Voltage Control of the Ćuk Converter for Grid-Forming in DC Grids: An Energy-Based Approach

Grid-forming converters in dc microgrids will have a key role in the next generation power system. These converters are responsible for stabilizing the bus voltage in a grid dominated by constant power loads, a task that requires highly dynamic voltage control loops. This article presents an energy-based method to control the output voltage of an isolated Ćuk converter, a high-order nonlinear system. The main motivation behind the energy-based method is to control the total energy of the converter. In many cases, most of the energy is stored in the output capacitor of the converter, and controlling total energy allows shaping the output voltage directly. By using feedback linearization, we show that it is possible to use a linear controller to control energy, and that the internal dynamics resulting from feedback linearization is stable. The energy-based method results in a single-loop controller capable of naturally handling constant power loads, characteristics that make it well suited for voltage control of grid-forming converters. The proposed controller is verified by experimental results, using an isolated Ćuk converter to supply a constant power load.