Intelligent Power Strip Bistable Relay In-Rush Current Management
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Solution Overview
Problem
Bistable relays in intelligent power strips face issues with in-rush currents during power restoration, which can damage relay contacts and trip upstream circuit protection devices, as they remain closed persistently and draw high currents when power is restored.
Innovation Solution
A power distribution unit (PDU) with a branch receptacle controller (BRC) and a rack power distribution unit controller (RPDUC) that monitor line voltage frequency to detect power loss and sequentially close bistable relays during power restoration, minimizing in-rush currents by coordinating relay closures with voltage zero-crossing points to prevent contact arcing and tripping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If bistable relays are used to maintain closed state persistently, then energy efficiency is improved, but in-rush current damage to relay contacts occurs during power restoration
Solution Approach 1:
The controller detects power restoration conditions and proactively sequences the closure of bistable relays before full power is applied to the load. By preparing the relay closure sequence in advance upon detecting power restoration, the system prevents in-rush current damage while maintaining the energy-efficient persistent closed state of bistable relays during normal operation.
Solution Approach 2:
The system implements periodic monitoring of power conditions and uses coordinated timing of relay closure according to voltage zero-crossing of line frequency. This periodic action at critical moments (power restoration) allows the bistable relays to maintain their energy-efficient persistent state during normal operation while preventing contact damage through synchronized closure timing.
2Speed
If all bistable relays are closed simultaneously upon power restoration, then power distribution speed is improved, but upstream circuit breakers trip due to cumulative in-rush current
Solution Approach 1:
The controller divides the simultaneous closure of all bistable relays into a segmented sequence, where relays are closed one at a time or in small groups according to a predetermined sequence. This segmentation prevents cumulative in-rush current from tripping upstream circuit breakers while still achieving rapid power distribution to all receptacles through coordinated sequential closure.
Solution Approach 2:
The controller pre-determines the closure sequence for all bistable relays upon detecting power restoration conditions. By preparing and executing a predetermined sequential closure plan in advance, the system ensures fast power distribution without overwhelming the upstream circuit protection devices with simultaneous in-rush currents.
3Ease of operation
If relay contacts are closed without coordinated timing, then operational simplicity is improved, but contact arcing and welding occur
Solution Approach 1:
The controller coordinates relay closure timing with the periodic voltage zero-crossing of the line frequency. By synchronizing relay contact closure with these natural periodic zero-voltage moments, the system eliminates contact arcing and welding without requiring complex control mechanisms, maintaining operational simplicity while preventing contact damage.
Solution Approach 2:
The system monitors the line voltage frequency and uses this feedback to determine the optimal timing for relay closure. By continuously tracking the periodic voltage waveform and triggering relay closure at zero-crossing points, the controller automatically prevents contact arcing and welding while maintaining simple operation through automated timing coordination.
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
The solution effectively limits in-rush currents and prevents upstream circuit breakers from tripping, ensuring the longevity of relay contacts and stable power distribution by strategically controlling bistable relays during power restoration.
Implementation Method 1
In such a bistable relay, the coil is pulsed to change the state of the contacts from open to closed and vice-versa
Implementation Method 2
The BRC may further detect a loss of AC power condition by monitoring the frequency of the line voltage and determining, from information relating to a zero crossing of the monitored frequency, that an AC power loss condition has occurred
Implementation Method 3
the relays that were previously in a closed position prior to the AC power loss condition are all sequentially commanded to again be closed after the AC Power is restored, in a manner that limits an in-rush of current to the PDU
Data Source
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AI summary
The present disclosure relates to a power distribution unit (PDU) having at least one power receptacle for enabling attachment of an AC power cord of an external device thereto. A branch receptacle controller (BRC) has at least one bistable relay and is associated with the one power receptacle for supplying AC power thereto from an AC power source. The BRC monitors a parameter of a line voltage and uses it to detect when AC power is lost, and then toggles the bistable relay, if the relay is in a closed position, to an open position. A rack power distribution unit controller (RPDUC) monitors the bistable relay and commands the BRC to close the bistable relay after AC power is restored.