Virtual Synchronous Generator Control Under Grid Overcurrent
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Solution Overview
Problem
Power generating units configured as virtual synchronous machines face damage from overcurrents during abnormal grid conditions, such as sudden grid voltage drops, due to their low thermal capacity and inability to handle high currents effectively.
Innovation Solution
A method for controlling power generating units that determines a virtual impedance based on current differences and overcurrent thresholds, reducing the acceleration of the virtual synchronous generator and limiting the current delivered by the power converter, thereby reducing the risk of damage to electronic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power converter is configured to exhibit virtual synchronous generator response, then grid-forming properties are improved, but the system becomes vulnerable to damaging overcurrents during abnormal grid conditions
Solution Approach 1:
The patent introduces a virtual impedance element as an intermediary between the power converter and the grid. This virtual impedance acts as a mediator that limits the current flow during abnormal conditions while maintaining the virtual synchronous generator's grid-forming capabilities. The virtual impedance is determined based on the current difference between the actual current magnitude and an overcurrent threshold value, effectively protecting the power converter from damaging overcurrents.
Solution Approach 2:
The patent dynamically changes the virtual impedance parameter based on the operating conditions. The virtual impedance value is adjusted according to the current difference, allowing the system to adapt its behavior: under normal conditions, the virtual impedance is minimal to maintain grid-forming properties, while under overcurrent conditions, the virtual impedance increases to limit current and protect the power converter.
2Power
If the virtual synchronous generator allows high current flow during voltage drops, then power delivery capability is improved, but the switching semiconductors are exposed to damaging currents
Solution Approach 1:
The patent implements a feedback mechanism where the virtual impedance is continuously adjusted based on the measured current magnitude. The current difference between the actual current and the overcurrent threshold is fed back to determine the virtual impedance value. This feedback loop ensures that when currents approach dangerous levels, the virtual impedance automatically increases to limit further current rise, protecting the switching semiconductors while allowing maximum power delivery within safe limits.
Data Source
AI summary
The invention relates to controlling a power generating unit. Aspects of the invention include determining a virtual impedance value (Zvir), determining a virtual grid power (Pvsm) based on the virtual resistance value (Rvir) and the grid current (Igrid), determining a virtual synchronous machine rotational speed (ωVSM) and/or a synchronous machine angle (θVSM) of a virtual synchronous generator, and determining a voltage reference (Vabc) for controlling a line side converter to generate the desired reactive power (Qgrid) based on the virtual synchronous machine rotational speed or angle (ωVSM, θVSM), a virtual voltage (ΔVαβ, ΔVdq) and the voltage magnitude reference (Vqref).