Improvement of Power Quality in Supply Network with Active Rectifiers by Selecting Optimal Switching Angle Tables of PWM
In this paper, an improved control system of the active rectifier of powerful three-level frequency converters implemented on the basis of selective harmonics elimination method with pulse-width modulation (PWM) was proposed. The new control system selects one of the switching angle tables depending on the modulation coefficient. Making use of additional tables of switching angles can improve power quality on the input bus-bars of the electric drive by eliminating the 35th harmonic. The parameters of the main electric drive of the cold rolling mill 2000 “Sheet Rolling Shop no. 11” of the “Magnitogorsk Iron & Steel Works” were used for the simulation model. On the basis of the developed simulation model of a frequency converter with an active rectifier, a comparative analysis of the conventional and the advanced control system is carried out taking into account their influence on the harmonic distortion (THD) of the voltage on 10 kV bus-bars in the internal power supply system, which showed a decrease in the average value of the voltage THD by more than 5 %.