Inter-Module SOC Balancing and Fault Tolerant Operation of Cascaded H-Bridge Converter Using Multi-dimensional Modulation For Electric Vehicle Application

This paper 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 PWM (MDPWM) 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 lithiumion 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 demonstrates 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.