Patent Publication Number: US-11028723-B1

Title: Gas turbine generator load level control system

Description:
TECHNICAL FIELD 
     This disclosure relates to gas turbine engines and, in particular, to gas turbine engine generator load leveling. 
     BACKGROUND 
     Gas turbine engines provide torque on a rotating shaft by combustion of fuel to rotate a compressor and downstream turbine. An AC (alternating current) or DC (direct current) generator converts mechanical power into electric power. Generators may include a rotor and a stator where the rotor or the stator is coupled with a rotating prime mover, such as a gas turbine engine to generate electric power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale. Moreover, in the figures, like-referenced numerals designate corresponding parts throughout the different views. 
         FIG. 1  illustrates a cross-sectional view of an example of a gas turbine engine; 
         FIG. 2  is a block diagram illustrating an example gas turbine engine generator (GTG) load leveling system; 
         FIG. 3  is a series of operational diagrams illustrating example operation of the GTG load leveling system; 
         FIG. 4  is another series of operational graphs illustrating example operation of the GTG load leveling system; 
         FIG. 5  is an operational flow diagram of example operation of the GTG load leveling system; and 
         FIG. 6  is a block diagram of an example of a portion of the GTG load leveling system. 
     
    
    
     DETAILED DESCRIPTION 
     The systems and methods described herein relate to a system that may include a gas turbine engine and a generator coupled with the gas turbine engine. The generator is rotatable by the gas turbine engine to generate electric power on a load bus. The system may also include controller circuitry configured to control the load bus to manage an output torque of the gas turbine engine in accordance with a load demand present on the generator. At least one first load and at least one second load may be selectively supplied power by the load bus as pulse loads. The controller circuitry may dynamically alternate supply of electric power from the load bus to the first load and the second load to maintain operational transient parameters of the gas turbine engine within a predetermined range. 
     An interesting feature of the system relates to the first load and the second load each being a pulse load of greater than 50% of rated output power of the generator. 
     Another interesting feature of system relates to the impedance of the first load and the second load being substantially equal. 
     During example operation, the generator may be rotationally driven by the gas turbine engine to output electric power to a load bus in order to supply a load demand present on a the load bus. The first load may be energized with the load bus and an output torque demand of the gas turbine engine may be increased in accordance with an increase in the load demand on the load bus. The controller circuitry may direct cycling between energizing, with the load bus, the first load and the second load to substantially maintain the increase in the load demand on the load bus as the first load and the second load are sequentially energized and deenergized. The output torque demand of the gas turbine engine may be maintained substantially unchanged during the cycling. 
     Another interesting feature of the systems and methods described relates to the second load being a load substantially duplicative of the first load, or being a dynamic braking resistor selectively available to slow a motor electrically coupled with a source of electric power other than the generator. The controller circuitry is configured to confirm the second load is duplicative of the first load or that the dynamic braking resistor is not currently being used to slow the motor before dynamically alternating supply of electric power to the first load and the second load. 
     Another interesting feature relates to the controller circuitry directing cycling between energizing the first load and the second load, since such cycling may include energizing the second load while the first load is being deenergized and subsequently energizing the first load while the second load is being deenergized. 
       FIG. 1  is a cross-sectional view of a gas turbine engine  100 . In some examples, the gas turbine engine  100  may supply power to and/or provide propulsion of a watercraft or aircraft. Examples of a watercraft include a ship, vessel or boat having a propeller, impeller or fan blades, which are provided electrical or mechanical power by the gas turbine engine, and examples of an aircraft may include a helicopter, an airplane, an unmanned space vehicle, a fixed wing vehicle, a variable wing vehicle, a rotary wing vehicle, an unmanned combat aerial vehicle, a tailless aircraft, a hover craft, and any other airborne and/or extraterrestrial (spacecraft) vehicle. Alternatively or in addition, the gas turbine engine  100  may be utilized in a configuration other supplying propulsion to an aircraft or watercraft such as, for example, an industrial application, an energy application, a power plant, a pumping set, a marine application, a weapon system, a security system, a perimeter defense and/or security system. 
     The gas turbine engine  100  may take a variety of forms in various embodiments. Though depicted as an axial flow engine, in some forms the gas turbine engine  100  may have multiple spools and/or may be a centrifugal or mixed centrifugal/axial flow engine. In some forms, the gas turbine engine  100  may be a turboprop, a turbofan, or a turboshaft engine. Furthermore, the gas turbine engine  100  may be an adaptive cycle and/or variable cycle engine. Other variations are also contemplated. 
     The gas turbine engine  100  may include an intake section  120 , a compressor section  160 , a combustion section  130 , a turbine section  110 , and an exhaust section  150 . During operation of the gas turbine engine  100 , fluid received from the intake section  120 , such as air, travels along the direction D 1  and may be compressed within the compressor section  160 . The compressed fluid may then be mixed with fuel and the mixture may be burned in the combustion section  130 . The combustion section  130  may include any suitable fuel injection and combustion mechanisms. The hot, high pressure fluid may then pass through the turbine section  110  to extract energy from the fluid and cause a turbine shaft of a turbine  114  in the turbine section  110  to rotate, which in turn drives the compressor section  160 . Discharge fluid may exit the exhaust section  150 . 
     As noted above, the hot, high pressure fluid passes through the turbine section  110  during operation of the gas turbine engine  100 . As the fluid flows through the turbine section  110 , the fluid passes between adjacent blades  112  of the turbine  114  causing the turbine  114  to rotate. The rotating turbine  114  may turn a shaft  140  in a rotational direction D 2 , for example. The blades  112  may rotate around an axis of rotation, which may correspond to a centerline X of the turbine  114  in some examples. 
       FIG. 2  is a block diagram illustrating an example gas turbine engine generator (GTG) load leveling system  200 . The GTG load leveling system  200  includes an auxiliary generator  202  rotatably driven by a shaft  204  of a gas turbine engine  100  in order to output electric power to supply a load bus  206 . The auxiliary generator  202  may be an AC or DC machine, and may include rectifiers, converters and the like (not shown) to control a load demand on the load bus  206 . The generator  202  may include any type of electrical generator. Examples of the generator  202  may include a synchronous generator, an induction generator, an asynchronous generator, a permanent magnet synchronous generator, an AC (Alternating Current) generator, a DC (Direct Current) generator, a synchronous generator with stator coils, or any other device that converts mechanical power to electric power. 
     The load bus  206  may selectively supply power to a number of different loads including a first load  208 , and a second load  210 . The load bus  206  may include any connector or connectors that conduct electricity. Examples of the load bus  206  may include a bus bar, a busway, a bus duct, a solid tube, a hollow tube, a wire, an electrical cable, or any other electrical conductor. 
     The GTG load leveling system  200  also includes a controller circuitry  216 . The circuitry of the controller  216  may include executable logic stored in memory to provide at least a portion of the functionality described herein. The controller  216  may include communication circuitry  220  to provide signal input/output capability for communication with the gas turbine engine  100 , the auxiliary generator  202 , the load bus  206 , the first load  208  and the second load  210 . The controller  216  may receive parameters, such as operational values via the communication circuitry  220 . In addition, the controller may output parameters and control commands via the communication circuitry  220 . Communication via the communication circuitry  220  may be wired or wireless, and may in the form of individual signals, groups of signals, network communication protocols, proprietary protocols and/or other forms of electronic based messaging or signal transmission. 
     The GTG load leveling system  200  may be coupled with a vehicle drive power system  230  having at least one motor  232 , which is controlled with a dynamic braking system  234 . The vehicle drive power system  230  may, for example, be for a watercraft such as a ship, in which propulsion is provide by the motor  232  via respective propeller(s) or fan(s)  236 . Power may be variably supplied to the motor  232  by an electric power source  240  via a primary bus  242 . The electric power source  240  may be any source of electric power. In the illustrated example, variable alternating current (AC) power is supplied by the primary bus  240  via a rectifier  246 , a direct current (DC) link  248  and an inverter  250  to the motor  232 , and a capacitor  252  may provide a high frequency shunt to ground. The dynamic braking system  234  may include a chopper circuit  254  providing a voltage regulation function and/or a switching function, and a dynamic brake resistor (DBR)  256  providing a resistive sink for excess power. During operation, when the motor  232  is rotating faster than desired, such as during stopping, slowing quickly, and/or reversing direction of motor rotation, the motor  232  acts as a generator and thereby produces electrical energy, which is directed to the dynamic braking system  234  for release through the DBR  236 . 
     The controller  216  may receive and transmit variables and control commands to the vehicle drive power system  230 . In an example, the vehicle drive power system  230  may include one or more separate and independent control systems operating and providing the functionality of the vehicle drive power system  230 . For example, speed and navigation of a watercraft using (among other things) the motor  232  may be separately monitored and controlled. Alternatively, or in addition, some portion, or all, of the functionality of the vehicle drive power system  230  may be provided by the controller  216 . In addition, GTG load leveling system  200  may be fully controlled by the controller  216 . Alternatively, or in addition, the GTG load leveling system  200  may include different controllers or control sub-systems performing portions of the functionality of the GTG load leveling system  200 . For example, the gas turbine engine  100  may be separately monitored and controlled with a control system such as a full authority digital electronics control (FADEC) that is in communication with the communications circuitry  220  of the controller  216 . 
     The controller  216  may be in communication with gas turbine engine  100  and the auxiliary generator  202  to receive operational parameters. For example, the auxiliary generator  202  may provide a load demand signal, and the gas turbine engine  100  may provide a temperature signal indicative of an operational temperature of the gas turbine engine  100 . In addition, the controller  216  may monitor and control the load bus  206  and the first and second loads  208  and  210 . In addition, the controller  216  may be in communication and/or receive and monitor other operational parameters of the GTG load leveling system  200  and/or the vehicle drive power system  230  via the communication circuitry  220 . 
     The controller circuitry  216  may also include power circuitry  260 . The load bus  206  and the first and second loads  208  and  210  may include or be electrically connected with the power circuitry  260 , such as a device or combination of devices that switch and/or control and/or convert electric power. Examples of the power circuitry  260  may include a power converter, a rectifier, an AC to DC converter, a switching device, a diode, a thyristor, an inverter, a transistor, and a capacitor. The power circuitry  260  may include semiconductor and/or solid state devices as well as circuit breakers, switches, fuses and other switching device(s) and/or systems capable of energizing and de-energizing the load bus  206  and/or the first and second loads  208  and  210  as described herein. 
     In an example system, each of the first and second loads  208  and  210  may be short duration high energy loads, such as, for example, 100-200 MW loads that are energized continuously for a predetermined relatively short period of time, such as less than 1 minute. Thus, each of the first and second loads  208  and  210  may be referred to as a pulse load. When energized and then de-energized, each pulse load may represent a dynamic load demand creating a transient step change in load. In an example the step change in load demand may range from about zero to five percent to about (+/−five percent) fifty to ninety-five percent, or from about (+/−five percent) zero to five percent to eighty to ninety-five percent of the total load on the load bus  206  with step changes in bus loading occurring over a time period of about 100 milliseconds or less (where about is +/−10 milliseconds). Examples of the first and second load include vehicle electronics, a vehicle, an aircraft, a directed-energy weapon, a laser, a plasma weapon, a railgun, a microwave generator, a pulse-powered device or other power consuming system controlled by the controller  216 . 
     The auxiliary generator  202  may be sized and rated to supply 100% of the expected peak power needed by the load on the load bus  206 . Accordingly, an additional power source, such as a battery or other energy source supplying power to the load bus  206  may be omitted. In an example, each of the first load  208  and the second load  210  may be a pulse load of greater than 50% of the rated output power of the auxiliary generator  202 , which are wholly supplied electric power from the auxiliary generator  202 . Power generated by the auxiliary generator  202  is provided as function of rotational torque supplied to the shaft  204  with the gas turbine engine  100 . As the load on the load bus  206  varies, the voltage and current on the load bus  206  and therefore the load demand on the auxiliary generator  202  correspondingly varies. Short term relatively small variations in load demand may be transients that are handled, or absorbed, by the auxiliary generator  202  by, for example, allowing variation in generator output voltage within an acceptable range. If, however, variations in load on the load bus  206 , and corresponding changes in load demand, are too large and/or of too long duration, the auxiliary generator  202  may demand greater or lesser rotational output torque from the gas turbine engine  100 . Variations in rotational torque of the gas turbine engine  100  may undesirably vary the operating temperature of the gas turbine engine  100  resulting in thermal cycles, which may lead to higher maintenance frequency, accelerated material fatigue, and the like. 
     In the GTG load leveling system  200 , the controller  216  may dynamically manage the first and second loads  208  and  210  with load management circuitry  262  included in the controller circuitry  216 . The load management circuitry  262  may include logic used to anticipate and avoid thermal cycling of the gas turbine engine  100 . Anticipation and avoidance of thermal cycling may be accomplished by a prediction model included in the controller  216 . The prediction model may provide predictions based on the operational parameters being monitored and lookup tables, artificial intelligence, machine learning, historical data and/or other information used to anticipate performance of the system. 
     The load management circuitry  262  may adjust the timing of energization and de-energization of the first and second load  208  and  210  to minimize thermal cycling of the gas turbine engine  100  above a predetermined threshold. In an example, The first load  208  and the second load  210  may be substantially equal, or substantially duplicative, such that the second load  210  is duplicative of the first load  208  and the timing of switching between the first load  208  and the second load  210  may be managed by the load management circuitry  262  in conjunction with the power circuitry  260  to minimize thermal cycling. “Substantially equal” or “substantially duplicative” in this context means that the impedance of the first load  208  and the second load  210  consume an amount of electric power from the load bus  206 , such that the load demand on the auxiliary generator  206  is within +/−10% when supplying electric power to either of the first load  208  or the second load  210 . 
     An example of cycle time management control by the controller  216  may involve, a situation where the timing of de-energizing the first load  208  and energizing the second load  210  creates transients in load demand on the load bus  206  that causes corresponding thermal cycling of the gas turbine above a pre-determined threshold. In this situation, the controller  216  may increase or decrease the cycle timing between de-energizing the first load  208  and energizing the second load  210  to lower the magnitude of transient load demand experience by the load bus  206 . 
     In an example GTG load leveling system  200 , the controller  216  may control load leveling on the load bus  206  with the load management circuitry  262  to indirectly manage the output torque of the gas turbine engine  100  in accordance with the load demand present on the generator  202 . Load leveling may be performed by the controller  216  using the power circuitry  260  and the load management circuitry  262  to dynamically alternating supply of electric power from the load bus  206  to the pulse loads of the first load  208  and the second load  210 . The dynamic switching may be performed with the controller  216  to maintain transient operational parameters, such as the operating temperature, of the gas turbine engine  100  within a predetermined range or below a predetermined threshold. In other examples, any number of first and second loads  208  and  210  may be included, and the controller  216  may use the power circuitry  260  and the load management circuitry  262  to dynamically alternate energizing and de-energizing pulse loads of any number of first and second loads  208  and  210 . 
     Control of the gas turbine engine  100  may be separate and independent from control of the load demand on the generator  202  and/or the first and second loads  208  and  210 . For example, during operation the gas turbine engine  100  may be separately and independently speed controlled to maintain a speed setpoint. As the load on the load bus  206 , and the corresponding load demand on the generator  202  changes, the level of output torque from the gas turbine engine  100  to maintain rotational speed of the gas turbine engine  100  and the generator  202  at the speed setpoint may vary. The controller  216  may manage the loading of the load bus  206  independent of the control of the gas turbine engine  100 . 
     Controlling the load on the load bus  206  may include the controller  216  monitoring one or more transient operational parameters of the gas turbine engine, such as an operational temperature. The loading of the load bus  206  may be managed by the controller  216  to avoid transient variations in the output torque of the gas turbine engine  100  resulting in the presence of undesirable cyclical changes in transient parameters of the gas turbine engine  100  as the first load  208  and the second load  210  are alternately supplied as pulse loads by the load bus  206 . An example of a desirable predetermined range or predetermined cycling threshold of a transient operational parameters of the gas turbine engine  100  is maintaining an operational temperature of the gas turbine engine in a range of +/−25% or +/−30% of rated temperature. 
     Thus, the GTG load leveling system  200  may manage load leveling of the dynamic pulse loads (first load  208  and second load  210 ) with the goal of protecting the gas turbine engine  100  from experiencing undesirable repeated cycles, such as thermal cycles. Undesirable cycling of the gas turbine engine  100 , such as thermal cycling, may result in accelerated component fatigue and a correspond decline in engine lifespan. To avoid such undesirable cycling, instead of using a single pulsed load in this dynamic pulse loading scenario, multiple pulse loads are coordinated to allow for a substantially continuous load level on the load bus  206  and corresponding substantially continuous torque demand at the gas turbine engine  100 . 
     In an example, the first and second loads  208  and  210  may be selectively energized by the controller  216  in conjunction with one or more resistive dynamic load(s). The load management circuitry  262  may perform logic, such as a supervisory control algorithm, to manage an alternating load demand so that a level load profile may be maintained on the load bus  206 . Thus, the GTG load leveling system  200  may effectively operate a number of pulse loads sequentially while maintaining transient operational parameters of the gas turbine engine  100  within a predetermined range as the load bus  206  may be used as an “endless energy magazine”, repeatedly and sequentially supplying power to the pulse loads without undesirable cycling of the gas turbine engine  100 . 
     The controller  216  may also discontinue dynamically cycling the pulse loads of the first and second loads  208  and  210 . To avoid a large transient change in load on the load bus  206  when the dynamic cycling ends, the controller  216  may energize the dynamic braking resistor  256  as a continuously energized load (not a pulse load). The controller circuitry  216  may then direct a decrease in the output torque demand on the gas turbine engine  100 , thereby decreasing the power output by the generator to the load bus  206 . Since the dynamic braking resistor  256  is a resistive load, lower voltage and/or current as the generator  202  load demand is reduced does not negatively impact the load bus  206  and/or the dynamic braking resistor  256 . Moreover, the output torque of the gas turbine engine  200  may be linearly and efficiently reduced without transient cycling, such as thermal cycling. 
     During example operation with the vehicle drive power system  230 , the controller circuitry  216  may monitor one or more operational parameters of the gas turbine engine  100  and control a load demand of the auxiliary generator  202  to output electric power on the load bus  206 . The generator  202  may be rotatably driven to generate the electric power by the output torque of the gas turbine engine  100 . In other examples, the controller  216  may also, or alternatively, monitor other parts of the vehicle power drive system  230 , such as the motor  232 , the dynamic braking system  234 , the rectifier  246 , the inverter  250  or other operational parameters of the vehicle power drive system  230 . The load demand on the generator  100  may be controlled by the controller  216  by controlling energization and de-energization of a first load  208  as the load on the load bus  206  and controlling energization and de-energization of the second load  210  as the load on the load bus. The controller  216  may control the transition between the load on the load bus being the first load and being the second load so as to maintain the load on the load bus  206  substantially unchanged by timing the transition between the load on the load bus  206  being the first load  208  and being the second load  210 . 
       FIG. 3  is a series of operational diagrams illustrating example operation of the GTG load leveling system. Referring to  FIGS. 2 and 3 , in this example, the controller  216  may perform load leveling on the gas turbine engine  100  by controlling the first and second loads  208  and  210  over time (t). In  FIG. 3 , at time (t)=5 the controller  216  may control the GTG load leveling system  200  such that the first load  208  is energized in the form of a pulse load  302 . In response to the pulse load  302 , the demand on the auxiliary generator  202  increases. In an example, a full load rating of the generator  202  is 105%-110% of the first load  208  or the second load  210 . Accordingly, when the first load  208  is energized, the load demand on the generator  202  may increase from between 0% and 10% to between 90% and 100% of rated output of the generator  202 . Operational parameters, such as an operational temperature  304 , of the gas turbine engine  100  correspondingly vary as the output torque of the gas turbine engine  100  is increased (or decreased) to satisfy the load demand on the generator  202 . 
     At time (t) of about 7, the first load  208  is de-energized and the second load  210  is energized in the form of a pulse load  306 . The controller  216  may coordinate the energization of the second load  210  and the de-energization of the first load  208  such that the load demand on auxiliary generator  202  may remain substantially unchanged. The load demand may remain substantially unchanged since the controller  216  dynamically alternates supply of electric power from the load bus  206  to the first load  208  and the second load  210  to maintain transient operational parameters, such as the temperature of the gas turbine engine  100  within a predetermined range. Accordingly, the controller  216  may control the load on the load bus  206  to manage the output torque of the gas turbine engine  100  in accordance with a load demand present on the auxiliary generator  202 . In other words, the load demand on the auxiliary generator  202  may be managed by the controller  216  to be substantially unchanged by controlling the load on the load bus  206  so that the rotational torque requirements of the generator  202  remain within a range that does not create undesirable variations in the operational parameters of the gas turbine engine  100 . 
     In an example, load variations (or transients) on the load bus  206 , due to transitioning between the first load  208  and the second load  210 , of less than 25% for under 0.5 seconds may be absorbed by the generator  202 . The auxiliary generator absorbing such “instantaneous” load demand may, for example, result in changes in voltage and/or current flow on the load bus  206  without creating a significant change in demand for rotational torque output by the gas turbine engine  100 . In addition, or alternatively, load variations that may cause changes in output torque demand of the gas turbine engine  100  of a relatively short duration may be absorbed by the gas turbine engine, resulting in acceptable variations in transient operational parameters. For example, relatively small thermal constants in the gas turbine engine  100  may resulting in little or no variation in the temperature of the gas turbine engine. An example factor affecting changes in a transient operational parameter is a time constant for gas temperature changes at the turbine section outlet, which may be referred to as turbine outlet temperature (TOT). The TOT may respond relatively quickly, such as within 0.5 seconds, with undesirable temperature variations to relatively large load variations (such as a 50% or greater step change in load), whereas with lesser step changes in load, the temperature variations due to variations in load may be lower and/or within an acceptable range for a long enough period of time, thereby avoiding undesirable cycling. 
     In this regard, the actual amount of load variations (or transients) that are undesirable will be a function of characteristics of the generator  202  and the gas turbine engine  100 , along with other parameters such as the aggressiveness of the torque demand for output torque from the gas turbine engine  202 . Accordingly, dynamic cycling between the first load  208  and the second load  210  may be controlled by the controller  216  such that the load demand of the generator  202  remains substantially unchanged as the controller  216  dynamically alternates between the first load  208  and the second load  210 . Thus, by controlling cycling between the first load  208  and the second load  210  with the controller  216 , the output torque of the gas turbine engine  100  may also be substantially unchanged. As used herein, the output torque of the gas turbine engine being “substantially unchanged” or “substantially maintained” or “substantially constant” refers to changes in the operation of the gas turbine engine that do not result in undesirable cycling of the gas turbine  100 , such as thermal cycling. The load demand on the generator  202  or load on the load bus  206  being “substantially unchanged” or “substantially maintained” or “substantially constant” as used herein refers to an absence of corresponding changes in output power of the generator  202  that result in undesirable cycling of the gas turbine  100 , such as thermal cycling. 
       FIG. 4  is another series of operational graphs illustrating example operation of the GTG load leveling system. In this example, the controller  216  may control energization and de-energization of only one of the first load  208  or the second load  210  as a pulse load over time (t). As illustrated in the example of  FIG. 4 , with reference to  FIG. 2 , the first load  208  as represented by pulse load  402 , is sequentially supplied electric power by the load bus  206 , whereas the second load  210  remains at a zero pulse load  406  (de-energized). As a result, upon energization and de-energization of the pulse load  402 , undesirable cyclically variations (or transients) in the operational parameters, such as an operational temperature  404  of the gas turbine engine  100  may occur due to changes in rotational torque output requirements of the gas turbine engine  100 . 
     Referring again to  FIG. 2 , in the event that one of the first load  208  or the second load  210  is unavailable for energization, the GTG load leveling system  200  may still minimize undesirable cyclical operation of the gas turbine engine  100  using another existing load in place of the load unavailable for energization. For example, in the illustrated example of  FIG. 2 , the GTG load leveling system  200  is coupled with a vehicle drive system  230  that includes a dynamic braking system  234 . In the illustrated configuration, the controller  216  may selectively use the dynamic braking resistor  256  for load leveling. The impedance of the dynamic braking resistor  256 , or some portion thereof, may be substantially equal to the impedance of the first load  208  or the second load  210 . In other examples, other existing loads with substantially equal impedance to the first load  208  and the second load  210  may be used as the another existing load. 
       FIG. 5  is an operational flow diagram of example operation of the GTG load leveling system in connection with use of an existing load and/or at least one of the first and second loads. Referring to  FIGS. 2 and 5 , in this example, the GTG load leveling system  200  is coupled with the vehicle drive system  230 , which is independently operated to provide propulsion to the vehicle. In other examples, the controller  216  may control operation of both the GTG load leveling system  200  and the vehicle drive system  230 . The operation begins with receipt, by the controller  216  of a request to energize a pulse load from the load bus  206 . ( 502 ) Such a request may be a signal initiated by a user, or from another system, such as the vehicle drive system  230 . The controller  216  may determine if sufficient pulse loads are available for selective energization to control and manage level loading on the load bus  206 . ( 504 ) In addition, the controller  216  may confirm that the impedance of the second load is duplicative of the first load. 
     If sufficient pulse loads are available for energization, the controller  216  may direct the power circuitry  260  to dynamically cycle between energizing, with the load bus  206 , the first load(s)  208  and the second load(s)  210  to substantially maintain the increased load demand on the load bus  206  as the first load(s)  208  and the second load(s)  210  are sequentially energized and de-energized as pulse loads. ( 506 ) The controller  216  may energize the second load  210  and de-energize the first load  208  in parallel, and energize the first load  208  and de-energize the second load  210  in parallel such that the load demand present on the load bus  206  remains substantially unchanged, thereby maintaining the load demand on the auxiliary generator  202  substantially constant. ( 508 ) Parallel energization and de-energization of the loads may be simultaneous, or may include a time gap or delay so long as the transients on the load bus  206  resulting from the switching are absorbed by the auxiliary generator  200  or otherwise avoid cycling of transient operational parameters of the gas turbine engine  100 , as discussed elsewhere. Due to the controller  216  leveling the load provided by the load pulses on the load bus  206 , the output torque demand of the gas turbine engine  100  may be maintained as substantially unchanged during the cycling of the pulse loads. ( 510 ) 
     If the controller  216  determines there are insufficient pulse loads available to maintain the load on the load bus  206  substantially constant, the controller  216  may determine if additional existing loads are available in the existing system, such as the vehicle drive system  230 . ( 514 ) In the illustrated example, the additional existing load(s) may be the dynamic load resistor  256  in the dynamic braking system  234 . Thus, the dynamic braking resistor  256  may selectively replace either the first or second load  208  or  210  and be used as a pulse load as well as being used to selectively slow rotation of the motor  232 . In other examples, other existing load(s) in the existing system, such as compressors, pumps and the like, which have a predetermined impedance that substantially match the pulse load being energized by the load bus  206  may be used. In still other examples, GTG load leveling system  200  may include a resistor or other energy sink with a predetermined impedance substantially matching the first and second loads  208  and  210  that is capable of being a pulse load when needed for load leveling the load bus  206 . 
     In the example of  FIG. 2 , the motor  232  included in the vehicle drive system  230  may be operating to provide propulsion to the vehicle, and the dynamic braking system  234  may be intermittently used by the drive motor  232  to produce a braking torque during overhauling conditions. Thus, the controller  216  may determine availability of the additional load in the existing system for use as a pulse load by determining if the existing system, in this example motor  232 , is requesting or anticipating use of the additional load (dynamic braking resistor  256 ) during operation to provide propulsion to the vehicle. ( 514 ) For example, the motor  232  may be requesting braking using the dynamic braking system  234 . Thus, the controller circuitry  216  may confirm that the dynamic braking resistor  256  is not being used to slow rotation of the motor  232  before directing supply of power to the dynamic braking resistor  256 . 
     If the additional load is not anticipated to be used, the controller  216  may confirm that the additional load is available and not currently being used/controlled in the existing system. ( 516 ) Upon confirmation that the additional load(s) is not being used, the additional load(s) may be energized and de-energized via the controller  216  as a pulse load in place of or in addition to the first load  208  and the second load  210 . ( 520 ) The pulse loads may be dynamically cycled to maintain load demand on the auxiliary generator  202 , and avoid undesirable cycling of the gas turbine engine  100  ( 506 ,  508 ,  510 ) 
     In other examples, availability may relate to whether the additional load(s) is fully operational, off line for maintenance, and/or requested but not yet being used. For example, the existing system may have requested but not yet energized the dynamic braking system  234  thereby rendering the additional load unavailable. In example configurations, the existing system may have priority or precedence regarding use of the additional load. For example, the use of the load braking system  234  by the drive motor  232  may take precedence over use of the dynamic load resistor  256  as an additional pulse load. 
     In an example, the controller circuitry  216  may include Request Cypher Lock (RCL) control logic as part of the load management circuitry  262 . The Cypher lock logic may place priority for which system has precedential access to use an additional load, such as the dynamic braking resistor  256 . In an example of a vehicle drive system  230 , the primary focus in the controller  214  gaining access to the additional load for use as a pulse load may be to avoid compromising operation of the vehicle drive system  230  so that the existing vehicle drive system  230  is not forced to operate in a dangerous or operationally deficient condition. In this example, the priority may be given to the drive motor&#39;s  232  use or anticipated use of the dynamic braking system  234  such that the controller  216  will forego use of the dynamic load resistor  256  as a pulse load until the motor  232  no longer needs the dynamic braking system  234 . 
     If the additional load is presently in use in the existing system, the requested use of the additional load by the controller  216  as a pulse load is blocked. ( 518 ) If it is determined by the controller  214  at ( 514 ) that there is no expected use of the additional existing load(s) in the existing system (available), the controller  216  may confirm that the additional load(s) are not presently in use as a pulse load. ( 522 ) If the additional load(s) are presently in use as pulse loads, further use may be blocked. ( 518 ) If the additional load(s) are not presently being used as pulse loads, the existing additional load(s) may be used as pulse loads ( 520 ), by being dynamically cycled to maintain load demand on the auxiliary generator  202 , and avoid undesirable cycling of the gas turbine engine  100  ( 506 ,  508 ,  510 ). 
     During operation, the GTG load leveling system  200  is configured to maintain the load demand of the generator  202  substantially unchanged as the controller circuitry  216  dynamically alternates between the first load  208  and the second load  210  such that the output torque of the gas turbine engine  100  is also substantially unchanged. The first load  208  and the second load  210  may represent pulse loads that are substantially the same magnitude and duration. The controller circuitry  216  may control cycling of power between energizing the first load  208  and the second load  210  by sequentially pulsing the first load  208  and then the second load  210  with electric power from the load bus  206 . Cycling between energizing the first load  208  and the second load  210  may be accomplished by energizing the second load  210  while the first load  208  is being de-energized and subsequently energizing the first load while the second load is being de-energized. 
     The GTG load leveling system  200  may use an additional existing load, such as a dynamic brake resistor in addition to and/or in place of one of the first and second loads  208  and  210 . In an example, the second load  210  is another load substantially equal to the first load  208 , or is the dynamic braking resistor  256  configured for selective energization to slow the motor  232  supplied electric power from another power source  240 . In this example, cycling between energizing the first load  208  and the second load  210  may include the controller  216  confirming the another load is unavailable, and then confirming that the dynamic braking resistor  256  is not being used to slow the motor  232  before energizing the dynamic braking resistor  256  as the second load  210 . 
       FIG. 6  is a block diagram of an example of a portion of the GTG load leveling system  600 . The GTG load leveling system  600  may be included in, implemented in, or electrically coupled with a vehicle drive power system for a vehicle such as a ship. In  FIG. 6 , the GTG load level system  600  includes a first load  602  and a second load  604 , which are pulse loads selectively energized and de-energized by the controller from the load bus. The load bus may be suppled electric power by a generator, which is rotatabley driven by a gas turbine engine. For purposes of brevity, the discussion and illustration of the features and functionality discussed with reference to  FIGS. 1-5  may not be discussed or presented in  FIG. 6 . The features and functionality of  FIGS. 1-5  may be included partially or in their entirety in the system(s) discussed with reference to  FIG. 6 , unless otherwise noted. Likewise, the features and functionality of  FIG. 6  may be included partially or in their entirety in the system(s) discussed with reference to  FIGS. 1-5 . 
     In an example system that includes the GTG load leveling system  600  the controller circuitry  216  may include tandem circuitry  608  for use in load leveling the pulse loads present on the load bus. In this example, the first load  602  and the second load  604  may be equipment loads in the form of lasers. The tandem circuitry  608  may be used in tracking a target  610  of the first load  602  and the second load  604 . In other examples, the first and second loads  602  and  604  may be other types of equipment loads that may be tracked to the target  610 . 
     The tandem circuitry  608  may use information from a navigation system, such as a radar or satellite to identify a geographic location of the target  610  and the first and second loads  602  and  604 . For example, the vehicle drive power system may include a radar or satellite based tracking system providing coordinates in the form of global positioning coordinates. Based on these coordinates, the tandem circuitry  608  may determine a distance d 1  from the tandem circuitry  608  to the target  610  based on the known distances d 2  and d 3  between the respective load  1   602  and load  2   604  and the target  610  and length L between the respective load  1   602  and load  2   604  and the controller circuitry  216 . The tandem circuitry  608  may then determine independent angular positions of the first and second loads  602  and  604  such that both loads, lasers in this example, are aligned to strike the target  610  from different locations. Determination of the independent respective angular positions θ 2  and θ 4  for the respective loads  602  and  604  may be determined from: 
     
       
         
           
             
               
                 
                   
                     θ 
                     2 
                   
                   = 
                   
                     
                       sin 
                       
                         - 
                         1 
                       
                     
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                           d 
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                           ⁡ 
                           
                             ( 
                             
                               θ 
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                             d 
                             1 
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                             L 
                             2 
                           
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                             2 
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                             ⁢ 
                             L 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 
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                                   1 
                                 
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                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
             
               
                 
                   
                     θ 
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                           sin 
                           ⁡ 
                           
                             ( 
                             
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                             d 
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                   Equation 
                   ⁢ 
                   
                       
                   
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                   2 
                 
               
             
           
         
       
     
     Thus, using centrally located controller circuitry  216 , each of the first and second loads  602  and  604  may be independently maneuvered and sited on the target  610 . Once cited on the target  610 , the first and second loads  602  and  604  may be sequentially energized and de-energized as pulse loads to load level and thereby avoid thermal cycling of the gas turbine engine driving the auxiliary generator. In another example implementation with a moving target, the measured time derivatives of d 1  and ⊖(theta)1 may be propagated through Equations 1 and 2 for the computed time derivatives of ⊖(theta)5, ⊖(theta)4 and ⊖(theta) 2 to provide the appropriate localization algorithm for such a moving target. 
     The methods, devices, processing, circuitry, and logic described herein may be implemented in many different ways and in many different combinations of hardware and software. For example, all or parts of the implementations may be circuitry that includes an instruction processor, such as a Central Processing Unit (CPU), microcontroller, or a microprocessor; or as an Application Specific Integrated Circuit (ASIC), Programmable Logic Device (PLD), or Field Programmable Gate Array (FPGA); or as circuitry that includes discrete logic or other circuit components, including analog circuit components, digital circuit components or both; or any combination thereof. The circuitry may include discrete interconnected hardware components or may be combined on a single integrated circuit die, distributed among multiple integrated circuit dies, or implemented in a Multiple Chip Module (MCM) of multiple integrated circuit dies in a common package, as examples. 
     Accordingly, the circuitry may store or access instructions for execution, or may implement its functionality in hardware alone. The instructions may be stored in a tangible storage medium that is other than a transitory signal, such as a flash memory, a Random Access Memory (RAM), a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM); or on a magnetic or optical disc, such as a Compact Disc Read Only Memory (CDROM), Hard Disk Drive (HDD), or other magnetic or optical disk; or in or on another machine-readable medium. A product, such as a computer program product, may include a storage medium and instructions stored in or on the medium, and the instructions when executed by the circuitry in a device may cause the device to implement any of the processing described above or illustrated in the drawings. 
     The implementations may be distributed. For instance, the circuitry may include multiple distinct system components, such as multiple processors and memories, and may span multiple distributed processing systems. Parameters, databases, and other data structures may be separately stored and managed, may be incorporated into a single memory or database, may be logically and physically organized in many different ways, and may be implemented in many different ways. Example implementations include linked lists, program variables, hash tables, arrays, records (e.g., database records), objects, and implicit storage mechanisms. Instructions may form parts (e.g., subroutines or other code sections) of a single program, may form multiple separate programs, may be distributed across multiple memories and processors, and may be implemented in many different ways. Example implementations include stand-alone programs, and as part of a library, such as a shared library like a Dynamic Link Library (DLL). The library, for example, may contain shared data and one or more shared programs that include instructions that perform any of the processing described above or illustrated in the drawings, when executed by the circuitry. 
     Components of the GTG load leveling system and/or the vehicle drive power system described herein may include additional, different, or fewer components. For example, the output of the generator may be provided to a converter such as a DC to DC converter or an AC to DC converter or an AC to AC converter. In addition, the features and functionality of the GTG load leveling system and/or the vehicle drive power system described herein may include additional, different, greater or fewer operations than illustrated and/or discussed. In addition, the operations illustrated may be performed in an order different than illustrated. 
     To clarify the use of and to hereby provide notice to the public, the phrases “at least one of &lt;A&gt;, &lt;B&gt;, . . . and &lt;N&gt;” or “at least one of &lt;A&gt;, &lt;B&gt;, . . . &lt;N&gt;, or combinations thereof” or “&lt;A&gt;, &lt;B&gt;, . . . and/or &lt;N&gt;” are defined by the Applicant in the broadest sense, superseding any other implied definitions hereinbefore or hereinafter unless expressly asserted by the Applicant to the contrary, to mean one or more elements selected from the group comprising A, B, . . . and N. In other words, the phrases mean any combination of one or more of the elements A, B, . . . or N including any one element alone or the one element in combination with one or more of the other elements which may also include, in combination, additional elements not listed. Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.” 
     While various embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible. Accordingly, the embodiments described herein are examples, not the only possible embodiments and implementations. 
     The subject-matter of the disclosure may also relate, among others, to the following aspects:
         1. A system comprising:
           a gas turbine engine;   a generator coupled with the gas turbine engine, the generator rotatable by the gas turbine engine to generate electric power on a load bus;   controller circuitry configured to control the load bus to manage an output torque of the gas turbine engine in accordance with a load demand present on the generator; and   a first load and a second load, the controller circuitry configured to dynamically alternate supply of electric power from the load bus to the first load and the second load to maintain operational transient parameters of the gas turbine engine within a predetermined range.   
           2. The system of aspect 1, wherein the first load and the second load are each a pulse load of greater than 50% of rated output power of the generator.   3. The system of aspect 2, wherein the impedance of the first load and the second load are substantially equal.   4. The system as in any of aspects 1-3, wherein the second load is a dynamic braking resistor used to selectively slow rotation of a motor electrically coupled with a source of electric power other than the generator.   5. The system of aspect 4, wherein the controller circuitry is further configured to confirm that the dynamic braking resistor is not being used to slow rotation of the motor before directing supply of power to the second load from the load bus.   6. The system as in any of aspects 1-5, wherein the second load is a load substantially duplicative of the first load, or is a dynamic braking resistor selectively available to slow a motor electrically coupled with a source of electric power other than the generator, and the controller circuitry is configured to confirm the second load is duplicative of the first load or that the dynamic braking resistor is not currently being used to slow the motor before dynamically alternating supply of electric power to the first load and the second load.   7. The system as in any of aspect 1-6, wherein the load demand of the generator is substantially unchanged as the controller circuitry dynamically alternates between the first load and the second load such that the output torque of the gas turbine engine is also substantially unchanged.   8. A method comprising:
           rotationally driving a generator with a gas turbine engine;   
           outputting electric power to a load bus with the generator to supply a load demand present on a the load bus;
           energizing a first load with the load bus and increasing an output torque demand of the gas turbine engine in accordance with an increase in the load demand on the load bus;   cycling between energizing, with the load bus, the first load and a second load to substantially maintain the increase in the load demand on the load bus as the first load and the second load are sequentially energized and deenergized; and   maintaining the output torque demand of the gas turbine engine substantially unchanged during the cycling.   
           9. The method of aspect 8, wherein cycling between energizing the first load and the second load comprises energizing the second load and denergizing the first load in parallel, and energizing the first load and deenergizing the second load in parallel such that the load demand present on the load bus remains substantially unchanged.   10. The method as in aspect 8 or 9, wherein the first load and the second load are pulse loads that are substantially a same magnitude and duration, and cycling between energizing the first load and the second load comprises sequentially pulsing the first load and then the second load with electric power supplied from the load bus.   11. The method as in any of aspects 8-10, wherein the second load is a dynamic braking resistor configured for selective energization to slow a motor supplied electric power from another power source, and cycling between energizing the first load and the second load comprises confirming that the dynamic braking resistor is not being selectively energized to slow the motor before energizing the second load.   12. The method as in any of aspects 8-11, wherein cycling between energizing the first load and the second load comprises energizing the second load while the first load is being deenergized and subsequently energizing the first load while the second load is being deenergized.   13. The method as in any of aspects 8-12, wherein the second load is another load substantially equal to the first load, or is a dynamic braking resistor configured for selective energization to slow a motor supplied electric power from another power source, and wherein cycling between energizing the first load and the second load comprises confirming the another load is unavailable and then confirming that the dynamic braking resistor is not being used to slow the motor before energizing the dynamic braking resistor.   14. The method of 13, further comprising discontinuing cycling, maintaining energization of the dynamic braking resistor and decreasing an output torque of the gas turbine engine.   15. The method as in any of aspects 8-14, further comprising monitoring an operating temperature of the gas turbine engine, and adjusting a cycling time of cycling between energizing, with the load bus, the first load and a second load to minimize thermal cycling of the operating temperature above a predetermined threshold.   16. A system comprising:
           controller circuitry configured to:   
           monitor an operational parameter of a gas turbine engine;   control a load demand of a generator to output electric power on a load bus, the generator rotatably driven to generate electric power by output torque of the gas turbine engine;   control energization and de-energization of a first load as a load on the load bus;   control energization and de-energization of a second load as the load on the load bus;   transition between the load on the load bus being the first load and being the second load; and   maintain the load on the load bus substantially unchanged by timing the transition between the load on the load bus being the first load and being the second load.   17. The system of aspect 16, wherein the first load and the second load are substantially equal pulse loads.   18. The system as in aspect 16 or 17, wherein the first load is a first equipment load, and the second load is a dynamic braking resistor or a second equipment load.   19. The system of aspect 18, wherein the controller circuitry is further configured to selective control energization and de-energization of the dynamic braking resistor by confirmation, prior to energization, that the dynamic braking resistor is not being energized by a power source supplying a drive motor for a vehicle.   20. The system of aspect 19, where the vehicle is a ship, and the drive motor is supplied power by the power source to provide propulsion of the ship.       

     In addition to the features mentioned in each of the independent aspects enumerated above, some examples may show, alone or in combination, the optional features mentioned in the dependent aspects and/or as disclosed in the description above and shown in the figures.