Date of Graduation

12-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering and Computer Science

Advisor/Mentor

Zhao, Yue

Committee Member

Balda, Juan C.

Second Committee Member

Chen, Zhong

Third Committee Member

Hu, Han

Keywords

DC/DC converter; Magnetics; Power electronics

Abstract

Thanks to the advancement of semiconductor technology, the silicon carbide (SiC) devices with high voltage and power capability are developed and widely used in several industry applications, e.g., gird-connected photovoltaic (PV) system, data center power supply, and electrical vehicle (EV) charging station. After the concept of solid-state transformer (SST) was proposed as an important solution to the medium voltage (MV) power conversion systems, this bidirectional isolated DC/DC converter has attracted much attention in academia and industry. One of the main advantages of SST is to improve both the power density and efficiency of the power conversion system by replacing the bulky line-frequency transformer (LFT) with the medium-frequency transformer (MFT). In addition, SST has proved to have high voltage and power regulation capabilities with proper control methods.

As a crucial component of SST, the MFT can significantly influence the performance of the power conversion system. The MFT represents a large proportion of the entire power conversion system in both loss and size aspects, and its temperature rise has a direct impact on reliability. Even though some research has discussed the design of MFT in SST, there still exist many challenges in the process with more and more stringent requirements. To achieve high power density, efficiency, and thermal capability, the MFT should be designed based on detailed analysis of SST operation principle, accurate electromagnetic thermal coupling models of MFT, and advanced optimization algorithms. In addition, some new structures of MFT can be proposed with different thermal and isolation considerations. In this work, the matrix core transformer (MCT) is presented and analyzed for high power bidirectional isolated DC/DC converters to address the aforementioned issues in MFT design. Combined with the operation principle of the power converter, the loss, leakage inductance, and thermal network models of MCT are proposed. With the above electromagnetic thermal coupling models, Pareto optimization and the nondominated sorting genetic algorithm III (NSGA-III) are introduced as the optimization engines for MCT design. Two high-power-density MCT prototypes (100 kW/50 kHz and 100 kW/100 kHz) for different applications are designed based on the optimization results and built with additive manufactured bobbin designs, which are designed to control the leakage inductance and provide airflow path. With both finite element analysis (FEA) simulation and experimental studies, the performances of optimal MCT designs are validated, especially including excellent heat dissipation capability.

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