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 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 (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.