Optimum Design Of Maritime Stand-alone PV System And Its Maximum Power Point Tracking

Ocean exploration needs high-tech equipments while the equipments can not live without energy. The biggest source of energy on the sea is solar energy. Optimum design of stand-alone photovoltaic supply system and the technology of Maximum Power Point Tracking are always important parts of energy management research.The difficulty of the optimum design on maritime standalone photovoltaic system is how to calculate the output energy of PV panels in a day. Due to the presence of the waves, PV panels tilt angle and azimuth are changing all the time, so the received valid light intensity of PV panels is also changing. But the azimuth is constant for a moment and the tilt angle is changing in cycles. So this problem can be solved by the method of integration and averaging. By this method, the effective irradiance received by PV panels which are horizontal can be transformed to that of maritime PV panels in the split time. Then the output energy of PV panels under non-standard conditions is obtained by formula. Finally the capacity of storage device is decided by living conditions and system load while the scale of PV module is obtained by constantly iteration of the energy output in the split time for satisfying several conditions.The Perturbation and Observation technique is simple and economical, so it has been the most popular MPPT strategy. But the effective intensity received by PV panels is constantly varying on the sea. When the effect of light intensity is stronger than the step size, the system will fail to judge. When the step size is large, the system can judge correctly even though the light intensity change rate is large, but the output of system will be unstable. So the MPPT strategy of combined open-loop and closed-loop fractional short-circuit current technology is presented. Closed-loop FSCC is useful within a certain range of light intensity change rate while open-loop FSCC is used when out of this range. So PV panels can output more energy without system unstable.Simulations verified the superiority of this MPPT strategy under the condition of varying light intensity, and found out the reasonable range of duty cycle with a capacitive load. In the experiment, the main topology is synchronous Buck circuit and the super capacitor is directly connected to the output for obtaining higher efficiency of energy transmission. It is verified that the load duty had a reasonable range with the load of super capacitor, and the super capacitor was charged effectively by P&O and closed-loop FSCC. But the superiority of this MPPT strategy was not verified under the condition of varying light intensity.