Abstract:
Systems, methods, and devices are provided for redundant control of parallel inverter installations. In one example, a parallel uninterruptible power supply (UPS) system may include several inverter feed paths and several UPS controllers. The inverter feed paths may supply double-conversion power to a load. The UPS controllers may be communicatively coupled to one another via at least two redundant data busses. The UPS controllers may operate in conjunction with one another to control the plurality of feed paths.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The presently disclosed subject matter relates to redundant control of parallel uninterruptable power supplies (UPSs). 
         [0002]    An uninterruptable power supply (UPS) is an electrical device that can supply power to a load despite variations in quality and/or availability of utility-based power. One common type of UPS is a double-conversion UPS. A double-conversion UPS receives power from a power source (typically a utility power grid), converts the power from alternating currents (AC) to direct current in a rectifier, and stores at least some of its power in an energy storage device. An inverter changes the DC power from the rectifier and/or the energy storage device into an AC power waveform. This AC power waveform may be supplied to the load. Several double-conversion UPSs may be connected in parallel to feed a load. At times, all of the inverters in the parallel UPS system may feed the load. During low-load conditions, some of the inverters may be switched off. Switching off some of the inverters may increase efficiency, since each inverter that is on may introduce some inefficiency. 
         [0003]    In some installations of parallel UPS systems, an external agent may control when and how UPS modules are switched on and off via a serial connection to one of the UPS units. In other installations, the agent may be internal to the UPS system. The agent may gather information regarding system operation (including current load) and command the inverters in the parallel UPS system by switching specific UPS inverter modules online or on standby depending on load demand. This configuration posses some reliability issues, however, as it presents several single-point-of-failure conditions. Namely, a failure in the agent (e.g., software or hardware), a failure in the serial connection, and/or a failure in the UPS module receiving the serial connection could lock the system status and prevent the parallel UPS system from reacting to load steps. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
         [0005]    In a first embodiment, a parallel uninterruptible power supply (UPS) system may include several inverter feed paths and several UPS controllers. The inverter feed paths may supply double-conversion power to a load. The UPS controllers may be communicatively coupled to one another via at least two redundant data busses. The UPS controllers may operate in conjunction with one another to control the plurality of feed paths. 
         [0006]    In a second embodiment, an uninterruptible power supply (UPS) controller includes communication circuitry and data processing circuitry. The communication circuitry may communicate with other UPS controllers in a parallel UPS system via at least two redundant communication busses. The communication circuitry may include logic to identify when one of the redundant data busses has failed. This circuitry may also enable communication using the remaining one of the two redundant data busses that has not failed. The data processing circuitry may control at least one of several double-conversion feed paths of the parallel UPS system based at least in part on data received from the other UPS controllers in the parallel UPS system. 
         [0007]    In a third embodiment, an article of manufacture includes one or more tangible, machine-readable media at least collectively storing machine-executable instructions. These instructions may run on an uninterruptible power supply (UPS) controller in a parallel UPS system and may include instructions to receive first electrical measurements associated with at least one of several inverter feed paths of the parallel UPS system. The instructions may also include instructions to determine whether the controller itself or one of the other controllers is a master controller over all of the controllers in the parallel UPS system. The instructions may also include instructions to, when the controller is determined to be the master controller, receive from the other controllers indications of other electrical measurements associated with all but the at least one of the plurality of inverter feed paths. Moreover, the instructions may include instructions to, when the controller is determined to be the master controller, control the at least one of the plurality of inverter feed paths based at least in part on the first electrical measurements and the other electrical measurements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0009]      FIG. 1  is a block diagram of a parallel uninterruptable power supply (UPS) system that employs a redundant control scheme, in accordance with an embodiment; 
           [0010]      FIG. 2  is a block diagram of two UPSs in the parallel UPS system employing the redundant control scheme, in accordance with an embodiment; 
           [0011]      FIG. 3  is a block diagram of a redundant data bus communication frame used in the redundant control scheme, in accordance with an embodiment; 
           [0012]      FIG. 4  is a block diagram generally illustrating the operation of controllers in the parallel (UPS) system, in accordance with an embodiment; 
           [0013]      FIG. 5  is a flowchart describing a method for controlling the parallel (UPS) system using one of the controllers as a master, in accordance with an embodiment; and 
           [0014]      FIG. 6  is a flowchart describing a method for transitioning to a new master controller when the original master controller becomes unavailable, in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0016]    When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0017]    The present disclosure relates to redundant control of parallel uninterruptable power supply (UPS) systems. One example of such a parallel UPS system  10  appears in  FIG. 1 . In the example of  FIG. 1 , the parallel UPS system  10  includes any suitable number of UPSs  12 , here shown as UPS  12 A through  12 N. Under normal operation all of the UPSs  12 A- 12 N may supply power to a load  14 . When the load  14  requires less power, only a subset of the UPSs  12 A- 12 N may be switched on. Each UPS  12  may receive power from a power source  16 , which may enter an inverter feed path  18  controlled by a controller  20 . The power source  16  may be the same or different for each UPS  12 . Suitable power sources may include, for example, an electrical grid or a local or remote generator. The inverter feed path  18  may include power electronic devices to provide enhanced protection in case of disruptions in the power source  16 . Thus, even when the power from the power source  16  is disrupted or of more quality, the inverter feed path  18  may provide a steady supply of high-quality power to the load  14 . A controller  20  may control each inverter feed path  18 . As illustrated in  FIG. 1 , the controllers  20  in the parallel UPS system  10  may not be controlled exclusively by some external agent, but rather may operate in a master-slave or peer-to-peer system of control. 
         [0018]      FIG. 2  presents a slightly more detailed block diagram view of one example of a parallel UPS system  10 . The example of  FIG. 2  shows two parallel UPSs  12 A and  12 B connected in parallel to supply power to a load  14 . The first UPS  12 A may include a rectifier  24 A, a battery  26 A, an inverter  28 A, an output transformer  30 A, and line conditioning capacitors C 1 . A controller  20 A may control the inverter  28 A. The second UPS  12 B may include a similar rectifier  24 B, battery  26 B, inverter  28 B, output transformer  30 B, and line conditioning capacitors C 1 . A controller  20 B may control the inverter  28 B. The operation of the UPS  12 A will be described, but it should be understood that the UPS  12 B may operate in a similar manner. In particular, power from the power source  16  may enter the rectifier  24 A. The rectifier  24 A may convert alternating current (AC) power from the power source  16  into regulated direct current (DC) power. Some of this power may be stored in the battery  26 A or some other energy storage device. The inverter  28 A may receive the DC power from the rectifier  24 A and/or the battery  26 A. The inverter  28 A may convert this DC power to AC power based on control signals from the controller  20 A. 
         [0019]    The controllers  20 A and/or  20 B may connect to one another via redundant data buses  22 . In the example of  FIG. 2 , two redundant data buses communicatively couple the controllers  20 A and  20 B. Any suitable number of redundant buses may be employed, however, to further reduce the likelihood of communication failure between the controllers  20 A and  20 B. The controllers  20 A and  20 B may collectively control the parallel UPS system  10 , ensuring that the load  14  receives sufficient power while promoting efficiency. With fewer UPSs  12  online, the parallel UPS system  10  may be more efficient. 
         [0020]    With this in mind, the controllers  20 A and/or  20 B may carry out any suitable adaptive capacity control technique. For instance, the controllers  20 A and/or  20 B may decide to switch off one of the UPSs  12  (e.g., the first UPS  12 A) when the demand from the load  14  is low enough. The second UPS  12 B may continue to supply power to the load  14 . In some embodiments, power from the UPS  12  that remains online (e.g., the second UPS  12 B) may feed power back into the output transformer  30  of the UPS  12  in standby (e.g., the output transformer  30 A of the first UPS  12 A). 
         [0021]    The controllers  20 A and  20 B may communicate with one another based on an asynchronous communication time division multiple access (TDMA) scheme. One example of a communication frame  32  that may be employed across the redundant data buses  22  appears in  FIG. 3 . In the example communication frame  32  of  FIG. 3 , various time slots  34 ,  36 A,  36 B . . .  36 N are employed. At least one of the time slots in the communication frame  32  may be an arbitration time slot (e.g., time slot  34 ). The arbitration time slot  34  may be used for an arbitration mechanism based on a carrier sense multiple access bit arbitration (CSMA-BA) scheme. As will be described below, the arbitration mechanism employed in the arbitration time slot  34  may allow the controllers  20  to select a master controller  20  that will drive the system operation. The arbitration time slot  34  may be used to ensure that, in the case of a communication loss or failure of the current master controller  20 , a new master controller  20  can be seamlessly reallocated. Moreover, each of the controllers  20  in the parallel UPS system  10  may be allocated a specific time slot  36 . For instance, the first controller  20 A may be assigned the first time slot  36 A, the second controller  20 B may be assigned the second time slot  36 B, and so forth. 
         [0022]    Turning to  FIG. 4 , a first data bus  38  and a second data bus  40  of the redundant data buses  22  may carry copies of the communication frame  32  between the controllers  20  in the parallel UPS system  10 . Each of the controllers  20 A- 20 N, as seen in  FIG. 4 , may receive data from the first data bus  38  and the second data bus  40  of the redundant UPS data buses  22 . Each controller  20  may include a processor  42  and memory or storage  44  to carry out any suitable control technique. Each processor  42  may be operably coupled to its respective memory or storage  44  to carry out the control techniques described therein. Namely, the processor  42  and/or other data processing circuitry may carry out instructions stored on any suitable article of manufacture with one or more tangible, machine-readable media at least collectively storing such instructions. The memory or storage  44  may represent such an article of manufacture. Among other things, the memory or storage  44  may represent random-access memory, read-only memory, rewriteable memory, a hard drive, or an optical disc. 
         [0023]    In general, each controller  20  may receive electrical measurements associated with its respective UPS  12  (e.g., inverter  28  output current I L ′ or I L ″). These electrical measurements may be shared with other of the controllers  20  as generally will be described below. The controllers  20  also may generate inverter control signals (e.g., S i ′ and S i ″) to control the respective inverters  28  associated with each controller  20 . 
         [0024]    Each controller may also include communication control circuitry  46 . In the example of  FIG. 4 , the communication control circuitry  46  is a field programmable gate array (FPGA). Additionally or alternatively, the communication control circuitry  46  may include any other suitable logic, such an application-specific integrated circuit (ASIC) or another processor. The communication control circuitry  46  in each controller  20  interfaces the processor  42  to the redundant communication data buses  22 . The communication control circuitry  46  may perform integrity checks on the communication over the first data bus  38  and the second data bus  40  to identify when one or the other has failed. In case either the first data bus  38  or the second data bus  40  fails, the communication control circuitry  46  may select the other, functional bus over which to receive communication. 
         [0025]    In some embodiments, one of the controllers  20  may be designated as a master controller that controls the operation of other controllers  20  in the parallel UPS system  10 . For instance, as illustrated in a flowchart  50  of  FIG. 5 , the controllers  20  may decide among themselves one controller  20  that will be designated as the master (block  52 ). This master controller  20  may receive the electrical measurements (e.g., I L ′ and/or I L ′) from the other controllers  20  of the parallel UPS system  10  (block  54 ). The master controller  20  may employ any suitable adaptive capacity control technique to ascertain which of the inverters  28  of the parallel UPS system  10  should supply power to the load  14 . As such, the master controller  20  may determine whether and when to switch inverters  28  of the parallel UPS system  10  on or into standby and/or to cycle through which inverters  28  are on or are in standby modes by issuing control signals to the other respective controllers  20  (block  56 ). 
         [0026]    In some cases, however, the designated master controller  20  could lose contact with the other controllers  20  of the parallel UPS system  10 . As described by a flowchart  60  of  FIG. 6 , the remaining controllers may simply determine a new master control and continue operation in a fully redundant manner. The flowchart  60  of  FIG. 6  may begin when the parallel UPS system  10  is controlled using a first controller designated as a master (block  62 ). When the master controller  20  loses communication with the other controllers  20  of the parallel UPS system  10  (block  64 ), the parallel UPS system  10  may not simply cease to function. Rather, the remaining controllers  20  may determine, via the arbitration mechanism provided by the arbitration time slot  34  of the communication frame  32 , to designate another controller  20  to be the master controller  20  (block  66 ). This new master controller  20  may take the place of the original master controller  20  at least until the communication with the original master controller  20  is restored. In some embodiments, which controller  20  served as the master may rotate from controller  20  to controller  20  over time. 
         [0027]    Technical effects of the present disclosure include improved redundancy in case of communication failures. Rather than rely on a single, static master device located internally or externally to the parallel UPS system, the master device may be selected from among the various controllers in the parallel UPS system. Thus, the parallel UPS system may be scalable, and a single communication error may not cause the parallel UPS system to cease functioning. 
         [0028]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.