Modeling and analysis of an LCC HVDC system using DC voltage control to improve transient response and short-term power transfer capability

A new control method for a line-commutated converter-based (LCC) high-voltage direct-current (HVdc) system is presented and compared to a conventional strategy. In the proposed method, both the dc voltage and current of an LCC HVdc system are regulated to increase the short-term operating margin of dc power transfer and improve transient responses to dc power references. In particular, an increased operating margin of dc power transfer is achieved via the dc voltage regulation method. To verify the effectiveness of the proposed method, a state space model of an LCC HVdc system is developed considering dc voltage and current references as input variables and analyzed for various values of the dc line inductance and converter controller gains. The state space model can be used for time-efficient analyses of the dynamic characteristics of an LCC HVdc system. Simulation case studies are performed using MATLAB, where the state space model of the Jeju-Haenam HVdc system is implemented as a test case and compared to its comprehensive PSCAD model. The case study results suggest that the proposed method increases the short-term operating margin and speeds up the transient response of the HVdc system. Therefore, it will effectively improve real-time grid frequency regulation.