Power Supply Backfeed Protection via Voltage Monitoring
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Solution Overview
Problem
The existing power supply units with bidirectional inverters face challenges in ensuring backfeed protection, particularly when the AC switch fails, leading to potential electrical shocks during disconnection from commercial power, as the reliability of backfeed protection depends on the AC switch's integrity, and failures like welding or short-circuiting can result in unsafe voltage outputs.
Innovation Solution
The implementation of a power supply unit with two voltage sensors and a control unit that detects AC switch failures by monitoring input and output voltages, determining if the AC switch is faulty, and stopping the bidirectional inverter to prevent unsafe voltage outputs, enhancing backfeed protection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an AC switch is used to disconnect the bidirectional inverter and commercial power supply, then backfeed protection is provided, but the reliability of backfeed protection deteriorates when the AC switch fails (welding or short-circuiting)
Solution Approach 1:
The control unit continuously monitors the operational state of the bidirectional inverter and detects whether current is flowing through the AC switch. By comparing the expected state (switch open during battery discharge) with the actual detected state, the system provides feedback to identify switch failures. When a failure is detected, the control unit stops the bidirectional inverter to prevent backfeed, thereby maintaining backfeed protection reliability even when the AC switch fails.
Solution Approach 2:
The control unit acts as an intermediary between the AC switch and the bidirectional inverter. It monitors the switch's operational state and mediates the connection by stopping the inverter when switch failure is detected, preventing direct backfeed to the commercial power supply and eliminating electrical shock risk.
2Reliability
If voltage sensors and control unit are added to detect AC switch failures, then backfeed protection reliability is improved, but device complexity increases
Solution Approach 1:
The system uses its own operational parameters (inverter state, input voltage, output voltage) to detect AC switch failures. The control unit analyzes existing electrical signals already present in the system, allowing the system to self-diagnose switch failures without requiring external monitoring equipment or complex additional sensors.
Solution Approach 2:
The control unit detects AC switch failures by monitoring changes in electrical parameters (voltage levels at input and output, current flow patterns). By analyzing parameter changes that occur when the switch is open versus closed, the system can identify switch failures using simple voltage comparisons rather than complex monitoring circuits.
Data Source
AI summary
This power supply unit includes: an AC path from an input end to an output end; a first voltage sensor configured to detect an input voltage at the input end; a second voltage sensor configured to detect an output voltage at the output end; a bidirectional inverter connected to the AC path; a storage battery connected to the AC path via the bidirectional inverter; an AC switch provided between the input end and a point at which the bidirectional inverter is connected to the AC path; and a control unit configured such that, in a state in which the AC switch is controlled to be opened, if current conduction via the AC switch is detected on the basis of an operation state of the bidirectional inverter, the input voltage, and the output voltage, the control unit determines that the AC switch has failed, and stops the bidirectional inverter.