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This paper offers a new approach for specifying the waveforms of driving voltages for a Piezo LEGS motor. A novel idea of coordinate transformation to define the waveforms of driving voltages, based on the motor static model, is presented. This transformation defines driving voltages according to the desired motion of the motor legs in the x-and y-directions. The approach allows a user to first define force acting on the motor rod in the ydirection and define the rod's x-direction trajectory profile. Waveforms of the driving voltages are subsequently defined to meet these requirements. The proposed approach also enables the possibility of defining the desired step shape for the motor and, according to that definition, producing driving voltages. Based on the given coordinate transformation, a simple method for Piezo LEGS motor control, identified as virtual time control, is presented. This method results in overshoot-free high precision positioning.

The popularity of renewable energy conversion systems, and especially of wind energy, has been growing in recent years. Doubly fed induction generator (DFIG)-based wind energy systems are extensively used due to their wide range of active and reactive power controllability. Conventional DFIG control structures consist of decoupled PI rotor current controllers with stator flux orientation and machine parameter-dependent compensating terms. The accuracy of stator flux calculations is dependent on how accurately the stator resistance is known. Integration problems also exist and additional low-pass filters are implemented to accurately calculate the stator flux. In the current study, machine-dependent compensating terms are estimated with a first-order low-pass filter disturbance observer. Therefore, a single proportional (P) controller is sufficient to control decoupled rotor currents. The proposed controller structure is implemented on a MATLAB/Simulink platform with the parameters of 500 kW DFIG used in the MİLRES (Turkish National Wind Energy) project. The proposed controller is also experimentally validated in an experimental setup.

Original scientific paperThis paper presents a novel current control methodology for grid connected doubly-fed induction generator (DFIG) based wind energy conversion systems. Controller is based on a proportional controller with additional first order low pass filter disturbance observer which estimates the parameter dependent nonlinear feed-forward terms. The results in simulations and experimental test bed obviously demonstrate that decoupled control of active and reactive power is achieved without the necessity of additional machine parameter. Key words: DFIG, Disturbance observer, Wind energyNovi regulator struje za dvostrano napajani asinkroni generator. U ovom radu prikazana je nova metoda upravljanja strujom za vjetroagregat s dvostrano napajanim asinkronim generatorom spojen na mrežu. Regulator se temelji na proporcionalnom regulatoru uz dodatak niskopropusnog fitra prvog reda za estimaciju poremećaja koji estimira parametarski ovisne nelinearne predupravljačkečlanove. Simulacijski i eksperimentalni rezultati pokazuju da je postignuto raspregnuto upravljanje radnom i jalovom snagom bez potrebe za dodatnim parametrima generatora.

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