Fault tolerance in wind turbines is considered crucial to increase their reliability and availability levels. This paper presents a fault-tolerant direct-drive permanent magnet synchronous generator (PMSG) using new direct control techniques, with the ability to handle power semiconductor open-circuit faults in the full-scale back-to-back converter. The fault-tolerant topology consists of a five-leg converter, with a shared leg connected to a generator phase and to its corresponding grid phase, through a triode for alternating current (TRIAC). The main contribution of this paper consists of the development of an alternative direct torque control and direct power control schemes for both machine-side converter and grid-side converter, respectively. Moreover, a reliable fault diagnostics algorithm without requiring additional sensors is also integrated, providing the information required to instantaneously trigger fault-tolerant remedial strategies. Simulation and experimental results are presented to validate the effectiveness of the proposed fault-tolerant PMSG drive.

Synchronous Reluctance Machines (SynRMs) are facing a revamped industrial interest. A comparison between SynRMs and other types of electric machines allow listing the advantages and proving the choice of such machines. This paper presents a review of SynRMs, regarding particularly their thermal analysis. First of all, a description of the basic principles of SynRM is illustrated. The thermal analysis is based mainly on the study of the heat sources and the heat extraction mechanisms which are listed and described. Nevertheless, the coupling effects between the thermal field and the magnetic material parameters are discussed. Then, the three heat extraction phenomena (conduction, convection and radiation) are analyzed. Along the work, important facts about the thermal analysis are discussed. A comparison between the different approaches used for the thermal analysis is highlighted, and new developments and perspectives are identified.

Significant changes may occur in the thermal behavior of a directly grid-fed induction machine when subjected to unbalances in the voltage supply. This article studies and analyzes the thermal behavior of a low power, three-phase, squirrel-cage induction motor, connected in star configuration with floating neutral point, when subjected to different levels of unbalanced voltage. The dependence of the thermal motor behavior on the severity level of the unbalance is studied and analyzed. In addition to amplitude unbalances, this article focuses on the effects of phase unbalances, as well, which were not addressed in detail in previous published studies. Moreover, situations of mixed unbalance, where amplitude and phase unbalances occur simultaneously, are also studied. The finite element method was used to simulate the thermal behavior of the machine. The experimental setup consists of a three-phase programmable AC power supply, suitable to precisely emulate unbalanced conditions that may occur in real-scale power systems, supplying a 2.2 kW induction motor. Experimental data were acquired resorting to resistance temperature detectors PT100, placed in the machine phase whose supply current value changed the most. Finally, the simulation results are verified and critically discussed through experimentally obtained results.

Fault detection and fault accommodation, as well as fault tolerance, are important issues in closed-loop controlled three-phase converters. For such systems, power semiconductors and sensors are the most affected components by the occurrence of failures. Therefore, fault diagnosis and remedial operating strategies involving such components are highly required. In this paper, a new reliable approach is proposed, which aims to diagnose current sensor faults and power semiconductor open-circuit faults in permanent magnet synchronous motor drives. The proposed fault diagnosis scheme uses only the measured currents, which makes it suitable for real-time implementation. The performance of the proposed technique is analyzed through experiments.

The use of electronic equipment and other dc-compatible appliances in homes and offices is increasing at a very fast rate, as well as the distributed generation of energy. These two statements will most likely trigger, in a near future, the adoption of district-scale dc grids, connecting dc microgeneration plants and consumers, in an effort to cut the number of conversion steps required to deliver power to dc appliances. DC-DC converters will be fundamental in these systems, allowing the establishment of several voltage levels. The reliability of these converters plays a critical role, ensuring service continuity of the loads connected to them. With the increment of reliability in mind, this paper proposes a simple yet effective open-circuit fault diagnostic method suitable for interleaved dc-dc boost converters, but equally functional for other dc-dc converter topologies. The improvements introduced in this paper greatly simplify the diagnostic action, while making the correct diagnostic of faults independent of the switching duty cycle. Moreover, an alternative reconfiguration scheme is proposed to mitigate the adverse impacts of such faults. To prove the effectiveness of these strategies, a three-phase interleaved boost converter prototype was used in the experiments.