Interleaved PWM for Parallel Converters with Single DC Link for Zero Circulating Current

The work proposes an interleaved modulation method for two three-level converters connected in parallel for grid applications such as high-power active front end rectifiers, STATCOMs, and so on. The parallel converter system is controlled using a centralised predictive controller and 60° discontinuous pulse width modulation, with phase-shifted/interleaved carriers. The proposed PWM utilises the switching state redundancy of ‘0’ state of the flying capacitor topology such that instantaneous pole voltage difference between the converters is zero. The proposed method eliminates the circulating current flow between the converters, and shifts the dominant grid current harmonics to twice the switching frequency. The method also ensures the balancing of flying capacitor voltages along with a reduction in common mode voltage.