Optimizing a servo drive using Field Oriented Control

Sammanfattning: An optimization of a servo system for a satellite antenna system wasperformed. A brushless DC motor with an angle encoder was used, whoseangular velocity had to be controlled with great precision. Specializedhardware was used to implement field oriented control to directlycontrol the torque and magnetic flux of the motor. Multiple velocitycontrollers were tested for the closed servo system, which controlledthe amplitude of the motor current to achieve the given reference valuefor the angular velocity. A PI regulator was tested and evaluated aslacking in terms of precision, which was caused by low resolution of theerror signal for the angular velocity of the motor. This in turn wascaused by low resolution of the angular velocity measurement. Theanguluar velocity error signal was filtered to combat this, and a feedforward method was implemented where the reference value for the angularvelocity was integrated over time to generate a reference value for theangular position. Since the angular position could be measured withbetter precision, a better error signal based on the angular positioncould be generated which was then used as input to another regulatorwhose output signal was added to the original regulator to increase theaccuracy of the system significantly. The two regulator output signalswere then weighted based on the reference value for the angularvelocity. This was done because the two regulators performed well fordifferent velocity bands, which this method took into consideration. Thefinal servosystem fullfilled the set requirements by a good margin.