Patent Publication Number: US-2013241502-A1

Title: Regulating Generators Using Battery Charge Information

Description:
GOVERNMENT RIGHTS 
     This invention was made with government support under government contract number F873. The Government may have certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to vehicle electrical systems, and more particularly, to regulating generators using battery charge information. 
     BACKGROUND 
     A vehicle electrical system may include a battery and a generator. To start the vehicle, the battery may provide electrical energy in order to start the engine. Once the engine is running, the engine may power the generator. The generator may produce electrical energy to charge the battery. In some vehicles, the generator voltage may be manually adjusted when the vehicle is not in operation. 
     SUMMARY 
     According to one embodiment, an electrical system comprises a generator, a battery, and a regulator. The generator is operable to provide electrical energy at a plurality of voltage levels. The battery is in electrical communication with the generator. The regulator is operable to compare a charge level of the battery to a reference charge level, determine a voltage level for the generator based on the comparison, and provide a signal indicative of the determination toward the generator. 
     Particular embodiments of the present disclosure may provide one or more technical advantages. A technical advantage of one embodiment may include the capability to automatically control the voltage of electrical energy provided by the generator. A technical advantage of one embodiment may also include the capability to reduce the time necessary to charge the battery. A technical advantage of one embodiment may also include the capability to prevent the generator from producing electrical voltages outside a safe operating range of the electrical system. 
     Certain embodiments of the present disclosure may include some, all, or none of the above advantages. One or more other technical advantages may be readily apparent to those skilled in the art from the figures, descriptions, and claims included herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows an electrical system according to one example embodiment; 
         FIG. 2  shows the regulator of  FIG. 1  according to one example embodiment; and 
         FIG. 3  shows a method for regulating generator voltage in the aircraft electrical system of  FIG. 1  according to one example embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     As stated above, a vehicle electrical system may include a battery and a generator. To start the vehicle, the battery may provide electrical energy in order to start the engine. Once the engine is running, the engine may power the generator. The generator may produce electrical energy to charge the battery. 
     The electrical system may operate at a lower voltage when the battery supplies the electrical power rather than the generator. In one example scenario, an aircraft battery supplies electrical power at approximately 24 to 25 volts, whereas an aircraft generator may electrical power at a fixed 28 volts. This variance in supply voltage does not affect most aircraft electrical devices because most devices are designed to operate over a wide range of voltages (e.g., 22 to 30 volts). 
     In this example scenario, starting the engine substantially reduces the charge of the battery. For example, starting an aircraft engine may deplete one-third or more of the aircraft battery&#39;s capacity. The amount of battery depletion during engine start-up may depend on the size of the battery and the power used to start the engines. For example, some aircraft may have limited battery capacity due to weight considerations and thus may deplete battery capacity more quickly. In addition, aircraft engines may require more energy to start as compared to other vehicles such as automobiles. 
     After the engine is running, however, the generators may provide electrical energy at a higher voltage (e.g., 28 volts.). This voltage may be sufficient to begin replacing the energy lost during preflight activities and engine start-up. In this example scenario, however, the battery energy is replenished slowly because the aircraft generator provides electrical power at a fixed 28 volts. Thus, the battery cannot provide its full capability in the event of an in-flight generator failure. A generator failure at takeoff may be especially dangerous because the battery has not yet fully recharged after starting the engines. 
     Accordingly, teachings of certain embodiments recognize the capability to speed up charging of the battery. For example, if the generator voltage is increased during charging (e.g., to 28.5 or 29 volts), the battery may be charged more quickly. Increasing the voltage permanently, however, could damage the battery due to overcharging. Accordingly, teachings of certain embodiments recognize the ability to adjust generator voltage based on battery charge information. 
     Some aircraft may allow the generator voltage to be manually adjusted when the aircraft is on the ground. Relying on manual adjustment, however, can still result in damage to the battery due to overcharging. In addition, adjusting the generator voltage when the aircraft is on the ground may be based on guesses by the pilot (or other ground personnel) and not based on calculations using battery charge information, which change during flight. Battery needs may be affected by air temperature, difficult engine starting, the average length of the aircraft&#39;s missions, and other factors that may be difficult to predict before flight. Accordingly, teachings of certain embodiments recognize the capability to adjust generator voltage automatically during flight using battery charge information. 
       FIG. 1  shows an electrical system  100  according to one example embodiment. System  100  includes aircraft devices  110 , a generator  120  coupled to a generator control unit  125 , a generator  130  coupled to a generator control unit  135 , a battery  140 , and a regulator  150 . Embodiments may include more or fewer generator control units, generators, batteries, and/or regulators. Components of electrical system  100  may be in electrical communication directly and/or indirectly. For example, battery  140  is in electrical communication with generators  120  and  130  through the aircraft busses and through regulator  150  and generator control units  125  and  135 . 
     Aircraft devices  110  are electrical devices powered by electrical system  100 . Examples of aircraft devices  110  may include lights, radios, and antennas. Aircraft devices  110  may be powered by generators  120  and  130  when aircraft engines are running and by battery  140  when the aircraft engines are not. Aircraft devices  110  may be capable of operating over a wide range of voltages (e.g., 22 to 30 volts). 
     Generators  120  and  130  provide electrical energy to electrical system  100 . Examples of generators  120  and  130  may include engine-driven generators, ram-air turbines, and auxiliary power units. Generators  120  and  130  may charge battery  140  by providing electrical energy greater than the electrical energy used by aircraft devices  110 . 
     Generator control units  125  and  135  control the voltage of electrical energy provided by generators  120  and  130 . In the example of  FIG. 1 , generator control units  125  and  135  set the voltage for generators  120  and  130  based on signals received from regulator  150 . 
     Battery  140  stores electrical energy from electrical system  100  and provides stored electrical energy to electrical system  100 . In one example embodiment, battery  140  is a lithium ion battery. 
     Battery  140  may include an internal monitoring circuit for collecting information about battery  140 , such as voltage (e.g., terminal voltage which may indicate the voltage produced by generators  120  and  130 ), current (e.g., “charge” or “discharge” current indicating the amount of current moving into/out of battery  140 ), and charge level information (e.g., charge percentage). Such internal monitoring circuit may measure information for individual power cells within battery  140 . Battery  140  may also include a data bus for communicating information about battery  140 . For example, in one embodiment, battery  140  communicates information about battery  140  using ARINC  429 , a data transfer standard for aircraft avionics. 
     Regulator  150  determines the voltage level for generators  120  and  130 . A voltage level may be represented, for example, by a voltage value (e.g., 28 volts) or a voltage change (e.g., increase voltage by 0.5 volts). 
     In operation, according to one embodiment, regulator  150  receives charge level information from battery  140 . Regulator  150  compares the charge level with a reference charge level and determines whether to increase the voltage of the electrical energy produced by generators  120  and  130 . For example, if the charge level of battery  140  is lower than the reference charge level, regulator  150  sends signals to generator control units  125  and  135  indicative of the determination. The signals may, for example, instruct generator control units  125  and  135  to increase the voltage set for generators  120  and  130 . Generator control units  125  and  135  set generators  120  and  130  to provide electrical energy at the increased voltage. 
     In another example embodiment, regulator  150  may compare charge level information with two reference charge levels. For example, a first reference charge level may be 95%, and a second reference charge level may be 99%. If the charge level of battery  140  is lower than both reference charge levels, regulator  150  instructs generator control units  125  and  135  to increase the voltage set for generators  120  and  130 . If the charge level of battery  140  is higher than both reference charge levels, regulator  150  instructs generator control units  125  and  135  to decrease the voltage set for generators  120  and  130 . Regulator  150  maintains the existing voltage if the charge level of battery  140  is between the two reference charge levels. 
     Regulator  150  may adjust the voltage of generators  120  and  130  iteratively. For example, if the charge level of battery  140  is less than a reference charge level, regulator  150  may instruct generator control units  125  and  135  to increase the voltage set for generators  120  and  130  by 0.5 volts. If, after an iterative period (e.g., period of time), the charge level of battery  140  is still less than the reference charge level, regulator  150  may instruct generator control units  125  and  135  to increase the voltage set for generators  120  and  130  by another 0.5 volts. 
     In some embodiments, charge level information may include current information. Teachings of certain embodiments recognize that regulator  150  may use current information as an approximation for charge percentage and other types of charge level information. For example, in one embodiment, regulator  150  measures the current of battery  140  during engine start and then raises generator voltage until a like amount of energy has been returned to battery  140 . In some embodiments, regulator  150  may use current information if charge percentage is unavailable. Charge percentage may be unavailable, for example, if battery  140  lacks internal monitoring circuitry or if such circuitry malfunctions. 
     As stated above, aircraft devices  110  may be capable of operating over a wide range of voltages (e.g., 22 to 30 volts). Teachings of certain embodiments recognize the capability to limit generators  120  and  130  to producing electrical power within the range of voltages allowable for aircraft devices  110 . In one example embodiment, regulator  150  is limited to selecting one of a plurality of voltage levels that fall within the range of voltages allowable for aircraft devices  110 . In another example embodiment, regulator  150  is capable of selecting any voltage, but then regulator  150  and/or generator control units  125  and  135  may reject the voltage selection if it is outside the range of allowable voltages. In some embodiments, generator control units  125  and  135  and/or regulator  150  are limited to a subset of voltages within the range of voltages allowable for aircraft devices  110 . For example, if aircraft devices  110  can operate between 22 and 30 volts, generator control units  125  and  135  and/or regulator  150  may be limited to 27 to 29 volts. 
       FIG. 2  shows regulator  150  according to one example embodiment. As shown in  FIG. 2 , regulator  150  includes a receiver module  152 , a determination module  154 , and communication modules  156 . 
     Receiver module  152  receives and decodes information received from battery  140 . In the example of  FIG. 2 , receiver module  152  is a low-speed ARINC  429  input module. The low-speed ARINC  429  input module may be configured to recognize two inputs. The first input is battery current in amps. According to this input, charge current is positive, and discharge current is negative. The least significant bit (LSB) is 1 amp. The first input is present in both half-second data frames. The second input is battery state of charge in percent. The LSB is 1 percent. The second input is present on one of the two half-second data frames. In some embodiments, receiver module  152  may be configured to receive additional inputs, such as voltage. 
     Determination module  154  determines the voltage for generators  120  and  130 . Determination module  154  receives current and charge percentage information from battery  140  through receiver module  152  and transmits voltage settings to generators  120  and  130  through communication modules  156  and generator control units  125  and  135 . In the example of  FIG. 2 , determination module  154  selects the generator voltage from four voltage levels: 27.5 volts, 28 volts, 28.5 volts, and 29 volts. 
     Communication modules  156  send signals indicative of the voltage determination by determination module  154  toward the generator. These signals instruct generator control units  125  and  135  to set the generator voltage. In the example of  FIG. 2 , communication modules  156  include two pairs of switches  156   a - 156   b.  The first pair, switches  156   a  and  156   b,  communicates with generator control unit  125 , and the second pair, switches  156   c  and  156   d,  communicates with generator control unit  135 . 
     Each switch may be open or closed. In the example of  FIG. 4 , each pair of switches may communicate one of four voltages by opening or closing each switch. For example, regulator  150  may communicate a voltage of 27.5 volts by grounding both switch  156   a  and switch  156   b.  Regulator  150  may communicate a voltage of 28 volts by opening switch  156   a  and grounding switch  156   b.  Regulator  150  may communicate a voltage of 28.5 volts by grounding switch  156   a  and opening switch  156   b.  Finally, regulator  150  may communicate a voltage of 29 volts by opening both switch  156   a  and switch  156   b.    
     Receiver module  152 , determination module  154 , and communication modules  156  may be implemented by components such as processors, communication links, memory, and logic. Regulator  150  may be operable to perform one or more operations of various embodiments. Although the embodiment shown provides one example of regulator  150  that may be used with other embodiments, such other embodiments may utilize computers other than regulator  150 . Additionally, embodiments may also employ multiple regulators  150 . 
     Processors represent devices operable to execute logic contained within a medium. Examples of processor include one or more microprocessors, one or more applications, and/or other logic. Regulator  150  may include one or multiple processors. 
     Communication links are operable to facilitate communication between regulator  150  and other components. In one example embodiment, regulator  150  is a printed circuit board having communication links for receiving power and communicating with generator control units  125  and  135  and battery  140 . 
     Memory represents may store any data for use by regulator  150 . Memory may comprise one or more tangible, computer-readable, and/or computer-executable storage medium. Examples of memory include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), database and/or network storage (for example, a server), and/or other computer-readable medium. 
     In some embodiments, memory stores logic. Logic facilitates operation of regulator  150 . Logic may include hardware, software, and/or other logic. Logic may be encoded in one or more tangible, non-transitory media and may perform operations when executed by a computer. Logic may include a computer program, software, computer executable instructions, and/or instructions capable of being executed by regulator  150 . In particular embodiments, the operations of the embodiments may be performed by one or more computer readable media storing, embodied with, and/or encoded with a computer program and/or having a stored and/or an encoded computer program. Logic may also be embedded within any other suitable medium without departing from the scope of the invention. 
       FIG. 3  shows a method  200  for regulating generator voltage in an aircraft electrical system according to one example embodiment. At step  210 , the aircraft engines are powered on using electrical energy stored in battery  140 . At step  220 , regulator  150  sets the generator voltage to an initial voltage setting: 28 volts. Regulator  150  monitors the charge current of battery  140  at step  230 . 
     Regulator  150  waits until the charge current of battery  140  reaches or exceeds a reference charge current (e.g., 20 amps). At step  240 , regulator  150  monitors the charge level of battery  140 . If the charge level of battery  140  is less than a reference charge level (e.g., 95% charge), regulator  150  determines that generator voltage should be increased (e.g., by 0.5 volts). 
     In one example embodiment, regulator  150  may determine the generator voltage in an effort to regulate the charge current of battery  140 . If the charge current is less than 100 amps, for example, regulator  150  may increase generator voltage by 0.5 volts. Regulator  150  may continue to increase generator voltage until one of the following occurs: (1) the charge current is greater than 100 amps; (2) the generator voltage is 29 volts; or (3) the charge level of battery  140  reaches 95 percent. If the charge current is greater than 175 amps, on the other hand, regulator  150  may decrease generator voltage by 0.5 volts. Regulator  150  may continue to decrease generator voltage until one of the following occurs the charge current is less than 175 amps or the generator voltage is 27.5 volts. 
     Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. 
     Although several embodiments have been illustrated and described in detail, it will be recognized that substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the appended claims.