Cascaded Control of Back-to-Back Converter DC Link Voltage Robust to Grid Parameters Variation

The article elaborates on the mathematical modeling and control structure design of a grid-connected back-to-back voltage source inverter with a complex dc link and an LC filter for the current harmonics reduction. A cascaded, three-loop control structure is designed for controlling the converter current, the grid current, and the dc link voltage. The derived control structure, utilizing two sets of current sensors and a dc link voltage measurement, is based on proportional-integral controllers and a Truxal-Guillemin model-based controller for the dc link voltage control. The chosen control structure provides consistent results for great variations of the grid impedance. Robustness is tested for various scenarios of variations in grid filter parameters, controller parameters, chosen operating point for linearization, and grid impedance. Results are validated by simulations and experiments on a 7.5 kW converter and show highly robust performance for $\pm$20% parameter change and a large span of grid impedance variation.