Bounded Nonlinear Stabilizing Speed Regulators for VSI-Fed Induction Motors in Field-Oriented Operation

A new nonlinear controller design is developed for speed regulation of voltage source inverter (VSI)-driven induction motors. The proposed controller directly provides the duty-ratio input of the VSI in the permitted range to ensure linear modulation, is fully independent from the system parameters and suitably regulates the motor speed and the stator flux to the desired values. Considering the complete nonlinear model of the converter-motor system and applying advanced nonlinear methods, boundedness of the full system states is proven. Furthermore, exploiting the Hamiltonian-passive structure of the system, state convergence to the equilibrium is shown using LaSalle´s Invariance Principle. Though the controller design is developed in the frame of the field-oriented control methodology, stability holds true even without accurate field orientation guaranteeing an effective performance in cases where parameter variations occur. Extensive simulation results on an industrial size system are conducted to evaluate the proposed controller performance, under rapid changes of the reference speed or load torque as well as system parameter variations. In addition, a lab size induction motor system is experimentally tested. In all cases, the system response shows fast convergence to the equilibriums after limited transients, thus verifying the theoretical results.