Over the last decade, dc-dc power converters have attracted significant attention due to their increased use in a number of applications from aerospace to renewable energy. The interest in wide bandgap (WBG) power semiconductor devices stems from outstanding features of WBG materials, power device operation at higher temperatures, larger breakdown voltages, and the ability to sustain larger switching transients than silicon (Si) devices. As a result, recent progress and development of converter topologies, based on WBG power devices, are well-established for power conversion applications in which classical Si-based power devices show limited operation. Currently, Si carbide (SiC) and gallium nitride (GaN) are the most promising semiconductor materials that are being considered for the new generation of power devices. The use of new power semiconductor devices, such as GaN high electron mobility transistors (GaN HEMTs), leads to minimization of switching losses, allowing high switching frequencies (from kHz to MHz) for realizing compact power converters. Finally, design recommendations and future research trends are also presented.

This paper investigates the accuracy of the estimation of efficiency maps for permanent magnet (PM) machines using the stator resistance, d- and q-axis flux-linkages versus the corresponding axis current and the iron loss versus speed characteristic. The ultimate goal is to apply this approach to experimental measurements but this paper performs initial investigation using only finite-element data. Detailed FE data for 50-kW surface and interior PM machines is used to determine the “actual” or exact efficiency map and hence the accuracy of using approximations. The paper examines the effect on the torque-speed capability curve when ignoring cross-saturation effects. It also examines the modelling of the variation of iron losses as a function of load in the constant torque and power regions. A novel approach based on scaling the no-load losses as a function of load is proposed and shown to give promising results. Finite-element results from two other machines are also provided which show good correspondence.

Stator faults are the most critical faults in induction motors as they develop quickly hence requiring fast online diagnostic methods. A number of online condition monitoring techniques are proposed in the literature to respond to such faults, including the signature analysis of the stator current, vibration monitoring, flux leakage monitoring, negative sequence components of voltage and current and sequence components monitoring based on the identification of asymmetrical behavior in a machine. Negative sequence components of voltage and current and sequence components monitoring are commonly considered for the identification of asymmetrical behavior of induction motors. Negative sequence current analysis is a sensitive technique for the detection of shorted turns as it directly measures the asymmetry produced by the fault. However, the technique is sensitive to other asymmetrical faults and disturbances, which can also produce negative sequence currents. These disturbances include sensor errors, inherent asymmetry and voltage unbalance. This paper provides a comprehensive investigation of the disturbances using a motor model along with experimental measurements under varying load conditions. Then, a new phasor compensation technique is explained to eliminate such disturbances effectively. This technique enables the accurate detection of even relatively small shorted turn faults, even at an early stage. The technique is tested experimentally, and a set of practical results are given to validate the methods developed.

Spectrum analysis of the stator current is commonly used for detecting broken rotor bar faults in induction motors. In this paper we examine the practicality of estimating the number of broken bars using stator current and axial leakage flux measurements. The work is based on experimental current and flux measurements taken from induction motors as the number of broken rotor bars is progressively increased. The test results are compared with theoretical predictions and empirical results from other researchers. The effect of partial load operation is also examined.