VSC Microgrid DC Link Multi-Frequency Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current microgrid systems operating in islanded or stand-alone modes cannot manage multiple frequencies effectively, limiting their ability to adapt to varying power quality levels across different microgrids connected via AC power lines, which is essential for economic and stable operation.
Innovation Solution
A system utilizing voltage source converters (VSCs) to connect multiple stand-alone microgrids through a DC line, normalizing frequencies, and performing multi-frequency control by adjusting power supply through current control, enabling robust and stable frequency management across microgrids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple stand-alone microgrids are connected through AC power lines, then power transmission is enabled among microgrids, but frequency synchronization forces all microgrids to operate at the same frequency, making multi-frequency control impossible
Solution Approach 1:
The patent introduces a DC line as an intermediary medium between AC-based stand-alone microgrids. The voltage source converter performs AC-DC conversion, enabling connection through DC line while preserving individual AC frequency characteristics of each microgrid. This mediator allows power transmission without forcing frequency synchronization.
Solution Approach 2:
The patent changes the connection parameter from AC-to-AC direct connection to AC-DC conversion connection. By converting AC power to DC for transmission and then back to AC at the receiving end, the system enables frequency independence while maintaining power transmission capability among microgrids.
2Stability of the object's composition
If conventional microgrids operate at rated frequency (60 Hz or 50 Hz), then stable operation is achieved, but microgrids with different power quality requirements incur excessive facility investment
Solution Approach 1:
The patent enables dynamic frequency adjustment capability in microgrids through the voltage source converter. Each microgrid can operate at different frequencies according to its specific load requirements and power quality standards, making the system adaptable rather than fixed. This eliminates the need for expensive facility modifications to accommodate different frequency requirements.
3Adaptability or versatility
If frequency management is implemented for each stand-alone microgrid, then power quality requirements are met, but existing AC-based connection technology cannot support multi-frequency control
Solution Approach 1:
The patent replaces the conventional AC-to-AC direct connection mechanism with an AC-DC conversion mechanism. The voltage source converter substitutes the simple AC connection with a conversion system that includes rectification, DC transmission, and inversion components, enabling frequency independence while managing complexity through standardized conversion technology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for rapid adjustment of power supply to cope with frequency fluctuations, ensuring stable operation and enabling multi-frequency control within the same allowable frequency range, even in the event of failures, thereby maintaining reliable power transmission among microgrids.
Implementation Method 1
a voltage source converter (VSC) connecting multiple stand-alone microgrids through a DC line and performing power conversion for the DC connection of AC based stand-alone microgrids
Implementation Method 2
performing, by a PI controller, a correction for making the output error between the normalized frequencies be 0
Data Source
AI summary
The present invention relates to a voltage source converter based DC connection method and a control method for implementing a system for maintaining respective different frequencies (multi-frequencies) by reflecting load quality levels of respective microgrids when multiple stand-alone microgrids are connected to each other in which voltage source converters (VSCs) installed at connection points of the microgrids for effectively controlling respective microgrids having different frequency control ranges present an effective control method based on a concept using normalizing frequencies of unit microgrids to be similarly applied in an islanded operation mode of multiple grid-connected microgrids as well as multiple stand-alone microgrids to avoid the same frequency criterion and enable an economic operation to which the load power quality level of the microgrid is reflected, thereby minimizing a transient to stably operate a microgrid system.