DC/AC Converter Automatic Grid Disconnection
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Solution Overview
Problem
State-of-the-art DC/AC converter systems require user intervention to switch to AC backup output mode and are not adapted to operate automatically based on grid conditions, leading to potential islanding hazards and inefficient power distribution during grid failures.
Innovation Solution
A DC/AC converter apparatus with a switch arrangement and control unit that automatically disconnects the output from the grid if the AC voltage falls below a threshold, connecting it to an AC backup output, allowing for seamless power transfer without user intervention and ensuring safety and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a manual transfer switch is used to connect the DC/AC converter output to the AC backup output, then the system can provide AC backup power, but the system requires user intervention and is not fully automatic
Solution Approach 1:
The control unit automatically detects grid failures and actuates the transfer switch without user intervention, enabling the system to serve itself by monitoring its own operating conditions and autonomously switching to backup power when needed
Solution Approach 2:
The control unit continuously monitors the AC grid voltage and uses this feedback to determine when to switch between grid-connected mode and AC backup output mode, creating a closed-loop automatic control system that responds to real-time grid conditions
2Reliability
If the DC/AC converter operates in islanding mode with AC backup output, then continuous power supply is provided, but the system may create dangerous islanding conditions
Solution Approach 1:
The transfer switch physically disconnects the DC/AC converter output from the AC grid terminals when switching to AC backup output mode, extracting and isolating the power conversion unit from the grid to prevent dangerous islanding conditions while maintaining continuous power supply to critical loads
3Reliability
If the system provides AC backup output during grid failures, then critical loads remain powered, but the system complexity increases
Solution Approach 1:
The transfer switch and control unit serve multiple functions: they enable automatic grid failure detection, execute switching between grid-connected and AC backup modes, prevent islanding conditions, and provide continuous power to critical loads, consolidating multiple protective and operational functions into integrated components
Data Source
Figure 1~2
AI summary
A DC/AC converter apparatus comprising: .input terminals (10) to be connected to a DC power source; .a DC/AC conversion unit (11) adapted to receive input DC electrical power via the input terminals and to convert the input DC electrical power into AC electrical power, the DC/AC conversion unit comprising two output terminals (12); . two AC backup output terminals (14); .a switch arrangement (13) adapted to selectively connect the two AC output terminals to the grid terminals and to the two AC backup output terminals; .a control unit (16) associated to the switch arrangement and adapted to: - drive the switches of the switch arrangement, - sense when an AC voltage at the grid terminals is below a predetermined threshold; and - automatically drive the switches of the switch arrangement in such a way to disconnect the two AC output terminals from the grid terminals and to connect the two AC output terminals to the two AC backup output terminals when the AC grid voltage is below a said predetermined threshold.