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EP-4290722-B1 - OUTLET IN-RUSH CURRENT LIMITER FOR INTELLIGENT POWER STRIP

EP4290722B1EP 4290722 B1EP4290722 B1EP 4290722B1EP-4290722-B1

Inventors

  • FERGUSON, KEVIN R.
  • GILSON, CASEY
  • COOPER, SCOTT
  • ARMSTRONG, JASON

Dates

Publication Date
20260506
Application Date
20230605

Claims (15)

  1. A rack power distribution unit (100) comprising: at least one power receptacle (192) configured to enable attachment of an alternating current (AC) power cord (206) of an external device to the power receptacle: a power output module (POM, 132) having a plurality of bistable relays (140) and associated with the at least one power receptacle for supplying AC power to the at least one power receptacle from an external AC power source, each of the bistable relays having contacts able to be set to an open position and to a closed position, the POM further comprising an interchangeable monitoring device (IMD, 104) wherein the POM is configured to: determine a load connection status over an open contact of one of the plurality of bistable relays based on a change in at least one of RMS voltage or peak voltage; predict a voltage zero-crossing of a line voltage from the external AC power source; transmit a communication that includes the load connection status and the voltage zero crossing to the interchangeable monitoring device (IMD); and close the open contact based on a command from the IMD; and the IMD, configured to: monitor a state of the bistable relays; receive the communication from the POM; command the POM to close the open contact based on the communication, wherein closing the open contact limits an in-rush of current to the rack power distribution unit.
  2. The rack power distribution unit as claimed in claim 1, wherein the POM utilizes one or more control algorithms to determine the load connection status over the open contact of one of the plurality of bistable relays based on the change in at least one of RMS voltage or peak voltage.
  3. The rack power distribution unit as claimed in claim 1 or 2, wherein the POM is configured to predict the voltage zero-crossing of the line voltage from the external AC power source by monitoring a line frequency of the line voltage.
  4. The rack power distribution unit as claimed in any one or more of the claims 1-3, wherein the POM is configured to predict the voltage zero-crossing of the line voltage from the external AC power source by monitoring stored zero-crossing voltage transition data.
  5. The rack power distribution unit as claimed in any one or more of the claims 1-4, wherein the POM is configured to determine the load connection status via a load detection circuitry.
  6. The rack power distribution unit as claimed in claim 5, wherein the load detection circuitry includes a plurality of resistors (312a-f) with known resistances and a difference amplifier (326) configured to determine an output voltage based on a difference of two comparator voltages.
  7. A method for monitoring and controlling an application of AC power to a plurality of load devices, the method comprising: providing at least one AC power receptacle (192) forming a power attachment point for an alternating current (AC) power cord (206) of an independent load device; using a power output module (POM, 132) having at least one bistable relay (140) associated with one of the at least one AC power receptacle for supplying AC power to the at least one AC power receptacle from an external AC power source, the bistable relay having contacts which are configured to be set to an open position and to a closed position; using the POM to: determine a load connection status over an open contact of one of a plurality of bistable relays based on a change in at least one of RMS voltage or peak voltage; predict a voltage zero-crossing of a line voltage from the external AC power source; transmit a communication that includes the load connection status; and close the open contact based on the determination of the load connection status and the predicted voltage zero crossing.
  8. The method as claimed in claim 7, wherein the predict the voltage zero-crossing of the line voltage from the external AC power source includes monitoring a line frequency of the line voltage.
  9. The method as claimed in claim 7 or 8, wherein the predict the voltage zero-crossing of the line voltage from the external AC power source includes monitoring stored zero-crossing voltage transition data.
  10. A rack power distribution unit (100) comprising: at least one power receptacle (192) configured to enable attachment of an alternating current (AC) power cord (206) of an external device to the power receptacle; a power output module (POM, 132) having a plurality of bistable relays (140) and associated with the at least one power receptacle for supplying AC power to the at least one power receptacle from an external AC power source, each of the bistable relays having contacts able to be set to an open position and to a closed position, the POM configured to: monitor a state of one of the plurality of bistable relays; determine a load connection status over an open contact of the one of the plurality of bistable relays based on a change in at least one of RMS voltage or peak voltage; predict a voltage zero-crossing of a line voltage from the external AC power source; and close the open contact based on a determination of the load connection status and a predicted voltage zero crossing.
  11. The rack power distribution unit of claim 10, wherein the POM utilizes one or more control algorithms to determine the load connection status over the open contact of one of the plurality of bistable relays based on the change in at least one of RMS voltage or peak voltage.
  12. The rack power distribution unit as claimed in any one or more of the claims 10-11, wherein the POM is configured to predict the voltage zero-crossing of the line voltage from the external AC power source by monitoring a line frequency of the line voltage.
  13. The rack power distribution unit as claimed in any one or more of the claims 10-12, wherein the POM is configured to predict the voltage zero-crossing of the line voltage from the external AC power source by monitoring stored zero-crossing voltage transition data.
  14. The rack power distribution unit as claimed in any one or more of the claims 10-13, wherein the POM is configured to determine the load connection status via a load detection circuitry.
  15. The rack power distribution unit of claim 14, wherein the load detection circuity includes a plurality of resistors (312a-f) with known resistances and a difference amplifier (326) configured to determine an output voltage based on a difference of two comparator voltages.

Description

TECHNICAL FIELD The present disclosure relates to intelligent power strips with multiple outlets and bistable relays, and more particularly to an intelligent power strip which is configured to limit in-rush current as external devices are being connected and disconnected to the intelligent power strip while the outlets are turned on. BACKGROUND Intelligent power strips, such as those used for server clusters, often use power relays, typically rated 250V/20 Amps, to switch a line of a receptacle for the main purpose of rebooting a connected load device, such as a server. Depending upon the internal power supply design of the load device, substantial in-rush currents may occur while input bulk capacitors charge up the moment the relay contacts are closed. This brief, but large current surge, can permanently damage the relay contacts. For example, the in-rush currents may weld the relay contact closed so that the relay contact is no longer operative. These high-energy events may even cause explosive expansion and ejection of molten metal, possibly leading to secondary arcing faults within the chassis. In-rush currents may also cause the upstream circuit protection device, typically a circuit breaker, to trip. Some relay manufacturers offer more expensive devices that can handle momentary current surges up to four times their design rating. To further supplement the protection of the relay contacts, the in-rush currents can be mitigated by coordinated timing of relay closure according to the voltage zero-crossing of line frequency. A type of Intelligent power strip commonly referred to as rack power distribution units (RPDUs), used in racks that hold server equipment, have switching capabilities associated with multiple receptacles. A reason for the switching capabilities has been two-fold: (a) to be able to remotely recycle power to a connected equipment that is hung up; and (b) to be able to sequentially start up all connected equipment to ensure that upstream breakers do not trip due to all connected loads drawing high in-rush currents concurrently. Typical IT (information technology) loads, for example servers, can draw as much as 5 times their normal current at the time of startup. Bistable relays are increasingly being used in RPDUs as they are more energy efficient, because their coils do not need to remain energized to maintain the state of their contacts. In such a bistable relay, the coil is pulsed to change the state of the contacts from open to closed and vice-versa. The contacts will then remain in their existing state until the coil is pulsed again. In contrast, in a typical normally open relay, when it is desired to close the contacts of the relay, the coil of the relay must be energized and kept energized to keep the contacts closed. When the coil of the typical normally open relay is de-energized, the relay contacts revert to their normally open state. Similarly, in a typical normally closed relay, when it is desired to open the contacts of the relay, the coil of the relay must be energized and kept energized to keep the contacts open. When the coil of typical normally closed relay is de-energized, the relay contacts revert to their normally closed state. RPDUs with switching capabilities are particularly useful in managing in-rush current during power cycle and circuit breaker closures, where they can be programmed to sequence power to each receptacle in a prescribed time. However, RPDUs currently are unable to mitigate potential in-rush current in situations where a user manually connects and/or disconnects the load while a receptacle is powered. Complicating matters is the inability of these systems to indicate whether a load device is connected or disconnected when the relay contacts are open. These limitations within the RPDUs for detecting load connectivity and in-rush current can lead to high-energy events as listed above. US2020/059088A1 describes a power distribution unit (PDU) having at least one power receptacle for enabling attachment of an AC power cord of an external device thereto, with a branch receptacle controller (BRC) having at least one bistable relay and associated with the one power receptacle for supplying AC power thereto from an AC power source. EP2404354A1 describes a power distribution unit (PDU) disposable in an electrical equipment rack with a housing, a power input penetrating the housing, outlets in the housing, a processor disposed in the housing, voltage and current sensors, and a voltage calculation procedure communicable with the processor. US2019058354A1 describes a circuit breaker includes a control circuit capable of generating and transmitting a test pulse through its attached circuit and any connected load. US2014144897A1 describes an apparatus for providing a voltage reduction capability in a welding power source for safety purposes. Therefore, it may be advantageous for a system and method to remedy the shortcomings of the conventional approaches ident