SENSORLESS INDUCTION MOTOR DRIVE WITH INDEPENDENT SPEED AND ROTOR MAGNETIC FLUX CONTROL PART I - Theoretical Background

Stephen J. Dodds - Ján Vittek - Viktor A. Utkin

   A new control system for induction motor drives without shaft sensors is presented. The novel features of the system are a) polyphase stator currents produced automatically by a variable frequency oscillatory mode obtained by the application of a nonlinear control law and b) responses to the reference speed demand and the rotor magnetic flux magnitude reference inputs which are independent from one another and have first order linear dynamics with time constants that may be chosen by the user of the electric drive. The torque producing current and magnetic flux vectors approach mutual orthogonality (as in the vector control methods) when the load torque on the motor is increased. The simulations, which were done for ideal high gain and bang-bang control law for alpha_beta model of induction machine are presented in the second part of the paper. The simulations predict the system to be robust with respect to external load torques and realistic uncertainties in the motor parameters, including the rotor resistance. Preliminary experimental results for small induction motor P_n=120 W are presented in the second part of the paper too. They show good correspondence with the realistic simulations of three-phase system, where achieved sampling frequency and final word-lengths were taken into account.

Keywords: induction motor, non-linear systems, feedback linearisation, sliding-mode control, variable-structure systems, hierarchical structures, observers

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