Patent Publication Number: US-2012043822-A1

Title: Modular electrical accumulator unit

Description:
BACKGROUND 
     The present application is directed toward power generation systems, and more particularly toward a power generation system using an electrical accumulator unit. 
     In order to provide power to electrical systems many vehicles, such as military aircraft, feature an on-board generator which converts rotational movement within the engines to electrical power using known power generation techniques. The generated electrical power is used to power on-board electrical components such as flight controls, sensors, or weapons controls. During standard operations, such a system has an electrical load which normally draws power at a certain level. When some on-board electrical systems, such as weapons systems, are activated a temporary elevated load spike occurs. 
     In order to compensate for the temporary load spike, a generator is typically used which is rated at least as high as the highest anticipated power spike. This ensures that adequate power can be provided to the on-board electrical systems at all times, including during elevated load spikes. In a typical power generation system, the physical size of the generator is directly related to the power rating of the generator. Consequently, use of a higher rated generator to account for high load spikes results in a heavy generator. 
     SUMMARY 
     A modular electrical accumulator unit has multiple electrical accumulator unit modules. Each electrical accumulator unit module has an energy storage component, a power converter electrically coupled to the energy storage component, a pair of electrical connectors for connecting the modules to a power bus, and a power switch capable of isolating the module from the power bus. The electrical accumulator unit also includes an electrical controller that is coupled to each of the power switches, thereby allowing the electrical controller to control a connection between each of the modules and the power bus. 
     A method for operating an aircraft power system includes the steps of: generating power with a three-phase generator, converting the power into DC power format, providing the DC power to a DC power bus, the DC power bus providing power to a variable load and to a plurality of electrical accumulator unit modules, and controlling the plurality of electrical accumulator unit modules using a dedicated electrical accumulator unit controller. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a sample aircraft having an on-board power generation system. 
         FIG. 2  schematically illustrates an aircraft power generation system including an electrical accumulator unit. 
         FIG. 3  schematically illustrates an example modular electrical accumulator unit. 
         FIG. 4  schematically illustrates another example modular electrical accumulator unit. 
         FIG. 5  illustrates a flow chart of an example method for operating a modular electrical accumulator unit. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates a sample aircraft  10  having an on-board power generation system. A generator  20  converts rotational motion within an engine  22  into electrical power using known power generation techniques. The generator  20  is electrically coupled to a rectifier  30 . The rectifier  30  converts the power generated in the generator  20  (typically three-phase power) into a form usable by on-board electronics  50  (typically DC power). The rectifier  30  is electrically coupled to a power bus  40  which supplies power to the on-board electronics  50  through power supply lines  42 . Additionally connected to the power bus  40 , is an electrical accumulator unit  60 , which can store excess power generated by the generator  20  when the load created by the on-board electronics  50  is low, and reinsert that power into the power system when the load created by the on-board electronics  50  undergoes a high load spike. 
       FIG. 2  schematically illustrates a power generation system  100  described with regards to  FIG. 1 . A three phase generator  110  is connected to an AC/DC rectifier  120  via three phase outputs  112 A,  112 B,  112 C. The three phase generator  110  may also be referred to as generator  110 . The AC/DC rectifier  120  converts the generated three phase power into DC power, and outputs the DC power to a power bus  130 . Connected to the DC power bus  130  is a variable load  140 . The variable load  140  may represent a variable number and size of electrical loads that can change over time and/or be selectively added, removed, or modified. Additionally connected to the DC power bus  130  is an electrical accumulator unit  150 . The three phase generator  110 , AC/DC rectifier  120 , DC power bus  130 , variable load  140 , and electrical accumulator unit  150  represent embodiments of the generator  20 , rectifier  30 , power bus  40 , the load created by the on-board electronics  50 , and electrical accumulator unit  60  of  FIG. 1  respectively. A generator controller  160  (also referred to as controller  160 ) is connected to both the electrical accumulator unit  150  (via link  162 ) and the three phase generator  110 , and provides control signals for both. The generator controller  160  is also connected to the output of the AC/DC rectifier  120  via power sensors, and is capable of detecting the power output of the AC/DC rectifier  120  and the power demands of the variable load  140 . Alternately, the electrical accumulator unit  150  can be controlled via an electrical accumulator unit controller independently of the controller  160 . 
     In the example power generation system  100  of  FIG. 2 , the generator  110  generates power at its maximum rating and the variable load  140  often uses less than all of the generated power. The excess power in this case is siphoned off by the electrical accumulator unit  150 , which stores the excess power in a power storage component such as a battery or ultra capacitor. When the variable load  140  spikes, and exceeds the generating capacity of the generator  110 , the electrical accumulator unit  150  reverses and begins supplementing the power provided to the DC power bus  130  with the power which has been stored within the power storage component, thereby ensuring that the variable load  140  receives adequate power throughout the high power spike. 
       FIG. 3  illustrates a schematic diagram of an example electrical accumulator unit  200 . The electrical accumulator unit  200  and power bus  250  represent embodiments of the electrical accumulator unit  150  and DC power bus  130  of  FIG. 2 . The electrical accumulator unit  200  has multiple stages  202  (also referred to as modules  202 ), each of which has four primary components, an energy storage unit  220  (also referred to as power storage component  220 ), a power converter  230 , a filter  240 , and a power switch  262 . Each stage  202  also includes a pair of electrical connectors  242 ,  244  for connecting the stage  202  to a power bus  250 . In the example of  FIG. 2 , the power switch  262  interrupts one of the electrical connectors  242 . Also included is a dedicated electrical accumulator unit controller  260 . The controller  260  has an output  264  for controlling each of the power switches  262  and multiple inputs  266 ,  267 ,  268  for detecting the states of the energy storage unit  220 , the power converter  230  and the filter  240 . The controller  260  operates in conjunction with each of the power switches  262 , thereby connecting and disconnecting each of the electrical accumulator unit stages  202  as required. The controller  260  allows the multiple stages  202  to be used in conjunction with each other. As illustrated in  FIG. 3 , each of the electrical accumulator unit stages  202  are connected to the power bus  250  in a parallel arrangement. It is known, however, that alternate connection arrangements could be used with minor modifications to the electrical accumulator unit  200 . 
     The filter  240  is a combination of an input ripple filter and an electromagnetic interference (EMI) filter. The input ripple filter portion of the filter  240  removes ripple currents, which have leaked onto the power bus  250  due to the presence of power electronics in the load, such as variable load  140  of  FIG. 2 . Similarly, the EMI filter portion of the filter  240  filters out electromagnetic interference present on the power bus  250 . Ripple currents and electromagnetic interference are common occurrences in electrical systems and result from the connection the power bus  250  has to the variable load  140  as well as the electrical systems exposure to other sources of electrical noise. Allowing the interference and ripple currents to reach the power converter  230  is undesirable. 
     After passing through the filter  240 , the electrical power enters a bi-directional power converter  230  where it is converted from the form of electrical power used by the power bus  250  into a form which can be accepted and stored by the power storage component  220 . The bi-directional power converter  230  is also capable of converting power output from the power storage component  220  into the form used on the power bus  250  when the electrical accumulator unit  200  is providing power to the system, such as during a high load spike or while operating in emergency mode. Furthermore, each of the power converters  230  can be a buck-boost power converter using any known buck-boost circuits. Alternately, the power converters  230  can be a network of parallel phase shifted buck-boost converter circuits, which are configured to operate in conjunction with each other according to known principles. 
     The power storage component  220  can be any device or component which is capable of accepting power from the power converter  230  and storing that power for later use. In the illustrated example of  FIG. 3 , a battery or ultra capacitor (ultra cap) could be used. However, other power storage components could be used with minor modifications to the electrical accumulator unit  200 . Using multiple stages  202  additionally allows for different energy storage unit types (such as batteries and ultra-capacitors) to be used in each stage  202 , thereby allowing for greater optimization of the power and energy capabilities. The controller  260  can additionally isolate a stage  202  with a fault condition or that is otherwise incapacitated, thereby allowing for continued operation of the power generation system  100 . Furthermore, the controller  260  allows the modules  202  to be connected in an interleaved manner according to known techniques. 
       FIG. 4  illustrates an alternate modular electrical accumulator unit  200 . In the example of  FIG. 4 , the filter  240  has been removed from each stage  202 , and a single filter  440  that is capable of filtering input power for all of the stages  202  connects each of the modules  202  to the power bus  250 . Each of the components  220 ,  230 ,  262 ,  260  and  440  function in a similar fashion as described above with regard to  FIG. 3 . By moving the filter  440  out of each stage  202 , a single more efficient filter  440  can be used, which can allow for a reduction in the weight requirement of the electrical accumulator unit  200 . 
       FIG. 5  illustrates a flowchart of operations of the modular electrical accumulator unit  150 ,  200  of  FIGS. 2 and 3 . Initially power is generated by the generator  110  in the “generate power” step  310 . After the power has been generated, it is converted into a DC power format used by the DC power bus  130  in the “convert power to DC” step  320 , and the power is provided to the DC power bus  130  in the “provide power to DC bus” step  330 . Power conversion may be performed by the AC/DC rectifier  120  of  FIG. 2 . The controller  160  then determines whether the variable load  140  connected to the DC power bus  130  is currently exceeding the amount of power which can be provided by the generator  110  in the “does load exceed power provided by the generator” step  340 . 
     If the variable load  140  exceeds the amount of power which can be generated by the generator  110 , the method proceeds to the electrical accumulator unit “provides supplemental power” step  355 . In the “provides supplemental power” step  355 , a controller for the electrical accumulator unit  150  determines a number of modules required to provide an amount of power equal to the amount by which the variable load  140  exceeds the generation capabilities of the generator  110  and connects an equivalent number of modules  202  to the DC power bus, thereby providing the required power. The power is pulled from the power stored within the power storage component  220  of each connected module  202  of the electrical accumulator unit  150 ,  200  of  FIGS. 2 and 3 . 
     If the variable load  140  does not exceed the amount of power which can be generated by the generator  110 , the method moves to the electrical accumulator “accepts and stores excess power” step  360 . In this step, the controller  260  detects any modules  202 , which are not fully charged and connects them to the DC bus  250 , thereby allowing the under charged modules  202  to accept any power generated by the generator  110 , which is not required to power the variable load  140 . The undercharged modules  202  can be connected to the load using the power switch  262 , which is controlled by the electrical accumulator unit controller  260 . 
     While the power demands of variable load  140  are being checked in the “does load exceed power provided by generator” step  340 , an additional step may be performed. The “does load provide power back to the generator” step  375  checks to see if the variable load  140  is generating power such that electrical power will be transmitted back through the electrical system to the generator  110 . If the variable load  140  is not generating power, the method proceeds as described above. If the variable load  140  is generating power, then the electrical accumulator unit  150  accepts and stores the power generated by the variable load  140  in an “accept and store excess load power” step  380 . The “accept and store excess load power” step  380  operates in a similar manner as the “accept and store excess power” step  360 . 
     Optionally, the method can include an additional step where the controller  260  determines if any of the modules  202  are faulty or are otherwise inoperative. If any of the modules are faulty, the controller  260  can disable/disconnect the faulty module until repairs can be made. The presence of multiple electrical accumulator unit modules  202  allows the modular electrical accumulator unit  200  to continue functioning while a portion of the modules  202  are disabled due to faults within the modules  202 . 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.