Instantaneous p-q power Theory for compensating nonsinusoidal systems

This paper presents a tutorial about compensation of nonsinusoidal systems based on the instantaneous active and reactive power theory or the p-q Theory. The history related to this theory is presented and then the definitions of real, imaginary and zero-sequence powers are introduced. The physical meanings of each of these powers are explained and some basic compensation examples are shown considering different active power conditioners. It is shown that this theory can be very practical for understanding problems due to nonsinusoidal voltages or currents. It is especially interesting for the design of power conditioners for three-wire or four-wire three-phase system with or without distortions in voltages and currents.

I. Introduction

Electric systems with high content of nonlinear loads are common since the introduction of power electronics devices for controlling ac voltage or current or for converting them into different frequency, including de, These devices brought more efficiency for the system and especially brought much more flexibility allowing very lightweight power supply for, wide range speed control in ac and de drives and so on. However, harmonic pollution came together with these developments and its associated problems became worse as the percent of these nonlinear load increased. All the problems related to the harmonics components in the electric system forced the researches to study, understand, and propose new ways to eliminate these harmonics. In this sense, one of the theories is the instantaneous power theory or p-q theory.