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Induction motor time-stepping finite-element analysis requires a lengthy transient response time to build up the complete steady-state magnetic field distribution in both stator and rotor. Various methods to speed up the convergence of the time-stepping finite-element (TS-FE modeling are investigated in this article. A so-called “virtual blocked rotor” technique is developed by using an eddy-current solver in the frequency domain to approximate the initial conditions, including the frozen permeabilities, potentials/energies, the stator winding and rotor bar currents, etc. Then, these well-prepared initial conditions are imported into the transient TS-FE time-domain solver (model). Significant reduction of the length of the transient response to reach convergence is accomplished. In addition, the promise of this method lies in its use in future large-scale design optimization studies. In order to further reduce the computational burden, a “virtual blocked rotor” concept/method in the TS-FE time-domain solution is also developed, which effectively reduces the required number of ac cycles and central processing unit real time to reach steady state. [ABSTRACT FROM AUTHOR]

This paper presents optimization of the skew angle of rotor magnetic poles in permanent magnet brushless dc machines. The skew angle optimization is achieved using the gradient based inverse problem methodology. The paper introduces the armature winding flux linkages and associated induced emfs for the first time as the object function. Meanwhile, this object function involves the use of stored energy and excitation perturbation techniques. An example 1.2 hp permanent magnet brushless dc machine is used to demonstrate the validity and usefulness of the method. Keywords: Permanent magnet brushless dc motor, skewed rotor poles, optimization, Finite Elements, gradient method.

On-line condition monitoring is of paramount importance for multilevel power converters used in safety-critical applications. A novel on-line nonintrusive diagnostic method for detecting open-circuit switch faults in silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs)-based T-type multilevel converters is introduced in this paper. The principle of this method is based on monitoring the abnormal variations of the dc-bus neutral-point current in combination with the existing information on instantaneous switching states and phase currents. Advantages of this method include faster detection speed and simpler implementation compared to other existing diagnostic methods in the literature. Moreover, this diagnostic method is immune to the disturbances of inverter's dc-bus voltage unbalance and load unbalance. In this method, only one additional current sensor is required for measuring the dc-bus neutral-point current; therefore, the implementation cost is low. Simulation and experimental results based on a lab-scale 20 kVA adjustable speed drive with a three-level SiC T-type inverter validate the effectiveness and robustness of this novel diagnostic method. [ABSTRACT FROM PUBLISHER]

The performance of a novel three-phase four-leg fault-tolerant T-type inverter topology is introduced in this paper. This inverter topology provides a fault-tolerant solution to any open-circuit and certain short-circuit switching faults in the power devices. During any of the fault-tolerant operation modes for these device faults, there is no derating required in the inverter output voltage or output power. In addition, overload capability is increased in this new T-type inverter compared to that in the conventional three-level T-type inverter. Such increase in inverter overload capability is due to the utilization of the redundant leg for overload current sharing with other main phase legs under healthy condition. Moreover, if the redundant phase leg is composed of silicon carbide metal-oxide-semiconductor field-effect transistors, quasi-zero-voltage switching, and zero-current switching of the silicon insulated-gate bipolar transistors (IGBTs) in the conventional main phase legs can be achieved at certain switching states, which can significantly relieve the thermal stress on the outer IGBTs and improve the whole inverter efficiency. Simulation and experimental results are given to verify the efficacy and merits of this high-performance fault-tolerant T-type inverter topology. [ABSTRACT FROM PUBLISHER]