Gojko Joksimović

Electrical machines in the high-voltage class are usually designed with open stator slots. This wide open slots cause an increase of higher order harmonics, vibrations, noise, and temperature; thus, the machine efficiency is decreased. To counteract this disadvantage, magnetic slot wedges are applied. Due to the impact of high magnetic and mechanical forces, these wedges can fall out and may cause further serious damages. Up to now, reliable detection methods for single missing slot wedges are coupled with a disassembling of parts of the machine. In this paper, a method is investigated which provides the possibility of detection, based on the measurement of electrical terminal quantities only.

Faults of wind turbine generator electromechanical parts are common and very expensive. This paper introduces a generator fault-tolerant control scheme for variable-speed variable-pitch wind turbines that can be applied regardless to the AC generator used. The focus is on generator stator isolation inter-turn fault that can be diagnosed and characterised before triggering the safety device. An extension of the conventional wind turbine control structure is proposed that prevents the fault propagation while power delivery under fault is deteriorated as less as possible compared to healthy machine conditions. Fault-induced and inherent asymmetries of the generator are estimated and respected by the field-oriented control of the generator to eliminate torque oscillations. Presented fault-tolerant control strategy is developed taking into account its modular implementation and installation in available control systems of existing wind turbines to extend their exploitable life span and increase energy production. Simulation results for the case of a megawatt class wind turbine are presented.

Fault-tolerant Control of a Wind Turbine with a Squirrel-cage Induction Generator and Rotor Bar Defects

A crucial part of every electrical machines course is the introduction to the basic elements of alternating current (a.c.) windings design. An introduction to and definition of the full-pitch coil magnetomotive force (m.m.f.) usually continues with analysis based on fundamental m.m.f. harmonics. This paper presents a winding function approach to a.c. winding analysis, which is more familiar to practising engineers than those in education. This approach has at least two principal advantages over the conventional one. First, it takes into account the exact m.m.f. waveform, i.e. all of the m.m.f. space harmonics simultaneously. Secondly, this approach is mainly computer-oriented and consequently interdisciplinary. All the basic terms in the field such as distribution factor, pitch factor, synchronous speed etc. can and are derived in this paper using a winding function definition. Additionally, basic elements of Fourier's analysis using built-in MATLAB® functions are described and its applications are illustrated.