Patent Publication Number: US-2011048485-A1

Title: Integrated battery management system for vehicles

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following applications that have all been filed by the present inventors. Ser. No. 12/321,310 filed on Jan. 15, 2009 and entitled “Embedded Monitoring System for Batteries”. Ser. No. 12/380,236 filed on Feb. 25, 2009 and entitled “Embedded Microprocessor System for Vehicular Batteries”. And Ser. No. 12/454,454 filed on May 18, 2009 and entitled “Embedded Algorithms for Vehicular Batteries”. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM LISTING ON CD 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to vehicular battery technology and the field of computers. In particular it relates to how changes can be made to battery cell technology and to battery management systems in order to reduce the cost of electric and hybrid vehicles, to improve battery cell efficiency and to reduce the likelihood of physical damage to the battery management system. 
     2. Prior Art 
     Modern electric and hybrid vehicles that derive their motive power from lithium-based or nickel-based batteries require sophisticated battery management systems to insure the safety of the passengers and to prolong battery life. These batteries can catch fire, rupture or explode if not properly maintained. 
     The new Chevrolet Volt hybrid vehicle contains over 200 lithium-ion cells in its battery pack. Each cell&#39;s voltage is monitored. Temperature sensors and current sensors are strategically placed throughout the battery pack. All of these sensors plus the voltage taps for the individual cells reside outside the lithium-ion cells. The battery management system that is wired to these sensors is, itself, also external to the lithium-ion cells. 
     One of the key functions performed by the battery management system is cell-balancing. Cell-balancing is typically required when lithium-based or nickel-based cells are connected in series. The weakest cell in the series governs the performance of the battery. Cell-balancing is designed to reduce the stress on the weaker battery cells and is performed by shunting current around individual battery cells. For example, during a charge cycle, those cells approaching full charge get a portion of their current shunted around the cell to slow down their charge rate while can be driven to the same state of charge. 
     The shunted current must be driven through resistive, capacitive or inductive loads. Through complex and often proprietary schemes the energy shunted through capacitive and inductive loads can be transferred to the weaker cells in the battery pack. This is the approach used by the Chevy Volt. The downside to this approach is that active and passive network and control components must reside outside the cell. On the other hand, resistive loads as used in the Toyota Prius result in the generation of wasted heat that is, in itself, detrimental to maintaining the ideal operating temperature of a cell. Neither the Chevy Volt nor the Toyota Prius approach is ideal. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention makes use of computer systems that are described by the present inventors in application Ser. No. 12/321,310 filed on Jan. 15, 2009 and entitled “Embedded Monitoring System for Batteries” and in application Ser. No. 12/380,236 filed on Feb. 25, 2009 and entitled “Embedded Microprocessor System for Vehicular Batteries”. These computer systems are designed to reside inside the battery. 
     The present invention makes use of embedded computer systems to implement a battery management system for multi-cell batteries that require cell-balancing. The notion of using computer systems to manage lithium-based and nickel-based batteries is neither new nor unexpected and is required to insure passenger safety and to prolong battery life. General Motors is using such a system with its new Chevy Volt hybrid vehicle. Bosch is doing the same for the new BMW hybrid. 
     The present invention makes uses of a Peltier device for controlling the temperature of individual cells. To use a Peltier device in the proximity of a battery cell is neither new nor unexpected. U.S. Pat. No. 7,061,208 by Nishihata; Hideo, et al. suggests such an arrangement. 
     What is missing in the prior art is the synergy that results by manufacturing a Peltier device into the surface of a battery cell, installing the battery management system inside the cell and supplying the normally wasted power, which is a byproduct of cell-balancing, to the Peltier device using no external connections. The polarity of the wasted energy applied to the Peltier device, under the control of the battery management system, causes the battery cell to be either heated or cooled. By regulating the temperature of the cell with wasted cell-balancing energy the efficiency of the system, in general, and the battery cell, in particular, is improved. By placing the battery management system inside the cell, the temperature of the cell is more accurately monitored, the battery management system&#39;s active components become safely entombed inside the cell&#39;s wall and there are no external connections to the Peltier device. The only external remnant of the battery management system is the wires used for inter-cellular and inter-battery communication. If a wireless communication scheme is adopted even these wires go away and the battery management system disappears from sight. 
     Manufacturing costs are driven down because the battery management system is integrated within the cell, cell efficiency is driven up because the Peltier device moderates the cell&#39;s temperature with free energy and the physical integrity of the system is improved since the battery management system safely resides inside the cell&#39;s walls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a computer-based system shown embedded inside a battery cell. A Peltier device is shown manufactured into the surface of one side of the cell. This computer system includes means for measuring the voltage, current and temperature inside the cell (not shown). The computer system includes algorithms that perform cell-balancing and includes a means for switching power to the Peltier device. 
         FIG. 1A  is a flow chart illustrating the steps taken by the computer system of  FIG. 1  to supply power to the Peltier device using the excess energy made available from cell-balancing. 
         FIG. 2  is a block diagram of a computer-based system shown embedded inside a battery cell. A Peltier device is shown manufactured into the surface of one side of the cell. This computer system includes means for measuring the voltage, current and temperature of the cell. The computer system includes facilities for communication across a wireless channel. The computer system includes a means for controlling the polarity of the voltage applied to the Peltier device. 
         FIG. 2A  is a flow chart illustrating the steps taken by the computer system of  FIG. 2  to supply power to the Peltier device using the excess energy made available from cell-balancing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following descriptions are provided to enable any person skilled in the art to make and use the invention and are provided in the context of two particular embodiments. Various modifications to these embodiments are possible and the generic principles defined herein may be applied to these and other embodiments without departing from the spirit and scope of the invention. Both embodiments describe cell-balancing during the charge cycle but the means described herein also apply to the discharge cycle. Special notification is made with regard to battery technology. The generic principles described herein apply to any battery cell type that makes use of cell-balancing. It is not limited to lithium-based or nickel-based battery cells. Thus the invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles, features and teachings disclosed herein. 
     In accordance with one embodiment, the present invention makes use of a computer system that resides inside a battery cell. A Peltier device is manufactured into the surface of one side of the cell&#39;s casework. The computer system includes temperature, current and voltage sensors (not shown). The computer system&#39;s central processing unit also has a means to measure time and includes facilities for storing data. The computer system&#39;s non-volatile memory includes algorithms that perform cell-balancing by shunting power to the Peltier device when the current passing through the power of the cell is to be mitigated. 
       FIG. 1  is a block diagram illustrating central processor unit  1  shown embedded inside battery cell  2 . Central processor unit  1  includes a means for switching power from power posts  4  and  5  to the Peltier device  3  by using control signal  7  and electronic switch  6 . 
       FIG. 1A  is a flowchart illustrating those steps taken by central processor unit  1  in  FIG. 1  in order to calculate the state of charge of the cell and control the operation of the Peltier device based upon the state of charge. In step  20  of  FIG. 1A  the internal battery temperature is sampled by central processor unit  1  of  FIG. 1  and saved. At step  21  of  FIG. 1A  the cell&#39;s current is sampled by central processor unit  1  and saved. At step  22  of  FIG. 1A  the cell&#39;s voltage is sampled by central processor unit  1  of  FIG. 1  and saved. At step  23  of  FIG. 1A  the state of charge of the cell is calculated based upon temperature, current and voltage. At step  24  of  FIG. 1A  central processor unit  1  of  FIG. 1  compares the state of charge against the permissible upper charge limit as stored in central processor unit  1 &#39;s non-volatile memory. If the permissible upper limit has been exceeded, program control is directed to step  25  where Peltier device  3  of  FIG. 1  is switched on using control signal  7  of  FIG. 1  to turn on electronic switch  6  of  FIG. 1 . If the permissible upper limit has not been exceeded, program control is directed to step  26  where Peltier device  3  of  FIG. 1  is switched off using control signal  7  of  FIG. 1  to turn off electronic switch  6  of  FIG. 1 . Program control then proceeds to step  20 . The flowchart repeats. 
     In accordance with another embodiment, the present invention makes use of a computer system that resides inside a battery cell and communicates with external devices through an antenna manufactured on or near the surface of the cell&#39;s case. A Peltier device is manufactured into the surface of the cell case with one side exposed. The computer system includes temperature, current and voltage sensors. The computer system&#39;s central processing unit also has a means to measure time and includes facilities for storing data and program instructions. The computer system&#39;s memory includes algorithms that perform cell-balancing by shunting power to the Peltier device when the current passing through the cell is to be moderated. The computer system includes a means for applying either cold or heat to the cell by controlling the polarity of the power applied to the Peltier device. The computer system includes a means to receive new algorithms and operational instructions from external devices. 
       FIG. 2  is a block diagram illustrating central processor unit  30  shown embedded inside battery cell  31 . Central processor unit  30  includes a means for switching power from power posts  4  and  5  to the Peltier device  3  by using control signal  8  and electronic switch  32  or control signal  9  and electronic switch  33 . Central processor unit  30  includes an electrical connection to antenna  39  through transceiver  37 . Transceiver  37  makes use of conductor  38  to transfer digital data over the wireless connection to one or more external devices (not shown). Voltage sensor  36  internally measures the voltage drop between battery cell posts  4  and  5  (the connection between this sensor and the two battery posts not shown). Temperature sensor  35  measures the temperature inside the cell&#39;s case. Current sensor  34  measures the current between battery cell posts  4  and  5  (the connection between this sensor and the two battery posts not shown). Central processor unit  30  uses transceiver  37  to monitor wireless traffic that may include command and control information or may contain new cell-balancing algorithms. 
       FIG. 2A  is a flowchart illustrating those steps taken by central processor unit  30  in  FIG. 2  in order to perform cell-balancing and shunt the resultant excess energy through the Peltier device in order to either heat or cool the battery cell. 
     In step  40  of  FIG. 2A  the data channel in  FIG. 2  consisting of antenna  39 , conductor  38  and transceiver  37  is monitored for activity. If no data traffic is present program control proceeds to step  47  of  FIG. 2A . If data activity is present program control proceeds to step  41  of  FIG. 2A  where the incoming data is sampled in order to is being downloaded program control proceeds to step  42  of  FIG. 2A  where the new algorithm is downloaded and replaces the existing cell-balancing algorithm stored in central processor unit  30  of  FIG. 2 . Program control returns to step  40  of  FIG. 2A  and the flowchart repeats. If step  41  of  FIG. 2A  determines that a new algorithm is not being download program control proceeds to step  43  of  FIG. 2A  where command information is downloaded. At step  44  of  FIG. 2A  if a command has been received to turn on the Peltier device  3  of  FIG. 2 , program control proceeds to step  45  of  FIG. 2A  where the Peltier device  3  of  FIG. 2  is turned on. Depending upon the internal temperature of the cell either control signal  8  of  FIG. 2  turns on switch  32  of  FIG. 2  in order to apply heat to a cold cell or control signal  9  of  FIG. 2  turns of switch  33  of FIG.  2  in order to apply cold to a hot cell. Program control then returns to step  40  of  FIG. 2A  and the flowchart repeats. If at step  44  of  FIG. 2A  a command has been received to turn off Peltier device  3  of  FIG. 2 , program control goes to step  46  where both control signal  8  and control signal  9  of  FIG. 2  are de-asserted in order to remove all power to Peltier device  3  of  FIG. 2 . Program control returns to step  40  causing the flow chart to be repeated. 
     Step  47  of  FIG. 2A  receives program control from step  40  of  FIG. 2A  when there is no wireless traffic. In step  47  of  FIG. 2A  the battery temperature is sampled by central processor unit  30  of  FIG. 2  and saved. At step  48  of  FIG. 2A  the cell&#39;s current is sampled by central processor unit  30  and saved. At step  49  of  FIG. 2A  the cell&#39;s voltage is sampled by central processor unit  30  of  FIG. 2  and saved. At step  50  of  FIG. 2A  the state of charge of the cell is calculated based upon temperature, current and voltage. At step  51  of  FIG. 2A  central processor unit  30  of  FIG. 2  compares the state of charge against the permissible upper charge limit as defined by the cell-balancing algorithm. If the permissible upper limit has been exceeded, program control proceeds to step  45  of  FIG. 2A  where the Peltier device  3  of  FIG. 2  is turned on. Depending upon the internal temperature of the cell either control signal  8  of  FIG. 2  turns on switch  32  of  FIG. 2  in order to apply heat to a cold cell or control signal  9  of then returns to step  40  of  FIG. 2A  and the flowchart repeats. If the permissible upper limit has not been exceeded, program control goes to step  46  where both control signal  8  and control signal  9  of  FIG. 2  are de-asserted in order to remove all power to Peltier device  3  of  FIG. 2 . Program control returns to step  40 . The flow chart repeats. 
     Advantage 
     The advantage of this invention is that it recognizes the synergy that results by manufacturing a Peltier device into the surface of a battery cell, installing the battery management system inside the cell and supplying the normally wasted power, which is a byproduct of cell-balancing, to the Peltier device using no external connections. The polarity of the wasted energy applied to the Peltier device, under the control of the battery management system, will cause the battery cell to either be cooled or heated. By regulating the temperature of the cell with wasted cell-balancing energy the efficiency of the system is improved. By placing the battery management system inside the cell, the temperature of the cell is more accurately monitored, the battery management system&#39;s active components become safely encased inside the cell&#39;s wall and there are no external connections to the Peltier device. The only external remnant of the battery management system is the wires used for inter-cellular and inter-battery communication. If a wireless communication scheme is adopted even these wires go away and the battery management system disappears from sight. 
     Manufacturing costs are driven down because the battery management system is integrated within the cell, cell efficiency is driven up because the Peltier device moderates the cell&#39;s temperature with free energy and the physical integrity of the system is improved since the battery management system safely resides inside the cell&#39;s walls.