A direct power control strategy for three level neutral-point-clamped rectifier under unbalanced grid voltage

• Published in: Electric power systems research 2018-08, Vol.161, p.103-113
• Main Authors: Kahia, Billel, Bouafia, Abdelouahab, Chaoui, Abdelmadjid, Zhang, Zhenbin, Abdelrahem, Mohamed, Kennel, Ralph
• Format: Article
• Language: English
• Subjects: Active and reactive power; Direct power control; Neutral-point clamped; Switch table; Unbalanced grid voltage
• ISSN: 0378-7796; 1873-2046
• DOI: 10.1016/j.epsr.2018.04.010

•A new definition of instantaneous active power is used for DPC strategy development.•The proposed DPC is applied in case of unbalanced grid voltages.•Simulation results prove that the proposed DPC is able to overcome the drawbacks of the conventional DPC strategy under unbalanced grid voltages (i.e. achieves balanced input currents with low THDi).•The proposed DPC strategy proves high performance compared to two other proposed DPC strategies, under unbalanced grid voltages. Direct power control (DPC) strategy has attracted wide attention due to its advantages of simple structure, quick response, strong robustness, and elimination of current regulation loops/PWM blocks. Unfortunately, under unbalanced grid voltage, the conventional DPC (CDPC) scheme with the conventional definitions of active and reactive power cannot work well. In order to solve this problem, a new definition of the active power instead of the conventional one is proposed, discussed and used in this paper. As a result, good performance of the system is achieved and neither complicated calculation of a power compensation term nor positive/negative sequence extraction of grid voltages/currents are required. Then, a switching table based DPC strategy is designed based on the new definition of active power and conventional definition of reactive power. The corresponding switching table is suitable to achieve constant active power, constant reactive power and sinusoidal grid currents with very low total harmonic distortions (THDs). Simulation results are presented to confirm the theoretical study and the effectiveness of the proposed DPC with the new definition of active power (DPC-NP). The performance of the proposed DPC-NP is compared with that of the CDPC and that of the DPC with a new definition of reactive power (DPC-NQ).