Improved Sensorless Operation of Double Inverter Fed Wound Rotor Induction Machine With Seamless Mode Transitions

Abstract

The performance of a sensorless induction motor drive depends on the accuracy in estimating the flux position from the supply voltage and machine parameters. Accurate estimation of flux position at low speed operation is difficult due to the low supply frequency. In a double inverter fed induction motor drive (IMD), the low speed operation can be obtained by maintaining the relative frequency between stator and rotor supply <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">voltage</i> without reducing the individual supply frequency to a very low value. In this article, a novel frequency profile for the stator and rotor supplies of a doubly fed induction motor (DFIM) drive is proposed, in which the minimum supply frequency of any side inverter is around 0.5 p.u. for the whole speed range of operation. With this proposed scheme, the zero speed operation of the drive is obtained by maintaining both the stator and rotor supply frequencies as 1.0 p.u. To achieve this, the DFIM is required to be operated as a squirrel cage induction motor for certain speed range. The control scheme for both the stator and rotor side inverters along with seamless mode transitions are also presented. In this DFIM drive, the required motor power is only 50% of the rated load power and the total <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">volt–ampere</i> (VA) rating of the two inverters is same as that of a conventional squirrel cage IMD. Experimental studies are carried out on a 45 kW wound rotor induction machine to validate the control scheme with the proposed frequency profile and results are presented.