Research on MMC-HVDC multi-objective model predictive control strategy under asymmetric faults

Abstract

When an asymmetric fault occurs on the AC side of the MMC-HVDC system, a large number of non-characteristic harmonics will be generated on both sides of the system, which will affect the operation of the system. Model predictive control has the advantages of intuitive modeling and fast dynamic response. And considering its advantages in MMC application and the ability of multi-objective control, this paper proposes a multi-objective model predictive control strategy based on a two-phase stationary coordinate system as the MMC-HCDC system control strategy when an asymmetric fault occurs. This strategy, which combines classic vector control and adds weight coefficients, divides the control system into three parts: current command prediction, multi-objective control and voltage output control based on the idea of functional equivalence. In addition, the strategy avoids the complicated coordinate transformation and enhances the control ability of MMC-HVDC under asymmetric faults. Finally, a 21-level MMC-HVDC system is built based on PSCAD/EMTDC, which verifies the control effect of the control strategy.