ORNL’s cascade multilevel inverter was developed 30 years ago and is widely used today by global energy, machinery and plant solution providers including General Electric, Siemens, Hyosung, Hitachi Energy, Toshiba-Mitsubishi and ABB Energy Industries. In 1994, researchers in the Power Electronics and Electric Machinery group, now based at DOE’s National Transportation Research Center, invented an inverter that can transform voltage through two separate direct current sources—the Wye, or Y, and Delta, or Triangle-shaped circuit configurations.
This inverter was patented by ORNL for use in high voltage and high-power applications. The multiple levels and modular build of the inverter means it can handle flexible alternating current transmission systems, static volt amp reactive systems, power line conditioning, series compensation, phase shifting and voltage balancing. It can also be deployed for use in fuel cell and photovoltaic utility interface systems.
In 2009, Siemens adapted this technology using the Delta-connected cascade multilevel inverter and renamed it Modular Multilevel Converter, or MMC. This technology became known as MMC STATCOM, for Static Synchronous Compensator, a term understood by utility companies familiar with traditional synchronous converters, which are large rotating mechanical generators.