Transitioning computing devices from secondary power to primary power after corresponding, independent delay times

A method for powering a system is described. The method includes receiving a signal that indicates availability of a primary power source to supply operating power to a plurality of computing devices, and responsive to the received signal, transitioning each of the plurality of computing devices from a secondary power source to receiving power from the primary power source after a delay time that is a function of a substantially unique seed value for each computing device.

TECHNICAL FIELD

The following disclosure relates to a power distribution architecture for data centers, for example, techniques and associated apparatus to efficiently deliver uninterruptible power to scalable and/or modular data processing equipment.

BACKGROUND

Computers have become widely adopted for various applications, for both personal and corporate uses. Some computers operate as stand-alone data processing equipment, with perhaps a peripheral such as a printer and a display device. Although useful for many purposes, additional features and benefits may be achieved if multiple computers are networked together to share information and resources.

A computer network may be formed by connecting two or more computing devices with an information channel. One type of network is a local area network (LAN). A typical residential LAN, for example, may connect two computers to a printer. A typical corporate LAN, for example, may allow many users to share resources and large amounts of information, including databases and application software.

A second type of network is a wide area network (WAN). A prime example of a WAN is the Internet. WANs such as the Internet allow many computer devices to communicate messages and share information. When multiple LANs are interoperable with one or more WANs, opportunities for computing devices to communicate and share information greatly expand.

From the perspective of an individual computing device that is connected to a network, users may direct the communication of information over a network with a user interface generated by a web browser application. A web browser is typically configured to enable the user to access web sites on the Internet or the World Wide Web. Web browsers allow users to easily send and receive messages over a network in packets of information. Such packets of information may include the address of a search engine website, such as www.dogpile.com, for example.

The popularity and simplicity of sharing information over networks, such as the Internet, has resulted in demand for data processing and storage capacity to support high network traffic volume. One mechanism to address this need may be referred to as a data center. In the context of the Internet, a data center may provide processing, storage, and support functions that improve performance or enhance the utility of the Internet. Data centers may also be deployed in other contexts. Financial institutions, for example, may employ one or more data centers to store financial account and transaction information.

A data center may provide data processing and storage capacity. In operation, a data center may be connected to a network, and may receive and respond to various requests from the network to retrieve, process, and/or store data. In addition to extensive data processing and data storage capabilities, data centers typically support high speed data transfer and routing capabilities. To meet future network demands, data center capacity may continue to expand.

SUMMARY

The present specification relates to powering up power supplies.

In a first general aspect, a method for powering a system is described. The method includes receiving a signal that indicates availability of a primary power source to supply operating power to a plurality of computing devices, and responsive to the received signal, transitioning each of the plurality of computing devices from a secondary power source to receiving power from the primary power source after a delay time that is a function of a substantially unique seed value for each computing device.

In a second general aspect, a method for transitioning from a secondary power source to a primary power source is described. The method includes powering a plurality of systems with secondary power sources, where each system comprises at least one secondary power source that powers the system, detecting a primary power source, and transitioning from being powered by the at least one secondary power source to being powered by the primary power source. The transitioning is staggered so that a portion of the plurality of systems transitions at different times.

In another general aspect, a system is described. The system includes an interface for receiving a signal that indicates availability of a primary power source to supply operating power to a computing device, a data store to store a delay time that is a function of a substantially unique seed value for each computing device, and means for transitioning the computing device to receiving power from a secondary power source to receiving power from the primary power source after the stored delay time. The transitioning is initiated in response to the received signal.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1is a schematic diagram illustrating an exemplary power distribution architecture100for a data center105in which each of a number of modular rack-mounted bases (which may also be referred to as trays)110includes an uninterruptible power supply (UPS)115integrated with a computer motherboard120. Efficient power delivery may be achieved by configuring the UPS115to perform the only AC-to-DC rectification that occurs between the AC mains power received from the electric utility grid and the DC power consumed by the motherboard120. In this example, AC mains refers to the AC power source available at the point of use in the data center105. When received in the data center105at the UPS115, the AC mains voltage is a substantially sinusoidal AC signal (e.g., 50 Hz, 60 Hz) that was generated, transmitted, and distributed by the electric utility. The AC mains input voltage is converted to a single DC voltage on a DC bus that delivers operating power to the motherboard120. In the event of a fault on the AC mains, a battery circuit is electrically connected across the DC bus to supply operating power to the motherboard120.

In the depicted example, the data center105includes a number of racks125A,125B,125C that contain a number of the trays110. The racks125A-125C may be powered by three phase AC power line voltages that are delivered to the data center105from an electric utility130. The AC power line voltages delivered to each of the racks125A-125C may originate from a rotating generator operated by the electric utility and driven by a steam or gas turbine, for example. The AC voltage signals, which are substantially sinusoidal, may be transmitted to a distribution point, such as a substation (not shown) in the utility grid, for example. The power line voltages (e.g., 480 V line-to-line) may be distributed from the substation to the data center105. In the data center105, individual phase voltages (e.g., 208 V line-to-neutral) are routed to the individual racks125A-125C. Suitable AC-to-AC transformers (not shown) may be employed, as necessary, to deliver the AC power at a specified AC voltage. For example, step-down transformers may transform AC power from high voltage levels suitable for transmission to levels that can be substantially directly applied to the UPS115. In some three phase configurations, for example, such transformers may make appropriate transformations between WYE and DELTA connections if required.

Unless otherwise indicated, references to AC voltages are understood to refer to substantially sinusoidal voltages, and voltage amplitudes are understood to refer to root mean square (r.m.s.) values. The utility130may deliver substantially symmetric three phase voltages suitable for powering substantially balanced three phase loads.

In the depicted example, one phase voltage and a neutral line are distributed to each rack125. The racks125and trays110may be configured to form a substantially balanced load. In other embodiments, a similar distribution may be used if the data center105included additional (or fewer) racks125. As an example, the exemplary tray110(shown in magnified detail) in the rack125A receives a phase A voltage and the neutral line. Each of the trays110in the rack125A receives the same AC input voltage signal, namely the Phase A-to-neutral voltage.

Similarly, each of the trays110in the rack125B receives a Phase B-to-neutral as the AC input voltage signal, and each of the trays110in the rack125C receives Phase C-to-neutral as the AC input voltage signal. In other implementations, different phase voltages may be distributed among the trays110in one of the racks125A-125C, and/or the AC input voltage signal to each of the trays110may be line-to-line voltages instead of line-to-neutral voltages. In various embodiments, any practical number of phases (e.g., 1, 2, 3, 4, 5, 6, . . . 12 or more) may be distributed to provide operating power to individual trays110.

Each of the trays110in the depicted example is coupled to a network connection140. The network connection140provides an information channel to a network145, which may include, for example, a local area network, virtual private network, wide area network (e.g., the Internet), or a combination of such networks, which may be wired, fiber optic, and/or wireless. A remote computer150represents one of many possible devices that could communicate data directly or indirectly with one or more trays to access, store, process, and/or retrieve information using a processor160and associated memory165on the motherboard120. In some implementations, additional processors (e.g., servers) may facilitate such communication. For example, the exemplary remote computer device150may be included in a server, a desktop computer, a laptop computer, and/or a handheld processor-based device. One or more servers may pre- or post-process, supervise, route, and/or balance the flow of data associated with the communication.

In various embodiments, the motherboard120may include one, two, three, four, or any other practicable number of processors160. In some embodiments, the motherboard120may be replaced with tray of data storage devices (e.g., hard disc drives, flash memory, RAM, or any of these or other types of memory in combination). In such embodiments, the data storage devices, the UPS115with the battery185may be integrated with the data storage devices and supported on the tray110. In other embodiments, the data storage devices, the UPS115with the battery185can be integrated with the motherboard120. In various embodiments, a digital processor may include any combination of analog and/or digital logic circuits, which may be integrated or discrete, and may further include programmable and/or programmed devices that may execute instructions stored in a memory. The memory165may include volatile and/or non-volatile memory that may be read and/or written to by the processor160. The motherboard120may further include some or all of a central processor unit(s) (CPU), memory (e.g., cache, non-volatile, flash), and/or disk drives, for example, along with various memories, chip sets, and associated support circuitry.

In some embodiments, the motherboard120may provide one or more DC-to-DC converters to convert the DC bus voltage to a suitable voltage for operating the circuitry in the motherboard120. For example, one or more DC-to-DC converters may provide regulated output voltages, which may include but are not limited to, for example a +3.3VDC power signal, a +5VDC power signal, a −5VDC power signal, a +12VDC power signal, and a −12VDC power signal.

In an exemplary implementation, the processor160and the memory165on the motherboard120may form at least a part of a processing system configured to handle network operations. As an illustrative example, the motherboard120may help to process Internet requests. The motherboard may process information either alone or in combination with other parallel processes running on other processor-based devices, such as one or more other trays110in the data center105.

An AC input voltage signal is delivered to each of the trays10to be processed by the UPS115. In some examples, the AC input voltage signal may be received from the AC mains. The UPS115includes an AC-to-DC converter170that converts the AC input voltage signal to a regulated DC voltage. The converter170outputs the regulated DC voltage onto a DC bus175. In some embodiments, the AC-to-DC converter170may regulate the DC voltage to a static set point. In some other embodiments, the set point may be dynamically determined. In some of the static and dynamic embodiments, the set point may be based on a characteristic of the battery. Examples of such set point regulation will be described in additional detail with reference toFIG. 3.

The AC-to-DC converter170may maintain voltage regulation on the DC bus175when the AC input voltage signal is in a normal range. A normal range for a typical sinusoidal AC signal may be specified in various ways. For example, one or more thresholds may be specified between about 80 V and 500 V for line frequencies that may be between about 40 Hz and 1000 Hz, such as around 50 Hz, 60 Hz, 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, . . . , and up to about 1000 Hz or more. As an illustrative example, for a 120 V nominal (r.m.s.) AC input voltage signal, a fault may be identified if the r.m.s. voltage drops below a second threshold of 100 V for a predetermined amount of time. In other implementations, a fault may be identified based on peak voltage, for example, a fault can be sensed if the AC peak input voltage falls below a first threshold of 90 V in any half cycle. Fault conditions may include, without limitation, blackouts, brownouts, voltage sags, surges, instabilities related to switchgear operation, or other electrical transient associated with the AC mains. In some implementations, a fault condition may cause or potentially cause improper operation of a processing unit in the DC load, for example, if the AC-to-DC converter170is unable to maintain adequate regulation of the voltage on the DC bus175, and/or to supply sufficient current to operate the DC loads serviced by the DC bus175.

If the AC input voltage signal falls outside of a normal range, such as during a fault condition, a detection circuit (not shown) may send a signal indicative of this condition. In response to detecting the fault condition, a battery circuit180may be configured to connect a battery185across the DC bus175so that the motherboard120can continue to operate substantially without interruption. The battery185may continue to provide operating power to the circuits on the motherboard115until the battery185substantially discharges. The battery circuit180may include circuitry capable of controlling the charging and/or discharging the battery across the DC bus175in various operating modes. An exemplary battery circuit is described in further detail with reference toFIGS. 5A,5B.

FIGS. 2-4are block diagrams that illustrate exemplary power distribution architectures for delivering power to operate DC loads that have at least one processor. For example, the motherboard120may constitute a DC load in various embodiments. In these examples, the AC-to-DC converter170provides the only AC-to-DC rectification that occurs between the AC utility grid (e.g., substation transformer, transmission line, generator, and the like) and the microprocessor160in any of the trays110.

FIG. 2shows an exemplary power distribution architecture in a system300, which may be implemented in a large facility with large power requirements, for example. The system200includes a utility AC mains generator205to supply AC mains voltage from a utility such as the electric utility130. The exemplary system200also includes two back-up AC generators, including a diesel fuel powered generator210and a co-located (e.g., turbine) generator215. Power from the generators205,210,215may be combined and/or selected by the AC switchgear220, and then delivered to the tray110via an AC bus225. In the event of a fault on the AC mains from the generator205, the generators210,215may provide a backup AC input voltage signal on the AC bus225.

In some implementations, a substantially asynchronous energy source may be used to generate a substantially sinusoidal AC voltage signal. For example, a flywheel energy storage and recovery system may be used. Wind or solar generated energy, such as that provided by a wind farm or a solar farm, respectively, may serve as sources of energy to generate a substantially sinusoidal AC voltage in an electric utility grid. In such implementations, the generated substantially sinusoidal signal is transmitted through the utility grid to an input of the AC-to-DC converter170without intervening AC-to-DC rectification.

In cooperation with the battery backup provided by the battery185, the generators205,210,215may provide substantially uninterruptible power to operate a DC load230on the tray110for short, intermediate, and/or longer term periods.

An exemplary use of the generators210,215, may be illustrated in the event of a fault (e.g., brownout, blackout) or unavailability (e.g., circuit maintenance) of the AC mains voltage from the generator205. In response to detecting the fault on the AC input voltage signal, the battery185is connected to deliver substantially battery voltage across the DC bus175. As such, short term (e.g., at least 10, 20, 30, 40, 50, 60 seconds at full load) operation of the DC load is maintained by power supplied from the battery185. The diesel generator210may be started to provide power to the AC bus225, preferably before the battery185fully discharges. For more extended AC power faults, the co-located generator215may be brought on-line to provide a more cost-effective operation, or to avoid exceeding government-regulated limits on diesel fuel generation.

In some implementations, one or both of the generators210,215may provide peak load shedding capability. For example, the co-located generator215may be used during expected peak demand hours each day. In some cases, this may permit negotiation of preferential rates for electric power from the electric utility130.

FIG. 3shows an exemplary schematic in additional detail. In various embodiments, the AC-to-DC converter170may regulate the single output voltage on the DC bus to a set point. The set point may be a static value in some embodiments, or it may be dynamically determined during operation. For example, the set point may be based, at least in part, on one or more electrical characteristics of the battery.

Characteristics on which a set point can be established may include battery characteristics such as battery chemistry, battery age, charge/discharge history, nominal maximum charge, temperature, charging profile (e.g., voltage charge rate under constant current), estimates of battery internal impedance, or other parameters relating to the electrical performance of the battery.

In addition to internal battery characteristics, the set point may be based at least in part on electrical circuit parameters of the battery circuit180and the DC bus175. In some embodiments, the set point to which the AC-to-DC converter170regulates the voltage on the DC bus175can be a function of a battery charging circuit topology. If the battery charging circuit provides a voltage boost circuit (e.g., boost converter, charge pump, flyback), then the set point voltage may be substantially at or below a desired maximum charge voltage. If the battery charging circuit only provides a voltage step-down (e.g., linear regulator, buck converter) capability, then the set point can be set to a value sufficiently above the maximum nominal charge voltage to achieve the required charge performance over relevant temperatures, taking account of tradeoffs in power loss and charging current and corresponding charge time. In light of such trade-offs, the set point may be only as high as necessary to meet charge time specifications. For example, the set point may be set to between about 0.050 and about 1 Volt above the nominal expected battery voltage.

In certain embodiments, the battery (or battery strings) has a higher output voltage than the voltage that is supplied to a DC load, such as the motherboard120. A step-down converter can be used to reduce the voltage output from the battery to the voltage required to supply the DC load. For example, the charge/discharge control305(shown inFIG. 5C) can include the step-down converter used to reduce the battery's voltage.

In other embodiments, the battery can have a lower output voltage than the voltage provided to the DC load. Here, the charge charge/discharge control305can include a step converter, such as a boost converter, used to increase the voltage from the battery so that it supplies adequate voltage to the DC load.

In various embodiments, the set point voltage may be set based on a specified temperature, such as 0, 10, 25, 30, 40, 50, . . . , 80 degrees Celsius. In an illustrative example, the set point may be dynamically adjusted based on a temperature in or around the battery185as measured by at least one temperature sensor (not shown).

In the depicted embodiment, the UPS115includes a charge/discharge control circuit305in series connection with the battery185, and further includes the controller245in operative connection with a non-volatile memory (NVM)310.

The series connected battery185and circuit305are connected across the DC bus175. Responsive to a signal indicative of a fault on the AC input voltage signal, the circuit305can operatively connect the battery185across the DC bus175to permit the battery to discharge to the DC load230through a low impedance path. When the AC input voltage signal on the AC bus225is not faulted, the circuit305may selectively permit charging current to flow from the DC bus175to charge the battery185.

In the depicted embodiment, the NVM310may store set point information for regulating the output of the AC-to-DC converter170. The set point information may be stored during manufacturing time, upon first use, and/or dynamically updated during operation of the tray110. The controller245and/or the AC-to-DC converter170may read and/or use the stored set point information to determine how to control the AC-to-DC converter170. In addition to set point information, information about threshold conditions for switching over between AC input and battery operation may be stored in the NVM310, for example.

In other implementations, the output of the AC-to-DC converter is not regulated; however, a step-up or step-down converter can be interposed between the AC-to-DC converter and the load to provide the load with an appropriate voltage. Additionally, the AC-to-DC converter can be used in combination with step-up or step-down converter to provide the load with an appropriate voltage.

Access to information stored in the NVM310may be provided through a serial or parallel interface (which may have a wired and/or unwired (e.g., infrared) physical layer), for example, between the NVM310and one or more processors160on the DC load230. The processors160may be used to access and/or update information in the NVM310via the network connections140(FIG. 1) to each tray110.

Additional data storage devices may be provided on the DC load230. In the depicted example, the DC load230includes two processors160in operative connection with the memory165and a hard disc drive (HDD)315.

FIG. 4illustrates an exemplary power distribution architecture400on the rack125. In the architecture400, the UPS115delivers power through the DC bus175to multiple DC loads230in a processing unit405. Each DC load230is connected in parallel across the DC bus175. Power delivered to the DC loads230is rectified from AC-to-DC only one time between the utility mains205and the DC load230. In one embodiment, a processing unit405includes an array of disks, an interconnect card, and an uninterruptible power supply with a battery.

In various implementations, each DC load230may have similar circuits or different circuits. Various ones of the DC loads may provide primarily data storage, data processing, data communication, or a combination of these or other functions. In one embodiment, the DC loads230are located on multiple trays in the rack125. In another embodiment, the entire processing unit405is located on one of the trays110. In some embodiments, the UPS115is integrated on a single tray110with the processing unit110. In other embodiments, the UPS115may be located elsewhere on the rack125. Processing unit405may refer to a one or more trays, racks, or other structure containing one or more DC loads230, which structure may include at least one bay, cabinet, portable or stationary building, or an entire facility, such as the data center105, for example.

FIGS. 5A-5Bare schematic diagrams showing details of a battery circuit in an exemplary power distribution architecture.

FIG. 5Ashows an exemplary schematic500for a portion of the charge/discharge control circuit305, which is described with reference toFIG. 3. The schematic500includes a comparator circuit505to control a signal Vups when the voltage on the DC bus175falls below a threshold, Voff. The schematic500also includes a comparator circuit510to control a signal VBatt when the voltage on the DC bus175falls below a threshold, Batt_Low. The signals Vups and Vbatt are described in additional detail with reference toFIGS. 6-7.

In other implementations, the circuit510acts as an operational amplifier (op amp) that measures voltages instead of a comparator that generates an output based on a comparison of the two input signals. The measured voltages can then be compared in software executed by the controller.

The schematic500further includes an over-current protection element515, which in this example includes a fuse. One terminal of the fuse515connects to a positive terminal of the battery, and the other terminal connects to a positive rail of the DC bus175. Alternatively, the fuse515can be coupled to the negative terminal of the battery. In yet other examples, additional series and/or shunt devices to provide over-current, over-voltage, reverse protection, EMI mitigation, and/or other functions.

In the depicted embodiment, a pair of terminals (+Battery, −Battery) is connectable to a battery. The negative battery terminal (−Battery), connects to two parallel paths, each of which is controllable by operation of a switch. One of the parallel paths connects the negative battery terminal to a negative rail of the DC bus175through a resistor520and a switch525. This path permits a charging current to flow when the switch is closed. The amplitude of the charging current is substantially limited by the value of the resistance520and the difference between the voltage on the DC bus175and the battery (not shown). The internal resistance of the battery is typically much less than the value of the resistance520. In some applications, the voltage drop across the resistance520may be used to measure and/or control the charging current.

The other parallel path connects the negative battery terminal to a negative rail of the DC bus175through a switch530. When the switch530is closed, the battery is operatively connected across the DC bus175. In this state, the battery can discharge and supply operating power to any DC loads (not shown) that are also connected across the DC bus175.

The switches525,530may be passively and/or actively controlled. An exemplary embodiment, shown inFIG. 5B, is illustrative of one implementation, and is not to be taken as limiting.

InFIG. 5B, the battery185is modeled with a series resistance540that may represent internal and/or contact resistance, for example. The ideal switch525(FIG. 5A) for charging the battery is implemented as a diode with no active control input. In this implementation, the AC-to-DC converter170(not shown) may regulate the DC bus175to a voltage that is sufficient to forward bias the diode (switch)525over temperatures of interest and to provide a desired charging current. As such, the set point may be at least the maximum charging voltage plus a diode drop voltage. In some implementations, the diode is optional. For example, the diode can be replaced by a switch, if it is assumed that the supply voltage will be higher than the battery voltage.

In the depicted example ofFIG. 5B, the battery charging current is determined, at least in part, by a series resistance and a unidirectional current mechanism, such as a diode or other semiconductor switch, for example. In other embodiments, the battery charger may include a series-pass regulator (e.g., low drop out (LDO) linear regulator) or a switch mode power converter (e.g., buck, boost, buck-boost, Cepic, Cuk, flyback, charge pump, or resonant, etc.), either alone or in combination. The battery charge current may be controlled by current mirror techniques, or using current measurement feedback techniques involving current sense resistance or inductive coupling measurement, for example.

The ideal switch530(FIG. 5A) for discharging the battery is implemented as a back-to-back MOSFET (metal oxide semiconductor field effect transistor) switch configured to block current in both directions when in a non-conductive state. This switch530opens and closes in response to a control signal535that may be generated, for example, by the controller245(FIG. 3), for example. In various embodiments, the switches525,530may include Schottky diodes, insulated gate bipolar transistors (IGBTs), or other semiconductor or electromechanical switches (e.g., relays). In other embodiments, discharging the battery is implemented using a step-down regulator, such as a buck converter.

FIG. 5Cshows an exemplary schematic550for a battery charge/discharge control topology. The schematic550includes a charging voltage supply that is separate from the power supply used to power a load, such as the motherboard120. The charging voltage can be used to charge the battery185(e.g., instead of, or in addition to, the power supply used to power the load), which can optionally be connected to the power supply's output during battery operation.

FIG. 5Dshows an alternative exemplary schematic580for the battery charge/discharge control. One of the differences between the schematic580and the schematic500is that in the schematic580the −/+VCHGis received from the charging voltage supply552instead of directly from the AC-DC converter170.

FIGS. 6-7are flow diagrams illustrating exemplary methods that may be performed in embodiments of the power distribution architecture.

Referring toFIG. 6, a flowchart600illustrates an exemplary method that the UPS115may perform to handle a fault condition on the AC input voltage signal. In some embodiments, the UPS115may perform the method to coordinate switchover to and/or from the battery as a temporary power source. In some cases, performing the method may substantially reduce and/or prevent performance disruptions (e.g., data errors) as a consequence of the AC fault condition. For example, the battery185may provide sufficient operating power to maintain operation of the DC loads230until an AC source, such as the utility mains205or backup generators210,215, can be brought on-line. In some embodiments, the battery185may continue to provide operating power while the DC loads230execute instructions to perform graceful power-down operations. Such graceful shutdown operations can vary widely, but generally attempt to mitigate performance disruptions that could result from the fault condition. Such disruptions may, for example, manifest themselves as stale or corrupted data when the processing system is subsequently restarted.

Generally, the method includes operations that may be performed by a controller (e.g., the controller245). The operations may further be performed under the control, supervision, and/or monitoring of one or more of the processors160in the system100. Operations may also be supplemented or augmented by other processing and/or control elements that may be in operative communication with the controller through a network connection140coupled to the tray110. Some or all of the operations may be performed by one or more processors executing instructions tangibly embodied in a signal. The processing may be implemented using analog and/or digital hardware or techniques, either alone or in cooperation with one or more processors executing instructions.

The method begins at step605when the controller determines that there is a fault on the AC input voltage signal. For example, the controller may identify the occurrence of AC power failures by monitoring, for example, the AC bus225, a voltage status condition signal provided by a voltage monitoring/fault detection circuit on the tray100, and/or an output voltage (e.g., VUPSinFIG. 5A) at the DC bus175. In some embodiments, the UPS115may include an analog to digital converter that converts VUPSinto a digital value (e.g., a 10 bit digital value). When the controller detects that a key voltage drops below a threshold, the controller may initiate an AC power fault routine. In other embodiments, the controller may receive signals from an external component, such as a power combiner in the AC switchgear220. Such signals may indicate a failure in the AC input voltage signal. In other embodiments, the AC-to-DC converter170may send a message to the controller to indicate an AC power fault.

If the controller determines that the AC power is not faulted, then step605is repeated. If the controller determines that the AC power is in a fault condition, then, in step610, the controller switches the UPS115from AC operation to battery operation. For example, the controller may send signals to open the switch525and to close the switch530(FIG. 5A) to operatively connect the battery185across the DC bus175such that the battery185can support the DC loads230. In some implementations, the battery is not directly connected to the DC loads230. For example, a step-down converter, such as a buck converter can be interposed between the battery185and the DC bus175so that when the switch530is closed, the voltage is reduced before it is supplied to the DC loads230.

Next, in step615, the controller sets a timer to a backup duration time. The timer may be a register in the controller which is decremented or incremented as time advances. In some embodiments, the backup duration time may represent a duration that the battery power may be used or relied upon. For example, the controller may compute the backup duration time using an estimate of an expected battery life, less the time required for the DC loads230to perform graceful power down operations.

In other embodiments, the controller may load the backup duration time from the NVM310. In step620, the controller determines whether the AC power is restored. For example, the controller may receive a message from the AC-to-DC converter about the present status of the AC input power. As another example, the controller may poll the AC-to-DC converter to determine whether the AC power is restored. If the controller determines that the AC power is restored, then the controller may perform operations in step625to switch back to operating from AC power, and the method600then ends. An exemplary method for switching from battery power to AC power is described in further detail with reference toFIG. 7.

If, at step620, the controller determines that the AC power is not restored, then in step630the controller checks whether VUPSis less than a minimum voltage for battery backup (VOFF). If the controller determines that VUPSis less than VOFF, then the controller may set the timer to a power down time in step630. For example, the power down time may be an estimation of the time required for the DC loads to perform the power down operations. In some examples, the power down operations of the DC loads may prevent data loss and/or avoid damage due to sudden loss of DC power. If, in step630, the controller determines that VUPSis not less than VOFF, then, in step640, the controller may determine whether an output voltage of the battery (VBATT) is less than a battery low threshold (BATT_LOW). In some embodiments, when VBATTis lower than BATT_LOW, it may indicate that the power stored in the battery is low and proper power down operations may be executed to prevent data loss, for example. If the controller determines that VBATTis less than BATT_LOW, then the step635is performed. If the controller determines that VBATTis not less than BATT_LOW, then the controller may check whether the backup duration time is expired. If the controller determines that the backup duration time is expired, then the step635is performed. If the controller determines that the backup duration time is not expired, then the step620is repeated.

Additionally, in certain embodiments, a host is notified if VBATTis less than BATT_LOW. The host may then initiate operations, such as reducing the operating load of the processor160or initiating a power-down process for the tray110. This may be in addition or in place of shortening back-up duration time by moving from the step640to the step635inFIG. 6.

After the controller sets the timer to the power down time in step635, the controller may check whether the AC power is restored in step650. If the controller determines that the AC power is restored, then the step625is performed. If the controller determines that the AC power is not restored, then the controller determines whether the power down time is expired in step655. If the controller determines that the power down time is not expired, then the step650is repeated. If the controller determines that the power down time is expired, then the controller may, in step660, power down the UPS (e.g., open the switch530inFIG. 5) and the method ends.

FIG. 7shows a flow chart that illustrates an exemplary method700of operations for switching from battery backup power to AC input power. For example, a controller may switch from battery operation to AC operation after AC power is restored after an AC power failure (e.g., see step625ofFIG. 6), or after a maintenance operation (e.g., a battery test operation).

In some embodiments, the controller may delay the transfer from battery power operation to AC power operation to mitigate, for example, high peak (e.g., inrush) currents into the data center105. A small fixed delay may further be provided to ensure that the AC input voltage is stable.

As described with reference to step625(FIG. 6), the method700may begin when the controller determines that the AC input power is restored. First, in step710, the controller may determine a random delay parameter. For example, a random delay parameter may be stored in the NVM310that represents a length of time (e.g., time, clock cycles) to delay (e.g., 1 ms, 1 second, 100 seconds, etc.) before switching to AC powered operation.

In some embodiments, the random delay parameter may be randomly or pseudo-randomly determined. For example, the controller may generate a pseudo-random delay parameter using a seed (e.g., a serial number stored in a memory register on the UPS115and/or the motherboard120, a machine time when the tray is first started-up, etc.) and a random number generator to generate the delay parameter. The delay parameter may then be used by the controller245and/or stored in the NVM310. In another example, the delay parameter may be a random number (e.g., recorded from a physical process such as radioactive decay) that is stored in the NVM310during manufacturing process of the UPS115.

In other embodiments, the delay parameter may be nonrandom, but based on a substantially unique value. For example, each delay time may be based on the serial number associated with the tray110, the UPS115, or another component of the system.

In one embodiment, the controller sets a timer to the random delay at step715. In other embodiments, the controller may monitor the delay using a counter, a real time clock, an analog ramp or decay circuit with a threshold comparator, or other suitable delay device. Then, the controller determines, in step720, whether VBATTis less than BATT_LOW. If VBATTis less than BATT_LOW, indicating that the battery is running out of charge, then the controller may switch from battery power to AC power in step725and the method700ends. For example, the controller may switch off battery power by opening the switch530in the circuit500(FIG. 5A). In the exemplary data center105, it is unlikely that all the batteries will reach a discharge limit at the same time, so this method is not expected to substantially increase peak currents on the AC input voltage lines in most embodiments.

If VBATTis not less than BATT_LOW in step720, then, in step730, the controller checks whether the timer has expired. If the specified delay is not reached, then the step720is repeated. If the specified delay is reached, then the step725is executed and the method700ends.

In certain implementations, the system100can have multiple power sources including an AC power source, a battery, and a bootstrap circuit. The AC power source may be a primary power source that can power all or part of an electrical load, such as the DC loads230and the controller245. The battery can serve as a secondary power source that backs up the primary power source in case of failure of the primary power source. The battery can also power all or part of the electrical load, and can be capable of powering substantially the same electrical load as the AC power source. The bootstrap circuit can power a portion of the electrical load. For example, if the electrical load includes the DC loads230and the controller, the bootstrap circuit can power the controller, but not the DC loads230.

The bootstrap circuit may draw its power from a battery, such as battery185, or a separate battery. In some implementations, the bootstrap circuit may be powered by a super-capacitor that is charged after the tray has been booted.

The method700can be used when the controller switches from battery operation to AC operation during an initial power-up, or boot, sequence of the trays110. In some implementations, the bootstrap circuit can power the controller before the battery185is turned on. While powered by the bootstrap circuit, the controller can put the tray110in a battery mode that draws power from the battery185before an initial power-up of the tray. After the tray is powered by the battery, the controller can proceed with the method700.

In other implementations, the controller is powered by the bootstrap circuit and switches to the AC operation without first switching to battery operation. For example, the bootstrap circuit can provide power to the controller, so that when the controller detects that AC power is present, the controller may initialize the method700. In this example, the measurements and actions dependent upon the battery can be performed in relation to the bootstrap circuit. For instance, instead of VBATTbeing measured in step720, a voltage output of the bootstrap circuit, VBOOTis measured. If VBOOTindicates that the bootstrap circuit does not have sufficient voltage to power the controller, the controller switches from the bootstrap circuit to the AC power (which is analogous to step725) without waiting for the timer to expire.

In some implementations, the bootstrap circuit only provides power to the microcontroller after receiving a signal indicating the presence of AC power. In other implementations, the bootstrap circuit can provide power at a predetermined time. For example, the bootstrap circuit can provide power to the controller periodically (e.g., once per minute) so that the controller can check for the presence of AC power. In another example, the bootstrap circuit may provide power to the controller at a particular time, such as a scheduled start-up time for the trays.

In some implementations, the controller can monitor additional signals (as well as the signal indicating AC presence) to determine when to start a counter programmed with the delay parameter. For example, a “start” signal can be combined with the AC presence signal in a logical AND operation. If AC is present and the start signal is asserted, then the counter is started. Otherwise, the counter is not started.

In various embodiments, the battery voltage may be above and/or below the regulated voltage on the DC bus. In some embodiments, the AC-to-DC converter may regulate to a set point voltage that is within 50, 100, 200, 250, 400, 500, . . . , 1000 mV of the battery's nominal fully charged voltage. In various implementations, the regulation set point may be dynamically determined, for example, based on battery characteristics, such as the age, usage history, temperature, internal resistance, charge time response, discharge time response, or other battery circuit-related characteristics. If the battery voltage is above the set-point voltage, then the charger may include a step-up and/or buck-boost type converter circuit.

In some embodiments, a tray110may be a modular support structure configured to be mounted in one of a number of locations, slots, or positions in the rack125. Each tray110may include a substrate, such as a printed circuit board (PCB), on which the UPS175and the motherboard120and/or other DC loads230may be integrated. The trays110may provide features for a thermal management system, including ports for air flow, when installed in one of the racks125. The term “tray” is not intended to refer to a particular arrangement, but instead refers to any arrangement of computer-related components coupled together to serve a particular purpose, such as on a motherboard. Trays may be generally mounted parallel to other trays in a horizontal or vertical stack, so as to permit denser packing than would otherwise be possible with computers having free-standing housings and other components. The term “blade” may also be employed to refer to such apparatuses. Trays may be implemented in particular configurations, including as computer servers, switches (e.g., electrical and optical), routers, drives or groups of drives, and other computing-related devices.

Embodiments of the UPS115may be configured to accept various primary or secondary battery technologies. Technologies may include, but are not limited to super-capacitors, sealed lead acid, nickel metal hydride, nickel cadmium, spiral wound lead acid, alkaline, and lithium ion. The UPS115may include circuitry to auto-detect battery chemistry, and adapt charging and discharge profile information according to the determined battery characteristics. In some embodiments, the set point to which the AC-to-DC converter170regulates the DC bus175may be responsive to the auto-detected battery characteristics. In various embodiments, the battery voltage may be between about 8 Volts and about 26 Volts, such as about 9, 10, 11, 12, 13, . . . , 23, 24, or 30 Volts.

For example, a nominal 12 Volt lead acid battery may have a corresponding set point regulation on the DC bus of about 13.65 Volts, for example, to provide for substantially fully charging the battery. In the event of a switchover from 13.65 Volts regulation on the DC bus to battery voltage, the transient step (in this case, a drop) in voltage on the input to the DC load will be relatively small, such as less than 1 Volt, for example. Such a small change in the input voltage may substantially mitigate adverse transients in the DC loads.

The battery185may be a single cell, or a combination of cells arranged in series and/or parallel. In some embodiments, one or more batteries in a UPS may be hot swappable in modes other than battery back-up mode in which the battery is discharging into the load during a fault condition on the AC bus225. A visual or audible indicator may be provided to alert service personnel whether the battery may be hot swapped.

When mounted on a tray10, a battery may be located and supported for quick and convenient replacement. Various quick connect/quick disconnect wire harnesses (e.g., Fast-on style connectors), spring-biased electrical contacts, snap features, locking tabs, or the like may be employed to retain batteries for secure connection and quick replacement.

AC mains voltage, as used herein, may refer to AC voltage sources that typically have a fundamental frequency between about 47 Hz and about 500 Hz, without being necessarily so limited. Sources of AC voltage may be derived from stationary or mobile sources, examples of which may include rotating electric generators on transport vehicles, trucks, trains, ships, aircraft, or the like. Rotating generators refer to sources of electric power that substantially derive from coupling a time-varying magnetic field to one or more conductors to produce a substantially sinusoidal voltage. In some implementations, a magnetic field is rotated relative to one or more conductive windings. In some other implementations, one or more conductive windings are rotated relative to a stationary magnetic field.

The AC-to-DC converter170, in one implementation, being the only AC-to-DC rectification in the power path from the AC generator to the DC load230, may include features to reduce harmonic distortion, mitigate conducted emissions, manage inrush current, and the like. Accordingly, the converter170may incorporate hardware, software, or a combination thereof, to provide power factor correction, spread spectrum (e.g., frequency hopping) switching frequency, filtering, and/or current controlled start-up, for example.

Regulation of the DC bus voltage output by the converter170may be accomplished by employing any suitable switching converter and control strategy for providing the single output voltage at a determined set point. Switching topologies may include, but are not limited to, forward, flyback, Cuk, SEPIC, buck, buck-boost, or any suitable resonant or quasi-resonant AC-to-DC converter. In one illustrative embodiment, the AC-to-DC rectification and conversion is accomplished, at least in part, with appropriate operation of an active switching matrix having four controllable switches that modulate the AC input voltage applied to an inductive element in a buck arrangement. In another illustrative embodiment, the AC input voltage is rectified by an uncontrolled diode rectifier stage, followed by a magnetically coupled DC-to-DC conversion stage using a forward or flyback topology, for example. In yet another illustrative example, a power factor input stage is followed by one or more cascaded step-down DC-to-DC converter stages to yield the regulated voltage at the determined set point. Linear regulation may be used in combination with switch-mode power conversion. From this disclosure, one of ordinary skill in the art will recognize a number of implementations for the AC-to-DC converter170.

With reference for example toFIG. 4as an illustrative example, some embodiments of the system400may operate in any of at least four modes. In a first mode, the processing unit405is shut down, as is the UPS115. In a second mode, the battery185is charged using power received from the DC bus175. In this second mode, the battery185may fast charge or trickle charge according to a charging algorithm. In a third mode, the battery is “floated” being effectively disconnected from the DC bus and neither charging nor discharging while the AC-to-DC converter supplies operating power to the DC load230. In a fourth mode, the battery is operatively connected to the DC bus175, and discharges to supply operating power to the DC loads230. This fourth condition may be initiated in response to a fault condition on the AC bus225.

In various implementations, transfers between voltage sources may involve certain transition sequences. The AC switchgear220(FIG. 2), for example, may transfer between any of the generators205,210,215using either a substantially make-before-break or a substantially break-before-make transfer sequence. When switching from AC input operation to battery operation, the UPS115may, in some embodiments, disable operation of the AC-to-DC converter before, substantially during, or after the battery185is connected across the DC bus175. If all the converter175output current passes through a series diode, for example, then the converter175may be disabled by simply disabling operation of the DC-to-DC switching at the switch-mode controller (not shown). In other embodiments, the output may be actively disconnected by a semiconductor switch, for example.

A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, both the back-up battery and the power supply unit can be located off the tray110. Also, advantageous results may be achieved if the steps of the disclosed techniques were performed in a different sequence, if components in the disclosed systems were combined in a different manner, or if the components were replaced or supplemented by other components. Accordingly, other embodiments are within the scope of the following claims.