Patent Publication Number: US-RE45431-E

Title: Energy storage system for electric or hybrid vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Notice: More than one reissue application has been filed for the reissue of U.S. Pat. 7,489,048. The reissue application numbers are Ser. Nos. 13/025,102 and 13/681,686 (the present application). Reissue application Ser. No. 13/681,686, filed on Nov. 20, 2012 is a continuation reissue application of application Ser. No. 13/025,102, filed on Feb. 10, 2011, which is an application for reissue of U.S. Pat. No. 7,489,048, filed on Jan. 9, 2006, which are incorporated herein by reference.  
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to electric drive systems and, more particularly, to a battery load leveling system that may be utilized with a hybrid or an electric vehicle. 
     At least one known vehicle includes batteries, typically lead-acid batteries, to provide electric power for vehicle propulsion. For example,  FIG. 1  is a prior art vehicle that includes a conventional alternating current (AC) electric propulsion system  10  that is used in electric propelled and also hybrid-electric vehicles. The electric propulsion system includes at least one energy storage unit such as a lead acid battery  12 , and a direct current (DC) contactor  14  to electrically disconnect the energy storage unit  12  from a traction inverter  16  via a DC link  18 . Specifically, the battery  12  is connected to a DC link which connects to a frequency controlled inverter such as traction DC-AC inverter  16  for controlling power to an AC motor  20 . 
     In the operation of the vehicle, the battery is often called upon to deliver short bursts of power at high current levels, typically during acceleration of the vehicle or while operating the vehicle up a steep grade, for example. When high current is drawn from conventional batteries, battery terminal voltage drops. Such voltage reduction can interfere with proper operation of the vehicle or reduce efficiency of the switching devices in the power control circuit since the control circuit must also be designed to operate at high efficiency at full battery voltage, i.e., when the vehicle is drawing nominal current in a constant speed mode. 
     One method for reducing the effect of high current requirements on electric drive system batteries is to use an auxiliary passive energy storage device coupled to the DC link to provide additional power during high current situations. One implementation of this method is shown in the prior art  FIG. 2 . Specifically,  FIG. 2  illustrates an energy storage system  30  that includes a traction battery  32  and an ultracapacitor  34 , and a relatively low-cost ultracapacitor electronic interface  36  that allows the ultracapacitor  34  to share power with the traction battery  32  during vehicle acceleration and other high power demands while climbing steep grades. 
     During operation, when the known vehicle is operated during a lower power cruise condition, a diode  40  allows the ultracapacitor voltage to remain at a slightly higher voltage than the battery voltage. Immediately after the high power acceleration is complete, the required current from the energy storage system substantially decreases and the battery voltage increases to the nominal battery voltage or possibly higher voltages, while the ultracapacitor remains at approximately the voltage immediately after the acceleration. Moreover, when the vehicle is decelerating, a silicon-controlled rectifier  42  is gated and the regenerative energy from the electric motor  44  and associated traction drive  46  initially charges the ultracapacitor  34  until the voltage increases to a point where the diode  40  conducts, at which point both the ultracapacitor  34  and battery  32  are partially recharged. As such, the known energy storage system functions quite well and also provides an efficient and low-cost interface between the ultracapacitor and the traction battery in low speed electric vehicles, including golf cars and small utility vehicles. However, during operation, the amount of energy stored in the ultracapacitor  34  is limited by the square of the voltage difference between the maximum battery voltage plus the voltage drop across the diode  40 , and the minimum battery voltage plus the voltage drop across the diode  40 . 
     As a result, known energy storage systems are less effective for providing relatively high power levels over an extended period of time while the vehicle is either accelerating under heavy loads and/or climbing steep grades. Moreover, known energy systems include an electronic interface that may be less effective in matching the ultracapacitor output voltage with the voltage level required for the traction drive with acceptable efficiency and at a reasonable cost. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a battery load leveling system for an electrically powered system in which a battery is subject to intermittent high current loading is provided. The system includes a first battery, a second battery, and a load coupled to the batteries. The system also includes a passive storage device, a unidirectional conducting apparatus coupled in series electrical circuit with the passive storage device and poled to conduct current from the passive storage device to the load, the series electrical circuit coupled in parallel with the battery such that the passive storage device provides current to the load when the battery terminal voltage is less than voltage on the passive storage device, and a battery switching circuit that connects the first and second batteries in either a lower voltage parallel arrangement or a higher voltage series arrangement. 
     In another aspect, an electric vehicle is provided. The electric vehicle includes a first battery, a second battery, a load coupled to the first and second batteries; the first and second batteries configured to provide the propulsive force for moving the vehicle, and a battery load leveling system. The battery load leveling system includes a passive storage device, a unidirectional conducting apparatus coupled in series electrical circuit with the passive storage device and poled to conduct current from the passive storage device to the load, the series electrical circuit coupled in parallel with at least one of the first and second batteries such that the passive storage device provides current to the load when the battery terminal voltage of at least one of the first and second batteries is less than voltage on the passive storage device, and a battery switching circuit that connects the first and second batteries in either a lower voltage parallel arrangement or a higher voltage series arrangement. 
     In a further aspect, a hybrid vehicle is provided. The hybrid vehicle includes a first battery, a second battery, a load coupled to the first and second batteries; the first and second batteries configured to provide the propulsive force for moving the vehicle, and a battery load leveling system. The battery load leveling system includes a passive storage device, a unidirectional conducting apparatus coupled in series electrical circuit with the passive storage device and poled to conduct current from the passive storage device to the load, the series electrical circuit coupled in parallel with at least one of the first and second batteries such that the passive storage device provides current to the load when the battery terminal voltage of at least one of the first and second batteries is less than voltage on the passive storage device, and a battery switching circuit that connects the first and second batteries in either a lower voltage parallel arrangement or a higher voltage series arrangement. 
     In a further aspect, a method of assembling a battery load leveling system for an electrically powered system in which a battery is subject to intermittent high current loading is provided. The system includes a first battery, a second battery, and a load coupled to the first and second batteries. The method includes coupling a unidirectional conducting apparatus in a series electrical circuit with a passive storage device such that the unidirectional conducting apparatus is poled to conduct current from the passive storage device to a load, coupling the series electrical circuit in parallel with the first and second batteries such that said passive storage device provides current to the load when the battery terminal voltage is less than voltage on the passive storage device, and utilizing a battery switching circuit to the first and second batteries in either a lower voltage parallel arrangement or a higher voltage series arrangement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is prior art electric propulsion system; 
         FIG. 2  is a prior art energy storage system; 
         FIG. 3  is a battery load leveling system including an exemplary battery switching circuit; 
         FIG. 4  is an exemplary battery switching circuit which may be used with the battery load leveling system shown in  FIG. 3 ; 
         FIG. 5  is an exemplary battery switching circuit which may be used with the battery load leveling system shown in  FIG. 3 ; 
         FIG. 6  is an exemplary battery switching circuit which may be used with the battery load leveling system shown in  FIG. 3 ; 
         FIG. 7  is an exemplary battery switching circuit which may be used with the battery load leveling system shown in  FIG. 3 ; and 
         FIG. 8  is graphical illustration of the system shown in  FIG. 3  during operation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  illustrates a battery load leveling system  100 . The battery load leveling system  100  includes a first battery  102  and a second battery  104  that are utilized to supply power to a load  106 . Load  106  may be an alternating current (AC) or direct current (DC) load such as an electric traction motor for powering electric vehicles. Battery load leveling system  100  also includes a battery switching circuit  110  that includes a plurality of contactors that are operable to connect the first and second batteries  102  and  104 , respectively, in either a lower voltage parallel or a higher voltage series arrangement. 
     Battery switching circuit  110  enables the positive and negative terminals of first battery  102  and second battery  104  to be connected to respective ones of a positive bus  112  and negative bus  114 . Positive and negative buses  112  and  114 , also referred to herein as the positive and negative DC links, couple batteries  102  and  104  to a power electronics circuit  116  which may include a switching regulator  118  such as a DC-to-AC inverter for supplying alternating current to an AC load or AC motor, or a DC chopper or pulse width modulation circuit (not shown) for providing direct current to a DC load or DC motor. 
     More specifically, battery switching circuit  110  includes a first contactor  120  that is coupled between the positive terminal of first battery  102  and the positive bus  112 , a second contactor  122  that is coupled between the negative terminal of the first battery  102  and the negative terminal of the second battery  104 , and a third contactor  124  that is coupled between the positive terminal of the first battery  102  and the negative terminal of the second battery  104 . 
     To operate battery load leveling system  100  in a lower voltage parallel arrangement, contactors  120  and  122  are closed and contactor  124  is opened such that batteries  102  and  104  are electrically coupled in a parallel arrangement to buses  112  and  114 , respectively. Optionally, to operate battery load leveling system  100  in a higher voltage series arrangement, contactors  120  and  122  are opened and contactor  124  is closed such that batteries  102  and  104  are electrically coupled in a series arrangement to buses  112  and  114 , respectively. 
     Battery load leveling system  100  also includes a main contactor  130  that is coupled in series between the outputs of batteries  102  and  104  and power electronics circuit  116  and a pre-charge circuit  132 . Battery load leveling system  100  also includes a passive storage device  140 , such as an ultracapacitor for example, that is wired in series with a unidirectional conducting apparatus  142 , such as a diode for example, a current limiting switch  144 , a first resistor  146 , a second resistor  148 , and a semiconductor switch  150  such as, but not limited to a silicon-controlled rectifier, a bipolar transistor, a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), and a Gate Turnoff Thyristor (GTO). An energy storage system controller  160  responsive to a throttle or brake command generated by the operator provides control signals over a control link to power electronic circuit  118 . Ultracapacitor as used herein is comprised of multiple series connected capacitor cells where each ultracapacitor cell has a capacitance that is greater than 100 Farads. In the exemplary embodiment, the ultracapacitors described herein have a cell capacitance that is greater than 1000 Farads per cell. 
     As such, battery load leveling system  100  is operable in either a higher voltage series arrangement or a lower voltage parallel arrangement. For example, at low traction drive motor speeds, the battery switching circuit  110  is configured in the lower voltage parallel mode, i.e. contactors  120  and  122  are both closed and contactor  124  is open. As such, the batteries  102  and  104  are coupled in parallel to buses  112  and  114 , respectively. Approximately simultaneously, the passive storage device  140 , e.g. the ultracapacitor initially starts to pre-charge via the current limiting switch  144 . More specifically, resistor  146 , given sufficient time, allows the ultracapacitor  140  to be charged to a maximum of within a diode drop of the battery terminal voltage, i.e. the combined voltages of batteries  102  and  104  arranged in a series or parallel configuration. Alternatively, especially in a hybrid vehicle, the drive system initially could function on the battery energy storage alone and the ultracapacitor  140  can be pre-charged during vehicle deceleration using the vehicles&#39;s kinetic energy or regenerative power during operation of motor  106  as a generator through inverter  118  through SCR  150  and current limiting resistor  148 . Pre-charge circuit  132  is utilized to charge the DC link filter capacitor, contained within the traction drive system  118  as shown in  FIG. 2 , thereby reducing the transient current stress on the main DC contactor  130 . 
     Specifically, the current limiting switch  144  is sensitive to current amplitude, and is selected to have a relatively low resistance at low current and a high resistance to high current. Accordingly, when load  106  is drawing a nominal amount of current, batteries  102  and  104  provide charging current for passive storage device  140  through the relatively low impedance of current limiting switch  144  without dissipating excessive power in the resistance of switch  144 . However, if energy storage device  140  has been deeply discharged so that its voltage is substantially less than the nominal combined battery voltages, increased current drawn through current limiting switch  144  will cause the switch  144  to transition into a relatively high resistance state selected to be substantially greater than the resistance of fixed resistor  146 . 
     Accordingly, the ultracapacitor or passive energy storage device  144  will be recharged by current through resistance  146 . Preferably, the ohmic value of resistance  146  is selected to provide a current level that will recharge the capacitor  144  in approximately thirty to sixty seconds, depending upon battery conditions. Current limiting apparatus  144  thus provides improved load leveling of the batteries by preventing high current recharge of ultracapacitor  140  from the batteries  102  and  104  immediately after the system experiences high power pulse loads due to heavy current draw in load  106  such as would be occasioned by rapid vehicle acceleration where load  106  comprises an AC or DC electric motor. The design of current limiting switch  144  is selected such that the switch does not oscillate as the ultracapacitor  140  charge current exponentially decreases with increasing voltage on the ultracapacitor. 
     Moreover, in one embodiment, the energy storage system controller (ECSS) may be a processor that utilizes feedback signals from a plurality of relative low-cost voltage sensors  162  and conventional contactor driver circuits coupled to contactors  120 ,  122 , and  124 , to facilitate operating contactors  120 ,  122 , and  124 , respectively. As such, when the vehicle is operating at a relatively low speed, the parallel contactors,  120  and  122 , are configured as “normally closed” with the assumption that the traction drive spends the majority of the time operating at a relatively low speed, as typical in stop and go driving for utility delivery vehicle applications. Logic in the energy storage system controller  160  also provides sufficient sequencing “lockouts” and appropriate time delays to enable the “parallel” mode contactors,  120  and  122  to be opened prior to the “series” mode contactor  124  being closed, and visa-versa. 
     More specifically, when the vehicle is operated in a regenerative mode, e.g. during light braking for example, battery load leveling system  100  is configured such that the main contactor  130  is opened after initially being in the “parallel mode” during periods of moderate regenerative energy capture that is based on the level of operator input brake commands. 
     Additionally, when operating the batteries in relative low power parallel mode, the SCR  150  is gated “on” allowing current to flow through current limiting resistor  148  to charge the ultracapacitor  140 , thus allowing the voltage on the ultracapacitor  140  to increase substantially above the battery voltage thereby providing an increased level of energy storage compared to the known configuration illustrated in  FIG. 2 . Provided that the voltage on the ultracapacitor  140  is less than a predetermined threshold voltage of the nominal voltage in the “series mode”, the main contactor  130  remains open to allow a portion of the energy stored in ultracapacitor  140  to be utilized during the next acceleration event. At a point where the voltage difference between the parallel battery arrangement, e.g.  102  and  104  are arranged in a parallel, and the ultracapacitor  140  is within a predetermined voltage level, the ECSS  160  issues a command to close the main contactor  130 . Similarly, during operation at light regenerative energy capture, the ESSC ensures that the main contactor  130  remains closed to facilitate increasing the life of the mechanical contactor. Additional control details are described with reference to  FIG. 8 . 
     The battery load leveling system  100  shown in  FIG. 3  allows an increased level of energy storage within the ultracapacitor, compared to the prior art as shown in  FIG. 2  with the assumption that the nominal voltage of both the battery, in the series configuration, and the ultracapacitor, are the same voltage rating. Moreover, battery load leveling system  100  provides a relatively low-cost implementation that provides partial decoupling of the traction battery from the DC link and therefore increases the overall drive system efficiency. 
       FIG. 4  is a system  200  that includes a battery switching circuit  210 . System  200  is substantially similar to battery load leveling system  100  with the exception of battery switching circuit  210 . In the exemplary embodiment, circuit  210  is a series/parallel circuit that allows the main contactor  130  (shown in  FIG. 3 ) to be eliminated. Circuit  210  includes a first contactor  212 , a second contactor  214 , a third contactor  216 , and a fourth contactor  218  that are each normally open contactors. 
     Specifically, contactors  212  and  218  are coupled in series to facilitate reducing the voltage across the individual contactors. Optionally, circuit  210  includes a single contactor that includes a sufficient voltage rating such that at least one of the contactors  212  or  218  may be eliminated, and this simplification is included in this embodiment. In the exemplary embodiment, circuit  210  also includes a mechanical interlock  215  to facilitate preventing both series and parallel contactors from closing simultaneously, in the remote situation where the ESSC logic, electrical noise on the gate driver commands, and/or contact welding prevents one of the sets of contactors from opening. 
     More specifically, first and fourth contactors  212  and  218  are coupled in series between the positive terminal of first battery  102  and the negative terminal of the second battery  104 , second contactor  214  is coupled between the positive terminal of first battery  102  and the positive bus  112 , and third contactor  216  is coupled between the negative terminal of the first battery  102  and the negative terminal of the second battery  104 . 
     System  200  also includes a first precharge circuit  230 , a second precharge circuit  232 , and a third precharge circuit  234  that are utilized to precharge the DC link filter capacitor located within the DC-AC inverter  118 , (similar function as the precharge circuit  132  in  FIG. 3 ) thus reducing the current stress on the contactors and DC link filter capacitor during transient operation while closing contactors  212 ,  214 ,  216 , and  218 , respectively. Fourth precharge circuit  134  is an optional circuit that allows precharge of ultracapacitor  140  from the battery system in a shorter time compared to the current limited switch and resistor  146  as discussed previously. 
     To operate system  200  in a lower voltage parallel arrangement, mechanical interlock  214  is positioned in a first position such that contactors  212  and  218  are open and such that contactors  214  and  216  are closed. As such, batteries  102  and  104  are coupled in parallel to provide power to bus  112 . To operate system  200  in a higher voltage series arrangement, mechanical interlock  214  is positioned in a second position such that contactors  212  and  218  are closed and such that contactors  214  and  216  are open. As such, batteries  102  and  104  are coupled in series to bus  112 . 
     Moreover, the pre-charge circuit  230 ,  232 , and  234  are utilized to pre-charge the DC link capacitor, C dc , (shown on  FIG. 2 ) that is housed within the electric motor traction drive or DC Load. Control of this embodiment is similar to the control of battery load leveling system  100  shown in  FIG. 3  and will be discussed later herein. 
       FIG. 5  illustrates a system  300  that includes a battery switching circuit  310 . System  300  is substantially similar to battery load leveling system  100  with the exception of battery switching circuit  310 . In the exemplary embodiment, the parallel contactors  214  and  216  (shown in  FIG. 4 ) are replaced with diodes  312  and  314  respectively. 
     During acceleration or operation at relatively constant speed and low motor speed operation, the series contactor  120  is open and the batteries  102  and  104  are configured in a parallel arrangement via diodes  312  and  314 . As such, the power required to accelerate or operate at nearly constant speed is provided to the electric motor drive or load  106  by a combination of the batteries  102  and  104  and the ultracapacitor  140 , as shown in  FIGS. 3 and 4 . Optionally, during vehicle deceleration, regenerative power is blocked from flowing into the batteries  102  and  104  by the diodes  312  and  314 , and therefore the regenerative energy is captured in the ultracapacitor  140 . As such, the voltage of the ultracapacitor  140  increases approximately linearly as a function of the regenerative current that flows through SCR  150  and current limiting resistor  148 . For high levels of regenerative power, i.e. during vehicle operation on a long down-hill grade, the voltage on the ultracapacitor  140  will increase substantially. As the ultracapacitor voltage rises to within a predetermined voltage of the projected battery voltage in the series configuration, contactor  120  is closed and the regenerative power is now applied to both the batteries  102  and  104  (arranged in a series configuration) and the ultracapacitor  140 . 
       FIG. 6  is a system  400  that includes a battery switching circuit  410 . System  400  is substantially similar to system  300  with the exception of battery switching circuit  410 . In the exemplary embodiment, the function of the electrical disconnect, i.e. series contactor  120  shown in  FIG. 5 , is implemented utilizing back-to-back SCR&#39;s  412  and  414 , respectively. Optionally, circuit  410  includes at least two fuses  430  and  432  to facilitate limiting the current from batteries  102  and  104 , respectively. 
     During operation, when the vehicle is accelerating or climbing a relatively steep hill and additional power is required, SCR  414  is activated such that first battery  102  and second battery  104  are placed in a series arrangement between buses  112  and  114 , respectively. Additionally, a fuse  432  facilitates limiting the current to bus  112 . 
     When the vehicle is operating a mode wherein less power is required, both SCR  412  and SCR  414  are deactivated such that first battery  102  and second battery  104  are placed in a parallel arrangement between buses  112  and  114 , respectively. Specifically, current from first battery  102  is channeled through a diode  422  and fuse  430  to first bus  112 , and current is channeled from second battery  104  through diode  426  and fuse  432  to bus  112  to power load  106   
     Optionally, when the vehicle is descending a relatively steep incline the vehicle is configured to operate in a regeneration mode. Specifically, SCR  412  is activated and SCR  414  is deactivated such that current flows from bus  112  through fuse  432  through battery  104  through SCR  412  through first battery  102  through fuse  430  to complete the electrical circuit to bus  114  and thus facilitates charging both the first battery  102  and second battery  104  connected in a series arrangement. Diodes  422  and  426  restrict current from being channeled to the first and second batteries in a parallel arrangement. 
       FIG. 7  is a system  500  that includes a battery switching circuit  510 . System  500  is substantially similar to system  400  with the exception of battery switching circuit  510 . In the exemplary embodiment, circuit  510  also includes a first contactor  540  and a second contactor  542 . In the exemplary embodiment, the function of the electrical disconnect, i.e. series contactor  120  shown in  FIG. 5 , is implemented utilizing back-to-back SCR&#39;s  512  and  514 , respectively. Optionally, circuit  510  includes at least two fuses  530  and  532  to facilitate limiting the current from batteries  102  and  104 , respectively. Circuit  510  also includes a first contactor  540  and a second contactor  542  that facilitate allowing galvanic isolation and to also facilitate preventing leakage current flowing through batteries  102  and  104  while the battery temperature is low and in the “frozen state”. As used herein the batteries are operating in a froze state when the operational temperature of the battery is less than approximately 140 degrees Celsius. 
     In the exemplary embodiment, batteries  102  and  104  are implemented using at least one of a sodium nickel chloride battery or a sodium sulfur battery that are each configured to operate at a temperature that is greater than 260 degrees Celsius. In the exemplary embodiment, the sodium nickel chloride battery and the sodium sulfur battery each have a high specific energy that is greater than approximately 100 Watt/hours per kilogram. Moreover, the batteries are relatively inexpensive and may be effectively cooled utilizing ambient air conditions, such as air or water cooling, for example. 
     In another embodiment, batteries  102  and  104  are implemented using a fuel cell, a nickel metal hydride battery, a lithium ion battery, a lithium polymer battery, a nickel cadmium battery, and a lead acid battery. Moreover, although system  500  illustrates contactors  540  and  542  positioned on only one side of a respective battery  102  and  104 , it should be realized that contactors may be coupled to both terminals of each respective battery  102  and  104  to provide further protection from the detrimental leakage current and are therefore also included in this embodiment. 
     In a first mode of operation operating the vehicle in a steep downhill grade for example, when the vehicle is reaching relatively high regenerative power levels, and/or operating over long distance such that the voltage on the series connected batteries reaches approximately the maximum limit, an over-voltage protection algorithm installed within the electric motor traction drive (not shown in above embodiments) gradually reduces the level of regenerative power while maintaining the DC link voltage, i.e. bus  112  voltage, at acceptable limits. As this occurs, the vehicle operator will sense a reduction in electrical braking torque and will compensate by depressing the brake pedal further, thus effectively increasing the mechanical braking power as the electrical braking power is reduced. 
     During operation, system  500  utilizes feedback indicative of the motor  106  speed and torque, ultracapacitor voltage, and battery voltage to operate system  500 . Moreover, whenever possible, system  500  utilizes the energy stored within ultracapacitor  140  to supplement vehicle operation. For example, during heavy vehicle acceleration, batteries  102  and  104  are placed in series arrangement, the ultracapacitor  140  voltage is charged to within approximately a diode drop of the battery voltage, and both the ultracapacitor  140  and battery  102  and  104 , share the power primarily based on the open circuit voltage and associated internal resistance of the battery  102  and  104  and ultracapacitor  140 . Optionally, during low speed operation, batteries  102  and  104  are arranged in a parallel arrangement and regenerative energy capture allows the voltage on the ultracapacitor  140  to increase to levels above the (parallel configured) battery voltage. In this situation, the next acceleration uses stored energy from the ultracapacitor  140  until the ultracapacitor voltage is approximately equal to the battery voltage. 
       FIG. 8  is a graphical illustration of a method of controlling the systems shown in  FIGS. 3-7 . In the exemplary embodiment, the initial motor speed is shown to be approximately zero rpm and the ultracapacitor is pre-charged to essentially the battery voltage with the batteries configured in parallel. As shown, nearly constant torque is initially applied, the motor speed increases and power is supplied by both the parallel configured battery and the ultracapacitor. When the torque is suddenly decreased to approximately 30% of rated, i.e. the vehicle and/or drive is in the cruise mode, the battery voltage increases abruptly, while the ultracapacitor slowly increases due to either the current limited switch or the pre-charge circuit. However, during regenerative braking, the energy is applied to the ultracapacitor and the voltage increase is approximately a linear function of the regenerative brake current. For this example, the ultracapacitor voltage during the regenerative braking mode did not reach the voltage threshold where the Energy Storage System Controller commands the batteries to be configured in the series mode. Thus during the next acceleration, initially all of the energy to accelerate the drive and/or vehicle is supplied from the ultracapacitor. When the ultracapacitor voltage reaches a threshold voltage of the batteries in the parallel configuration, then power is smoothly transitioned and supplied by both the batteries and ultracapacitors. 
     At a point approximately 50% motor speed and above, the ultracapacitor voltage is increased. The exact method of increasing the voltage on the ultracapacitor is a function of the specific embodiment and application. In general the capacitor is either pre-charged from the batteries configured to the series configuration (shown in  FIGS. 3-7 ), or by another source, including regenerative braking. During the period when the ultracapacitor voltage is lower than the battery voltage, the battery is supplying all of the power. In a hybrid vehicle, for example, a combination of engine power plus configuring the drive in a regenerative mode, could be used to reduce the time to recharge the ultracapacitor, compared to a conventional pre-charge circuit using the batteries alone. It is envisioned that the majority of the time the drive will be operating at lower speeds and therefore the frequency of this specific transition during full power is minimal. An alternative control technique is to have an automatic, computer controlled, algorithm that during highway mode type of operation, where the drive is routinely operated in the higher speed and power ranges, the control would force the batteries in the series configuration. Only after predetermined conditions, i.e. when the drive is again operated in a lower speed operation for a given length of time or distance, the automated control would switch the batteries back to the parallel configuration the next time the vehicle is stationary. 
     Although,  FIG. 8  illustrates the system switching the batteries from a parallel arrangement to a series arrangement when the motor speed is approximately 50%, it should be realized that the systems described herein will reconfigure the batteries from a parallel mode to a series mode utilizing a plurality of inputs received from the system such as but not limited to, vehicle speed, motor torque, motor speed, and other inputs. As such,  FIG. 8  is an exemplary embodiment, and it should be realized that the batteries may be switched from parallel to series or from series to parallel above 50% motor speed or below 50% motor speed. 
     Described herein is a plurality of energy storage systems that may be utilized with electric and/or hybrid vehicle which requires high power for acceleration and high energy to climb long grades. Hybrid vehicle as used herein represents a vehicle that utilizes a combination of an electric motor and a heat engine to provide propulsive force to the vehicle. Moreover, as used herein, an electric vehicle represents a vehicle that includes a motor and a plurality of batteries, wherein the batteries provide the provide the propulsive force to operate the vehicle. 
     The systems include combinations of high specific power ultracapacitors and high energy rechargeable batteries with high specific energy. The ultracapacitor is sized to provide sufficient power for initial acceleration and deceleration during stop and go urban driving and for short bursts of power during passing maneuvers. Moreover, a relatively low cost ultracapacitor electronic interface allows decoupling of the battery from the ultracapacitor during specific periods and therefore utilizes a higher percentage of the ultracapacitor&#39;s ideal stored energy, during regenerative energy capture. This stored energy is used during future accelerations, thus saving fuel and increasing range. The system described herein also allows for proper matching of the input voltage of the traction drive to efficiently operate for both low speed urban and high speed highway driving. 
     As such, the system described herein facilitates providing a low cost ultracapacitor/battery interface apparatus that does not require a relatively expensive DC-DC converter. The system is robust, reliable, and provides a smooth transition between battery switching events. The solid state battery switching circuits, contactors (if used) do not have high transient current stress. The system control is based on simple voltage, motor speed feedback sensors, and/or torque command signals. The ultracapacitor interface provides an increased utilization of energy storage compared to known interface techniques. Low speed urban driving type cycles may be run primarily using the ultracapacitor thus enhancing battery life. High specific power ultracapacitor component exhibits high round-trip efficiency. The ultracapacitor is essentially on the DC link to facilitate eliminating DC-DC converter losses. The combination of ultracapacitor and a battery provide sufficient energy storage that may be utilized during long up-hill and down-hill grades for both low speed and high speed operation. Moreover, the system also provides improved overall system round-trip efficiency, i.e. ultracapacitor, battery, and/or traction drive, especially during low motor speed operation when the DC link is operated at approximately 50% of rated voltage as compared to high-speed high-power operation. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.