Flux-observer-based multi-level modulation technique for AC drives with variable-structure logic controller

A novel control scheme for AC motor drives is proposed, unified for synchronous and induction motor drives. It is based on variable structure direct modulation of flux and current modules, and of the ´torque´ current component. The feasibility of a full-logic real-time modulator-controller is investigated. The inverter´s commands would be obtained by processing few input logic signals. These are a two-bit (hysteresis-like) representation of the regulation errors and a ´few´-bit knowledge of the stator flux and of the drive operating conditions. A flux observer-based control structure is considered, aiming to very good dynamic performances and low steady-state ripple from standstill to flux-weakened operation. The commutation rate is controlled by properly varying the hysteresis widths. Synchronous reluctance and induction motor drives have been simulated, showing good modulation prerogatives and interesting control capabilities, typical of hysteresis controllers.<>