A Modular Multilevel Interface for Transformerless Grid Integration

Abstract

This paper presents a system configuration for transformer-less grid integration of large-scale charging infrastructures for electric vehicles (EVs) with wireless inductive charging. The proposed configuration relies on a Modular Multilevel Converter (MMC) topology as the grid interface of the charging infrastructure, where one wireless EV charger can be supplied from each individual module. This system topology could provide significant reduction in footprint and complexity of cable installations by allowing for transformer-less connection and direct integration with the medium voltage distribution grid. The requirements for power flow management when charging EVs that are unevenly distributed within the infrastructure are evaluated analytically. On this basis, a control strategy is presented for ensuring horizontal and vertical energy balancing among the MMC arms, and voltage balancing among the modules of each arm. Time-domain simulations demonstrate how the system can operate with severe unbalances resulting from different number and location of charging EV s.