Reconfigurable Power Converters with Increased Utilization for Unbalanced Power Distribution System Applications

TL;DR

This paper tackles phase unbalance mitigation in distribution networks by introducing reconfigurable four-wire voltage-source converters (4W VSCs) with adjustable leg capacities to enlarge the feasible power-transfer set. It defines capability charts that quantify the region of feasible injections $P$ under current and switching constraints, and develops numerical methods (brute-force grids, boundary-radius analysis via the Clarke transform, and discontinuity considerations) to compute capability-area and capability-volume measures for Standalone and Interconnected 4W VSCs. Through HB sizing case studies, it compares fixed designs with an idealised continuous-capacity converter, showing that conventional designs may require up to $75.3\%$ more capacity to match an ideal reconfigurable, while reconfigurable designs provide substantial gains in both area and volume of the capability charts. The results indicate that low-cost reconfiguration can significantly improve converter utilization and mitigate distribution-system congestion, offering a practical pathway to cheaper and more flexible unbalance mitigation in future energy systems.

Abstract

A low-cost reconfiguration stage connected at the output of balanced three-phase, multi-terminal ac/dc/ac converters can increase the feasible set of power injections substantially, increasing converter utilization and therefore achieving a lower system cost. However, the approach has yet to be explored for phase unbalance mitigation in power distribution networks, an important application for future energy systems. This study addresses this by considering power converter reconfiguration's potential for increasing the feasible set of power transfers of four-wire power converters. Reconfigurable topologies are compared against both conventional four-wire designs and an idealised, fully reconfigurable converter. Results show that conventional converters need up to 75.3% greater capacity to yield a capability chart of equivalent size to an idealised reconfigurable converter. The number and capacity of legs impact the capability chart's size, as do constraints on dc-side power injections. The proposed approach shows significant promise for maximizing the utilization of power electronics used to mitigate impacts of phase unbalance.

Figures (12)

• Figure 1: A four-wire (4W) voltage source converter (VSC) system can be used to balance phase currents by injecting unbalanced active powers. Balanced phase currents ensures that network assets can be fully utilized.
• Figure 2: In this work, we classify Four Wire VSC Systems as either (a) Standalone, which cannot transfer power to or from the dc subsystem (but can transfer power between phases), or (b) Interconnected, with some resource connected to the dc subsystem to enable net power transfer across the VSC.
• Figure 3: Conventional and proposed four-wire VSC system designs. The conventional design (a) has four legs hard-wired to the ac output wires, where the proposed reconfigurable design (b) has any number of legs $m$ with arbitrary current ratings $\alpha$ whose output can be reconfigured to redistributed current carrying capacity as necessary.
• Figure 4: An example reconfigurable 4W VSC system with battery energy storage system and two HB packages.
• Figure 5: Constraints that create capability chart $C$ for a fixed converter $\mathcal{U}^{\mathrm{Fix}}(4)$ and the idealised converter $\Omega$.