Abstract:
A battery management system that monitors and controls the charging and discharging of a battery pack in the most versatile way at the block level with little dissipative loss but fast balancing is disclosed. The system has capability of using blocks of cells using different chemistry in the same battery pack. Such versatility makes it very useful for usage with erratic grid conditions, solar, wind and other natural energy sources for charging the battery.

Description:
TECHNICAL FIELD 
     The present invention relates generally to the field of battery systems, and more particularly to a method and system for charge equalization in a flexible chemistry and flexible capacity battery system. 
     BACKGROUND ART 
     The following terminology is adopted in this disclosure. 
     Cell: The Cell  10  as described in  FIG. 1  is the most basic element of a battery system, with positive and negative terminals, storing and dispensing electrical energy through an electrochemical process. For example, it could be a nominal 3.7 V Lithium ion cylindrical cell or a nominal 2.1V Lead-Acid prismatic cell. A Cell is usually characterized by its AC Impedance (ACI), Equivalent Series Resistance (ESR), Capacity (in Amp.Hour, or in short, Ah), and Nominal Cell Voltage. The manufacturer typically provides many other parameters, such as cycle life, optimal temperature, maximum charge and discharge rate. 
     Block: The Block  20 , as described in  FIG. 2 , is a collection of Cells  10  wired directly in parallel, providing the same voltage as individual Cells. All the Cells in a block must belong to the same chemistry. For instance, all Lithium Carbonate (LCO) cells, or all Lead-Acid cells. A typical Block may have as few as 1 Cell and some times as many as 1000 Cells or more. The current collector  21  is a conductive path, typically a metallic plate that is connected to all the positive terminals of the Cells in the Block. There are many methods of connection including soldering, welding, and spring contact. The current collector  22  is a conductive path, typically a metallic plate that is connected to all the negative terminals of the Cells in the Block. Methods of connection are similar to that of the positive side. 
     Although a stacked approach is shown in  FIG. 2  for building a Block out of Cells, there are many other ways of making a Block as known to an expert in the field of battery manufacturing. For instance, many cells may be inserted into a set of spring-contact connectors, and the respective conductive contacts may then be electrically joined together to make a Block. 
     While these examples are cited for the reason of comprehension, it is to be understood that a Block is essentially a collection of Cells connected electrically in parallel. 
     Battery: A collection of Blocks wired in series. For instance, a 3S4P Lead-Acid battery consists of 3 Blocks wired in Series, with each Block containing 4 Cells in parallel. Such a battery would have a nominal voltage of 6.3V (Three in series multiplied by 2.1V of nominal Cell voltage). In  FIG. 3  an example of a 3S4P Battery is shown. The battery  30  consists of three Blocks— 35 ,  36  and  37 . The positive terminal of the first battery  35  is typically connected to a current carrying wire  31 , and is available to external devices as the positive terminal for the entire battery. The negative terminal of the last battery  37  is typically connected to a current carrying conductor  32 , and is available to external devices as the negative terminal for the entire battery. 
     The Series connection is realized by connecting opposite parity terminals of consecutive blocks. For instance, in  FIG. 3 , the negative plate  22  of the top block  35  is connected electrically to the positive terminal  21  of the middle block  36 . 
     The Blocks connected such may be enclosed in a mechanical cover  33  for safety or mechanical convenience. 
     In certain instances a Battery may be packaged in such a way that Cells of the same Block may be placed at different mechanical locations, but electrically they would be considered to belong to the same Block. In  FIG. 4  we show an example of this, wherein the Battery  40  consists of two mechanical assemblies  44  and  45 . It is to be noted that the two assemblies are indeed connected in parallel at the Block level. For example, the group of Cells  46  are electrically connected in parallel with the group of Cells  47 . The same applies to other groups of Cells. In this case, the groups of Cells  46  and  47  belong to a single Block. For the purposes of this disclosure, this Battery would be considered as 3S8P, consisting of 3 Blocks, with each Block containing 8 Cells. The groups  46  and  47  for instance, form one Block of 8 Cells. 
     Battery Management System (BMS): An electronic system that has components addressing, monitoring and communicating between Blocks to control the electron flow to create a balance between all the Blocks according to a pre-determined logic. The BMS also makes decisions, such as disengaging the Battery from the outside electricals in the event of high voltage, high charge or discharge current, high internal or external temperatures, Cell failures, and re-engaging when such conditions are rectified. 
     Pack: A Battery mechanically and electrically packed with a Battery Management System (BMS) voltage, current, and thermal sensors, and optionally active or passive thermal control devices to keep the battery at a desired temperature range. 
       FIG. 5  shows a Battery with 3 Blocks in series. The Battery may have been charged and discharged through any number of cycles. If voltages of all the Blocks are identical or nearly identical (typically within +/−3%), then the Battery is considered to be balanced. In the case of  FIG. 5 , all the three Blocks have 4.2V across them—hence the Battery is balanced. In  FIG. 6 , the Battery has 3 Blocks, but at a given instant of time, the voltages across the Blocks are 4.4V, 4.0V and 4.2V—all different significantly from one another. (at least one Block &gt;3% off from at least one other Block). Such a Battery is called unbalanced. 
     In  FIG. 7  we show a BMS that exists in the prior art and is commercially available. The Battery  30  is connected to a charger  51  and a load  52  at its positive terminal. A BMS  55  is connected to the Battery in a way that it has electrical access to every terminal of every Block. For instance, the electrical line  56  is connected to the connection wire  34  between the top and the middle Block. 
     The electrical circuit from the charger or the load goes through the Battery positive and negative terminals, and is terminated back through the BMS. The negative terminal connections are not shown to maintain the clarity of the figure. A practicing engineer in the field will know that the negative terminals of the Battery, the Charger, the Load and the BMS would be tied together. The BMS therefore has the capability to close or open the electrical circuits for charging or discharging (through the load) upon certain conditions. In  FIG. 7 , the electrical lines  53  and  54  from the BMS control the circuit closure of the charger and the load, respectively. A temperature sensor  57  such as thermistor is also placed into the Battery  30  and is wired to the BMS  55  with an electrical connection  58 . 
     Such a BMS has the following major intentions—
         To monitor the Blocks in the Battery   To protect the battery   To estimate the battery&#39;s state of charge or instantaneous capacity   To maximize the Battery&#39;s performance by balancing the Blocks.   To communicate any important parameters of the battery to an external device or a user.       

     The general management functions of such a BMS are—
         1. Protection: Not allowing the battery, any block or any cell to operate outside of recommended operating parameters. Such function can be further subdivided as—
           (a) Prevent the voltage of a Block from exceeding a limit, by stopping the charging current. In Lead-Acid batteries an excess voltage would cause excess generation or hydrogen and oxygen, while in a Lithium Ion battery it can cause the cell to fail and explode, thus compromising safety.   (b) Prevent the temperature of any Cell or any Block from exceeding a limit by stopping the battery current, or requesting that it be cooled. Most Lithium Ion cells are prone to a thermal run-away if such safety mechanism is not incorporated by a BMS.   (c) Prevent the voltage of any Cell or Block from dropping below a limit by stopping the discharging current. For instance, in Lithium Ion batteries, an electrode may dissolve in the electrolyte if the Cell is allowed to discharge below a certain low voltage—around 2.3V. In case of Lead-Acid Cells, sulfation of electrodes may occur at very low battery voltages. In many cases such effects cause irreversible damage to the Cell.   (d) Prevent charging current from exceeding a limit by reducing or stopping the current. For instance, in Lead acid and Lithium Ion Cells, a higher charging current than recommended causes permanent damage to electrodes, and may result in unsafe conditions. Typically, the charge current limit is a function of Block voltage, temperature, state of charge and the previous level of current.   (e) Prevent discharging current from exceeding a certain limit by reducing or stopping the current. For instance, in Lead acid and Lithium Ion Cells, a higher discharging current than recommended causes permanent damage to electrodes, and may result in unsafe conditions. Typically, the charge current limit is a function of Block voltage, temperature, state of charge and the previous level of current.   
           2. Thermal Management: Controlling the thermal actuators and devices for the Pack to maintain the temperature of the Battery, its Cells and its Blocks within a recommended range. For instance, the Pack may contain thermoelectric devices (TEC) that can add to or subtract heat from the Pack with the application of a controlled current. The Cell manufacturer&#39;s recommendation may be to run the Battery then between 15 deg C. and 35 deg C. During the operation of the battery, if the temperature falls below 15 deg C. for any block, then the TEC could be instructed to heat the pack, whereas if the temperature goes above 35 deg C., the TEC could be instructed to cool the pack. Such decisions would be taken by the BMS.   3. Balancing: Maximizing the battery&#39;s capacity by distributing or redistributing the charge among the Blocks as the battery undergoes charging and discharging.       

     This invention pertains to the balancing action of the BMS. During charge and discharge of the Battery, one pushes a certain amount of charge into each Cell. If each Cell were identical in all respect, then the Battery would stay balanced at all times, but two Cells are never the same. Due to manufacturing variations, and post-manufacturing treatments, the Cells develop different characteristics, as follows, which result in their different capacity behavior.
         1. Cell resistance or Equivalent Series Resistance (ESR). If the ESR of a Cell is higher compared to other Cells, it will respond with a larger polarization voltage than others in series to the response of the same charging current.   2. Capacity. Two different Blocks may not have the same electrochemical capacity, in which case, in response to the same charging current, the voltages will be different.   3. Leakage. Depending on the age of the Blocks, two different Cells in two different Blocks may have different internal leakage currents. Leakage current is responsible for self-discharge of a Cell, and therefore affecting the capacity of the Cell and in turn, of the Block. As a result, the effective charge and discharge capacities will be different, and will have different voltages in response to same charging current.   4. SOC. If the blocks started operating with different SOCs to start with, or if parasitic loads are taken off from intermediate blocks in a battery, the battery as a whole will stay unbalanced.       

     Different BMS devices do the balancing in different ways. The schemes known so far include the following—
         (a) Shunt Regulator Bypass: In this case a shunt power regulator is placed across each block in the BMS. During charging, when a block reaches the maximum recommended voltage, the shunt bypasses the block. Although this seems simple, the shunt regulator has to be able to carry the entire charging current in the bypass mode, which results in expensive electronics. Besides, when this happens with one or more cells, the battery charging voltage must drop keeping the current the same, thus charging the rest of the blocks. The charger needs to be able to accommodate such a voltage swing, which is not easy. Besides, if the charger is connected to a load, the load specifications may not allow this voltage swing to happen. Consequently, such a scheme is not very popular and is used only where the charging current is low (&lt;1 A or so)   (b) Dissipation: In this case, at a pre-determined range of voltage or SOC, all the blocks that have higher voltage or SOC burn some power by trickling some current to the ground or another cell. While this remains as a popular method, it is wasteful in terms of energy. This method also creates a lot of heat in the Pack, due to which thermal management becomes difficult.   (c) Distribution: In this case, during the charging of the battery, the Blocks that have higher voltage or SOC transfer some of their capacity to the entire Battery chain or a section of it by switching regulators. While this is less wasteful than dissipative methods, it requires high current switching passives (such as inductors and capacitors), need a lot of discrete components, and reliability and cost concerns are high.       

     While all the above methods are in use today, they still cannot satisfy some fundamental needs of the industry.
         1. All of them still have some dissipation, and as the Cells grow older, the dissipation becomes a significant portion of the total energy transacted during charging and discharging. Besides reducing the efficiency of the product, it creates heating problems in enclosed Packs.   2. If different Blocks in a battery have Cells of different chemistries, the blocks would then have different charge and discharge termination voltages and therefore none of the schemes above would work.   3. If some Blocks have significantly higher leakage, then balancing becomes even more wasteful and may never eventually bring the Cells to an effective balance.   4. If the Blocks have different number of Cells, or have different operational history, then their effective capacities may be different, and therefore the schemes would be highly dissipative or be generally ineffective.   5. These schemes generally do not offer a good way to keep the Blocks balanced during discharging.       

     SUMMARY OF INVENTION 
     It is an object of this invention to provide a method of balancing a Battery with minimal dissipation. 
     It is also an object of this invention to provide a method of balancing a Battery very fast when Cells or Blocks of very different initial states of charge are introduced at the beginning. 
     It is also an object of this invention to provide a method of balancing a Battery when the effective capacities of the individual Blocks in series have become different as a result of usage history. 
     It is also an object of this invention to provide a method of balancing a Battery that may have Blocks of different chemistries, different SOCs, different capacities and different operational history. 
     It is also an object of this invention to provide a method of balancing a Battery with that keeps balancing the Blocks during both, charging and discharging of the Battery. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 : Representation of a basic electrochemical cell. 
         FIG. 2 : Representation of a Block of electrochemical cells. 
         FIG. 3 : Representation of a Battery built out of Blocks. 
         FIG. 4 : A Battery with segregated packs. 
         FIG. 5 : A Battery with balanced Blocks. 
         FIG. 6 : A Battery with unbalanced Blocks. 
         FIG. 7 : A Battery with a BMS as known in the prior art. 
         FIG. 8 : A DPST (Dual Pole Single Throw) switch in its default NO (Normally Open) state. 
         FIG. 9 : A DPST switch in its activated CLOSED state. 
         FIG. 10 : A Voltage Monitoring Card for Blocks. 
         FIG. 11 : A Temperature Monitoring Card for Blocks. 
         FIG. 12 : Monitors, Actuators and Switch connections for a Battery according to the current invention. 
         FIG. 13 : Switch connections for a Battery with one switch activated according to the current invention. 
         FIG. 14 : Balance of the System for the BMS and Battery according to the current invention. 
         FIG. 15 : Diagram of an isolated current charger used in the invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     DPST Switch 
     The disclosed invention uses a key component—Dual Pole Single Throw (DPST) electrical switch. In  FIG. 8 , a logical and functional diagram of the DPST switch  100  is shown. The function may be incorporated with a variety of technologies, including electromechanical relay, and solid state optically driven Mosfets. The switch  100  has four main electrical terminals  101  &amp;  102  on one side, and  103  &amp;  104  on the other side. The pins  101  and  103  are separated by an electrical bridge  107 . The same bridge  107  also separates the pins  102  and  104 . The bridge  107  may be actuated with a physical actuation signal  105  such as an electrical voltage, a magnetic field or an optical signal. When actuated, the bridge  107  closes the path  101  to  103  and the path  102  to  104  electrically. The actuation terminal  105  (Control or CTL) accepts a binary on/off signal to the switch  100 . The signal may be of electrical, optical or other kind of physical stimulus. The electrical configurable path  105  responds to CTL in the following way:
         (a) When CTL is OFF, the electrical path between  101  and  103  is open. The electrical path between  102  and  104  is also open.   (b) When CTL is ON, the electrical path between  101  and  103  is closed. The electrical path between  102  and  104  is also closed.   (c) Irrespective of the state of CTL,  101  never makes a connection with  102  or  104 . Irrespective of the state of CTL,  103  never makes a connection with  102  or  104 .   While  FIG. 8  shows the connection model of the DPST in its CTL=OFF state, the  FIG. 9  shows the connection model of the DPST in its CTL=ON state.       

     Such DPST switches are currently available in the form of electromechanical relay or solid state Mosfet. An example of electromechanical relay form of DPST is G2RL-2 series from Omron. An example of solid state Mosfet form of DPST is AQW214EAX series from Panasonic Electric Works. These devices are used in the preferred embodiment of the invention. 
     It may be noted that some switches may be available with the control polarity opposite to what is described above, and it is understood that a practitioner of the art in the field would still be able to use them for the same purpose by reversing the driving algorithm. 
     It is also to be noted that it is the switching function that is essential to the embodiment of the invention. Although the DPST is introduced here as a means, the same function may be achieved by many other well-known circuits and devices. 
     Isolated Current Injection Supply (ICIS): 
     Embodiment of this invention calls for an Isolated Current Injection Supply (ICIS)  150 , described in  FIG. 15 . The terminals  151  and  152  are connected to a voltage supply at its positive and negative terminals, respectively. These are called input terminals. The terminals  153  and  154  are the positive and negative of the output. The output is a current supply with a maximum voltage clamp. The barrier  155  represents the electrical isolation between the input and output. The control  157  tells the circuit how much current it can supply on the output subject to a maximum output voltage, or can completely turn the current off. 
     The positive output terminal  153  is connected to a power buss  251 . The negative terminal  154  is connected to a power buss  261 . The busses  251  and  261  form a power supply that is electrically isolated from any other potential in the system as long as all the CTL signals are OFF 
     The input terminals  151  and  152  are connected to battery terminals  31  and  32 , respectively in the preferred embodiment, but can be connected to any other potential difference available in the system as long as that would support the current and voltage required by the ICIS. 
     In a the preferred implementation, the ICIS is a fly-back switch mode isolated power supply running from an input voltage and supplying current at the output, the current being controlled by a closed-loop optical feedback to the primary circuit. 
     In a simpler implementation, the ICIS is a flyback switch mode isolated power supply running from an input voltage and supplying a programmable or constant voltage on the output, the current being limited by a resistor. 
     It may be noted that the fundamental intention is to provide electrical energy at the output terminals  153  and  154  that is electrically isolated from the rest of the electrical potentials in the system. Such intention may be accomplished with many other power supply topologies known to a practitioner of the art in the field. 
     Voltage Monitoring Circuit (VMC): 
     Another key component in the current invention is a voltage monitoring circuit  110  that measures the voltage of each Block  20  as shown in  FIG. 10 . The circuit  110  connects to the positive and negative terminals of Block  20  with inputs  113  and  114 , respectively. The difference in the voltage between the two terminals  113  and  114  is amplified and conditioned by an amplifier  115 , and a proportional signal is provided on terminal  112 . Depending on the type of the circuit, the very act of reading the voltage results in a minor drainage of current from the Block, and hence to minimize that, a control signal  111  may be provided to the circuit  110  to enable it while being read, and disable it otherwise. The input impedance of the circuit, for example, impedance between terminals  113  and  114  is high, so that no substantial amount of current flows. Therefore, it prevents any substantial energy loss from the block while voltage is being measured. Input impedance of 100 kilo-Ohms or larger are preferred. 
     Temperature Monitoring Circuit (TMC): 
     Another key component in the current invention is a temperature monitoring device and circuit as described in  FIG. 11 . A temperature measuring element  127  is placed on or in the Block  20 , and its stimulus is quantified by the monitoring device  120  through its inputs  123  and  124 . An appropriate amplifier  125  conditions the signal and provides a proportionate signal on the terminal  122 . 
     The temperature monitoring device  127  may be comprised of many different kinds of technologies, such as thermistor, RTD, and Mosfet. In the preferred embodiment of this invention, a 50,000 Ohm Thermistor bearing part number NTSD1WD503FPB30 from Murata Electronics has been used. 
     Primary Embodiment 
     The incorporation of these elements in the current invention of BMS in the battery pack is described as system  200  in  FIG. 12 . In system  200 , three Blocks  221 ,  222 , and  223  are shown to make up the Battery. They are arranged in the sequence of decreasing voltage in the Battery. Although only 3 Blocks are shown, the same invention can be applied in a similar method to any number of Blocks ranging in number from 2 to any large number. The Blocks  221 ,  222  and  223  are read by VMCs  211 ,  212 , and  213 , respectively. The outputs of the VMCs are connected to the Voltage Reading Buss (VRB)  203 . The amplifier enable ports of the VMCs are connected to the Voltage Enable Buss (VEB)  202 . The Blocks  221 ,  222  and  223  have thermistors incorporated in the packaging, and the respective thermistors are read by Temperature Monitoring Circuits (TMC)  214 ,  215  and  216 , respectively. Outputs of the TMCs are connected to the Temperature Measurement Buss (TMB)  204 . The Busses  202 ,  203  and  204  are connected to a central circuit to be described later. 
     The ICIS  150  is connected to the battery terminals  221 (B+) and  241 (B−), on its inputs. The positive  153  and negative  154  isolated output lines are connected to the isolated busses  251  and  261 , respectively. 
     Three DPST switches are used in this description. The switches  281 ,  282 , and  283  are dedicated to the Blocks  221 ,  222  and  223 , respectively. The connections are made in such a way that one terminal of one side of the DPST switch is connected to the positive polarity of the Blocks and the other terminal of the same side is connected to the negative polarity of the same Block. 
     The other side of the DPST switches is connected to the isolated power Busses  251  and  261 , such that when any switch closes, the positive power Buss  251  would make an electrical connection to the positive terminal of the respective Block, and the negative power Buss  261  would make an electrical connection to the negative terminal of the respective Block. 
     The negative terminal of the Block  223  is connected to the negative terminal of the Battery  241  (B−). 
     A current sensor  243  is incorporated on the B-line to measure the Battery current which is reported through a signal  242  to a central processing unit as described later. It is to be noted that the current sensor could be installed on the positive line B+ as well. A Hall-Effect current sensor from Honeywell CSLA1CE was used in this embodiment, although other kinds, such as shunt resistors may be used for the purpose as well. 
     The control ports of the switches  281 ,  282  and  283  are connected to a Switch Control Buss (SCB)  201 , which is connected to a central processing unit to be described later. 
     When the all the CTL ports of the switches receive an OFF signal through the buss  201 , the electrical connections of the switches to the Blocks are shown as in  FIG. 12 . It can be observed that no current flows from the isolated busses to any Block, hence no balancing activity takes place. 
     When one of the CTL ports receives an ON signal, for instance the switch  282 , then the situation is shown in  FIG. 13 . In response to the signal, the DPST  282  closes both the terminals, and as a result, current from isolated busses  251  and  261  flow into the Block  222 . It may be noted that this kind of injection current is independent of the main charging and discharging currents that flow through the main stack and does not disturb the normal Battery activities. The cell  222  gets some more charging than the rest of the Blocks as a result of this activity. 
     The connection of the Battery in the Pack is shown in  FIG. 14  as Balance of the System (BOS)  300 . The Battery Charger  51  provides the voltage and current according to the need of the system. In this implementation it is a Constant-Current-Maximum-Voltage (CCMV) charger wherein the charger pushes a prescribed about of current into the Pack as long as the Pack voltage is less than a prescribed Maximum Voltage. When the Maximum Voltage is reached, the Charging Current is tapered down so as to keep the Pack voltage a constant at the value of Maximum Voltage. The negative terminal of the Charger  51  is connected to the system ground  301 . The positive terminal of the Charger  51  is connected to the Battery positive  240  (B+), which further flows in  FIGS. 12 &amp; 13 . The pack discharges into a Load  52  which may have varying current requirements and may even have its own power conditioning circuits to change the voltage or current levels for a final application. The negative terminal of the Load  52  is connected to the system ground  301 . The positive terminal of the Load  52  is connected to the battery positive  240  (B+), which further flows in  FIGS. 12 &amp; 13 . The period of switching between the voltages of the blocks are measured and the activation of the DPST switches are in effect, is less than 10 times of a total average charge time of the battery block assembly required by an application. 
     An electronic switch  302  in the form of a solid state switch is placed on the return line  241  (B−) before it goes to the ground. The electronic switch acts in response to a control signal  303  delivered from the system electronics to be described below. The system algorithm may activate this switch to open the Battery current path from the charger  51  or load  52  during many circumstances including, but not limited to, over-charging, over-discharging, short-circuit, and over-temperature. While the electrical interruption device  302  is in the open state, and the charger loses its power, necessitating the pack to provide current to the load, the device  302  detects the power failure and closes itself during a time period not material to the operation of the load. 
     The whole Pack system is controlled by a microprocessor unit (MPU)  321 , which includes a microprocessor and many auxiliary units, such as memory, Analog to Digital Converter (ADC), Amplifiers and other signal conditioners and recorders. It also communicates with the sensors and actuators in the battery pack via a Driver and Multiplexer Card (DMC)  311 . The MPU  321  communicates with the DMC  311  through the channel  304  to control the Switch Control Buss (SCB)  201 . The MPU  321  communicates with the DMC  311  through the channel  305  to control the Voltage Enable Buss (VEB)  202 . The MPU  321  communicates with the DMC  311  through the channel  306  to read the Voltage Reading Buss (VRB)  203 . The MPU  321  communicates with the DMC  311  through the channel  307  to read the Temperature Reading Buss (TRB)  204 . 
     The MPU  321  reads the current measurement  242 . It also stores and retrieves system and temporal information, such as calibration constants, real time clock, and algorithm parameters with a memory device through the port  335 . The MPU  321  communicates with the outside world through the communication post  325 . In this example, it is an RS-232 port that transmits and receives data in both wire-line and wireless means. 
     The MPU  321  actuates and controls a thermal control device through the port  315 . In this embodiment, it is a bi-directional thermoelectric (TEC) device that is capable of both, cooling, and heating the device, depending on the need. 
     The algorithm of the BMS implemented for the operation of the Battery is described below. 
     In this implementation, the Pack was required to be charged at 0.5 C rate. Therefore the time taken to fully charge the system from zero state of charge is about 2 hours. The load for the application was about 0.2 C. Therefore a fully charged Pack would take about 5 hours to fully discharge. 
     Algorithm During Charging: 
     During Charging, the voltages of the Blocks are measured by activating elements in the VEB  202  and reading the Block voltages through the VRB  203 . The Block with the minimum voltage is determined to be the Xth Block. As the next step, the DPST switch corresponding to the Xth Block is turned ON through the SCB  201 , with all other switches being OFF. That gives the Xth Block a chance to catch up in voltage with the rest of the blocks. Such condition is maintained for 1 minute, after which all the DPST switches are turned OFF. Such condition is maintained for 5 seconds so that all the Block voltages are stabilized. Now the process is started again with measuring all the voltages and finding out the lowest voltage block and isolating it. This cyclic operation is done about 100 times during 2 hours of charging, and that gives enough iteration to balance all the Blocks within reasonable means. Even if all the Blocks may not be balanced during one cycle, doing such algorithm over several cycles will balance them. 
     During the charging cycles, if any of the Blocks reach a prescribed maximum Block voltage, then the charging of the entire stack is deemed complete, and the MPU  321  opens the switch  302  to stop further charging. This prevents over-charging and damage to the battery. As described earlier, the device  302  reacts quickly to close itself upon a loss of power of the charger in order for the pack to provide power to the load. 
     During charging cycles, if any of the temperature sensors reads a temperature higher than 40 deg C. or lower than −20 deg C., then the TEC is turned on through the port  315  for cooling or heating, respectively. If all the temperature sensors do not get back to the given limits within 10 minutes, then MPU  321  throws the switch  302  is open, taking the Pack out of any external electrical influence. 
     Algorithm During Discharging: 
     During Discharging, the voltages of the Blocks are measured by activating elements in the VEB  202  and reading the Block voltages through the VRB  203 . The Block with the minimum voltage is determined to be the Xth Block. As the next step, the DPST switch corresponding to the Xth Block is turned ON through the SCB  201 , with all other switches being OFF. That gives the Xth Block a chance to catch up in voltage with the rest of the blocks. Such condition is maintained for 1 minute, after which all the DPST switches are turned OFF. Such condition is maintained for 5 seconds so that all the Block voltages are stabilized. Now the process is started again with measuring all the voltages and finding out the lowest voltage block and isolating it. This cyclic operation can be done about 100 times during 2 hours of charging, and that gives enough iteration to balance all the Blocks within reasonable means. Even if all the Blocks may not be balanced during one cycle, doing such algorithm over several cycles will balance them. 
     During the discharging cycles, if any of the Blocks reach a prescribed minimum Block voltage, then the discharging of the entire stack is deemed complete and the MPU  321  opens the switch  302  to stop further discharging. This prevents over-discharging and damage to the battery. 
     During charging cycles, if any of the temperature sensors reads a temperature higher than 40 deg C. or lower than −20 deg C., then the TEC is turned on through the port  315  for cooling or heating, respectively. If all the temperature sensors do not get back to the given limits within 10 minutes, then MPU  321  throws the switch  302  is open, taking the Pack out of any external electrical influence. 
     During Either Charging or Discharging: 
     The health of the system and its Blocks is monitored every minute and the data are conveyed to an external computing device for further analysis. An offline or online analysis may be done with or without human participation. 
     Other Implementations: 
     The disclosed example shows a typical application of the invention, and a practitioner of the field would derive many similar applications based on the invention, which are covered under the rights of this invention. 
     Although in the given example, the time period during which a particular Block is given current injection depends on the voltage readings of all the Blocks, leading to a Voltage-based algorithm, in another implementation, the decision may be based on calculation on State of Charge (SOC) or based on Coulomb Counting. 
     In another implementation, one or more Blocks would have a different nominal capacity than the rest of the Blocks. The Blocks can still be charged and discharged simultaneously, thereby providing maximum capacity, by injecting current into the lower capacity Blocks with a systematically lower duty factor, as determined by an appropriate algorithm. 
     In yet another implementation, one of more Blocks would have cells of a different chemistry than other Blocks, leading to a different Block voltage and a different voltage-current characteristics. The Blocks can still be charged and discharged simultaneously, thereby providing maximum capacity, by injecting current into the lower capacity Blocks with a systematically higher duty factor, as determined by an appropriate algorithm.