Nonlinear Control Design for Multi-Terminal Voltage-Sourced Converter High Voltage Direct Current Systems with Zero Dynamics Regulation

This paper presents a nonlinear control strategy with a nested control structure for a class of multi-terminal VSC HVDC systems. An output control law is first proposed, which is based on the passive output. When the output variables converge to zero with the developed output control law, the system behavior is governed by the uncontrolled zero dynamics. However, due to some desired control variables such as the DC voltage that belong to the internal dynamics, an outer control loop is then suggested to arbitrarily drive the zero dynamics, which provides a reference to be tracked by the output control law. The performance of the proposed control algorithm is evaluated by numerical simulations which show that the system has a much faster convergence rate than the controller without the outer loop.