Tuning of controllers in grid-connected multilevel converters

This paper analyzes and compares different control tuning strategies for a grid connected converter in a Back-To-Back (BTB) topology, based on Neutral Point Clamped (NPC) converters. The NPC is modeled and linearized around an operation point characterized by the DC-link voltage and the quadrature current component. In this research, a Voltage Oriented Control (VOC) strategy is used with Proportional-Integral (PI) controllers. Current and voltage control loops are tuned designing fast and simple controllers. It is evidenced that the best tuning method depends on the features of the control loop, therefore, each PI has its own tuning method. Furthermore, the nonlinearity of the DC-link voltage performance shows some particularities in the tuning of the voltage PI that make the method less direct. Finally, the results are verified through simulation models.