Comparison of PIR and MPC Control Schemes to Reduce Circulating Current in a Modular Multilevel Converter Terminal

Modular Multilevel Converter (MMC) has become an attractive solution in high-voltage and high-power applications to bring the bulk power from long-distance generation centers to substations. This is mainly due to its modular design, high power capacity and ability to control active and reactive power independently. Different control schemes to operate the MMC during normal conditions and to ensure stability during disturbances have been proposed. This paper compares the output current and the circulating current in a 200 kV/200 MW MMC, with seven submodules per arm, using three control schemes: Proportional-Integral Controller (PI), Proportional-Integral Resonant Controller (PIR), and Model Predictive Controller (MPC). Time-domain simulations are carried-out on an MMC terminal operating as inverter. Changes in the active and reactive powers are considered to show the behavior of the studied variables. Results show that the PIR controller presents lower circulating current oscillations than other controllers. However, current unbalances are presented as the active power delivered by MMC changes. The MPC approach have a better response, when compared with the other controllers, during power changes.