Grid-Forming Inertia Control Under High ROCOF Saturation
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Solution Overview
Problem
The reduction in inertia in power system networks due to the transition to renewable energy sources like wind and solar power generation leads to stability concerns, and existing grid-forming control methods fail under high Rate of Change of Frequency (ROCOF) and off-grid scenarios, causing converter trips and undesirable transients.
Innovation Solution
A grid-forming control method and system that adjusts the voltage vector by generating a virtual angle and magnitude based on inertia values, which are varied to a minimum pre-set value during current saturation, ensuring synchronization and maintaining grid-forming mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If grid-forming control is implemented with fixed inertia value, then stability is improved, but converter trips occur under high ROCOF conditions
Solution Approach 1:
The inertia value is made dynamic rather than fixed. The control system continuously adjusts the inertia value based on real-time operating conditions, specifically switching between a first inertia value during normal operation and a second inertia value during current saturation events. This dynamic adaptation allows the system to maintain stability during normal conditions while preventing converter trips during high ROCOF events by reducing inertia when current saturation occurs.
Solution Approach 2:
The system changes the inertia parameter based on operating conditions. When current saturation is detected, the inertia value is switched from a first value to a second value, which is determined based on the rate of change of frequency. This parameter change allows the controller to adapt to high ROCOF conditions and prevent converter trips while maintaining grid-forming capability.
2Stability of the object's composition
If inertia value is increased to maintain stability, then frequency resistance is improved, but current saturation occurs under high ROCOF
Solution Approach 1:
The inertia value is dynamically adjusted based on the operating state. During normal operation, a higher first inertia value is used to maintain frequency stability. When current saturation is detected, the system switches to a lower second inertia value that is specifically determined based on the rate of change of frequency, thereby preventing further current saturation while maintaining adequate frequency support.
Solution Approach 2:
The control system uses feedback from current saturation detection to adjust the inertia value. When current saturation occurs, the system detects this condition and switches the inertia value from the first value to the second value, which is calculated based on the rate of change of frequency. This feedback mechanism ensures that the inertia parameter adapts to prevent harmful current saturation while maintaining stability.
3Reliability
If grid-following control is used during current saturation, then synchronism is maintained, but grid-forming capability is lost
Solution Approach 1:
The control mode is dynamically adjusted based on operating conditions. The system operates in grid-forming mode during normal conditions, establishing voltage and frequency references. When current saturation occurs, the controller dynamically switches to grid-following mode to maintain synchronism, then transitions back to grid-forming mode when the saturation condition resolves. This dynamic mode switching allows the system to maintain both grid-forming capability and synchronism under varying conditions.
Data Source
Figure 1
Figure 2
Figure 3~3(b)
AI summary
A control system (100) and a grid-forming control method for adjusting a voltage vector of an output signal generated by a power electronic device (111) are provided. The control system (100) is configured to generate a virtual angle value (θ) for adjusting an angle (δv) of the voltage vector of the output signal; generate a virtual voltage value (|Vv|) for adjusting the magnitude (Vv) of the voltage vector of the output signal; and control the frequency and magnitude of the output signal generated by the power electronic device (111) based on the virtual angle value (θ) and virtual voltage value (|Vv|). The virtual angle value (θ) is generated based on an inertia value (H), a measured power and frequency of the output signal. The control system (100) is configured to set the inertia value (H) such that the inertia value (H) is varied between a maximum value and a pre-set minimum value based on a current magnitude (|Im|) of the output signal of the power electronic device (111).