Patent Publication Number: US-2006005736-A1

Title: Hybrid energy off highway vehicle electric power management system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      The invention of the present application is a Continuation-in-Part that claims of U.S. patent application Ser. No. 10/378,431, filed on Mar. 3, 2003, and entitled “HYBRID ENERGY OFF HIGHWAY VEHICLE ELECTRIC POWER MANAGEMENT SYSTEM AND METHOD”, which claims priority from U.S. patent application Ser. No. 10/033,172, filed on Dec. 26, 2001, and entitled “HYBRID ENERGY POWER MANAGEMENT SYSTEM AND METHOD”, allowed Dec. 23, 2002, and from U.S. Provisional Application Ser. No. 60/278,975, filed on Mar. 27, 2001, the entire disclosure of which is incorporated herein by reference. The following commonly owned, co-pending applications are related to the present application and are incorporated herein by reference:  
      U.S. patent application Ser. No. 10/378,335, filed on Mar. 3, 2003, and entitled “HYBRID ENERGY OFF HIGHWAY VEHICLE POWER STORAGE SYSTEM AND METHOD”;  
      U.S. patent application Ser. No. 10/033,347, filed on Dec. 26, 2001, and entitled “HYBRID ENERGY LOCOMOTIVE POWER STORAGE SYSTEM”;  
      U.S. patent application Ser. No. 10/033,191, filed on Dec. 26, 2001, and entitled “HYBRID ENERGY LOCOMOTIVE SYSTEM AND METHOD”; and  
      U.S. patent application Ser. No. 10/032,714, filed on Dec. 26, 2001, and entitled “LOCOMOTIVE ENERGY TENDER”.  
    
    
     FIELD OF THE INVENTION  
      The invention relates generally to energy management systems and methods for use in connection with a large, Off Highway Vehicle such as a railway locomotive, mining truck or excavator. In particular, the invention relates to a system and method for managing the storage and transfer of electrical energy, such as dynamic braking energy or excess prime mover power, produced by Off Highway Vehicles driven by electric traction motors.  
     BACKGROUND OF THE INVENTION  
       FIG. 1A  is a block diagram of an exemplary prior art Off Highway Vehicle. In particular,  FIG. 1A  generally reflects a typical prior art diesel-electric Off Highway Vehicle. Off Highway Vehicles include locomotives and mining trucks and excavators, where mining trucks and excavators range from 100-ton capacity to 400-ton capacity, but may be smaller or larger. Off Highway Vehicles typically have a power weight ratio of less than 10 h.p. per ton with a ratio of 5 h.p. per ton being common. Off Highway Vehicles typically also utilize dynamic or electric braking. This is in contrast to a vehicle such as a passenger bus that has a ratio of 15 h.p. per ton or more and utilizes mechanical or resistive braking.  
      As illustrated in  FIG. 1A , the Off Highway Vehicle  100  includes a diesel primary power source  102  driving an alternator/rectifier  104 . As is generally understood in the art, the alternator/rectifier  104  provides DC electric power to an inverter  106  that converts the AC electric power to a form suitable for use by a traction motor  108 . One common Off Highway Vehicle configuration includes one inverter/traction motor per wheel  109 , with two wheels  109  comprising the equivalent of an axle (not shown). Such a configuration results in one or two inverters per Off Highway Vehicle.  FIG. 1A  illustrates a single inverter  106  and a single traction motor  108  for convenience. By way of example, large excavation dump trucks may employ motorized wheels such as the GEB23™ AC motorized wheel employing the GE150AC™ drive system (both of which are available from the assignee of the present system).  
      Strictly speaking, an inverter converts DC power to AC power. A rectifier converts AC power to DC power. The term “converter” is also sometimes used to refer to inverters and rectifiers. The electrical power supplied in this manner may be referred to as prime mover power (or primary electric power) and the alternator/rectifier  104  may be referred to as a source of prime mover power. In a typical AC diesel-electric Off Highway Vehicle application, the AC electric power from the alternator is first rectified (converted to DC). The rectified AC is thereafter inverted (e.g., using power electronics such as Insulated Gate Bipolar Transistors (IGBTs) or thyristors operating as pulse width modulators) to provide a suitable form of AC power for the respective traction motor  108 .  
      As is understood in the art, traction motors  108  provide the tractive power to move Off Highway Vehicle  100  and any other vehicles, such as load vehicles, attached to Off Highway Vehicle  100 . Such traction motors  108  may be an AC or DC electric motors. When using DC traction motors, the output of the alternator is typically rectified to provide appropriate DC power. When using AC traction motors, the alternator output is typically rectified to DC and thereafter inverted to three-phase AC before being supplied to traction motors  108 .  
      The traction motors  108  also provide a braking force for controlling speed or for slowing Off Highway Vehicle  100 . This is commonly referred to as dynamic braking, and is generally understood in the art. Simply stated, when a traction motor  108  is not needed to provide motivating force, it can be reconfigured (via power switching devices) so that the motor operates as an electric power generator. So configured, the traction motor  108  generates electric energy which has the effect of slowing the Off Highway Vehicle. In prior art Off Highway Vehicles, such as illustrated in  FIG. 1A , the energy generated in the dynamic braking mode is typically transferred to resistance grids  110  mounted on the vehicle housing. Thus, the dynamic braking energy is converted to heat and dissipated from the system. Such electric energy generated in the dynamic braking mode is typically wasted.  
      It should be noted that, in a typical prior art DC hybrid vehicle, the dynamic braking grids  110  are connected to the traction motors  108 . In a typical prior art AC hybrid vehicle, however, the dynamic braking grids are connected to the DC traction bus  122  because each traction motor  108  is normally connected to the bus by way of an associated inverter  106  (see  FIG. 1B ).  FIG. 1A  generally illustrates an AC hybrid vehicle with a plurality of traction motors; a single inverter is depicted for convenience.  
       FIG. 1B  is an electrical schematic of a typical prior art Off Highway Vehicle  100 . It is generally known in the art to employ a single electrical energy source  102 , however, two or more electrical energy sources may be employed. In the case of a single electrical energy source, a diesel engine  102  coupled to an alternator  104  provides the primary source power  104 . In the case where two or more electrical energy sources  102  are provided, a first system comprises the prime mover power system that provides power to the traction motors  108 . A second system (not shown) provides power for so-called auxiliary electrical systems (or simply auxiliaries). Such an auxiliary system may be derived as an output of the alternator, from the DC output, or from a separate alternator driven by the primary power source. For example, in  FIG. 1B , a diesel engine  102  drives the prime mover power source  104  (e.g., an alternator and rectifier), as well as any auxiliary alternators (not illustrated) used to power various auxiliary electrical subsystems such as, for example, lighting, air conditioning/heating, blower drives, radiator fan drives, control battery chargers, field exciters, power steering, pumps, and the like. The auxiliary power system may also receive power from a separate axle driven generator. Auxiliary power may also be derived from the traction alternator of prime mover power source  104 .  
      The output of prime mover power source  104  is connected to a DC bus  122  that supplies DC power to the traction motor subsystems  124 A- 124 B. The DC bus  122  may also be referred to as a traction bus  122  because it carries the power used by the traction motor subsystems. As explained above, a typical prior art diesel-electric Off Highway Vehicle includes two traction motors  108 , one per each wheel  109 , wherein the two wheels  109  operate as an axle assembly, or axle-equivalent. However, a system may be also be configured to include a single traction motor per axle or configured to include four traction motors, one per each wheel  109  of a two axle-equivalent four-wheel vehicle. In  FIG. 1B , each traction motor subsystem  124 A and  124 B comprises an inverter (e.g., inverter  106 A and  106 B) and a corresponding traction motor (e.g., traction motor  108 A and  108 B, respectively).  
      During braking, the power generated by the traction motors  108  is dissipated through a dynamic braking grid subsystem  110 . As illustrated in  FIG. 1B , a typical prior art dynamic braking grid subsystem  110  includes a plurality of contactors (e.g., DB 1 -DB 5 ) for switching a plurality of power resistive elements between the positive and negative rails of the DC bus  122 . Each vertical grouping of resistors may be referred to as a string. One or more power grid cooling blowers (e.g., BL 1  and BL 2 ) are normally used to remove heat generated in a string due to dynamic braking. It is also understood that these contactors (DB 1 -DB 5 ) can be replaced by solid-state switches like GTO/IGBTs and can be modulated (like a chopper) to control the effective dynamic brake resistance.  
      As indicated above, prior art Off Highway Vehicles typically waste the energy generated from dynamic braking. Attempts to make productive use of such energy have been unsatisfactory. For example, one system attempts to use energy generated by a traction motor  108  in connection with an electrolysis cell to generate hydrogen gas as a supplemental fuel source. Among the disadvantages of such a system are the safe storage of the hydrogen gas and the need to carry water for the electrolysis process. Still other prior art systems fail to recapture the dynamic braking energy at all, but rather selectively engage a special generator that operates when the associated vehicle travels downhill. One of the reasons such a system is unsatisfactory is because it fails to recapture existing braking energy and fails to make the captured energy available for reuse on board the Off Highway Vehicle.  
      Therefore, there is a need for an energy management system and method that control when energy is captured and stored, and when such energy is regenerated for later use.  
     SUMMARY OF THE INVENTION  
      In one aspect, the invention relates to an energy management system for use with a hybrid energy off-highway vehicle system. The off highway vehicle system includes a vehicle having a primary energy source and a power converter driven by the primary energy source providing primary electric power. A traction bus is coupled to the power converter and carries the primary electric power. A traction drive is connected to the traction bus and has a motoring mode in which the traction drive is responsive to the primary electric power for propelling the off highway vehicle and a dynamic braking mode of operation wherein said traction drive generates dynamic braking electrical energy. The energy management system includes an energy management processor for determining a power storage parameter and a power transfer parameter. An energy storage system is connected to the traction bus and is responsive to the energy management processor. The energy storage system selectively stores electrical energy available from the traction bus as a function of the power storage parameter and selectively supplying secondary electric power from the stored electrical energy to the traction bus as a function of the power transfer parameter. The traction drive is responsive to the secondary electric power.  
      In another aspect, the invention is an energy management system for use with a hybrid energy off highway vehicle. The off highway vehicle includes a primary energy source and a power converter driven by the primary energy source for providing primary electric power. A traction bus is coupled to the power converter and carries the primary electric power. A traction drive is connected to the traction bus. The traction drive has a motoring mode in which the traction drive is responsive to the primary electric power for propelling the off highway vehicle. The traction drive has a dynamic braking mode of operation wherein said traction drive generates dynamic braking electrical energy. The energy management system includes an energy management processor for determining a power storage parameter and a power transfer parameter. An energy storage system is connected to the traction bus and is responsive to the energy management processor. The energy storage system selectively stores electrical energy as a function of the power storage parameter and selectively supplying secondary electric power from the stored electrical energy to the traction bus as a function of the power transfer parameter.  
      In another aspect, the invention is an energy management method for use with a hybrid energy off highway vehicle system. The off highway vehicle system includes a vehicle having a primary energy source and a power converter driven by the primary energy source to provide primary electric power. A traction bus is coupled to the power converter and carries the primary electric power. A traction drive is connected to the traction bus and has a motoring mode in which the traction drive is responsive to the primary electric power for propelling the off highway vehicle and a dynamic braking mode of operation wherein said traction drive generates dynamic braking electrical energy. The energy management method includes determining a power storage parameter and determining a power transfer parameter. The method further includes storing electrical energy available from the traction bus in an energy storage device connected to the traction bus as a function of the determined power storage parameter; and providing secondary electric power to the traction bus from the electrical energy stored in the energy storage device as a function of the determined power transfer parameter. The traction drive is responsive to the secondary electric power for propelling the off highway vehicle.  
      In yet another aspect of the invention, a hybrid energy system for propelling an off highway vehicle includes a primary energy source and a power converter driven by the primary energy source for providing primary electric power. A traction motor system receives the primary electric power and propels the off highway vehicle in response to the received primary electric power. The traction motor system has a dynamic braking mode of operation generating electrical energy. An energy storage system captures the electrical energy generated by the traction motor system in the dynamic braking mode and transfers a portion of the captured electrical energy to the traction motor system to augment the primary electric power. An energy management system controls the energy storage system. The energy management system determines a power storage parameter and a power transfer parameter whereby the energy management system controls the capture of electrical energy by the energy storage system as a function of the power storage parameter and controls the transfer of the portion of the captured electrical energy to the traction motor system as a function of the power transfer parameter.  
      In still another aspect of the invention, an energy management system for use in connection with a hybrid energy off highway vehicle includes a primary source and a power converter driven by the primary power source for providing primary electric power. A traction motor system receives the primary electric power and selectively propels the off highway vehicle in response to the received primary electric power. The traction motor system has a dynamic braking mode of operation generating dynamic braking electrical power. An energy storage system selectively stores a portion of the dynamic braking electrical power generated by the traction motor system in the dynamic braking mode and selectively supplies secondary electric power derived from the portion of the dynamic braking electrical power stored therein to the traction motor system that is responsive to the secondary electric power. The energy management system comprises an energy management processor that determines a power storage parameter and a power transfer parameter. The energy management processor controls the storage of dynamic braking electrical power by the energy storage system as a function of the power storage parameter. The energy management processor controls the supply of secondary electric power from the energy storage system to the traction motor system as a function of the power transfer parameter.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a block diagram of a prior art Off Highway Vehicle.  
       FIG. 1B  is an electrical schematic of a prior art AC diesel-electric Off Highway Vehicle.  
       FIG. 2  is a block diagram of one embodiment of hybrid energy Off Highway Vehicle system.  
       FIG. 3  is a block diagram of one embodiment of hybrid energy Off Highway Vehicle system configured with a fuel cell and a load vehicle.  
       FIG. 4  is a block diagram illustrating one embodiment of an energy storage and generation system suitable for use in connection with hybrid energy Off Highway Vehicle system.  
       FIG. 5A  is a block diagram illustrating an energy storage and generation system suitable for use in a hybrid energy Off Highway Vehicle system, including an energy management system for controlling the storage and regeneration of energy.  
       FIG. 5B  is a block diagram illustrating the interaction between components of the energy management system, power sources and power loads.  
       FIGS. 6A-6D  are timing diagrams that illustrate one embodiment of an energy management system for controlling the storage and regeneration of energy, including dynamic braking energy.  
       FIGS. 7A-7D  are timing diagrams that illustrate another embodiment energy management system for controlling the storage and regeneration of energy, including dynamic braking energy.  
       FIGS. 8A-8E  are timing diagrams that illustrate another embodiment energy management system for controlling the storage and regeneration of energy, including dynamic braking energy.  
       FIGS. 9A-9G  are electrical schematics illustrating several embodiments of an electrical system suitable for use in connection with a hybrid energy vehicle.  
       FIGS. 10A-10C  are electrical schematics illustrating additional embodiments of an electrical system suitable for use in connection with a hybrid energy vehicle.  
       FIG. 11  is an electrical schematic that illustrates one embodiment of connecting electrical storage elements.  
       FIG. 12  is a flow chart that illustrates one method of operating a hybrid energy Off Highway Vehicle system. 
    
    
      Corresponding reference characters and designations generally indicate corresponding parts throughout the drawings.  
     DETAILED DESCRIPTION OF ASPECTS OF THE INVENTION  
       FIG. 2  is a block diagram of one embodiment of a hybrid energy Off Highway Vehicle system  200 . In this embodiment, the hybrid energy Off Highway Vehicle system preferably captures and regenerates at least a portion of the dynamic braking electric energy generated when the vehicle traction motors operate in a dynamic braking mode.  
      The Off Highway Vehicle system includes an Off Highway Vehicle  200  having a primary energy source  104 . In some embodiments, a power converter is driven by the primary energy source  102  and provides primary electric power. A traction bus  122  is coupled to the power converter and carries the primary electric power. A traction drive  108  is coupled to the traction bus  122 . The traction drive  108  constitutes a vehicle propulsion system mechanically coupled to the wheels  109  of the vehicle  200  and has a motoring mode in which the traction drive is responsive to the primary electric power for propelling the Off Highway Vehicle  200 , in which the traction drive  108  acts as a power load in the motoring mode. The traction drive  108  has a dynamic braking mode of operation wherein the traction drive generates dynamic braking electrical energy and thus acts as a power generator or source in the braking mode. An energy management system  206  comprises an energy management processor (not shown). The energy management system  206  determines a power storage parameter and a power transfer parameter. An energy capture and storage system  204  is responsive to the energy management system  206 . The energy capture and storage system  204  selectively stores electrical energy as a function of the power storage parameter and thus acts as a power load during power storage. The energy capture and storage system  204  selectively supplies secondary electric power from the electrical energy stored therein as a function of the power transfer parameter and thus acts as power generator or source during power discharge when it converts stored mechanical or chemical energy into electrical power.  
      In one embodiment, the energy capture and storage system  204  selectively receives electrical power generated during the dynamic braking mode of operation and stores it for later regeneration and use. In the alternative or in addition to receiving and storing dynamic braking power, energy capture and storage system  204  can also be constructed and arranged to receive and store power from other sources. For example, excess prime mover power from primary energy source  104  can be transferred and stored. Similarly, when two or more Off Highway Vehicles  200  operate in tandem and are electrically coupled, excess power from one of the Off Highway Vehicles can be transferred and stored in energy capture and storage system  204 . Also, a separate primary energy source  102  (e.g., diesel generator, fuel cell, trolley line, etc.) can be used to supply a charging voltage (e.g., a constant charging voltage) to energy capture and storage system  204 . Still another source of charging is an optional off-vehicle charging source  220 . For example, energy capture and storage system  204  can be charged by external charging generator or source  220  such as a battery charger. The hybrid vehicle  200  may also be operated so that at the completion of a leg of its travel path, energy will remain stored in the energy storage system  204  and thus be available for transfer to a suitable external power load  224  such as other vehicles (e.g., pushers to help propel another train), or to an external energy system (not shown), such as an electric grid via electrical interface connection to the vehicle&#39;s electrical system, a third rail or an overhead power line.  
      The energy capture and storage system  204  preferably includes at least one of the following storage subsystems for storing the electrical energy generated during the dynamic braking mode: a battery subsystem, a flywheel subsystem, an ultra-capacitor subsystem, and a fuel cell fuel generator (not shown). Other storage subsystems are possible. Ultra-capacitors are available from Maxwell Technologies. These storage subsystems may be used separately or in combination. When used in combination, these storage subsystems can provide synergistic benefits not realized with the use of a single energy storage subsystem. A flywheel subsystem, for example, typically stores energy relatively fast but may be relatively limited in its total energy storage capacity. A battery subsystem, on the other hand, often stores energy relatively slowly but can be constructed to provide a relatively large total storage capacity. Hence, a flywheel subsystem may be combined with a battery subsystem wherein the flywheel subsystem captures the dynamic braking energy that cannot be timely captured by the battery subsystem. The energy thus stored in the flywheel subsystem may be thereafter used to charge the battery. Accordingly, the overall capture and storage capabilities are preferably extended beyond the limits of either a flywheel subsystem or a battery subsystem operating alone. Such synergies can be extended to combinations of other storage subsystems, such as a battery and ultra-capacitor in combination where the ultra-capacitor supplies the peak demand needs. In the case where the primary energy source  102  is a fuel cell, the energy capture and storage system  204  may include an electrolysis system that generates hydrogen from the fuel cell wastewater. The stored hydrogen is provided to the fuel cell as an energy source for providing primary or secondary power.  
      It should be noted at this point that, when a flywheel subsystem is used, a plurality of flywheels is preferably arranged to limit or eliminate the gyroscopic effect each flywheel might otherwise have on the Off Highway Vehicle and load vehicles. For example, the plurality of flywheels may be arranged on a six-axis basis to greatly reduce or eliminate gyroscopic effects. It should be understood, however, that reference herein to a flywheel embraces a single flywheel or a plurality of flywheels.  
      Referring still to  FIG. 2 , energy capture and storage system  204  not only captures and stores electric energy generated in the dynamic braking mode of the Off Highway Vehicle, it also supplies the stored energy to assist the Off Highway Vehicle effort (i.e., to supplement and/or replace primary energy source power).  
      It should be understood that it is common for each Off Highway Vehicle  200  to operate separately from other Off Highway Vehicles. However, two or more Off Highway Vehicles could operate in tandem where they are mechanically and/or electrically coupled to operate together. Furthermore, another optional arrangement includes an Off Highway Vehicle that is mechanically coupled to a load vehicle. While  FIG. 2  illustrates a single Off Highway Vehicle,  FIG. 3  illustrates an Off Highway Vehicle  200  operating in a tandem arrangement with optional load vehicle  300 . Load vehicle  300  may be a passive vehicle that is pulled or pushed by the Off Highway Vehicle  200  or optionally may include a plurality of load vehicle traction motors  308  that provide tractive effort to load vehicle wheels  318 . The electrical power stored in energy capture and storage  204  may be selectively supplied (e.g., via tandem traction bus  314 ) to the load vehicle traction motors  308  via load vehicle traction bus  312 . Thus, during times of increased demand, load vehicle traction motors  308  augment the tractive power provided by Off Highway Vehicle traction motors  108 . As another example, during times when it is not possible to store more energy from dynamic braking (e.g., energy storage system  204  is charged to capacity), efficiency considerations may suggest that load vehicle traction motors  308  also augment Off Highway Vehicle traction motors  108 .  
      It should be appreciated that when energy capture and storage system  204  drives load vehicle traction motors  308 , additional circuitry will likely be required. For example, if energy capture and storage system  204  comprises a battery storing and providing a DC voltage, one or more inverter drives  106  may be used to convert the DC voltage to a form suitable for use by the load vehicle traction motors  308 . Such drives are preferably operationally similar to those associated with the Off Highway Vehicle.  
      Rather than, or in addition to, using the electrical power stored in energy capture and storage  204  for powering load vehicle traction motors  308 , such stored energy may also be used to augment the electrical power supplied to Off Highway Vehicle traction motors  108  (e.g., via line  212 ).  
      Other configurations are also possible. For example, the Off Highway Vehicle itself may be configured, either during manufacturing or as part of a retrofit program, to capture, store, and regenerate excess electrical energy, such as dynamic braking energy, excess primary energy source power or excess trolley line power. In another embodiment, an energy capture and storage subsystem  306  may be located on some or all of the load vehicles attached to the Off Highway Vehicle.  FIG. 3  illustrates a load vehicle  300  equipped with a load vehicle energy capture and storage system  306  which receives load vehicle dynamic braking power from load vehicle traction motor  308  via bus  312  during dynamic braking. Such a load vehicle  300  may optionally include separate traction motors  308 . In each of the foregoing embodiments, the load vehicle energy capture and storage subsystem  306  can include one or more of the subsystems previously described.  
      When a separate load vehicle  300  is used, the load vehicle  300  and the Off Highway Vehicle  200  are preferably mechanically coupled via mechanical linkage  316  and electrically coupled via tandem traction bus  314  such that dynamic braking energy from the Off Highway Vehicle traction motors  108  and/or from optional load vehicle traction motors  308  is stored in energy capture and storage system  206  on board the Off Highway Vehicle and/or is stored in load vehicle capture and storage system  306  on the load vehicle  300 . During motoring operations, the stored energy in the energy capture and storage system in one or the other or both the Off Highway Vehicle  200  and the load vehicle  300  is selectively used to propel Off Highway Vehicle traction motors  108  and/or optional load vehicle traction motors  308 . Similarly, when the Off Highway Vehicle primary power source  102  produces more power than required for motoring, the excess prime mover power can be stored in energy capture and storage  204  and or load vehicle energy capture and storage  306  for later use.  
      If load vehicle  300  is not electrically coupled to the Off Highway Vehicle (other than for standard control signals), the optional traction motors  308  on the load vehicle  300  can also be used in an autonomous fashion to provide dynamic braking energy to be stored in energy capture and storage  306  for later use. One advantage of such a configuration is that load vehicle  202  can be coupled to a wide variety of Off Highway Vehicles.  
      It should be appreciated that when load vehicle traction motors  308  operate in a dynamic braking mode, various reasons may counsel against storing the dynamic braking energy in energy capture and storage  204  and/or  306  (e.g., the storage may be full). Thus, it is preferable that some or all of the dynamic braking energy generated by the load vehicle traction motors  308  be dissipated by grids  310  associated with load vehicle  300 , or transferred to Off Highway Vehicle  200  to be dissipated by grids  110  (e.g., via tandem traction bus  316 ).  
      It should also be appreciated that load vehicle energy capture and storage system  306  may be charged from an external charging source  326  when such a charging source is available.  
      The embodiment of  FIG. 3  will be further described in terms of one possible operational example. It is to be understood that this operational example does not limit the invention. The Off Highway Vehicle system  200  is configured in tandem including an Off Highway Vehicle  200  and a load vehicle  300 . Tractive power for the Off Highway Vehicle  200  is supplied by a plurality of Off Highway Vehicle traction motors  108 . In one embodiment, the Off Highway Vehicle  200  has four wheels  109 , each pair corresponds to an axle pair as depicted as an optional embodiment of  FIG. 3  as  109 A and  109 B. Each wheel  109 A and  109 B includes a separate Off Highway Vehicle traction motor  108 A and  108 B, and each traction motor  108 A and  108 B is an AC traction motor. In one embodiment, each of the two rear wheels  109 A has a separate Off Highway Vehicle traction motor  108 A and operates as pair of wheels  109 A on a common axle, or axle-equivalent (illustrated as a single wheel  109 A in  FIG. 3 ). However, the wheels  109 A may or may not be actually connected by a common axle, as such an axle-equivalent. In fact, in one embodiment, each wheel  109  is mount by a separate half-axle. The Off Highway Vehicle  200  includes a primary energy source  102  that drives an electrical power system. In one embodiment, the primary energy source is a diesel engine drives an alternator/rectifier  104  that comprises a source of prime mover electrical power (sometimes referred to as traction power or primary power). In this particular embodiment, the prime mover electrical power is DC power that is converted to AC power for use by the traction motors. More specifically, one or more inverters (e.g., inverter  106 ) receive the prime mover electrical power and selectively supply AC power to the plurality of Off Highway Vehicle traction motors  108  to propel the Off Highway Vehicle. In another embodiment, the primary energy source  102  is a fuel cell. The fuel cell generates DC prime mover power and selectively supplies the DC primary mover power to a DC-to-DC converter  302  as shown in  FIG. 3 . In yet another embodiment, the Off Highway Vehicle  200  may utilize a trolley line (not shown) as the primary energy source, or as a secondary energy source that supplements the primary energy source when the Off Highway Vehicle is traversing an inclined travel path, e.g., trolley assist. Thus, Off Highway Vehicle traction motors  108  propel the Off Highway Vehicle in response to the prime mover electrical power.  
      Each of the plurality of Off Highway Vehicle traction motors  108  is preferably operable in at least two operating modes, a motoring mode and a dynamic braking mode. In the motoring mode, the Off Highway Vehicle traction motors  108  receive electrical power (e.g., prime mover electrical power via inverters) to propel the Off Highway Vehicle  200 . As described elsewhere herein, when operating in the dynamic braking mode, the traction motors  108  generate electricity. In the embodiment of  FIG. 3 , load vehicle  300  is constructed and arranged to selectively capture and store a portion of the electricity generated by the traction motors  308  and/or  108  during dynamic braking operations. This is accomplished by energy capture and storage system  204  and/or  306 . The captured and stored electricity is selectively used to provide a secondary source of electric power. This secondary source of electric power may be used to selectively supplement or replace the prime mover electrical power (e.g., to help drive one or more Off Highway Vehicle traction motors  108 ) and/or to drive one or more load vehicle traction motors  308 . In the latter case, load vehicle traction motors  308  and Off Highway Vehicle traction motors  108  cooperate to propel the tandem Off Highway Vehicle  200  and load vehicle  300 .  
      Advantageously, load vehicle energy capture and storage  306  can store dynamic braking energy without any electrical power transfer connection with the primary Off Highway Vehicle. In other words, energy capture and storage  306  can be charged without an electrical coupling such as tandem traction bus  314 . This is accomplished by operating the Off Highway Vehicle primary power source  320  to provide motoring power to Off Highway Vehicle traction motors  308  while operating load vehicle  300  in a dynamic braking mode. For example, the Off Highway Vehicle primary power source  102  may be operated at a relatively high power setting while load vehicle traction motors  308  are configured for dynamic braking. Energy from the dynamic braking process can be used to charge energy capture and storage  306 . Thereafter, the stored energy can be used to power load vehicle traction motors  308  to provide additional motoring power to the tandem Off Highway Vehicle  200  and load vehicle  300 .  
      Referring again to  FIG. 3  is another optional embodiment of hybrid energy Off Highway Vehicle system  300  configured with a fuel cell with a separate load vehicle. This embodiment includes a fuel cell as primary power source  102  that drives DC-to-DC converter  302 . Converter  302  provides DC power to inverter that provides primary tractive power. In another embodiment, where the traction motor  108  is a DC traction motor, the converter may provide tractive DC power directly to the DC traction motor  108  via traction bus  112 .  
      Referring again to  FIG. 3 , another optional embodiment includes a load vehicle configured with a load vehicle power source  320 . Load vehicle power source could be any type of power source as described above for the Off Highway Vehicle  200 . In one embodiment, load vehicle power source  320  is a fuel cell that generates a constant source of DC electrical energy. The DC electrical energy that is generated by the fuel cell is converted by a DC-to-DC converter  322  and provided to an Inverter  324  for the provision of load vehicle primary power. In this embodiment, load vehicle primary power may be provided by load vehicle bus  312  to the load vehicle traction motor  308 , to the Off Highway Vehicle traction motors  108 , to load vehicle energy capture and storage system  306 , or to Off Highway Vehicle energy capture and storage system  204 . In this embodiment, the load vehicle power source  320 , the power converter  322 , the converter  324  and/or the load vehicle energy capture and storage system  306  may be operable in response to a load vehicle energy management system (not shown) or to the energy management system  206  of the coupled Off Highway Vehicle via a energy management communication link  328 . Such an energy management communication link  328  may be a wired communication link or a wireless communication link.  
       FIG. 4  is a system-level block diagram that illustrates aspects of one embodiment of the energy storage and generation system. In particular,  FIG. 4  illustrates an energy storage and generation system  400  suitable for use with a hybrid energy Off Highway Vehicle system, such as hybrid energy Off Highway Vehicle system  200  or load vehicle system  300  ( FIG. 3 ). Such an energy storage and generation system  400  could be implemented, for example, as part of a separate load vehicle (e.g.,  FIGS. 2 and 3 ) and/or incorporated into an Off Highway Vehicle.  
      As illustrated in  FIG. 4 , a primary energy source  102  drives a prime mover power source  104  (e.g., an alternator/rectifier converter). The prime mover power source  104  preferably supplies DC power to an inverter  106  that provides three-phase AC power to a Off Highway Vehicle traction motor  108 . It should be understood, however, that the system  400  illustrated in  FIG. 4  can be modified to operate with DC traction motors as well. Preferably, there is a plurality of traction motors  108 , e.g., one per traction wheel  109 . In other words, each Off Highway Vehicle traction motor preferably includes a rotatable shaft coupled to the associated wheel  109  for providing tractive power to the associated wheel  109 . Thus, each Off Highway Vehicle traction motor  108  provides the necessary motoring force to an associated wheel  109  to cause the Off Highway Vehicle  200  to move. One arrangement includes a single wheel  109  on the Off Highway Vehicle to be equipped with a single traction motor  108 . Another embodiment is for two wheels  109  on opposing sides of the vehicle acting as an axle-equivalent, each equipped with a separate traction motor  108 .  
      When traction motors  108  are operated in a dynamic braking mode, at least a portion of the generated electrical power is routed to an energy storage medium such as energy storage  204 . To the extent that energy storage  204  is unable to receive and/or store all of the dynamic braking energy, the excess energy is routed to braking grids  110  for dissipation as heat energy. Also, during periods when primary power source  102  is being operated such that it provides more energy than needed to drive traction motors  108 , the excess capacity (also referred to as excess prime mover electric power) may be optionally stored in energy storage  204 . Accordingly, energy storage  204  can be charged at times other than when traction motors  108  are operating in the dynamic braking mode. This aspect of the system is illustrated in  FIG. 4  by a dashed line  402 .  
      The energy storage  204  of  FIG. 4  is preferably constructed and arranged to selectively augment the power provided to traction motors  108  or, optionally, to power separate traction motors  308  associated the load vehicle  300 . Such power may be referred to as secondary electric power and is derived from the electrical energy stored in energy storage  204 . Thus, the system  400  illustrated in  FIG. 4  is suitable for use in connection with an Off Highway Vehicle having an on-board energy capture and storage  204  and/or with a separate load vehicle  300  equipped with a load vehicle energy capture and storage  306 .  
       FIG. 5A  is a block diagram that illustrates aspects of one embodiment of an energy storage and generation system  500  suitable for use with a hybrid energy Off Highway Vehicle system. The system  500  includes an energy management system  206  for controlling the storage and regeneration of energy. Therefore, although  FIG. 5A  is generally described with respect to an Off Highway Vehicle system, the energy management system  500  illustrated therein is not to be considered as limited to Off Highway Vehicle applications.  
      Referring still to the exemplary embodiment illustrated in  FIG. 5A , system  500  preferably operates in the same general manner as system  400  of  FIG. 4 ; the energy management system  206  provides additional intelligent control functions.  FIG. 5A  also illustrates an optional energy source  504  that is preferably controlled by the energy management system  206 . The optional energy source  504  may be a second energy source (e.g., another Off Highway Vehicle operating in tandem with the primary Off Highway Vehicle) or a completely separate power source (e.g., trolley line, or a wayside power source such as a battery charger) for charging energy storage  204 . In one embodiment, such a separate charging power source includes an electrical power station for charging an energy storage medium associated with a separate load vehicle (e.g., vehicle  202  of  FIG. 2 ) while stationary, or a system for charging the energy storage medium while the load vehicle is in motion. In one embodiment, optional energy source  504  is connected to a traction bus (not illustrated in  FIG. 5 ) that also carries primary electric power from prime mover power source  104 .  
      As illustrated, the energy management system  206  preferably includes an energy management processor  506 , a database  508 , and a position identification system  510 , such as, for example, a global positioning satellite system receiver (GPS)  510 . The energy management processor  506  determines present and anticipated Off Highway Vehicle position information via the position identification system  510 . In one embodiment, energy management processor  506  uses this position information to locate data in the database  508  regarding present and/or anticipated travel path topographic and profile conditions, sometimes referred to as travel path situation information. Such travel path situation information may include, for example, travel path grade, travel path elevation (e.g., height above mean sea level), travel path curve data, speed limit information, and the like. In the case of a locomotive off highway vehicle, the travel path and characteristics are those of a railroad track. It is to be understood that such database information could be provided by a variety of sources including: an onboard database associated with processor  510 , a communication system (e.g., a wireless communication system) providing the information from a central source, manual operator input(s), via one or more travel path signaling devices, a combination of such sources, and the like. Finally, other vehicle information such as, the size and weight of the vehicle, a power capacity associated with the prime mover, efficiency ratings, present and anticipated speed, present and anticipated electrical load, and so on may also be included in a database (or supplied in real or near real time) and used by energy management processor  506 .  
      It should be appreciated that, in an alternative embodiment, energy management system  206  could be configured to determine power storage and transfer requirements associated with energy storage  204  in a static fashion. For example, energy management processor  506  could be preprogrammed with any of the above information, or could use look-up tables based on past operating experience (e.g., when the vehicle reaches a certain point, it is nearly always necessary to store additional energy to meet an upcoming demand). Such a program may be based on historical information of the preferred mode of power operation of the vehicle  200  (i.e., the amount of power to be generated, regenerated, stored or discharged from storage) at any point or location of the vehicle  200  along its travel path. The position of the vehicle  200  may be determined by conventional techniques, such as a GPS system  510  and track maps stored in a memory (e.g., database  508 ) on the vehicle  200 , AEI tag readers, vehicle heading and inclination for mining dump trucks, mileposts and other markers along the travel path. In other words, the energy management processor  506  identifies the energy storage and discharge activities of the electrical energy capture system  204  based on the anticipated future power load and power generation for the vehicle  200  (which includes at least one hybrid, electro-motive vehicle), and controls the transmission of electrical power among the primary electric power generator  102 , the vehicle propulsion system (e.g., traction motors  108 ), the electric energy capture system  204 , and the dynamic braking grid circuit  110  during the operation of the vehicle  200  to perform the identified energy storage and discharge activities.  
      Referring briefly to  FIG. 5B , a block diagram further illustrates the interaction between the energy management processor  506 , database  508 , power sources  510  and power loads  512 . Power sources  510  include, for example, the primary power source (e.g., primary power generator  102 ), on board auxiliary power (e.g. auxiliary power drive  904  such as shown  FIG. 9A ), external optional power (e.g., additional energy source  504 ), on-vehicle propulsion system (e.g., traction motors  108 ), the electric energy capture system  204 . Power loads include, for example, the dynamic braking grid circuit  110 , on-board auxiliary loads  524  (e.g., fans, blowers, and external loads (e.g.  224 ). In this embodiment, the database  508  stores vehicle operating data  530 , physical vehicle characteristics data  532 , and present real-time operating data  534 . Anticipated train data  530  includes data such as schedule/vehicle speed and upcoming track information (e.g., topography, elevation, curvature). Physical vehicle characteristics data  532  includes vehicle weight, power capacity, speed limit, energy storage capacity, and charge/discharge rates of the energy capture system  204 . Present real-time operating data  534  includes current speed, current location, current energy needs, and energy storage status. In addition, improved train performance data  536  may be supplied to the energy management processor  506  via operator input, a central command, or may also be included in the database  508 . Improved train performance data  536  includes information such as a target fuel efficiency, target power usage, power availability, a speed required to meet a schedule, and target noise and/or exhaust emissions. The energy management processor  506  is responsive to operating data and the improved performance data  536  to calculate an expected power load that will be experienced by the vehicle  200  when traveling on an upcoming section of the track, or path, and calculates the amount of power to generate to satisfy the expected load. Thereafter, the energy management processor  506  controls the transmission of electrical power among the primary electric power generator  102 , the vehicle propulsion system  108 , the electric energy capture system  204  and the dynamic braking grid circuit  110  in response to the calculated power load so as to enhance the performance of the vehicle  200  over its future anticipated route.  
      In a further embodiment, the energy management processor  506  comprises a first processor module  513  for identifying the energy storage and discharge activities of the electrical energy capture system  204  based on the anticipated future power load and power generation for the vehicle (which includes at least one hybrid, electromotive, self-powered railroad locomotive) for optimizing a train or vehicle performance parameter. The energy management system  206  further comprises a second processor module  514  on the vehicle  200  for controlling transmission of electrical power among the primary electric power generator  102 , the vehicle propulsion system (e.g., traction motors  108 ), the electric energy capture system  204 , and the dynamic braking grid circuit  110  during the operation of the vehicle  200  to perform the energy storage activities. The energy storage and discharge activities of the electrical energy capture system  204  comprise charging the storage devices (e.g., battery, flywheel, etc.) at a selected time, controlling the rate at which such charging should occur, discharging from the storage devices at a selected time, and controlling the rate at which such discharge should occur. The vehicle performance parameters comprise fuel consumption of the vehicle  200 , noise emissions from the vehicle  200  (such as the noise generated by the engine and the noise generated by the dynamic braking grid  110  cooling fans), rates of engine emissions of the train/vehicle at locations along the travel path, overall engine emissions of the vehicle  200  along the travel path and power consumption of the vehicle  200  over the travel path. The anticipated future power load and power generation for the vehicle  200  is a function of the location of the vehicle  200 , the topography of the track, the weight or load of the vehicle  200 , wind resistance, track or road conditions, available primary power generation on the vehicle  200  (i.e., principally the number of locomotives in a train), speed limits on the travel of the vehicle  200 , and vehicle  200  acceleration requirements. The operation of off-highway hybrid vehicles  200  that serve as mining dump trucks is similar to that described for a vehicle  200  having at least one hybrid locomotive, but with the travel path being along a road and each hybrid vehicle operating alone.  
      The first and second processor modules  513 ,  514  may be located at spaced locations and may communicate to each other either directly for automated operation, and indeed may be performed by the same processing device (e.g., a single energy management processor  506 ) or indirectly via a vehicle operator for advisory operation of the vehicle  200 . In addition, the first processor module  513  may be located off-board the vehicle  200  for directly or indirectly indicating the energy storage and discharge activities and thus controlling the second processor module  514  from an off-board location. This remote control may take the form of a control signal, as indicated by arrow  516 , to the second processor module  514  on the vehicle  200  from a dispatch center directing the second processor module  514  to change the energy storage and discharge activities of the vehicle  200 , such as when the dispatch center determines that the vehicle  200  has reached a predetermined location along its route. Alternatively, equipment alongside the route may communicate with the vehicle  200  to change the energy storage and discharge activities when the vehicle is adjacent such equipment.  
      The vehicle operator may also be advised to change the energy storage and discharge activities by instructions or other indicia from a dispatch center displayed at the operator&#39;s cab or otherwise communicated to the operator via an interface. For example, a display (not shown) such as a computer monitor is responsive to control signal  516  to advise the operator how to change the energy storage and discharge activities of the vehicle  200 . Such operator advice may take the form of instructions as to vehicle motoring, dynamic braking, air brake application and a mixture of air brake and dynamic brake as well as a mixture based on the status of energy storage, the location of the vehicle  200  or the status of the charge of the energy storage device.  
      On routine runs of the vehicle  200 , the operator may initiate energy storage and discharge operations based on his own knowledge of the trajectory of the route and vehicle conditions. The initiation may be executed via manual inputs to the second processor module  514  of the energy management processor  506  for either the storage or discharge of power. In a basic form of the present inventions, the vehicle operator may issue a command to the second processor module  514  or to a switch for enabling or disabling the energy capture system  204 . If the system is enabled, the operator may further elect between charging or discharging modes, and the rate at which such charging and discharging are to be performed. The operator&#39;s actions may be based on the operator&#39;s knowledge or experience as to the preferred energy storage system  204  charging and discharging activities in light of the anticipated train/vehicle operations either in terms of its future travel path or its future standby operations, as described hereinafter.  
      In any of these various techniques of anticipating the future power demands on the vehicle  200  (i.e., real-time determination, preprogrammed, remotely controlled or manual control), the condition of the track or road, as described above, may be taken into consideration in determining when to change the energy storage and discharge activities. With a railroad vehicle, wet or snowy conditions will reduce traction and impact the tractive effort of the traction motors and the amount of power regeneration. With an off-highway truck, wet or snowy route conditions, will typically slow travel of the truck.  
      The energy management processor  506  preferably uses the present and/or upcoming travel path situation information, along with Off Highway Vehicle status information, to determine power storage and power transfer requirements. Energy management processor  506  also determines possible energy storage opportunities based on the present and future travel path situation information. For example, based on the travel path profile information, energy management processor  506  may determine that it is more efficient to completely use all of the stored energy, even though present demand is low, because a dynamic braking region is coming up (or because the Off Highway Vehicle is behind schedule and is attempting to make up time). In this way, the energy management system  206  improves efficiency by accounting for the stored energy before the next charging region is encountered. As another example, energy management processor  506  may determine not to use stored energy, despite present demand, if a heavier demand is soon to be encountered in the travel path.  
      Advantageously, energy management system  206  may also be configured to interface with primary energy source controls. Also, as illustrated in  FIG. 5 , energy storage  204  may be configured to provide an intelligent control interface with energy management system  206 .  
      In operation, energy management processor  506  determines a power storage requirement and a power transfer requirement. Energy storage  204  stores electrical energy in response to the power storage requirement. Energy storage  204  provides secondary electric power (e.g. to a traction bus connected to inverters  106  to assist in motoring) in response to the power transfer requirement. The secondary electric power is derived from the electrical energy stored in energy storage  204 .  
      As explained above, energy management processor  506  preferably determines the power storage requirement based, in part, on a situation parameter indicative of a present and/or anticipated travel path topographic characteristic. Energy management processor  506  may also determine the power storage requirement as a function of an amount of primary electric power available from the prime mover power source  104 . Similarly, energy management processor  506  may determine the power storage requirement as function of a present or anticipated amount of primary electric power required to propel the Off Highway Vehicle.  
      Also, in determining the energy storage requirement, energy management processor  506  preferably considers various parameters related to energy storage  204 . For example, energy storage  204  will have a storage capacity that is indicative of the amount of power that can be stored therein and/or the amount of power that can be transferred to energy storage  204  at any given time. Another similar parameter relates to the amount of secondary electric power that energy storage  204  has available for transfer at a particular time.  
      As explained above, system  500  preferably includes a plurality of sources for charging energy storage  204 . These sources include dynamic braking power, excess prime mover electric power, and external charging electric power. Preferably, energy management processor  506  determines which of these sources should charge energy storage  204 . In one embodiment, present or anticipated dynamic braking energy is used to charge energy storage  204 , if such dynamic braking energy is available. If dynamic braking energy is not available, either excess prime mover electric power or external charging electric power is used to charge energy storage  204 .  
      In the embodiment of  FIG. 5 , energy management processor  506  preferably determines the power transfer requirement as a function of a demand for power. In other words, energy storage  204  preferably does not supply secondary electric power unless traction motors  108  are operating in a power consumption mode (i.e., a motoring mode, as opposed to a dynamic braking mode). In one form, energy management processor  506  permits energy storage  204  to supply secondary electric power to inverters  106  until either (a) the demand for power terminates or (b) energy storage  204  is completely depleted. In another form, however, energy management processor  506  considers anticipated power demands and controls the supply of secondary electric power from energy storage  204  such that sufficient reserve power remains in energy storage  204  to augment prime mover power source during peak demand periods. This may be referred to as a “look-ahead” energy management scheme.  
      In the look-ahead energy management scheme, energy management processor  506  preferably considers various present and/or anticipated travel path situation parameters, such as those discussed above. In addition, energy management processor may also consider the amount of power stored in energy storage  204 , anticipated charging opportunities, and any limitations on the ability to transfer secondary electric power from energy storage  204  to inverters  106 .  
      FIGS.  6 A-D,  7 A-D, and  8 A-E illustrate, in graphic form, aspects of three different embodiments of energy management systems, suitable for use with a hybrid energy vehicle, that could be implemented in a system such as system  500  of  FIG. 5 . It should be appreciated that these figures are provided for exemplary purposes and that, with the benefit of the present disclosure, other variations are possible. It should also be appreciated that the values illustrated in these figures are included to facilitate a detailed description and should not be considered in a limiting sense. It should be further understood that, the examples illustrated in these figures relate to a variety of large Off Highway Vehicles, including locomotives, excavators and mine trucks and which are generally capable of storing the electric energy generated during the operation of such vehicles. Some of these vehicles travel a known, repetitive or predictable course during operation. For example, a locomotive travels a known travel path, e.g., the railroad track. Such Off Highway Vehicles include vehicles using DC and AC traction motor drives and having dynamic braking/retarding capabilities.  
      There are four similar charts in each group of figures (FIGS.  6 A-D, FIGS.  7 A-D, and FIGS.  8 A-D). The first chart in each group (i.e.,  FIGS. 6A, 7A , and  8 A) illustrates the required power for both motoring and braking. Thus, the first chart graphically depicts the amount of power required by the vehicle. Positive values on the vertical axis represent motoring power (horsepower); negative values represent dynamic braking power. It should be understood that motoring power could originate with the prime mover (e.g., diesel engine, fuel cell or other primary energy source), or from stored energy (e.g., in an energy storage medium in a separate vehicle), or from a combination of the prime mover and stored energy. Dynamic braking power could be dissipated or stored in the energy storage medium.  
      The horizontal axis in all charts reflects time in minutes. The time basis for each chart in a given figure group are intended to be the same. It should be understood, however, that other reference bases are possible.  
      The second chart in each group of figures (i.e.,  FIGS. 6B, 7B , and  8 B) reflects theoretical power storage and consumption. Positive values reflect the amount of power that, if power were available in the energy storage medium, could be drawn to assist in motoring. Negative values reflect the amount of power that, if storage space remains in the energy storage medium, could be stored in the medium. The amount of power that could be stored or drawn is partially a function of the converter and storage capabilities of a given vehicle configuration. For example, the energy storage medium will have some maximum/finite capacity. Further, the speed at which the storage medium is able to accept or supply energy is also limited (e.g., batteries typically charge slower than flywheel devices). Other variables also affect energy storage. These variables include, for example, ambient temperature, the size and length of any interconnect cabling, current and voltage limits on dc-to-dc converters used for battery charging, power ratings for an inverter for a flywheel drive, the charging and discharging rates of a battery, or a motor/shaft limit for a flywheel drive. The second chart assumes that the maximum amount of power that could be transferred to or from the energy storage medium at a given time is 500 h.p. Again, it should be understood that this 500 h.p. limit is included for exemplary purposes. Hence, the positive and negative limits in any given system could vary as a function of ambient conditions, the state and type of the energy storage medium, the type and limits of energy conversion equipment used, and the like.  
      The third chart in each figure group (i.e.,  FIGS. 6C, 7C , and  8 C) depicts a power transfer associated with the energy storage medium. In particular, the third chart illustrates the actual power being transferred to and from the energy storage medium versus time. The third chart reflects limitations due to the power available for storage, and limitations due to the present state of charge/storage of the energy storage medium (e.g., the speed of the flywheel, the voltage in an ultra-capacitor, the charge in the battery, and the like).  
      The fourth chart in each figure group (i.e.,  FIGS. 6D, 7D , and  8 D) depicts actual energy stored. In particular, the fourth chart illustrates the energy stored in the energy storage medium at any particular instant in time.  
      Referring first to FIGS.  6 A-D, these figures reflect an energy management system that stores energy at the maximum rate possible during dynamic braking until the energy storage medium is completely full. In this embodiment, all energy transfers to the storage medium occur during dynamic braking. In other words, in the embodiment reflected in FIGS.  6 A-D, no energy is transferred to the energy storage medium from excess prime mover power available during motoring, or from other energy sources. Similarly, energy is discharged, up to the maximum rate, whenever there is a motor demand (limited to and not exceeding the actual demand) until the energy storage medium is completely discharged/empty. FIGS.  6 A-D assume that the energy storage medium is completely discharged/empty at time 0.  
      Referring now specifically to  FIG. 6A , as mentioned above, the exemplary curve identified therein illustrates the power required (utilized) for motoring and dynamic braking. Positive units of power reflect when motoring power is being applied to the wheels  109  of the vehicle (e.g., one or more traction motors are driving Off Highway Vehicle wheels). Negative units of power reflect power generated by dynamic braking.  
       FIG. 6B  is an exemplary curve that reflects power transfer limits. Positive values reflect the amount of stored energy that would be used to assist in the motoring effort, if such energy were available. Negative units reflect the amount of dynamic braking energy that could be stored in the energy storage medium if the medium were able to accept the full charge available. In the example of  FIG. 6B , the energy available for storage at any given time is illustrated as being limited to 500 units (e.g., horsepower). As explained above, a variety of factors limit the amount of power that can be captured and transferred. Thus, from about 0 to 30 minutes, the Off Highway Vehicle requires less than 500 h.p. If stored energy were available, it could be used to provide all of the motoring power. From about 30 minutes to about 65 or 70 minutes, the Off Highway Vehicle requires more than 500 h.p. Thus, if stored energy were available, it could supply some (e.g., 500 h.p.) but not all of the motoring power. From about 70 minutes to about 75 minutes or so, the Off Highway Vehicle is in a dynamic braking mode and generates less than 500 h.p. of dynamic braking energy. Thus, up to 500 h.p. of energy could be transferred to the energy storage medium, if the medium retained sufficient capacity to store the energy. At about 75 minutes, the dynamic braking process generates in excess of 500 h.p. Because of power transfer limits, only up to 500 h.p. could be transferred to the energy storage medium (again, assuming that storage capacity remains); the excess power would be dissipated in the braking grids. It should be understood that  FIG. 6B  does not reflect the actual amount of energy transferred to or from the energy storage medium. That information is depicted in  FIG. 6C .  
       FIG. 6C  is reflects the power transfer to/from the energy storage medium at any given instant of time. The example shown therein assumes that the energy storage medium is completely empty at time 0. Therefore, the system cannot transfer any power from the storage at this time. During a first time period A (from approximately 0-70 minutes), the vehicle is motoring (see  FIG. 6A ) and no power is transferred to or from the energy storage. At the end of the first time period A, and for almost 30 minutes thereafter, the vehicle enters a dynamic braking phase (see  FIG. 6A ). During this time, power from the dynamic braking process is available for storage (see  FIG. 6B ).  
      During a second time period B (from approximately 70-80 minutes), dynamic braking energy is transferred to the energy storage medium at the maximum rate (e.g., 500 units) until the storage is full. During this time there is no motoring demand to deplete the stored energy. Thereafter, during a third time period C (from approximately 80-105 minutes) the storage is full. Consequently, even though the vehicle remains in the dynamic braking mode or is coasting (see  FIG. 6A ), no energy is transferred to or from the energy storage medium during time period C.  
      During a fourth time period D (from approximately 105-120 minutes), the vehicle resumes motoring. Because energy is available in the energy storage medium, energy is drawn from the storage and used to assist the motoring process. Hence, the curve illustrates that energy is being drawn from the energy storage medium during the fourth time period D.  
      At approximately 120 minutes, the motoring phase ceases and, shortly thereafter, another dynamic braking phase begins. This dynamic braking phase reflects the start of a fifth time period E that lasts from approximately 125-145 minutes. As can be appreciated by viewing the curve during the fifth time period E, when the dynamic braking phase ends, the energy storage medium is not completely charged.  
      Shortly before the 150-minute point, a sixth time period F begins which lasts from approximately 150-170 minutes. During this time period and thereafter (see  FIG. 6A ), the vehicle is motoring. From approximately 150-170 minutes, energy is transferred from the energy storage medium to assist in the motoring process. At approximately 170 minutes, however, the energy storage is completely depleted. Accordingly, from approximately 170-200 minutes (the end of the sample window), no energy is transferred to or from the energy storage medium.  
       FIG. 6D  illustrates the energy stored in the energy storage medium of the exemplary embodiment reflected in FIGS.  6 A-D. Recall that in the present example, the energy storage medium is assumed to be completely empty/discharged at time 0. Recall also that the present example assumes an energy management system that only stores energy from dynamic braking. From approximately 0-70 minutes, the vehicle is motoring and no energy is transferred to or from the energy storage medium. From approximately 70-80 minutes or so, energy from dynamic braking is transferred to the energy storage medium until it is completely full. At approximately 105 minutes, the vehicle begins another motoring phase and energy is drawn from the energy storage medium until about 120 minutes. At about 125 minutes, energy from dynamic braking is again transferred to the energy storage medium during another dynamic braking phase. At about 145 minutes or so, the dynamic braking phase ends and storage ceases. At about 150 minutes, energy is drawn from the energy storage medium to assist in motoring until all of the energy has been depleted at approximately 170 minutes.  
      FIGS.  7 A-D correspond to an energy management system that includes a “look-ahead” or anticipated needs capability. This embodiment applies particularly when the travel path of the Off Highway Vehicle is known or is planned. Such a system is unlike the system reflected in FIGS.  6 A-D, which simply stores dynamic braking energy when it can, and uses stored energy to assist motoring whenever such stored energy is available. The energy management system reflected by the exemplary curves of FIGS.  7 A-D anticipates when the prime mover cannot produce the full required demand, or when it may be less efficient for the prime mover to produce the full required demand. As discussed elsewhere herein, the energy management system can make such determinations based on, for example, known present position, present energy needs, anticipated future travel path topography, anticipated future energy needs, present energy storage capacity, anticipated energy storage opportunities, and like considerations. The energy management system depicted in FIGS.  7 A-D, therefore, preferably prevents the energy storage medium from becoming depleted below a determined minimum level required to meet future demands.  
      By way of further example, the system reflected in FIGS.  7 A-D is premised on a Off Highway Vehicle having a primary energy source that has a “prime mover limit” of 4,000 h.p. Such a limit could exist for various factors. For example, the maximum rated output could be 4,000 h.p., or operating efficiency considerations may counsel against operating the primary power source above 4,000 h.p. It should be understood, however, that the system and figures are intended to reflect an exemplary embodiment only, and are presented herein to facilitate a detailed explanation of aspects of an energy management system suitable for use with off highway hybrid energy vehicles such as, for example, the Off Highway Vehicle system illustrated in  FIG. 2 .  
      Referring now to  FIG. 7A , the exemplary curve illustrated therein depicts the power required for motoring (positive) and braking (negative). At approximately 180 minutes, the motoring demand exceeds 4,000 h.p. Thus, the total demand at that time exceeds the 4,000 h.p. operating constraint for the primary energy source. The “look-ahead” energy management system reflected in FIGS.  7 A-D, however, anticipates this upcoming need and ensures that sufficient secondary power is available from the energy storage medium to fulfill the energy needs.  
      One way for the energy management system to accomplish this is to look ahead (periodically or continuously) to the upcoming travel path/course profile (e.g., incline/decline, length of incline/decline, and the like) for a given time period (also referred to as a look-ahead window). In the example illustrated in FIGS.  7 A-D, the energy management system looks ahead 200 minutes and then computes energy needs/requirements backwards. The system determines that, for a brief period beginning at 180 minutes, the primary energy source would require more energy than the limit.  
       FIG. 7B  is similar to  FIG. 6B .  FIG. 7B , however, also illustrates the fact that the energy storage medium is empty at time  0  and, therefore, there can be no power transfer from the energy storage medium unless and until it is charged.  FIG. 7B  also reflects a look-ahead capability.  
      Comparing FIGS.  6 A-D with FIGS.  7 A-D, it is apparent how the systems respectively depicted therein differ. Although the required power is the same in both examples (see  FIGS. 6A and 7A ), the system reflected in FIGS.  7 A-D prevents complete discharge of the energy storage medium prior to the anticipated need at 180 minutes. Thus, as can be seen in  FIGS. 7C and 7D , prior to the 180 minute point, the system briefly stops transferring stored energy to assist in motoring, even though additional stored energy remains available. The additional energy is thereafter transferred, beginning at about 180 minutes, to assist the prime mover when the energy demand exceeds 4,000 h.p. Hence, the system effectively reserves some of the stored energy to meet upcoming demands that exceed the desired limit of the prime mover.  
      It should be understood and appreciated that the energy available in the energy storage medium could be used to supplement driving traction motors associated with the prime mover, or could also be used to drive separate traction motors (e.g., on a load vehicle). With the benefit of the present disclosure, an energy management system accommodating a variety of configurations is possible.  
      FIGS.  8 A-E reflect pertinent aspects of another embodiment of an energy management system suitable for use in connection with Off Highway Vehicle energy vehicles. The system reflected in FIGS.  8 A-E includes a capability to store energy from both dynamic braking and from the prime mover or another charging power source. For example, a given power source may operate most efficiently at a given power setting (e.g., 4,000 h.p.). Thus, it may be more efficient to operate the power source at 4,000 h.p. at certain times, even when actual motoring demand falls below that level. In such cases, the excess energy can be transferred to an energy storage medium.  
      Thus, comparing FIGS.  8 A-D with FIGS.  6 A-D and  7 A-D, the differences between the systems respectively depicted therein are apparent. Referring specifically to  FIGS. 8A and 8D , from about 0-70 minutes, the motoring requirements ( FIG. 8A ) are less than the exemplary optimal 4,000 h.p. setting. If desirable, the power source could be run at 4,000 h.p. during this time and the energy storage medium could be charged. As illustrated, however, the energy management system determines that, based on the upcoming travel path profile and anticipated dynamic braking period(s), an upcoming dynamic braking process will be able to fully charge the energy storage medium. In other words, it is not necessary to operate the primary energy source at 4,000 h.p. and store the excess energy in the energy storage medium during this time because an upcoming dynamic braking phase will supply enough energy to fully charge the storage medium. It should be understood that the system could also be designed in other ways. For example, in another configuration the system always seeks to charge the storage medium whenever excess energy could be made available.  
      At approximately 180 minutes, power demands will exceed 4,000 h.p. Thus, shortly before that time (while motoring demand is less than 4,000 h.p.), the primary energy source can be operated at 4,000 h.p., with the excess energy used to charge the energy storage medium to ensure sufficient energy is available to meet the demand at 180 minutes. Thus, unlike the systems reflected in  FIGS. 6D and 7D , the system reflected in  FIG. 8D  provides that, for a brief period prior to 180 minutes, energy is transferred to the energy storage medium from the prime mover, even though the vehicle is motoring (not braking).  
       FIG. 8E  illustrates one way that the energy management system can implement the look-ahead capability to control energy storage and transfer in anticipation of future demands.  FIG. 8E  assumes a system having a 200 minute look-ahead window. Such a look-ahead window is chosen to facilitate an explanation of the system and should not be viewed in a limiting sense. Beginning at the end of the window (200 minutes), the system determines the power/energy demands at any given point in time. If the determined demand exceeds the prime mover&#39;s capacity or limit, the system continues back and determines opportunities when energy can be stored, in advance of the determined excess demand period, and ensures that sufficient energy is stored during such opportunities.  
      Although FIGS.  6 A-D,  7 A-D, and  8 A-E have been separately described, it should be understood that the systems reflected therein could be embodied in a single energy management system. Further, the look-ahead energy storage and transfer capability described above could be accomplished dynamically or in advance. For example, in one form, an energy management processor (see  FIG. 5 ) is programmed to compare the vehicle&#39;s present position with upcoming travel path/course characteristics in real or near real time. Based on such dynamic determinations, the processor then determines how to best manage the energy capture and storage capabilities associated with the vehicle in a manner similar to that described above with respect to FIGS.  7 A-D and  8 A-E. In another form, such determinations are made in advance. For example, an off-vehicle planning computer may be used to plan a route and determine energy storage and transfer opportunities based on a database of known course information and projected conditions such as, for example, vehicle speed, weather conditions, and the like. Such pre-planned data would thereafter be used by the energy management system to manage the energy capture and storage process. Look-ahead planning could also be done based on a route segment or an entire route. In some Off Highway Vehicle applications, such as a mine truck or excavator, the travel path may be substantially the same on a day-to-day basis, but may change on a weekly or monthly basis as the mine is worked and the travel path changes to adapt to the mine configuration. In these cases, look-ahead planning may be changed as changes to the travel path occur.  
      It should further be understood that the energy management system and methods described herein may be put into practice with a variety of vehicle configurations. The energy management systems and methods described herein may be employed as part of an Off Highway Vehicle in which the energy storage medium is included as part of the vehicle itself. In other embodiments, such systems and methods could be practiced with a Off Highway Vehicle having a separate load vehicle configured to house an external energy capture and storage medium. As another example, the energy management systems and methods herein described could be employed with a Off Highway Vehicle having a separate load vehicle that employs its own traction motors. Other possible embodiments and combinations should be appreciated from the present disclosure and need not be recited in additional detail herein.  
       FIGS. 9A-9G  are electrical schematics illustrating several different embodiments of an electrical system suitable for use in connection with a hybrid energy Off Highway Vehicle. In particular, the exemplary embodiments illustrated in these figures relate to a hybrid energy Off Highway Vehicle system. It should be understood that the embodiments illustrated in  FIGS. 9A-9G  could be incorporated in a plurality of configurations, including those already discussed herein (e.g., a Off Highway Vehicle with a separate load vehicle, a Off Highway Vehicle with a self-contained hybrid energy system, an autonomous load vehicle, and the like). Other vehicles like off highway dump trucks for mining use the same type of configuration using one, two or four traction motors, one per each driving wheel  109 .  
       FIG. 9A  illustrates an electrical schematic of an Off Highway Vehicle electrical system having a energy capture and storage medium suitable for use in connection with aspects of the systems and methods disclosed herein. The particular energy storage element illustrated in  FIG. 9A  comprises a battery storage  902 . The battery storage  902  is preferably connected directly across the traction bus (DC bus  122 ). In this exemplary embodiment, an auxiliary power drive  904  is also connected directly across DC bus  122 . The power for the auxiliaries is derived from DC bus  122 , rather than a separate bus. The auxiliary loads may be operated during periods of vehicle  200  standby operation when the vehicle  200  is available for service (including perhaps being manned), but not being moved under its own propulsive effort. The first processor module  513  of the energy management processor  506  identifies the energy storage and discharge activities of the electrical energy power capture for powering the auxiliary electrical power load  524  during the vehicle standby periods. The auxiliary loads comprise one or more of the utilities for the operator cab, communications equipment, and train operational control equipment. The auxiliary equipment may also comprise an air compressor for maintaining the air pressure in the air brake system for the vehicle  200 . Further the auxiliary loads may comprise an engine for maintaining the temperature of the engine coolant above the freezing point. An auxiliary electric power generator (not shown) may also be provided that is carried on the vehicle  200  and connected to the power bus  122 , with the energy management processor  506  controlling the transmission of electrical power from the auxiliary electric power generator to the power bus of the vehicle  200 . The auxiliary electric power generator may be in the form of an engine-generator set. The power generation equipment may also be in the form of an electrically powered fan that is subject to the application of mechanical force tending to operate the fan at speeds greater than its commanded speed of operation and generating electrical power when it does. It may also be in the form of an electrically powered turbocharger that is subject to the application of mechanical force tending to operate the turbocharger at speeds greater than its commanded speed of operation and generating electrical power when it does.  
      It should be appreciated that more than one type of energy storage element may be employed in addition to battery storage  902 . For example, an optional flywheel storage element  906  can also be connected in parallel with battery storage  902 . The flywheel storage  906  shown in  FIG. 9A  is preferably powered by an AC motor or generator connected to DC bus  122  via an inverter or converter. Other storage elements such as, for example, capacitor storage devices (including ultra-capacitors) and additional battery storages (not shown) can also be connected across the DC bus and controlled using choppers and/or converters and the like. It should be understood that although battery storage  902  is schematically illustrated as a single battery, multiple batteries or battery banks may likewise be employed.  
      In operation, the energy storage elements (e.g., battery storage  902  and/or any optional energy storage elements such as flywheel  906 ) are charged directly during dynamic braking operations. Recall that, during dynamic braking, one or more of the traction motor subsystems (e.g.,  124 A- 124 B) operate as generators and supply dynamic braking electric power that is carried on DC bus  122 . Thus, all or a portion of the dynamic braking electric power carried on DC bus  122  may be stored in the energy storage element because the power available on the bus exceeds demand. When the power source is motoring, the battery (and any other optional storage element) is permitted to discharge and provide energy to DC bus  122  that can be used to assist in driving the traction motors. This energy provided by the storage element may be referred to as secondary electric power. Advantageously, because the auxiliaries are also driven by the same bus in this configuration, the ability to take power directly from DC bus  122  (or put power back into bus  122 ) is provided. This helps to minimize the number of power conversion stages and associated inefficiencies due to conversion losses. It also reduces costs and complexities.  
      In an alternative embodiment, a fuel cell provides all or a portion of the primary power. In this embodiment, the energy storage device may include an electrolysis or similar fuel cell energy source generation. As one example, the energy generated during dynamic braking powers electrolysis to create hydrogen from water, one water source being the waster water created by the fuel cell during prime energy generation. The generated hydrogen is stored and is used as a fuel for the primary power source, the fuel cell.  
      It should be appreciated that the braking grids may still be used to dissipate all or a portion of the dynamic braking electric power generated during dynamic braking operations. For example, an energy management system is preferably used in connection with the system illustrated in  FIG. 9A . Such an energy management system is configured to control one or more of the following functions: primary energy generation, energy storage; stored energy usage; and energy dissipation using the braking grids. It should further be appreciated that the battery storage (and/or any other optional storage element) may optionally be configured to store excess prime mover electric power that is available on the traction bus.  
      Those skilled in the art should appreciate that certain circumstances preclude the operation of a diesel engine or fuel cell operating as the primary energy source when the Off Highway Vehicle needs to be moved. For example, the engine or fuel cell may not be operable. As another example, various rules and concerns may prevent the operation of a diesel engine inside buildings, yards, maintenance facilities, mines or tunnels. In such situations, the Off Highway Vehicle may be moved using a fuel cell or stored secondary power. Advantageously, various hybrid energy Off Highway Vehicle configurations disclosed herein permit the use of stored power for battery jog operations directly. For example, the battery storage  902  of  FIG. 9A  can be used for battery jog operations. Further, the prior concept of battery jog operations suggests a relatively short time period over a short distance. The various configurations disclosed herein permit jog operations for much longer time periods and over much longer distances.  
       FIG. 9B  illustrates a variation of the system of  FIG. 9A . A primary difference between  FIGS. 9A and 9B  is that the system shown in  FIG. 9B  includes chopper circuits DBC 1  and DBC 2  connected in series with the braking grids. The chopper circuits DBC 1  and DBC 2  allow fine control of power dissipation through the grids that, therefore, provides greater control over the storage elements such as, for example, battery storage  902 . In one embodiment, chopper circuits DBC 1  and DBC 2  are controlled by an energy management system (see  FIG. 5 ). It should also be appreciated that chopper circuits DBC 1  and DBC 2 , as well as any optional storage devices added to the circuit (e.g., flywheel storage  906 ), could also be used to control transient power. In some embodiments, a combination of dynamic braking contactors and chopper circuits may be utilized.  
      In the configuration of  FIG. 9A , the dynamic braking contactors (e.g., DB 1 , DB 2 ) normally only control the dynamic braking grids in discrete increments. Thus, the power flowing into the grids is also in discrete increments (assuming a fixed DC voltage). For example, if each discrete increment is 1,000 h.p., the battery storage capability is 2,000 h.p., and the braking energy returned is 2,500 h.p., the battery cannot accept all of the braking energy. As such, one string of grids is used to dissipate 1,000 h.p., leaving 1,500 h.p. for storage in the battery. By adding choppers DBC 1 , DBC 2 , the power dissipated in each grid string can be more closely controlled, thereby storing more energy in the battery and improving efficiency. In the foregoing example, choppers DBC 1  and DBC 2  can be operated at complementary 50% duty cycles so that only 500 h.p. of the braking energy is dissipated in the grids and 2,000 h.p. is stored in the battery.  
       FIG. 9C  is an electrical schematic of a Off Highway Vehicle electrical system illustrating still another configuration for implementing an energy storage medium. In contrast to the systems illustrated in  FIGS. 9A and 9B , the battery storage  902  of  FIG. 9C  is connected to DC bus  122  by way of a dc-to-dc converter  910 . Such a configuration accommodates a greater degree of variation between DC bus  122  voltage and the voltage rating of battery storage  902 . Multiple batteries and/or DC storage elements (e.g., capacitors) could be connected in a similar manner. Likewise, chopper control, such as that illustrated in  FIG. 9B  could be implemented as part of the configuration of  FIG. 9C . It should be further understood that the dc-to-dc converter  910  may be controlled via an energy management processor (see  FIG. 5 ) as part of an energy management system and process that controls the storage and regeneration of energy in the energy storage medium.  
      In operation, the electric power carried on DC bus  122  is provided at a first power level (e.g., a first voltage level). The dc-to-dc converter  910  is electrically coupled to DC bus  122 . The dc-to-dc converter  910  receives the electric power at the first power level and converts it to a second power level (e.g., a second voltage level). In this way, the electric power stored in battery storage  902  is supplied at the second power level. It should be appreciated that the voltage level on DC bus  122  and the voltage supplied to battery storage  902  via dc-to-dc converter  910  may also be at the same power level. The provision of dc-to-dc converter  910 , however, accommodates variations between these respective power levels.  
       FIG. 9D  is an electrical schematic of an Off Highway Vehicle electrical system that is similar to the system shown in  FIG. 9C . One difference between these systems is that the auxiliary power subsystem  904  reflected in  FIG. 9D  is connected to DC bus  122  via a pair of dc-to-dc converters  912  and  914 . Such a configuration provides the advantage of allowing the use of existing, lower voltage auxiliary drives and/or motor drives having low insulation. On the other hand, in this configuration, the auxiliary power traverses two power conversion stages. It should be understood that although  FIG. 9D  illustrates the auxiliaries as consuming power all of the time—not regenerating—bi-directional dc-to-dc converters can also be used in configurations in which it is desirable to have the auxiliaries regenerate power (see, for example,  FIG. 9G ). These dc-to-dc converters  912  and  914  are preferably controlled via an energy management system that controls the storage and regeneration of energy in the energy storage medium.  
      There are auxiliary power loads  524  on the vehicle  200  which may generate power under certain conditions and thus operate as auxiliary power generators. For example, when the speed of a blower or fan is increased power is consumed from the DC bus  122 , but conversely when the speed of a blower or fan is decreased power is regenerated and returned to the bus. Similarly, when wind or the speed of the vehicle  200  drives the fan a speed higher than its commanded speed, power is regenerated and returned to the bus  122 . Further if electric turbochargers are used on the vehicle  200 , electric power drives the turbocharger at low engine speeds, but engine exhaust drives the turbocharger at high engine speeds, thereby producing electrical power returned to the bus. In each of these examples, the power returned to the bus by the auxiliary power loads  524  is available for storage or to drive the traction motors  108  or other auxiliary equipment that is then consuming power.  
      Auxiliary power generation equipment (also known as an auxiliary power unit or APU) of the type described in U.S. Pat. No. 6,470,844 may also be provided to power the auxiliary equipment when the primary power generation equipment is not in operation. Typically, such auxiliary power generation equipment takes the form of a relatively small engine-generator set and allows the primary power generation equipment to remain inactive during periods of time in which only light power loads, such as only auxiliary power loads, are imposed on the power system. The auxiliary power generation equipment may be operated at high speeds and thus at near its maximum performance point during such periods of light load, whereas the primary power generation equipment would be operate at relatively slow speeds, which is fuel inefficient.  
      To maximize fuel efficiency, it is known in the prior art to shut down the primary power generation equipment rather than to run the engine at idle. Batteries on the prior art vehicle (and/or the above-noted APU, if installed on the vehicle) provide power to the auxiliary equipment on the vehicle  200  such as operator cab heating and cooling, lights, communications and control, during periods of shut-down. However the batteries on the prior art vehicle are of relatively small power storage capacity and thus the primary power generation equipment must be started relatively frequently (such as every few hours), whenever the battery charge is low. Similarly, the prior art batteries lack the power storage capacity to power the air compressors for increasing the air pressure when air brake pressure drops or to warm the engine water temperature if it drops close to freezing. In these instances the primary power generation equipment must be started again. In contrast, with the hybrid power system of the instant inventions, the power storage system is of significantly greater capacity so that auxiliary equipment may be operated for prolonged periods of time. The power storage devices also have the capacity to power the air compressors and even to warm the engine so that engine start up can be avoided for extended periods of time. Thus the shut down periods can be extended from hours in the prior art systems to days in the hybrid power system of the instant inventions for increased fuel savings, reduced wear on the engine, reduced engine emissions and reduced noise generation in populated areas.  
       FIG. 9E  illustrates, in electrical schematic form, still another configuration of an energy storage medium. Unlike the examples illustrated in  FIGS. 9A-9D , however, the configuration of  FIG. 9E  includes a separate DC battery bus  922 . The separate battery bus  922  is electrically isolated from main DC bus  122  (the traction bus) by a dc-to-dc converter  920  (also referred to as a two-stage converter). Accordingly, the power flow between the traction bus (DC bus  122 ), the energy storage elements, and the auxiliaries preferably passes through the bi-directional dc-to-dc converter  920 . In the configuration of  FIG. 9E , any additional storage elements (e.g., flywheels, capacitors, and the like) are preferably connected across the DC battery bus  922 , rather than across the main DC bus  122 . The dc-to-dc converter  920  may be controlled via an energy management system that controls the storage and regeneration of energy in the energy storage medium.  
       FIG. 9F  reflects a variation of the configuration of  FIG. 9E . In the configuration of  FIG. 9F , any variable voltage storage elements (e.g., capacitors, flywheels, and the like) that are used in addition to battery  906  are connected directly across main DC bus  122  (the traction bus). However, battery  906  remains connected across the isolated DC battery bus  922 . Advantageously, in this configuration dc-to-dc converter  920  matches the voltage level of battery storage  902  but avoids two conversions of large amounts of power for the variable voltage storage elements. Like the other configurations, the configuration of  FIG. 9F  may be implemented in connection with an energy management system that oversees and controls the storage and regeneration of energy in the energy storage medium.  
       FIG. 9G  reflects a variation of the configuration of  FIG. 9F  in which only the auxiliaries are connected to a separate auxiliary bus  930  through two-stage converter  920 . Accordingly, electric power carried on DC bus  122  is provided at a first power level and power carried on the auxiliary bus  930  is provided at a second power level. The first and second power levels may or may not be the same.  
       FIGS. 10A-10C  are electrical schematics that illustrate additional embodiments, including embodiments particularly suited for modifying existing AC Off Highway Vehicles. It should be understood, however, that the configurations illustrated and described with respect to  FIGS. 10A-10C  are not limited to retrofitting existing Off Highway Vehicles.  
       FIG. 10A  illustrates a variation of the embodiment illustrated in  FIG. 9C . The embodiment of  FIG. 10A  uses only battery storage devices and does not include a non-battery storage, such as optional flywheel storage  906 . In particular,  FIG. 10A  illustrates an embodiment having a converter  1006  (e.g., a dc-to-dc converter) connected across DC bus  122 . A battery storage element  1002  is connected to the converter  1006 . Additional converters and battery storage elements may be added to this configuration in parallel. For example, another converter  1008  may be connected across DC bus  122  to charge another battery storage element  1004 . One of the advantages of the configuration of  FIG. 10A  is that it facilitates the use of multiple batteries (or battery banks) having different voltages and/or charging rates.  
      In certain embodiments, power transfer between energy storage devices is facilitated. The configuration of  FIG. 10A , for instance, allows for energy transfer between batteries  1002  and  1004  via the DC bus  122 . For example, if during motoring operations, the primary power source supplies 2,000 h.p. of power to the dc traction bus, the traction motors consume 2,000 h.p., and battery  1002  supplies 100 h.p. to the traction bus (via converter  1006 ), the excess 100 h.p. is effectively transferred from battery  1002  to battery  1004  (less any normal losses).  
      The configuration illustrated in  FIG. 10B  is similar to that of  FIG. 10A , except that it uses a plurality of converters (e.g., converters  1006 ,  1008 ) connected to the DC bus  122  to supply a common battery  1020  (or a common battery bank). One of the advantages of the configuration of  FIG. 10B  is that it allows the use of relatively smaller converters. This may be particularly advantageous when retrofitting an existing Off Highway Vehicle that already has one converter. A similar advantage of this configuration is that it allows the use of higher capacity batteries. Still another advantage of the configuration of  FIG. 10B  is that it permits certain phase shifting operations, thereby reducing the ripple current in the battery and allowing the use of smaller inductors (not shown). For example, if converters  1006  and  1008  are operated at 1,000 Hz, 50% duty cycles, and the duty cycles are selected such that converter  1006  is on while converter  1008  is off, the converter effect is as if a single converter is operating at 2,000 Hz, which allows the use of smaller inductors.  
       FIG. 10C  an electrical schematic illustrating another embodiment that is particularly well suited for retrofitting an existing Off Highway Vehicle to operate as a hybrid energy Off Highway Vehicle. The configuration of  FIG. 10C  uses a double set of converters  1006 ,  1030  and one or more batteries  1020  (of the same or different voltage levels). An advantage of the system depicted in  FIG. 10C  is that the battery  1020  can be at a higher voltage level than the DC bus  122 . For example, if the converters  1006 ,  1008  illustrated in  FIGS. 10A and 10B  are typical two quadrant converters, they will also have freewheeling diodes associated therewith (not illustrated). If the voltage of battery  1002 ,  1004  ( FIG. 10A ), or  1020  ( FIG. 10B ) exceeds the DC bus voltage, the battery will discharge through the freewheeling diode. A double converter, such as that illustrated in  FIG. 10C , avoids this situation. One advantage of this capability is that the voltage level on the DC bus can be modulated to control power to the dynamic braking grids independently.  
       FIG. 11  is an electrical schematic that illustrates one way of connecting electrical storage elements. In particular,  FIG. 11  illustrates an electrical schematic of a system that may be used for retrofitting a prior art Off Highway Vehicle to operate as a hybrid energy Off Highway Vehicle, or for installing a hybrid energy system as part of the original equipment during the manufacturing process. The embodiment illustrated assumes an AC diesel-electric Off Highway Vehicle with four wheels, a pair of wheels located on two axle-equivalents. Two wheels  109  of a single axle-equivalent are driven by individual traction motor subsystems. However, in other embodiments all four wheels  109 A and  109 B of the two axle-equivalents may be driven by four traction motor subsystems, or any number of traction motors are envisioned consistent with the current invention. For instance, while not commonplace for Off Highway Vehicles would be to have two wheels  109 A on a single axle with a single traction motor subsystem for the single axle two wheel arrangement.  
      Typically, the primary energy source has extra capability (e.g., power capacity) available in the majority of operating conditions. Such extra capability may be due to lower actual ambient conditions, as compared with the design criteria. For example, some Off Highway Vehicles are designed to operate in ambient temperatures of up to 60 degrees Celsius, which is well above typical operating conditions. Considerations other than thermal conditions may also result in extra capacity during significant operating periods. In a typical Off Highway Vehicle, for instance, the use of all of the traction motors may only be required for low speed and when the Off Highway Vehicle operates in an adhesion limited situation (poor tractive conditions). In such case, the weight on the driven wheels  109  determines the pulling power/tractive effort. Hence, all available wheel/motors need to be driven to obtain maximum tractive effort. This can be especially true if the Off Highway Vehicle is heavily loaded during poor tractive conditions (snow, mud, or wet). Such conditions may normally be present for only a fraction of the operating time. During the majority of the operating time, all of the traction motors/inverters are not fully utilized to supply tractive effort. Thus, for example, when retrofitting an existing prior art Off Highway Vehicle, or manufacturing a new Off Highway Vehicle, it is possible to take advantage of this partial underutilization of the traction motors/inverters.  
      By way of a specific example, the embodiment of  FIG. 11  is configured such that one of the two traction motor subsystems is connected to the energy storage element  1102 , through a transfer switch  1104  and a plurality of inductors  1110 . More particularly, the traction motor subsystem  124 B includes an inverter  106 B and a traction motor  1108 B. Such a configuration is suited for retrofitting a single wheel  109  of an existing prior art Off Highway Vehicle. It should be understood that retrofitting a typical prior art Off Highway Vehicle requires the addition of power conversion equipment and associated cooling devices. The space available for installing the retrofit equipment, however, is generally limited. Therefore, one of the advantages of the “single-wheel” configuration of  FIG. 11  is that it tends to minimize impacts and makes retrofitting a more viable option. Similar advantages, however, may also be enjoyed when the hybrid energy system is installed as original equipment during manufacturing.  
      The transfer switch  1104  preferably comprises a three-phase set of contactors or a set of motorized contacts (e.g., bus bars) that connect inverter  106 B to traction motor  1108 B when all of the wheels  109 A and  109 B are needed, and connects inverter  106 B to inductors  1110  and battery  1102  when battery charging or discharging is desired. Thus, transfer switch  1104  has a first connection state and a second connection state. In the first connection state, transfer switch  1104  connects inverter  106 B to traction motor  1108 B. In the second connection state, transfer switch connects inverter  106 B to battery  1102 .  
      Transfer switch  1104  is preferably controlled by a switch controller  1120 . In one form, the switch controller  1120  is a manual operator-controlled switch that places transfer switch  1104  into the first or the second connection state. In another form, the switch controller reflects control logic that controls the connection state of transfer switch  1104  in accordance with one operating scheme. Table I (below) is indicative of one such operating scheme. Other schemes are possible.  
      Although  FIG. 11  illustrates a three-phase connection between battery  1102  and transfer switch  1104 , it is not necessary that all three phases be used. For example, if the power requirement is relatively low, only one or two phases may be used. Similarly, three separate batteries could be independently connected (one to each phase), or one large battery could be connected to two phases, with a relatively smaller battery connected to the third phase. Further, power transfer between multiple batteries having different voltage potentials and/or capacities is also possible.  
      The configuration of  FIG. 11  is especially advantageous in the context of retrofitting existing Off Highway Vehicles because transfer switch  1104  is believed to be much less expensive than adding additional inverters and/or dc-to-dc converters. Such advantage, however, is not limited to the retrofit context. Also, it should be understood that the configuration of  FIG. 11  is not limited to a single inverter per transfer switch configuration.  
       FIG. 11  further illustrates an optional charging source  1130  that may be electrically connected to DC traction bus  122 . The charging source  1130  may be, for example, another charging energy source or an external charger, such as that discussed in connection with  FIG. 5 .  
      The general operation of the configuration of  FIG. 11  will be described by reference to the connection states of transfer switch  1104 . When transfer switch  1104  is in the first switch state, the second wheel  109 B is selectively used to provide additional motoring or braking power. In this switch state, battery  1102  is effectively disconnected and, therefore, neither charges nor discharges.  
      When the second wheel  109 B is not needed, switch controller  1120  preferably places transfer switch  1104  in the second connection state-battery  1102  is connected to inverter  106 B. If, at this time, the other traction motor (e.g., traction motor  108 A) is operating in a dynamic braking mode, electrical energy is generated and carried on DC traction bus  122 , as described in greater detail elsewhere herein. Inverter  106 B transfers a portion of this dynamic braking electrical energy to battery  1102  for storage. If, on the other hand, the other traction motor is operating in a motoring mode, inverter  106 B preferably transfers any electrical energy stored in battery  1102  onto DC traction bus  122  to supplement the primary electric power supplied by prime mover power source  104 . Such electrical energy transferred from battery  1102  to DC traction bus  122  may be referred to as secondary electric power. In one embodiment, inverter  106 B comprises a chopper circuit for controlling the provision of secondary electric power to DC traction bus  122  from battery  1102 .  
      It should be understood, however, that battery  1102  can also be charged when the other traction motors are not operating in a dynamic braking mode. For example, the battery can be charged when transfer switch  1104  is in the second connection state (battery  1102  is connected to inverter  106 B) and the other traction motors are motoring or idling if the amount of power drawn by the other traction motors is less than the amount of primary electric power carried on DC traction bus  122 .  
      Advantageously, battery  1102  can also be charged using charging electric power from optional energy source  1130 . As illustrated in  FIG. 11 , optional energy source  1130  is preferably connected such that it provides charging electric power to be carried on DC traction bus  122 . When optional energy source  1130  is connected and providing charging electric power, switch controller  1120  preferably places transfer switch  1104  in the second connection state. In this configuration, inverter  106 B transfers a portion of the electric power carried on DC traction bus  122  to battery  1102  for storage. As such, battery  1102  may be charged from optional energy source  1130 .  
      In summary, in the embodiment of  FIG. 11 , when transfer switch is in the second connection state, battery  1102  may be charged from dynamic braking energy, from excess Off Highway Vehicle energy (i.e., when the other traction motors draw less power than the amount of primary electric power carried on DC traction bus  122 ), and/or from charging electric power from optional charging source  1130 . When transfer switch  1104  is in the second connection state and the other traction motor draws more power than the amount of primary electric power carried on DC traction bus  122 , inverter  106 B transfers secondary electric power from battery  1102  to DC traction bus  122  to supplement the primary electric power. When transfer switch  1104  is in the first connection state, battery  1102  is disconnected and traction motor  1108 B is operable to assist in motoring and/or dynamic braking. Table I summarizes one set of operating modes of the embodiment of  FIG. 11 .  
                           TABLE I                                   One Axle   Two Axles                          Low Speed and Low   Battery Fully Charged &amp;           Tractive Effort   Dynamic Braking           Settings           High Speed Motoring   No Battery Charging &amp; Motoring               Battery Discharged &amp; Motoring               Very High Speed Dynamic Braking                      
 
      While  FIG. 11  illustrates an energy storage device in the form of a battery, other energy storage devices, such as flywheel systems or ultra-capacitors, may also be employed instead of or in addition to battery  1102 . Further, it should be understood that the configuration of  FIG. 11  may be scaled. In other words, the configuration can be applied to more than one axle.  
      Although the foregoing descriptions have often referred to AC Off Highway Vehicle systems to describe several pertinent aspects of the disclosure, the invention should not be interpreted as being limited to such Off Highway Vehicle systems. For example, aspects of the present disclosure may be employed with diesel-electric, fuel cell, “all electric,” third-rail, trolley or overhead powered Off Highway Vehicles. Further, aspects of the hybrid energy Off Highway Vehicle systems and methods described herein can be used with Off Highway Vehicles using a DC generator rather than an AC alternator and combinations thereof. Also, the hybrid energy Off Highway Vehicle systems and methods described herein are not limited to use with AC traction motors. As explained elsewhere herein, the energy management system disclosed herein may be used in connection with locomotives, mine trucks, large excavators, etc. In addition, the primary power generation equipment may include not only diesel engine generators and fuel cells, but also turbine generators, which run at relatively high speeds of rotation and have a high power to weight and size ratio. The turbines may be powered by liquid fuel or gas in either a gaseous or liquefied form.  
      The fuel cells may be of any suitable cell construction or chemistry, including phosphoric acid, proton exchange membrane or solid polymer fuel cell, molten carbonate, solid oxide, alkaline, direct methanol, regenerative, zinc air, and/or protonic ceramic. As noted above, the fuel cell may be used for the generation of electrical power, the storage of energy or both generation and storage. Further the fuel cell may be the primary power generation and/or storage device, used in combination with diesel engines, turbines or APU&#39;s for power generation or used in combination with batteries, ultra-capacitors or flywheels for power storage.  
      As noted in the Field of Invention section, the hybrid systems of the instant inventions are adapted for use on various off-highway vehicles, including so-called road locomotives, and large mining dump trucks capable of moving large loads. Road locomotives have engines that supply 4000-6000 hp and move trains carrying loads (including the weight of the railcars) of up to 40,000 to 60,000 tons. Mining dump trucks have engines providing 1500 hp or more, and carry loads (including the weight of the truck itself) of up to 1500 tons.  
      Road locomotives, as noted above, have engine power generation capability in the range of 4000-6000 HP. The power regeneraton capability of the traction motors for such locomotives is in the range of 4000-8000 HP, and the electric energy capture system has a storage capacity of 750-5000 HPHR. Thus the charging time (or charging ratio) of the capture system is approximately 0.1 hour to 1 hour with the use of only engine generated power, somewhat less than that with the use of traction motor regeneration power, and approximately half of that, if both the engine generation and traction motor regeneration power are used. The size of the electrical energy capture system relative to the available space on the locomotive is a limiting factor on the capacity of the energy capture system that can be used.  
      Road switcher vehicles have engine power generation capability in the range of 1000-4000 HP. The power regeneraton capability of the traction motors for such vehicles is in the range of 1000-5000 HP, and the electric energy capture system has a storage capacity of 500-1500 HPHR. Thus the charging time (or charging ratio) of the capture system is approximately 0.1 hour to 1.5 hours with the use of only engine generated power, somewhat less than that with the use of traction motor regeneration power, and approximately half of that, if both the engine generation and traction motor regeneration power are used.  
      Yard switcher vehicles have engine power generation capability of approximately 1000 HP and power regeneration capability of its traction motors also of approximately 1000 HP. The electric energy capture system of such vehicles has a storage capacity of 250-1000 HPHR. Thus the charging time (or charging ratio) of the capture system is approximately 0.25 hour to 1 hour, with the use of only engine generated power, the same ratio with the use of traction motor regeneration power, and approximately half of that, if both the engine generation and traction motor regeneration power are used.  
      Yard switcher vehicles using an auxiliary power unit (APU) of the type described above have engine power generation capability in the range of 250-500 HP. The power regeneration capability of the traction motors for such vehicles is in the range of 1000-2000 HP, and the electric energy capture system has a storage capacity of 250-1000 HPHR. Thus the charging time (or charging ratio) of the capture system is approximately 0.5 hour to 4 hours, with the use of only engine generated power, approximately 0.1 to 1 hour with the use of traction motor regeneration power, and somewhat less than that, if both the engine generation and traction motor regeneration power are used.  
      Passenger locomotives, as noted above, have engine power generation capability in the range of 2000-4000 HP. The power regeneration capability of the traction motors for such locomotives is in the range of 2000-5000 HP, and the electric energy capture system has a storage capacity of 50-200 HPHR. Thus the charging time (or charging ratio) of the capture system is approximately 0.01 hour to 0.1 hour, with the use of only engine generated power, somewhat less than that with the use of traction motor regeneration power, and approximately half of that, if both the engine generation and traction motor regeneration power are used. Thus the preferred charging ratio for hybrid vehicles of the current inventions with traction motor power regeneration is less than 4. The capacity of the various electric energy capture systems of these various hybrid vehicles is effective to enable optimization of the performance parameters of the vehicles.  
      The capacity of the energy storage devices enable a corresponding period of operation of the vehicle, without the operation of the primary power generation equipment, such as for limp home operation upon the loss of the primary power generation equipment. As described above the electrical energy storage devices enable prolonged periods of vehicle standby operation when only the vehicle auxiliary equipment needs to be powered as well as the operation of air compressors, and the operation of engine heating devices in cold weather  
      It should be appreciated that the principles of the instant inventions may apply to any suitable computer equipment, such as other mainframes, minicomputers, microprocessors, microcontrollers, network servers, supercomputers, personal computers, or workstations, as well as other electronics applications. Therefore, while the specification herein focuses on particular applications, it should be understood that the instant inventions are not limited to the particular hardware designs, software designs, and communications protocols disclosed herein. The inventions can also be embodied, in part, as computer readable code on a computer readable medium. The computer readable medium is any data storage device that can store data, which thereafter can be read by a computer system. Examples of computer readable medium include read-only memory, random-access memory, CD-ROMs, DVDs, magnetic tape, optical data storage devices. The computer readable medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.  
      Based on the foregoing specification, the inventions may be implemented using computer programming or engineering techniques including computer software, firmware, hardware or any combination or subset thereof. Any such resulting program, having computer-readable code means, may be embodied or provided within one or more computer-readable media, thereby making a computer program product, i.e., an article of manufacture, according to the invention. The computer readable media may be, for example, a fixed (hard) drive, diskette, optical disk, magnetic tape, semiconductor memory such as read-only memory (ROM), etc., or any transmitting/receiving medium such as the Internet or other communication network or link. The article of manufacture containing the computer code may be made and/or used by executing the code directly from one medium, by copying the code from one medium to another medium, or by transmitting the code over a network.  
      An apparatus for making, using or selling the inventions may be one or more processing systems including, but not limited to, a central processing unit (CPU), memory, storage devices, communication links and devices, servers,  1 /O devices, or any sub-components of one or more processing systems, including software, firmware, hardware or any combination or subset thereof, which embody the invention as set forth in the claims.  
      User input may be received from the keyboard, mouse, pen, voice, touch screen, or any other means by which a human can input data to a computer, including through other programs such as application programs.  
      One skilled in the art of computer science will be able to combine the software created as described with appropriate general purpose or special purpose computer hardware to create a computer system or computer sub-system embodying the method of the invention.  
      It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims.  
      As can now be appreciated, the hybrid energy systems and methods herein described provide substantial advantages over the prior art. Such advantages include improved performance parameter such as fuel efficiency, increased fuel range, and reduced emissions such as transient smoke. Other advantages include improved speed by the provision of an on-demand source of power for a horsepower burst. Significantly, the hybrid energy Off Highway Vehicle system herein described may also be adapted for use with existing Off Highway Vehicle systems.  
      When introducing elements of the invention or embodiments thereof, 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.  
      In view of the above, it will be seen that several aspects of the invention are achieved and other advantageous results attained.  
      As various changes could be made in the above exemplary constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. It is further to be understood that the steps described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated. It is also to be understood that additional or alternative steps may be employed.