Analysis and optimized design methodology of a fourth-order LCLC resonant converter for high-voltage DC applications

High-voltage (HV) DC power supplies, defined here as sources providing DC output in the kilovolt range (typically a few to a few tens of kilovolts), are critical in scientific and industrial applications that demand low ripple, high efficiency, precise voltage regulation, and low stored energy. Achieving these requirements is challenging due to the significant parasitic elements of HV high-frequency transformers, such as leakage inductance (Lleak), reflected winding capacitance (Cp), and magnetizing inductance (Lp), which increase circulating currents and reduce efficiency. To address these challenges, this work proposed an optimal design methodology for a fourth-order LCLC resonant converter that gainfully integrates Lleak, Cp, and Lp into the resonant tank circuit. A steady-state analysis and design methodology is developed to ensure unity power factor (UPF) operation, soft-switching in entire load range (ZCS turn-on\turn-off), and load-independent constant voltage output characteristics. In addition, a kVA/kW size optimization technique is presented to minimize stored reactive power at the optimal quality factor (Qs,opt=1/γ, where γ = Lp/Ls denotes the magnetizing to series inductance ratio. A scaled down -5 kV prototype validates the proposed research, demonstrating UPF operation, soft-switching, a peak efficiency of 97.26%, and ∼6.4% voltage regulation at 20% load, thereby confirming the validity of the theoretical analysis.