A simplified sensorless speed computation algorithm for squirrel cage induction motor

A new simple and straightforward algorithm for the computation of rotor speed in squirrel cage induction machines is proposed in this paper. The algorithm does not involve the estimation of quantities such as stator flux and thus makes it immune to problems associated with the use of ideal integrators. The algorithm merely uses basic mathematical operations based on the machine equations and readily available measurements of stator quantities to reliably and implicitly compute the rotor speed. Despite the open loop nature, the algorithm, does not use complex operations such as integration, recursion or inverse trigonometry and facilitates its implementation on fixed point processors. The algorithm, extensively tested using MATLAB/SIMULINK based simulations under a wide variety of fluctuating grid conditions, performs considerably well, with a worst case transient error of less than 3% and almost zero steady state error. Closed loop speed control of EVI drive using the proposed speed computation algorithm is also verified using simulations.