Analysis and control of a dual stator winding squirrel cage induction machine drive

A novel dual stator induction motor drive, DSIM, is presented in this thesis. The new drive is based on an induction motor consisting of a standard squirrel cage rotor and two separate stator windings wound for a dissimilar number of poles. The two stators are fed from two three-phase inverters that share a common DC-link. This structure offers the advantage of producing two independent torque components that are only coupled through the mechanical shaft. The speed is controlled by adding or subtracting the two torque components. This feature is utilized to partially decouple the mechanical speed from the electrical frequencies fed to the stator winding sets. In principle it is possible to maintain the electrical frequency above a pre-set minimum value while the drive operates at zero speed and any load, hence simplifying the practical implementation of sensorless control schemes during low and zero speed operation.;Using this idea two torque control strategies for operation under constant V/Hz and field orientation are presented and evaluated through simulation and experimental work.;A detailed mathematical model, as well as an equivalent circuit, of the dual stator machine proposed are derived. These are used to evaluate the performance of the proposed DSIM and compare it to that of a standard induction motor of the same frame size and with identical squirrel cage rotor. From this comparison it is concluded that the DSIM offers such advantages as a larger break down torque at low speed and almost the same constant power region. However, the steady state torque for the same total inverter kVA rating results are slightly smaller.;A 4/12-pole prototype based on an existing 12-pole induction motor design was built and tested. From the experimental results the sensorless operation at zero speed under both constant V/Hz and field orientation was verified. It was also found that the DSIM is capable to produce slightly less steady state torque than the original machine for the same total input current. However, the break down torque is larger in the DSIM.