Abstract:
A load bank comprises one or more load resistors connected to an engine-generator and a control system for maintaining a minimum generator load when necessary for optimal operation. The control system operates the load bank to mitigate harmful effects of generator neglect and maintains loading for efficient DPF regeneration while allowing the generator to quickly dump the load bank when real load increases.

Description:
TECHNICAL FIELD 
       [0001]    The disclosed embodiments relate generally to systems of engine-generators with load banks. 
       BACKGROUND 
       [0002]    Electric generators, particularly portable engine-generator units, are often operated under variable load conditions. Such portable units are also often left unattended, which further causes them to be operated in sub-optimal conditions. It is well known that operating engine-generators under fluctuating load conditions can present a number of problems. As explained in U.S. Pat. No. 3,530,300 to Gunther, et al., diesel-fueled engine-generators are especially susceptible to problems associated with light-load conditions. In particular, a lightly loaded, diesel-fueled engine-generator may cause the engine portion of the machine to operate such that fuel within the engine remains unburned. This unburned fuel forms tar or carbon deposits, or both, which can collect within various parts of the engine, including exhaust pipes. This condition has historically been referred to as “wet stacking.” 
         [0003]    Diesel engines also create soot during their combustion process. When an engine is operating under lightly load conditions, it tends to create more soot. Historically, the soot was exhausted from the engine to the atmosphere via exhaust pipes. More recently, however, increasing concern about, and regulation of particulate emissions has lead to changes in the manner in which diesel engines may legally operate. Modern diesel engines, including so-called Tier IV Interim and newer engines, are equipped with particulate filters that serve to capture and remove soot from engine exhaust. The problem is that these particulate filters, which are also called diesel engine particulate filters or DPF, tend to clog with the particulate that they filter. Those clogs inhibit engine exhaust, which may significantly or entirely decrease the operability of an engine. To combat this DPF-clogging issue, modern diesel engines are often equipped with a “regeneration” feature. Regeneration involves a process in which the engine doses a DPF with diesel and then ignites that diesel to burn-off accumulated soot. The soot is reduced to ash, which falls away from the DPF, thus clearing the DPF and the engine exhaust system. 
         [0004]    Complicating DPF regeneration in engine-generator applications is the effect of generator loading on engine performance. Engine exhaust temperature is proportional to generator loading. Thus, a lightly loaded generator causes the engine to operate with lower exhaust temperature than a generator operating under greater loading conditions. The problem is that regeneration efficiency is inversely proportional to exhaust temperature. That is, regeneration works better when an engine is operating with higher exhaust temperatures. So, in engine-generator applications, regeneration is more efficient when a generator is operating under loaded conditions. 
         [0005]    It is known in the art that wet stacking may be mitigated by connecting to the generator a “dummy” load in parallel with the actual, or “real,” load. Such dummy loads often comprise banks of resistors that may be switched in steps, often automatically, in inverse proportion to the real load. In this way, a generator may be connected so that it always experiences some minimum demand. As Gunther, et al. explains, this is represented by the equation P G =P RL +P DL , where P G  is the total generator demand, P RL  is the demand of the real load, and P DL  is the demand of the dummy load. This same method of operation helps reduce soot in the engine. 
         [0006]    But despite the benefits of the system of Gunther, et al., and other similar configurations, such schemes tend to be wasteful because they cause the engine portion of the engine-generator to burn a set amount of fuel, at all times, in order to maintain P G . This is because the engine must burn more fuel to maintain an increased generator output. So while the system is burning cleaner, it uses more fuel than necessary. In a world of rapidly decreasing oil supplies, and rapidly increasing fuel costs, it is desirable to balance the benefits of minimum generator loading with economic realities. Said differently, it is advantageous to decrease soot production and wet-stacking events with dummy loads (aka load banks), while at the same time being mindful of the fuel costs associated with operating dummy loads. Furthermore, load banks have not previously been employed to aid with DPF regeneration. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    Disclosed here is a load bank that provides a dummy load to an electric generator, which allows an engine-generator unit to more efficiently operate by decreasing the frequency of regeneration cycles an engine must initiate, and, when regeneration occurs, ensures a minimum generator load to raise exhaust temperatures and thus increase regeneration efficiency. 
         [0008]    In accordance with some embodiments of the disclosed technology, an engine-generator and load bank system comprises a plurality of load resistors and load step contactors for engaging the load resistors. The plurality of load resistors are configured to allow for variability, or “stepping,” of the total resistance of the dummy load. In other words, when the load bank is engaged, or connected, the load bank is configured to add or remove load resistors in steps, as required by system parameters. The disclosed technology is operable to entirely disconnect, or “dump,” the load bank from the generator within a specified time, which may be necessary when the real load of the generator rapidly increases. 
         [0009]    In accordance with some embodiments of the disclosed technology, the system is equipped with a generator controller and a load bank controller, which could be physically combined, that are configured to monitor both the engine side and the generator load of an engine-generator and to operate the load bank. In according with some embodiments, the system is equipped with a single controller that is configured to monitor the engine side of an engine-generator and to operate the load bank. 
         [0010]    In accordance with some embodiments of the disclosed technology, the generator and load bank controllers are configured to initiate the load bank when certain conditions exist. The load bank is initiated when there is a “neglect scenario” or “neglect case.” The generator controller, via the load bank controller, monitors the load connected to the generator to ensure that the load is within a “window” or “load window” bounded by pre-set lower and upper load levels. If the load connected to the generator remains at or below some pre-set load condition—i.e., below the window—for a pre-set duration, the generator controller signals the load bank controller to initiate the load bank. The load bank controller then increases or decreases the total resistance of the load bank by connecting or disconnecting load step resistors as necessary to maintain the load within window. If the load rises above the window, the steps of the load bank are disconnected as necessary. In this way, the total load on the generator—i.e., the real load and the resistance of the load bank—remains within pre-set limits. The pre-set load corresponds to a power demand on the generator that provides for optimal operation, which minimizes wet stacking and soot build up. 
         [0011]    Restricting the load bank to operation in a neglect case allows one to save fuel because the load bank will only draw power from the generator when necessary to prevent wet stacking and soot build up. The generator will thus be allowed to operate in a sub-optimal state until such time as wet stacking and soot build up are likely to occur. The load window and duration variables necessary for determining a neglect scenario will thus be based on manufacturer or user-defined values directed at pinpointing the time when wet stacking and soot build up is likely to begin. 
         [0012]    In accordance with some embodiments of the disclosed technology, the duration variable for neglect is cumulative. The generator controller will constantly monitor load levels and will track the time period for which load levels are below the window. If the cumulative time the system is operated below the window reaches the pre-set duration, the generator controller signals the load bank controller to initiate the load bank. This cumulative timing of sub-optimal operation occurs even the system is operated for short periods of time at load levels within and above the window. If, however, the system operates for a pre-set time within the window, a neglect scenario may be avoided. The system thus accounts for the cumulative nature of soot build up in the engine. The problems associated with this soot accumulation can be avoided if the engine is operated under loaded conditions for a pre-determined duration. The generator controller therefore ensures the system is operated under a designated load for a pre-set duration. This operation for a pre-set duration under set load conditions at full engine speed is disclosed here a “load cycle.” 
         [0013]    In accordance with some embodiments of the disclosed technology, the generator controller is configured to signal the load bank controller to initiate the load bank when the engine control module initiates regeneration to clean the DPF. In such a “regeneration scenario” or “regeneration case,” as it is referred to here, the generator controller will signal the load bank controller to initiate the load bank, thus providing a minimum load for the system in order to maintain an engine exhaust temperature necessary for the DPF regeneration to effectively clean the DPF. 
         [0014]    In accordance with some embodiments of the disclosed technology, the generator controller will monitor engine idle time. In a configuration disclosed here as “excessive idle control,” the generator controller may be configured with a pre-set maximum allowed idle time. If the maximum idle time is reached—a condition referred to here as an “excessive idle scenario” or an “excessive idle case”—the generator controller will signal the load bank controller to initiate the load bank. The system will then be required to complete a load cycle, as described above, before resuming idle speeds. If a user attempts to disrupt the load cycle, the generator controller will initiate a warning to the user. If a user nonetheless disrupts the load cycle, the generator controller will disable the system and will not allow operation until a load cycle has been completed at full engine speed. The load under which the generator operates during the load cycle could include any combination of real load and dummy load levels, as long as P G  is maintained. In accordance with some embodiments, for every three (3) hour period of engine idle time, the engine must complete a load cycle of one (1) hour. 
         [0015]    In accordance with some embodiments of the disclosed technology, the generator controller may be configured with what is disclosed here as a “load dump” feature. In such a configuration, the generator controller signals the load bank controller to disconnect, or dump, the load bank if the generator controller and/or load bank recognizes a “load spike” of monitored load. Load spike, as used here, is a scenario in which the load connected to the engine-generator exceeds some pre-set value. 
         [0016]    In accordance with some embodiments of the disclosed technology, the generator controller controls the load bank directly, thus obviating the need for a separate load bank controller. 
         [0017]    In accordance with some embodiments of the disclosed technology, the system may be equipped with remote monitoring. 
         [0018]    In accordance with some embodiments of the disclosed technology, the generator controller is configured with a manual setting. In the manual setting, the load bank may be engaged or disengaged by manual operation. In the manual setting, an operator may manually direct the controller to increase or decrease total resistance of the load bank. 
         [0019]    In accordance with some embodiments of the disclosed technology, the load bank may be completely disabled and locked out of operation. In such a state, the total load of the generator is equal to the real load. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1A  is a single-line diagram of an embodiment of the disclosed system. 
           [0021]      FIG. 1B  is a single-line diagram of an embodiment of the disclosed system. 
           [0022]      FIG. 2  is a flow chart depicting an operating configuration of an embodiment of the disclosed system. 
           [0023]      FIG. 3  is a block diagram depicting a method of operating embodiments of the disclosed system. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosed concepts. It will, however, be apparent to one of ordinary skill in the art that the disclosed concepts may be practiced without these specific details. Well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments. 
         [0025]      FIG. 1A  depicts an engine-generator and load bank system  10  comprising an engine  12  mechanically connected and configured to drive an alternator  14 . This combination is referred to as an engine-generator. The generator portion of the engine-generator, or alternator  14 , is connected to an output bus  16 , which is connected to a real load  17 , and a load bank bus  18 , which is connected to a load bank  19 . The output bus  16  and load bank bus  18  are connected to the alternator  14  by way of disconnects  21 . The disconnects  21  could comprise circuit breakers or fused switches. 
         [0026]    The alternator  14  may be sized and configured for a variety of rated output. In some embodiments, the alternator  14  is adjustable to provide a variety of voltage outputs as selected by a user. The alternator  14  may be single-phase or poly-phase; and it may be rated for a variety of operating frequencies. In one embodiment, the alternator  14  is rated 240Y/139 V, three-phase, four-wire, 60 Hz, and is adjustable for operation at 208Y/120 V. In one embodiment, the alternator  14  is rated 480Y/277 V, three-phase, four-wire, 60 Hz. 
         [0027]    The engine  12  is equipped with an engine control module  20  and a diesel particulate filter (DPF)  22 . The system  10  also has at least one load monitoring device  24  that is in electrical communication with the output bus  16  and the load bank bus  18 . The load monitoring device  24  could be any piece or combination of electrical metering equipment suitable for gathering and communicating data about system voltage, current, and/or power. In a preferred embodiment, the load monitoring device  24  comprises current transformers. 
         [0028]    The system  10  comprises a generator controller  26  which is connected to the engine control module  20  via a communication means  27 . The communication means  27  could be any communication bus suitable for communication between, and for diagnostics of engine components. In a preferred embodiment, the communication means  27  comprises SAE J1939-based protocol. 
         [0029]    The generator controller  26  has a load dump output  28  and a load enable output  30 . The system  10  also includes a load bank controller  32  which has a load enable input  34 , a load dump input  36 , and a load sensor  38 . The load sensor  38  is connected to and accepts an input from the load monitoring device  24  for monitoring the combined load of the real load  17  and the load bank  19 . 
         [0030]    The load bank controller  32  is also equipped with at least one load step output  40 . The load bank controller  32  could have one or a plurality of load step outputs  40 . The at least one load step output  40  is connected to at least one load step contactor  42 , which control(s) the electrical connection of at least one load step resistor  44  to the load bank bus  18 . The output bus  16 , load bank bus  18 , and load step resistor(s)  44  may be single- or poly-phase, as required for operation with the configuration of the alternator  14 . In a preferred embodiment, the load bank controller  32  is equipped with four load step outputs  40 . In a preferred embodiment, there are four (4) load step resistors  44 , each rated 25 kW at 480 V, such that the total rated resistance of the load bank  19  is 100 kW at 480 V, with a power factor of 1.0. 
         [0031]    In one embodiment, the engine  12 , which is equipped with a radiator, and alternator  14  are mounted within one enclosure, and the load bank  19  is mounted within a separate enclosure that is physically connected to the engine-generator enclosure adjacent to the radiator of the engine  12 . In such an embodiment, the radiator of the engine  12  forces air over the load step resistor(s)  44 . In another embodiment, the load bank  19  is remotely located, and it is physically connected to the engine  12  and alternator  14  only to the extent necessary to facilitate electrical communication and control. In another embodiment, the load bank  19 , the engine  12 , and the alternator  14  are configured on a common base, which could include a common trailer or skid, within a single enclosure. 
         [0032]    The system  10  may also be equipped with a remote communications module  46  and an antenna  48 . The remote communications module  46  could comprise terrestrial wireless or satellite communications technology, or a combination of both, in tandem or redundantly. The remote communications module  46  allows the system  10  to periodically, or on demand, transmit data that may be monitored. Such data may include the status of the engine  12 , the DPF  22 , and the load bank  19 . The remote communications module  46  could also be equipped with means for transmitting a location via a global positioning system (GPS), or the like. The remote communications module  46  may also be equipped to receive data and relay it to the generator controller  26  for remote control of the system  10 . In one embodiment of the system  10  equipped with a remote communications module  46 , a fault condition in any portion of the system  10  will cause an alert to be sent to an operator via phone text message (SMS) or via electronic mail. 
         [0033]    Specific data transmitted by the remote communications module  46  may include: the fuel level of the engine  12  in a range from 0 to 100%; the fuel consumption rate of the engine  12  in gallons per hour; oil pressure of the engine  12  in pounds per square inch; temperature of the coolant in the engine  12  in degrees Fahrenheit or degrees Celsius; the on/off status of the DPF  22 ; the soot level of the DPF  22 ; whether the DPF  22  regeneration function has been inhibited or disabled; the temperature of the exhaust of the engine  12  at various points within engine  12 ; the operating status of the load bank  19 , and whether the load bank  19  has correctly responded to a demand request from the generator controller  26 . 
         [0034]      FIG. 1B  depicts an embodiment of an engine-generator and load bank system  10  comprising an engine  12  mechanically connected and configured to drive an alternator  14 . The alternator  14  is connected to an output bus  16 , which is connected to a real load  17 , and a load bank bus  18 , which is connected to a load bank  19 . The outputs bus  16  and load bank bus  18  are connected to the alternator by way of disconnects  21 , which could comprise circuit breakers or fused switches. In such an embodiment, the alternator  14  may be sized and configured as described above. 
         [0035]    In the embodiment of  FIG. 1B , the engine  12  is equipped with an engine control module  20  and a DPF  22 . The system  10  comprises a generator controller  26  that is connected to the engine  12  via a communication means  27 , which could be any suitable communication bus as described above. The generator controller  26  is equipped with at least one load step output  40 ; it could have one or a plurality of load step outputs  40 . The load step output(s)  40  is/are connected to one or more load step contactor(s)  42 , which control the electrical connection of at least one load step resistor  44  to the load bank bus  18 . The electrical system of such an embodiment may be single- or poly-phase, as described above. 
         [0036]    In the embodiment of  FIG. 1B , the generator controller  26  monitors the loading of the alternator  14  by extrapolation. The generator controller  26  receives engine operation information from the engine control module  20  via the communication means  27 , which information the generator controller  26  uses to determine loading conditions of alternator  14 . The generator controller  26  then directly controls the load bank  19  by way of the load step output(s)  40  and load step contactor(s)  42  as necessary in cases of neglect, regeneration, and excessive idle. 
         [0037]      FIG. 2  depicts a control system that the generator controller  26  may employ to control the system  10 . The generator controller  26  first evaluates generator operating status  50  to determine if the engine  12  is in an acceptable operating condition  52 . Whether the engine  12  is in an acceptable operating condition is a function of whether a neglect scenario or excessive idle scenario is present. Cases of neglect and excessive idle correspond to an engine  12  being in an unacceptable operating condition. Further, whether the engine  12  is in an acceptable operating condition depends on whether the exhaust temperature is sufficient to provide for effective regeneration. If the exhaust temperature is too low for effective regeneration, and if the engine  12  is in a regeneration scenario, the engine is not in an acceptable operating condition. 
         [0038]    If the engine  12  is in an acceptable operating condition, the load bank  19  is or remains disconnected  54 . If the engine  12  is not in an acceptable operating condition, the generator controller  26  determines whether the engine  12  has operated in an unacceptable state for a pre-set time  56 . If the engine  12  has operated in an unacceptable condition for a pre-set time, the load bank  19  is connected  58 . That is, the generator controller  26  signals the load bank controller  32  via the load enable output  30  and load enable input  34  to initiate the load bank  19  by way of the load step output  40  and the load step contactor(s)  42 . Or, in an embodiment without a load bank controller  32 , the generator controller  26  controls the load bank  19  directly. The load bank  19  is then operated as described supra. If the engine  12  has not operated in an unacceptable condition for a pre-set time, the load bank  19  is or remains disconnected  54 . 
         [0039]    Once the load bank  19  is connected, it remains connected for a pre-set time, as required for a load cycle. While the load bank  19  is connected, the generator controller  26  and/or the load bank controller  32  determine whether a load spike is present  60 . If a load spike is present, the generator controller  26  effects a load dump by signaling the load bank controller  32 , either directly or via load dump output  28  and load dump input  36 , so that the load bank  19  is disconnected  54 . If a load spike is not present, the generator controller  26  determines whether the load cycle is complete  64 . If the load cycle is complete, the evaluation begins anew  50 . If the load cycle is not complete, the load cycle will resume upon restarting  62  the system  10 . 
         [0040]      FIG. 3  depicts a method of operating the system  10  by configuring the generator controller  26 . The method involves first setting a rated operating load  68 . Then, it requires setting: a load window  70 , a duration  72 , a max idle time  74 , and a minimum acceptable load  76  for DPF regeneration. Next, it involves monitoring: the load  78 , idle time  80 , and regeneration status  82 . Then, it involves initiating a load cycle  84  when monitored conditions reach set points that correspond to cases of neglect, regeneration, or excessive idle. Finally, it involves dumping the load bank  86  in the presence of a load spike. 
         [0041]    The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. The illustrative discussion above, however, is not intended to be exhaustive or to limit the disclosed concepts to any particular form. The embodiments were chosen and described in order to best explain the principles of the disclosed concepts in order to enable others skilled in the art.