Torque Control of an Induction Machine Based on Partial Dynamic Inversion

In the paper induction machine (IM) torque control is studied as an example of a three-dimensional non-holonomic integrator that includes drift terms. By expanding Brockett's controller derived for the driftless systems, a control structure is proposed that guarantees natural adjustment of both the amplitude and the frequency modulation of the sinusoidal stator current vector. The rotor flux linkage vector is implicitly forced to track natural periodic orbits satisfying non-holonomic constraints of the IM. Main features of the proposed control include fast dynamics of the torque response, maximal torque per amp ratio for nominal parameters, exponential stability, and robustness regarding expected parameter variations. The overall IM control scheme requires cascaded high-gain current controllers together with rotor flux linkage vector estimation. Simulation and experimental results illustrate the main characteristics of the proposed control with the emphasis on the quality of the generated machine torque and estimated rotor flux linkage orbits.