T20.7 - Analysis and Control of Third-Harmonic Current Injection Based On-Board Charger Under Unbalanced Grid Conditions

Active third-harmonic current injection along with three-phase unfolding is one of the promising alternatives to the conventional two-stage ac-dc conversion due to reduced filter requirement. Most of the existing studies on the operation and control of these converters assume a balanced grid condition. Usually, the back-end dc-dc converter is controlled to draw constant power from the input to achieve sinusoidal grid currents. However, if this method is adopted during grid imbalance, low frequency distortions appear in grid currents. This article proposes a novel modified control strategy for an integrated active filter based topology that ensures balanced sinusoidal line currents even with unbalanced grid voltages. The proposed modulation strategy is experimentally verified in a 6.6 kW hardware prototype demonstrating sinusoidal currents with equal amplitude when 5 % negative sequence component is present in the grid voltages.