Patent Publication Number: US-7592784-B2

Title: Power manager for an electrical power generator

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
   This application is a divisional of application Ser. No. 11/156,216, filed Jun. 17, 2005 and entitled “Power Manager for an Electrical Power Generator” by Wei Wei Qi, Michael Rubbo and Richard Wainwright. 
   Reference is hereby made to U.S. Pat. No. 7,272,514 entitled “Protection System for an Electrical Power Generator” of Wei Wei Qi, Michael Rubbo, and Richard Wainwright. This application is hereby incorporated by reference as set forth fully herein. 

   BACKGROUND 
   The present invention relates generally to electrical power generation systems, and more particularly to an electrical power generator having self-monitoring capabilities that cooperate with at least one intelligent load to safely utilize traditionally untapped power generating capabilities of the generator. 
   Electrical generators are used in a wide variety of dedicated electrical system applications and locations that require power independent of a standard electrical grid. Commonly, electrical generators are the primary, if not only, source of electrical power on a vehicle or ship, or in a remote location such as on an oil platform, in a small town, on an island or along a pipeline. Electrical generators are also commonly used as a backup power source in locations operating primarily off the standard electrical grid. 
   Because of this primary role served by electrical generators, it is often desired to keep the generator fully functioning, or at least partially functioning, in all circumstances. Maintaining the generator at full capacity is complicated by the fact that the conventional generator is a slave to its loads, the maximum sum of which may greatly exceed a rated capacity of the generator. The generator itself cannot directly control its outputted power; it can only control its own output voltage. Rather, it is the generator&#39;s loads that control the draw of power from the generator. Thus, to avoid overloading conditions that may harm the generator, the conventional generator simply shuts itself off upon detection of overloading condition indicators, such as excessive temperature. 
   Generators typically have a rated continuous capacity that is determined as the maximum quantity of power the generator can produce for an indefinite amount of time without risking damage to the generator. Generators also have a rated surge capacity determined as a value the generator can sustain for a limited time, such as when the generator experiences a surge in power demands due to the transitioning of the generator&#39;s loads between on and off states. 
   The rated continuous and surge capacities are typically very conservative estimates of what the generator can actually handle. That is, most conventional generators can produce much more power than their ratings allow, and in use, much of the generator&#39;s power generating capacity is neglected. Nonetheless, to ensure their continuous operation, generators typically are selected to have a sufficient continuous capacity rating to handle all loads operating simultaneously at full capacity. This assumption often results in the selection of a larger capacity generator than what may otherwise be required or the addition of a second generator to allow a reduction in the load attached to the first generator. In many situations, however, these solutions are not appropriate due to cost, weight, size, and efficiency considerations. Thus, there exists a need for a generator capable of utilizing more of its capacity. 
   SUMMARY 
   The present invention is a system and a method for making a full power capacity of an electrical power generator available for consumption by at least one intelligent load coupled to an output of the generator. In accord with the present invention, data is obtained from which both a present output power of the generator and a power capacity of the generator can be determined. Data indicative of both present output power and the power capacity of the generator are provided to the intelligent load for use by the load in determining its power consumption. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a graph of two power time relationships of a typical generator for illustrating a full power generating capacity of the generator. 
       FIG. 2  is block diagram of an electrical system in accord with the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention is a generator that incorporates a power management system that, in contrast to prior art generators that simply limit the generator to its rated capacity, seeks to capture and utilize the full power capacity of a generator.  FIG. 1  is a graph illustrating power-time relationships  6  and  8  of a typical generator for illustrating this full capacity of the generator.  FIG. 1  plots a quantity of power produced by a generator as a function of time that the generator can sustain production of that quantity of power without risking damage to itself given existing system parameters of the generator, such as an ambient temperature, a temperature of various components of the generator, a rotational speed of the generator, and a frequency of the generator output. As the system parameters change, so too does the capacity of the generator. For example, as the generator&#39;s ambient temperature increases, the power capacity of the generator decreases. Thus, power-time relationships  6  and  8  shown in  FIG. 1  exist for different system parameters, with power-time relationship  6  illustrating a capacity of the generator for a first set of system parameters (e.g., a low ambient temperature) and power-time relationship  8  illustrating the generator&#39;s capacity for a second set of system parameters (e.g., a high ambient temperature). 
   As shown in  FIG. 1 , the typical generator can produce a relatively high quantity of power; however, it can sustain this quantity for only a very short period of time. As the produced quantity of power decreases, the length of time that the generator can sustain this production increases. Eventually, the sustainable power levels off at a steady state value. 
   A rated continuous capacity and a rated surge capacity of a conventional generator are generally conservatively drawn from these power-time characteristics of the generator. That is, these rated values are typically determined from the generator&#39;s power-time relationship corresponding to a worse case scenario. The rated continuous capacity is generally determined as the steady-state value of the worse case scenario power-time relationship, while the rated surge capacity is determined as a multiple of the continuous capacity. The rated surge capacity may in fact be less than the actual maximum power the generator can produce. 
   The present invention enables the generator to produce power over its full range of capacities, rather than simply limiting the generator to its rated continuous capacity.  FIG. 2  is a block diagram of electrical system  10  in accord with the present invention. Electrical system  10  includes electrical power generator  12  for supplying power to any of a plurality of different types of loads. For illustrative purposes only, generator  12  is shown in  FIG. 2  with three loads  14 ,  16 , and  18 . 
   As shown in  FIG. 2 , generator  12  is a brushless generator that converts the rotational energy generated by prime mover  19  into a multiphase alternating current (AC). The present invention, however, is not limited to only brushless generators, and other types of generators may be substituted for brushless generator  12 . As is conventionally known, brushless generator  12  includes voltage regulator  20  (or controller or processor), an exciter having stator field windings  22  and rotor field windings  24 , rotating rectifier  25 , and a main generator having rotor field windings  26  and stator field windings  28 . Exciter rotor field windings  24 , rotating rectifier  25 , and main generator field windings  26  share a rotor and are separated by an air gap from the stator having exciter stator field windings  22  and main generator stator field windings  28 . 
   The conventional power generating operations of generator  12  are well known. In operation, voltage regulator  20  receives a direct current (DC) voltage from battery  30 . Alternatively, battery  30  could be replaced with a permanent magnet generator or another source of DC voltage. Voltage regulator  20  supplies a first DC voltage to exciter stator field windings  22 , which in turn develop a magnetic field. Exciter rotor field windings  24  are rotated in this magnetic field to produce a first multiphase AC voltage. The first AC voltage is then supplied to rotating rectifier  25 , which rectifies the first AC voltage into a second DC voltage for supply to main generator rotor field windings  26 . The current in main generator rotor field windings then generates a magnetic field which in turn produces a induces a multiphase AC power at an output of main generator stator windings  28 . This AC power is supplied to loads  14 ,  16 , and  18  of generator  12 , and also as feedback to voltage regulator  20 . 
   Voltage regulator  20  uses this feedback to help maintain a constant voltage at the output of generator  12 , which may otherwise vary due to factors such as a variable rotational speed of the rotor of generator  12 . Voltage regulator  20  accomplishes this goal by measuring the output voltage of generator  12  and adjusting a current provided to exciter stator windings  22  as needed in a closed-loop fashion. 
   Generator  12  improves upon conventional generators by adding power management logic and communication abilities that allow for the capture and utilization of the full power generating capacity of generator  12 . As will be more fully described below, the present invention essentially adds capabilities to generator  12  to monitor its own power production and various other system parameters and to determine therefrom its present power generating capacity. In other words, the present invention provides intelligence to generator  12  to enable it to determine answers to the questions: “What am I presently doing?” and “What am I capable of doing?” This information is then communicated to at least one intelligent load, which can adjust its consumption based upon the capabilities of generator  12 . Thus, electrical system  10  is afforded the opportunity make use of traditionally untapped power capabilities of generator  12 . In the embodiment of  FIG. 2 , these abilities are added to voltage regulator  20 , but in alternative embodiments, a separate controller may be added to implement these features. 
   As described above with reference to  FIG. 1 , the power generating capacity of generator  12  (i.e., what it can do) is directly affected by the system parameters of generator  12  (i.e., what it is presently doing). For this reason, an important aspect of the present invention is the ability of generator  12  to be aware of its own system parameters. Accordingly, generator  12  includes system sensors  32  for sensing and/or measuring a plurality of system parameters related to the operation of generator  12 , such as its ambient temperature, the temperature of its stator, the temperature of its rotor, the power produced by its exciter, the rotational speed of its rotor, or the frequency of its output signal. System sensors  32  may include hardware and/or software that may be contained in a single or multiple devices for sensing, measuring, or otherwise determining these various system parameters. Further, system sensors  32  may be implemented in any of a plurality of conventional methods. Data indicative of these system parameters is then supplied to voltage regulator  20 . Thus system sensors  32  include hardware and/or software for determining the voltage provided at, and the current drawn from, the output terminal. 
   Importantly, these system parameters also include the voltage supplied at the output terminal of generator  12  and the current drawn from the output terminal of generator  12 . From these two values, voltage regulator  20  can compute a proxy for the present output power as the product of the voltage supplied at the output of generator  12  and the current drawn from the output of generator  12 . While this value does not equal the actual power supplied by generator  12 , it does serve as a fair representation of the power supplied. Thus system sensors  32  include hardware and/or software for determining the voltage provided at, and the current drawn from, the output terminal. 
   Another system parameter that voltage regulator  20  may include information about is the amount of time generator  12  has been operating at a particular output power. As described above, high power outputs can be sustained for a limited time period. Thus, generator  12  may include hardware and/or software for monitoring the length of time generator  12  has supplied a power outside the rated continuous capacity of generator  12 . 
   Voltage regulator  20  evaluates the present output power proxy and the remaining system parameters to determine a present operating point of generator  12 . In other words, voltage regulator  20  effectively determines which power-time curve is the appropriate curve, and where on that curve it is. From this information, voltage regulator  20  can determine the present power capacity of generator  12 . This power capacity is the maximum power generator  12  can produce based upon the data indicative of output voltage, output current, and system parameters of generator  12 . The power capacity of generator  12  may be greater than, less than, or the same as the present power being supplied; but importantly, it may exceed the rated capabilities of generator  12 . For example, generator  12  will be able to produce more power on a cold day with prime mover  19  operating at high speeds than on a hot day with prime mover  19  operating at a low speed. 
   A further aspect of the present invention is use of intelligent loads (i.e., loads having their own controller for controlling their own power consumption) communicatively connected to voltage regular  20  over communications network  44 . As shown in  FIG. 2 , generator  12  provides power to loads  14 ,  16 , and  18 . Here, load  14  is a conventional “dumb” load, that is, a load with no intelligence associated therewith. However, loads  16  and  18  are “intelligent loads” in that both include their own controller for controlling distribution of power to their own loads. In particular, load  16  includes load controller  34  and its own load  36 , while load  18  includes load controller  38  and its own loads  40  and  42 . Load controllers  34  and  38  are each communicably coupled with each other and with voltage regulator  20  of generator  12  via communications network  44 . By providing intelligence to both generator  12  and loads  16  and  18 , and communicably connecting each of the devices together via communications network  44 , the present invention allows for improved distribution of power. 
   Communications network  44  may be implemented with any communications protocol. For example, communications network  44  may be implemented with a controller area network (CAN), which is one of the ISO standard communications protocols. 
   Load controllers  34  and  38  receive and convert power delivered to loads  16  and  18  into useful forms for their associated loads. Load controllers  34  and  38  further receive and evaluate the present output power proxy and the power capacity of generator  12  to determine whether to adjust the power consumption of a respective one of loads  16  and  18 . Load controllers  34  and  38  of loads  16  and  18  each have a performance set point to which they strive. Load controller  34  and  38  further include sensors (not shown in  FIG. 2 ) for measuring an actual performance of loads  16  and  18 . By evaluating how much work it has yet to do to achieve its set point, the quantity of power that generator  12  is presently supplying, and the quantity of power available to it from generator  12 , load controllers  34  and  38  can make an intelligent decision about how much power to consume. 
   For example, load  18  would constitute a large load if it were a vehicular air conditioning system in which load  40  is a compressor motor and load  42  is a compressor fan motor. In this example, the air conditioning controller (load controller  38 ) can evaluate both a quantity of power that generator  12  can supply and how the air conditioning system (load  18 ) is performing to determine whether to adjust its consumption. Thus, when the air conditioning system (load  18 ) is initially turned on to cool a hot space, and where generator  12  has excess capacity (that is, its power capacity exceeds its present power production), air conditioning controller (load controller  38 ) may prefer to operate the air conditioning system (load  18 ) at a higher consumption rate until its set point has been met or until generator  12  reduces its capacity. If generator  12  is operating above its capacity (the power capacity is less that its present power production), the air conditioning control (load controller  38 ) may choose to decrease its power consumption. Thus, rather than running continuously at lower settings, air conditioning system (load  18 ) may perform its job faster, taking advantage of the additional operating envelope of generator  12  for a period of time. 
   Load controllers  38  and  34  may also compute their own power consumption by including sensors to measure input voltages to loads  16  and  18  and currents drawn by loads  16  and  18 . As with generator  12 , load controllers  38  and  34  may compute and rely upon a proxy for the actual power consumed, such as voltage consumed multiplied by current drawn. By knowing their own consumption, load controllers  34  and  38  can evaluate their own operating point to determine their own capacity. Thus, much like generator  12  can operate over its rated continuous capacity, intelligent loads  16  and  18  may be able to operate over their rated continuous consumption levels. This is an improvement over prior art load controllers which evaluate only temperature or current, and shut off the device when either exceeds a predetermined limit. Another advantage to evaluating power consumption is that load controllers  34  and  38  can compare the actual power consumption to estimated power consumption for identification of component wear out, required maintenance, or imminent failure. 
   Loads  16  and  18  are prioritized within system  10  to prevent each of intelligent loads  16  and  18  from simultaneously grabbing excess power from generator  12  upon generator  12  announcing (broadcasting) its increased capacity. Thus, the load with the lower priority will not have an opportunity to increase its consumption until after the load with a higher priority makes its decision to adjust its consumption. 
   Load controllers  38  and  34  may also communicate their power consumption proxy with each other and with generator  12  over communication network  44  to allow for a more intelligent distribution of power. In this way, each of generator  12  and intelligent loads  16  and  18  can act in the best interest of electrical system  10 , rather than operating in a vacuum where each is concerned only about its own performance. Such communication may also allow for dynamic assignment of load priorities. For instance, if load  16  is assigned a higher priority and is closer to achieving its set point than load  18 , generator  12  may reassign priorities to result in an improved system performance. 
   By enabling load controllers  38  and  34  to communicate with voltage regulator  20 , load controllers  38  and  34  can make requests of voltage regulator  20  to adjust the power provided to it. For example, if load controller  38  realizes that load  16  could use additional power to best meet its set point, but also aware that load  16  cannot tolerate any increase in current, load controller  38  may broadcast a request to voltage regulator  20  of generator  12  to “trim,” or temporarily increase, its output voltage—the resultant effect being an increase in power without an increase in current. 
   Electrical system  10  can further be improved by adding “intelligence”, or a controller, to prime mover  19  which causes rotation of the rotor of generator  12 . This can be helpful in allowing prime mover  19  to control the electrical power generation load on it when needed. For instance, where prime mover  19  is an engine in a vehicle, and the vehicle is required to accelerate, as when the vehicle is attempting to pass in traffic or climb a hill, prime mover  19  can communicate a request to voltage regulator  20  of generator  12  to reduce power consumption. Voltage regulator  20  can respond to this request by reducing the output voltage of generator  12 , thus reducing its generated power and its load on prime mover  19 . Alternatively, prime mover  19  may request that the power generated by generator  12  be diverted from electrical system  10  to an alternative system of loads, such as a transmission system of the vehicle. 
   Voltage regulator  20  cannot control consumption by its loads. If intelligent loads  16  and  18  do not respond to requests by voltage regulator  20  to reduce their consumption, voltage regulator  20  can force a reduced power by lowering its output voltage. Because power is the product of the output voltage and the output current, this action results in a reduction in the power produced by generator  12 . 
   In sum, the present invention is an electrical power generator that makes its full power capacity available for consumption by at least one intelligent load coupled to its output. The generator includes self-monitoring abilities that enable it to determine a present output power of the generator (i.e., what it is presently doing) and, from that, a power capacity of the generator (i.e., what it can do). These values are then broadcast to the intelligent loads via a communications network for use by the intelligent loads in controlling their own consumption. 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.