A study of parallel operations of active and passive filters

This paper reports investigations of the parallel operations of a current controlled active filter and passive filters in a system with current harmonic sources. The task of reactive power and harmonic compensation is shared by the active filter and passive filters. The passive filters are used for supplying reactive power to the connected AC system and eliminating some harmonics, the active filter is used to cancel out the other harmonics. This can be achieved by taking the suitable reference current of the active filter and signal processing filters in the control loop. In parallel combination arrangements of the active and passive filters can operate relatively independently, also the compensation flexibility of the active filter can be fully exploited, such as one active filter for several harmonic sources. The simulation studies on various systems have been performed to evaluate the effectiveness of the systems. The results show that the power factor is corrected by the passive filters, harmonics are minimized by both active and passive filters and overloading of the filter system can be avoided.