Abstract: Combining low-power auxiliary converters with diode rectifier units (DRUs) in parallel to replace large-capacity modular multilevel converters is a key approach to reduce offshore wind farm DC transmission costs. Current research mainly focuses on topology and control but with a limited investigation into harmonics and reactive power characteristics. To address this research gap, both simplified and detailed models of the hybrid converter system are established in this paper, including offshore wind farms, DRUs, and auxiliary converters. The switching dynamics and commutation of the system are comprehensively studied. It is found that voltage harmonics at the Point of Common Coupling dominate the issue, rather than current harmonics. In addition, the impact of AC and DC reactance parameters on harmonic amplitude is studied, thus offering parameter design guidance. Based on this analysis, a harmonic voltage suppression strategy is proposed for offshore wind power systems with parallel hybrid converters. Finally, simulation and Hardware-in-the- Loop experiments validate our commutation theory, harmonic characteristics, and harmonic voltage suppression strategy.