Mitigation of harmonic distortion and voltage dips in electrical distribution networks

Due to the growing share of converter fed loads and converter coupled distributed generation units in the distribution network, power quality issues become more and more important. The behavior of the existing converters, in most cases peak rectifiers, may result in a distorted network voltage. The recent interest in power factor correction converters shows the importance of resistive converter behavior. Resistive converters damp network oscillations, but their damping potential is dependent of their power level. Power factor correction converters with a programmable damping resistance as secondary control function can be used to reduce the voltage distortion on the grid independently of their power level. With these converters it is possible to set a harmonic input resistance independent of the fundamental input impedance. Consequently, the harmonic input resistance remains low, even when the input power of the converter is decreased. Most attention is paid to the damping of voltage harmonics. However, this control strategy allows also to mitigate voltage dips. Experimental tests on a 1 kW prototype of a digitally controlled full bridge bidirectional converter show the practical behavior of the algorithm. The reaction of the control algorithm on voltage harmonics and voltage dips is examined.