Fast Current Control of Grid-Tied Converter Using Asynchronous Coordinate Transformation Under Unbalanced Grid Voltage Condition

Fast transient response is a desirable feature for grid-tied converters, especially when suffering grid faults. While, the symmetrical component decomposition (SCD) in control loop will slow down the response under unbalanced voltage conditions. This paper therefore proposes a current control method with the asynchronous dq-transformation to extract the fundamental frequency component with less delay cost. The detailed implementation issues are fully investigated. The steady state error related to the sampling of the SCD is investigated. Based on the understanding of the mechanism, a frequency adaptive approach is developed. This approach is fully utilized the flexibility of the asynchronous coordinate transformation (ACT) on adjusting the relation between the sampling and the grid frequency, which yield a steady state error-free outcome.