Multiport Converter Topologies for Distributed Energy System Applications

Abstract

In the midst of a present-day global energy renaissance, power electronics has evolved into a top-tier technology discriminator in distributed energy resource (DER) systems. Faced with the formidable task of integrating various types of DER technologies into singular systems, there is a growing appetite for multiport converter (MPC) design. In response, three unique DER MPC topologies are presented: the power sharing converter (PSC), the multi-level nine switch converter (ML9SC), and the modular fuel cell hybrid energy storage (MFC+HES) converter.

First, low-voltage and medium-voltage PSC architectures are shown to decouple series-connected source currents and enable independent control. Multidimensional modeling and analysis is then discussed. Next, three system designs are discussed: single-zone, dual-zone, and multi-zone. Each implements PSC technology and high-frequency isolated full-bridge converters to interface multiple fuel cell sources to a medium voltage grid via a single multilevel neutral point clamped inverter interface. A 1-MW simulation and a reduced-scale hardware prototype offer collaborative insight into the inherit benefits of the proposed PSC systems: increased output power, operational flexibility, thermal balancing, source availability, and cost-effectiveness.

Secondly, the ML9SC is presented as a component-minimized multi-port converter with low cost, high efficiency, high power quality, and low noise. The multiport characteristic of the ML9SC can be effectively employed in uninterruptible power systems, six-phase wind generators, and doubly-fed induction wind generators. Next, operating constraints and modulation index limits are analyzed at different operating conditions. Loss breakdown is analyzed and compared with the conventional back-to-back multi-level converter. Finally, simulation results are included as proof of concept.

Lastly, the proposed MFC+HES converter integrates energy-dense MFC technology with power-dense storage technology. System modularization and hybridization are discussed initially, followed by a selection between supercapacitors and lithium-ion batteries (LIBs). Next, system topology and design is discussed, and the MFC and LIBs are electrically modeled such that Middlebrook’s Extra Element Theorem can mitigate unwanted system resonance and optimize system design. Simulation and hardware results for a 100W MFC+HES system realizes a 300% boost current response capability as well as the following system benefits: limp-home capability, evenly distributed heat/aging, and maximized output power.