This work presents the design and analysis of two Litz wire transformers for a 500 kHz, 18 kW inputparallel outputseries partial power processing converter (IPOS PPP). Because the two power paths in the IPOS PPP operate as “dc transformers” (DCX), both transformers are designed with the goal of leakage inductance minimization in order to reduce gain variation around the resonant frequency. The selected winding topology with the lowest leakage inductance results in an impedance mismatch among parallel secondaries used in the majority power path transformer, resulting in poor current sharing. In order to balance the goals of leakage inductance minimization and even current sharing, a new winding technique called “intraleaving” is presented which reduces current sharing error from 50%, to 5%. A design rule for “intraleaving” is also established which extends the winding method to different winding configurations and higher numbers of parallel winding. A novel cooling duct designed with computational fluid dynamics is used for transformer thermal management. The cooling duct uses two 30 mm 7.7 CFM fans to cool the transformer winding and achieves a small height of 43 mm and only 6.8 W power consumption. Using the cooling duct, 106 °C peak winding temperature and 76 °C peak core temperature is achieved at 15 kW load, an ∼ 8% reduction compared to using a conventional 120 mm fan 41 CFM fan. The two transformers with the cooling system achieve 635 W/in3 power density, 1U height compliance, and 99.4% peak efficiency. / M.S. / As society moves towards the electric grid of the future, there have been increased calls for the research and development of resonant power converters due to their high efficiency, high power density, and low electromagnetic interference. The high frequency transformer is one of the main components of the resonant converter system as it contributes substantially to the converters volume, power loss, and thermal management risks. This work seeks to address the tradeoffs between leakage inductance minimization and transformer current sharing and proposes a winding method called “intraleaving” which achieves both. Using “intraleaving” current sharing error was reduced from 50%, to 5%. Operating transformers at high frequency reduces their volume in accordance with Faraday’s law but also increases thermal risks due to decreased core surface area, higher winding fill factor, and higher loss per unit volume. A novel cooling duct designed using computational fluid dynamics is presented using two 30 mm 7.7 CFM fans and achieves a small height of 43 mm and only 6.8 W power consumption. Using the cooling duct, 106 °C peak winding temperature and 76 °C peak core temperature is achieved at 15 kW load, an ∼ 8% reduction compared to using a conventional 120 mm fan 41 CFM fan. The transformers with the cooling system designed in this work achieve 635 W/in³ power density, 1U height compliance, and 99.4% peak efficiency.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106781 |
| Date | 28 September 2021 |
| Creators | Ngo, Minh T. H. |
| Contributors | Electrical and Computer Engineering, Dong, Dong, Burgos, Rolando, Boroyevich, Dushan |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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