A non-invasive phase current reconstruction strategy for three - level inverters with fixed sampling instants

The conventional current reconstruction strategies for three-level inverters require current sampling at varying instants, and employ modified PWM to compensate periodic current reconstruction dead zones (CRDZ) in high- and low-modulation regions as well as at sector boundaries. However, those approaches not only increase algorithm complexity but also introduce additional current harmonics due to asymmetric PWM. To address these issues, a non-invasive phase current reconstruction strategy with fixed sampling instants is proposed in this paper. First, this strategy employs a pair of redundant small vectors output at the start and center of the SVPWM cycle as effective current reconstruction vectors (ECRV), thereby simplifying the sampling process by fixing it at the start and center instants of the carrier. Second, a single-current-sensor topology that couples both phase and the DC-link neutral point branches is developed to eliminate CRDZ at sector boundaries. And in the low-modulation region, zero-voltage vector groups are utilized to replace redundant small-voltage vector groups for current sampling, thus eliminating CRDZ in this region. As a result, non-invasive phase current reconstruction without modifying the PWM is achieved across all areas within the hexagonal space voltage vector contour. Additionally, a mathematical method is provided to design the current reconstruction topology. Based on the switch states of selected ECRVs, a unified mapping matrix is established to map directly sampled currents and phase currents, using multiple coupled branches and their coupling times as independent variables. The coupling positions and coupling times are determined by solving the full-rank condition of the matrix. Finally, experimental results validate the effectiveness of the proposed strategy. • A novel non-invasive phase current reconstruction strategy with fixed sampling instants is proposed to eliminate current reconstruction dead zones (CRDZ) in three-level inverters. • The strategy employs redundant small vectors as effective current reconstruction vectors (ECRVs) and a single-current-sensor topology coupling two positions to eliminate CRDZ at sector boundaries and in the low-modulation region. • A mathematical framework is developed to design the current reconstruction topology, ensuring effective elimination of CRDZ across all modulation regions. • Experimental results validate the effectiveness of the proposed strategy in achieving non-invasive phase current reconstruction.