Inter-module state-of-charge balancing and fault-tolerant operation of cascaded H-bridge converter using multi-dimensional modulation for electric vehicle application

This study presents a method for module-level state-of-charge (SOC) balancing and fault-tolerant operation of the cascaded H-bridge (CHB) converter-based battery energy storage system for electric vehicle (EV) application. The proposed methods are based on the multi-dimensional pulse-width modulation (MD-PWM) strategy. It is shown that the proposed methods are conveniently integrated with the PWM generation algorithm. A conceptual design of modular battery pack (or micro-pack) system using lithium-ion cells for the CHB converter is described to show its feasibility for EV application. A brief review on the MD-PWM strategy and a detailed explanation on the method to integrate the inter-module SOC balancing and fault-tolerant control with the PWM generation are presented. Experimental results from the laboratory setup of a five-level CHB converter driving an induction motor with a battery system consisting of six 52.8 V 60 Ah (16 lithium-ion cells in series) modules are presented to verify the system operation for fault-tolerant control and the proposed SOC balancing method. The results demonstrate the need of SOC balancing, and efficacy of the proposed methods in achieving fault-tolerant as well as SOC-balanced operation to prolong the system operation.