Abstract:
In a hybrid electric motor vehicle , a power supply system for storing and supplying electrical power includes a motor-generator located onboard the vehicle, driveably connected to the vehicle wheels and producing AC electric power, an energy storage device for alternately storing and discharging electric power, an inverter coupled to the motor-generator and the energy storage device for converting alternating current produced by the motor-generator to direct current transmitted to the energy storage device, and for converting direct current stored in the energy storage device to alternating current transmitted to the motor-generator, an off board source of AC electric power located external to the vehicle, and a charger coupled to said electric power source and the energy storage device for supplying DC electric power to the energy storage device from said AC electric power source.

Description:
[0001]    This application is a continuation-in-part of pending U.S. application Ser. No. 11/651,899, filed Jan. 12, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The preferred embodiment relates generally to an electric power supply system and method for charging an electric storage battery of a hybrid electric vehicle. 
         [0004]    2. Description of the Prior Art 
         [0005]    The powertrain of a hybrid electric vehicle includes multiple power sources, an internal combustion engine (ICE), principally used when highway speeds are sustained; an electric motor for charging electric storage batteries; and a traction motor for launching the vehicle, i.e., for accelerating the vehicle from a stopped condition. 
         [0006]    Generally, when using sealed lead acid batteries, which are also called power batteries, a constant voltage charge method is the preferred means for charging battery cells. Under a constant voltage regime currents are limited by the internal resistance of the battery. When the battery is in a low state of charge and the internal resistance is low, in-rush currents can be very large and energy can be restored to the battery very quickly. As the battery becomes charged, it reaches a transition point where a sudden rise in internal resistance occurs and, under constant voltage, the battery will accept less and less current. This self-regulating effect prevents overcharging of the battery, leading to longer battery lifetimes. Such constant voltage charge regimes are conducted at an equalization voltage, which is the recommended voltage at which the batteries can be maintained at a high state of charge (SOC). 
         [0007]    After this transition a low current equalization charge is required to return the complete capacity of the battery and to ensure that the individual cells within the battery are brought to an approximately equal charge state. 
         [0008]    Most of the charging and discharging of the battery is done in a bulk region below the transition point. 
         [0009]    Conventional hybrid electric vehicle powertrains on the other hand use energy batteries, such as NiMH or Li-ion batteries, where the battery charging and equalization is performed through an electric motor driven by the ICE as a battery charger. Since these batteries are composed of many individual cells connected to form high-voltage configuration, charging or discharging these batteries during normal vehicle operations can result in individual cells being at different voltages or state of charge, thereby resulting in unbalanced individual cells. Control of the balancing these individual cells through an equalization process is difficult due to the mismatch in power ratings of the electric motor-ICE combination and the battery power required to perform a precise equalization of the storage battery. Therefore, individual cells balancing in such powertrain requires sophisticated systems and methods in the equalization process. 
         [0010]    With the advent of plug-in hybrid electric vehicle powertrains, there are two source available for charging and equalization of these batteries, first source being onboard power source (ICE) and the second source being the off board power source (plug-in charger). 
         [0011]    The availability of two power sources, one being onboard and the other being off board, provides for opportunities for improving charging cost and better equalization of battery. There is a need in the industry for such a system and method that provides a mechanism for determining appropriately the charging and equalization of a storage battery in a hybrid electric system using both onboard the vehicle and off board the vehicle power sources. This system and method can determine customized battery power profiles in a hybrid electric powertrain system to improve battery charging and equalization for a vehicle with a plug-in charger together with the ICE. 
       SUMMARY OF THE INVENTION 
       [0012]    A power supply system for storing and supplying electrical power in a hybrid electric vehicle, includes a motor-generator driveably connected to vehicle wheels for producing AC electric power, an energy storage device for storing and discharging electric power, internal combustion engine, a source of AC electric power located external to the vehicle, a charger coupled to said electric power source and the energy storage device for supplying DC electric power to the energy storage device from said electric power source, and a controller configured to use a state of charge of the energy storage device and a base electric power profile having regions relating electric power and said state of charge, and to use the motor-generator and internal combustion engine to provide a bulk charge to the energy storage device in accordance with the base electric power profile and a current state of charge. 
         [0013]    The energy storage battery being charged by the system is equalized very infrequently, perhaps every three to four months. The electric storage system employs only one storage battery, no second electric storage battery, which would add unnecessary weight to the system and vehicle, is required in addition to the storage battery being charged. A second storage battery external to the vehicle would add cost, lower system charge efficiency, and double the equalization problem because it must be charged periodically. 
         [0014]    The energy storage device has the flexibility of being replenished by the ICE or a source external to the vehicle, such as the electrical utility power grid. 
         [0015]    The ICE may continue to operate and provide energy to drive a load up to a certain state of charge, after which the utility power grid supplies energy to the storage battery. 
         [0016]    Advantages of the plug-in device and system include precise equalization of the battery efficiently, optional choice of the energy source ICE or public utility grid, and more flexibility in cost optimization for charging the battery. These advantages drive the design of the hybrid architecture including the size of the charger, charge integration and battery charge topology. 
         [0017]    One of the advantages is the precise equalization of the battery through optimal determination of battery power from the on board power source, electric machine /ICE, and the off board power source, the plug-in charger. Using customizable battery power an on board power source, electric machine /ICE, can be used to bring the battery pack quickly to a high (about 90%) SOC, then a plug-in charger can be used to perform precise battery pack equalization. Such a method of battery pack equalization can provide very precise balancing of individual cells in a battery pack which is fairly impossible using just an on board power source of electric machine /ICE. 
         [0018]    Another advantage is the flexibility in cost optimization for charging the battery through optimal determination of battery power from the on board power source, electric machine /ICE, and the off board power source, the plug-in charger. 
         [0019]    Use of alternate power sources, the electric machine and ICE separately or in combination and an external power source, provide control flexibility toward optimizing cost associated with each of the power sources. For example, when fuel prices are relatively low compared to the cost of the external power source, the ICE would be used to provide the bulk charge of the energy storage device, i.e., to charge the battery pack to the high SOC, and the external power source and charger would be used for the equalization charge, i.e., from a high SOC to a maximum (about 100%) SOC. But when fuel costs rise relative to those of utility power source, the ICE would be used to provide a bulk charge to the energy storage device that is proportionately lower than the high SOC, and the external power source and charger would be used for an equalization charge that is proportionately greater than a low (about 10%) SOC. 
         [0020]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0021]    These and other advantages will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which: 
           [0022]      FIG. 1  is schematic diagram of a hybrid electric vehicle battery power control system; 
           [0023]      FIG. 2  is the transfer function shown in  FIG. 1  relating battery SOC and the battery power request; and 
           [0024]      FIG. 3  is a schematic diagram showing a for the hybrid fuel cell/storage device system. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Turning first to  FIG. 1 , a piecewise linear transfer function  10 , stored in electronic memory accessible to a controller  12 , relates the state of charge (SOC) of an onboard electric storage battery to the magnitude of power produced by the battery, i.e., the battery power request  14 . A battery power arbitration control algorithm  16  receives input signals representing the current battery power request  14 , current battery internal parameters (such as SOC, battery temperature, internal resistance, open circuit voltage)  18 , and various vehicle inputs  20 , including accelerator pedal position, brake pedal displacement, the position of the gear selector lever or PRNDL, the current degree of vehicle telematics usage, and driver interfaces. The algorithm  16  produces as its output a signal representing an arbitrated desired battery power  22 . In response to input signals representing vehicle inputs  20  and the arbitrated desired battery power  22 , a hybrid electric vehicle (HEV) blending and optimization algorithm  24  produces output command signals  26 ,  28 , which are used as input to an electric machine  30 , and an internal combustion engine  32  (ICE), which signals are used optimally to charge an energy storage device, such as an electric storage battery, using the two power sources  30 ,  32 . 
         [0026]    The battery power request  14  is a dead band piecewise linear function consisting of four points: a battery power lower saturation limit  34 , a zero point lower saturation limit  35 , a zero point upper saturation limit  36 , and a upper point batter power upper saturation limit  37 . 
         [0027]      FIG. 2  illustrates an example of the battery power request transfer function  10  before any changes (PLF A)  38  and after the electric motor/ICE charges the battery pack during the drive cycle PLF B)  40 . In this way, the magnitudes of the variables represented by the four points  34 - 37  of the transfer function are modified during the drive cycle using a battery charger. For the illustrated example, the system used to modify the battery power request shifts transfer function  38  rightward to the position of transfer function  40 , thereby allowing the vehicle to remain at a higher SOC capacity prior to recharge. 
         [0028]    Transfer function (PLF A)  38  has a power-SOC profile, which is divided into five regions  81 - 85  comprising: (i) a base fast active discharge region  81  beginning at the point having coordinates ( 70 , 10 ) and extending parallel to the SOC axis; (ii) a base increasing active discharge region  82  extending along an ascending ramp between coordinates ( 60 , 0 ) and ( 70 , 10 ); a base opportunistic passive discharge region  83  extending parallel to the SOC axis between coordinates ( 50 ,  0 ) and ( 60 , 0 ); a base increasing active charge region  84  extending along an ascending ramp between coordinates ( 40 ,- 10 ) and ( 50 , 0 ); and a base fast charge region  85  extending parallel to the SOC axis and terminating at the point whose coordinates are ( 40 ,- 10 ). 
         [0029]    Controller  12  prevents the motor-generator  30  and internal combustion engine  32  from charging the energy storage device  56  when the region of operation in the base electric power profile  38  is the fast discharge region  81 . 
         [0030]    Controller  12  minimizes use of the motor-generator  30  and internal combustion engine  32  for charging the energy storage device  56  when the region of operation in the base electric power profile  38  is the increasing active discharge region  82 . 
         [0031]    Controller  12  prevents the motor-generator  30  and internal combustion engine  32  from discharging the energy storage device  56  when the region of operation in the base electric profile  38  is the fast charge region  85 . 
         [0032]    Controller  12  minimizes use of the motor-generator  30  and internal combustion engine  32  for discharging the energy storage device  56  when the region of operation in the base electric power profile  38  is the active charge region  84 . 
         [0033]    Controller  12  uses the motor-generator  30  and internal combustion engine  32  for discharging and charging the energy storage device  56  when the region of operation in the base electric power profile  38  is opportunistic passive discharge region  83 . 
         [0034]    Controller  12  uses a modified five-region electric power-SOC profile  40  that shifts the base five-region electric power profile  38  rightward to relatively high state of charge when the vehicle is being driven and high-voltage battery cell voltage equalization, i.e., balancing, is required needed. 
         [0035]    The modified transfer function (PLF B)  40  has a power-SOC profile, which is divided into five regions  91 - 95  comprising: (i) a modified fast discharge region  91  beginning at the point having coordinates ( 90 , 10 ) and extending parallel to the SOC axis; (ii) a modified increasing active discharge region  92  extending along an ascending ramp between coordinates ( 85 ,  0 ) and ( 90 , 10 ); (iii) a modified opportunistic passive discharge region  93  extending parallel to the SOC axis between coordinates ( 80 ,  0 ) and ( 85 , 0 ); (iv) a modified increasing active charge region  94  extending along an ascending ramp between coordinates ( 75 ,- 10 ) and ( 80 , 0 ); and (iv) a modified fast charge region  95  extending parallel to the SOC axis and terminating at the point whose coordinates are ( 75 ,- 10 ). 
         [0036]    Controller  12  prevents the motor-generator  30  and internal combustion engine  32  from charging the energy storage device  56  when the region of operation in the modified electric power profile  40  is the fast discharge region  91 . 
         [0037]    Controller  12  minimizes use of the motor-generator  30  and internal combustion engine  32  for charging the energy storage device when the region of operation in the modified electric power profile  40  is the increasing active discharge region  92 . 
         [0038]    Controller  12  prevents the motor-generator  30  and internal combustion engine  32  from discharging the energy storage device  56  when the region of operation in the modified electric power profile  40  is the fast charge region  95 . 
         [0039]    Controller  12  minimizes use of the motor-generator  30  and internal combustion engine  32  for discharging the energy storage device  56  when the region of operation in the modified electric power profile  40  is the increasing active charge region  94 . 
         [0040]    Controller  12  uses the motor-generator  30  and internal combustion engine  32  for discharging and charging the energy storage device  56  when the region of operation in the modified electric power profile  40  is the opportunistic passive region  93 . 
         [0041]    The method further (i) activates the plug-in charger-based energy storage device equalization when the vehicle is off; (ii) activates the plug-in charger based energy storage device equalization when the charger is electrically connected to the high voltage AC electric power source by being plugged-in; (iii) activates the plug-in charger-based energy storage device equalization when the region of operation in the modified electric power profile  40  is the increasing active discharge region  93  or the fast discharge region  91 ; and (iv) provides the plug-in charger-based equalization charge to the energy storage device  56  when the region of operation in the modified electric power profile  40  is the increasing active discharge region  94  or the fast discharge region  91  while energy storage device equalization is being performed. 
         [0042]    If several requests for plug-in based energy storage device equalization are unsuccessful, controller  12  (i) activates the engine based energy storage device equalization; (ii) activates engine-based energy storage device equalization when the region of operation in the modified electric power profile  40  is the increasing active discharge region  92  or the fast discharge region  91 ; and (iii) provides engine-based equalization charge to the energy storage device  56  when the region of operation in the modified electric power profile  40  is in the increasing active discharge region  92  or the fast discharge region  91  while energy storage device equalization is being performed. 
         [0043]      FIG. 3  illustrates schematically the architecture of a hybrid electric equalization system  50 . Two power sources onboard the vehicle includes the ICE  32  and electric machine  30 , which may be a starter-generator or motor-generator. The electric machine  30  is driveably connected to the vehicle wheels  60  through series and/or parallel drive connections. The ICE  32  may drive the electric machine  30  when it operates in a generator mode, and the ICE may drive the vehicle wheels  60 . The electric machine  30  may operate in a starter mode to start the ICE  32 , in a motor mode to drive the vehicle wheels  60 , and in a generator mode to charge electrically an energy storage device  56 . In the generator mode, the electric machine  30  may be driven by the vehicle wheels, by the ICE  32  and by these in combination. 
         [0044]    The ICE  32  is either continually driveably connected by a mechanical interface  58  to the electric machine  30 . The mechanical interface  58  may be a portion of the powertrain of the motor vehicle or a clutch, which can be alternately engaged and disengaged. The output of the electric machine  30  is connected through an electric interface  62  to a motor inverter  64 . 
         [0045]    The motor inverter  64  converts AC current produced by the electric machine  30  to DC current, which is supplied on line  68  to the energy storage device  56 , and it converts DC current from the energy storage device to AC current, which is supplied on line  68  to the electric machine  62 . 
         [0046]    The energy storage device  56  may be an electric storage battery, a battery pack, capacitors, or a combination of a storage battery and capacitors. When the energy storage device  56  comprises battery packs, they may be arranged in battery pack groups  72 ,  73 ,  74 ,  75 , which are interconnected in any combination including series, parallel, and series-parallel connections. 
         [0047]    A high voltage (HV) charger  70  and the energy storage device  56  may share two different electric interfaces  76 ,  78 , thereby allowing the storage device  56  to be split while being charged, if desired. In this way, current from the HV charger  70  may be divided or split among the groups of battery packs  72 - 75 , which comprise the energy storage device  56 . The HV charger  70  may be located onboard the vehicle, in which case it may be integrated with the inverter  64  or a separate unit from the inverter. Alternatively, the HV charger  70  may be located external to the vehicle. 
         [0048]    In either case, power from a source  76  external to the vehicle, such as an electric utility grid, is electrically connected by a line  78  to the HV charger  70 . The external power source may supply single phase or three phase AC current to the charger  70 . The charger  70  converts current from source  76  to DC current, which is supplied on lines  72 ,  74  to the energy storage device  56 . The HV charger can supply energy at a magnitude that either rebalances, i.e., fully recharges the energy storage device  56 . A rebalancing charge is sometimes referred to as an equalization charge. 
         [0049]    For the illustrated example of  FIG. 2 , the method used to modify the battery power request shifts curve  38  rightward allowing the vehicle to remain at a higher SOC capacity prior to recharge. This higher SOC provides operational flexibility, such as allowing the capacity of the charger  70  to be smaller, or the period required to perform an equalization charge of the energy storage device  56  to be shorter than they would be otherwise. 
         [0050]    Use of alternate power sources, ICE  32  and external power source  76 , provide control flexibility in precise equalization of the battery using both the power sources. For example, to perform precise equalization of battery, controller  12  controls the electric machine  30  and ICE  32 , either separately or in combination, to quickly charge the energy storage device  56 , i.e., to charge the battery pack to a high (about 90%) SOC and the controller uses the external AC power source  76  and charger  70  to provide the equalization charge very precisely, i.e., from the high SOC to a maximum (about 100%) SOC. Such a method of battery pack equalization results in very precise balancing of state of charge or voltage of individual cells in a battery pack which is fairly impossible using just the electric machine  30  and ICE  32  combination. 
         [0051]    Again, use of alternate power sources, ICE  32  and external power source  76 , provide control flexibility in optimizing costs associated with each of the power sources. For example, when gasoline or diesel fuel prices are relatively high compared to the cost of electric power from the AC external power source, controller  12  controls the electric machine  30  and ICE  32 , either separately or in combination, to bulk charge the energy storage device  56 , i.e., to charge the battery pack to a normal (about 50% to 60%) SOC, and the controller uses the external AC power source  76  and charger  70  to provide the rest of the charge, i.e., from the normal SOC to a high (about 90%) SOC. Similarly, when gasoline or diesel fuel prices are relatively low compared to the cost of electric power from the AC external power source, controller  12  controls the electric machine  30  and ICE  32 , either separately or in combination, to bulk charge the energy storage device  56 , i.e., to charge the battery pack to a normal high (about 60% to 85%) SOC, and the controller uses the external AC power source  76  and charger  70  to provide the rest of the charge, i.e., from the normal high SOC to a high (about 90%) SOC. 
         [0052]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.