A Common-Mode Balancing Accelerator for Single-Phase T-type Converter with LCL Filter

The single-phase T-type converter has an imbalance issue of dc-link voltages to deal with. Instead of active neutral point (NP) control, natural balancing properties are typically preferred owing to their superior spectral performance of output voltage. However, existing techniques to accelerate the natural balancing process inevitably require several extra passive elements. To improve the power density, this paper proposes a common-mode (CM) balancing accelerator to identify and drive specific harmonics channeled into dc-link by reusing the LCL filter. Moreover, a precise high-frequency (HF) balancing model focusing on any sideband harmonic is established to predict the dominant balancing time. Based on the resultant CM harmonic distributions, the accelerator is configured accurately using the recommended sideband harmonics resonating around twice switching frequency. Ultimately, the feasibility of CM balancing accelerator and its theoretical analysis are verified experimentally.