Very low speed control of induction machine by instantaneous speed and inertia estimation

This paper presents a control method for an induction machine in the low speed region with instantaneous speed and inertia estimation. When a low precision incremental-type encoder is used for the speed detection, only the average speed between the interval of the encoder pulses is obtained and this usually makes the speed controller unstable in the low speed range. This paper, therefore, introduces a low speed control method in which instantaneous speed estimation is implemented by a disturbance torque observer for the purpose of stable speed control, using such an encoder and it is shown that the proposed method is superior to conventional methods using simulation and experimental results. Furthermore, in order to reduce the sensitivity of instantaneous speed estimation to inertia variations of the induction machine and to implement a practical system, an identification method for the inertia moment is introduced