LPF-Free Harmonic Current Control in Multi-Synchronous Reference Frames for Dual Three-Phase PMSMs

Abstract

Harmonic current regulation in multi-phase motor drives remains challenging under dynamic operating conditions due to non-sinusoidal back electromotive force (EMF) and inverter nonlinearities, which introduce dominant low-order harmonics. Multi-synchronous reference frame (MSRF) based methods are widely adopted for multi-frequency current regulation; however, conventional implementations typically rely on low-pass filters (LPFs) for harmonic decoupling, introducing detection delay and phase distortion that limit transient performance. This paper proposes an LPF-free MSRF-based harmonic current control method for dual three-phase permanent magnet synchronous motor (DTP-PMSM) drives. By introducing harmonic transformation matrix coefficients (HTMCs), the proposed method retains the independent regulation of multiple harmonic components within the MSRF framework, while eliminating the filtering step in the harmonic decoupling path, without the need for harmonic plane reconstruction or additional coordinate transformations. To support adaptive changes, a Goertzel-based harmonic amplitude extraction scheme is employed to periodically update the HTMC. Experimental results demonstrate that the proposed method significantly enhances dynamic performance, achieving a 19.3% reduction in speed transition stabilization time compared to other methods. The proposed LPF-free formulation provides a practical solution for MSRF-based harmonic current control in industrial motor drive applications where fast dynamic response is required.