Real-time method to prevent voltage collapse and power instability of HVDC systems

As HVDC transmission is increasingly used in electric power grids its influence on overall voltage and power stability is under special focus. For the classic HVDC system using current sourced line-commutated converters voltage and power stability is of concern. For the light type of HVDC systems utilizing voltage sourced self-commuting converters voltage stability is in general no problem, however, transmission angle stability and, connected to this, power stability can be crucial. Essential for both types of HVDC system is the identification of unstable operating regions and their avoidance. Certain off-line analytical methods and on-line control concepts exist but they do not provide complete security. This paper demonstrates that a real-time stability analyzer and an adaptive power controller free the system from this risk of voltage and power instability. Voltage and power are stabilized at a maximum transferable power level.