Output Feedback control of wind energy conversion system with hybrid excitation synchronous generator

Abstract

This paper deals with the problem of wind energy conversion systems control. The considered aero-generator involves a hybrid excitation synchronous generator (HESG). To extract the maximum power from wind energy system, it is recommended to operate at variable speed. However, this control requires the measure of wind speed, rotor speed and aerodynamics torque, which are both difficult in practice and not very reliable. This paper presents a design of sensorless maximum power point tracking (MPPT) speed controller for achievement of the above energetic goal without resorting to mechanicals sensors (wind velocity, HESG rotor speed and aerodynamic torque). To this end, the control observation strategy is developed, based on the nonlinear model of the whole controlled system and only using electrical variables measurements. The control strategy involves: (i) online reference-speed optimizer designed using the turbine power characteristic to meet the maximum power point tracking requirement. (ii) an interconnected state observer providing online estimates of stator resistance, rotor permanent flux, rotor speed, aerodynamic torque and wind speed. (iii) a nonlinear MPPT speed regulator designed (using the backstepping technique) for the case where the wind speed remains lower than a maximum level (denoted wb). (iv) an optimization of the electromagnetic torque provided (by controlling the machine timing angle ()) to improvement the HESG efficiency. The performances of the proposed regulator are analyzed using tools from the Lyapunov stability. These theoretical results are validated by a series of simulations to show the contribution of hybrid excitation with a wide variation of the wind speed.