An Improved ARS-VSFPWM Strategy for Phase and Zero-Sequence Circulating Current Control in Paralleled Interleaved Multilevel Inverters

In parallel interleaved multilevel inverter (PIMI) applications, the objectives of suppressing the phase circulating current (PCC) and the zero-sequence circulating current (ZSCC) under conventional SVPWM are often conflicting. This makes it challenging for conventional modulation strategies to achieve their coordinated mitigation. To address this issue, this paper proposes an improved asymmetric regular sampling variable-switching-frequency PWM (ARS-VSFPWM) strategy incorporating a cost function model. First, to overcome the failure of symmetric regular sampling (SRS) under low-switching-frequency conditions, a predictive model for PCC and ZSCC is established based on ARS while accounting for control delay. Then, cost-function-based online optimization of vector selection achieves qualitative coordinated suppression of both circulating currents. Furthermore, variable switching frequency introduces an additional degree of freedom, dynamically adjusting the switching frequency per control cycle to quantitatively constrain peak circulating currents to predefined thresholds. Finally, results from 36-MW simulations and experiments validate the effectiveness and superiority over conventional methods.