High voltage, high power density electronic power conditioners for microwave power modules (MPMs)

Abstract

Recent advancements in Wide Bandgap (WBG) semiconductor devices have enabled the next generation of power electronics. Applications such as battery electric vehicles and consumer electronic chargers are increasingly incorporating these devices to achieve substantial improvements in achievable power density through increased switching frequencies, enhanced efficiency, and superior thermal performance. High voltage applications such as Electronic Power Conditioners (EPCs) for Microwave Power Modules (MPMs) strive to optimize design for power density to minimize payload weight for Traveling Wave Tube (TWT) based radar transmission systems within airborne applications such as Unmanned Aerial Vehicles (UAVs). There is a significant lack of research regarding the utilization of WBG transistors in such systems with frequencies approaching 1MHz. This thesis begins by giving a brief introduction to the requirements for an EPC within an MPM system, such as the requirement for ultra-low-noise outputs due to the relationship between AC voltage variations and phase-noise performance of the radar transmission process and the required controller bandwidth to ensure adequate voltage regulation under periodic, highly dynamic variations within the output loading depending on the required operating mode. An in-depth literature review is performed to give an overview of current state-of-the-art high voltage converters, transformer design, and advanced control techniques in the scientific literature and commercial products. A novel hybrid fully independently controlled DC/DC converter is proposed for the collector and cathode electrodes of the TWT to allow individual optimization for their specific requirements. A series-parallel resonant converter is proposed for the collector electrode, processing 600W of power at an output voltage of -3kV with a variable switching frequency of between 176kHz-300kHz. The cathode regulator, which is critical for phase noise performance, consists of a fixed-frequency resonant active-clamped fly-back converter operating at frequencies of at least 600kHz, delivering an output power of 60W at voltages of -6kV. A comprehensive discussion of the effects of excessive transformer parasitic capacitance and how this affects maximum achievable switching frequency is discussed. It is demonstrated within this work that commonly accepted equations for the active clamp fly-back converter are no longer valid as the switching frequency approaches the transformer’s Self-Resonant Frequency (SRF) where significant parallel resonant behaviour exists. Simulation results of both converters are presented including steady state performance and dynamic response against multiple radar transmission regimes. An additional four-element multi-resonant active clamp fly-back converter is simulated which can achieve substantially higher gain and bandwidth through reductions in magnetizing inductance. A set of practical results are presented which illustrate the suitability of the proposed topologies through generation of significantly high voltage potentials at elevated switching frequencies with WBG devices which agree well with proposed design procedures. Due to the high frequency nature of the converter, significant issues such as EMI generation and inductive coupling into sensitive feedback lines have limited the ability to form a closed-loop controller. A comprehensive set of recommendations are provided for further work to mitigate these issues.