Load Balancing of a Modular Multilevel Grid-Interface Converter for Transformer-Less Large-Scale Wireless Electric Vehicle Charging Infrastructure

Abstract

This paper analyses the requirements for load balancing of a new transformer-less grid interface topology for large-scale electric vehicle (EV) charging infrastructures. The proposed configuration utilizes a Modular Multilevel Converter (MMC) to supply wireless EV chargers from each module. The inherent galvanic isolation provided by wireless inductive power transfer and the scalability of the MMC topology enable transformer-less connection to medium voltage (MV) distribution grids. This can reduce the footprint and copper volume of the internal power distribution for the parking infrastructure. The load distribution within the MMC topology depends on the location and power requirements of each EV to be charged. Requirements for load balancing by controlling the internal circulating currents of the proposed topology when supplying unevenly distributed loads are derived. It is also demonstrated how a second harmonic component of the circulating currents can be utilized to ensure balancing capability within each MMC arm, and how its required amplitude depends on the load distribution. The theoretical analysis and the performance of a corresponding control strategy are first verified by time-domain simulations of a large-scale infrastructure. Experimental results from a small-scale prototype based on an MMC where each arm has 12 modules with individual controllable loads are presented.

Optimal load management strategy for large electric vehicle charging stations with undersized charger clusters

“…Besides, comprehensive descriptions of LCS-suitable topologies can be found only in few sources in the literature such as Ref. [12,13]. The most suitable topology for LCSs is still an open question that needs to be answered by further research.…”

“…The objective function (13) penalises the deviations from the schedules calculated in the optimal scheduling step.…”

Optimal Management for Megawatt Level Electric Vehicle Charging Stations With a Grid Interface Based on Modular Multilevel Converter

“…This paper addresses a special grid interface topology that is particularly interesting for large scale EVCSs in space-constrained urban areas, as it has the potential to significantly reduce the footprint and the requirements for the internal electrical installations. This topology is based on a modular multilevel converter (MMC) where each module supply voltage at floating potential to a single wireless charging unit (WCU) [6]. An overview of the studied configuration is shown in Fig.…”

“…However, for the system to remain connected to public grid, it is necessary to keep the three-phase grid current balanced and sinusoidal despite the loading unbalances between MMC phases and arms. Moreover, loading unbalances between the modules of a single arm may require high circulating currents within the MMC topology to avoid voltage collapse or over-voltage in the MMC modules [6], [7].…”

Water Eutrophication based on Multilevel Grid

“…In this paper, by analyzing the causes of eutrophication of water body, simulating the process of eutrophication of water body, building a MLG of eutrophication of water body, making full use of limited resources to realize the calculation of rain and flood of lakes, the hydrological parameters in the flow field collected by the MLG of eutrophication of water body are more authentic and more representative in describing the temporal and spatial change laws of rain and flood processes of lakes. Under the condition of the same model principle and method, the lake rain and flood calculation model using the MLG of water body as the calculation unit has higher simulation accuracy, wider application range and more efficient model operation [4][5].…”