CN116762254A - Power supply management system and method for use with one or more different utility agents - Google Patents

Abstract

The present disclosure relates to a power supply management system adapted for use with at least one utility agent power source to control powering a first load and a second load when an AC mains power source cannot be used to provide power to the loads. The system receives power from the utility agent using an internal DC bus of the power converter and receives power from the short term recharging battery subsystem using a DC/DC converter/charger of the power converter. The DC/DC converter/charger is for supplying a first AC output signal to power a first load. The AC/DC rectifier of the power converter uses DC power from the utility agent supplied onto the internal bus to generate a second AC output signal that is independently applied to the second load to power the second load completely independent of the first load.

Description

Power supply management system and method for use with one or more different utility agents

Cross Reference to Related Applications

The present application is PCT international application and claims priority from U.S. non-provisional patent application No. 17/236,462 filed on 21 st 4 th 2021, which U.S. non-provisional patent application No. 17/236,462 is a continuation of the section of U.S. patent application No. 17/171,555 filed on 9 nd 2021, which U.S. patent application No. 17/171,555 in turn claims the benefit of U.S. provisional patent application No. 63/009,096 filed on 13 th 4 th 2020 and U.S. provisional patent application No. 62/972,521 filed on 10 th 2 nd 2020. The entire disclosure of each of the above applications is incorporated herein by reference.

Technical Field

The present disclosure relates to power supply management systems and methods, and more particularly, to power supply management systems and methods that utilize both utility agents and supplemental DC power to provide independent AC outputs in an efficient manner to power both IT loads and mechanical loads, respectively, when power from the utility becomes unavailable.

Background

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

In many applications, particularly applications such as data centers, hospitals, financial institutions, and the like, reliable power is required to power various computer-related equipment and other types of electronic equipment. To this end, such environments may typically implement two or more backup power sources in the event of a loss of AC primary power.

There is increasing concern over using both fuel cells and integrated battery power subsystems as utility agents in critical applications. However, fuel cells in particular have traditionally been subject to significant limitations that have limited their applicability as utility agents. One particularly significant limitation is that conventional fuel cells, such as solid oxide fuel cells, do not respond in real time fast enough to meet the load requirements when required to do so. Fuel cells are known to have a generally "spongy" response when loaded, meaning that they generally cannot respond almost immediately to an increase or decrease in load. To a lesser extent, this limitation may also be experienced when using an integrated battery power subsystem (which provides AC output) as a utility agent. Furthermore, such "spongy" responses are also typically found in generators driven by both diesel and natural gas, but to a lesser extent than fuel cells.

Another disadvantage of fuel cells is that their power output is more difficult to fine tune, which may result in periods of time where the fuel cells produce more power than is required by the critical load. In this case, the excess power must be directed to the supplemental load, which is equivalent to wasting energy.

Another limitation is that IT loads and mechanical loads (e.g., motor drives, valves, fans, etc.) consisting of IT (information technology) equipment (e.g., servers, network switches, PDUs, etc.) need to be powered simultaneously during a power outage affecting the utility. In such cases, IT is highly desirable to be able to provide separate AC outputs to the IT load and the mechanical load, for example, to ensure that the IT load is receiving highly regulated AC power. However, for today's backup power systems, this can be challenging, especially if only a single power converter is available. In general, backup power may be available from more than one external utility agent power source, but using power from multiple available backup power sources to independently power both IT loads and mechanical loads in an efficient manner remains a challenge.

Accordingly, there is a need for a system and method that better and more efficiently uses both fuel cells and integrated battery power subsystems as utility agents for powering critical loads, and that overcomes the well-known drawbacks associated with these types of utility agents as described above.

Disclosure of Invention

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

In one aspect, the present disclosure relates to a power supply management system adapted for use with at least one utility agent power source to help control powering a first independent load and a second independent load when an AC mains power source cannot be used to provide power to the loads. The system may include: a power converter forming an uninterruptible power supply, the power converter comprising an internal DC bus, an AC/DC rectifier, a DC/DC converter/charger and a DC/AC inverter. The system may also include a short term recharging battery subsystem in communication with the power converter and a utility agent. The power converter is configured such that: the DC/AC inverter receives DC current flowing on the internal DC bus from the short-term recharging battery subsystem and generates a first AC power signal that is transmitted to the first load to power the first load. The AC/DC rectifier receives the DC current from the utility agent and generates a second AC power signal from the DC current, which is transmitted to the second load to independently power the second load.

In another aspect, the present disclosure is directed to a power supply management system adapted for use with at least one utility agent power source to help control powering a first independent load and a second independent load when an AC mains power source cannot be used to provide power to the loads. The system may include a power converter that forms an uninterrupted power supply. The power converter may include a first DC bus forming an internal DC bus, an AC/DC rectifier, a DC/DC converter/charger, and a DC/AC inverter. The system may also include a second DC bus and a short-term supplemental battery subsystem in communication with the second DC bus at a first point thereof. The second DC bus is coupled to the DC/DC converter/charger of the power converter at a second point thereof to enable DC power from the short-term recharging battery subsystem to be supplied to the DC/DC converter/charger. The system may also include a third DC bus configured to be coupled to the utility agent at a first point thereof and to the internal bus of the power converter at a second point. The power converter is configured such that: the DC/AC inverter receives DC current flowing on the internal DC bus supplied from the short-term supplemental battery subsystem through the DC/DC converter/charger and generates a first AC power signal that is transmitted to the first load to power the first load. The AC/DC rectifier simultaneously receives DC current from the utility agent on the internal bus and generates a second AC power signal from the DC current, which is transmitted to the second load to independently power the second load.

In yet another aspect, the present disclosure relates to a method for independently supplying AC power to a first load and a second load when a utility supplying power to the first load and the second load becomes unavailable. The method may include supplying power from a remote short-term recharging battery subsystem to a DC/DC converter/charger of the power converter via a first external bus, wherein the DC/DC converter/charger is in communication with an internal DC bus of the power converter. The method may further include supplying DC current from the utility agent to an internal bus of the power converter via a second external bus. The method may further include generating a first AC power signal using the DC/DC converter/charger, the first AC power signal being applied to a first load to power the first load; and feeding DC current supplied by the utility agent onto the internal bus into the AC/DC rectifier in an opposite direction using the internal bus, and generating a second AC power signal using the AC/DC rectifier. The method may further include feeding a second AC power signal from the power converter to the second load to power the second load independently of the first load.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

Drawings

The drawings described herein are for illustration purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

FIG. 1 is a high-level schematic diagram of one embodiment of a system according to the present disclosure;

FIG. 2 is another embodiment of the present disclosure showing "isolation" (i.e., isolation) of an integrated battery storage subsystem from other power sources;

FIG. 3 is a table listing the operation of a power converter operating in a conventional Uninterruptible Power Supply (UPS) application without an available generator when power from a utility is lost;

FIG. 4 is a table listing the operation of a power converter with an available generator;

FIG. 5 is a table listing the operation of a power converter with an integrated battery storage subsystem available but without a generator, employing an extended run lithium ion battery pack ("extended run LIB") for assistance in the event of power loss from the utility;

fig. 6 is a flowchart showing one example of operations that may be performed by the system of fig. 1 in managing the start-up of a fuel cell incorporated into the system;

FIG. 7 is a flowchart illustrating one example of operations that may be performed by the system of FIG. 1 in handling both step load increases and step load decreases;

FIG. 8 is a high-level block diagram of various sub-modules that may be included in the intelligent power optimization software module of the system of FIG. 1;

FIG. 9 is a high-level block diagram of another embodiment of the present disclosure, wherein a hydrogen fuel cell is used and coupled in a manner that feeds a power bus or input power bus connecting the LIB subsystem and a DC/DC converter/charger of the power converter, and wherein the power converter communicates with a utility and a hydrogen fuel cell utility agent;

FIG. 10 is a flow chart illustrating the primary operation of a system for bringing a utility agent online; and

fig. 11 is another embodiment of the present disclosure showing a final state in which the fuel cell utility is started and running while directly coupled to the internal DC bus of the power converter to supply power to the mechanical load through the rectifier of the power converter, while the LIB supplies power to the IT load through the DC/DC converter/charger and the inverter.

Detailed Description

Example embodiments will now be described more fully with reference to the accompanying drawings.

Referring to fig. 1, one embodiment of a power supply/management system 10 according to the present disclosure is shown. The system 10 in this example uses four different power supplies: a fuel cell subsystem 12, an electrical utility power source 14 (i.e., AC mains), an external generator subsystem 16 (diesel-driven or natural gas-driven), and an integrated battery power subsystem 18. The power supply 12, 14, 16, or 18 may be used to power the load 20 in any hierarchical order. The power supplies 12, 16, and 18 in this example form a utility "proxy," meaning that the power supplies 12, 16, and 18 serve as alternatives to the electrical utility power source 14 when the utility power source 14 is not available. It will be appreciated that other utility agents, such as backup systems for the power supply 12, 16 or 18, may be incorporated into the system 10. Further, while the fuel cell subsystem, external generator subsystem, and integrated battery power subsystem have been shown as alternative power sources, it will be appreciated that the system 10 is not limited to use with only these types of alternative power sources. Almost any other form of alternative power source may be incorporated into the system 10 with little or no modification to the system.

The load 20 in this example is shown as four rows of equipment racks 20 a-20 d, each row receiving 125kW of power. Of course, other types of loads may be powered by the system 10, as will be discussed further in the following paragraphs. Thus, the system 10 is not limited to use with only rack-mounted electrical computing components. The supply of power to the loads 20a to 20d may be controlled by a plurality of circuit breakers 22 and 20a1/20a2, 20b1/20b2, 20c1/20c2, 20d1/20d2, the operation of which will be more fully described in the following paragraphs.

The system 10 in this example also uses two power converters 26 and 28 coupled to each of the power supplies 12-18 and to the loads 20 a-20 d. By "power converter" is meant a device capable of operating in the manner of a conventional Uninterruptible Power Supply (UPS) that supports a load by drawing power from a battery or battery pack when utility power fails, and has the additional capability of directing power from any power source to any load or to another power source connected thereto. In this example, power converters 26 and 28 are configured in a well-known "redundant 1+1" configuration to further improve reliability. A supplemental battery subsystem 30, in this example a lithium ion battery pack located remotely from the power converters 26 and 28 (hereinafter referred to as "power converter LIB" 30), is provided, which supplemental battery subsystem 30 may be coupled to either or both of the power converters 26 and 28 via selective closure of circuit breakers 32a and 32b located on a dedicated power bus 32 c. The function of the power converter LIB 30 is an important feature of the system 10 and will be described in more detail in the following paragraphs.

The coupling of the power converter 26 to the power sources 12-18 may be controlled by the selective closure of the circuit breakers 34a, 34b, and 34c, and the coupling of the power converter 26 to the load 20 may be controlled via the selective closure of the circuit breaker 34 d. The coupling of the power converter 28 to the power supply sources 12 to 18 is controlled by the selective closing of the circuit breakers 36a and 36b, and the coupling of the power converter 28 to the load 20 is controlled by the selective closing of the circuit breaker 36 d. The power converter 26 includes a bypass circuit 26a, a rectifier subsystem 26b, a DC/DC converter 26c, a DC/AC inverter 26d, and an electronic controller 26e. The power converter 28 likewise includes identical subsystems 28a through 28e. The fuel cell subsystem 12 may include a fuel cell 12a, in this example a solid oxide fuel cell ("SOFC"), that receives natural gas from a gas utility 40. The DC/DC converter 12b converts the DC output from the fuel cell 12a to a different magnitude DC output, which can then be fed to the power converter 26 by closing the circuit breaker 12c and the circuit breaker 34 c. The power converter 26 receives the DC power supplied from the fuel cell subsystem 12 at its inverter 26d and converts the DC power to AC power, which is then supplied to the load 20.AC power may also be used by the DC/DC converter 26c of the power converter 26 to assist in recharging the power converter LIB 30. These operations are controlled by the electronic controller 26e. Advantageously, if the fuel cell subsystem 12 generates more power than is required by the load 20, the excess power may be used to charge the power converter LIB 30 and/or the extended run LIB 18a of the integrated battery power subsystem 18 (described in more detail in the following paragraphs), and if the power converter LIB 30 and/or the extended run LIB 18a are sufficiently charged, the excess power may be delivered to the utility 14 or to an external generator port (not shown) of the power generator 16a to help power other loads in the field. As a final means when the fuel cell system 12 generates excess power, a supplemental load (not shown) may be added to absorb the excess power, or the output of the fuel cell subsystem 12 may be slowed down.

The utility power source 14 includes an electrical utility 42, which electrical utility 42 may be used to supply AC power to the circuit breaker 14a and the under-voltage relay 14b, and (depending on which of the circuit breakers 34a, 34b, 36a, or 36b are selectively closed) to the bypass circuit 26a or 28a of either (or both) of the power converters 26 or 28, or alternatively to the rectifier 26b or 28b (or both), 415Vac in this example. While the under-voltage relay 14b may not be required in all applications, it still helps sense the under-voltage (i.e., low voltage) condition present at the output of the utility power source 14 and immediately opens the circuit breaker 14a and signals the system 10 to switch to power from an alternative power source. In the example shown in system 10, the alternate power source is an integrated battery power subsystem 18.

The generator subsystem 16 may receive natural gas from the gas utility 40, or it may use diesel fuel as its fuel source. For convenience, the following discussion will refer to natural gas for powering the generator subsystem 16. The generator subsystem 16 includes a generator 16a that produces an AC output. The AC output in this example is 415Vac, which may be supplied to the rectifiers 26b or 28b or bypasses 26a or 28a of the power converters 26 and 28 by way of the circuit breaker 16b, or also to the load 20 via the circuit breaker 16b and the circuit breakers 36c and 22 and one or more of the circuit breakers 20a1/20a2, 20b1/20b2, 20c1/20c2 and 20d1/20d 2.

The integrated battery power subsystem 18 may include a battery pack with an extended operation LIB 18a having an associated inverter that converts the DC output of the extended operation LIB 18a to an AC output, in this example a 415Vac output. The AC output from the integrated battery power subsystem 18 may be applied to the rectifier 26b of the power converter 26 and/or the rectifier 28b of the power converter 28 through the circuit breaker 18b, or also directly to the load 20 via the selective closing of the circuit breakers 36c and 22 and one or more of the circuit breakers 20a1/20a2, 20b1/20b2, 20c1/20c2 and 20d1/20d 2.

Alternatively, the output of the fuel cell subsystem 12 or the output of the integrated battery power subsystem 18 may be used to supply power to one or more auxiliary loads 44. This would involve the selective closing of the circuit breakers 12c, 34d, 46 and 48, for example, when the fuel cell subsystem 12 is in use. In the case of an integrated battery power subsystem 18, this would involve the selective closing of circuit breakers 18b, 36c, 48 and 46. Alternatively, the fuel cell subsystem 12 or the integrated battery power subsystem 18 may also be used to supply AC power to one or more mechanical loads 50 through selective closing of a circuit breaker 52. And of course either or both of the power converters 26 and 28 may also drive the loads 44 and 50, regardless of the power source from which either or both of the power converters 26 and 28 are powered.

As understood in the industry, the utility breakers 12c, 14a, 16b and 18b operate in a "break-before-make" manner when switching between different power supplies 12, 14, 16 and 18. A particular advantage of system 10 is that power converter LIB 30 may be used as a "bridge" to provide power to power converters 26 or 28 while switching from one power source to another.

To coordinate overall operation and monitoring of system 10, an orchestration electronic controller 54 having intelligent power orchestration software modules 54a (hereinafter simply referred to as "software modules" 54 a) may be included. Orchestration electronic controller 54 (hereinafter simply referred to as "controller" 54) receives inputs from electronic controller 12d associated with fuel cell subsystem 12, from electronic controller 16c associated with natural gas driven generator subsystem 16, and from electronic controller 18c associated with integrated battery power subsystem 18. The controller 54 is also in bi-directional communication with the electronic controller 26e of the power converter 26 and the electronic controller 28e of the power converter 28. The controller 54 and its software modules 54a use information received from the electronic controllers 26e and 28e to monitor the overall operation of the power converters 26 and 28. The controller 54 also uses information received in real-time from the electronic controllers 12d, 16c, and 18c to monitor which power supply 12-18 is currently being used at any given time. Optionally, the controller 54 may also communicate with a separate remote controller (not shown) via a wired or wireless connection to receive additional information or commands to aid the operating system 10.

Software module 54a may be configured to assist system 10 in performing any desired hierarchical power usage scheme. For example, software module 54a may include one or more programs or sub-modules that control system 10 to use power from electric utility power supply 14 (if available), but to use power from integrated battery power subsystem 18 (if available), and to use power from fuel cell subsystem 12 (if available), and to use power from natural gas generator subsystem 16 if not available. Virtually any level of power usage scheme may be employed, and software module 54a may be readily modified or updated to accommodate other new power sources added later. If any of the utility agents are removed from the system 10, the software module 54a may also be updated to incorporate modifications to the existing hierarchical power usage scheme. As described in the following paragraphs, the software modules 54a may also be constructed to include programs or sub-modules that may perform functions such as demand management, energy cost optimization, and grid stabilization.

The power converter controllers 26e and 28e may also perform the following functions: the power received via any of the power supplies 12-18 is "limited," which involves monitoring the frequency, voltage, and/or current of the received signal, and taking action to notify the controller 54 if the power received from the currently selected power source changes unacceptably in any manner (e.g., unacceptable frequency changes, above a set upper voltage threshold, below a set lower voltage threshold, etc.). The controller 54 may use this information to command switching to different power sources in real time by selectively closing and opening the various circuit breakers used in the system 10.

A particularly important advantage of the system 10 is the use of the power converter LIB 30 to increase the AC power provided by any of the power supplies 12, 14, 16 or 18. In particular, the use of the fuel cell subsystem 12 (having a "spongy" response to the load, meaning that it is actually unable to respond immediately to the load's demand) benefits significantly by using the power converter LIB 30. During start-up of the fuel cell subsystem 12, the power converter LIB 30 may also be used to supply power from the power converter 26 to the DC/DC converter 12b of the fuel cell subsystem 12 via the circuit breakers 32a, 34c, and 12c to help "heat" the fuel cell subsystem. When the power converter receives output from the fuel cell subsystem 12, depending on which of the circuit breakers 32a or 32b is closed, the power converter LIB 30 may be used to increase the output of the power converter 26 or 28 to better ensure uniform output from the power converter 26 and/or 28. Closing both circuit breakers 32a and 32b enables power converter LIB 30 to provide DC power to both power converters 26 and 28 simultaneously if both power converters are operating. Depending on the particular model/fabrication of the integrated battery power subsystem 18 used, the subsystem may also experience unacceptably long response times and/or be unable to quickly respond to demands from the load, and thus also benefit from the use of the power converter LIB 30.

Referring to fig. 2, a system 100 according to another embodiment of the present disclosure is shown. Components identical to those of system 10 are labeled with the same reference numerals as their counterparts in system 10. To avoid cluttering the drawing, the controllers 54, 26e, 28e, 12d, 16c, and 18c are omitted from fig. 2, although it will be appreciated that these components may be present and perform the same operations as described with respect to the system 10 of fig. 1. To simplify the discussion of system 100, only power converter 28 is shown as part of the system, with the understanding that power converter 26 may be readily incorporated in the manner shown in fig. 1.

The system 10 of fig. 1 and the system 100 of fig. 2 are each configured to "stand alone" the integrated battery power subsystem 18. By "isolated" is meant that the integrated battery power subsystem 18 is isolated from the power supplies 12-16. This eliminates any direct circuit path for directly flowing output from the integrated battery power subsystem 18 into any of the power supplies 12-16, while still providing a configuration that is capable of recharging the integrated battery power subsystem 18 when one of the other power supplies 12, 14 or 16 becomes available for use. A configuration that "isolates" the integrated battery power subsystem 18 may be recommended by the manufacturer of the subsystem. For example, some of the integrated battery groupings available from Tesla (Tesla) corporation that may be used with the system 10 or 100 as the integrated battery power subsystem 18 are recommended to be isolated from all other available power sources.

The system 100 of fig. 2 is less complex than the system 10 of fig. 1 and will therefore be referred to throughout the following paragraphs to provide a more convenient illustration of the isolation. Isolation of the integrated battery power subsystem 18 (i.e., isolation from the electric utility power supply 14 and the generator subsystem 16 via the circuit breakers 14a and 16 b) still allows the output side of the circuit breaker 18b to communicate directly with the load 20 and with the power converter 26. This is accomplished by connecting the output side of the circuit breaker 18b to both the power bus portion 22a of the system through the circuit breaker 36f and to the bypass circuit 28a and the input side of the rectifier circuit 28b of the power converter 28 (through circuit breakers 36c and 36b, respectively).

In operation, when the circuit breakers 18b and 36c are closed and the circuit breakers 14a, 16b, 36b and 36f are open, the output of the integrated battery power subsystem 18 may be applied to the bypass circuit 28a of the power converter 28. When the circuit breaker 20a1/20b1/20c1/20d1 on the input side of the load 20 is closed, then AC power from the integrated battery power subsystem 18 will be applied directly to the power bus section 22a and used to power the load 20. In such a configuration, it is not possible for the integrated battery power subsystem 18 to apply any portion of its output to any of the power supplies 12, 14, or 16. If it is desired to increase the output of the battery power subsystem 18, the power converter LIB 30 may assist by applying their output to the DC/DC converter 28c, the output of the power converter LIB 30 being converted to an AC output by the inverter 28d before being placed (via the circuit breaker 36 d) on the power bus portion 22 a.

In the event of a failure of the power converter 28, the integrated battery power subsystem 18 may still be used to directly power the load 20 by closing the circuit breakers 18b and 36f and opening the circuit breakers 14a, 16b, 36b and 36 c. In this configuration, the maintenance line 36e is used to help create a direct path from the integrated battery power subsystem 18 to the power bus section 22a and thus to the load 20.

When it is desired to recharge the integrated battery power subsystem 18, the circuit breaker 18b is closed, the circuit breaker 36f is open, and either of the circuit breakers 14a or 16b is closed. This enables power to be provided by either of the power sources 14 or 16 to the battery integrated power subsystem 18 for recharging, and simultaneously to the rectifier circuit 28b or bypass circuit 28a of the power converter 28, depending on which of the circuit breakers 36b and 36c is closed. Thus, recharging may be accomplished simultaneously when the power source 14 or 16 supplies power to the power converter 28.

Fig. 3-5 provide examples of operations that may be performed by the system 10 when the power converter 26 or 28 is used with different power sources or power combinations, i.e., the utility power supply 14 and/or the utility agent power supplies 12, 16, and 18. FIG. 3 shows a table 200, the table 200 showing various operations that may be performed by the system 10 when there is only power from the utility (i.e., power from the utility power source 14) and at least one of the power converters 26 or 28 is present. In these operations, the power converter 26 or 28 functions as a conventional UPS when utility power is lost. FIG. 4 illustrates a table 300, the table 300 illustrating operations that may be performed by the system 10 when the utility power supply 14 is present with the generator subsystem 16. FIG. 5 illustrates a table 400, the table 400 illustrating operations that may be performed by the system 10 when both the utility power supply 14 and the integrated battery power subsystem 18 are available, but the generator subsystem 16 is not. The "walk-in" procedure for switching to power supply mentioned in the three scenarios of fig. 3-5 is a procedure known in the art by which power from a walk-in source is gradually applied to a load as power supplied to the load from an alternative power supply is gradually removed. The "soft-loading" process also referred to in fig. 3-5 is also a process known in the art by which power is gradually drawn from a source to support a load (or load increase) while additional power required to support the load is supplied by an alternative power source.

Referring now to fig. 6, a flowchart 500 is shown to illustrate various operations that may be performed by the system 10 when starting up the fuel cells 12a of the fuel cell subsystem 12. Initially, at operations 502, 504, 506, and 508, a check is made, in this example in a sequential manner, to determine whether utility power is available to power the fuel cell heater (operation 502), whether a generator is available to power the fuel cell heater (operation 504), whether an extended run LIB is available to power the fuel cell heater (operation 506), or whether a power converter LIB is available to power the fuel cell heater (operation 508). The "priority" order of these four checks may be modified according to design preferences, and thus this particular check order is meant only to be one example of a suitable "priority" for using the various supplemental power sources that may be available. Furthermore, fuel cells typically include multiple stacks with independent heaters that are in-line one at a time, and this assumption will be made for this example.

Depending on which of the checks at operations 502-508 yields a first "yes" answer, that particular power source will be used to start (or continue) heating the fuel cells 12a one stack at a time, as indicated at operation 510. If utility power or generator power is present (i.e., operation 502 or operation 504 produces a "yes" answer), then the power converter 26 or 28 applies a DC voltage from its DC bus to the fuel cell heater. If utility power and generator power are not available, the power converter 26 or 28 applies a DC voltage to the fuel cell heater from the extended run LIB 18a (at operation 506) or from the power converter LIB 30 (at operation 508) via its DC bus, but at a reduced power level. A check is made at operation 512 to determine if the particular stack currently being heated is fully heated, and if the check yields a no answer, operations 510 and 512 are repeated. If the check at operation 512 returns a "yes" answer indicating that the heated stack is fully heated, the fuel cell stack is brought online and used to begin delivering power, as indicated at operation 514. A check is then made at operation 516 as to whether all stacks of fuel cells 12a have been fully heated. If the check yields a "yes" answer, the fuel cell start-up operation is successfully ended. If operation 516 produces a "no" answer, then at operation 518 the stack that has just been fully heated is used to begin heating the next stack and support the load along with any previously fully heated stacks. Operations 510 through 518 may be repeated until the check at operation 516 indicates that all stacks are fully heated and delivering power.

If the check at operation 508 (the last of the four options for powering the fuel cell stack heater) produces a "no" answer, the fuel cell start-up process is suspended.

Fig. 7 illustrates a flow chart 600, the flow chart 600 illustrating one example of operations that may be performed by the system 10 to monitor, detect, and respond to changes in a load when using the fuel cell subsystem 12 to power the load. For this example, it will be assumed that the fuel cell subsystem 12 fully supports the critical load and that the preferred mode of fuel cell operation is to remain at a constant load. Further, it will be assumed that the extended run LIB 18a has remained in a partially recharged state, which may be a charge level less than its maximum capacity, which may be preselected by the system designer. A check is made at operation 602 as to whether a step change in load has occurred. If the check yields a "NO" answer, then the system 10 repeats operation 602, continuously monitoring and detecting load changes; this may be done at the sub-loop level, for example at about 3 kHz. If the check at operation 602 yields a "yes" answer, operation 604 determines whether the load change is a step increase.

If the check at operation 604 yields a "yes" answer, indicating that a step increase in load has been experienced, then at operation 606, the power converter LIB 30 may be used to initiate/continue soft loading of the fuel cell subsystem 12. "soft-loading" in this example means that the additional energy required to support the load increase is supplied by the power converter LIB 30 while gradually drawing energy from the fuel cell subsystem 12. A check is then made at operation 608 to determine if the fuel cell subsystem 12 is fully loaded. If not, soft loading of the fuel cell subsystem 12 continues at operation 606. If the check yields a "yes" answer, operation 602 may be repeated while system 10 continues to monitor for load changes.

If the check at operation 604 yields a "no" answer, indicating that a step down in load is detected (operation 610), then the fuel cell subsystem 12 is currently producing more power than is needed to support the reduced load (operation 612). If desired, a series of operations may be performed to recharge power converter LIB 30 and extended run LIB 18a using excess power from fuel cell subsystem 12. At operation 614, a check is made to determine if the charge level of power converter LIB 30 is at its minimum run time level. By "minimum run time level" is meant the level of charge required to maintain the battery in an operational state for a user-specified time. In one example, the minimum run-time level may be 80% of the maximum battery level, although the system designer may change this level to be higher or lower. If the check at operation 614 yields a "yes" answer, no recharging of the power converter LIB 30 is required, and a check may be made at operation 616 to determine if the extended run LIB 18a is at its maximum charge level. The maximum charge level of the extended operating LIB 18a may reflect a system performance factor such as fuel cell response speed, or may be preset to 100% capacity, 80% capacity, or any other level selected by the system designer. If the check at operation 616 also produces a "yes" answer, then there is no need to recharge the extended run LIB 18a, and at operation 624 the system 10 determines whether the fuel cell subsystem 12 is still producing excess power. If so, at operation 626, supplemental load may be added to keep the system 10 balanced, and if the critical load has not recovered, the system 10 may need to command the fuel cell subsystem 12 to reduce its capacity. After operation 626, or if the fuel cell subsystem 12 is no longer producing excess power at operation 624, the system 10 continues to monitor for load changes at operation 602.

If the check at operation 616 indicates that the extended run LIB 18a is not at its maximum charge level, the system 10 may command the extended run LIB 18a to enter (or maintain) a recharging mode of operation, as indicated at operation 618. The power converter 26 then sends excess power available from the fuel cell subsystem 12 back to the rectifier input (i.e., the input side of the rectifier subsystem 26 b) to begin/continue charging the extended operation LIB 18a at operation 620. Operations 616 through 620 are repeated until extended run LIB 18a is detected to be charged to its maximum charge level at operation 616, at which point a check at operation 624 may be performed.

If the check at operation 614 yields a "no" answer, indicating that power converters LIB 30 are not charged to their minimum run-time charge level (80% of maximum battery charge in this example), then at operation 622 power converter 26 begins to charge power converter LIB using excess power from fuel cell subsystem 12. Operations 614 and 622 are then repeated until the check at operation 614 yields a "yes" answer, indicating that power converters LIB 30 are charged to their maximum predetermined charge level.

It will be appreciated, then, that setting and maintaining the charge level of power converter LIB 30 and extended run LIB 18a at a value less than 100% of capacity causes excess power from fuel cell subsystem 12 that suddenly becomes available due to a step down in load to be "absorbed" or utilized by power converter LIB 30 and extended run LIB 18a for recharging purposes. Without this feature, it would be desirable to immediately introduce a supplemental load that would serve to immediately assist in absorbing excess power available from the fuel cell subsystem 12, but not provide any other useful purpose. Thus, setting and maintaining the charge level of power converter LIB 30 and extended run LIB 18a at a level of less than 100% serves two useful purposes: helping to provide a means by which excess power can be absorbed, and to use the excess power to recharge power converter LIB 30 and extended run LIB 18 a.

The intelligent power orchestration software module 54a is shown in more detail in fig. 8. The software module 54a helps implement an intelligent control/utilization scheme by which the ultimate goal of the power converters (e.g., power converters 26 and 28) is to deliver ITIC-compatible power to critical loads at all times. To this end, the software module 54a may control a plurality of programs or sub-modules. For example, the demand management sub-module 54a1 may be involved in enforcing preset limits on utility power draw, such as enforcing limits in response to utility requirements, guidelines, or discount plans. The "orchestration layer" 54b, acting as a control layer, uses external signals or internal predetermined settings to limit the amount of power drawn from the utility. The power converters 26 and 28 share sources between the utility and other available energy sources in the manner described above. For example, if fuel cell subsystem 12a is available, system 10 may draw energy therefrom, and in an emergency, system 10 may draw energy from power converter LIB 30 and/or extended operations LIB 18 a.

The software module 54a may also include an energy cost optimization sub-module 54a2 to help determine which of the two or more available energy sources is the lowest cost energy source at any given time of day. Energy cost optimization submodule 54a2 may be used to help select the lowest cost energy source based in part on information provided by orchestration layer 54b, such as information from external signals or data or possibly from saved settings or data that enable it to determine the real-time energy cost of each available energy source. While the software module 54a may be configured to account for other unusual situations or conditions (if for some reason the lowest cost energy source should not be used), it is contemplated that in most cases the lowest cost energy source will be expected to power the critical load.

With grid-tie enabled by the system 10, the system 10 may output energy if the cost of the generated energy is less than the recovered grid-tie revenue. The system 10 preferably always keeps the power converters LIB 30 charged to their minimum run-time limit. System 10 may delay recharging extended operation LIB 30 as long as its partial recharging state can be maintained. If the extended run LIB 30 is not at its maximum charge level, it may be recharged until it is at its maximum charge level (as noted above, the maximum charge level may not be 100% of the maximum charge value, but a lower value such as 80%).

The software module 54a may also include a grid stabilization submodule 54a3. Grid stabilization submodule 54a3 works with orchestration layer 54b, and optionally with energy cost optimization submodule 54a2, and further optionally with external signals that provide either or both of power draw information and cost information to determine how much grid stabilization energy is needed. Power converters 26 and/or 28 may use energy cost optimization operations to deliver available power to their/their respective limits to provide the desired grid stabilization energy.

The software modules 54a may also include a hierarchical power usage sub-module 54a 4. As previously described, if utility power supply becomes unavailable, the hierarchical power usage sub-module 54a4 may determine the order in which utility agents are used.

Referring to fig. 9, another embodiment 700 of the present disclosure is shown in which a utility agent, in this example a hydrogen fuel cell utility agent 702 (hereinafter simply referred to as "utility agent" 702), is directly coupled to a DC power bus 704 that connects the LIB subsystem 30 and the power converter 26 a. Although only a single power converter 26 is shown herein, in practice two or more power converters may be equally easily coupled to utility agent 702 and LIB subsystem 30, for example, in the manner shown in fig. 1, and thus system 700 should not be construed as limited to use with only a single power converter.

The system 700 also has a LIB subsystem 30 configured with an electronic controller 30a and a communication subsystem 30b (e.g., wired or wireless), the communication subsystem 30b being used to facilitate communication with various other components of the system and with the utility and utility agents 702. LIB subsystem 30 may also include non-volatile memory 30c for storing control algorithm 30d to facilitate execution of different operational aspects with which system 700 may be used.

Fig. 9 also shows the power converter 26 coupled to control buses 706 and 708, the control buses 706 and 708 being used to communicate (e.g., control signals) to/from the utility agent 702 and the LIB subsystem 30, respectively. In this embodiment, both power converter 26 and LIB subsystem 30 are also capable of two-way communication with orchestration electronic controller 54, and orchestration electronic controller 54 is in two-way communication with utility agent 702 and the utility. LIB subsystem 30 may optionally include the capability to communicate bi-directionally directly with utility and/or utility agent 702.

The main advantage of system 700 is that the utility agent 702 is directly coupled to the DC power bus 704 that connects the power converter 26 and the LIB subsystem 30. This enables the utility agent 702 to provide power directly to the DC/DC converter/charger 26c of the power converter 26. It also enables utility agent 702 to provide power directly to LIB 30 to recharge LIB 30 if excess power is available from the utility agent.

Another benefit of system 700 is the ability of power converter 26 to bi-directionally communicate (e.g., control signals) with utility and utility agent 702 through orchestration controller 54 a. This communication capability enables the power converter 26 to poll the utility and/or utility agent 702 for information, such as, when a power outage occurs, whether information regarding the expected length of the outage condition is available from the utility or utility agent. This important feature will be discussed further in the following paragraphs.

Referring to fig. 10, a flow chart 800 illustrates, at a high level, various operations that may be performed by any of the systems 10, 100, or 700 in response to a power outage condition. At operation 802, it is initially checked whether a power outage condition has been detected. If the check yields a "no" answer, the check at operation 802 is repeated after a predetermined period of time. If the check yields a "yes" answer, at operation 804 the long term LIB (e.g., utility agent LIB 18 in FIG. 1) or LIB subsystem 30 (acting as a "short term" LIB) may begin powering IT loads and thermal loads (e.g., loads 20 and 50, respectively, in FIG. 1). At operation 806, the power converter (e.g., power converter 26) may poll the utility to determine if information about the expected length of the outage is available. At operation 807, the power converter waits a predetermined period of time for a response from the utility. After expiration of the predetermined period of time, a check is made at operation 808 to determine if the requested outage information is received from the utility. If the check yields a "no" answer, the power converter polls the utility to determine if power is still interrupted and waits a predetermined time for a response at operation 809. At operation 810, it is checked whether the received information indicates that power is still interrupted. If the check yields a "yes" answer, operations 804 through 808 are repeated. If the check at operation 810 indicates that the utility power has recovered, the system 700 switches back to utility power to power the IT load and the mechanical load at operation 822.

If the check at operation 808 indicates that the power converter received the requested outage information from the utility (i.e., a "yes" answer), then a check is made as to whether the utility agent (e.g., fuel cell) is to be brought online, as indicated at operation 812. If the check yields a "NO" answer, operations 804 through 808 are repeated. If the check at operation 812 yields a "yes" answer, then a check is made at operation 814 to determine if the LIB supporting the load is sufficiently discharged to be able to absorb excess energy from the utility agent (e.g., fuel cell) when the utility agent is at full capacity. If the check yields a "no" answer, the system waits for a predetermined period of time, as indicated at operation 816, to discharge the LIB at least a small amount, before again performing operation 812. However, if the check at operation 814 yields a "yes" answer, the system begins (or continues) to supply power to the load using the utility agent (e.g., fuel cell).

At operation 820, the system again checks whether the utility is online again. If the check yields a "NO" answer, operation 818 continues. If the check at operation 820 yields a "yes" answer, the system switches back to the utility for power at operation 822 and the control routine ends.

Referring now to fig. 11, a system 900 in accordance with another embodiment of the present disclosure is shown. The system 900 in this embodiment differs from the systems 10 and 700 in that: the utility agent 902, in this example a hydrogen fuel cell (hereinafter simply "hydrogen fuel cell" 902), is directly coupled to the internal DC bus 906e of the power converter 906 via the DC bus 904. The power converter 906 includes standard components of an AC/DC rectifier 906a, a DC/AC inverter 906b, a bypass circuit 906c, and a DC/DC converter/charger 906d. In this embodiment, the output bus 906f is coupled to an IT load 910a. The input bus 908 of the system 900 is coupled to a mechanical load 910b. Short-term LIB subsystem 912 is coupled directly to DC/DC converter/charger 906d via DC bus 912a in a manner similar to system 10.

Fig. 11 also shows a management subsystem 914, which may be the orchestration electronic controller 54 shown in fig. 1, which in this embodiment has two components, an energy management application software layer 914a and a UPS communication layer 914b, for communicating information to other components of the system 900. In particular, components 914a and 914b may be used to perform bi-directional communications with power converter 906, hydrogen fuel cell 902, and short-term LIB subsystem 912 via communication buses 916 and 918. A separate communication bus 920 may be used to facilitate bi-directional communication between the hydrogen fuel cell 902, the short-term LIB subsystem 912, and the power converter 906. It should be appreciated that the power converter 906 (i.e., also sometimes referred to as a "UPS") may include its own electronic controller and communication components similar to those shown in fig. 9, but omitted from fig. 11 to avoid unnecessarily cluttering the drawing.

The power converter 906, and/or the hydrogen fuel cell 902 and/or the short-term LIB subsystem 912 may use information and/or commands from the utility to optimize the overall operation of the system 900. The energy management layer 914a provides on/off and start-up control, energy cost optimization, demand management participation, and grid service operation.

The main advantages of the system 900 are: using completely separate and independent input power sources, a single power converter may be used to help supply power to both the IT load 910a and the mechanical load 910b at the same time. This is achieved by configuring the power converter 906 in the following manner: this approach allows ITs main subsystems to be used independently of each other to help provide power to both the IT load 910a and the mechanical load 910 b. This is achieved by: DC power is provided to the DC/DC converter/charger 906d and the internal bus 906e using the short-term LIB subsystem 912, and then regulated AC power is provided to the IT load 910a via bus 906f using the DC/AC inverter 906 b. AC power delivered to the IT load 910a is represented by arrow 922. At the same time, the direct connection of the DC bus 904 to the internal DC bus 906e of the power converter 906 enables additional DC power from the hydrogen fuel cell 902 to also be supplied directly onto the internal DC bus 906e, which is then passed through the AC/DC rectifier 906a in the opposite direction (i.e., opposite to the conventional power flow from the utility into the power converter) to produce a fully separated and independent AC power output signal. The AC power output signal is represented by arrow 924. Thus, the DC power from the hydrogen fuel cell 902 is converted using the AC/DC rectifier 906a to produce an AC power output signal 924 in the opposite direction, and then the AC power output signal 924 is passed onto the main input bus 908 where the AC power output signal 924 is fed to the mechanical load 910b, completely independent of the AC power supplied to the IT load 910 a.

System 900 effectively enables the power converter to perform a "dual duty" when coupled to short-term LIB subsystem 912 and hydrogen fuel cell 902 as shown in fig. 11; that is, ITs DC/AC inverter 906b is used to supply a first output to the IT load 910a while ITs AC/DC rectifier 906a is used independently and simultaneously to provide separate AC power to also power the mechanical load 910 b.

Various embodiments of the present disclosure provide the ability to use two or more different utility agents as power sources according to a predetermined usage hierarchy. In particular, various embodiments of the present disclosure overcome the disadvantages associated with using a fuel cell and a battery power subsystem as primary power sources. Such power supplies are generally not sufficiently responsive to real-time changes in the load being powered, and various embodiments of the present disclosure eliminate these drawbacks without significantly complicating or increasing the cost of the overall system design.

The foregoing description of the embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. The individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable where applicable and can be used in a selected embodiment, even if not specifically shown or described. The individual elements or features of a particular embodiment may also vary in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that the example embodiments may be embodied in many different forms without the use of specific details, and should not be construed as limiting the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known techniques have not been described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein should not be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically indicated. It should also be understood that additional or alternative steps may be employed.

When an element or layer is referred to as being "on," "engaged to," "connected to" or "coupled to" another element or layer, it can be directly on, engaged to, connected to or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in the same manner (e.g., "between … …" and "directly between … …", "adjacent" and "directly adjacent", etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. The terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as "inner," "outer," "lower," "below," "lower," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below" may include both an orientation above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Claims (21)

1. A power supply management system adapted for use with at least one utility agent power source to assist in controlling powering a first independent load and a second independent load when an AC mains power source is unavailable to provide power to the loads, the system comprising:

a power converter forming an uninterruptible power supply, the power converter comprising an internal DC bus, an AC/DC rectifier, a DC/DC converter/charger, and a DC/AC inverter;

A short term supplemental battery subsystem in communication with the power converter;

a utility agent;

wherein the power converter is configured such that:

the DC/AC inverter receives DC current flowing on the internal DC bus from the short-term supplemental battery subsystem and generates a first AC power signal that is transmitted to the first load to power the first load; and is also provided with

The AC/DC rectifier receives DC current from the utility agent and generates a second AC power signal from the DC current, the second AC power signal being transmitted to the second load to independently power the second load.

2. The system of claim 1, wherein the utility agent is coupled to an internal bus of the power converter to supply DC current from the utility agent to the AC/DC rectifier in an opposite direction.

3. The system of claim 1, further comprising:

a DC bus coupled to a DC/DC converter/charger of the power converter at a point; and is also provided with

Wherein the short-term recharging battery subsystem is coupled to the DC bus to directly deliver DC current to the DC/DC converter/charger.

4. The system of claim 1, wherein the first load forms a load comprising an Information Technology (IT) component.

5. The system of claim 1, wherein the second load forms a load comprising a mechanical component.

6. The system of claim 1, wherein the first AC power signal and the second AC power signal are generated simultaneously by the power converter.

7. The system of claim 1, wherein the short term recharging battery subsystem comprises a Lithium Ion Battery (LIB) subsystem.

8. The system of claim 1, wherein the utility agent comprises a fuel cell.

9. The system of claim 8, wherein the fuel cell comprises at least one of:

a hydrogen fuel cell; or alternatively

Solid Oxide Fuel Cells (SOFCs).

10. The system of claim 1, wherein the power converter comprises an electronic controller.

11. The system of claim 1, wherein the power converter is configured to receive control signals from and bi-directionally communicate with the utility agent.

12. The system of claim 1, wherein the power converter is configured to transmit a control signal to the short-term recharging battery subsystem.

13. The system of claim 1, wherein the power converter is configured to check if the short-term supplemental battery subsystem is sufficiently charged prior to bringing the utility agent online when a power outage condition is detected.

14. A power supply management system adapted for use with at least one utility agent power source to assist in controlling powering a first independent load and a second independent load when an AC mains power source is unavailable to provide power to the loads, the system comprising:

a power converter forming an uninterruptible power supply, the power converter comprising a first DC bus forming an internal DC bus, an AC/DC rectifier, a DC/DC converter/charger, and a DC/AC inverter;

a second DC bus;

a short-term replenishment battery subsystem in communication with the second DC bus at a first point of the second DC bus, the second DC bus being coupled to the DC/DC converter/charger of the power converter at a second point of the second DC bus to enable DC power from the short-term replenishment battery subsystem to be supplied to the DC/DC converter/charger;

a third DC bus configured to be coupled to a utility agent at a first point of the third DC bus and to an internal bus of the power converter at a second point;

Wherein the power converter is configured such that:

the DC/AC inverter receives DC current supplied from the short-term recharging battery subsystem through the DC/DC converter/charger flowing on the internal DC bus and generates a first AC power signal that is transmitted to the first load to power the first load; and is also provided with

The AC/DC rectifier simultaneously receives DC current from the utility agent on the internal bus and generates a second AC power signal from the DC current, the second AC power signal being transmitted to the second load to independently power the second load.

15. The system of claim 14, wherein the third DC bus is directly coupled to an internal bus of the power converter.

16. The system of claim 14, further comprising the utility agent.

17. The system of claim 16, wherein the utility agent comprises at least one of:

a hydrogen fuel cell;

a solid oxide fuel cell; or alternatively

Long-term lithium ion battery.

18. A method for independently supplying AC power to a first load and a second load when a utility supplying power to the first load and the second load becomes unavailable, the method comprising:

Supplying power from a remote short-term recharging battery subsystem to a DC/DC converter/charger of a power converter via a first external bus, the DC/DC converter/charger in communication with an internal DC bus of the power converter;

supplying DC current from a utility agent to an internal bus of the power converter via a second external bus;

generating a first AC power signal using the DC/DC converter/charger, the first AC power signal being applied to a first load to power the first load; and

feeding DC current supplied by the utility agent onto the internal bus into the AC/DC rectifier in an opposite direction using the internal bus, and generating a second AC power signal using the AC/DC rectifier; and

the second AC power signal is fed from the power converter to a second load to power the second load independently of the first load.

19. The method of claim 18, further comprising querying the utility using the power converter when a power outage condition occurs that interrupts power to at least one of the first load or the second load, whether information regarding an expected length of the power outage condition is available.

20. The method of claim 18, further comprising causing the power converter to use the information received from the utility regarding the expected length of the outage condition to determine whether to bring the utility agent online and begin powering at least one of the first load or the second load.

21. The method of claim 20, further comprising using the power converter to determine whether the supplemental battery subsystem is currently in a state of charge as follows: the state of charge is sufficient to enable the supplemental battery subsystem to absorb excess energy from the utility agent when the utility agent is operating at full capacity.