This paper examines a number of techniques for junction temperature estimation of silicon carbide (SiC) MOSFETs devices based on the measurement of temperature sensitive electrical parameters for use in online condition monitoring. Linearity, sensitivity to temperature, and circuit design for practical implementation are discussed in detail. A demonstrator based on the measurement of the quasi-threshold voltage, the turn-on transient characteristic (di/dt), the on-state voltage, and the gate current peak is designed and validated. It is shown that the threshold voltage, the estimation of the gate current peak, and the on-state voltage have potentially good sensitivity to temperature variation and linearity over a wide operating range. Very low sensitivity to temperature is shown for di/dt. The proposed method can provide a valuable tool for continuous health monitoring in emerging applications of SiC devices to high-reliability applications.

This paper evaluates a three-phase ac main exciter (ME) for a wound-field synchronous aircraft starter-generator capable of operating in both starting and generating modes. The research has been based around a 225-kVA generator utilizing the existing single-phase ME hardware. Initially, a reconfiguration of the existing single-phase unit into a three-phase one has been carried out. Subsequently, an optimization of the ME stator has been performed. The hardware evaluations have been performed in parallel to the development of design methodologies suitable for future starter/generator design. The three-phase ac ME design needs to satisfy the required current output at both start and generate modes with minimum input voltampere rating of the inverter required to drive the ME. The ME's output capabilities have been predicted in all operating conditions using a computationally efficient combination of 3-D finite-element models together with a lumped-parameter circuit approach. The theoretical findings from the analyses have been validated on a prototype ME, confirming that the three-phase ac ME is capable of generating the required current output in both operating modes. The developed modeling system allowed for the identification of the ME's optimal operating points with regard to the minimum input apparent power (in voltamperes) at the required output power and a methodology for the accurate and computationally efficient evaluation of future starter/generator designs.

Fast and reliable detection of stator faults is of key importance for fail-safe and fault-tolerant machine drives in order to immediately trigger appropriate fault mitigation actions. The paper presents a detailed analytical and experimental analysis of the behavior of a closed-loop controlled permanent magnet machine drive under interturn fault conditions. It is shown that significant second harmonic components in the dq voltages, currents, instantaneous active power (IAP), and instantaneous reactive power (IRP) are generated during turn fault conditions. The analyses further show that the increase of the second harmonic in IAP and IRP during fault conditions is comparatively higher than that of voltage and current, making them ideal candidates as turn fault indicators. A turn fault detection technique based on second harmonic in IAP and IRP is implemented and demonstrated for a triple-redundant, fault-tolerant permanent magnet assisted synchronous reluctance machine drive. The effectiveness of the proposed detection technique over the whole operation region is assessed, demonstrating fast and reliable detection over most of the operating region under both motoring and generating mode.

Accurate prediction of temperature-dependent ac winding loss effects is crucial in the design of electrical machinery. Average ac winding loss as a function of operating frequency is commonly characterized by the ratio of the equivalent ac and dc resistances (R_ac/R_dc). However, as the ac and dc components of the winding loss scale differently with temperature, a single value of R_ac/R_dc derived for one temperature can be inadequate when used in thermal modeling. In this paper, methods of deriving the R_ac/R_dc ratio, together with scaling techniques of the ac winding loss accounting for thermal effects, are discussed. As an alternative to computationally intensive 3-D finite-element analysis, an experimental approach based on tests on full-scale stator assemblies is proposed. A previously proposed scaling technique of the ac winding loss is discussed and developed further. The proposed techniques of deriving the ac winding loss accounting for temperature variation are illustrated using both theoretical analysis and experimental data.

This paper presents a detailed analysis of the dynamic behaviour of a hybrid ac-dc electric power system under large disturbances. The system under study is representative of a power distribution network which is currently being developed for future "more electric" aircraft (MEA). Brayton-Moser mixed potential is employed along with Lyapunov stability theorems to determine an analytical estimation of the large-signal stability boundary of the system. Extensive time- domain simulations using detailed behavioural models of the power system components are undertaken. It is shown that the analytically derived region of attraction agrees reasonably well with that obtained from the time-domain simulation. The predicted instability is experimentally validated.

The present paper describes an angle and speed estimation algorithm suitable for the control of a wound-field synchronous starter/generator (S/G) without position sensors for aircraft engine starting applications. The proposed control strategy is based on the injection of a high-frequency voltage signal and the subsequent demodulation of the resulting high-frequency stator current components. The coupling due to high-speed operation that degrades the estimation accuracy of similar algorithms based on signal injection is taken into account. Modeling of the machine response to a high-frequency voltage signal injected into the estimated d-axis is presented, also considering the influence of damping circuits both on the d- and q-axis. Local asymptotic stability of the proposed observer is also demonstrated. Through extensive experimental results, the proposed control technique is shown capable of guaranteeing full-torque sensorless operation at zero speed and sustained operation up to engine ignition speed.