Patent Publication Number: US-2022224143-A1

Title: Intelligent load control to support peak load demands in electrical circuits

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to Indian Application Serial No. 2021/11001823 titled “INTELLIGENT LOAD CONTROL TO SUPPORT PEAK LOAD DEMANDS IN ELECTRICAL CIRCUITS,” filed on Jan. 14, 2021, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field of the Disclosure 
     At least one example in accordance with the present disclosure relates generally to uninterruptible power supplies. 
     2. Discussion of Related Art 
     Power devices, such as uninterruptible power supplies (UPSs), may be used to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems and other data processing systems. Existing UPSs include online UPSs, offline UPSs, line-interactive UPSs, as well as others. Online UPSs provide conditioned AC power as well as back-up AC power upon interruption of a primary source of AC power. Offline UPSs typically do not provide conditioning of input AC power but do provide back-up AC power upon interruption of the primary AC power source. 
     SUMMARY 
     According to at least one aspect of the present disclosure, an uninterruptible power supply (UPS) is provided comprising an input configured to be coupled to, and receive input power from, a circuit breaker, an output configured to be coupled to, and provide output power to, at least one load, an energy-storage-device interface configured to be coupled to, and receive back-up power from, an energy-storage device, and at least one controller configured to determine whether a current through the circuit breaker meets at least one over-current criterion, and control, responsive to determining that the current through the circuit breaker meets the at least one over-current criterion, the uninterruptible power supply to provide the output power to the load, the output power being derived from the input power and the back-up power. 
     In some examples, the at least one over-current criterion includes a current threshold, and determining whether the current through the circuit breaker meets the at least one over-current criterion includes determining whether the current through the circuit breaker meets the current threshold. In at least one example, the current threshold is a current rating of the circuit breaker. In various examples, the UPS includes at least one power converter coupled to the energy-storage-device interface, and the at least one controller is further configured to determine, responsive to determining that the current through the circuit breaker meets or exceeds the current threshold, a current difference between an output current to be provided to the at least one load and an input current drawn from the circuit breaker, and control the at least one power converter to draw back-up current from the energy-storage-device interface based on the current difference. 
     In some examples, the UPS includes at least one power converter coupled to the circuit breaker and configured to draw an input current from the circuit breaker, and the at least one controller is further configured to control the at least one power converter to limit the input current such that the current through the circuit breaker does not exceed the current threshold. In at least one example, the at least one controller is communicatively coupled to at least one current sensor coupled in series with the circuit breaker, and the at least one controller is configured to receive current information indicative of the current through the circuit breaker from the at least one current sensor. In various examples, the UPS is coupled in parallel with one or more loads each coupled to a respective disconnection switch of one or more disconnection switches, and the at least one controller is communicatively coupled to each disconnection switch of the one or more disconnection switches. 
     In some examples, the one or more loads includes a first external load coupled to a first disconnection switch, and the at least one controller is configured to control, responsive to determining that the current through the circuit breaker meets the over-current criterion, the first disconnection switch to cause the first external load to draw less current from the circuit breaker. In at least one example, the one or more loads are ranked from a lowest-priority load to a highest-priority load, and the at least one controller is configured to control, responsive to determining that the current through the circuit breaker meets the over-current criterion, a respective disconnection switch coupled to the lowest-priority load to cause the lowest-priority load to draw less current from the circuit breaker. 
     In various examples, the at least one controller is configured to control, responsive to determining that the current through the circuit breaker meets the over-current criterion subsequent to controlling the respective disconnection switch coupled to the lowest-priority load to cause the lowest-priority load to draw less current from the circuit breaker, a respective disconnection switch coupled to a second-lowest-priority load to cause the second-lowest-priority load to draw less current from the circuit breaker. In some examples, the UPS includes at least one power converter coupled to the energy-storage-device interface, and the at least one controller is further configured to control, responsive to determining that the current through the circuit breaker does not meet the over-current criterion, the at least one power converter to provide a charging current derived from the input power to the energy-storage device. 
     In at least one example, the UPS includes at least one power converter coupled to the energy-storage-device interface, and the at least one controller is further configured to control, responsive to determining that the input power is not available from the circuit breaker, the at least one power converter to provide the output power from the energy-storage device to the output. In various examples, the at least one controller is further configured to determine that the current through the circuit breaker does not meet the at least one over-current criterion, control the UPS to be in a standby mode of operation responsive to determining that the current through the circuit breaker does not meet the at least one over-current criterion, and monitor the input power during the standby mode of operation. 
     In some examples, the at least one controller is further configured to determine, during the standby mode of operation, that the input power is not acceptable, control the UPS to be in a back-up mode of operation responsive to determining that the input power is not acceptable, and control the uninterruptible power supply to provide the output power to the load in the back-up mode of operation, the output power being derived from the back-up power. In at least one example, controlling the uninterruptible power supply to provide output power derived from the back-up power to the load prevents a voltage drop of the output power. In various examples, the UPS includes a housing configured to house the input, the output, the energy-storage-device interface, and the at least one controller, and wherein the circuit breaker is external to the housing. 
     In some examples, the circuit breaker is a main circuit breaker configured to provide a first portion of the current through the circuit breaker to the input and a second portion of the current through the circuit breaker to at least one branch circuit breaker, and the at least one controller is further configured to determine whether a current through the branch circuit breaker meets at least one second over-current criterion, and control, responsive to determining that the current through the branch circuit breaker meets the at least one second over-current criterion, the uninterruptible power supply to provide the output power to the load, the output power being derived from the input power and the back-up power. In at least one example, the at least one second over-current criterion includes a current threshold, and determining whether the current through the branch circuit breaker meets the at least one second over-current criterion includes determining whether the current through the branch circuit breaker meets the current threshold. In various examples, the current threshold is a current rating of the branch circuit breaker. 
     According to an example of the disclosure, a non-transitory computer-readable medium storing thereon sequences of computer-executable instructions for controlling an uninterruptible power supply (UPS) having an input coupled to and configured to receive input power from a circuit breaker, an output coupled to and configured to provide output power to a load, and an energy-storage-device interface coupled to and configured to receive back-up power from an energy-storage device is provided, the sequences of computer-executable instructions including instructions that instruct at least one processor to determine whether a current through the circuit breaker meets at least one over-current criterion, and control, responsive to determining that the current through the circuit breaker meets the at least one over-current criterion, the uninterruptible power supply to provide the output power to the load, the output power being derived from the input power and the back-up power. 
     In some examples, the at least one over-current criterion includes a current threshold, and determining whether the current through the circuit breaker meets the at least one over-current criterion includes determining whether the current through the circuit breaker meets the current threshold. In at least one example, the UPS further includes at least one power converter coupled to the energy-storage-device interface, and the instructions further instruct the at least one processor to determine, responsive to determining that the current through the circuit breaker meets or exceeds the current threshold, a current difference between an output current to be provided to the at least one load and an input current drawn from the circuit breaker, and control the at least one power converter to draw back-up current from the energy-storage-device interface based on the current difference. 
     In various examples, the UPS further includes at least one power converter coupled to the circuit breaker and configured to draw an input current from the circuit breaker, and the instructions further instruct the at least one processor to control the at least one power converter to limit the input current such that the current through the circuit breaker does not exceed the current threshold. In some examples, the current threshold is a current rating of the circuit breaker. In at least one example, the UPS is coupled in parallel with one or more loads including a first external load coupled to a first disconnection switch, and the instructions further instruct the at least one processor to control, responsive to determining that the current through the circuit breaker meets the over-current criterion, the first disconnection switch to cause the first external load to draw less current from the circuit breaker. 
     In various examples, the one or more loads are ranked from a lowest-priority load to a highest-priority load, and the instructions further instruct the at least one processor to control, responsive to determining that the current through the circuit breaker meets the over-current criterion, a respective disconnection switch coupled to the lowest-priority load to cause the lowest-priority load to draw less current from the circuit breaker. In some examples, the instructions further instruct the at least one processor to determine that the current through the circuit breaker does not meet the at least one over-current criterion, control the UPS to be in a standby mode of operation responsive to determining that the current through the circuit breaker does not meet the at least one over-current criterion, and monitor the input power during the standby mode of operation. 
     In at least one example, the instructions further instruct the at least one processor to determine, during the standby mode of operation, that the input power is not acceptable, control the UPS to be in a back-up mode of operation responsive to determining that the input power is not acceptable, and control the uninterruptible power supply to provide the output power to the load in the back-up mode of operation, the output power being derived from the back-up power. In various examples, controlling the uninterruptible power supply to provide output power derived from the back-up power to the load prevents a voltage drop of the output power. 
     In some examples, the circuit breaker is a main circuit breaker configured to provide a first portion of the current through the circuit breaker to the input and a second portion of the current through the circuit breaker to at least one branch circuit breaker, and the instructions further instruct the at least one processor to determine whether a current through the branch circuit breaker meets at least one second over-current criterion, and control, responsive to determining that the current through the branch circuit breaker meets the at least one second over-current criterion, the uninterruptible power supply to provide the output power to the load, the output power being derived from the input power and the back-up power. In at least one example, the at least one second over-current criterion includes a current threshold, and determining whether the current through the branch circuit breaker meets the at least one second over-current criterion includes determining whether the current through the branch circuit breaker meets the current threshold. In various examples, the current threshold is a current rating of the branch circuit breaker. 
     According to at least one aspect of the disclosure, an uninterruptible power supply is provided comprising an input configured to be coupled to, and receive input power from, a circuit breaker, an output configured to be coupled to, and provide output power to, at least one load, an energy-storage-device interface configured to be coupled to, and receive back-up power from, an energy-storage device, and means for maintaining a current through the circuit breaker below a current threshold of the circuit breaker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide an illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of any particular embodiment. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and embodiments. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures: 
         FIG. 1  illustrates a block diagram of a power system; 
         FIG. 2  illustrates a block diagram of a power system according to an example; 
         FIG. 3  illustrates a block diagram of a portion of the power system of  FIG. 2  according to an example; 
         FIG. 4  illustrates a process of controlling an uninterruptible power supply according to an example; 
         FIG. 5  illustrates a block diagram of a power system according to another example; and 
         FIG. 6  illustrates a block diagram of a power system according to another example. 
     
    
    
     DETAILED DESCRIPTION 
     Examples of the methods and systems discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and systems are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, components, elements and features discussed in connection with any one or more examples are not intended to be excluded from a similar role in any other examples. 
     Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, embodiments, components, elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any embodiment, component, element or act herein may also embrace embodiments including only a singularity. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. 
     References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. In addition, in the event of inconsistent usages of terms between this document and documents incorporated herein by reference, the term usage in the incorporated features is supplementary to that of this document; for irreconcilable differences, the term usage in this document controls. 
     Circuit breakers prevent excessive current from passing through electrical components. For example, circuit breakers may have a “current rating” indicating a maximum current that the circuit breaker will conduct. If a current through the circuit breaker exceeds the current rating, the circuit breaker interrupts the current. For example, the circuit breaker may open a relay to interrupt the current and thereby prevent excessive current from passing through (and, in some instances, damaging) electrical components. Circuit breakers may thus protect electrical components from overcurrent events. 
     Although circuit breakers may be effective in preventing excessive current through electrical components, interrupting power to the electrical components may render the electrical components (or “loads”) unusable while power is unavailable. Such load drops may undesirably inconvenience users. Although some loads may be coupled to an uninterruptible power supply (UPS) capable of providing uninterrupted power to a connected load while mains power from a circuit breaker is unavailable, loads that are not connected to a UPS (referred to herein as “unconnected loads”) may not have access to uninterruptible power. 
       FIG. 1  illustrates a block diagram of a power system  100 . The power system  100  includes a circuit breaker  102 , a UPS  104 , one or more UPS-connected loads  106  (“connected loads  106 ”), an arbitrary number of unconnected loads  108 , and an energy-storage device  110 . The connected loads  106  and unconnected loads  108  may include any type of device configured to operate in connection with electrical power, such as residential loads (for example, dishwashers, drying machines, washing machines, blenders, toasters, ovens, lights, and so forth), commercial or industrial loads (for example, lights, copy machines, telephones, manufacturing equipment, and so forth), or other types of loads. The circuit breaker  102 , connected upstream from the loads  106 ,  108 , may be configured to prevent an excessive current from passing through the loads  106 ,  108 . 
     The circuit breaker  102  is coupled to the UPS  104  and the unconnected loads  108  at an output, and is configured to be coupled to a source of input power (for example, a mains power supply) at an input. The UPS  104  is coupled to the circuit breaker  102  at a mains input, is coupled to the connected loads  106  at an output, and is coupled to the energy-storage device  110  at a backup-power input. The connected loads  106  are coupled to the UPS  104  and may, depending on a type of a respective load, be coupled to one or more additional components. The unconnected loads  108  are coupled to the circuit breaker  102  and may, depending on a type of a respective load, be coupled to one or more additional components. The energy-storage device  110  is coupled to the UPS  104 . 
     Input current received by the circuit breaker  102  is provided to the UPS  104  and the unconnected loads  108 . The UPS  104  may provide power to the connected loads  106 . If the input current is below a current rating of the circuit breaker  102 , the circuit breaker  102  allows current to pass to the UPS  104  and to the unconnected loads  108 . If the input current is equal to or above a current rating of the circuit breaker  102 , the circuit breaker  102  may “trip” and interrupt current to the UPS  104  and unconnected loads  108 , such as by opening a relay. As appreciated by one of ordinary skill in the art, certain circuit breakers may trip only if a current in excess of the current rating passes through the circuit breaker for more than a threshold amount of time, which may vary depending on a current level. 
     Although the circuit breaker  102  may advantageously prevent excessive current from passing through the loads  106 ,  108 , the unconnected loads  108  may no longer be operational without power from the circuit breaker  102 . The UPS  104  may continue to provide power derived from the energy-storage device  110  to the connected loads  106 , but if the energy-storage device  110  is depleted of stored energy before mains power is again available from the circuit breaker  102 , the UPS  104  may cease providing power to the connected loads  106 . The connected loads  106  may no longer be operational without power from the UPS  104 . 
     In light of the foregoing, although circuit breakers may be effective in preventing excessive current through electrical components, interrupting current to the electrical components may disadvantageously render the electrical components inoperable while power is unavailable. Examples of the disclosure therefore provide a UPS capable of reducing a current drawn from a circuit breaker such that a current rating of the circuit breaker is not exceeded. In one example, a UPS determines whether a current through a circuit breaker meets one or more over-current criteria (for example, by exceeding, or being close to exceeding, a current rating of the circuit breaker). If the criteria are met, the UPS may reduce an amount of mains power drawn from the circuit breaker and draw backup power from an energy-storage device to compensate for the reduced mains power. Accordingly, the UPS may avoid tripping the circuit breaker without reducing power supplied to a connected load. 
     Current power systems implementing circuit breakers may drop loads when the circuit breaker is tripped. Such power systems may operate inefficiently, because load drops reduce an uptime of the loads. This is a technical problem. An exemplary embodiment of a power system provides an uninterruptible power supply comprising an input configured to be coupled to, and receive input power from, a circuit breaker, an output configured to be coupled to, and provide output power to, at least one load, an energy-storage-device interface configured to be coupled to, and receive back-up power from, an energy-storage device, and at least one controller configured to determine whether a current through the circuit breaker meets at least one over-current criterion, and control, responsive to determining that the current through the circuit breaker meets the at least one over-current criterion, the uninterruptible power supply to provide the output power to the load, the output power being derived from the input power and the back-up power. 
     At least this foregoing combination of features comprises a power system that serves as a technical solution to the foregoing technical problem. This technical solution is not routine and is unconventional. This technical solution is a practical application of the power system design that solves the foregoing technical problem and constitutes an improvement in the technical field of power supply at least by increasing load uptime without compromising circuit-breaker operation. 
       FIG. 2  illustrates a block diagram of a power system  200  according to an example. The power system  200  includes a circuit breaker  202 , one or more current sensor(s)  204  (“current sensor  204 ”), a UPS  206 , one or more UPS-connected loads  208  (“connected loads  208 ”), and one or more unconnected loads  210 , and at least one energy-storage device  212  (“energy-storage device  212 ”). In various examples, the circuit breaker  202 , connected loads  208 , unconnected loads  210 , and energy-storage device  212  may be substantially similar or identical to the circuit breaker  102 , connected loads  106 , unconnected loads  108 , and energy-storage device  110 , respectively. 
     The circuit breaker  202  is coupled to the current sensor  204  at an output, and is configured to be coupled to, and receive input power from, a mains power supply at an input. The current sensor  204  is coupled to the circuit breaker  202  at an input, is coupled to the UPS  206  and unconnected loads  210  at an output, and is communicatively coupled to the UPS  206  via a wired or wireless communication link. The UPS  206  is coupled to the circuit breaker  202  at a mains input, is coupled to the energy-storage device  212  at a backup-power input, is coupled to the connected loads  208  at an output, and is communicatively coupled to the current sensor  204 . 
     The connected loads  208  are coupled to the UPS  206  and may, depending on a type of a respective load, be coupled to one or more additional components. The unconnected loads  210  are coupled to the current sensor  204  and may, depending on a type of a respective load, be coupled to one or more additional components. The energy-storage device  212  is coupled to the UPS  206 . 
     As discussed in greater detail below, the UPS  206  is configured to determine a current through the circuit breaker  202 . If the UPS  206  determines that the current through the circuit breaker  202  meets one or more over-current criteria, the UPS  206  may reduce, or limit, an amount of current that the UPS  206  draws from the circuit breaker  202 . For example, the one or more over-current criteria may indicate that the circuit breaker  202  is at risk of being tripped, which the UPS  206  may be configured to address. To avoid reducing an amount of power provided by the UPS  206  to the connected loads  208 , the UPS  208  may draw power from the energy-storage device  212  that would otherwise be drawn from the circuit breaker  202 . 
       FIG. 3  illustrates a block diagram of a portion of the power system  200  including the current sensor  204 , the UPS  206 , the unconnected loads  208 , and the energy-storage device  212 . The UPS  206  includes a power-factor-correction circuit (PFC)  300 , a DC/AC inverter  302 , a DC/DC converter  304 , an energy-storage-device interface  306 , and a controller  308 . It is to be appreciated that  FIG. 3  provides only one example of components of the UPS  206 , and that alternate implementations of the UPS  206  are within the scope of the disclosure. Furthermore, it is to be appreciated that components of the UPS  206  may be omitted for purposes of clarity. 
     The PFC  300  is coupled to the current sensor  204  at an input and is coupled to the DC/AC inverter  302  and the DC/DC converter  304  at an output. The PFC  300  is configured to receive an input current I_in from the current sensor  204 . The PFC  300  is also communicatively coupled to the controller  308 . 
     The DC/DC converter  304  is coupled to the PFC  300  and the DC/AC inverter  302  at a first connection, and is coupled to the energy-storage-device interface  306  at a second connection. The DC/DC converter  304  is also communicatively coupled to the controller  308 . The energy-storage-device interface  306  is coupled to, and is configured to receive a backup current I_backup from, the DC/DC converter  304  at a first connection, and is configured to be coupled to the energy-storage device  212  at a second connection. For example, the energy-storage-device interface  306  may be or include one or more ports, terminals, or other connectors to couple to, and exchange power with, the energy-storage device  212 . In some examples, the energy-storage-device interface  306  is also coupled to the controller  308 . The DC/AC inverter  302  is coupled to the PFC  300  and the DC/DC converter  304  at an input, and is coupled to, and is configured to provide a load current I_load to, the connected loads  208 . In various examples, the load current I_load is derived from one or both of the backup current I_backup or the input current I_in pursuant to Equation (1): 
         I   load ≈ƒ( I   in )+ƒ( I   backup )
 
     In Equation (1), ƒ(I in ) is a function of the input current I_in and ƒ(I backup ) is a function of the backup current I_backup. In various examples, the energy delivered to a load by the UPS  100  is derived from the energy received at the PFC  300  and the energy received at the energy-storage-device interface  306 . As appreciated by one of ordinary skill in the art, the load current I_load may not be precisely equal to a sum of the backup current I_backup and the input current I_in where, for example, the input current I_in and/or the load current I_load are a first type of current (for example, AC current) and the backup current I_backup is a second type of current (for example, DC current). Furthermore, as discussed herein, energy provided by at least a portion of the input current I_in and/or backup current I_backup may be utilized by the UPS  100  itself (for example, in connection with a logic power supply), lost as heat, and so forth. Accordingly, while the load current I_load may be determined as a function of the input current I_in and a function of the backup current I_backup, the load current I_load may not be precisely equal to a sum of the input current I_in and the backup current I_backup. 
     The DC/AC inverter  302  is also communicatively coupled to the controller  308 . The controller  308  is communicatively coupled to the current sensor  204 , PFC  300 , the DC/AC inverter  302 , the DC/DC converter  304 , and the energy-storage-device interface  306 . 
     The current sensor  204  is coupled to, and is configured to receive a circuit-breaker current I_CB from, the circuit breaker  202  at an input, and is coupled to the PFC  300  and the unconnected loads  210  at an output. The current sensor  202  is also communicatively coupled to the controller  308 . The current sensor  202  is configured to provide the input current I_in to the PFC  300  and is configured to provide an unconnected-load current I_unconnected to the unconnected loads  210 . In some examples, the input current I_in and the unconnected-load current I_unconnected are derived from the circuit-breaker current I_CB pursuant to Equation (2): 
     
       
      
       I 
       CB 
       ≈I 
       in 
       +I 
       unconnected  
      
     
     As discussed above, the circuit breaker  202  may be configured to discontinue providing the circuit-breaker current I_CB if the circuit-breaker current I_CB meets or exceeds a current rating of the circuit breaker  202 . The UPS  206  (and, more particularly, the controller  308 ) receives information indicative of the circuit-breaker current I_CB from the current sensor  204 . In various examples, the UPS  206  may reduce or limit the input current I_in drawn from the circuit breaker  202  if, for example, information indicates that the circuit-breaker current I_CB is approaching or exceeding the current rating, as defined by one or more over-current criteria. Pursuant to Equation (2), reducing or limiting the input current I_in may also reduce or limit the circuit-breaker current I_CB such that the circuit-breaker current I_CB does not meet or exceed the current rating. 
     To maintain a constant load current I_load while reducing or limiting the input current I_in, pursuant to Equation (1), the backup current I_backup may be increased to compensate for current that would otherwise be drawn from the circuit breaker  202  absent the reducing or limiting. Accordingly, the UPS  206  may avoid tripping the circuit breaker  202  without adversely impacting the load current I_load provided to the connected loads  208 . Operation of the UPS  206  is discussed in greater detail below with respect to  FIG. 4 . 
       FIG. 4  illustrates a process  400  of operating the UPS  206  according to an example. The process  400  may be executed by the UPS  206 . For example, the process  400  may be executed by the controller  308 . The process  400  may be executed while the UPS  206  is operational, that is, powered on. In various examples, the process  400  may be repeatedly executed (for example, periodically, aperiodically, continuously, and so forth) during operation of the UPS  206 . 
     At act  402 , the process  400  begins. 
     At act  404 , a circuit-breaker current is determined. For example, the current sensor  204  may sense the circuit-breaker current I_CB and provide information indicative of the circuit-breaker current I_CB to the controller  308 . 
     At act  404 , a determination is made as to whether mains power is available to the UPS  206 . For example, the controller  308  may determine if mains power is available. In one example, the controller  308  determines whether mains power is available by determining whether the circuit-breaker current I_CB, which is derived from mains power, has an acceptable value and/or is within an acceptable range. In another example, the UPS  206  may determine whether mains power is available based on additional or different information. For example, the UPS  206  may include or be coupled to one or more voltage sensors configured to provide voltage information to the UPS  206 , and the UPS  206  may determine whether the voltage is acceptable (for example, by having a value within an acceptable range of voltage values). In other examples, other methods of determining whether mains power is available may be implemented. If mains power is not available ( 404  NO), then the process  400  continues to act  406 . 
     At act  406 , the controller  308  controls the UPS  206  to operate in a discharge mode. In the discharge mode, the UPS  206  is configured to provide output power derived from the energy-storage device  212  to the connected loads  208 . Because mains power is unavailable, the input current I_in may be substantially zero and, pursuant to Equation (1), the load current I_load may be supplied substantially entirely by the backup current I_backup. More particularly, the controller  308  may control the DC/DC converter  304  to draw the backup current I_backup from the energy-storage device  212  via the energy-storage-device interface  306 . The DC/DC converter  304  may convert the DC power received from the energy-storage device  212  (for example, by stepping up or down the voltage of the DC power) and provide the converted DC power to the DC/AC inverter  302 . The DC/AC inverter  302  converts the converted DC power to AC power and provides the AC power (and the load current I_load) to the connected loads  208 . The controller  308  may control the UPS  206  to provide output power derived from the energy-storage device  212  to the connected loads  208  until mains power is restored or the energy-storage device  212  is depleted below a threshold state of charge, for example. 
     At act  408 , the process  400  ends. However, it is to be appreciated that the process  400  may be re-executed immediately after act  408 , or after a delay. 
     Returning to act  406 , if mains power is available ( 406  YES), then the process  400  continues to act  410 . At act  410 , the controller  308  determines whether the circuit-breaker current I_CB meets one or more over-current criteria. The over-current criteria may indicate a condition under which the circuit breaker  202  is at a risk of tripping, which the UPS  206  may attempt to avoid. 
     In various examples, an over-current criterion may be based on a current rating of the circuit breaker  202 . For example, an over-current criterion may be satisfied if the circuit-breaker current I_CB is equal to or greater than the current rating at all, or for more than a threshold amount of time. In another example, an over-current criterion may be satisfied if the circuit-breaker current I_CB is less than the current rating but within a threshold amount of the current rating (for example, within 10% of the current rating, within 1.5% of the current rating, within 1 A of the current rating, within 0.5 A of the current rating, and so forth). In some examples, the one or more over-current criteria may include a current-magnitude criterion and a current-duration criterion. For example, the one or more over-current criteria may not be satisfied until a current exceeds a threshold amount for a threshold amount of time. In still other examples, other over-current criteria may be implemented. 
     If the controller  308  determines that the one or more over-current criteria are not met ( 410  NO), then the process  400  continues to act  412 . At act  412 , the controller  308  controls the UPS  206  to operate in a utility mode (also referred to herein as a “normal” or “standby” mode). In one example of the utility mode, the controller  308  may determine that the circuit breaker  202  is not at imminent risk of being tripped, and that the UPS  206  thus need not draw power from the energy-storage device  212  to limit an amount of current drawn from the circuit breaker  202 . Accordingly, in one example of the utility mode, the backup current I_backup may be substantially zero and, pursuant to Equation (1), the input current I_in drawn from the circuit breaker  202  may be substantially equal to the load current I_load or a function of the load current. 
     In one example of the utility mode, the controller  308  may control the PFC  300  to draw AC power from the circuit breaker  202 . The PFC  200  performs power-factor correction on the DC power and provides the corrected DC power to the DC/AC inverter  302 . The DC/AC inverter  302  converts the corrected DC power to AC power and provides the AC power to the connected loads  208 . 
     At optional act  412 , the controller  308  may control the UPS  206  to charge the energy-storage device  212  using mains power derived from the circuit breaker  202 . For example, the controller  308  may control the UPS  206  to charge the energy-storage device  212  if the energy-storage device  212  has below a threshold amount of charge (for example, below 99% charge, below 95% charge, below 80% charge, and so forth). If a state of charge of the energy-storage device  212  is not below the threshold amount, then optional act  412  may not be executed. In various examples, the controller  308  may not control the UPS  206  to charge the energy-storage device  212  if the charging current would cause the one or more over-current criteria to be met at act  410 . In other examples, optional act  412  is not executed, and the UPS  206  does not charge the energy-storage device  212 . 
     At act  408 , the process  400  ends. However, it is to be appreciated that the process  400  may be re-executed immediately after act  408 , or after a delay. 
     Returning to act  410 , if the controller  308  determines that the circuit-breaker current I_CB meets the one or more over-current criteria ( 410  YES), then the process  400  continues to act  416 . At act  416 , the controller  308  controls the UPS  206  to operate in a power-balance mode. In one example of the power-balance mode, the controller  308  may determine that the circuit breaker  202  is at risk of being tripped by virtue of the one or more over-current criteria being met ( 410  YES). Accordingly, the controller  308  may control the UPS  206  such that at least a portion of the load current I_load is derived from the backup current I_backup. As discussed above, if the load current I_load is held constant while increasing the backup current I_backup, the input current I_in (and, consequently, the circuit-breaker current I_CB) may be reduced. 
     In various examples, the power-balance mode may include adjusting the load current I_load and the backup current I_backup to maintain the circuit-breaker current I_CB at or below a current threshold in some examples. For example, the current threshold may be equal to a current rating of the circuit breaker  202  or a portion thereof, such as 90% of the current rating. If the circuit-breaker current I_CB exceeds the current threshold, the controller  308  may control the UPS  206  to reduce the input current I_in such that the circuit-breaker current I_CB is reduced below the current threshold. For example, the unconnected loads  210  may draw additional current which, pursuant to Equation (2), may increase the circuit-breaker current I_CB. Similarly, if the controller  308  determines that additional load power is desired from the connected loads  208 , but that drawing additional power from the circuit breaker  202  would increase the input current I_in above the current threshold, the controller  308  may instead draw the additional power from the energy-storage device  212  by increasing the backup current I_backup drawn. In some examples, the controller  308  may determine a difference between an output current to be provided by the circuit breaker  202  and the current threshold, and control the UPS  206  to draw the difference from the energy-storage device  212 . Accordingly, the controller  308  may modulate the amount of backup current I_backup drawn from the energy-storage device  212  to maintain the circuit-breaker current I_CB at or below a current threshold. 
     In one example of the power-balance mode, the controller  308  controls the PFC  300  to draw AC power from the circuit breaker  202  in substantially the same manner as discussed above with respect to the utility mode, and controls the DC/DC converter  304  to draw DC power from the energy-storage device  212  in substantially the same manner as discussed above with respect to the discharge mode. The controller  308  controls the DC/AC inverter  302  to receive DC power from the PFC  300  and from the DC/DC converter  304 , convert the received DC power to AC power, and provide the AC power to the connected loads  208 . 
     The controller  308  may control the PFC  300  to reduce or limit the input current I_in in conjunction with controlling the DC/DC converter  304  to draw DC power from the energy-storage device  212  such that a current and/or voltage to the connected loads  208  is not substantially affected (for example, by avoiding a current or voltage drop or spike). For example, the controller  308  may control the PFC  300  to reduce an amount of current drawn from the circuit breaker  202  at a first rate and control the DC/DC converter  304  to increase an amount of current drawn from the energy-storage device  212  at a second rate, where the first rate and the second rate have a substantially equal magnitude. 
     At act  408 , the process  400  ends. However, it is to be appreciated that the process  400  may be re-executed immediately after act  408 , or after a delay. 
     Accordingly, in some examples the UPS  206  is configured to modulate the circuit-breaker current I_CB pursuant to Equation (2) at least in part by modulating the input current I_in, without affecting the load current I_load. That is, a current through the circuit breaker  202  may be limited or reduced at least in part by limiting or reducing a current drawn by the UPS  206 , and instead drawing at least a portion of the load current I_load from the energy-storage device  212 . Power to the connected loads  208  and to the unconnected loads  210  may therefore be uninterrupted without exceeding a current rating of the circuit breaker  202 . In additional examples, the UPS  206  may alternately or additionally be configured to control a current through the unconnected loads  210  to avoid tripping the circuit breaker  202 . 
     For example,  FIG. 5  illustrates a block diagram of a power system  500  according to an example. The power system  500  is substantially similar to the power system  200 , and like components are labelled accordingly. In addition, the power system  500  includes a plurality of disconnection switches  502 , each coupled to a respective one of the unconnected loads  210 . Each of the disconnection switches  502  is configured to be communicatively coupled to the UPS  206  through a wired or wireless connection (for example, via the controller  308 ). In some examples, each of the unconnected loads  210  may include a respective disconnection switch of the disconnection switches  502 , and each of the unconnected loads  210  may be communicatively coupled to the UPS  206  (for example, via the controller  308 ). That is, at least some of the disconnection switches  502  may be internal to the unconnected loads  210 , and at least some of the disconnection switches  502  may be external to the unconnected loads  210 . The controller  308  may control the disconnection switches  502  directly or may instruct a corresponding one of the unconnected loads  210  to control the respectively disconnection switches  502 . In various examples, fewer than all of the unconnected loads  210  may be coupled to, or include, a disconnection switch. 
     In some examples, the UPS  206  may be configured to selectively connect or disconnect unconnected loads of the unconnected loads  210  from the circuit breaker  202  by actuating a respective disconnection switch of the disconnection switches  502 . The disconnection switches  502  may include relays, or other actuatable switches, configured to be opened and/or closed by the controller  308 . The controller  308  may be configured to control respective disconnection switches of the disconnection switches  502  to open, and thereby cause a respective one of the unconnected loads  510  coupled to the respective disconnection switch to draw less current from the circuit breaker  202 , to avoid tripping the circuit breaker  202 . In some examples, causing at least one of the unconnected loads  510  to draw less current from the circuit breaker  202  includes causing the at least one of the unconnected loads  510  to draw no current from the circuit breaker  202 . Accordingly, although an unconnected load coupled to an open disconnection switch may be powered down, the circuit breaker  202  may not be tripped, and the remaining loads may continue to receive electrical power. 
     In various examples, the controller  308  may be configured to select a disconnection switch to open based on one or more parameters. For example, the controller  308  may open disconnection switches in a hierarchical order based on a stored priority list of the unconnected loads  210 . If the circuit-breaker current I_CB approaches a current rating of the circuit breaker  202 , the controller  308  may open a disconnection switch of a lowest-priority load of the unconnected loads  210 , thereby disconnecting the corresponding load from the circuit breaker  202  and reducing the circuit-breaker current I_CB. If the circuit-breaker current I_CB again approaches the current rating of the circuit breaker  202  while the unconnected load is disconnected, the controller  308  may control a disconnection switch of a second lowest priority load of the unconnected loads  210  to open, and so forth. In some examples, a disconnection switch may not be opened if, for example, the unconnected load coupled to the disconnection switch is not drawing power (for example, because the unconnected load is off or otherwise powered down). 
     In some examples, the controller  308  may select a disconnection switch to open based on a current draw of a respective unconnected load. For example, the controller  308  may open a disconnection switch corresponding to an unconnected load drawing the most or least current at the time. In some examples, the controller  308  may select a disconnection switch to open based on a combination of a current draw of a respective unconnected load and based on a priority list. For example, a first unconnected load may be a lowest priority load at certain current-draw levels (for example, a current draw of the first unconnected load or of one or more other unconnected loads) but may not be a lowest priority load at other current-draw levels. In still other examples, the controller  308  may select a disconnection switch to open based on additional or different parameters. 
     In some examples, the UPS  206  may be implemented in a power system having a single circuit breaker. In other examples, the UPS  206  may be implemented in a power system having multiple circuit breakers. For example,  FIG. 6  illustrates a multi-breaker system  600  according to an example. The multi-breaker system  600  includes a main circuit breaker  602 , one or more main current sensors  604  (“main current sensor  604 ”), and a plurality of power systems  606 . In various examples, each power system of the plurality of power systems  606  may be implemented as power systems discussed above, such as the power systems  200 ,  500 . In other examples, only one power system of the plurality of power systems  606  may be implemented in a similar manner as the power systems  200 ,  500 , and the remaining power systems may not include a UPS, for example. 
     The main circuit breaker  602  is coupled to the main current sensor  604  at an output, and is configured to be coupled to, and receive input power from, a mains power source at an input. The main current sensor  604  is coupled to the main circuit breaker  602  at an input, and is coupled to the power systems  606  at an output. Each of the power systems  606  is coupled to the main current sensor  604  at an input and is communicatively coupled to the main current sensor  604  (for example, via a respective controller of each of the power systems  606 ). 
     For purposes of example, a first power system  606   a  of the power systems  606  may be an implementation of the power system  200 . The UPS  206  of the first power system  606   a  may operate in the manner discussed above to avoid tripping the branch circuit breaker  202 . In addition, the UPS  206  may operate in a similar manner with respect to the main circuit breaker  602  to avoid tripping the main circuit breaker  602 . For example, the UPS  206  may determine a main-branch current based on current-sense information received from the main current sensor  604  and modulate a current drawn from the main circuit breaker  602  (for example, by modulating a current drawn from the energy-storage device  212  and/or controlling one or more disconnection switches) to avoid tripping the main circuit breaker  602 . In some examples, the first power system  606   a  may also be communicatively coupled (for example, via the UPS  206 ) to the remaining power systems  606   b ,  606   n . In at least one example, the first power system  606   a  may determine a current through at least one component of each of the remaining power systems  606   b ,  606   n , such as a branch circuit breaker thereof, and may modulate a current drawn from the energy-storage device  212  to avoid tripping the other branch circuit breakers in addition to, or in lieu of, avoiding tripping the main circuit breaker  602 . 
     In some examples, each of the power systems  606  may operate in a substantially similar or identical manner to modulate a current through the main circuit breaker  602  and/or branch circuit breakers of other power systems. In other examples, the power systems  606  may operate differently. For example, one of the power systems  606  may be a master power system, and the remaining power systems may be slave power systems. The power systems  606  may be communicatively coupled to one another (for example, at each respective UPS  206 ) such that a master power system (for example, the first power system  606   a ) controls the slave power systems. The first power system  606   a  may control or instruct the other power systems  606   b ,  606   n  to modulate an amount of current drawn from the main circuit breaker  602  to avoid tripping the main circuit breaker  602 . In some examples, one or more power systems (for example, the first power system  606   a ) may be communicatively coupled (for example, via a respective UPS  206 ) to one or more current sensors in the other power systems. In various examples, each of the power systems  606  modulates a current through its respective branch circuit breaker to avoid tripping the branch circuit breakers in addition to avoiding tripping the main circuit breaker  602 . In another example, a power system of the power systems  606  may include a master UPS  206  configured to modulate a current through each branch circuit to avoid tripping any individual branch circuit breaker in addition to avoiding tripping the main circuit breaker  602 . 
     In some examples, the power systems  606  may be configured to modulate a current through the main circuit breaker  602  in a hierarchical order. For example, the first power system  606   a  may be configured to initially reduce or limit a current draw from the main circuit breaker  602  until one or more conditions are met, after which the second power system  606   b  may be configured to reduce or limit a current draw from the main circuit breaker  602 . The one or more conditions may include, for example, a maximum current being drawn from the energy-storage device  212  of the first power system  606   a  such that the first power system  606   a  cannot further reduce a current draw without powering down one or more loads. 
     Additionally or alternatively, one or more of the power systems  606  may selectively disconnect one or more loads in the manner discussed above with respect to  FIG. 5  to reduce a current draw on the main circuit breaker  602 . For example, at least one of the power branches  606  may be implemented in the configuration discussed above with respect to the power system  500 . In one example, the power systems  606  may first reduce or limit a current draw on the main circuit breaker  602  by drawing a maximum backup current from a respective energy-storage device before beginning to disconnect loads. In various examples, loads may be disconnected in priority order. The priority order may be established across all of the power systems in some examples. For example, a lowest priority load may be an unconnected load of the first power system  606   a , a second lowest priority load may be an unconnected load of the second power system  606   b , and so forth. In various examples, a master UPS (for example, the UPS  206  of the first power system  606   a ) may control or instruct the remaining UPSs to disconnect the loads in the priority order. 
     Accordingly, examples discussed herein modulate a current draw through a circuit breaker to avoid tripping the circuit breaker without compromising a current provided to one or more loads downstream from the circuit breaker. In some examples, a current through the circuit breaker may be limited below a current threshold at least in part by drawing at least a portion of an output current from an energy-storage device in lieu of the circuit breaker. In various examples, a current through the circuit breaker may be limited below a current threshold at least in part by selectively disconnecting one or more loads coupled to the circuit breaker such that the disconnected loads do not draw power from the circuit breaker. In some examples, multiple such power systems may be coupled in parallel and to a main circuit breaker. Each power system may reduce or limit a current through a respective branch circuit breaker in addition to reducing or limiting a current through the main circuit breaker. 
     Although certain examples are illustrated in connection with AC-powered loads, it is to be appreciated that the principles discussed herein are applicable to DC-powered loads. Similarly, although certain examples are illustrated in connection with AC power sources, it is to be appreciated that the principles discussed herein are applicable to DC power sources. 
     Furthermore, although certain examples illustrate a single UPS configured to modulate a current draw through a circuit breaker, it is to be appreciated that in alternate examples a power system may include multiple UPSs configured to modulate a current through a circuit breaker. Example configurations of components are provided for purposes of example only and are not intended to be limiting. For example, although in some illustrated examples a circuit breaker is coupled upstream from a current sensor, in other examples a circuit breaker may be coupled downstream from a current sensor. 
     Various controllers, such as the controller  308 , may execute various operations discussed above. Using data stored in associated memory and/or storage, the controller  308  also executes one or more instructions stored on one or more non-transitory computer-readable media, which the controller  308  may include and/or be coupled to, that may result in manipulated data. In some examples, the controller  308  may include one or more processors or other types of controllers. In one example, the controller  308  is or includes at least one processor. In another example, the controller  308  performs at least a portion of the operations discussed above using an application-specific integrated circuit tailored to perform particular operations in addition to, or in lieu of, a general-purpose processor. As illustrated by these examples, examples in accordance with the present disclosure may perform the operations described herein using many specific combinations of hardware and software and the disclosure is not limited to any particular combination of hardware and software components. Examples of the disclosure may include a computer-program product configured to execute methods, processes, and/or operations discussed above. The computer-program product may be, or include, one or more controllers and/or processors configured to execute instructions to perform methods, processes, and/or operations discussed above. 
     In various examples, components discussed herein may be housed within respective housings. For example, and with reference to  FIG. 3 , the UPS  206  may include a housing to house the components  300 - 308 , and the circuit breaker  202 , current sensor  204 , connected loads  208 , unconnected loads  210 , and/or energy-storage device  212  may be external to the housing. 
     Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of, and within the spirit and scope of, this disclosure. Accordingly, the foregoing description and drawings are by way of example only.