Development and research of improved PWM algorithm of an active rectifier with variable switching angle tables

Abstract

Modern electric drives of rolling mills are based on frequency converters with active rectifiers (AR). During operation, active rectifiers consume non-sinusoidal current, having a negative effect on the supply network. In order to improve the performance index of voltage quality, AR special algorithms of pulse-width modulation are used. Selective harmonic elimination (SHE) PWM algorithm has become widespread. However, application of SHE PWM algorithm does not always allow to optimize the operation of the AR under the conditions of changing parameters of the electro-technical complex under various operating modes. Therefore, a solution is needed to improve the electrical power quality index of plant networks with powerful frequency converter with AR. To carry out the research, a mathematical model of the frequency converter with active rectifiers was implemented with an improved PWM algorithm in the Matlab-Simulink environment based on the parameters of the main electric drive of the 2000 cold rolling mill “LPC-11” of PJSC “ММК”. The main assumption of the simulation model is that the inverter is represented as a current source. An improved algorithm with the ability to select tables of switching angles based on SHE PWM has been developed. The operation of the FC with AR with the proposed improved PWM algorithm with variable tables of switching angles has been investigated. A comparative analysis of the instantaneous values of AR voltages and currents when transferring to the tables with similar switching angles and significantly different ones has been made. It has been found that changing the tables of switching angles does not have a significant negative effect on the operation of the FC with AR. The proposed improved PWM algorithm can be used to improve the performance index of power quality in electrotechnical complexes with FC and AR by using optimal tables of switching angles in conditions of various modes of the power supply system. The adequacy of the simulation model has previously been confirmed by experimental data and previous studies.