Voltage stability improvement with coordinated ULTC–STATCOM controller and VSC-HVDC in high wind penetration cases

In recent years, implementing renewable energy systems such as wind power systems into interconnected grids play a vital role in energy management and production. Besides the good aspects of this energy policy, there may be some undesirable cases if not controlled. Increasing penetration of wind generation into the electricity grid negatively affects the power system stability and the required reactive power that might cause serious voltage stability problems. In order to overcome this problem, especially in the weakest areas of the system with respect to voltage stability, it is necessary to support the reactive power reserve. In this study, a coordinated ULTC–STATCOM controller has been designed to improve the reactive power reserve and enhance voltage stability by the penetration of wind power through the VSC-HVDC wind farm system into weak area of the AC system. The novelty of the proposed coordination control than the classical coordination approaches is changing the tap position of the ULTC especially at high penetration levels and thus to maintain the reactive power reserve of STATCOM. The proposed approach is tested in a two-bus sample system and adapted to the weakest area of the IEEE 10-machine 39-bus test system that simulations are conducted in DIgSILENT PowerFactory 15.0 software. Comparative simulation results show that the proposed approach has enhanced both reactive power reserve and voltage stability margin of the test systems.