, the linearity collapses. However, assuming that there is no temperature change within several ms, the proportionality (voltage) coefficient between the maximum output and optimal current is searched for using the hill-climbing method. This procedure is done when the irradiation (mean value) is more than half the rated power. Below the mean value, the MPPT control is done based on the inherent linearity regarding solar arrays using the proportionality (voltage) coefficient obtained at the mean irradiation. The proposed MPPT method can enlarge the controllable range of the output power for lower solar radiation in comparison with the conventional method. Effectiveness of the method is verified by experiments.