Stability Analysis of Maximum Power Point Tracking (MPPT) Method in Wind Power Systems

The maximum power point tracking (MPPT) method is the key to notably improve efficiency and energy extraction in wind turbine systems. The MPPT method through the characteristic power curve is one of the popular MPPT methods. The reference current can be obtained using the relationship between power and current without requiring real-time wind speed information. This paper presents the steady-state and dynamic analyses of this MPPT method and proposes a single-pole transfer function to describe the effect of variation of wind speed on the generator speed. This is conducted by applying the small-signal analysis on a nonlinear turbine-rotor mechanical system. To verify the performance of the wind turbine system, both simulation and experimental systems are implemented based on MPPT power control. By the variation of wind speed, the behavior of the generator speed presents good consistency among the proposed theory, simulation, and experiments.

I. Introduction

As one of the most commonly used renewable energy sources, wind is the most promising one for replacing the fossil fuel in the near future. To achieve high efficiency in a wind power conversion system, the maximum power point tracking (MPPT) in variable-speed operation systems, like doubly fed induction generator (DFIG) and permanent-magnet synchronous generator systems, attracts a lot of attention [1]–[3]. The studied MPPT methods in the history include three strategies, namely: 1) methods relying on wind speed; 2) methods relying on output power measurement and calculation; and 3) methods relying on characteristic power curve.