Intelligent battery backup system for increasing rack density of idc

Abstract

Various embodiments of the present invention can use a battery backup system (BBS) in a computer server rack to provide power to servers in excess of the power grid power supplied to the rack. This supplemental power can permit additional servers to be added to the rack while still permitting peak loads to be accommodated. The BBS can also act as an uninterruptible power supply (UPS) in the event of a power grid power interruption, thus providing both UPS and supplemental power functionality.

Description

TECHNICAL FIELD

[0001] Various embodiments of the present invention relate to battery backup systems for Internet Data Centers (IDCs), with particular emphasis on increasing rack density through managed power control. BACKGROUND

[0002] The growth of very large data centers has led to so-called "server farms" that can contain thousands or tens of thousands of servers. To use space efficiently, servers are often arranged in standardized 19-inch wide racks, each rack holding multiple servers, with many racks in a room or building. The installed base of server racks has become very large, with hundreds of thousands or possibly millions of racks in place. Each rack can be limited to a defined peak power from the power budget for each rack at the IDC level. IDC upgrade progress has fallen far behind the upgrade progress of servers and racks, so that many of today's racks must still be deployed in IDCs built many years ago under the limitations of that era. Rack space utilization is often low because the racks themselves, and the grid power allocated by the IDC to each rack, were designed with older technology in previous eras. In addition, servers can require additional power (over their long-term steady state value) for periods of time ranging from minutes to hours. It is impractical to meet this demand by providing increased grid power to the racks, because the installed base of power sources in the IDC and racks and other existing infrastructure is very large.

[0003] Within a rack, the allocated power can often be large enough to cope with temporary surges (over average power consumption) in the power required by the servers in that rack, as long as those surges do not last more than a defined period of time. Exceeding this defined period of time can result in harmful consequences, such as emergency computer shutdowns or even thermal damage. Therefore, the number of servers in a rack can be kept intentionally low to avoid overstressing the power system when servers require additional power.

[0004] A battery backup system (BBS) is often used to provide uninterruptible power supply (UPS) functionality, in which the battery is used to provide power only when the primary power source is lost (e.g., grid power to the building housing the server farm fails). In such cases, the BBS can be kept fully charged when grid power is available, to maximize the length of time that the BBS can subsequently survive after a grid outage. However, the BBS does not typically supplement grid power when it is available. BRIEF DESCRIPTION OF DRAWINGS

[0005] Some embodiments of the application can be better understood by reference to the following description and accompanying drawings that illustrate embodiments of the application. In the drawings:

[0006] Figure 1 An embodiment of a prior art server rack is shown.

[0007] Figure 2 A chart of exemplary power consumption in a rack according to an embodiment is shown. Figure 1

[0008] Figure 3 A rack with a backup battery system (BBS) according to an embodiment of the application is shown.

[0009] Figure 4A and Figure 4B A flowchart of a method of controlling total rack input power according to an embodiment of the application is shown. DETAILED DESCRIPTION

[0010] In the following description, numerous specific details are set forth. However, it is understood that embodiments of the application can be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

[0011] References to "one embodiment," "an embodiment," "example embodiments," "various embodiments," etc., indicate that the embodiment(s) so described can include a particular feature, structure, or characteristic, but not every embodiment necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrases "for example," "for instance," "e.g.," "for example," etc., does not refer to the same feature, structure or characteristic each time it is used. Rather, these phrases mean to logically connect one feature, structure or characteristic to another in an apparatus or method.

[0012] In the following description and claims, the terms "coupled" and "connected," along with their derivatives, can be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, "connected" is used to indicate that two or more elements are in direct physical or electrical contact with each other. "Coupled" is used to indicate that two or more elements co-operate or interact with each other, but they can or can not be in physical or electrical contact.

[0013] As used in the claims, unless otherwise specified, the use of ordinal adjectives, such as "first", "second", "third", etc., to describe different elements or instances of the same element is to distinguish between the different elements or instances from one another and does not imply a particular ranking or order to the elements or instances.​

[0014] Various embodiments of the application can be implemented in whole or in part in software and / or firmware. This software and / or firmware can take the form of instructions contained in or on a non-transitory computer-readable storage medium. The instructions can be read and executed by one or more processors to enable performance of the operations described herein. The instructions can be in any suitable form, such as but not limited to source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. Such a computer-readable medium can include any tangible non-transitory medium for storing information in a form readable by one or more computers, such as but not limited to read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory, etc.

[0015] For reference, Figure 1 A typical prior art server rack is shown. Although considered to be prior art, it is shown in this detailed description section because it forms the basis for the various embodiments of the application described later. The rack shown is shown to have a horizontal dimension of 19 inches, which has been common in the computer industry for the past several decades, but other dimensions can be used. The rack is also shown to have a vertical mounting space of 50 units for mounting servers, but other vertical dimensions can be used. For redundancy, each server is shown to have two power supply units (PSUs), each of which is energized by a separate source of electrical grid power (source 1 or source 2). This permits the server to continue to operate in the event of a failure of one of the PSUs or the source of electrical grid power that powers it. In a typical configuration, each PSU can supply enough power to the server to operate when the other PSU fails. But in the absence of such a failure, each PSU can supply approximately half of the power required by the server, and the server or PSU can contain circuitry that balances the load in this manner.

[0016] Figure 1 The rack of Figure 1 contains only 60% of the servers that the rack has space to accommodate, which is a typical configuration in prior art server farms. The reason for this enormous waste of space can be seen in Figure 2 Figure 2.

[0017] Figure 2 Figure 3 shows a rack according to an embodiment Figure 1A chart of exemplary power consumption in a rack. The specific rack of this example has a maximum power rating of 8.8 kilowatts (kW), and a short-term power rating of 8.0 kW (e.g., less than 5 minutes), and a long-term power rating of 7.2 kW (e.g., more than 5 minutes and even up to several hours). The steady-state power consumption is shown to be near 6.5 kW. Given the possible tolerances from the power consumed by each component in the server and rack (e.g., CPU, DDR, HDD, etc.), there can be no easy way to prevent short-term peak demands from exceeding their expected range. Therefore, a 0.8 kW buffer band is shown in this example to prevent short-term peak demands from inadvertently exceeding the maximum power rating of the rack. In this example, this can limit the actual peak power of the rack to 8.0 kW.

[0018] In the example shown, the short-term peak load of the server can increase the steady-state demand on the PSU by approximately 1.5 kW. Similarly, the long-term peak load of the server can increase the steady-state demand on the PSU by approximately 0.7 kW. These two factors, combined with the 0.8 kW buffer band, result in a maximum of 6.5 kW of steady-state power consumption for all servers in the rack, even though the rack itself can be rated at 8.8 kW. This also indicates how short-term peak power can be a key factor in limiting the number of servers that can be deployed in a rack. Therefore, the number of servers in a rack can be significantly limited to far less than the physical space available for those servers.

[0019] Figure 3 A rack with a backup battery system (BBS) is shown, according to an embodiment of the application. Utility power 1 is shown as a source of AC power for the rack, which in the embodiment shown, provides power to power supply units (PSUs) on the left side of the servers in the rack (as seen in both Figure 1 and Figure 3 ). Similarly, utility power 2 is shown as a separate source of AC power for the rack, which in the embodiment shown, provides power to a rectifier. The rectifier then provides DC power in order to charge the battery backup system (BBS), and also provides DC power to the PSUs on the right side of the servers in the rack. The PSUs shown are capable of operating on AC or DC power, which allows the rectifier and BBS to be retrofitted into an existing rack without replacing the PSUs. However, other embodiments can replace some of the AC-only PSUs with DC-only PSUs or AC / DC PSUs.

[0020] Figure 3 The rectifier and BBS are shown to be at the top of the rack. However, other embodiments can place the rectifier and / or BBS in any convenient location. Figure 3Rectifiers and BBSs that occupy 4 units of rack space are also shown, for over Figure 1 16 units of rack space are set aside for additional servers and their respective PSUs in the quantities shown in FIG. 3. However, other embodiments can use other quantities of units for these purposes. For clarity, Figure 3 only one additional server in this space is shown, but other embodiments can have more servers.

[0021] For the Figure 3 and subsequent description of FIG. 4, the following definitions can be used:

[0022] P gp1 — Actual power provided by grid power 1.

[0023] P gp2 — Actual power provided by grid power 2.

[0024] P R — Output power of the rectifier.

[0025] P B — Output power of the BBS.

[0026] P _rack — Total input power consumed by the rack (as measured from outside the rack), which includes P gp1 + P gp2 .

[0027] P rack_limit — Predetermined maximum input power limit setting of the rack without regard to BBS output P B , i.e., the maximum value that P gp1 + P gp2 is permitted.

[0028] P — Amount by which the power (P _rack ) consumed by the rack exceeds P rack_limit .

[0029] In some embodiments, each server will automatically balance the amount of power drawn by its two PSUs (assuming that a failure of a PSU or its power source does not prevent such balancing). Thus, assuming no failures, P gp1 = ½ P _rack . Similarly, when the BBS is not contributing power, P R = ½ P _rack in normal operating conditions. If the rectifier has 100% efficiency, P gp2 will also be = ½ P _rack . Since the efficiency of the rectifier is less than 100%, P umay be slightly lower (in this case 98%), so P gp2 may be slightly greater than P R . However, for simplicity of explanation, the following description can assume P R = P gp2 . One of ordinary skill in the art will be able to calculate to what extent the efficiency of the rectifier affects the following description herein.

[0030] In addition to the amount of power just described, when the output power of the BBS is called upon by the power control module, the BBS can provide the output power P B . In normal steady state power conditions, grid power 1 and grid power 2 can each provide half of the required rack power, as in the case of Figure 1 , where Figure 3 The difference in

[0031] Figure 4 shows a flowchart of a method of controlling total rack input power, according to one embodiment of the present application. The operations of flowchart 400 can be performed by a control unit comprised of one or more processors, monitoring logic, control logic, software, firmware, and / or other modules. They are not shown in Figure 4 due to their distribution in the system and the variety of modules and their configurations that can be used to perform these functions. However, in various embodiments, the control module can be within the rectifier, outside the rectifier, or partially within the rectifier and partially outside the rectifier.

[0032] The process can begin at 405, and in the initial state 410, grid source P gp1 and P gp2 may each provide approximately ½ of the total rack power P _rack . At 415, the control unit can determine that the load on the rack has risen and now exceeds the rack power limit P rack_limit by an amount, which is defined here as 2P (i.e., twice the value of P). When compared to the graph of Figure 2 , P rack_limit will be 8.8 kW. As a result of the determination at 415, when P gp2 begins to exceed ½ P rack_limit , at 420, the power level from P gp2 may be reset to ½ P rack_limit .

[0033] In one embodiment, the system can contain a monitoring module (either inside or outside the rectifier) that is used to monitor the output P rack_limit of the BBS.B , and set the rectifier to convert its output power P R In some embodiments, the rectifier can adjust its output power by adjusting its output voltage (e.g., increasing the output voltage to increase the output power, or decreasing the output voltage to decrease the output power). The BBS can then naturally adjust its own output power to R Supply the additional power required by downstream servers when reduced.

[0034] At 425, the output P of the BBS can be B Set to P (415 per operation, power demand exceeds P rack_limit 1 / 2 of the amount). Accordingly, P gp2 Reset to ½ P rack_limit - P, so that the output power of BBS can be further increased by P, so that P B Reach 2P value.

[0035] At 430, the BBS output power P may be increased again. B , this time increased to 2P, and P gp1 Increase to ½ P rack_limit + P. At this time, P gp2 = ½ P rack_limit -P,P gp1 = ½ P rack_limit + P, and BBS outputs P B = 2P. Adding these together, P gp1 and P gp2 The total power supplied to the rack is P rack_limit , as seen at 435, while the power supplied to the server = P rack_limit + 2P. Thus, even though the rack has more servers than would be feasible in the prior art and those servers are drawing peak load, the servers still get the power needed to meet the peak load demand, and Grid Power 1 and Grid Power 2 do not exceed their design limits.

[0036] Operations 405-435 have been described where the total rack power required may be from less than or at P rack_limit Transformed to be higher than P rack_limit Operations 440-480 describe an embodiment in which the total rack power may be above or below P rack_limit An embodiment of dynamically fluctuating between various levels.

[0037] When the flowchart 400 moves from operation 435 to operation 440, it is assumed that the output power P from the BBS B is 2P. (Remember, P is defined as P_rack P rack_limit by ½). At 440, the control unit can monitor the BBS output power P B in real time. If P B increases (as determined at 445), then at 450, the amount of the increase can be defined as a first amount β, letting P B = 2P + β. To offset a similar increase from P gp1 , at 455, P gp2 can be reset to ½ P rack_limit - P - β. Then, to offset operation 455, at 460, P B can be increased to 2P + 2β. This can return the flowchart to 435, where the total power supplied by P gp1 and P gp2 is P rack_limit , while the server receives P rack_limit + new P B (which is now 2P + 2β).

[0038] The previous paragraph describes what can happen if an increase in BBS output is detected at 445. However, if no such increase is detected, then the flow can proceed to 465, where P B can be decreased by a second amount α, letting P B = 2P - α. At 470, it can be determined whether 2(P - α) > 0. If so, then at 475, P gp2 can be reset to ½ P rack_limit - P + α. Then, at 480, the BBS output power P B can be decreased to 2P - 2α, and the flow can return to 435. At this point, the total rack power P _rack may = P gp1 and P gp2 = P rack_limit . On the other hand, if 2(P - α) is not > 0, then the flow can return to 410, where the grid power is balanced by P gp1 and P gp2 each providing approximately ½ of the total rack power P _rack from the grid source.

[0039] Example

[0040] The following example relates to a particular embodiment:

[0041] Example 1 includes a control unit configured for use in a computer server rack having a first grid power source, a second grid power source, and a battery backup system (BBS), the control unit being adapted to: detect that a power demand of a plurality of servers in the rack exceeds a specified maximum power limit of the rack by two times a first determined amount; set the BBS output power to the first determined amount; set the output power from the second grid power source to half the maximum power limit minus the first determined amount; and set the BBS output power to two times the first determined amount and set the output from the first grid power source to half the maximum power limit plus the first determined amount.

[0042] Example 2 includes the control unit of Example 1, wherein the control unit is further adapted to: increase the BBS output power by a second determined amount in response to increased power demand of the plurality of servers; set the second grid power output to the half of the maximum power limit minus the first determined amount minus the second determined amount in response to the increased power demand; and reset the BBS output power to twice the first determined amount plus twice the second determined amount.

[0043] Example 3 includes the control unit of Example 1, wherein the control unit is further adapted to: reduce the BBS output power by a third determined amount in response to a reduced power demand of the plurality of servers; set the first grid power output to be equal to the second grid power output to be equal to half of the total rack power in response to a determination that two times the first determined amount minus two times the third determined amount is not greater than zero; set the second grid power output to the half of the maximum power limit minus the first determined amount plus the third determined amount in response to a determination that two times the first determined amount minus two times the third determined amount is greater than zero; and reset the BBS output power to the two times the first determined amount minus two times the third determined amount.

[0044] Example 4 includes the control unit of Example 1, further comprising a first power supply unit and a second power supply unit in each of the plurality of servers; wherein each of the first power supply units is coupled to a first grid power source, and each of the second power supply units is coupled to a BBS and a second grid power source.

[0045] Example 5 includes the control unit of Example 4, wherein each server is configured to balance a power demand from the first power supply unit and a power demand from the second power supply unit.

[0046] Example 6 includes the control unit of Example 1, further comprising a rectifier coupled between the second grid power source and the BBS.

[0047] Example 7 includes the control unit of Example 6, wherein the control unit is to monitor the output power of the BBS and is to control the output power of the rectifier.

[0048] Example 8 includes a method of controlling power in a computer server rack, the method comprising: detecting that power requirements of a plurality of servers in the rack exceed a specified maximum power limit of the rack by a first determined amount twice over; setting an output power of a battery backup system (BBS) to the first determined amount; setting an output power from a second grid power source to half of the maximum power limit minus the first determined amount; and setting the output power of the BBS to twice the first determined amount and setting an output power from a first grid power source to half of the maximum power limit plus the first determined amount.

[0049] Example 9 includes the method of example 8, the method further comprising: in response to an increased power requirement of the plurality of servers, increasing the output power of the BBS by a second determined amount; in response to the increased power requirement, setting the second grid power output to the half of the maximum power limit minus the first determined amount minus the second determined amount; and resetting the output power of the BBS to twice the first determined amount plus twice the second determined amount.

[0050] Example 10 includes the method of example 8, the method further comprising: in response to a decreased power requirement of the plurality of servers, decreasing the output power of the BBS by a third determined amount; in response to determining that twice the first determined amount minus twice the third determined amount is not greater than zero, setting the first grid power output to equal the second grid power output to equal half of the total rack power; in response to determining that twice the first determined amount minus twice the third determined amount is greater than zero, setting the second grid power output to the half of the maximum power limit minus the first determined amount plus the third determined amount; and resetting the output power of the BBS to the twice the first determined amount minus twice the third determined amount.

[0051] Example 11 includes the method of example 8, the method further comprising balancing power requirements from a first power supply unit and a second power supply unit within each server in the computer server rack.

[0052] Example 12 includes the method of example 8, the method further comprising monitoring the output power of the BBS.

[0053] Example 13 includes the method of example 8, the method further comprising controlling an output power of a rectifier coupled to the BBS.

[0054] Example 14 includes a computer-readable non-transitory storage medium containing instructions that when executed by one or more processors result in performance of operations comprising: detecting that power requirements of a plurality of servers in a rack exceed a specified maximum power limit of the rack by a first determined amount twice; setting an output power of a battery backup system (BBS) to the first determined amount; setting an output power from a second grid power source to half of the maximum power limit minus the first determined amount; and setting the output power of the BBS to twice the first determined amount and setting an output power from a first grid power source to half of the maximum power limit plus the first determined amount.

[0055] Example 15 includes the medium of Example 14, wherein the operations further comprise: in response to an increased power requirement of the plurality of servers, increasing the output power of the BBS by a second determined amount; in response to the increased power requirement, setting the second grid power output to the half of the maximum power limit minus the first determined amount minus the second determined amount; and resetting the output power of the BBS to twice the first determined amount plus twice the second determined amount.

[0056] Example 16 includes the medium of Example 14, wherein the operations further comprise: in response to a decreased power requirement of the plurality of servers, decreasing the output power of the BBS by a third determined amount; in response to determining that twice the first determined amount minus twice the third determined amount is not greater than zero, setting the first grid power output to equal the second grid power output to equal half of the total rack power; in response to determining that twice the first determined amount minus twice the third determined amount is greater than zero, setting the second grid power output to the half of the maximum power limit minus the first determined amount plus the third determined amount; and resetting the output power of the BBS to the twice the first determined amount minus twice the third determined amount.

[0057] Example 17 includes the medium of Example 14, wherein the operations further comprise balancing power requirements from a first power supply unit and a second power supply unit within each server in a computer server rack.

[0058] Example 18 includes the medium of Example 14, wherein the operations further comprise monitoring the output power of the BBS.

[0059] Example 19 includes the medium of Example 14, wherein the operations further comprise controlling an output of a rectifier coupled to the BBS.

[0060] Example 20 includes a control unit configured for use in a computer server rack having a first grid power source, a second grid power source, and a battery backup system (BBS), the control unit having means for: detecting that power requirements of a plurality of servers in the rack exceed a specified maximum power limit of the rack by more than a first determined amount; setting BBS output power to the first determined amount; setting output power from the second grid power source to half of the maximum power limit minus the first determined amount; and setting BBS output to twice the first determined amount and output power from the first grid power source to half of the maximum power limit plus the first determined amount.

[0061] Example 21 includes the control unit of example 20, the control unit further having means for: increasing BBS output power by a second determined amount in response to an increased power requirement of the plurality of servers; setting the second grid power output to half of the maximum power limit minus the first determined amount minus the second determined amount in response to the increased power requirement; and resetting BBS output power to twice the first determined amount plus twice the second determined amount.

[0062] Example 22 includes the control unit of example 20, the control unit further having means for: decreasing BBS output power by a third determined amount in response to a decreased power requirement of the plurality of servers; setting the first grid power output equal to the second grid power output equal to half of the total rack power in response to determining that twice the first determined amount minus twice the third determined amount is not greater than zero; setting the second grid power output to half of the maximum power limit minus the first determined amount plus the third determined amount in response to determining that twice the first determined amount minus twice the third determined amount is greater than zero; and resetting BBS output power to twice the first determined amount minus twice the third determined amount.

[0063] Example 23 includes the control unit of example 20, wherein each server in the computer server rack includes means for balancing power requirements from a first power supply unit and power requirements from a second power supply unit.

[0064] Example 24 includes the control unit of example 20, wherein the control unit includes means for monitoring output power of the BBS and means for controlling output power of a rectifier coupled to the BBS.

[0065] The foregoing description is intended to be illustrative and not limiting. Variations will occur to those of skill in the art. Such variations are intended to be included within the various embodiments of the present application limited only by the scope of the claims below.

Claims

1. A control unit configured for use in a computer server rack having a first grid power source, a second grid power source, and a battery backup system (BBS), wherein: Each of the plurality of servers in the rack includes a first power supply unit and a second power supply unit, wherein each of the first power supply units is coupled to the first grid power source, and each of the second power supply units is coupled to the BBS and the second grid power source, and the control unit is adapted to: detecting that a power demand of the plurality of servers in the rack exceeds a specified maximum power limit of the rack by two times a first determined amount; Initially setting the BBS output power to the first determined value; setting the output power from the second grid power source to half the maximum power limit minus the first determined amount; and The BBS output power is increased to twice the first determined amount, and the output from the first grid power source is set to half the maximum power limit plus the first determined amount.

2. The control unit according to claim 1, further adapted to: In response to the increased power demands of the plurality of servers, increasing the BBS output power by a second determined amount; In response to the increased power demand, setting a second grid power output to the half of the maximum power limit minus the first determined amount minus the second determined amount; and The BBS output power is reset to twice the first determined amount plus twice the second determined amount.

3. The control unit according to claim 1, further adapted to: reducing the BBS output power by a third determined amount in response to the reduced power requirements of the plurality of servers; In response to determining that two times the first determined amount minus two times the third determined amount is not greater than zero, setting the first grid power output equal to a second grid power output equal to half the total rack power; In response to determining that two times the first determined amount minus two times the third determined amount is greater than zero, setting the second grid power output to the half of the maximum power limit minus the first determined amount plus the third determined amount; as well as The BBS output power is reset to the twice of the first determined amount minus twice of the third determined amount.

4. The control unit according to claim 1, wherein: The control unit is configured to monitor an output of the BBS.

5. The control unit according to claim 4, wherein: Each server is configured to balance power demand from the first power supply unit and power demand from the second power supply unit.

6. The control unit of claim 1, further comprising a rectifier coupled between the second grid power source and the BBS.

7. The control unit according to claim 6, wherein: The control unit is to control the output of the rectifier.

8. A method of controlling power in a computer server rack having a first grid power source, a second grid power source, and a battery backup system (BBS), wherein: Each of the plurality of servers in the rack includes a first power supply unit and a second power supply unit, wherein each of the first power supply units is coupled to the first grid power source, and each of the second power supply units is coupled to the BBS and the second grid power source, and the method includes: detecting that a power demand of the plurality of servers in the rack exceeds a specified maximum power limit of the rack by two times a first determined amount; Initially setting the output power of a battery backup system (BBS) to the first determined amount; setting the output power from the second grid power source to half the maximum power limit minus the first determined amount; and The output power of the BBS is increased to twice the first determined amount, and the output power from a first grid power source is set to half the maximum power limit plus the first determined amount.

9. The method of claim 8, further comprising: In response to the increased power demands of the plurality of servers, increasing the output power of the BBS by a second determined amount; In response to said increasing said power demand, setting a second grid power output to said half of said maximum power limit minus said first determined amount minus said second determined amount; as well as The output power of the BBS is reset to twice the first determined amount plus twice the second determined amount.

10. The method of claim 8, further comprising: reducing the output power of the BBS by a third determined amount in response to the reduced power requirements of the plurality of servers; In response to determining that two times the first determined amount minus two times the third determined amount is not greater than zero, setting the first grid power output equal to a second grid power output equal to half the total rack power; In response to determining that two times the first determined amount minus two times the third determined amount is greater than zero, setting the second grid power output to the half of the maximum power limit minus the first determined amount plus the third determined amount; as well as The output power of the BBS is reset to the twice of the first determined amount minus twice of the third determined amount.

11. The method of claim 8, further comprising balancing the power demand from the first power supply unit and the power demand from the second power supply unit within each server in the computer server rack.

12. The method of claim 8, further comprising monitoring the output power of the BBS.

13. The method of claim 8, further comprising controlling an output of a rectifier coupled to the BBS.

14. An apparatus configured for use in a computer server rack having a first grid power source, a second grid power source, and a battery backup system (BBS), wherein: Each of the plurality of servers in the rack includes a first power supply unit and a second power supply unit, wherein each of the first power supply units is coupled to the first grid power source, and each of the second power supply units is coupled to the BBS and the second grid power source, and the device includes: means for detecting that a power demand of the plurality of servers in the rack exceeds a specified maximum power limit of the rack by two times a first determined amount; means for initially setting the BBS output power to the first determined amount; means for setting the output power from the second grid power source to half the maximum power limit minus the first determined amount; and Means for increasing the BBS output power to twice the first determined amount and setting the output from the first grid power source to half the maximum power limit plus the first determined amount.

15. The apparatus of claim 14, further comprising: means for increasing the output power of the BBS by a second determined amount in response to an increased power demand of the plurality of servers; means for setting a second grid power output to said half of said maximum power limit minus said first determined amount minus said second determined amount in response to said increased power demand; as well as Means for resetting the BBS output power to twice the first determined amount plus twice the second determined amount.

16. The apparatus of claim 14, further comprising: means for reducing the BBS output power by a third determined amount in response to the reduced power demand of the plurality of servers; means for setting the first grid power output equal to a second grid power output equal to half the total rack power in response to determining that two times the first determined amount minus two times the third determined amount is not greater than zero; means for setting the second grid power output to the half of the maximum power limit minus the first determined amount plus the third determined amount in response to determining that two times the first determined amount minus two times the third determined amount is greater than zero; as well as Means for resetting the BBS output power to the twice the first determined amount minus twice the third determined amount.

17. The apparatus of claim 14, wherein each server in the computer server rack includes components for balancing power demands from the first power supply unit and power demands from the second power supply unit.

18. The apparatus of claim 14, wherein the apparatus comprises means for monitoring an output of the BBS and means for controlling an output of a rectifier coupled to the BBS.

19. A computer-readable non-transitory storage medium containing instructions that, when executed by one or more processors, implement the following operations: detecting that a power demand of a plurality of servers in a rack exceeds a specified maximum power limit of the rack by two times a first determined amount, the rack having a first grid power source, a second grid power source, and a battery backup system (BBS), wherein comprising a first power supply unit and a second power supply unit in each of the plurality of servers, wherein each of the first power supply units is coupled to the first grid power source, and each of the second power supply units is coupled to the BBS and the second grid power source; Initially setting the output power of the BBS to the first determined amount; setting the output power from the second grid power source to half the maximum power limit minus the first determined amount; and The output power of the BBS is increased to twice the first determined amount, and the output power from the first grid power source is set to half the maximum power limit plus the first determined amount.

20. The medium of claim 19, wherein the operations further comprise: In response to the increased power demands of the plurality of servers, increasing the output power of the BBS by a second determined amount; In response to said increasing said power demand, setting a second grid power output to said half of said maximum power limit minus said first determined amount minus said second determined amount; as well as The output power of the BBS is reset to twice the first determined amount plus twice the second determined amount.

21. The medium of claim 19, wherein the operations further comprise: reducing the output power of the BBS by a third determined amount in response to the reduced power requirements of the plurality of servers; In response to determining that two times the first determined amount minus two times the third determined amount is not greater than zero, setting the first grid power output equal to a second grid power output equal to half the total rack power; In response to determining that two times the first determined amount minus two times the third determined amount is greater than zero, setting the second grid power output to the half of the maximum power limit minus the first determined amount plus the third determined amount; as well as The output power of the BBS is reset to the twice of the first determined amount minus twice of the third determined amount.

22. The medium of claim 19, wherein the operations further comprise balancing the power demand from the first power supply unit and the power demand from the second power supply unit within each server in a computer server rack.

23. The medium of claim 19, wherein the operations further comprise monitoring the output power of the BBS.

24. The medium of claim 19, wherein the operations further comprise controlling an output of a rectifier coupled to the BBS.

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