Development of a Methodology to Assess the Impact Degree of High-Power Drives with Active Rectifiers on the Electricity Quality in In-plant Power Supply Systems

Active rectifiers are widely used on industrial sites today. These units are part of high power regulated alternating current drives. Their use is due to a number of advantages over classic diode rectifiers, such as the ability to recover braking energy into the supply network and, according to the manufacturers, better electromagnetic compatibility. However, experience in operating these devices shows that due to the use of pulse-width modulation in active rectifiers, there is a high severe distortion probability of supply mains voltage by high order harmonics, with numbers higher than 40-50. The essence of this phenomenon is the occurrence of a voltage drop in the high impedance parts of the network frequency response when even a small high-frequency current is flowing. The presence of high impedance sections in the frequency response is due to the parallel resonance between the inductance of the network transformer and the equivalent capacitance of the cables from the substation. Modern power quality standards applied in different countries do not take into account harmonics above 40-50 which makes it very difficult to assess the impact of high-power drives with active rectifiers on power quality in the supply network by conventional, certified power quality analysers. Therefore, it is an urgent task to develop a specialised methodology to assess the impact degree of a particular active rectifier on the network.