Emulation of Wind Turbine System Using Vector Controlled Induction Motor Drive

Depleting fossil fuels and concerns about global warming have forced a paradigm shift toward renewable energy resources in meeting our energy requirements. Wind energy utilization has been growing at a rapid rate fuelling research and development in high power wind turbines (WTs). To advance research and education in wind energy conversion systems, a controlled test bed is necessary that does not depend on wind availability. Majority of the existing WT emulation schemes employ a torque compensation loop to account for the inertia difference between the WT and motor used for emulation. However, the loop suffers from noise and instability issues. Also, the torque compensation term is sensitive to parameter estimates. This article proposes one degree of freedom (1-DOF) and 2-DOF control structures for WT emulation. It first illustrates the design and performance of 1-DOF control structure. It further proposes two controllers along with their prefilters in 2-DOF structure, which has superior performance than 1-DOF structure. The design of the controllers and prefilters is explained with the help of root locus. The performance of the WT emulator with the proposed control structures is demonstrated through simulations and experiments on a 7.5 kW doubly fed induction generator driven by a 5.5 kW squirrel cage induction motor, where the dynamics and steady-state operation of a WT–generator system are emulated.