New Overall Control Strategy for Small-Scale WECS in MPPT and Stall Regions With Mode Transfer Control

This paper presents a new overall control strategy for small-scale wind energy conversion systems (WECS). The purpose of the proposed strategy is to utilize a maximum power point tracking control (MPPT) to maximize the captured energy when the wind speeds are below the rated speed. For high wind speed region; two stall controllers are developed: The constant speed stall controller which will limit the rotational speed of the generator to its rated value, and the constant power stall controller, which will regulate the captured power to be within the system rating. For the MPPT control, a modified perturb and observe (P&O) algorithm is utilized, where the dc side current is used as a perturbation variable and the dc-link voltage slope information is used to enhance the tracking speed and stability of the algorithm. For the speed and power regulation operation during high wind speeds, the system is controlled in the stall region to limit the rotational speed and the power of the generator. A stabilizing control loop is proposed to compensate for the stall region instability. A new mode transfer control strategy is developed to effectively control the transition between different modes of operation while ensuring the system stability without using any preknowledge of the system parameters. A 1 kW hardware prototype is developed and tested to validate the proposed new control strategy.