HIL-RT Implementation of UHVDC Transmission System Based on Series-Connected VSC Modules

This paper presents an ultra-high-voltage direct current (UHVDC) transmission system based on the series-connected voltage source converter (VSC) modules. A detailed DC voltage equalization control strategy is developed for the series-connected VSC modules at both terminals of the UHVDC transmission system. Moreover, the phase-shifted triangle carrier concept is applied for generating the pulse width modulation (PWM) signals to eliminate AC line current harmonics and reduce converter switching losses. Besides, harmonic elimination comparison between applying the conventional sine pulse width modulation (SPWM) and the phase-shifted triangle carrier-based pulse width modulation (PSCPWM) techniques is done. Furthermore, a hardware-in-the-loop (HIL) real-time (RT) UHVDC validation model was set up by connecting a real-time simulator of OPAL-RT which ran the power electronics-power system parts and a dSPACE 1103-based prototype controller which was used to implement the control part. Finally, the real-time dynamic performance of the series-connected VSC models UHVDC system is validated in operation at different transient and steady state modes.