Correcting current imbalances in three-phase four-wire distribution systems

摘要

The objective of this thesis is to present the theory, design, construction, and testing of a proposed solution to unbalanced current loading on three-phase four-wire systems. The Unbalanced Current Static Compensator is the name of the prototype; herein referred to as the UCSC. The purpose of this prototype is to redistribute current between the three phases of a distribution system. Through this redistribution, negative- and zero-sequence currents are eliminated and a balanced system is seen upstream from the point of installation.The UCSC consists of three separate single-phase H-bridge inverters that all share the same dc-link capacitor. Each of these inverters performs independently using a single-phase rotating reference frame controller. Each either draws or injects current onto the distribution system lines to balance the active currents and performs power factor correction for voltage compensation. A 34.5 kV, 6 MVA system was built and simulated in Matlab/Simulink™ to test the validity of this solution. A scaled-down UCSC prototype was then designed and constructed to compensate for a 208 V, 10 kVA system. Results from both the simulations and testing of this UCSC prototype are presented and analyzed.