Power converter with integrated control of reactive power and voltage harmonics

Abstract

Abstract With increased decentralized renewable energy production, it has become increasingly difficult for electricity providers to ensure adequate power quality. Local, distributed reactive power production and active voltage harmonic mitigation could be a step towards easier implementation of sustainable energy production, and improved control of power quality within microgrids. This thesis investigates the ability to integrate these functions into power electronics with other main purposes, without compromising the original function. A power converter for industrial mechanical loads was equipped with two proposed control schemes. One scheme relies on measurements of the current into a facility and a PI controller to minimize the total reactive power. The other mitigates harmonics by emitting a sinusoidal current that is slowly altered until an optimal amplitude and phase shift is found. The optimum corresponds to inducing a voltage in anti-phase with the harmonics, and is determined by using a Kalman filter to estimate the amplitude of different harmonics. The control schemes were investigated in a simulation environment and by implementation in a physical power converter. Simulations and measurements showed that both control schemes mainly work as intended, when used separately and when combined. The power converter managed to provide up to 14 kVAr for reactive power control while decreasing the 5th and 7th harmonic 79 % and 50 % respectively. The mechanical load’s power supply was not compromised in any of the investigated scenarios. A more stable power factor could be achieved by optimizing the current limitation scheme of the reactive power controller.