Current Ripple Analysis and Controller Design for Grid-Connected Converters Considering the Soft-Saturation Nature of the Powder Cores

The powder-core-based inductor has a wide inductance variation due to the soft-saturation nature when subjected to varying load current. Under such a condition, the current ripple is influenced, and the conventional inductor design principle may be inaccurate. Besides, the voltage of the inductor is distorted. Also, the bandwidth of the controller is hard to determine. In this paper, the current ripple under the condition of wide inductance variation is analyzed, and its change rule is revealed; then, a new inductance design principle is proposed. The harmonic components for the three-phase converter with the powder core inductor are investigated, and the harmonic characteristic of the input current is analyzed. According to the current harmonic characteristic, the resonance controllers are introduced to eliminate harmonics, and the quality of the current is improved. Besides, the bandwidth of the controller is found to vary with the output power. Then, a compensation method is proposed to eliminate the influence of inductance variation on the bandwidth. The experimental results verify the analysis.