LQG Current Control Strategy for a CHB Converter-Based Second-Life Battery Energy Storage System without Steady-State Error

Optimal control strategies for cascaded H-Bridge (CHB) converters have attracted significant interest in recent decades due to their high performance and flexibility in including multiple control objectives. Nevertheless, the steady-state performance of these control strategies can deteriorate if the converter model has parameter mismatches and/or sub-module capacitor voltage ripples are not measured. This work proposes a linear quadratic Gaussian (LQG) current control strategy for a CHB-based second-life battery energy storage system. The main novelty of the proposed LQG strategy lies in an augmented state space model that allows a Kalman Filter observer to estimate the instantaneous arm voltage disturbances representing the converter modelling errors in the second-life battery packs. These estimated voltage disturbances are used to enhance the arm current predictions and compute the steady-state arm voltage references used by a linear quadratic regulator current control strategy. As a result, the proposed LQG strategy eliminates the steady-state error in the CHB converter currents even if the second-life batteries are modelled as ideal constant voltage sources. Experimental results are provided for a three-phase CHB converter with nine SMs directly connected to second-life battery packs to validate the effectiveness of the proposed LQG strategy.