Data-Driven Adaptive Negative Sequence Current Control Method for PWM Rectifier Under Unbalanced Grid

Three phase pulse width modulation (PWM) rectifiers have excellent performance when the grid voltages are balanced, and it is widely adopted in the industry. However, the asymmetrical loads or grid faults will lead to the unbalanced grid voltages. In addition, the negative sequence (NS) voltages and currents in the unbalanced grid result in the fluctuation of the dc bus voltage. In this article, the intrinsic mechanism between the voltage ripple amplitude and the NS currents is revealed. Furthermore, this article proposes a data-driven adaptive current control method. By shaping the NS currents, the corresponding amplitudes of the second-order harmonic voltage on the dc bus are observed. Based on the observation data, the reference currents that can minimize the dc bus voltage ripple are adaptively derived online. As a result, the dc bus voltage ripple can be suppressed effectively. In addition, the proposed method does not need the NS decomposition or the parameters such as the grid voltages and inductances. Therefore, it has a strong robustness against parameter mismatch. Finally, the accuracy of the theoretical analysis and the effectiveness of the proposed method are validated by experiments.