Adjustable Speed Generator Control via AC Voltage Reference Modification
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Solution Overview
Problem
HVDC systems with adjustable speed generators face challenges in managing power generation during AC grid faults, leading to rapid DC voltage increases due to the inability to react to frequency variations, requiring costly and space-intensive DC choppers that disrupt system stability.
Innovation Solution
Control the AC voltage in the local AC bus using the first voltage source converter to adjust the power generation of the adjustable speed generator, eliminating the need for a DC chopper by modifying the AC voltage reference based on the AC grid voltage, allowing for immediate reaction to faults and smooth recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC chopper is used to manage power generation during AC grid faults, then DC voltage overvoltage is prevented, but system complexity increases and stability is disrupted
Solution Approach 1:
The patent extracts the DC chopper component from the system and replaces it with a control method that modifies the AC voltage reference. This eliminates the need for additional hardware while maintaining DC voltage stability during AC grid faults.
Solution Approach 2:
The patent replaces the mechanical/electrical DC chopper system with a control-based solution that modifies voltage references. This substitutes physical power electronic switching with a control algorithm that achieves the same protective function without additional hardware complexity.
2Reliability
If a DC chopper is installed to prevent DC voltage increases, then overvoltage protection is achieved, but system cost and space requirements increase
Solution Approach 1:
The patent removes the DC chopper hardware from the system configuration. By extracting this component and replacing it with control logic, the system achieves overvoltage protection without the associated cost and space requirements of physical chopper circuits.
Solution Approach 2:
The patent uses a software-based control solution (modifying voltage reference) instead of expensive hardware (DC chopper). This control approach is essentially 'disposable' in the sense that it can be implemented, modified, or updated without physical replacement, reducing long-term system costs.
Data Source
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AI summary
A method and a system to influence the power generation of at least one adjustable speed generator (9) are presented. The system comprises a first voltage source converter (4) connected to a local AC bus (2), where the local AC bus (2) is provided with power by the at least one adjustable speed generator (9), a second voltage source converter (6) connected to an AC grid (8), a DC link (5) connected between the first (4) and the second (6) voltage source converter, and at least one control unit (18) to control the first (4) and the second (6) voltage source converters. The at least one control unit (18) performs the method to control the AC voltage (Vloc) in the local AC bus (2) via the first voltage source converter (4) and to modify a reference value for the AC voltage magnitude (Vloc,ref) of the local AC bus (2) in dependence on the AC voltage magnitude (Vgrid) of the AC grid (8).