Sensor less Operation of CSI Fed Induction Motor Drive by Using MRAS

Abstract

The underground mines, oil and gas industries need remote operation of vector controlled medium voltage variable speed induction motor drives with long feeder. The usage of voltage source inverters in such cases leads to motor over voltage and harmonic problems. The current source inverter (CSI) has no such problems to these applications because of its motor friendly voltages output. This paper proposes sensor less operation of a CSI fed induction motor drive and improves the speed estimation. The proposed model uses model reference adaptive system (MRAS) speed estimator requires motor voltage and currents as inputs. Direct measurement of motor voltages and currents are impractical for long feeder drives due to feeder length and safety of environmental precautions. Hence the motor voltages and currents are drawn from the inverter out. In this paper the flux estimation needed for MRAS speed estimation is proposed to observe the performance of the induction motor with sudden change of loads under steady state. This model is simulated in The model reference adaptive system contains two models they are stator model and rotor model. The speed of the machine is estimated by using the above two models (2). The inputs required for the model reference adaptive system is the voltages and currents. The speed is estimated from the calculation of rotor flux linkages in the stationary reference frame from the both stator and rotor models. The estimated speed is calculated from the error obtained by cross multiplication of the flux linkages produced in the two models (stator and rotor models) with PI controller. The estimated speed is fed back to the one of the input of rotor model. Rotor model is also called as adaptive or adjustable model and the stator model is called the reference model. The two models are designed in Simulink by using the following equations and the block diagram is represented as shown in fig.1. The equations of reference model as follows