Shared Hybrid Transfer Switch for Fast AC Source Transfer
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Solution Overview
Problem
Existing transfer switches in data centers face challenges in achieving fast and reliable switching times between power sources due to limitations in electromechanical relays and additional delays from power quality detection and in-rush current management, making it difficult to meet performance standards like the ITIC Curve's one-half line cycle transfer timeframe.
Innovation Solution
A shared hybrid transfer switch system that uses a solid-state switch in series with relay contacts and configured to be momentarily coupled in parallel, enabling faster switching transitions and a 'soft start' feature to mitigate in-rush currents, with the solid-state switch shared between power sources to reduce complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If electromechanical relay contacts are used for power source switching, then the device complexity is reduced and cost is lowered, but the transfer time cannot meet the one-half line cycle (≤8ms) performance standard
Solution Approach 1:
The patent replaces electromechanical relay contacts with solid-state switching devices (SCRs and TRIACs) to achieve faster transfer times. The solid-state switches eliminate mechanical moving parts, enabling switching speeds two to three orders of magnitude faster than conventional relays, thus meeting the ≤8ms one-half line cycle requirement while maintaining system reliability.
Solution Approach 2:
The patent introduces an intermediary solid-state switch that bridges the power source and load during transition periods. This solid-state switch temporarily carries the load current while the electromechanical relay contacts are opening or closing, preventing current interruption and enabling seamless power transfer between sources.
2Loss of time
If a dedicated solid-state switch is used for both power sources to achieve fast transfer, then the transfer time is reduced, but the number of parts and cost increase
Solution Approach 1:
The patent makes the solid-state switching device universal by configuring it to handle switching for both power sources sequentially. The same solid-state switch (SCR/TRIAC) is used to transfer load current from the first power source during its transition, then later from the second power source during its transition, eliminating the need for separate dedicated solid-state switches for each source.
Solution Approach 2:
The patent merges the functions of multiple solid-state switches into a single shared solid-state switching device. By combining the switching functions for both power sources into one device, the system reduces component count, simplifies the circuit design, and lowers cost while maintaining the fast transfer capability.
3Reliability
If in-rush current is not limited during cold starts, then the circuit is simpler, but the relay contacts can be damaged or destroyed
Solution Approach 1:
The patent implements preliminary current limiting action by placing a current-limiting resistor in series with the load before power is applied. This resistor is automatically bypassed by the solid-state switch once the load capacitors are charged, but initially limits in-rush current to protect relay contacts during cold starts and power cycling events.
Solution Approach 2:
The patent introduces an intermediary current-limiting resistor that mediates between the power source and load during startup. This resistor temporarily limits in-rush current flow, protecting the relay contacts from damage, then is bypassed by the solid-state switch once the load is charged, maintaining normal operating efficiency.
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 system achieves significantly faster transfer times, up to two or three orders of magnitude faster than conventional electromechanical relays, while effectively managing in-rush currents and ensuring reliable operation within the desired timeframes, enhancing the reliability and longevity of components.
Implementation Method 1
A solid-state switch is included which is configured to receive control signals from a controller... to enable a switching transition to be made from one of the preferred or alternate AC power sources to the other
Implementation Method 2
A thermistor is coupled between one side of the SCR pair and the first common connection point and forms a current limiter to mitigate contact current overload when the anti-parallel SCR pair is turned on during a transition operation
Implementation Method 3
An anti-parallel SCR (silicon-controlled rectifier) pair is included... The anti-parallel SCR pair is turned on to provide an alternate current path from the alternate power source to the load
Implementation Method 4
The transfer switch's electrical switching uses contacts of electromechanical relays that are electrically interconnected in series and parallel combination
Data Source
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AI summary
The present disclosure relates to a shared hybrid transfer switch for transferring power received by a Load from a preferred AC power source to an alternate AC power source, or transferring power being received by the Load from the alternate AC power source to the preferred AC power source. The transfer switch makes use of a solid-state switch configured in communication with first and second pluralities of relay contacts, and also being coupled to the Load, and which receives control signals from a controller. The solid-state switch is controlled such that it is turned on to be in communication with select ones of the first and second pluralities of relay contacts, to provide a path for current flow to the Load from one of the preferred or alternate AC power sources being transitioned to, to carry out a switching transition from one of the preferred or alternate AC power sources to the other.