Design guidelines for inverter fed motor drives in distributed power system applications

Abstract

A distributed power system (DPS) is made up of several subsystems. For example, a two-stage distributed power system is made of a source subsystem consisting of line conditioners and a load subsystem consisting of loads. Motor drives used as a load subsystem form an important type of load in distributed power system applications. The input impedance of the load subsystem is an important factor in designing and analyzing the performance and stability of a distributed power system. In this thesis, a typical three-phase inverter-fed ac motor drive is modeled, analyzed and the input impedance characteristics are studied for the first time. Motor drives are found to have unique input impedance characteristics due to their electromechanical nature. The influence of these characteristics on the distributed power system are analyzed. The unique interaction problems that these characteristics lead to are studied. It is shown that a distributed power system designed without taking into account the unique input impedance characteristics of motors might suffer from performance degradation or might even become unstable. Design guidelines to avoid this situation in a distributed power system that uses motor drives as a load subsystem are developed and presented.