Advanced and sophisticated power switching devices such as power MOSFET and IGBT came into being during that time. This made a significant change in the trend of power electronic control, producing inverters and converters capable of switching at extremely high frequencies well into MHz range. (The old Thyristor converters could not do more that about 1 KHz at that time.) This level of very high switching frequency is essentials to realize complex control functions.
Circuit symbol of IGBT
