Examining a single-stage isolated three-phase AC-to-DC series resonant converter for efficient power conversion
Yusuf K枚sesoy defended his PhD thesis at the Department of Electrical Engineering on September 29th.
As renewable energy systems and electric vehicle infrastructure become more widespread, the need for compact, efficient, and sustainable power conversion grows increasingly critical. Yusuf K枚sesoy addresses this challenge in his PhD research. He does this by exploring a single-stage isolated three-phase AC-to-DC series resonant converter, highlighting its potential as an efficient and cost-effective solution for charging light electric vehicles and integrating renewable energy sources into the grid. The converter distinguishes itself by guaranteeing soft switching during all switching events, enabling high power density and high efficiency, potentially providing unity power factor, and reducing electromagnetic interference (EMI).
In his research, introduces a control technique combined with a switching scheme to maintain zero-voltage switching. The switching events near the resonant current zero crossings are addressed separately. Initial verification through simulations established a theoretical baseline, followed by experimental validation conducted on a 1 kW converter prototype operating with a 400 V AC input. Additionally, experimental studies cover converter operation, transient responses, and overall efficiency. K枚sesoy also discusses practical challenges, such as measurement time constraints, during experimental verification, and proposes solutions to overcome them.
The importance of soft switching techniques
Given the EMI concerns associated with Wide-Bandgap (WBG) semiconductor devices, this research underscores the importance of soft switching techniques. Traditional hard switching converters employing WBG devices often present higher EMI due to high dv/dt and di/dt, typically requiring bulky and complex EMI filters that result in a significant portion of a converter鈥檚 volume and weight. These filters also encounter practical limitations, as parasitic elements in components change the desired behavior from low pass to high pass characteristics at very high frequencies, lowering the filtering performance.
Multi-layer ceramic capacitors
To address EMI at its source, K枚sesoy investigates the use of multi-layer ceramic capacitors (MLCCs), particularly Class II ceramics like X7R, as parallel capacitors across switching devices. MLCCs exhibit nonlinear, voltage-dependent capacitance behavior, which inherently contributes to EMI reduction more effectively than traditional linear capacitors such as NP0/C0G. Through simulations and experimental tests, K枚sesoy demonstrates that the nonlinear characteristics of MLCCs enhance EMI mitigation. The investigation on MLCCs provides insights into optimal capacitor selection for grid-connected power converters.
Overall, this research provides valuable perspectives on advanced converter topologies, effective EMI mitigation strategies, and practical implementation guidelines for soft switching converters, promoting a more sustainable and efficient integration of renewable energy sources and electric vehicle infrastructure.
Title of PhD thesis: . Supervisors: Dr. Henk Huisman and Dr. Jan Schellekens.