A secondary voltage control method for an AC/DC coupled transmission system based on model predictive control

For an AC/DC coupled transmission system, the change of transmission power on the DC lines will significantly influence the AC systems´ voltage. This paper describes a method to coordinated control the reactive power of power plants and shunt capacitors at DC converter stations nearby, in order to keep the voltage of the pilot bus tracking its set point considering the DC system´s transmission schedule change. The approach is inspired by model predictive control (MPC) to compensate for predictable voltage change affected by DC side transmission power flow and the potential capacitor switching at DC converter stations. The control strategies are calculated from a multi-step dynamic optimization problem that is solved by mixed integer quadratic programming method. Time-domain simulations showed positive results of the proposed voltage controller.