In this brief, induction machine (IM) torque control is studied as an example of a 3-D non-holonomic integrator including drift terms. By expanding Brockett's controller derived for the driftless systems, a control structure is proposed that provides simultaneous modulation of both the amplitude and the frequency of the sinusoidal stator current vector. Although not explicitly controlled or programmed, the rotor flux linkage vector is implicitly forced to track natural periodic orbits satisfying non-holonomic constraints of the IM. The proposed control assures high dynamics in the torque response, maximal torque per amp ratio during transients and in steady-state and global asymptotic stability. The overall IM control scheme includes cascaded high-gain current controllers based on measured electrical and mechanical quantities together with rotor flux linkage vector estimator. Simulation and experimental results illustrate the main characteristics of the proposed control.
COBISS.SI-ID: 14609174
This paper deals with the two-axis sun tracking system for a photovoltaic system. The trajectories of the sun tracking system are determined in an optimization procedure. The optimization goal is maximization of an electric energy production in the photovoltaic system considering the tracking system consumption. Determination of the tilt angle and azimuth angle trajectories is described as a nonlinear and bounded optimization problem, where the objective function is not available in the explicit form. A stochastic search algorithm called Differential Evolution is used as an optimization tool. In the optimization procedure, the objective function is evaluated by using the models of available solar radiation, tracking system consumption, and the efficiency of solar cells with the appropriate dc/dc converters. The problem bounds are given in the form of lower and upper bounds for both angles and time and angle quantization. The results presented in the paper show, that the optimal trajectories for the tilt and azimuth angle depend on the available solar radiation, solar cell efficiency, tracking system consumption and the optimization bounds.
COBISS.SI-ID: 14971926
The magnetically nonlinear behavior of electric alternating current rotating machines is characterized by current dependent magnetic flux linkage characteristics. In this work, the impacts of iron core saturation, iron core saliency, permanent magnets, and squirrel cage in the rotor design on the machines' behavior, and the respective flux linkage characteristics in forms of hysteresis loops is analyzed. The analysis is based on experimental data by utilizing a stator with two phase-windings that produce magnetomotive forces displaced by electrical 90 degrees, enabling the direct evaluation of flux linkages by measurement of the windings' voltage and current on the machine terminals. Five rotors of different electromagnetic construction and manufactured from equal materials have been tested in combination with the afore mentioned stator. Thus, induction machines, synchronous reluctance machines, permanent-magnet synchronous machines, and their hybrid types are incorporated in the analysis. The work provides a deeper insight into the magnetically nonlinear behavior of the aforementioned machines, which is not available in the current literature.
COBISS.SI-ID: 67349761