In this dissertation, a design approach for medium voltage (MV) PCB-based components, such as the dc bus, is detailed. Key considerations, including electric field (E-field) grading near power terminals and PCB edges, cable feedthroughs, and the integration of components, are explored from the perspective of E-field management. A design example of a 3-level dc bus for a 6 kV-1 MW Power Electronics Building Block (PEBB) is presented. This PEBB was assembled using an array of low-voltage (LV) capacitors to create 3 kV PCB-based capacitor daughtercards, applying the same design principles as the dc bus. The scalability of this design approach is demonstrated with a 9-level dc bus rated for 24 kV. The insulation quality and MV performance of all PCBs have been assessed through partial discharge (PD) analysis using an Omicron MPD 600.
The high-voltage (HV) design approach takes into account the mitigation of peak electric field intensity to minimize insulation degradation caused by electrical stress. In addition to electrical stress, the current carrying capacity (CCC) of these printed circuit boards (PCBs) was assessed concerning steady-state thermal performance and short-circuit (SC) robustness. Multiple configurations were examined to determine the current density, with the aim of reducing temperature. The insulation performance following repetitive fault events was monitored. Although the Partial Discharge Inception Voltage (PDIV) reduced by 50% after 140 SC faults, it remained higher than the operational voltage. This demonstrates the feasibility of utilizing HV PCBs in practical applications.
Finally, the insulation performance of a complete 6 kV PEBB assembly was assessed. The PEBB was assembled component by component, with a focus on tracking the PDIV at each stage. This approach allowed for the qualification of the PEBB for use in a 24 kV PEBB-based converter with a common mode (CM) PDIV of 33.2 kV.
Subsequently, multiple PEBBs underwent testing to simulate their operation within a 24 kV converter configuration, ensuring dependable performance when assembled. Custom support structures were also designed and tested to accommodate the 24 kV PCB bus and dc-link capacitors, serving as interconnections between multiple phase legs and the external voltage source. / Doctor of Philosophy / Power electronic converters are used in many applications ranging from low power to high. Some applications include cellphone chargers, electric vehicle chargers, and even power distribution systems on land and sea. The electronics devices that are at the heart of these converters are rapidly advancing. Newer devices are being fabricated using so-called wide bandgap (WBG) materials such as silicon carbide as opposed to their older silicon counterparts. These WBG devices allow power converters to shrink in size due to their enhanced performance. As these device technologies evolve, the need to completely redesign systems to fully leverage their benefit arise. In this dissertation, the work centers around computer based simulations, coupled with hardware experiments, to design custom components that will allow engineers to significantly reduce the size and weight of medium voltage (MV) power electronic converters while also increasing their power.
The printed circuit board (PCB) is a standard component used in every day electronics. They are used to host electronic components while creating precise electrical connections between them. Although these are very useful in circuits operating at lower voltages, their use has not been widely explored for applications requiring higher voltage such those as where these advancing WBG devices would provide the most benefit. A design method is introduced which allows these boards to be used at relatively high voltage (HV). The robustness of these HV PCBs were evaluated to ensure the feasibility of their continued use after multiple fault events.
The size of power converter can be largely affected by the cooling system. Although the WBG devices can withstand higher temperature operation, the temperature of the device can still be a limiting factor. It is preferred to extract heat from the devices, allowing them to process more power. A standard component of cooling systems using forced air is the heatsink. The standard heatsink has corners that create sharp corners which are not ideal in high voltage systems; spacing between components must be increases to mitigate the effects caused by these sharp corners. Computer simulations were used to aid in the design of a heatsink profile which eliminates these sharp corners and was shown to reduce the clearance between cooling system components by up to 50%.
Each component was individually designed and tested to ensure its reliable operation. However, it's crucial to verify their performance when assembled with other components. In addition to designing components for high voltage operation, the insulation system for a complete converter assembly was evaluated. Once a full converter was successfully qualified, a similar approach was taken to evaluate multiple converters when assembled together, much like building blocks, to construct even larger converters. This rigorous testing and assembly process ensures the reliable operation of the entire system.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/119028 |
| Date | 20 May 2024 |
| Creators | Stewart, Joshua |
| Contributors | Electrical Engineering, Burgos, Rolando, Lu, Guo Quan, Lehr, Jane M., Scales, Wayne A., Dong, Dong |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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