Abstract:
A system and method for balancing the states of charge between a plurality of energy storage modules in a hybrid vehicle is disclosed. The method comprises determining states of charge of individual energy storage modules in said plurality of energy storage modules operatively connected to a power source in the hybrid electric vehicle. The vehicle is operated using a subset of the plurality of energy storage modules when the states of charge of said subset the plurality of energy storage modules is outside of a tolerances relative to the remaining energy storage modules of said plurality of said energy storage modules. The energy storage modules may be charged or discharged using the method in order to equalize the states of charge of the energy storage modules.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/US2014/021068 filed Mar. 6, 2014, which claims the benefit of U.S. Provisional Application No. 61/789,526 filed Mar. 15, 2013, which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention generally relates to energy storage systems for hybrid electric vehicles, and, more particularly, to a system and method for balancing the state of charge of energy storage modules in a hybrid electric vehicle. 
         [0003]    Over the past few years, there has been a growing concern over global climate change due to an increase in carbon dioxide levels as well as oil supply shortages. As a result, some automobile manufactures and consumers are beginning to have a greater interest in motor vehicles having low emissions and greater fuel efficiency. One viable option is a hybrid electric vehicle (HEV) which allows the vehicle to be driven by an electric motor, combustion engine, or a combination of the two. 
         [0004]    Though various features are important to the overall HEV design, the system which stores the energy available for use by the vehicle is a key component. The energy storage system is provided within the HEV to store the energy created by a generator in order for that energy to be available for use by the hybrid system at some later time. For example, the stored energy may be used to drive an electric motor to independently propel the motor vehicle or assist the combustion engine, thereby reducing gasoline consumption. 
         [0005]    However, energy storage systems face a variety of design complications. One of the major concerns during operation is maintaining a proper balance between the packs with respect to the state of charge (SOC) of individual packs in a multi-pack energy storage system. It is important that the individual packs are maintained at a SOC within a certain tolerance with respect to one another. If the difference in SOC between packs exceeds the tolerance, damage to the vehicle&#39;s electrical components can occur. 
         [0006]    Prior art systems have thus far achieved pack or cell balancing with complicated hardware and circuitry which suffers from various drawbacks, such as inefficiency, increased cost, and increased risk of failure. In addition, prior systems have focused on transferring charge between packs, which results in energy loss due to the inefficiency of the transfer process. 
         [0007]    Thus, there is a need for improvement in this field. 
       SUMMARY 
       [0008]    The system and method described herein addresses several of the issues mentioned above as well as others. According to one aspect, a method of balancing the state of charge of a plurality of energy storage modules in a hybrid vehicle is presented, comprising determining states of charge of individual energy storage modules in said plurality of energy storage modules, the energy storage modules operatively connected to a power source in the hybrid electric vehicle, and operating the hybrid vehicle using a subset of the plurality of energy storage modules when the states of charge of said subset of energy storage modules is outside of a tolerance relative to the remaining energy storage modules of said plurality of said energy storage modules. A system for implementing the method is also presented. 
         [0009]    Further forms, objects, features, aspects, benefits, advantages, and embodiments of the present invention will become apparent from a detailed description and drawings provided 4herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates a diagrammatic view of one example of a system for balancing energy storage modules in a hybrid vehicle according to one embodiment. 
           [0011]      FIG. 2  illustrates a process flow diagram for balancing energy storage modules in a hybrid vehicle using the system of  FIG. 1 . 
           [0012]      FIG. 3  illustrates a schematic block diagram of high voltage connections between an example energy storage modules and an example inverter, and control connections between the example energy storage modules and an example hybrid controller according to one embodiment. 
           [0013]      FIG. 4  illustrates a process flow diagram for balancing energy storage modules in a hybrid vehicle using the system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. One embodiment of the invention is shown in great detail, although it will be apparent to those skilled in the relevant art that some features not relevant to the present invention may not be shown for the sake of clarity. 
         [0015]      FIG. 1  shows a diagrammatic view of a hybrid system  100  according to one embodiment. The hybrid system  100  illustrated in  FIG. 1  is adapted for use in commercial-grade trucks as well as other types of vehicles or transportation systems, but it is envisioned that various aspects of the hybrid system  100  can be incorporated into other environments. As shown, the hybrid system  100  includes an engine  102 , a hybrid module  104 , an automatic transmission  106 , and a drive train  108  for transferring power from the transmission  106  to wheels  110 . The hybrid module  104  incorporates an electrical machine, commonly referred to as an eMachine  112 , and a clutch  114  that operatively connects and disconnects the engine  102  from the eMachine  112  and the transmission  106 . 
         [0016]    The hybrid module  104  is designed to operate as a self-sufficient unit, that is, it is generally able to operate independently of the engine  102  and transmission  106 . The hybrid module  104  includes a sump  116  that stores and supplies fluids, such as oil, lubricants, or other fluids, to the hybrid module  104  for hydraulics, lubrication, and cooling purposes. To circulate the fluid, the hybrid module  104  includes a mechanical pump  118  and an electrical (or electric) pump  120 . 
         [0017]    The eMachine  112  in the hybrid module  104 , depending on the operational mode, at times acts as a generator and at other times as a motor. When acting as a motor, the eMachine  112  draws alternating current (AC). When acting as a generator, the eMachine  112  creates AC. An inverter  132  converts the AC from the eMachine  112  and supplies it to an energy storage system  134 . The eMachine  112  in one example is an HVH410 series electric motor manufactured by Remy International, Inc. of Pendleton, Ind., but it is envisioned that other types of eMachines can be used. In the illustrated example, the energy storage system  134  stores the energy and resupplies it as direct current (DC). When the eMachine  112  in the hybrid module  104  acts as a motor, the inverter  132  converts the DC power to AC, which in turn is supplied to the eMachine  112 . 
         [0018]    The energy storage system  134  in the illustrated example includes three energy storage modules  136  that are connected together, preferably in parallel, to supply high voltage power to the inverter  132 . The energy storage modules  136  are, in essence, electrochemical batteries for storing the energy generated by the eMachine  112  and rapidly supplying the energy back to the eMachine  112 . The energy storage modules  136 , the inverter  132 , and the eMachine  112  are operatively coupled together through high voltage wiring as is depicted by the line illustrated in  FIG. 1  and in further detail by lines  350  and  352  in  FIG. 3 . While the illustrated example shows the energy storage system  134  including three energy storage modules  136 , it should be recognized that the energy storage system  134  can include more or less energy storage modules  136  than is shown. Moreover, it is envisioned that the energy storage system  134  can include any system for storing potential energy, such as through chemical means, pneumatic accumulators, hydraulic accumulators, springs, thermal storage systems, flywheels, gravitational devices, and capacitors, to name just a few examples. 
         [0019]    High voltage wiring connects the energy storage system  134  to a high voltage tap  138 . The high voltage tap  138  supplies high voltage to various components attached to the vehicle. A DC-DC converter system  140 , which includes one or more DC-DC converter modules  142 , converts the high voltage power supplied by the energy storage system  134  to a lower voltage, which in turn is supplied to various systems and accessories  144  that require lower voltages. As illustrated in  FIG. 1 , low voltage wiring connects the DC-DC converter modules  142  to the low voltage systems and accessories  144 . 
         [0020]    The hybrid system  100  incorporates a number of control systems for controlling the operations of the various components. For example, the engine  102  has an engine control module  146  that controls various operational characteristics of the engine  102  such as fuel injection and the like. A transmission/hybrid control module (TCM/HCM)  148  substitutes for a traditional transmission control module and is designed to control both the operation of the transmission  106  as well as the hybrid module  104 . The transmission/hybrid control module  148  and the engine control module  146  along with the inverter  132 , energy storage system  134 , and DC-DC converter system  140  communicate along a communication link as is depicted in  FIG. 1 . The energy storage modules  136  may include an energy storage module controller  380  ( FIG. 3 ) for communicating with the transmission/hybrid control module  148 . In a typical embodiment, the transmission/hybrid control module  148  and engine control module  146  each comprise a computer having a processor, memory, and input/output connections. Additionally, the inverter  132 , energy storage system  134 , DC-DC converter system  140 , and other vehicle subsystems may also contain computers having similar processors, memory, and input/output connections. 
         [0021]    To control and monitor the operation of the hybrid system  100 , the hybrid system  100  includes an interface  150 . The interface  150  includes a shift selector  152  for selecting whether the vehicle is in drive, neutral, reverse, etc., and an instrument panel  154  that includes various indicators  156  of the operational status of the hybrid system  100 , such as check transmission, brake pressure, and air pressure indicators, to name just a few. 
         [0022]      FIG. 2  shows a diagram of one example of a communication system  200  that can be used in the hybrid system  100 . While one example is shown, it should be recognized that the communication system  200  in other embodiments can be configured differently than is shown. The communication system  200  is configured to minimally impact the control and electrical systems of the vehicle. To facilitate retrofitting to existing vehicle designs, the communication system  200  includes a hybrid data link  202  through which most of the various components of the hybrid system  100  communicate. In particular, the hybrid data link  202  facilitates communication between the transmission/hybrid control module  148  and the shift selector  152 , inverter  132 , the energy storage system  134 , the low voltage systems/accessories  144 , and the DC-DC converter modules  142 . 
         [0023]    Within the energy storage system  134 , an energy storage module data link  204  facilitates communication between the various energy storage module controllers  380 . However, it is contemplated that in other embodiments the various energy storage system modules  136  can communicate with one another over the hybrid data link  202 . In the illustrated example, the hybrid data link  202  and the energy storage module data link  204  each have a 500 kilobit/second (kbps) transmission rate, but it is envisioned that data can be transferred at other rates in other examples. Other components of the vehicle communicate with the transmission/hybrid control module  148  via a vehicle data link  206 . In particular, the shift selector  152 , the engine control module  146 , the instrument panel  154 , an antilock braking system  208 , a body controller  210 , the low voltage systems/accessories  144 , and service tools  212  are connected to the vehicle data link  206 . For instance, the vehicle data link  206  can be a 250 k J1939-type data link, a 500 k J1939-type data link, a General Motors LAN, or a PT-CAN type data link, just to name a few examples. All of these types of data links can take any number of forms such as metallic wiring, optical fibers, radio frequency, and/or a combination thereof, just to name a few examples. 
         [0024]    In terms of general functionality, the transmission/hybrid control module  148  receives power limits, capacity available current, voltage, temperature, state of charge, status, and fan speed information from the energy storage system  134  and the various energy storage modules  136  within. The transmission/hybrid control module  148  in turn sends commands for connecting the various energy storage modules  136  so as to supply voltage to and from the inverter  132 . From the inverter  132 , the transmission/hybrid control module  148  receives a number of inputs such as the motor/generator torque that is available, the torque limits, the inverter&#39;s voltage current and actual torque speed. Based on that information, the transmission/hybrid control module  148  controls the torque speed and the pump  130  of the cooling system. From the inverter  132 , it also receives a high voltage bus power and consumption information. The transmission/hybrid control module  148  also monitors the input voltage and current as well as the output voltage and current along with the operating status of the individual DC-DC converter modules  142  of the DC-DC converter system  140 . The transmission/hybrid control module  148  also communicates with and receives information from the engine control module  146  and in response controls the torque and speed of the engine  102  via the engine control module  146 . 
         [0025]      FIG. 3  illustrates an additional schematic diagram of the high voltage power connections from the inverter  132  to the energy storage modules  136 . As shown, the energy storage modules  136  are connected to high voltage lines  350  and  352  in parallel. Within the energy storage modules  136 , high voltage contactors  360  and  362  are connected between high voltage batteries  364  and the high voltage lines  350  and  352 . The contactors  360  and  362  are configured to connect or disconnect the batteries  364  to or from the inverter  132  as commanded by individual energy storage module controllers  380 , which in turn are in communication with transmission/hybrid control module  148  via hybrid datalink  202 . 
         [0026]      FIG. 4 . illustrates a process for balancing the state of charge (SOC) of the energy storage modules  136  according to one embodiment. The process can be implemented using the existing hardware of the system  100  via software control. The process also does not require direct energy transfer between the individual energy storage modules  136 , thereby preventing the transfer losses of prior art systems. The process begins at start point  400 , where a master energy storage controller  390  in a master energy storage module  370  determines that at least one energy storage module  136  has a difference in state of charge that exceeds a predetermined tolerance with respect to the remaining energy storage modules  136  (stage  402 ). The master energy storage module controller  390  is in communication the other energy storage module controllers  380  and is therefore aware of the SOC for the other energy storage modules  136 . It shall be understood that the determination may be based on a differential between the energy storage modules  136 , a differential between each energy storage module  136  and a predetermined SOC value, or any other method used to determine that the energy storage modules  136  have differing states of charge. 
         [0027]    At stage  404 , the master energy storage module controller  390  closes the contactors  360  and  362  on a selected energy storage module  136  having a SOC which is farthest from the tolerance (the outlying module), while the contactors  360  and  362  in the remaining energy storage modules  136  remain open. In other embodiments, multiple energy storage modules  136  may be selected which have states of charge outside the desired tolerance or threshold and may have their contactors closed simultaneously. 
         [0028]    At stage  406 , the master energy storage module controller  390  communicates to the transmission/hybrid control module  148  that the selected energy storage module  136  is ready for discharging (or charging), in order to bring it within tolerance with respect to the remaining energy storage modules&#39; SOC. 
         [0029]    At stage  408 , the transmission/hybrid control module  148  operates various vehicle components to discharge (e.g., propel the vehicle, operate vehicle accessories, etc.) or charge (e.g., via regenerative braking) the selected energy storage module  136  until it reaches a SOC within the tolerance of the remaining energy storage modules  136 . In certain embodiments, the state of charge may be monitored as the vehicle is being operated using the selected energy storage module controller  380 , the master energy storage module controller  390 , or transmission/hybrid control module  148 , to ensure that the vehicle is only run in this fashion for the necessary time. 
         [0030]    At stage  410 , the SOC of the selected energy storage module  136  reaches the SOC of a second energy storage module  136 , where the state of charge of the second energy storage module is also outside the tolerance of the remaining modules (assuming more than two modules were initially found to have a SOC outside the tolerance). At this point, the contactors  360  and  362  on the second energy storage module  136  close and the process returns to stage  404  where the two selected energy storage modules are simultaneously discharged (or charged) until reaching the required SOC. The process repeats until all of the energy storage modules  136  are determined to have a SOC within the desired tolerance and the contactors in the remaining energy storage modules are closed (stage  412 ), with the process ending at stage  414 . 
         [0031]    It shall be understood that the above system and method may be utilized in vehicle energy storage systems as well as other non-vehicle energy storage systems where multiple energy storage modules are required. 
         [0032]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes, equivalents, and modifications that come within the spirit of the inventions defined by following claims are desired to be protected. All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.