Abstract

Delta-connected cascaded H-bridge (Δ-CHB) converters are an effective solution for Static Synchronous Compensators and an attractive candidate for next-generation battery energy storage systems and photovoltaic inverters. These applications usually require a zero sequence circulating current injection to control the power imbalance among the arms while maintaining balanced three-phase output currents. Accordingly, this work proposes an instantaneous circulating current reference generation method to track independent power references in each arm of the Δ-CHB converter. The key novelties of the proposed method include its ability to provide circulating current references without requiring phase-lock-loops and without computing the phasor sequence decomposition of the converter voltages and currents. Moreover, it allows independent reactive power control, in contrast to some conventional approaches that only consider the unity power factor. The proposed reference generation strategy obtains the single-phase αβ arm voltages and grid currents. Then, these instantaneous signals are used to solve a linear system of equations, obtaining the required circulating current reference to achieve the desired inter-arm power imbalance. Experimental results are provided for a Δ- CHB-based second-life battery energy storage system with three sub-modules per arm to validate the effectiveness of the proposed circulating current reference generation strategy.