Voltage Vector Redundancy Exploitation for Battery Balancing in Three-Phase CHB-Based Modular Energy Storage Systems

This article presents a flexible controller algorithm for bidirectional modular cascaded H-bridge (CHB)-based battery storage systems. The primary objectives are to maintain high-quality power on the ac side while balancing dc-side battery voltages under charging or discharging operations. The proposed algorithm is based on a finite-set model-predictive current control (FSMPC) technique, which performs in-phase and phase voltage equalization in two complementary balancing terms by taking advantage of intrinsic voltage vector redundancy characteristic of three-phase CHB converters. Additionally, the proposed modifications to the FSMPC provide lower demand on computational resources of the controller through offline reordering of vectors and adjacent vector introduction, which also brings the least differential-mode
$dv/dt$
as an added value. Effects of battery voltage variation in charge/discharge cycles and voltage drop caused by nonideal semiconductors are considered to ensure the most accurate performance during steady-state, transient, and common-mode voltage reduction operation. The proposed approach is an efficient easy-to-implement multiparameter controller, which handles all the tasks needless to any additional control loops. Simulations and experimental prototyping results validate the feasibility of the battery voltage balancer terms to be utilized in battery storage applications with no downside impact on key power exchange functions.