Single Degree of Freedom Solid Rotor Velocity Control Induction Drive

Abstract

This thesis studies a single degree of freedom (DOF), two-pole, three-phase, solid rotor, induction motor operating in closed loop angular velocity control via a proportional-integral (PI) controller applying a constant amplitude, variable frequency drive.

The stator consists of six iron teeth, evenly spaced and pointing radially inward, wound with 160 turns of copper wire each in a three-phase, two-pole configuration. A steel enclosure houses the stator and is supported by a 3D-printed polylactic acid (PLA) enclosure. The wiring is initially connected in wye configuration without a neutral wire but later converted to three independent phases, each with its own input and output wire. The teeth have a nominal air gap of 0.5mm with the rotor.

The rotor consists of a solid iron cylindrical core with a 1mm aluminum sleeve press fitted on the outside. Two mechanical bearings center the rotor inside the stator. A single- input single-output (SISO) PI controller commands three 750 mA amplitude currents with variable frequency, and offset by 120 degrees to provide a 3-phase drive resulting in a rotating magnetic field. Each coil is powered by a custom linear transconductance amplifier with 5 kHz bandwidth and 0.3 A/V DC gain.

The controller receives feedback through a contact-less magnetic encoder providing a linear voltage measurement of the rotor’s angle. We differentiate the position measurement to estimate the angular velocity of the shaft. A small diametrically magnetized cylindrical permanent magnet (PM) is attached to the end of the shaft and constrained by a 3-D printed PLA fixture. During operation, we produced up to 1.6 mNm of torque and velocities of up to 8,000 RPM.