| Abstract |
In this paper the computational methods for evaluating VA ratings of four different types of active
filters for ac systems are presented. These include a conventional shunt active filter, a VSI-based
series active filter, a hybrid shunt passive-active filter circuit and the one incorporating a resonant
circuit. The formulae for VA rating calculations are derived by analysing the per-phase equivalent
circuits of these filters operating in a three-phase balanced system supplying a nonlinear load. For
ease of comparison the harmonic current control schemes employed by all the above filters are
developed on the principle of synchronous reference frame theory[1,2,3]. In addition the load is
considered the only source of harmonic current in the system. Simulation results produced by
Electro-Magnetic Transient Program (EMTP) are presented to show both the impedance
characteristic of the system when each of these filters is used. Their performance in terms effective
harmonic current compensation and VA rating reduction are compared. |
