Abstract:
A battery system includes a cell group in a lead-acid battery power system (battery system A) coupled to a battery power system (battery system B) having a different chemistry, such as lithium ion-based battery. Each battery system, A and B, are interconnected at specific cathode and anode contacts chosen based on the voltages range present at those points to prevent damage to the different battery systems. The worst-case voltage range of the battery system A at the connection points is higher than the worst case voltage range of battery system B. The battery system includes a battery management system (BMS) that monitors voltages at each cell level and that monitors current at the pack level. The BMS can also be configured to control conductivity between packs A and B, and to protect battery systems A and B from going out of normal operating conditions.

Description:
PRIORITY 
       [0001]    This application claims the priority benefit of U.S. Provisional Application No. 61/979,936 filed on Apr. 15, 2014, which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present invention relates generally to battery systems, and more particularly, to battery systems comprising two or more different battery chemistries. 
       BACKGROUND 
       [0003]    Batteries are increasingly being used as a power source for many different kinds of devices, including small electronics, such as smartphones, to large devices, such as automobiles. The choice of battery chemistry to be used in a given device is typically a compromise of characteristics, such as weight, size, capacity, charge/discharge current, charge time, safety, heat generation, reliability, life span, etc. 
         [0004]    Attempts to mix battery chemistries in a given system to reduce the respective compromises presents certain drawbacks. For example, large current flow between cells can occur when voltage levels are different. This is even more dangerous for non-rechargeable batteries where a reverse flow of current may cause the battery to break or explode. 
         [0005]    Consequently, there is a need for battery systems and methods that reduce the need to compromise on certain battery system characteristics while addressing the drawbacks of conventional mixed-chemistry systems. 
       SUMMARY 
       [0006]    The present invention addresses the above-noted drawbacks of mixed-chemistry systems by, in certain embodiments, providing a careful selection of the cells and the accompanying voltage level between the portions having different chemistries. In one example embodiment, a battery system includes a cell group in a lead-acid battery power system (battery system A) coupled to a battery power system (battery system B) having a different chemistry, such as lithium ion-based battery. Each battery system, A and B, are interconnected at specific cathode and anode contacts chosen based on the voltages range present at those points to prevent damage to the different battery systems. The worst-case voltage range of the battery system A at the connection points is higher than the worst case voltage range of battery system B. The battery system includes a battery management system (BMS) that monitors voltages at each cell level and that monitors current at the pack level. The BMS can also be configured to control conductivity between battery systems A and B, and to protect battery systems A and B from going out of normal operating conditions. Battery systems A and B can also be both configured as Li batteries, each with a different Li chemistry. 
         [0007]    In another example embodiment, a battery system includes a first battery assembly having a first type of battery chemistry and a second battery assembly having a second type of battery chemistry. The second battery assembly is electrically connected in parallel with the first battery assembly. The second type of battery chemistry is different than the first type of battery chemistry. A first switch is disposed between the first battery assembly and second battery assembly. A second switch is disposed between the first battery assembly and second battery assembly. A first current sensor is disposed between the first battery assembly and electrical ground. A second current sensor is disposed between the first battery assembly and electrical ground. A battery management system is coupled to the battery system, the battery management system configured to monitor the voltage of the first battery assembly, monitor the voltage of the second battery assembly, monitor the current of the first current sensor, monitor the current of the second current sensor, and operate the first and second switches according to code resident in the battery management system to control the current path through the battery system such that the current path through the first system and the current path through the second system can be independently controlled. 
         [0008]    In a further example embodiment, a method of operating a battery system is disclosed. The battery system includes a first battery pack and a second battery pack. Each of the first and second battery packs comprises a different battery chemistry. The operating method includes coupling the first battery pack to the second battery pack, monitoring a voltage value of the first battery pack, monitoring a voltage value of the second battery pack, monitoring an electrical current value for the first battery pack, monitoring an electrical current value for the second battery pack, and operating a first switch and a second switch to control the current path through the battery system such that the current path through the first system and the current path through the second system can be independently controlled. 
         [0009]    In another example embodiment, a battery system includes a lead-acid battery assembly connected in parallel with a lithium-ion battery assembly. A first switch is disposed between the lead-acid battery assembly and the lithium-ion battery assembly. A second switch is disposed between the lead-acid battery assembly and the lithium-ion battery assembly. A first current sensor is coupled to the lead-acid battery assembly. A second current sensor is coupled to the lithium-ion battery assembly. A battery management system is coupled to the battery system. The battery management system is configured to monitor a voltage value for the lead-acid battery assembly and a voltage value for the lithium-ion battery assembly, monitor the first and second current sensors, and operate the first and second switches to ensure that current does not flow from the lithium-ion battery assembly into the lead-acid battery assembly. 
         [0010]    The above summary is not intended to limit the scope of the invention, or describe each embodiment, aspect, implementation, feature or advantage of the invention. The detailed technology and preferred embodiments for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. It is understood that the features mentioned hereinbefore and those to be commented on hereinafter may be used not only in the specified combinations, but also in other combinations or in isolation, without departing from the scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram of a multi-chemistry battery system according to certain example embodiments. 
           [0012]      FIG. 2  is a flow chart of a system charging operational state of a multi-chemistry battery system according to certain example embodiments. 
           [0013]      FIG. 3  is a flow chart of a system discharging operational state of a multi-chemistry battery system according to certain example embodiments. 
           [0014]      FIG. 4  is a flow chart of a system idling operational state of a multi-chemistry battery system according to certain example embodiments. 
           [0015]      FIG. 5  is another diagram of a multi-chemistry battery system according to certain example embodiments. 
       
    
    
       [0016]    While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular example embodiments described. On the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0017]    In the following descriptions, the present invention will be explained with reference to various exemplary embodiments. Nevertheless, these embodiments are not intended to limit the present invention to any specific example, environment, application, or particular implementation described herein. Therefore, descriptions of these example embodiments are only provided for purpose of illustration rather than to limit the present invention. 
         [0018]    Referring to  FIG. 1 , a multi-chemistry battery system  100  diagram is shown. The system includes a first  102 A lead-acid (LA) battery connected in series with a second LA battery  102 B. The assembly of batteries  102 A and  102 B will be collectively referred to as LA battery assembly  102 . In other embodiments, the LA battery assembly  102  can comprise only a single battery, or it may include any number of multiple LA batteries. 
         [0019]    The system  100  also includes a lithium-ion (Li) battery assembly  104 . The Li battery assembly  104  shown comprises first Li battery cells  104 A connected in series with second Li battery cells  104 B. Again, the Li battery assembly  104  may include a single cell or battery, or it may include any number of multiple cells or batteries to be matched with LA battery  102 A in voltage level. 
         [0020]    The LA battery assembly  102  is connected in parallel with the Li battery assembly  104 . 
         [0021]    Disposed between the LA battery assembly  102  ( 102 A and  102 B) and Li battery assembly  104  are a plurality of switches  106 A and  106 B. These switches  106 A and  106 B electrically connect discreet points along the LA battery assembly  102  to discreet points along the Li battery assembly  104  in order to be able to electrically isolate one or both of the assemblies  102  and  104 . The position of the discreet connection points depends on the chemistry, the voltage of the LA battery  102  and Li battery  104  implemented and the number of assemblies employed. 
         [0022]    First, at the point of connection to the switches  106 A and  106 B between the two battery assemblies  102  and  104  of different chemistries, the total voltage of the Li battery assembly  104  must be less than the total voltage of the LA batteries  102 A and  102 B. This ensures that electric current always flows from LA batteries  102 A and  102 B to Li batteries  104 A and  104 B. Note that in  FIG. 1 , the nominal total voltage of the LA battery assembly  102  is 24V, but the total voltage can be altered by adding or eliminating individual LA batteries. For example, four such 12V batteries connected in series in the LA assembly  102  would be 48V. 
         [0023]    Second, since there is a voltage differential between the LA battery assembly  102  and the Li battery assembly  104 , the switches  106 A and  106 B are intelligently controlled and the voltages at the discreet connection points are monitored to prevent the Li batteries  104 A and  104 B from being overcharged. 
         [0024]    Third, LA batteries and Li batteries have different charging characteristics. As a result, switch  108  is disposed adjacent the LA battery assembly  102 , and switch  110  is disposed adjacent the Li battery assembly  104 . Additionally, a switch  113  is disposed between the individual Li batteries  104 A and  104 B in the assembly  104 . Switches  108 ,  110  and  113  are intelligently controlled to allow for special cases such as LA floating charge conditions. 
         [0025]    A battery management system (BMS) control section  112  is operatively coupled to the battery assemblies  102  and  104 , and to the various switches described herein to provide for the intelligent control as described herein. The BMS can include a plurality of switches (e.g. power MOSFETs) and a micro-controller unit (MCU)  114 . The MCU  114  includes memory to store and a processor to execute computer code governing the MCU&#39;s operation to monitor and control the various aspects of battery system  100  described herein. 
         [0026]    The MCU  114  is coupled to an ADC (analog to digital conversion) unit  116  and a multiplexer, I/O (Input &amp; Output) control and level shifters  118 . These components  116  and part of  118  can alternatively be integrated into the MCU  114 . 
         [0027]    The switches  106 A and  106 B are digitally controlled by the MCU  114  to throttle the amount of charge flowing into the Li batteries from the LA batteries. The MCU  114  is programmed to turn the switches  106 A and  106 B on/off through control signals  130 C and  131 C. As a result, the amount of charge flowing from LA assembly  102  to Li assembly  104  can be determined by monitoring the voltages V 2 - 1 , V 2 - 2 , V 3 - 1 , V 3 - 2  as indicated in  FIG. 1  and also by monitoring current I 1  and I 2  via current sensors  120  and  122 , respectively. Current sensor  120  is disposed adjacent switch  108  and located opposite the LA battery  102 B connected to the switch  108 . Current sensor  122  is disposed adjacent switch  110  and located opposite the Li battery  104 B connected to the switch  110 . 
         [0028]    Switches  108 ,  110 ,  113  are controlled by MCU  114  for at least two purposes. First, MCU  114  controls the current path of the multi-chemistry battery system  100 . MCU  114  can choose to allow current to flow through either one selected battery chemistry/assembly ( 102  or  104 ) or both chemistries/assemblies combined. This control is performed during all modes of operation. Second, the switches  108 ,  110  and  113  provide protection to the overall battery system  100 , or portions thereof, by preventing the system, or parts thereof, from being operated outside of specified tolerances. MCU  114  is configured to selectively disable one selected battery chemistry/assembly current path or both battery chemistry/assembly current paths to prevent damage to the respective batteries or the causing of hazardous conditions. 
         [0029]    The battery system  100  can be configured, for example, either as a Li adapter electrically connected to an existing native LA battery pack, or as a stand-alone multi-chemistry battery pack. In the former example, the LA batteries  102 A and  102 B would represent the existing native battery pack, while the remaining components would be joined thereto as an adaptor system. 
         [0030]    In one example embodiment, the LA battery used is a standard LA battery having a nominal 12V per unit. However, the battery need not be limited to LA chemistry or to 12V. The Li chemistry used in one example embodiment is LiFePo4, which has a nominal operating voltage of 3.3 V. Although, other Li chemistries and voltages can be employed without departing from the scope of the invention. 
         [0031]    In additional embodiments, the Li batteries can be used for both different chemistry battery portions/assemblies. For example, the battery assembly  102  in  FIG. 1  can be a first Li-ion chemistry and the battery assembly  104  can be a Li-ion battery having a second chemistry that is different than the Li-ion chemistry of the first Li-ion battery assembly  102 . 
         [0032]    Referring to  FIGS. 2-4 , the operation of the multi-chemistry battery system  100  can be classified into one of three main operating states, system charging  201  ( FIG. 2 ), system discharging  210  ( FIG. 3 ), and system idling  220  ( FIG. 4 ). System charging  201  occurs when the battery system  100  is connected to a charger  150  powered by a major power source such as charging station or power grid. System discharging  210  occurs when the battery system  100  is the source of energy for powering external devices such as a golf cart. System idling  220  occurs when the battery system  100  is neither electrically connected to a power source nor powering an external device (at high loading condition). 
         [0033]    During system charging  201 , both LA  102  and Li  104  battery assemblies are being charged by the charger  150  initially indicated in  FIG. 2  as LA charging  202 A and Li charging  203 A. The voltage of charger  150  is set to the full charge voltage of 102 which is slightly higher than 104. The Li battery assembly  104  will reach full charge earlier since it has lower internal resistance and normally lower capacity than LA battery assembly  102 , and the combined voltage level of the Li battery assembly  104  is lower than and close to that of the LA battery assembly  102 . When this condition is met, the Li battery charging will be turned off  203 B by disabling switches  106 A and  106 B. Correspondingly, the LA battery assembly  102  will continue to charge by itself until it reaches low current charging  202 B. As the LA battery assembly  102  reaches its final stage of charging, LA float charging  202 C, is achieved. When the LA battery assembly  102  is fully charged, the charger  150  automatically enters floating charging mode  202 C. When the charger  150  is disconnected  204 , MCU  114  is configured to enable both battery chemistry current paths by closing switch  108 ,  110  and  113 . 
         [0034]    Referring to  FIG. 3 , system discharge  210  is determined by the MCU  114  when a certain current threshold is detected flowing through the Li current sensor  122 . During normal operation, switch  124  (disposed between the charger  150  and battery system  100 ) is normally closed unless both the LA battery assembly  102  and Li battery assembly  104  discharge to preset capacity, voltage and/or temperature. When MCU  114  determines that the system  100  is undergoing discharging and the Li assembly  104  is discharging  212 A, the MCU  114  will pulse open and close switches  106 A only, or both  106 A and  106 B, allowing the LA battery assembly  102  to also drive the load  152  (LA discharge  211 A) but at a lower driving current. Since the total Li battery  104  capacity is lower in this example than the LA battery  102  capacity, the Li battery  102  will discharge to empty first. At the same time, the MCU  114  is configured to control the switches  106 A,  106 B and  108  so that the LA battery assembly  102  will also be able to support the Li battery assembly  104  during discharging. When the Li battery  104  capacity is decreased to the point where its current driving capability is reduced, the LA battery assembly  102  will take over to drive the load  152  and potentially also charge the Li battery assembly  104 . 
         [0035]    If the Li battery assembly  104  is determined by the MCU  114  to be in an over-discharged condition, the MCU  114  is configured to turn off the Li current path  212 B by alternatively opening the switches  110  and  113  until the Li battery assembly  104  is sufficiently charged by the LA battery assembly  102  so as to no longer be in an over-discharged state, or once the Li battery assembly  104  reaches a certain charging value set point. If the LA battery assembly  102  capacity is also near its empty state, MCU  114  is configured to disable the entire battery system  211 B by opening switches  108  and  110  to prevent damage to the batteries  102  and  104 . MCU  114  will re-enable the system only if: 1) a charger  150  is connected to the system  100 , or 2) the LA battery assembly  102  has rested sufficiently to safely deliver more current. 
         [0036]    Referring to  FIG. 4 , system idling  220  occurs when no charger  150  is connected and all current paths indicate low or zero discharge. In this state, the LA battery assembly  102  is used to pulse charge the Li battery  104  ( 222 A) if there is enough capacity in the LA battery  102  to safely perform such action. This LA to Li charging stops when either the Li batteries  104  have charged to the same voltage level as the LA battery assembly  102  or the LA battery capacity is deemed to be below threshold. MCU  114  is configured to determine when to turn off the LA discharge  221 B or Li charging  222 B. 
         [0037]    In use, when the Li battery assembly or pack  104  is initially connected to the LA battery assembly or pack  102 , the control section of battery management system (BMS)  112  performs an initial system measurement and check before electrically connecting the two packs  102 ,  104  together. This is done in two stages, first is to measure Li pack  104  status, and second to measure LA pack  102  status. A determination is made by the MCU  114  to ensure that when the two packs conduct, no hazardous conditions exist. 
         [0038]    Distributed charging is used to improve LA battery assembly  102  charging rate. During charging, the LA pack  102  is carefully monitored to perform balancing. The Li pack  104  is to complete its charging before the LA pack  102  has been fully charged. This prior completion of the Li pack charging can be accomplished, for example, by electrically isolating the LA pack from the Li pack during Li pack charging. 
         [0039]    The multi-chemistry battery system shown in  FIG. 1  includes only one LA battery assembly  102  and one Li battery assembly  104 . However, in alternative embodiments, multiples of one or both assemblies can be provided, each being connected in parallel or series. An example of one such alternative is shown in  FIG. 5 . 
         [0040]    The system  300  of  FIG. 5  includes a first LA battery assembly  102  connected in parallel to a second LA battery assembly  302  (comprising two series-connected LA batteries  302 A and  302 B). Also, a second Li battery assembly  304  (comprising two series-connected Li batteries  304 A and  304 B) is connected in parallel with the first Li battery assembly  104 . 
         [0041]    Switches  106 A and  106 B are again disposed between the assemblies of different chemistries so that each collection of assemblies of the same chemistry can be selectively electrically isolated as discussed herein above. 
         [0042]    Individual Li batteries  104 A,  104 B,  304 A and  304 B each have a respective adjacent switch  113 ,  110 ,  313  and  310  for the reasons discussed previously. 
         [0043]    The system  300  can be connected to a load  152  and charger  150  also as discussed previously. Moreover, a BMS and or MCU can be used to control operation of the system  300  as discussed previously. 
         [0044]    Certain features and benefits are exhibited by certain embodiments. For example, Lead acid (LA) batteries are good at discharging but require careful charging profile. Lithium ion (Li) batteries are very powerful at discharging and charging is more tolerant and much faster. Thus, a combination of LA and Li battery chemistries with the control circuitry disclosed herein permits the Li pack to drain faster than the LA pack and the LA pack can be used to charge the Li pack in a controlled manner. As a result, the Li pack will be charged and discharged frequently but the LA pack will only be discharging as the battery system is being used. 
         [0045]    In another example, during charging, the Li pack can assist LA pack to balance out by intelligently conducting and draining charging current from an LA battery section that is weaker in capacity. This will help multiple LA batteries in series to be charged more evenly, especially when LA battery capacity varies due to aging. 
         [0046]    Since Lithium ion batteries have much higher current driving capacities, during high loading conditions, lead acid batteries are automatically protected by having the Lithium ion batteries carrying most of the load. During charging, Li batteries can be conducted to the LA batteries in a digitally controlled manner in order to balance the LA batteries. This is because Li batteries have much lower internal resistance and when conducted with the LA batteries, the Li battery will temporarily bypass some of the LA battery charging. By choosing which section of the LA battery to conduct with the Li battery, an effective charge balancing between the LA batteries can be achieved. The Li batteries can be charged after LA batteries are fully charged since Li batteries have a much lower internal resistance. Also, LA battery charge and discharge operations can be pulsed to prevent sulfur build-up. 
         [0047]    In one example implementation, the BMS  112  continues to monitor the current sensor  120  and the voltage level of V 3 - 1 . When a driver forgets turn off their car lights, or other power draining devices inside of the car when the driver leaves the car, the BMS  112  is configured to shut off (i.e. open) switch  126  (disposed between the battery system  100  and the load  152  when the battery capacity drops below a preset threshold. Thus, the power drain is eliminated. When the driver returns to the car and finds that there is no battery power (because switch  126  was opened), the driver can access the battery compartment and actuate a reset switch  128  to cause switch  126  to be closed again. This results in LA battery power being resumed while having preserved sufficient remaining battery capacity to restart the engine and return the vehicle to normal operation. 
         [0048]    Costs can also be reduced by implementation of the present invention. Li batteries are roughly four times more expensive than LA batteries at similar capacity and with roughly one third of the weight. Combining the two chemistries has the benefit of reducing cost, maintaining capacity and user base, and increased lifetime. An intelligent dual chemistry system as disclosed herein can be configured designed as an extension or add-on to existing, post-deployment LA batteries. The benefit is to extend the overall battery life, increase load capability, and enable intelligent monitoring and diagnostics. Such combination of battery chemistries will result in an advantageous cost vs. performance balance. 
         [0049]    Installation and adaptability is also improved. LA batteries are widely used in data centers, cars, golf carts and many other applications. Certain embodiments of the invention provide for an easy add-on Li battery pack for current LA batteries without any charger and existing infrastructure modification. 
         [0050]    Lifetime (full charge and discharge cycle) compared to convention LA batteries is improved. Typical lifetime for LA chemistry is about 200 cycles, whereas Li chemistry batteries enjoy a significantly longer lifetime of about 600 to 2000 cycles, depending on the Li chemistry. The combined solution thus greatly enhances the standalone LA solution battery life. 
         [0051]    In an additional aspect of certain embodiments, LA battery life and performance can be enhanced. For example, the invention can be used with a conventional vehicle LA battery to prevent the LA battery from over draining and needing to be jump-started or even be damaged, which would otherwise result in needing to replace the battery. In this embodiment, Li batteries need not be utilized for cost considerations. The implementation can be configured as an adapter that is attached to an existing LA vehicle battery. 
         [0052]    In a further aspect, temperature sensors, such as thermocouples, are coupled to each of the battery assemblies and to the microcontroller. This enables the microcontroller to monitor temperature of the individual batteries to ensure that a dangerous buildup of heat does not occur. In the event that temperature of one or more cells of one of the packs rises above a set threshold, that pack can be isolated from the system until it cools to a temperature below a set threshold. 
         [0053]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiments. It will be readily apparent to those of ordinary skill in the art that many modifications and equivalent arrangements can be made thereof without departing from the spirit and scope of the present disclosure, such scope to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products. Moreover, features or aspects of various example embodiments may be mixed and matched (even if such combination is not explicitly described herein) without departing from the scope of the invention.