Colloquium on Design and Performance Optimization of Power Converters for Energy Storage Systems

PhD Thesis Colloquium
Title: Design and Performance Optimization of Power Converters for Energy Storage Systems

Speaker: P. Roja
Date: Tuesday, Dec 31, 2024
Time: 3.00pm-4.00pm
Venue: MMCR – EE

Abstract:
Energy shortages and power outages have emerged as critical concerns in the contemporary energy landscape, exacerbated by escalating energy demands and the global imperative towards clean energy and decarbonization. Addressing these challenges necessitates the deployment of energy storage systems (ESS) to mitigate both long- and short-duration outages, coupled with the integration of renewable energy sources through power converter interfaces. While battery-based ESS are conventionally employed for short-term blackouts, this work focuses on developing ultracapacitor (UC)-based ESS tailored for pulsed power applications, chosen for their inherent high-power density and superior lifecycle characteristics. The research also investigates isolated DC-DC converters, specifically phase-shifted full-bridge (PSFB) topology, opted due to its constant frequency operation and inherent soft-switching features.

This research encompasses the optimization of UC stack sizing and power converter design for specific contingency requirements. The inherent non-linear behavior of UCs is analyzed, leading to the development of a framework for accurately characterizing the effective UC stack capacitance. This framework is utilized to propose a systematic design procedure that optimizes the discharge ratio and iteratively selects stack parameters, minimizing the overall system cost.
Furthermore, the research investigates PSFB converter for both low and high-power applications. A comprehensive analysis of the PSFB topology is conducted, examining the influence of various circuit parameters, including transformer parasitics and device capacitances, on converter operation and the design trade-offs. This analysis culminates in the development of a two-level loss-optimal iterative design algorithm that determines a unique set of design parameters across a wide range of specifications.

For high-power applications, the research explores a modular system of PSFB converters configured in an input parallel output parallel (IPOP) topology. Recognizing the limitations of traditional equal power-sharing schemes, this work proposes an asymmetrical module design coupled with a Lagrangian loss-optimal load-sharing control technique to enhance system efficiency. This approach enables the system to operate with high efficiency across the entire load range, effectively managing both fixed and dynamic loads.

The efficacy of modeling, analysis and the proposed design algorithms for the UC stack and the PSFB converter, including its modular configurations, is validated through experimental verification on 1-3kW hardware prototypes.