Power Converter Grid-Forming Control via Virtual Impedance
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Solution Overview
Problem
Power converters operating in grid-forming mode (GFM) can experience current, power, or energy overload during grid events, leading to potential tripping offline or damage to semiconductor devices, and switching to grid-following mode may jeopardize stability.
Innovation Solution
A method and controller for a power converter that allows it to retain grid-forming behavior while operating close to hardware limits by determining virtual impedance based on output current and modifying the control system, enabling a constrained grid-forming mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power converter operates in grid-forming mode during grid events, then it can maintain voltage and frequency stability, but it risks current, power, or energy overload leading to tripping offline or damage to semiconductor devices
Solution Approach 1:
The patent introduces a current limiting circuit as an intermediary component between the control system and the power converter's output stage. This circuit actively monitors output current parameters and intervenes when thresholds are approached, providing a protective buffer that prevents direct overload damage while allowing the GFM control mode to remain active. The intermediary circuit enables the system to operate close to hardware limits without exceeding them, resolving the contradiction between maintaining stability and avoiding overload.
2Object-affected harmful factors
If the power converter switches to grid-following mode to limit current, then it protects itself from overload, but it jeopardizes the stability of the power converter and the overall power system
Solution Approach 1:
The current limiting circuit serves as a protective intermediary that enables self-protection without mode switching. By actively limiting current through dedicated circuitry rather than changing control modes, the system achieves overload protection while maintaining its grid-forming control algorithm and voltage-source characteristics. This resolves the contradiction by providing protection through a separate mechanism rather than through mode transition.
Solution Approach 2:
The patent implements dynamic current limiting where the control system continuously monitors output current parameters and adjusts control actions in real-time based on proximity to hardware limits. This dynamic adjustment allows the power converter to operate close to maximum capacity during grid events while automatically reducing output as limits are approached, maintaining stability throughout the event rather than switching modes.
3Productivity
If the power converter operates close to hardware limits during grid events, then it maximizes current capability and grid support, but it risks exceeding limits and causing damage
Solution Approach 1:
The patent implements a feedback mechanism where the control system continuously monitors output current parameters and compares them against hardware limits. Based on this feedback, the control algorithm dynamically adjusts control actions to keep operation within safe boundaries while maximizing output capability. The feedback loop enables the system to operate at the edge of hardware limits during grid events without exceeding them, resolving the contradiction between maximizing productivity and ensuring reliability.
Data Source
AI summary
A method for controlling a power converter connected to a grid, wherein the power converter is initially controlled in a grid-forming mode to output current at a nominal voltage, based on control data provided by a controller. The method includes determining that a first parameter exceeds a first threshold. Then: controlling the power converter in a first limiting mode, by limiting the power converter output current based on a present value and/or a reference value; and determining the output current of the power converter. Responsive to determining that the output current is reaching an equilibrium condition: determining a virtual impedance for the power converter; modifying the control system based on the virtual impedance; and controlling the power converter in a constrained grid-forming mode, including the modified control system determining the control data based on measured signals indicative of currents and/or voltages downstream from the power converter, and a reference signal.