A Simplified Solution With Enhanced Filtering Performance Using Positively Coupled Inductors for Parallel Three-Level T-Type Inverters

To address circulating current and output current harmonic challenges in parallel three-level T-type inverters, this study proposes a cost-effective solution utilizing positively coupled inductors (PCIs) with synchronized carriers. The common-mode (CM) equivalent inductor of PCIs enhances filtering of the output current harmonics with smaller inductor sizes, reducing cost compared to uncoupled inductors. The differential-mode (DM) equivalent inductor, in conjunction with synchronized carriers, effectively suppresses the high-frequency circulating current (HFCC) compared to interleaved carriers with negatively coupled inductors (NCIs). The control strategies for output current regulation, low-frequency circulating current (LFCC) suppression and neutral point voltage balancing are designed based on the decoupled mathematical models. Besides, the parameter design processes of PCIs and controllers are provided, and the impact of parameter inconsistency on HFCC and system stability is analyzed. Simulations and experiments validate that the proposed solution achieves superior performance in terms of circulating current suppression, low harmonic distortion, neutral point voltage balancing and dynamic response.