Performance Improvement of Direct Power Control of PWM Rectifier Under Unbalanced Network.

Direct power control (DPC) has attracted wide attention due to its advantages of simple structure, quick response, strong robustness, and elimination of current regulation/pulse width modulation blocks. However, conventional table-based DPC cannot work well when the grid voltages are unbalanced. Some work has been done on DPC to mitigate the influence of grid unbalance by adding power compensations to the original power references. However, they are usually complicated due to the positive/negative-sequence extraction of grid voltage and/or currents. Furthermore, applying only one voltage vector during one control period leads to high steady-state power ripples. This paper proposes an improved DPC by using a new definition of instantaneous reactive power. As a result, the distortion in grid current is eliminated, and constant active power and new reactive power are obtained. Neither complicated calculation of power compensation nor positive/negative-sequence extraction of grid voltage/current is required. The corresponding switching table suitable to regulate both active power and the new reactive power is established. Furthermore, the concept of duty cycle control is introduced to further improve the steady-state performance. Both simulation and experimental results are presented to confirm the theoretical study and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]