Conference Paper

Rotor-side Cascaded PI Controller Design and Gain Tuning for DFIG Wind Turbines

DOI: 10.1109/PowerEng.2013.6635701 Conference: 2013 IV IEEE International Conference on Power Engineering, Energy and Electrical Drives (POWERENG), At Istanbul, Turkey


A novel and efficient solution to the problem of designing and tuning the gains of cascaded PI controllers used in DFIG wind systems is addressed in the present paper. The overall design takes into account the nonlinear dynamic model of the system while the analysis of the inner-loop controllers leads to some new concepts, namely that of the effective time constant, which in turn leads to a gain tuning rather independent from the system parameters. The controller structure is completed by exploiting the time-scale separation assumption in the design of the outer-loop controller. This approach provides the possibility to obtain a simple systematic method for tuning the outer-loop controller gains, based on the well-analyzed in the literature second order transfer function. Hence a more robust control scheme with some essentially enhanced stability and transient properties results, as it is clearly verified by extensive simulation tests.

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    ABSTRACT: The nonlinear induction motor model is appropriately integrated by incorporating the dynamics of the power electronic converter in a manner that permits the design of stable field-oriented control (FOC) operating with minimum losses. As already proven, the challenging issue of operating the induction machine with minimum copper losses requires a varying rotor flux opposed to the standard FOC technique, which keeps the rotor field magnitude constant and tracks the electric torque to the desired level. To this end, exploiting the Hamiltonian structure of the developed motor/converter model, an innovated nonlinear controller is proposed that guarantees the technical limits of the converter (linear modulation) and simultaneously operates under FOC at steady state to achieve accurate speed regulation with varying rotor flux according to the minimal losses requirements. Under these circumstances, the conventional FOC stability analysis does not hold anymore, and therefore for the first time, a new rigorous analysis is provided that proves stability and convergence to the desired equilibrium for the complete closed-loop motor converter system. Finally, the theoretical contribution is examined in comparison to the traditional FOC operation by simulations obtained for an industrial size induction motor, while it is further evaluated by real-time results of a motor with similar parameters.
    Full-text · Article · Sep 2015 · IEEE Transactions on Energy Conversion