Nearest State Discontinuous PWM Strategy for Entire Modulation Index With Interleaved Carriers in Three-Parallel Operation

Abstract

This article proposes a nearest-state interleaved discontinuous PWM (NSIDPWM) strategy for three-parallel interleaved three-phase converters. Prior work in parallel systems has largely targeted reductions of zero-sequence circulating current (ZSCC) and common-mode voltage-often in two-parallel settings and via modified carrier schemes. In contrast, NSIDPWM retains fixed interleaved triangular carriers and applies subsector-dependent dynamic offset voltages to realize nearest-three-vector (NTV) synthesis. A positive-, negative-, and zero-sequence (PNZ) filter is employed to suppress ZSCC, allowing the modulation to prioritize output-current harmonic quality and switching efficiency. The method is evaluated through simulation and experiments against ILPWM, 60DPWM, and EPDPWM. Performance is assessed using a total cost index that combines switching loss, total harmonic distortion (THD), and first-sideband magnitude. Results show that NSIDPWM reduces sideband/THD relative to ILPWM and 60DPWM, while avoiding the high switching activity associated with EPDPWM. Although ZSCC may increase modestly, it remains at a few-ampere level and is effectively handled by the PNZ path, whereas output-side harmonics dominate filter sizing. Overall, NSIDPWM achieves a favorable balance between harmonic performance and efficiency without carrier modification, supporting simple, scalable implementation in multiparallel converter systems.