A MCU-Controlled Photovoltaic System with Maximum Power Point Tracker

Abstract

Given the growing concern over climate change, air pollution, rising energy prices, and the uncertain reliability of conventional fuel sources, solar power has become more popular in a variety of applications. Solar power is free, safe, abundant, renewable, and has few negative impacts on the environment. The photovoltaic array is substantially influenced with unpredictable environmental conditions (sun illumination and array temperature), which in turn, results in nonlinear Voltage-Current (or Power-Voltage, Power-Current) characteristics. These characteristics make it difficult to estimate the maximum power operating point. To extract the maximum power available from photovoltaic (PV) arrays on a continuous basis, a device called the Maximum Power Point Tracker (MPPT) is needed to continuously deliver the highest possible power to the load given unpredictable variations in environmental conditions. The PV system used in our experiment has a maximum 300W capability. Two sets of PV arrays are used in parallel to demonstrate the scalability of the system; each branch consists of three series-connected PV modules that are individually rated at 50W. Two DC-DC buck-type converters are implemented. A 24V battery bank is used as a power storage unit and is also connected to the load. An MC-based 56F8013 and its demonstration board from Freescale are employed to implement different MPPT control schemes, with multiple-PWM channels. The design can therefore adequately handle two main independent switches for each power converter. Several MPPT control algorithms are validated and comparatively analyzed in both indoor and outdoor experiments in real time. A new control strategy (called Adaptive Hill-Climbing) is proposed as a modified version of the conventional Hill-Climbing method using an optimally adaptive power window. Other methods including dp/dv method and IncCond method are also implemented in the PV system. The experimental investigation is conducted using these control topologies to seek continuously varying Maximum Power Point (MPP) from solar arrays. The experimental results show that the new proposed control method strongly outperforms the other methods. This thesis shows that the proposed MPPT can increase the power generated by PV arrays by up to at least 30% more than a PV system without an MPPT. The proposed MPPT system is adaptive to environmental disturbances; it is flexible and can be expanded to an N-parallel PV system.