DYNAMIC PERFORMANCE LIMITATIONS FOR MRAS BASED SENSORLESS INDUCTION-MOTOR DRIVES .1. STABILITY ANALYSIS FOR THE CLOSED-LOOP DRIVE

The paper deals with a speed sensorless direct rotor flux orientated v ector controlled induction motor drive in which the speed and rotor fl ux angle are derived from a closed loop MRAS estimator. A small signal stability analysis is carried out on the combined estimator-controlle r, and allows for the stability effects of incorrect estimator paramet ers to be studied. The small signal stability analysis is sufficient t o show that incorrect parameters give rise to oscillatory drive behavi our that worsens, even to the point of instability, as the closed loop speed bandwidth of the drive is increased. Experimental results are g iven to validate the analysis. It is concluded that speed and load tor que rejection bandwidths comparable to sensored vector controllers can not be obtained without online parameter tuning. A companion paper add resses this problem and experimentally verifies the transient oscillat ory phenomena.