An Improved Flux Observer for Field-Oriented Control of Induction Motors Based on Dual Second-Order Generalized Integrator Frequency-Locked Loop

Flux estimation is of great importance for high-performance motor drives. In order to improve flux estimation accuracy and reduce system complexity, a new flux estimation method based on the second-order generalized integrator frequency-locked loop (SOGI-FLL) was presented recently. Compared with the conventional low-pass filter-based method, the SOGI-FLL does not need compensation and can effectively attenuate the high-order harmonics in the back electromotive force (back EMF). However, the dynamic performance of this method is not satisfactory, because the back EMF frequency estimated by FLL suffers from inaccuracy and double-frequency oscillation when the back EMF changes. This paper presents a detailed theoretical analysis on the dynamic errors of the SOGI-FLL-based flux estimation method. To overcome the drawback, an improved method based on dual SOGI-FLL (DSOGI-FLL) is proposed. The properties and performance of the DSOGI-FLL-based flux estimation method are analyzed in comparison with the SOGI-FLL, demonstrating its improved dynamic response. Simulations and experimental results on an 11-kW three-phase induction motor verify the excellent performance of the proposed DSOGI-FLL-based flux estimation method.