An Observer for Three-Phase Current Estimation Using Nonuniform Current Samples

A new approach of reconstructing three-phase currents by fitting sine waves, under the conditions of nonuniform distribution or even nonavailability of samples for substantial portions of a cycle, is proposed. Excessive smoothing by low-pass filters results in loss of accuracy due to damping and instability due to phase lag. A simple zero-order-hold may not be able to fill in large portions of a cycle when data samples are not available. A Luenberger observer, which does not require load-parameter specifications, has been used to estimate the sinusoidal phase currents in the load. The observer is robust and stable under steady and dynamic conditions. The performance of the observer-based, closed-loop current-control scheme has also been compared experimentally with that of a plain trigger-and-hold device