Simulation Based Grid Code Compliance Testing for Mega Watt Charging Systems

Abstract

Electrification of heavy-duty vehicles is pushing the demand for megawatt-level chargers (MCS) capable of delivering high-power loads in an efficient manner. The integration of such high-powered systems into the electric grid poses concerns regarding power quality and reliability issues due to the poor grid condition in many locations. The current research investigates the Grid Integrated MCS Validation Framework (GMVF) under the project called Grid code Compliance by Simulation (GCCS) for evaluating the performance of megawatt EV chargers under realistic network conditions. A comprehensive simulation model of megawatt class charging system was designed using MATLAB/Simulink software, which includes AC-DC interface converter for connection to the utility grid, isolated DC/DC converter, and battery charger following CC-CV control strategy. Simulations were conducted under different grid conditions, ranging from strong to moderate and weak grids, especially focusing on PCC performance. To be consistent with industry standards, testing according to EN 50549-2 standard procedures was carried out, including LVRT capability, OVRT capability, steady-state deviation of voltages up to ±10%, and off-nominal frequency operation of 49 Hz. Protection and operation were modelled to meet IEC 61851-23-3 guidelines for high power DC charging systems. From the findings, it can be concluded that the system works well at megawatt-scale operations, even in difficult circumstances like variation in voltage and frequency of the grid. In the ride through scenarios, the charger stays connected and is able to recover well, thereby fulfilling grid code requirements for continuous operation. Increased harmonic distortion and higher system stress were observed under weak-grid conditions, highlighting the importance of grid strength for stable megawatt charging system operation. Influence of converter topology on system performance for varying grid condition was identified. Two-level inverters were found better in strong grids, but limitations were observed when the grid is weak. Three-level inverters, by contrast, deliver better harmonic performance and stability under challenging conditions, making them more suitable for weak grids. The findings also highlight the importance of site-based grid evaluation prior to the deployment of megawatt charging systems. Reliable operation of chargers without violating standards is more important than obtaining perfect waveforms. This study shows that it is important to assess the characteristics of grids before designing and configuring the charging system with appropriate topology and protection measures. The proposed framework provides a practical simulation-based approach to evaluate grid-compliant megawatt charging stations prior to deployment.