Abstract
AC regenerative electric drives (AC REDs) are widely used in metallurgical rolling due to their reliability, efficiency, and power sufficient to maintain the process. This paper reviews the latest achievements in building the grid connection circuits for the main AC REDs of rolling mills. The paper discusses multipulse connection circuits formed by various transformer types and algorithms for preprogrammed pulse-width modulation with selective harmonic elimination technique (PPWM with SHE) of three-level active front ends (AFE), provides the theoretical and practical measurement results, and gives recommendations for improving existing systems. For 6-, 12-, and 18-pulse grid connection circuits, switching patterns of AFE semiconductor modules with a smooth downward trend within the modulation index range from 0.7 to 1.15 are provided. A simulation was performed under comparable conditions on simulation models in the Matlab/Simulink to objectively evaluate the performance and opportunities of 6-, 12-, and 18-pulse grid connection circuits, including the three-level AFE and transformer specifications. The waveforms and spectra of the grid currents and transformer secondary winding phase currents are shown; total harmonic distortion (THD) factors have been calculated up to the 60th harmonic for various PPWM with SHE patterns. The results of simulation and experimental measurement on operating equipment have been compared. The paper is expected to provide a broad overview of multipulse connection circuits of the rolling mill’s main AC REDs, in particular, identify the latest solutions capable of significantly improving their electromagnetic compatibility with the grid. The results obtained are of high genericity and can be used by researchers and engineers to provide the electromagnetic compatibility of non-linear consumers in similar circuits, as well as design them.