A New Control Scheme and Modeling Method for Enhancing Normal Operation and Abnormal Estimation of LCC HVDC System

Abstract

A new modeling method for high voltage direct current (HVDC) systems and associated controllers is presented for the Power System Simulator for Engineering (PSS/E) simulation environment. The aim is to improve the estimation of transient DC voltages and currents during temporary AC line-to-ground faults. The proposed method consists mainly of three interconnected modules for (a) equation conversion, (b) control-mode selection, and (c) DC-line modeling. Simulation case studies were carried out using PSS/E and a PSCAD/EMTDC model of the Jeju-Haenam HVDC system in Korea. Moreover, 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 simulation results are compared with real operational data and the PSCAD/EMTDC simulation results of the HVDC system during single-phase and three-phase line-to-ground faults, respectively. These comparisons show that the proposed PSS/E modeling method resulted in improved estimation of the dynamic variations in the DC voltage and current for AC network faults, with significant gains in computational efficiency, making it suitable for real-time analysis of HVDC systems. Another 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 the real-time grid frequency regulation.