For variable-speed wind energy conversion systems, control objectives may be different in partial and full load regions (or in low and high wind speed regions). Typical control objectives are to maximize the energy capture at low wind speeds, and to maintain the generated power and the rotational turbine speed within safety limits at high wind speeds. In such a case, it is difficult to design a single robust controller covering both partial load and full load conditions. This paper presents a systematic switching control method for a variable-speed variable-pitch wind turbine over a wide wind speed region. The whole framework is based on the linear parameter-varying (LPV) control theory, which is an extension of robust control for linear systems to nonlinear ones. Two LPV controllers are designed, each suitable in a different wind speed region. A hysteresis switching logic is applied to guarantee the stability when the switching event occurs between the two controllers. Nonlinear simulations are conducted to demonstrate the proposed control scheme.

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