Doctoral Defense

Electro-Mechanical-Thermal Co-design and Side Effect Mitigation for a 75 kVA SiC-based Intelligent Grid-Interface Bidirectional Converter

Abdul Basit Mirza

July 17, 2024
9:00 AM
Light Engineering, Room 250
Advisor:  Fang Luo

Grid-integration of renewables and energy storage through power electronic grid interface converters is essential for achieving a more sustainable smart grid. This mission involves developing compact and efficient converters with standardized hardware interface
and communication architecture to address redundancy and compatibility concerns.

In line with the mission, this dissertation presents an electro-mechanical-thermal co-design and packaging of a two-stage SiC-based 75 kVA Intelligent Grid-Interface Bidirectional Converter (IGIBC), comprising DC-DC and DC-AC power stages with standardized interconnects. The power stage is built using TO-247 discrete devices and is 3-D packaged on a cylindrical-hole-based three-face utilized heat sink, achieving 5.5 kW/L power density, including passive components. For the DC-AC stage, Two-Level Split-Phase topology (2L-SP) is employed, owing to its lower switching loss and output dv\dt and increased crosstalk immunity compared with simple Two-Level (2L) topology. Further, from the intelligence perspective, the proposed IGIBC features online non-invasive health monitoring of converter components using a Digital Twin (DT)-based approach.

Following the IGIBC design, the dissertation explores the lower output dv/dt benefit of 2L-SP topology for mitigating side effects, including conducted Common Mode (CM) Electromagnetic Interference (EMI) emissions and Reflected Wave Phenomenon (RWP) in
cable-connected motors. Firstly, the DC-side conducted CM EMI emissions of the 2L-SP are investigated and compared with the 2L topology. CM modeling of 2L-SP is performed in the frequency domain, followed by validation on an 18 kVA SiC-based hardware prototype. The experimental results demonstrate that increasing split inductance value significantly reduces the CM EMI noise magnitude, with a maximum reduction of 17.85 dB.

Further, the research delves into the investigation of RWP in the 2L-SP inverter-fed motor drive and compares it with the 2L configuration with the output reactor (2L-LF). The experimental results show a maximum reduction of 68% and 73% in load-side overvoltage and drive-side overcurrent. Moreover, split-inductors in 2L-SP decouple load and antiparallel diode parasitics from the device, achieving a 17 % lower switching loss than 2L-LF.