The complexity of large wind turbines increases due to fatigue, aerodynamics, structural flexibility and wind turbulence which lead to uncertainties in the wind turbine model. Hence, a robust controller is necessary to deal with these uncertainties. The uncertainties are represented in the wind turbine model by variations in the elements of the state space matrix comprising of mass, stiffness and damping elements. The generator speed is regulated with changes in the rotor collective blade pitch angle and disturbances in wind speeds. In this paper, we propose to design an H∞ controller which qualifies to regulate the generator speed of an uncertain wind turbine. The proposed H∞ controller demonstrates robust performance and stability on system with ±20% uncertainty. The obtained 14th order H∞ controller is reduced to 7th order by using a balanced truncation model order reduction method. The performances of the designed H∞ controller and the reduced controller are compared.

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This work describes an area efficient 10-bit time mode hybrid DAC with current settling error compensation. The proposed 10-bit hybrid DAC is realized using a current steering DAC for the lower bits conversion and a time mode DAC for the upper bits conversion. The time mode DAC consist of a single capacitor, amplifier, current mirror and several control switches which occupies less area than other DAC architectures. In addition, the time mode DAC error due to improper current settling is suppressed by the pulse width compensation scheme which does not critically increase the area. The proposed DAC is realized using 0.35µm CMOS technology with estimated core area of 0.00463mm 2 , which is less than most of the existing 10-bit DACs. The maximum DNL and INL with error compensation showed 0.5LSB and -0.6LSB, respectively.

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