Novel methodology for improving performance of sensorless speed observers in induction motors at variable load conditions

Speed observation of rotating machines under different operational conditions is required in applications from fault detection to traction. Sensorless rotating speed observation has become popular in recent years. The MRAS rotor-flux-oriented and synchronous models are common schemes used for sensorless speed observation. These techniques are affected under low rotating frequencies and variable load conditions. This work presents an experimental analysis on the performance of both schemes during rotating speed estimation under different rotational frequencies and variable-load conditions. Obtained results show performance deficiencies on their estimations according to the rotational speed and load. A double scheme methodology that mixes the MRAS-based and the synchronous speed observers through a compensation function is proposed. Its performance analysis indicates an improvement on the estimated speed at different rotational frequencies with variable load. An FPGA-based implementation is developed as a low-cost, portable system-on-chip solution for real-time online estimation of rotating speed on induction motors.