Development of a modular photovoltaic maximum power point tracking converter

Abstract

The solar photovoltaic (PV) as a renewable energy source is gaining popularity as it is free, clean and abundantly available. However, it main hindrance are low efficiency and high capital cost. To address the problem, the maximum power point tracking (MPPT) techniques are proposed to track the optimum voltage and current at the maximum power point. A DC-DC converter can be used to vary the duty ratio according to the control signal to force the load line to intersect with the I-V curve at the maximum power point. Therefore, the problem statement here is to design a MPPT algorithm that can track the optimum voltage and current corresponding to the maximum power point. Various MPPT techniques had been discussed in the literature and all have their advantages and disadvantages. Moreover, the I-V or P-V characteristics is highly non-linear with the left hand side of MPP have low process gain while at the right hand side of MPP, the process gain is significantly greater. Consequently using constant PI parameters will result in slow response or oscillations around MPP. Finally, the design of a DC-DC converter will require careful selection of component ratings, such as inductor and MOSFET to minimize power loss. Therefore, this project is aimed at designing and developing a software and hardware to implement the Incremental Conductance algorithm, evaluating the performance of MPPT under various light irradiation level and comparing its performance with the maximum power calculated from theoretical methods. In the research methodology, MPPT technique (Incremental Conductance), non-linear PI control using Luyben control technique and Amigo tuning rules for PI parameters are used. The control signal is converted to PWM output at PIC16F877A. The hardware of the microcontroller, IR-2117 and buck-boost converter circuit are designed and fabricated. This hardware was tested. The program is written in C language in MPLAB IDE v8.60 environment. Successful compilation generates hex file (machine code) that was downloaded into the mirco-controller through PICKIT2 and hardware In-Circuit Serial Programming (ICSP). The maximum power point values calculated by theoretical methods, solar output voltage and current, reference voltage and current tracked by MPPT, duty ratio were displayed and recorded. The test was repeated for different sunlight radiation levels. The result demonstrated that the reference voltage and current tracked by the MPPT deviates from the actual maximum power point by less than 5% under different radiation conditions, Additionally, the maximum power calculated by the MPPT algorithm developed also performed better than the maximum power calculated by theoretical manner.