Performance evaluation under the actual operating condition of a large capacity VSI inverter for steel mill applications

Large capacity motor drive equipment, especially those with low harmonics and high efficiency, are in demand in the industrial field. In general Voltage Source Inverters (VSI) have low harmonics and high efficiency and have been widely applied in many steel plants. However, the cycloconverter drives which were applied in 1980´s are still operating in many steel plants. The cycloconverter has low power factor and it is necessary to include harmonic filters to reduce the input power harmonics, making the whole equipment larger. Compared to the conventional cycloconverter, IGBT/IEGT VSI has the benefits of high input power factor and better speed control accuracy, including motor and load response. Moreover, the drive footprint is significantly smaller. Also, some existing cycloconverter drives have forcing voltages around 3600V. Until now there was no drive equipment that could directly replace all previous AC drives in both capacity and voltage. The rated capacity of the latest individual drive module is 9MVA with a maximum output of 3650V. With a power density of 1.3MVA/m³ this compact structural configuration offers space-saving advantages for new and upgraded installations.