Integration Modulation for Current Ripple and High-Frequency Zero-Sequence Circulating Current Reduction on Two-Parallel Three-Level Converters

Realizing simultaneous reduction of zero-sequence circulating current (ZSCC) and current ripple for two-parallel three-level neutral-point-clamped (3L-NPC) converters are always challenging. To overcome this obstacle, this article proposes a carrier-based integrated modulation method, which analyzes and controls the two-parallel 3L converters as an integrated five-level (5L) converter. First, the nearest three vectors are applied in each subsector to minimize the current ripple. Then, the corresponding 5L-vector sequences are optimally distributed into dual 3L-vector sequence combinations with the smallest common-mode voltage differences. A uniform distribution principle is also summarized based on reference signal decomposition and carrier type selection, which allows easy implementation in mainstream microcontrollers. Moreover, quantitative performance comparisons that compare the current ripple and the high-frequency ZSCC between the proposed method and several state-of-the-art strategies are subsequently conducted. Finally, comparative experiments are performed to verify the proposed method.