Instantaneous Power Control for Suppressing the Second-Harmonic DC-Bus Voltage Under Generic Unbalanced Operating Conditions

This paper proposes a simplified instantaneous output power control to suppress the second harmonic dc-bus voltage due to asymmetry in a three-phase pulsewidth-modulated (PWM) converter system without any sequential component decomposers. Normally, in the instantaneous output power control, the positive and negative sequence output voltages and currents are required, and they are usually decomposed by notch filters or dual second-order generalized integrals that are difficult to tune and complicated. While in the proposed method, the positive-sequence and negative-sequence currents are regulated by PI plus resonant (PI-R) controllers in the dq frame. Therefore, the sequential current decomposers can be avoided. Meanwhile, the positive-sequence and negative-sequence output voltages, which are essential for calculating the positive-sequence and negative-sequence current references, are simply obtained from the outputs of the proportional-integral (PI) and resonant controllers, respectively. The proposed method is robust to any asymmetries and its effectiveness is verified on a prototype asymmetric three-phase permanent-magnet synchronous generator (PMSG) system with inherent and externally added asymmetries.