Practical Issues and Implementation Circuits of the Digital-Analog Hybrid Full Feed-Forward Method with Unipolar and Bipolar Modulations

Full Feed-forward (FF) method has been proved to be an effective method to suppress the output current distortion of the grid connected inverter (GCI) which caused by grid voltage harmonics. Nowadays, most of the FF methods are realized through digital solutions. However, the digital delay of the digital control based FF (DFF) method reduces the suppression ability of the GCI current distortion and may cause the the system instability problem at weak grid case. In order to solve this problem, the concept of the digtal-analog hybrid full feed-forward (DAH-FF) approach has been firstly proposed in the recently reported work of the authors. In this paper, the DAH-FF method will be further discussed, which more focuses on the practical issues of implementaion circuits of the DAH-FF method with different modulation strategies, such as unipolar modulation and bipolar modulation. Furthermore, the selection principle of the digital part and analog part of the DAH-FF method is also discussed. Finally, the experimental results verify the correctness of the above theorectical analysis.