Power Management Strategy in Multi-Terminal VSC-HVDC System

Due to the significate increase of using renewable energy resources (such as wind, solar and etc.) interconnect into the AC systems, utilizing multi-terminal high voltage DC (MT-HVDC) systems is a promising solution in terms of economic and technical considerations. Manufacturers have offered HVDC Light and new Modular Multilevel VSC-HVDC technologies to increase the rating and improve the performance of VSC-HVDC system. From the stability and operation points of view, power management is important for the MT-HVDC system. In this paper, configuration, operating and decoupled control mode of VSC-HVDC have been discussed. The objective of this paper is to propose a communication-free strategy manage the power based on the available headroom in MT-HVDC systems. The decoupled dq-control method is used to change and keep active and reactive currents linear. Therefore, by using the PI controller, the steady-state errors in the control system can be cleared. Moreover, this method has solved the issue of using constant power share among the inverters interconnected to the girds with different frequency. The case study in this paper consists of a three-terminal VSC-HVDC system (detailed switching VSC model) interconnected with three AC generator (in three areas) with different voltage levels and frequencies. The test system has been simulated and analyzed in PSCAD/EMTDC.