Analysis of maximum power point tracking for small scale wind energy conversion system using direct power control

Abstract

Wind Energy Conversion System (WECS) is a promising Renewable Energy Source (RES) to generate electricity closer to the consumers in the area with suitable wind pattern. However, the Maximum Power Point Tracking (MPPT) algorithm design is a challenging task due to the random and unpredictable nature of the wind. Therefore, an efficient MPPT controller is essential to detect, track and extract the maximum extractable wind power at the optimal operating region of the Wind Turbine (WT). Direct Power Control (DPC) MPPT analyses the electrical properties of the power converter’s output to track the maximum power point (MPP). Perturb and Observe (P&O), and Incremental Conductance (INC) are the most commonly used DPC type algorithms for MPPT. P&O algorithm design is simple but the selection of perturbation step-size is cumbersome and affects the MPP settling time and oscillation significantly if it is too large or too small. The INC algorithm design has better performance in detecting MPP. But there is a lack of research data available on INC MPPT performance for WECS application which is a gap that is addressed in this thesis. The objectives of this research are to design a small scale WECS using fixed and variable step-size P&O and INC MPPT algorithms. The design is simulated using the MATLAB/Simulink tool. Finally, the MPP performance of each algorithm is analysed and compared in terms of MPPT convergence time, oscillation and accuracy. The WECS design comprises a Wind Turbine (WT), a three phase Permanent Magnet Synchronous Generator, a full bridge diode rectifier, a DC-DC buck converter and MPPT controllers. The MPPT control scheme uses the relationship between the converter current values and generator’s electromagnetic torque by increasing/decreasing the duty cycle to track the optimal power point. The steady state and dynamic response of the MPPT algorithms is observed and analysed through simulation. Larger step-size has high oscillation rate at the MPP. Smaller step-size takes longer to reach the maximum operating point. INC and Variable step-size P&O MPPT technique proves to achieve better efficiency and accuracy in terms of MPP tracking with relatively shorter convergence duration against conventional P&O MPPT. MPPT efficiency increases by 13.8% and 10.6% from Conventional P&O and INC to 96.4% with Variable P&O at rated condition.