Rating issues of unified power quality conditioners for load bus voltage control in distribution systems

Series-shunt unified power quality conditioners, including the dynamic voltage restorer, have demonstrated their capability of supporting bus voltages when faults occur on the AC system. This paper assesses the voltage, power and current compensation capabilities and requirements for these devices. For series voltage regulation, three methods are investigated. Sizes of the series and shunt devices, harmonic filtering requirement, and DC bus energy storage requirement are defined and discussed. The paper allows the design of a compensator that minimizes the kVA rating as a function of a given application.