New overall control strategy for wind energy conversion systems in MPPT and stall regions

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 (MPPT) control to maximize the captured energy when the wind speeds are below the rated maximum and when the wind speeds are above the rated value, the captured power is regulated to protect the system from over-power operation. 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 proposed algorithm. For the power regulation operation during high wind speeds, the system is controlled in the stall region to limit the rotational speed of the generator. A stabilizing control loop is proposed to compensate for the stall region instability. And a new mode transfer control strategy is developed to effectively control the transfer between the two modes of operation while ensuring the system stability. A 1.5KW hardware prototype is developed and tested to prove the proposed new control strategy.