Pilot Voltage Droop Control for HVDC Grid Stability
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Solution Overview
Problem
Multi-terminal power transmission systems, such as HVDC grids, face challenges in accurately controlling DC voltages and power distribution due to the lack of a naturally occurring signal reflecting power balance, leading to difficulties in managing unscheduled power imbalances and disturbances.
Innovation Solution
The pilot voltage droop control method generates a shared signal reflecting overall power in relation to DC voltage distribution across converter stations, allowing for coordinated control of power flow and voltage management through droop constants adjusted based on power transmission system parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If droop control methods are based on DC voltage measurements carried out locally at each converter station, then the control system is simple and decentralized, but voltage drops during power transfer cause difficulties in realizing highly accurate primary control of the DC grid
Solution Approach 1:
The patent introduces a pilot voltage signal as an intermediary that is communicated to all converter stations. This pilot voltage serves as a common reference that reflects the overall power balance in the DC grid, allowing each converter station to perform droop control with high accuracy without requiring complex communication of individual voltage measurements. The pilot voltage acts as a mediator that translates the global power balance state into local control actions.
2Device complexity
If there is no naturally occurring signal reflecting power balance in the DC power system, then the system architecture remains simple, but it becomes difficult to implement accurate droop control methods for managing unscheduled power imbalances
Solution Approach 1:
The patent implements a feedback mechanism where a pilot voltage signal is generated based on the power balance state of the DC grid and fed back to all converter stations. This feedback loop allows the system to automatically detect and respond to unscheduled power imbalances. The pilot voltage provides continuous information about the global power balance, enabling each converter station to adjust its operation accordingly without requiring complex centralized control.
3Ease of manufacture
If converter stations are controlled using fixed droop constants, then the control method is simple to implement, but the system lacks flexibility in controlling power distribution during different types of disturbances
Solution Approach 1:
The patent makes the droop constants dynamic by allowing them to be adjusted based on the sign of the power transmission system power flow parameter. When the pilot voltage indicates a power deficit, one set of droop constants is applied; when it indicates a power surplus, a different set is applied. This dynamic adjustment enables the system to adapt its control characteristics to different operating conditions and disturbance types, improving flexibility while maintaining implementation simplicity.
Data Source
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AI summary
A method (300) in a power transmission system is disclosed. The power transmission system comprises a plurality of interconnected converter stations. A pilot feedback signal is determined (301). The pilot feedback signal is based on at least one voltage level in the power transmission system and is common for all of the converter stations. A power transmission system power flow parameter, indicative of a difference between the power flow into the power transmission system and the power flow out of the power transmission system, is determined (302). The power transmission system power flow parameter is determined based on the pilot feedback signal. For each of the converter stations, a drooped error signal is determined (304) based on the power transmission system power flow parameter. For each of the converter stations, at least one control signal is determined (307) based at least on the drooped error signal determined for the converter station.