Abstract
The paper proposes the control system for a frequency converter active rectifier with a variable switching frequency of the AR power switches, taking into account the changes in the operating modes of the rolling mill stand electric drive. In the AR control system, Selective Harmonic Elimination PWM is used. When the load is reduced or the electric drive is idle, the AR control system selects the table of switching angles of the power switches corresponding to the current operating mode. The use of tables with an increased switching frequency makes it possible to exclude a greater number of harmonics from the consumed current spectrum, which has a positive effect on the supply voltage power quality. A method is proposed for switching tables based on comparing the value of the AR current with predetermined limit values obtained using the developed technique for analyzing the thyristor thermal balance. Simulation modeling was carried out in the Matlab-Simulink software package on a complex mathematical model of the internal distribution network of a metallurgical enterprise, which has EDs with FC-AR. A feature of this supply network is the presence of complex resonance phenomena. Comparative analysis of the data obtained during simulation modeling for the cycle of operation of the rolling mill with electric drives based on FC-AR showed a positive technical effect on the power quality of the 10 kV supply network when the mill electric drive is idle or operates at reduced load.
Keywords
Active rectifier, frequency converter, pulse width modulation, power quality, electro-magnetic capability, control system, electric drive operation mode.
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