Current Control of LCL-Filtered Grid-Connected VSC Using Model Predictive Control with Inherent Damping

The advancement on penetration of renewable energy sources in the power system is, in part, tied to the current control of grid-connected LCL-filtered voltage source converters. A challenge is current control with the addition of the LCL-filter resonance, which interacts with the digital converter-control switching action and creates the possibility for instability. In certain scenarios, active damping is needed to stabilize the system and ensure robust performance in steady-state and dynamic response. Another approach is detailed in this paper where a hybrid linear and nonlinear controller is implemented to ensure the dynamic current control performance. This is done by combining a linear outer-loop Proportional Resonant current controller with a nonlinear inner-loop Model Predictive voltage controller to replace the fixed switching-frequency Pulse Width Modulator. This allows for easy compensation of nonlinear effects, such as time delays and provides the controller with the ability to prioritize the dynamic performance during step changes. The details for implementing this control structure are provided, along with a discussion of the advantages, and guidelines for the design procedure of the hybrid control structure. Simulation results and experimental measurements are provided to illustrate the control performance and validate the proposed method. As a conclusion, the control method as a whole is discussed in relation to the presented work and further research options.