Control of multilevel direct AC converters

The growth in the demand for electric power is increasing stress on the existing grid infrastructure. Power utilities today require methods to provide dynamic grid control due to the increased penetration of renewable energy resources and increase in consumption of electricity. FACTs devices provide one possible solution. High cost and low reliability of these devices has impeded widespread use. A novel solution has been proposed in [2] where existing grid assets are augmented with thin AC converters to provide increased control capabilities. The low cost solution is realized by using a direct AC converter in tandem with existing grid assets. The converter uses a simple AC chopper as a building block with no bulk energy storage. Scaling has been shown possible in [2] by cascading the basic building block. Realistic and robust scaling of these converters lies in the ability to effectively control the voltages in every block to the desired level. This paper discusses the multilevel direct AC converter and provides methods to control the converter to ensure safe and reliable operation while maintaining low cost and high reliability.