Mini-Grid Converter Synchronization via State-of-Charge Frequency Control
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Solution Overview
Problem
Connecting different voltage sources in mini-grids requires complex synchronization due to the need for precise frequency and voltage matching, which is challenging when converters are far apart, necessitating expensive and complex communication cables.
Innovation Solution
A master synchronization method using a group of master converters dynamically sets a central network frequency based on the state of charge of connected batteries, allowing synchronization without dedicated communication links by adjusting the output power of slave converters as a function of this frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If converters are connected over long distances using wired communication bus (CAN or RS485), then real-time frequency and voltage information can be exchanged, but the communication cables become very expensive and complex to install
Solution Approach 1:
The patent extracts the communication function from the physical cable connection by using the existing AC power bus as the communication medium. The frequency and voltage information are transmitted through the power lines themselves rather than requiring separate communication cables, thereby eliminating the need for expensive long-distance communication infrastructure while maintaining synchronization reliability
Solution Approach 2:
The AC power bus serves dual functions: it simultaneously transmits electrical power and communication signals (frequency and voltage information) between converters. This multi-functionality eliminates the need for dedicated communication cables, reducing both installation complexity and cost while maintaining reliable real-time information exchange
2Productivity
If a photovoltaic inverter is connected to a mini-grid, then energy exchange is enabled, but the inverter may have significant impact and disrupt mini-grid operation due to the low power capacity of the mini-grid
Solution Approach 1:
The patent implements a feedback mechanism where the master converter continuously monitors the mini-grid's frequency and voltage, and adjusts its power output accordingly. Slave converters similarly adjust their output based on the centralized control signals. This closed-loop control ensures that power exchange operations maintain the mini-grid's frequency and voltage within acceptable ranges, preventing disruption while maximizing energy exchange efficiency
Solution Approach 2:
The control system dynamically adjusts the power output of each converter based on real-time mini-grid conditions, battery state of charge, and power demand. This dynamic control allows the system to adapt to changing conditions, maintaining stability during energy exchange operations while optimizing productivity
Data Source
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AI summary
Master synchronization method, implemented by a group of master converters (25a) belonging to a converter system (26), the group of master converters comprising at least one output connected to a central network (27), each group of slave converters comprising at least one input connected to said central network, the method comprising the steps of: - measuring an overall master state of charge representative of the states of charge of the batteries connected to the converters of the group of master converters (25a); - adjusting the frequency of the central network according to the overall master state of charge, so as to control each converter of each group of slave converters (25b) so that said converter produces an output power which is a function of the frequency.