Improved modeling and optimal compensation of unbalanced three-phase electrical systems using disc analysis

Unbalanced operation of three-phase electrical systems reduces efficiency and produces mechanical vibration and torque pulsations in rotating machines. These problems also apply to higher order unbalanced harmonics that may also be present in three-phase networks. The development of active compensation techniques for unbalanced electrical systems continues to be an active area of research. However, existing compensation methods have yielded limited results due to the complexity of the electrical dynamics of unbalanced systems. Consequently, previous research has only disclosed a variety of ad hoc techniques for compensating specific types of network topologies containing unbalanced components. An improved analysis method is needed which may be systematically applied to unbalanced three-phase systems. Such a method should then result in an improved model of the system dynamics so that advanced control theory may be applied in order to improve system performance. This work introduces the Decomposition of Instantaneous Sequence Components (DISC) concept for three-phase system analysis. The result is a real-valued state-space model of a three-phase system with arbitrary electrical imbalances. As a consequence, DISC analysis provides deeper understanding and insight into the dynamics of unbalanced three-phase electrical systems and leads to the development of optimal imbalance and harmonic compensation techniques. This dissertation demonstrates the utility of DISC analysis by minimizing the torque ripple and optimizing the power factor of a permanent magnet ac motor drive.