Paper Sharing: High Voltage Side DC-Bus Capacitor Voltage Balancing Control of a 350 kW Multiport EV Charging System

We are pleased to introduce the paper “High Voltage Side DC-Bus Capacitor Voltage Balancing Control of a 350 kW Multiport EV Charging System” written by Abhijit Choudhury, Yuichi Mabuchi, Kimihisha Furukawa, and Nawaz Husain.

Know more about this paper:

https://ieeexplore.ieee.org/document/9947794 

Brief Introduction

Solid-state transformer (SST) is promising for high-power EV charging due to its small footprint . It uses a shared DC bus to connect to EVs via DC/DC converters. However, this approach increases system costs and reduces efficiency due to multiple converter units in series connection.To overcome these challenges, this paper proposes a matrix switch-based solution. Outputs from cell converters are connected to a matrix switch, enabling three separate fast-charging ports (100 kW, 100 kW, and 150 kW). A DC-bus voltage balancing strategy is introduced to keep the high voltage side DC-bus voltages balanced, while even feeding inequal charging power to the connected EVs. Simulation and experimental tests on a 6.6 kV, 350 kW system validate the proposed control scheme.

“The large numbers of converter system simulation”with DSIM

DSIM is used to verify the control scheme for a 6.6 kV and 350 kW system in this paper，which is consisting of 21 cell units (contain 252 switches). “DSIM is used due to the large numbers of converter system simulation, which would not be possible to study using the conventional simulation software like PSIM or Matlab Simulink”. The system performance with balanced and unbalanced load condition is demonstrated from the simulation with DSIM. Under unbalanced load condition, DSIM simulation results show that (1) When the charging power of Electric Vehicle 2 is reduced from the rated power of 90 kW to 70 kW (a decrease of 23%), all three-phase high-voltage capacitor voltages stabilize at 1050 V. The modulation signal of Unit 2 (Vam_up2) is lower than that of Units 1 and 3, demonstrating the controllability of the system. (2) When the charging power of Electric Vehicle 2 is further reduced from the rated 90 kW to 45 kW (a decrease of 50%), all high-voltage capacitor voltages stabilize at the reference value, thereby verifying the stability of the control scheme proposed by the paper.