Improved direct power control for 3-level AC/DC converter under unbalanced and/or distorted voltage source conditions

In this paper, an improved direct power control with space vector modulation for a 3-phase 3-level neutral point clamped converter supplied by unbalanced and/or distorted grid voltage is proposed. The main objective of the control scheme is to obtain balanced and sinusoidal input current with unity power factor under nonideal voltage supply. To achieve the control objectives, compensated active and reactive powers are calculated and added to the referencing one. A theoretical analysis of active and reactive power under a nonideal source is clearly demonstrated. In order to calculate the compensated powers, the extraction of positive, negative, and harmonic sequences of voltage and current is needed and a multiple-complex coefficient filter-based method is used for rapid and accurate extraction. The proposed controller also ensures voltage balance in DC-link capacitors using redundant vectors in the space vector modulation block without the need for additional components. Simulation results verified the effectiveness of the modified control strategy.

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