  We propose a novel method for the estimation of rotor position, speed, and
torque of a motor-pump system consisting of a progressive cavity pump (PCP)
driven by an induction motor which operates under V/f open-loop control. We
compute the speed and rotor position of the PCP by applying a phase locked loop
to the pressure signal at the pressure side of the pump. An extended Kalman
filter is used to estimate the torque of the PCP based on the speed, effective
value of the stator current of the induction motor and a nonlinear motor model.
Furthermore, we derive a tractable condition under which the convergence of the
observer is guaranteed. We use a laboratory experiment to verify our results.
