4. Grid Current Improvement Strategy Under Non-ideal Grid Conditions

This chapter delves into the challenges of maintaining grid current quality in drives under non-ideal grid conditions, specifically addressing grid impedance variations and unbalanced grids. The text introduces two key strategies: harmonic energy regulation and full-feedforward control of rectifier voltage. Harmonic energy regulation focuses on improving system robustness to grid impedance by adjusting harmonic components in motor current and DC-link voltage. Full-feedforward control, on the other hand, aims to suppress grid current harmonics by reshaping the system's grid-side output impedance. The chapter provides a detailed analysis of these strategies, supported by experimental results that demonstrate their effectiveness. It concludes by highlighting the significant reduction in Total Harmonic Distortion (THD) of grid currents and the enhanced stability of the drive system under various operating conditions.