Overview
This research presents an analytical method for adjusting the active power setpoint of a Voltage-Source Converter High-Voltage Direct Current (VSC-HVDC) station. The objective of this adjustment is to maximize grid loadability when the system is operating under voltage-stressed conditions. The method is designed to provide optimal setpoints considering combined current and voltage constraints and aims for real-time emergency control by leveraging local measurements and an estimated wide-area voltage angle difference.
Research Context
VSC-HVDC links are identified as assets capable of controllable active and reactive power output. This characteristic positions them as a promising resource for providing emergency voltage support within electrical grids. The integration and operation of these links require sophisticated control strategies to harness their potential, particularly during challenging grid conditions such as voltage stress.
Approach
The core of the presented method involves exploiting the geometric structure inherent in converter capability limits. This exploitation facilitates the derivation of a closed-form expression for the optimal active power setpoint. The method accounts for both current and voltage constraints simultaneously. For its implementation, the method relies on two primary data inputs: local voltage measurements and an estimate of the wide-area voltage angle difference. This dependency on localized data and an estimate, rather than global optimization, suggests its suitability for real-time emergency control scenarios.
Findings
- A closed-form expression for the optimal active power setpoint of a VSC-HVDC station was derived, considering combined current and voltage constraints.
- Validation performed on the Nordic Test System indicated consistency between the analytically predicted optimum and the setpoint that yielded the highest loadability.
- Adjustments to the active power setpoint were observed to result in a more-than-proportional increase in loadability.
- The method demonstrated robustness to uncertainty in the angle estimate.
Why This Matters
The developed method offers a mechanism for VSC-HVDC stations to contribute to grid stability by maximizing loadability during periods of voltage stress. Its reliance on local measurements and an estimated wide-area voltage angle difference suggests an operational framework that avoids complex global optimization, potentially enabling rapid deployment in emergency situations for voltage support.