Backstepping control of three-levels VSC based back-to-back HVDC system

In this paper, a nonlinear backstepping controller is proposed for control a back-to-back high voltage direct current system using three-phase three-level voltage source converters (VSC-HVDC). The mathematical model and backstepping controller structure is discussed in a synchronous rotating reference frame (d-q) in the aim to provide high dynamic performance with complete decouple control of active and reactive power. The objective of maintaining balanced voltages in DC-link capacitors is achieved by using the three level space vector modulation with balancing strategy based on the effective use of the redundant switching states of the converters voltage vectors. Complete simulation of the VSC-HVDC system validates the efficiency of the proposed backstepping control law. Compared to the conventional control, the used of backstepping control allows to exhibit excellent transient response during large range of operating conditions.