Control of High Voltage Direct Current (HVDC) bridges for power transmission systems

Abstract

High Voltage Direct Current (HVDC) transmission systems are now getting more popular due to their low power losses and fast controllability of power in DC lines as compared to AC systems currently used. The primary goal for this study is to control the voltage and power flow direction by adjusting the firing angles of rectifier (α) and extinction angle of inverter (γ). Constant Extinction Angle (CEA) control and Constant Current (CC) control techniques are implemented for the DC link control. The power reversal can be achieved by changing the polarity of the DC voltage. The harmonic effects of the DC links are reduced by using AC and DC filters for a more stable transmission system. Fast Fourier Transform (FFT) analysis is used to calculate the Total Harmonic Distortion (THD) due to filtering effect. Short Circuit Ratio (SCR) test with variation of loads is carried out to determine the relative strength of AC system to DC power transfer. It is done for the optimum selection of suitable reactors. Besides, the overvoltage level is tested under the simulation flow of MATLAB SIMULINK which represents the virtual environment. Surge arresters are used to overcome the sudden increase of peak current so that the systems are always in the stable condition of operation.