Keith A. Corzine

In this study, a 1 MW double-rotor flux switching machine is designed for high-power density electric motors in all-electric aircraft. The motor features an air core stator that accommodates armature windings and field coils. Armature conductors utilize aluminum Litz wire at T=20K, while YBCO superconducting tapes are employed for the field coils operating at T=20 K. The inner and outer rotors are constructed with laminated Hiperco 50. Most notably, superconducting magnetic shields are positioned between the two rotor teeth to minimize leakage flux and guide magnetizing flux on a pre-determined path. This new motor is shown to have widely superior power density and efficiency. The motor design is evaluated across different pole/slot combinations, revealing that higher pole numbers increase power density. Specifically, a 20-pole/15-slot double rotor flux switching motor with a shield achieves a power density exceeding 100 kW/kg, with efficiency reaching up to 99.5%. This was twice the power density of a comparable design without the shield. The thermal management system has been designed for the proposed motor. The result is a machine that satisfies requirements for electric aviation propulsion applications.

Electromagnetic interference poses enormous challenges for feedback-controlled systems, especially at medium-voltage levels. As power converters are increasingly utilized for medium- and high-voltage applications, optically-based measurement methods must be explored. This paper investigates current measurement via electroluminescence from silicon carbide semiconductor devices. A SiC half-bridge MOSFET module, provided by Powerex, is manufactured with fiber optic cables placed against the semiconductor junctions. The new fiber ports are employed to characterize the light spectrum as a function of conducted current and junction temperature for the body diodes. Most of the light energy is concentrated around peaks at 390 nm and 500 nm. It is observed that although the energy at the 390 nm peak increases with rising temperature, the energy at the 500 nm peak decreases. Therefore, the total light output is seen to only slightly vary with temperature and mostly depends on conducted current. A function is fitted to the light transducer output as a in relation to the on-state current. This function is utilized in a microprocessor that implements feedback current control in a buck converter. This type of control forms the basis of torque regulation in a motor drive or an "inner-current loop" of motor drive speed control or converter voltage control. The new electroluminescence control was demonstrated in the laboratory on a prototype system where the current command is stepped from 0 to 25A, showcasing the effectiveness of the new optical sensing method.

The increasing demand for high-power density motors in electric transport industries opens a new research opportunity to develop motor topologies with less weight and high efficiency. In particular, all-electric aircraft applications require very high power density motors. This paper shows the design of a new 1 MW 20-pole/15-slot double rotor flux switching machine with high-temperature superconducting field coils and thermal management system. The proposed motor features an air-core stator. Aluminum Litz wire is used for the armature conductors, and the YBCO- high-temperature superconducting material is used for the field coils. The armature winding and field coils operate at 95K and 65K, respectively. The active part power density including rotors, armature windings and field coils obtained with the proposed design is 29.3kW/kg. The specific power density of proposed motor considering mechanical, support structure and TMS is about 18.5 kW/kg. The efficiency can be higher than 98.7% which satisfies the requirement of electric aviation.

In this paper a fault-tolerant isolated dc-dc converter is proposed for shipboard power applications. In this topology, an active 5-level T-type converter is used on the primary and secondary sides of a high-frequency transformer. The operation of the proposed converter is optimized based on minimizing the losses. A fault-tolerant analysis is carried out for this converter and post-fault switching methods are proposed for each faulty condition. The proposed converter features better fault tolerance options and higher efficiency compared to the common dual active bridge dc-dc converters. Finally, the operation of the proposed structure in the normal and faulty conditions are verified through experiments.

In this paper a bidirectional isolated dc-dc converter is proposed for application in shipboard power systems. In this topology, an active 5-level T-type converter is used on the primary and secondary sides of a high-frequency transformer. The operation of the proposed converter is optimized based on minimizing power losses. For the optimization, the transformer core loss, reactive power, and rms current are considered. Wide band gap devices are used for minimization of semiconductor switching losses. A control method based on the Fourier series and decomposition theorem is proposed. The proposed converter features higher efficiency, fault tolerant capability and smaller filter size compared to the common dual active bridge dc-dc converters. To reduce voltage overshoot, a laminated dc-link is designed and a two-level turn-off method is used for operating frequencies around 75 kHz. Finally, the step-up and step-down operations of the proposed structure are verified through experiments.

Flying-capacitor (FC) based multicell inverters have recently drawn more attentions due to their outstanding performances. In this paper, a new approach to actively control the FC voltages in seven-level full-bridge FC multicell (FCM) inverters is presented. In the proposed method, first, the output current's direction and voltage of the FCs are measured and are interpreted into logic variables. Next, these logic variables are fed into a set of equations, named as logic-equations, to achieve two goals: 1) to adjust the voltage of the FCs at their reference values; 2) to generate the required voltage level at the output which is determined by pulse-width-modulation (PWM) unit. Since the proposed method does need neither the optimization of cost functions nor the utilization of proportional integral (PI) controllers, it is straightforward and simple to be implemented, specifically for the FC-based industrial inverters. To verify the performance and feasibility of the proposed logic equations-based active voltage balancing method, the simulation and experimental results obtained from a seven-level full-bridge FCM inverter are provided. The proposed method is validated under the transient conditions such as variations of modulation index and the dynamic changes of dc link voltage to demonstrate its robustness and performance.

Multilevel inverters provide appealing advantages such as improved efficiency, superior thermal performance, better distribution of the switching and conduction power losses, smaller size of passive components including output ac filters and EMI filters, as compared to their two-level counterparts. The flying-capacitor (FC)-based topologies are attaining more attentions, and are finding lots of medium-voltage and low-voltage industrial and residential applications. The FC-based active neutral-point-clamped (ANPC) inverter, as a hybrid topology based on the 3-level ANPC and the FC-based configurations, offers outstanding advantages including the reduced number of FCs as well as switching power cells, improved efficiency, and enhanced power quality. However, the utilization of high-voltage line-frequency switches, as a major drawback, hinders the ANPC converter from expansion and penetration into the high-voltage ranges. The dual flying-capacitor (DFC)-ANPC topology resolves this issue through introducing the zero-voltage-switching (ZVS) feature into the line-frequency devices. This soft-switching makes it possible to use the series connection of several low-voltage devices for the realization of the high-voltage switches without having the transient voltage imbalance issues. This paper studies the thermal benefits that are achieved in the DFC-ANPC topology alongside the ZVS operation of its line-frequency high-voltage switches. Furthermore, an active voltage balancing technique, based on logic-equations, is proposed in this paper for control of the FCs voltages. The experimental results are provided to validate the improved thermal performance of the DFC-ANPC topology as well as the active balancing technique for the regulation of the FC voltages.

Extensive deployment of power electronics loads in naval ship power systems indicate the ship electrification is inevitable in future trends. Next generation warships require high power density weapons drawing pulse power from dc grid. A particularly concerning issue is that these pulse loads draw large currents in short periods of time similar to fault behavior; and may be indiscernible from a fault. This paper proposed a novel machine learning based algorithm – long short-term memory (LSTM) recurrent neural network (RNN) based autoencoder (AE) networks to detect dc faults and monitor load conditions applied to naval pulse loads. The novel load monitoring solution presented herein can be applied to any load profile that exhibits repetitive transients during normal operation. The frequency-domain features of the load current are extracted under wavelet transform for the network training to set the network weights and biases. Once the network training is completed, the LSTM RNN based AE will produce both signal classification and signal reconstruction of the pulse load based on wavelet features of input current. Any faults should yield large reconstruction errors for protective action. Finally the method is demonstrated in experimental results.