Abstract:
A hybrid battery includes a converter, a controller, a power source, and an ultracapacitor configured to be discharged. The converter is operable to receive a control signal and to regulate a current level that is allowed to be drawn from the power source to charge the ultracapacitor in accordance with the control signal. The controller is operable to generate and provide the control signal to the converter. The controller is operable to generate the control signal based at least in part on a measure of the voltage level of the ultracapacitor and a measure current being drawn to charge the ultracapacitor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of PCT application US2006/016913 filed Apr. 27, 2007 which claims priority of U.S. provisional application Ser. No. 60/675,555 filed Apr. 27, 2005. 
    
    
     BACKGROUND 
     Conventional lead-acid chemistry has several characteristics that limit their performance as an SLI (starting-lighting-ignition) battery in vehicles. In cold temperatures the capacity and ability to supply power for starting is significantly reduced. In temperatures above 120° F. lead-acid batteries can be damaged. Depending on how the battery is used its life can be relatively short necessitating frequent replacement. High starting currents and deep cycling are factors that contribute to reduction in cycle-life of batteries. This type of use is seen particularly in diesel military vehicles and semi trucks. Although there is a recycling infrastructure in place for lead-acid batteries, there is a significant environmental impact from the manufacturing and disposal of SLI batteries. 
    
    
     
       DRAWINGS 
         FIG. 1  is a schematic view of an exemplary hybrid battery integrated in to a starting subsystem of a vehicle according to an embodiment. 
         FIG. 2  is a schematic view of an exemplary controller according to an embodiment. 
         FIG. 3  is a schematic view of an exemplary Converter according to an embodiment. 
         FIG. 4  is a diagram charting the experimental current draw on a conventional battery compared to the experimental current draw of an exemplary hybrid battery. 
     
    
    
     DETAILED DESCRIPTION 
     I NTRODUCTION : Various embodiments described below provide for a hybrid battery is the combination of an electrochemical battery with ultracapacitors and digitally controlled power electronics. The pairing of these two energy storage devices provides the high power output of ultracapacitors with the high-energy storage of batteries. Significant improvements in performance and life cycle can be achieved by accurately controlling the energy out of the battery while taking advantage of the high power capabilities of ultracapacitors. 
     Although the various embodiments disclosed herein will be described with reference to use in starting a vehicle, the hybrid battery is not so limited. The hybrid battery in one or more embodiments may be utilized in any environment in which it may be desirable to incorporate a relatively high capacity energy storage device capable of producing a relatively high output power level. Examples of such uses include other engine starters, standby generators, and auxiliary power units. 
     THE HYBRID BATTERY:  FIG. 1  illustrates an exemplary hybrid battery  10  integrated into a vehicle&#39;s starting subsystem. Hybrid battery  10  includes a power source such as battery (Vb), ultracapacitor (Cuc), a relay made up switch (S 1 ) and actuating coil (L 1 ), light emitting diode (D 1 ), Converter  12 , controller  14 , and conditioning circuit  16 . The vehicle&#39;s starting subsystem includes key ignition switch (S 2 ), starting solenoid (S 3 ), and starter ( 18 ). The relay is configured to close switch (S 1 ) upon the closing or switch (S 2 ) by, for example, the turning of a key in a vehicle&#39;s ignition. 
     The large currents drawn by starter  18  are supplied by the ultracapacitor (Cuc). Energy is transferred from the battery (Vb) to the ultracapacitor (Cuc) through Converter  12 . The amount of current transferred from the battery (Vb) to the ultracapacitor (Cuc) is controlled by controller  14 . In this embodiment, controller  14  performs closed loop proportional-integral (PI) current control. The result of this control is a pulse width modulated (PWM) signal to Converter  12 . Regulating the current from battery (Vb) and preventing large current spikes can help extend the life of battery (Vb). Hybrid Battery  10  is able to better supply relatively high power levels at relatively cold temperatures as ultracapacitor (Cuc) are affected less by cold temperatures than conventional lead acid SLI batteries. 
     During starting of a vehicle&#39;s engine, the total energy of the ultracapacitor (Cuc) vs time drops because more current leaves the ultracapacitor (Cuc) than is supplied by the battery (Vb) via Converter  12 . Light emitting diode (D 1 ) indicates to the user when the ultracapacitor (Cuc) are charged. Starter  18  can be utilized to start a vehicle&#39;s engine when the LED indicates a sufficient charge. 
     Converter  12  represents generally any component or combination of components capable of regulating the level of current that can be drawn from the battery (Vb) to charge the ultracapacitor (Cuc) according to a control signal received from controller  14 . Controller  14  represents generally any component or combination of components that can supply converter  12  with a control signal where that control signal is generated according to one or more electrical characteristics of the ultracapacitor (Cuc). For example, when the voltage level of the ultracapacitor (Cuc) falls below a low threshold value, controller  14  may generate a control signal that causes DC-DC converter  14  to allow ultracapacitor (Cuc) to draw a current from the battery (Vb). When the voltage level of the ultracapacitor (Cuc) rises above a high threshold value, controller  14  may generate a control signal that causes DC-DC converter  14  to stop allowing the ultracapacitor (Cuc) to draw a current from the battery (Vb). 
     Conditioning circuit  16  represents a component or combination of components that operate to scale, add, subtract, and/or filter signals from the battery (Vb), ultracapacitor (Cuc), and Converter  12  and for use by controller  14 . In other words, conditioning circuit  16  acts on the various signals so that controller  14  can discern a current output of Converter and the voltages of the battery (Vb) and the ultracapacitor (Cuc). 
     T HE  C ONTROLLER :  FIG. 2  illustrates an exemplary control loop system implemented by controller  14 . In this Example, controller is a commercially available microcontroller such as a PIC18F452. In this example, controller  14  reads battery voltage and current at the output of Converter  12  as well as the voltage of ultracapacitor (Cuc). When the voltage of the ultracapacitor (Cuc) drops below a predetermined low threshold value, controller  14  commands a current (Iref) to a closed loop interrupt function. The interrupt function performs closed loop control to operate Converter  12  at a commanded current. Current transducer  18  represents a component of combination of components that can be used to measure the current exiting Converter  12 . 
     After an engine starts, for example, no current leaves the ultracapacitor (Cuc). Current continues to enter the ultracapacitor (Cuc) via Converter  12  causing the voltage level of the ultracapacitor (Cuc) to increase with respect to time. When the voltage of the ultracapacitor (Cuc) increases to a predetermined high threshold value, controller  14  stops commanding the reference current (Iref) to the interrupt function causing Converter  12  to stop providing current to the ultracapacitor (Cuc). This hysteretic control with separate turn off and turn on thresholds prevents oscillations that could otherwise occur as the ultracapacitor (Cuc) voltage approached a single threshold. 
     T HE  C ONVERTER :  FIG. 3  is a schematic view of an exemplary implementation of Converter  12 . In this example, Converter  12  is a DC-DC buck converter. As in  FIG. 1 , converter  12  receives a control signal (PWM) from controller  14  which it uses to regulate the level of current that is drawing from the battery (Vb) to charge the ultracapacitor (Cuc). 
     C URRENT  D RAW  C OMPARISON :  FIG. 4  is a diagram charting the experimental current draw on a conventional battery compared to the experimental current draw of an exemplary hybrid battery. The conventional battery starting current was tested in a 2002 Ford Explorer. Current drawn from the battery during starting spiked to approximately 500 amperes. With the hybrid battery  10  of  FIGS. 1-3  installed, current drawn from battery (Vb) during engine start ware zero and maximum battery current levels at other times were a maximum design value of 30 amperes. 
     It is noted that the maximum design value for current in and out of the battery (Vb) is a function of the designs of controller  14  and Converter  12 . Specifications for this maximum current value depends on system components such as the type and characteristics of the battery (Vb) and the particular electronic components used to constrict Converter  12 . 
     C ONCLUSION : The present invention has been shown and described with reference to the foregoing exemplary embodiments. It is to be understood, however, that other forms, details and embodiments may be made without departing from the spirit and scope of the invention that is defined in the following claims.