Single-Phase Charging of EV Embedded Batteries in an MMC with Submodule Override Capability

Abstract

The modular multilevel converter with embedded batteries is a viable alternative in electric vehicle drive systems. This research investigates integrated charging of the embedded batteries in a three-phase converter from a single-phase source without any additional hardware requirements. Two phases of the converter are connected to the supply while the third converter leg is not connected. In a typical charging of the converter batteries, the batteries with a lower state of charge are prioritised. Then all batteries are balanced at an average global state of charge. This research proposes a new sorting algorithm of the converter batteries with an override capability to bypass any individual submodule if required. This bypassing capability is modulation method independent, thus can be integrated with any modulation method. Simulation results and a real-time emulation of the charging system validate the proposed control method and the override algorithm. In addition, an open-loop switching technique is integrated with a new nearest level control-based measurement method of the battery terminal voltage to estimate its initial state of charge. This measurement facilitates a reduced number of voltage sensors for hardware implementation. This method was simulated and validated by comparing the calculated and the measured values of the battery initial state of charge. Real-time emulation of the system utilising hardware-in-the-loop apparatus was carried out, which confirmed the developed control system functions as expected.

Real-Time Emulation of a MMC with BESS for EV Application

“…The converter is tested utilizing two modulation techniques, Nearest Level Control (NLC) and Phase Shifted PWM (PSPWM). The sorting algorithm proposed in [9] is used to test the balancing of the batteries SOC inside one arm. No arm or leg balancing control is implemented in this study.…”

“…During normal operation while the SMs SOC are nearly equalized, there is no need for the additional resistor. 2) Using PSPWM modulation NLC is a simple and effective modulation strategy when used to switch large number of levels [9]. However, its performance is highly disturbed at low levels as shown in Fig.…”