6. Conclusion

A POSMC scheme has been developed for the VSC-HVDC system to rapidly compensate the combinatorial effect of nonlinearities, parameter uncertainties, unmodeled dynamics, and time-varying external disturbances. As the upper bound of perturbation is replaced by the smaller bound of its estimation error, an over-conservative control input is avoided such that the tracking accuracy can be improved.

Four case studies have been undertaken to evaluate the control performance of the proposed approach, which verify that POSMC can maintain a consistent control performance with less power overshoot during the power reversal, restore the system rapidly after the AC fault, suppress the oscillation effectively when connected to a weak AC grid, and provide significant robustness in the presence of system parameter uncertainties. At last, a dSPACE-based HIL test has been carried out which validates the implementation feasibility of POSMC.
