Unfunctionality of the instantaneous p-q theory for the control of series active filters

Proliferation of power electronics converters and electronic equipments has dramatically increased electric pollution in electrical distribution power systems. The distorted current draw by these nonlinear loads distorts the supply voltage which may then give rise to harmonic currents at distribution networks, even when at these locations no harmonic generating equipment is present. Furthermore, voltage unbalances, sags, and swells are other power quality issues related to the supply voltage required to be considered for compensation. Consequently, the use of active filters as an affordable solution for power quality is indispensable. These devices increase the efficiency and sustainability of modern power systems and can also help higher penetration of renewable fluctuating power into the network. Subsequently, many theories have been developed to control active filters and then perform compensation of unwanted harmonics, unbalances, sags, and swells. Depending on the issues, the control algorithms employed in series active filters differ. However, the majority of those algorithms deal with proportional integrator PI or PIDs which create a delay in the compensation. To eliminate this delay the latest approaches try to integrate the instantaneous compensation theory in Series active filters. This time domain approach was proposed by Akagi [1] under the name “p-q theory” or “instantaneous power theory”. It is the most widely spread theory for three-phase shunt active filters. This paper discusses the application of the mentioned theory for the control of series active filter and to evaluate its efficiency in a typical network using SimPowerSystems tools of MATLAB.