Uncertainty and disturbance estimator with improved steady-state performance for grid-connected power converters

The study suggests a method aimed to improve the performance of practical grid-connected converters connected to distorted mains, utilising total uncertainty and disturbance estimator (TUDE) based control structures with time-delay filter. Such a TUDE filter enhances disturbance rejection performance by possessing near-unity magnitude and near-zero phase at integer multiples of the base frequency, imposing repetitive-control-alike behaviour. However, it is well-known that in repetitive control, disturbance rejection at mid-frequencies, were non-periodic disturbances and noise may exist, is deteriorated. This study presents an enhancement, allowing to retain good disturbance rejection at mid-frequencies within the low-frequency portion of control bandwidth (relevant in practical systems) while trading-off the performance in the high-frequency control bandwidth part. The proposed methodology is verified by application to output current control of LCL-filter based inverter feeding distorted AC mains. The validity and performance of the proposed methodology are well-supported by simulations and experiments.