Abstract:
A modular power distribution system includes a three level approach to power distribution: a power module level, a transfer module level, and a distribution module level. At each level, the number of modules used can be varied based on the power requirements of the site. The power modules receive power from either a main, off-site generator (such as from an electric utility), or from an in-module backup generator. Additionally, the power, transfer, and distribution modules at each of the levels are arranged in a redundant topology, so that if any of the modules should fail, the remaining modules seamlessly assume the functions of the failing module.

Description:
BACKGROUND 
     1. Field 
     The present invention relates generally to power distribution systems and, more particularly, to fault tolerant power distribution systems capable of supporting critical loads with high power requirements. 
     2. Description of Related Art 
     The electrical power requirements of buildings housing large computer centers can be very high. The difficulty in efficiently supplying such buildings with adequate power is compounded when the computers are mission critical computers that must have a constant source of uninterrupted power. 
     Conventionally, mission critical computers are powered using the so-called uninterruptible power supply (UPS) power circuits. The UPS circuits monitor power flowing to the electrical loads (e.g., mission critical systems), and in the event of a power failure, seamlessly route power to the loads from a backup source such as a battery. From the point of view of the computers, power was never lost and they continue to operate as normal. 
     Supplying UPS power to high power consumption buildings can be a daunting task. Conventionally, such UPS solutions were individually designed and implemented at each site, resulting in a relatively expensive and time consuming design and engineering task. Additionally, maintenance of the power circuitry at each such site tends to require site-specific training, thus increasing cost. 
     Moreover, although UPS circuits effectively handle power disruptions leading to the site, the UPS circuit itself is still subject to failure. Accordingly, in order to increase the fault tolerance of a system, multiple redundant UPS systems were conventionally installed at a site. This type of redundancy, called system plus system redundancy, implements separate and parallel power systems and power pathways all the way through the site and leading to the loads. Although fault tolerant, these systems can be expensive as every part is duplicated for each level of redundancy. 
     Accordingly, thus is a need in the art for an improved UPS power solution at sites having high power requirements. 
     SUMMARY 
     Systems and methods are needed to address these needs as identified above. 
     One aspect of the present invention is directed to a multi-level modular power distribution system including a plurality of power modules, a plurality of transfer modules, and a plurality of power distribution modules. The power modules are each connected to receive power from an external source, the plurality of power modules including at least one alternate power module. Each of the transfer modules is associated with and connected to a corresponding one of power modules and to the at least one alternate power module. The power distribution modules receive power from the transfer modules and supply power to electrical loads of the power distribution system. When one of the power modules fails, the transfer module corresponding to the failing power module switches to power from the alternate power module. 
     A second aspect of the present invention is directed to a power module for supplying power in a modular power system. The power module comprises a temporary source of power; a petroleum powered backup generator; and an uninterruptible power supply (UPS). The UPS conditions power received from a main power supply and outputs the conditioned power. Further, the UPS receives power from the temporary source of power and the backup generator when the power from the main power supply fails. 
     Another aspect of the present invention is a method of supplying power to a building site. The method includes providing a predetermined number of power modules external to the building site, the predetermined number being at least equal to the total power requirement of the building site divided by two-thirds of the power capacity of the each power module. Further, each of the power modules is connected to associated transfer modules located within the building site. At least one of the power modules is designated as an alternate power module and connected to more than one of the transfer modules. The transfer modules are connected to distribution modules located proximate to the electric loads designated to use the supplied power. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this Specification, illustrate an embodiment of the invention and, together with the description, explain the objects, advantages, and principles of the invention. In the drawings: 
     FIG. 1 is a perspective view illustrating an exemplary installation of a modular power distribution system at a target site; 
     FIG. 2 is a high level block diagram illustrating an exemplary power distribution system having five power modules, three power transfer modules, and three distribution modules; 
     FIG. 3 is an electrical schematic diagram illustrating an exemplary embodiment of a power distribution module; 
     FIG. 4 is an electrical schematic diagram illustrating an exemplary embodiment of a power transfer module; 
     FIG. 5 is an electrical schematic diagram illustrating an exemplary embodiment of a power distribution module; and 
     FIG. 6 is an electrical schematic diagram illustrating an embodiment of a modular power system having N+2 redundancy at the power module level. 
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying drawings that illustrate the embodiments of the present invention. Other embodiments are possible and modifications may be made to the embodiments without departing from the spirit and scope of the invention. Therefore, the following detailed description is not meant to limit the invention. Rather the scope of the invention is defined by the appended claims. 
     A modular and fault tolerant power distribution system has a three level structure: a power module level, a transfer module level, and a power distribution module level. The modules can be prefabricated at an assembly plant, shipped to the installation site, and then relatively easily installed at the installation site. At the site, the modules are connected by power and communication cables. 
     As will be described in more detail below, the present modular power system features double and triple redundancy in all systems and at all levels of power distribution. This redundancy allows concurrent maintenance operations and provides multi-level fault tolerance. While duplication of equipment is reduced relative to conventional system plus system implementations, the system reliability and availability is not affected by the economy. 
     FIG. 1 is a perspective view illustrating an exemplary installation of a modular power distribution system at a target site. Eight power modules  101  are shown outside of building  102 . The power modules provide power to transfer and power distribution modules located inside the building  102 . 
     The detailed electrical design and interconnection of each of the power, transfer, and distribution modules will now be described with reference to FIGS. 2-6. 
     FIG. 2 is a high level block diagram illustrating a power distribution system having five power modules  203 - 207 , three power transfer modules  208 - 210 , and three distribution modules  212 - 214 . Power is received at each of power modules  203 - 207  from main power lines  219  connected to a utility company or from backup generators disposed locally to each of power modules  203 - 207 . In the power module arrangement illustrated, power modules  203 ,  204 , and  205  are the “normal” power modules while power module  206  and  207  function as backup or alternate power modules. In normal operation, all the power requirements of the system are supplied by power modules  203 - 205 . If one of power modules  203 - 205  fails, however, power from alternate power nodule  206  is seamlessly integrated by transfer modules  208 - 210  into the final power output of the system. If a second one of power modules  203 - 205 , fails, or if alternate power module  206  fails, the second alternate power module, module  207 , provides power for this failing module. Thus, at the power module level, system  200  is “N+2” redundant, meaning that there are two additional alternate power supplies that may be relied upon if anyone of the normal power modules fail. 
     For clarity, only one power distribution module  212  is shown in FIG. 2 for each transfer module  208 . Typically, more than one power distribution module, such as three or four power distribution modules, will be installed per transfer module. 
     The number of modules to use at a particular site is determined by the power requirement and the amount of redundancy desired at the site. The minimum number of primary modules implemented at any particular site is preferably equal to the total power requirement divided by two-thirds of the power capacity of a single module (e.g., approximately 480 kVA in the illustrated sample system). The factor of two-thirds is used to calculate the minimum number of primary modules (as opposed to a factor of one) because the failure of one of transfer modules  208 - 210  (described in more detail below) requires that two other power modules carry their own loads plus 50% of the load normally carried by the failed transfer module. 
     Each of transfer modules  208 - 210  is associated with one of power modules  203 - 205  and with the alternate power modules  206  and  207 . In normal operation, power from power module  203  is routed through transfer module  208  to power distribution modules  212  and  214 . Similarly, power from power module  204  is routed through transfer module  209  to power distribution modules  212  and  213 ; and power from power module  205  is routed through transfer module  210  to power distribution modules  213  and  214 . When one of power modules  203 - 205  fails, the transfer module associated with the failing power module routes power from alternate power modules  206  or  207  to its distribution modules. For example, if power module  205  fails, transfer module  210  routes power from alternate power module  206  to power distribution modules  213  and  214 . Transfer modules  208 - 210  are normally installed inside the building. 
     As well as being redundant at the power module level, system  200  is redundant at the transfer module level. Specifically, because each distribution module receives power from two transfer modules, if any one of the transfer modules fails, all three distribution modules  212 - 214  can continue to receive power from one of the remaining two transfer modules. 
     Auxiliary panels  220 - 223  provide services such as lighting and HVAC (heating, ventilation, and air conditioning) to the building. Each auxiliary panel  220 - 223  is connected to two of the power modules  203 - 207 . If power supplied from one of the power modules  203 - 207  fails, power from the panel&#39;s second power module is routed to the auxiliary panel through switches  225 - 227 . For example, if the power being supplied from power module  203  to auxiliary panel  220  fails, switch  225  detects the power failure and switches to power module  204 . Because power being supplied to auxiliary panels  220 - 223  can afford to be briefly interrupted without interfering with the effectiveness of the auxiliary panels, switches  225 - 227 , as opposed to the internal sub-cycle switching occurring in transfer modules  208 - 210 , may be simple mechanical power transfer switches. 
     As previously mentioned, each power distribution module  212 - 214  is redundantly supplied with power from two separate transfer modules  208 - 210 . The power distribution modules supply power to their loads  230  (e.g., mission critical computer systems) through standard power distribution panels installed proximate to the distribution modules  212 - 214 . Loads  230  are preferably dual cord loads, which allow them to redundantly receive power from two of the power distribution panels. Alternatively, each load  230  may be connected to a single power distribution module. 
     FIG. 3 is an electrical schematic diagram illustrating an exemplary embodiment of one of power distribution modules  203 - 206 . A typical power module is designed to be able to source approximately 800 kVA (720 kW) to its transfer module. Accordingly, these modules tend to be relatively large (e.g., 60 feet by 12 feet), and are therefore designed to be located exterior to the facility. However, the power modules may also be supplied within a building, which may be advantageous in that weatherproofing and sound attenuating features may be omitted from the design of the power module. 
     The power distribution module is fed from a step-down transformer  301  connected to the local electric utility or to an alternate power supply. Preferably, transformer  301  converts the power supplied from the external source to a 2500 kVA, 480 volt, signal. 
     Automatic transfer switch  330  provides suitable power to 480-volt auxiliary panel  331 , which provides lighting and HVAC services to the power module. A second 220/120 volt auxiliary panel  333  serves power module loads requiring 120-volt power. If power to auxiliary panels  331  and  333  fail, automatic transfer switch  330  transfers power to auxiliary panels  331  and  333  from one of the other power modules. 
     Power from transformer  301  is supplied to UPS (uninterruptible power supply)  303 . UPS  303  provides clean power (i.e., power suitable for input to sensitive computer and electronic devices) and uninterrupted power to output line  310 , which leads to the transfer modules and the building&#39;s auxiliary panels. Uninterruptible power refers to the UPS&#39;s ability to detect power failures from transformer  301  and immediately switch to backup power without any meaningful fluctuation in the power supply. 
     As shown in FIG. 3, UPS  303  contains a first power converter  311  for converting AC power to DC power and a second converter  312  that converts DC power to AC power. Input power is first converted by power converter  311  to DC power and then converted back to AC power by converter  312 . With this dual power conversion scheme, UPS  303  conditions and removes noise from the output power supplied on line  310 . 
     The DC power output from converter  311  is also input, after conversion to an AC signal by converter  313 , to a flywheel  305 , which provides short term backup power to UPS  303  in the event of a power failure of the power from transformer  301 . Flywheel  305  stores energy as mechanical rotational energy. If power to UPS  303  is cut-off, the potential energy of the rotating flywheel is converted into electrical energy by converter  313  and transmitted back to UPS  303 . UPS  303  uses the energy from flywheel  305  until a more permanent backup power source, such as power from a diesel generator, is brought on-line. Flywheels are well known in the art. 
     One of ordinary skill in the art will recognize that alternative methods, other than flywheel  305 , can be used to supply short-term backup power to UPS  303 , such as a battery storing energy as chemical potential energy. 
     Diesel generator  320  is a backup power supply to the main power supplied from the electric utility. A diesel engine generator control systems detect power failures from the main power supply, and in response, activates generator  320 . The UPS then begins to draw power from flywheel  305  while generator  320  is coming on-line. UPS  303  monitors generator  320 , and when it begins to supply stable power, switches from flywheel  305  to generator  320 . 
     UPS  303  includes a static bypass switch  321  connected the main power and to generator  320 . In the event of an internal failure of the UPS module, switch  321  turns on to isolate the power module. Static bypass switches are well known in the art. 
     FIG. 4 is an electrical schematic diagram illustrating an exemplary embodiment of a power transfer module  400  designed to accept power from a primary power module and two alternate power modules. 
     Power transfer module  400  receives power from three sources—its primary power module and two alternate power modules. During normal operation, power is received at the primary power module input and routed through circuit breakers  406  and static bypass switch  405  to bus  403 . Static bypass switches  407  isolate bus  403  from power being sourced by the alternate power modules. If the primary power module fails, static switch  405  detects the failure, and with circuit breakers  406 , isolate bus  403  from the primary power module. In conjunction with this operation, one of static transfer switches  407 , such as the one associated with the first alternate power source, begins to pass power from the alternate power source to bus  403 . In a similar manner, if the first alternate power module fails, the static bypass switch  407  associated with the second alternate power module may transfer the power load to the second alternate power module. 
     Each of static switches  405  and  407  are associated with a circuit breaker  408 . The combination of static bypass switches  405  and  407 , and circuit breaker  408 , functionally implement a single switch  415  having three inputs, one of which is output to bus  403 . Switch  415  will be referred to as a “triple source static transfer switch.” 
     Power transferred to bus  403  is forwarded to power distribution units through output ports  410 - 412 . Two power lines lead out from each of output ports  410 - 412 . These power lines are each connected to different power distribution units. In the example topography shown in FIG. 2, only one output port from each power transfer unit  208 - 210  is shown. 
     Although transfer module  400  is illustrated as containing connections for two alternate power sources, selectable through triple source transfer switch  415 , a transfer module designed for more than two alternate power sources could be similarly constructed. By adding a third alternate power module and connecting the third alternate power module to each transfer module, an additional level of redundancy can be achieved. 
     The static switches (i.e., elements  405  and  407 ) in transfer module  400  preferably are capable of the following features: (1) preferred source selection, (2) undervoltage and single phase detection, (3) over current circuit detection, (4) transfer lockout, (5) retransfer time delay, (6) retransfer lock out, (7) control logic to allow selection and control of the automatic transfer switch, (8) operator interface controls and status indications, and (9) dry contacts for remote monitoring and control. Such transfer switches are commercially available from manufacturers such as United Power Corporation, of Richmond, Va. 
     FIG. 5 is an electrical schematic diagram illustrating an exemplary embodiment of one of power distribution modules  212 - 214 . 
     Power distribution module  500  is connected to two different power transfer modules. Power received from the power transfer modules is passed through a step-down transformer  501  before entering the parallel combination of static switches  502  and circuit breakers  503 , which select whether or not power from their associated power transfer module is supplied to distribution panels  505 . More particularly, static transfer switches  502  and circuit breakers  503  select power from one of the two input power sources. If the selected power source fails, the full load of the distribution module  500  is handled by the remaining input connection to the active power transfer module. 
     Distribution panels  505  are standard electrical power distribution panels to which the power cords leading to the intended loads are plugged in. 
     In order to reduce cost, the power, transfer, and distribution modules are preferably made from commercially available parts. One possible implementation for the main parts in the modules are as follows: power distribution panels  505 , available from the General Electric Company; flywheel  305 , available from Piller GmbH, of Germany; and generator  320 , available from Detroit Diesel Corporation, of Michigan. 
     FIG. 6 is an electrical schematic diagram illustrating an embodiment of a modular power system  600  having eight power modules and N+2 redundancy at the power module level. For clarity, connections to the auxiliary panels associated with the transfer level are not shown. 
     Power,distribution system  600  has eight power modules, six of which, labeled as modules  601 , provide power to the transfer modules  604  during normal operation. Two alternate power modules  602  provide backup power to the transfer modules. If any one of power modules  601  fails, the transfer module being supplied by the failing power module detects the failure and switches to one of the two alternate power modules  602 . Similarly, if a second power module  601  fails, the transfer module associated with this failing power module detects the failure and switches to the other of the alternate power modules  602 . 
     As with the power distribution shown in FIG. 2, power distribution system  600  is also redundant at the transfer module level. Thus, if any one of transfer modules  604  fails, power is still sourced to its associated power distribution panel  610  using an alternate one of the transfer modules  604 . Further, as with loads  230  shown in FIG. 2, loads  612  are preferably connected to two power distribution modules  610  using a dual cord connection. 
     System Operation 
     Each of the power modules, transfer modules, and distribution modules are connected together to form a networked power grid that can be monitored and controlled from a single location. Preferably, the network topology is distributed and redundant so that the failure of a single module will not interrupt communications among the remaining modules. 
     The above described power modules, transfer modules, and power distribution modules are preferably assembled, wired, and tested at a factory. This has the advantage of decreasing costs and allowing efficient implementation when the modules are delivered at the site. To shorten the power implementation even further, site preparation may take place before the equipment arrives. Because the modules are not site specific, they may be interchangeable between similar locations and similar facility designs. 
     It will be apparent to one of ordinary skill in the art that the embodiments described above may be implemented using many different combinations of electric components than those illustrated in the figures. The foregoing description of preferred embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible consistent with the above teachings or may be acquired from practice of the invention. The scope of the invention is defined by the claims and their equivalents.