Microgrid Synchronization via Overlapping Voltage and Frequency Ranges
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Solution Overview
Problem
Resynchronization of islanded microgrids operating at different voltages and frequencies poses challenges in achieving stable power flow and quality during reconnection, as existing methods often require frequency and voltage matching based on a single point of common coupling, which can lead to transient issues and instability.
Innovation Solution
A method for synchronizing two microgrids by determining overlapping voltage and frequency ranges for each microgrid, selecting a third voltage and frequency within these ranges, and controlling both microgrids to match this new set before reconnecting, ensuring optimal operation and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional frequency and voltage matching is performed based on a single point of common coupling, then reconnection can be achieved, but transient issues and instability occur during synchronization
Solution Approach 1:
The patent segments the synchronization process by determining overlapping voltage and frequency ranges separately for each microgrid, then selecting a third voltage and frequency within these ranges. This divides the single-point matching into multiple parameter dimensions (voltage range overlap, frequency range overlap), allowing independent optimization of each parameter to reduce transient instability.
Solution Approach 2:
The patent performs preliminary actions by determining the overlapping voltage and frequency ranges before actual reconnection. The control system pre-calculates acceptable voltage and frequency ranges for both microgrids, identifies their overlap, and selects target values within the overlap zone beforehand. This preliminary parameter matching ensures stable synchronization conditions are established before the breaker closes, preventing transient issues.
2Device complexity
If only one microgrid's parameters are adjusted for synchronization, then reconnection is simpler, but power flow management and power quality deteriorate
Solution Approach 1:
The patent merges the parameter adjustment process by selecting a third voltage and frequency that both microgrids will adopt. Instead of adjusting only one microgrid, the solution combines both microgrids' parameter sets into a common target (the overlapping range values), ensuring both systems are optimized for the synchronization point. This mutual adjustment improves power flow management and power quality while maintaining balanced control complexity.
3Reliability
If a third voltage and frequency within overlapping ranges is selected for both microgrids, then stability and power quality improve, but control complexity increases
Solution Approach 1:
The control system performs self-service by automatically determining the overlapping voltage and frequency ranges and selecting the third voltage and frequency without external intervention. The system autonomously calculates the ranges for each microgrid, identifies their intersection, and selects optimal values within the overlap zone. This self-service capability manages the increased control complexity through automation, allowing improved stability without requiring complex manual coordination.
4Loss of time
If traditional synchronization methods are used, then reconnection is achieved quickly, but power quality and steady state attainment are compromised
Solution Approach 1:
The patent applies preliminary action by pre-determining the overlapping voltage and frequency ranges and selecting the third voltage and frequency before reconnection occurs. This advance preparation ensures that when the breaker closes, both microgrids are already matched to the target parameters, achieving quick reconnection without compromising power quality. The preliminary parameter matching eliminates the need for post-reconnection adjustments, maintaining both speed and power quality.
Data Source
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AI summary
The present disclosure relates to a method for synchronization of a first microgrid la, having a first voltage Vi and a first frequency fi, and a second microgrid lb, having a second voltage V2 and a second frequency f2, with each other. The method comprises for each of the first and second microgrids: determining a possible voltage range, and determining a possible frequency range. The method also comprises determining an overlapping voltage range comprised within both the possible voltage range of the first microgrid and the possible voltage range of the second microgrid. The method also comprises determining an overlapping frequency range comprised within both the possible frequency range of the first microgrid and the possible frequency range of the second microgrid. The method also comprises selecting a third voltage within the overlapping voltage range. The method also comprises selecting a third frequency within the overlapping frequency range. The method also comprises controlling the first microgrid to change from the first voltage and frequency to the third voltage and frequency. The method also comprises controlling the second microgrid to change from the second voltage and frequency to the third voltage and frequency. The method also comprises connecting the first and second microgrids to each other by closing a switch there between.