EFFICIENCY OPTIMIZATION OF INDUCTION MOTOR DRIVE USING LOSS MODEL CONTROL

Abstract

Due to robustness, reliability, low price and maintenance free, induction motors (TMs) are used in most of the industrial applications. The influence of these motors (in terms of energy consumption) in energy intensive industries is significant in total input cost. Optimal control covers both the broad approaches namely, loss model control (LMC) and search control (SC). This report primarily focuses on efficiency optimisation of induction motor drive through loss model control. Induction motor is a high efficiency electrical machine when working close to its rated torque and speed. However, at light loads, no balance in between copper and iron losses, results considerable reduction in the efficiency. The part load efficiency and power factor can be improved by making the motor excitation adjustment in accordance with load and speed. To implement the above goal, the induction motor should either be fed through an inverter or redesigned with optimization algorithms. For optimal energy control of induction motor, flux level in a machine is adjusted to give minimum operating cost for the industrial load. The flux controller improves the economics in terms of operating cost and test results show that the flux level in the most economic motor is adjusted according to load and speed, particular at light load. In the present work, induction motor loss model is developed and optimal value of flux is obtained through the motor loss model to give maximum efficiency of the motor. Maximum and minimum levels of flux and stator currents are forced as constraints in the algorithm. Here, loss model controller is designed and implemented for different variations in speed and torque. DC-link power is measured in each case and is compared with that of conventional constant flux control technique. Mine hoist diagram used in mineral industry is also considered as a practical example and the effect of LMC on it is studied. Induction motor parameters vary with temperature. So, parameters obtained by conducting no load and blocked rotor test may vary with loading of induction motor. LMC is sensitive to parameter variation and its performance is affected when parameters change. An attempt is made to gain a deeper physical insight into the induction motor operation through sensitivity analysis of LMC under parameter variation. The study reveals the effect each of the circuit parameters namely Rs, Rr, L,, Lr and Lm has on torque, speed, flux and DC-link power respectively.