Passive Filter Aided by Shunt Compensators Based on the Conservative Power Theory

Passive filters are widely used in electrical system for power quality improvements. Their first installations from 1940 s and their advantages make them an attractive and standard solution up to nowadays. However, passive filters have their filtering characteristics deteriorated due to parameter variation caused by aging or temperature. In addition, a capacitor bank for power factor correction is designed for specific loads and may not supply the right amount of reactive power when loads keep being added or changed. When these issues make the passive filter and the capacitor bank incapable to keep the system operating within acceptable level of power quality, an inconvenience arises and a solution must be provided. A common one is to replace both of them either by new elements or by active power compensators. However, replacing the passive filter and the capacitor bank may not be economically feasible, because they belong to a past investment. This paper presents a solution to overcome such inconvenience keeping the passive filter and the capacitor bank installed and unchanged. It consists of installing two shunt compensators specially designed for performing what the passive filter and the capacitor bank are incapable to do. The result is a reduced processed power in the compensators. The generation of the references is based on conservative power theory (CPT). A case study is presented to prove the compensators’ efficacy and the power quality improvement.