CONFIGURABLE BATTERY

MANAGEMENT SYSTEM FOR

PORTABLE DEVICES

DESCRIPTION 1. Field of Invention
The present disclosure relates to enhancement of existing features available in battery management systems and also adds new features such as the smartness, configurability and application based state of charge estimation and the configurable protection features for any portable device for any secondary ( say, lithium ion) battery pack.

2. Background of the Invention

Secondary batteries, which are rechargeable, are commonly used in automotive applications, electric vehicles and portable device applications. Though, a large share of applications involves the use of lead acid battery, lithium ion batteries are considered extensively for portable device applications. Lithium ion batteries have higher energy density, higher operating voltage compared to that of the lead acid batteries. All these battery, systems come along with a battery management system. The battery management system is an electronic system used for monitoring, computation, protection and optimization of the battery system using inputs like voltage, current and temperature for the measurement of state of charge and state of health of a battery. The criticality of the battery management system . depends on the chemistry of the battery involved. For portable device applications which involve the use of lithium ion batteries, parameters such as over voltage, under voltage and' over temperature are highly critical parameters. Thus, a proper design of battery management system is of paramount importance. The state of charge is a numerical representation of the amount of charge present in the battery. The state of charge can be estimated using the data captured by voltage, current and temperature sensor as inputs. Various, techniques, such as open circuit voltage, Coulomb counting and Kalman filtering method are used for the measurement of state of charge. But, as the techniques become more advanced, its implementation in real time becomes very complex. Hence, there is a need to come up with the algorithms which combine the use of existing estimation methods which involve lesser amount of mathematical computation. However, simple algorithms like open circuit voltage and Coulomb counting method are highly dependent on the recent inputs of voltage, current and temperature. A sudden change in load or the operating condition dents the accuracy of state of charge estimation. Also they fail to focus on time remaining estimation. Thus, to overcome these shortcomings, a new method based on the type of applications is used for improving the time remaining along with temperature protection is envisaged in the present disclosure.

3. Prior Art
The US .patent Application No. 6,983,212 B2 by Charles E. Burns and others on "Battery Management System and Method" is concerned with a system that. allows. monitoring and detection of faults in single cells of the battery string using a charger, voltmeter and a microprocessor. The problems with individual cells can be detected and corrected using the selection control of the microcontroller.
The US patent Application No. US 7,825,631 B2 by Joseph C. Chen and others on "Battery management system and method" is concerned with a system that includes a battery monitoring circuit, a user interface, and a battery management module. The battery management module is operable to receive the user-input allocation and the battery capacity signal, and to selectively disable each subsystem circuit or function when each subsystem circuit or function has depleted its allocation of battery capacity.
The US patent Application No. 5,701,068 by Jose T. Baer and others on "Battery Management System" is concerned with management and control of rechargeable batteries connected in series. It is concerned with multiple chargers charging batteries connected in series with the help of temperature and voltage sensors for automatic turning off of batteries.
The US patent Application No. 7,710,074 by Kim and others on "Determining an amount of charge in a battery based on voltage and portable device having the same" is concerned with measurement of residual charge present in the battery based on the discharge voltage of the battery. The proposed work relates current and voltage to measure the charge capacity present in the battery.
The US patent Application No. 7,493,501 by and Kim others on "Apparatus and method for controlling system operation based on battery state" is concerned with the control of applications run in the portable device based on the state of charge of the battery. The proposed work controls and measures the state of charge of the battery and does not control the applications in the device.
The US patent Application No. 6,515,413 by and Hans Fiel others on "Method of predicting the state of charge as well as the use time left of a rechargeable battery", is concerned with the estimation of state of charge of the battery based on the voltage. The proposed work relates current and voltage to measure the charge capacity present in the battery. It does not focus on application dependency.
The US patent Application No. by 20140232411 Vinay Govmd Valdya and Tarun Kancharla on "System and method for battery monitoring", is concerned with method and system for estimating the state-of-charge (SOC) and state-of-health (SOH) of a battery. The method of
the invention accurately determines the battery SOC by estimating the values of the recurring constants determined by the battery parameters based on the current and SOC values obtained during the charging and discharging cycle of the battery.
the European patent Application No. TW200818574 by You Jing-Dong and others on "Over-temperature protection device of battery module and its fabrication method " is concerned with over temperature protection and under temperature protection for charging. and discharging separately. The proposed work performs two stage temperature protection, thus enhancing the life of the battery unlike the single stage temperature protection proposed in the patent.

4. Summary of the Invention
The current battery management system continuously records the critical parameters such as voltage, current, temperature and State of Charge using appropriate sensors and hardware electronic modules. Existing battery management system employs temperature corrected Coulomb Counting method for State of Charge estimation. But, this method is found to be erroneous with an inaccurate numerical figure of the charge remaining in the device. With prior knowledge of the power consumed by each application, State of Charge is estimated based on the application type running in the portable device. Since, inputs and outputs are temperature dependent, higher operating temperature damages the estimation as.: well as the battery use. The temperature data stored in the electronic data logger is used for . continuously monitoring the temperature of the system, with a protection and a warning system in place for over temperature. The operation of the device is stopped in the event of over temperature and the operation is restored automatically once the temperature is within the limits. The current battery management system is configurable and various parameters like over voltage, under voltage and over temperature can be set according to the device and application. In order to effectively monitor these paramaters, we come up with a smart battery management system which uses load data for State of Charge estimation and proper maintenance of the temperature of the system using a two stage protective system to ensure proper operation as well as the extension of life of battery.

5. Brief Description of Drawings
Figure 1 is a flow diagram explaining the operation of battery management system.
Figure 2 is a block diagram explaining the hardware set up of the battery management
system of a portable device in charging mode.
Figure 3 is a block diagram explaining the hardware set up of the battery management
system of a portable device in discharging mode.
Figure 4 is a circuit diagram explaining the charging circuit of the battery pack for a portable device
Figure 5 is a circuit diagram explaining the passive cell balancing of battery pack for a portable device
Figure 6 is a flow chart explaining the operation of temperature protection in the battery management system.
Figure 7 is a flow chart explaining the operation of voltage protection in the battery management system.
Figure 8 is a flowchart explaining the complete operation of the battery management system of a portable device -
Figure 9 shows the comparison of cell voltages of battery packs with passive cell balancing.
Figure 10 is a flowchart showing the algorithm flow of determining state of charge of a battery system.
Figure 11 shows the graphical representation of Time remaining for various applications vs State of charge for text processing.
Figure 12 shows the user / manufacturer interface showing the smart programmable battery management system for any rechargeable battery.

6. Description of the invention
The proposed battery management system estimates the time remaining along with the protection of the battery pack from under voltage, over voltage and over temperature conditions.
The state of charge and time remaining is estimated using the available electronic logged data of voltage, current, temperature and the type of application in use. The voltage and current is used typically for State Of Charge measurement. However, to compensate the sudden changes in State Of Charge estimation due to load and temperature, the knowledge of the type of application in use is to be known and should be used for updating of State Of Charge values. Similarly, the State Of Charge estimation and input monitoring is done under a particular range of temperature in two stages. Hence, if the temperature is increasing, it becomes necessary to protect the system from further damage as well as to avoid erroneous computation.
The battery management performs the task of protection of battery pack with features of over voltage and under voltage. Any battery chemistry can be only operated over a certain region of voltages. For example, a lithium ion battery is normally operated in the region of 2.7V-4.2V with an upper temperature limit of 75°C. If the battery is operated above the limit of 4.2V, it leads to the heating, bulging and explosion of battery. Hence, over voltage parameter is critical in battery management system and the charger must be disconnected from the battery in the event of over voltage. Similarly, during discharge of battery, if battery is allowed to discharge below 2.7V, the battery needs to be disconnected from the load. If not, the chemical composition of the battery electrodes will change which can lead to permanent damage and hence loss of life to the battery. So, an electronically managed " controller should constantly monitor the battery voltage to ensure that the battery voltage does not cross the limits on either side. Similarly, the reaction rate will increase tremendously with the increase in temperature. This increased reaction rate can reduce the life of the battery and hence it must be ensured that the over temperature limit is not exceeded.
Fig 1 explains the block diagram of major subsystems used in our proposed battery . management system. The battery pack consists of a series parallel combination of individual cells. These cells combine together to form the battery pack. On top of the battery pack is a battery management system. Battery management system can be divided into two portions namely, the hardware and the software portion. The hardware module consists of sensors, signal conditioning circuits, microcontroller and cell balancing circuits as shown in Fig 1. Monitoring of the inputs from the battery such as Voltage V, current I and temperature T are performed using sensors for each parameter. The battery management system also retrieves load related information, which will be used for estimation of State of charge and time remaining. These sensor outputs are fed to signal conditioning circuits which in turn gives the required inputs to the microcontroller. The hardware also consists of cell balancing circuits which help to overcome the cell imbalances during the charging and discharging of the battery pack. The software performs the tasks of protection such as overvoltage, under voltage and over temperature, algorithm design of state of charge plus time remaining arid display of the inputs and battery associated parameters. The hardware is also interfaced with a wireless access to a cloud (such as SMS, MMS). Using this interface, the BMS can send the information about the life cycle of batteries at regular intervals. The algorithm running at the cloud can monitor the life cycle and when it reaches a threshold value, it can send alerts to battery manufacturer and user for battery replacement. The embedded microcontroller is made configurable which will be used for offering the various features of battery management system. Thus, the battery pack along with battery management system on top of it is connected to the load. The load is a portable device such as laptop, tablet, mobile phone, a music player etc. With each device having its own ratings, it is important to ensure that proper input is given to the device.

Fig 2 and Fig 3 show the block diagram of the charging and discharging operation of a battery management system for any portable device application. The battery management system consists of an adapter/charger, battery bank, signal conditioning unit, microcontroller/microprocessor and a load (a portable device). In Fig 2, at any instance, when an adapter or a charger is connected to the portable device, the device operates along with the charging of batteries. If the battery is charged fully, the microcontroller sends signals to the charger to disconnect from the battery. The device continues to operate with the power retrieved from the charger. At all instances, various parameters such as voltage V, current I and temperature T inputs are detected using sensors located at relevant places on the battery system and these parameters serve as an input to the operation of battery management system. The signal conditioning circuits serve the purpose of limiting the inputs to the microcontroller within the permissible range. The signal conditioning circuits employ the necessary circuits to ensure that the voltages do not exceed the upper limit nor negative voltages are given as input to the controller. With these inputs fed to the controller, the microcontroller monitors the values of voltage, current and temperature at all instances. The controller also performs the estimation of state of charge and time remaining of the battery. During charging, microcontroller ensures that the conditions of over voltage and over temperature do not occur. The charger gets connected automatically, once the system is within the permissible voltage and temperature limits.
If the adapter is disconnected, the device derives the power from the battery as shown in Fig 3. During discharging, the controller monitors the current to identify the type of load attached, in order to improve the accuracy of State of Charge and time remaining calculation. The controller also ensures that the conditions of under voltage do not occur. In the event of under voltage, the user is given an alarm (alert) and after a small amount of time, the battery gets disconnected from the device. The battery cannot be connected to the load until the voltage comes above the under voltage limit. Thus, the battery management system performs the operations of over voltage protection, under voltage protection, over temperature protection and estimation of state of charge and time remaining.

Fig 4 shows the charging circuit of a typical battery pack (for example, lithium ion type) for a portable device. The charging is done using the constant current - constant voltage (CC-CV) method. In figure 4, the input voltage from the adapter is regulated to the maximum charging voltage. The charging voltage is fed into the integrator circuit which decides the magnitude of charging current with the help of sensing resistor Rsense> zener reference and resistor divider of R3, R4 and R5. The output from the operational amplifier is given as gate voltage to the MOSFET. The battery pack is connected to the ground through the source of the MOSFET where Rsense is used to track the current magnitude which helps in constant current - constant voltage transition.

Fig 5 shows the passive cell balancing circuit of a typical battery pack(for example, lithium ion ) for portable device. Cell balancing involves the elimination of imbalance in the voltages of series connected cells. The cell balancing can be done either passively (dissipation of energy through resistor) or actively (flow of energy from a cell of higher voltage to cell of lower voltage). Fig 4 shows the passive cell balancing circuit. The passive cell balancing involves periodic measurement of voltages of the series connected cells. The individual voltages measured are summed up and the average of the cells is measured. The controller checks for cell imbalance. In the event of cell imbalance, the battery with voltage above the average voltage is made to dissipate energy through resistor controlled by a transistor. Thus, passive cell balancing is a dissipative technique of cell balancing.

Fig 6 shows the flowchart explaining the temperature protection of the battery management system for any application. Temperature limit is pretty important for extending the life of a battery. For every increase of 10°C, the rate of reaction increases and the life of battery decreases. Hence, temperature protection is important for the proper operation of the batteries. Temperature rise is possible in two scenarios, one attributed to the charging of batteries at high currents and the other due to the increase in local temperature. Hence, temperature protection forms the top layer of protection for any battery management system.

The temperature T is monitored continuously. Hence, in the event of over temperature Tmax, battery is disconnected from the charger or the battery is disconnected from the portable, device, after prior intimation to the user via a relevant display system.
Fig 7 shows the flowchart explaining the voltage protection of the battery management system for any application. After the temperature protection is ensured, voltage protection has to be ensured. Two kinds of voltage protection namely, under voltage protection and over voltage protection should be ensured. In the event of under voltage condition of the given battery Vmm, the battery must be disconnected from the portable device and it must be ensured that portable device cannot be turned on with battery. In the event of over voltage condition Vmax, the charger must be disconnected from the battery to ensure protection.

Fig 8 shows the comparison of cell voltages of battery packs with passive cell balancing. When the batteries are connected in series, Imbalance of cell voltages occur due to the different individual values of internal impedance and the health of the batteries. However, imbalance in cell voltages deteriorates the life of the cell. Hence, cell balancing methods have to be in place in a battery management system. The proposed circuit uses passive cell balancing method. The figure shows the monitoring of individual cell voltages and the average voltage.

Fig 9 shows the flowchart for the operation of battery management system for any particular application. The temperature T is measured first to ensure that it does not exceed the over temperature limit. If the temperature exceeds a predefined value Tmax, an alert is given to the user and then the charger and the load is disconnected from the battery system. After sufficient cooling, if temperature comes back to the safe region of operation, again the charger is connected once again to the system. Now, the charging and discharging of battery is done. As charging or discharging occurs, the voltage V, current I, temperature T, State of Charge SOC, time remaining and load type are measured continuously. The charging current, Icharge and discharging current Idischarge are measured and compared. The load type is used based on the fact that particular application running in the portable device amounts for a rated power. These loads are classified into some of the commonly used tasks such as text processing, audio tasks, video tasks, WIFI, audio-video processing such and gaming. Among the classifications, text processing and WIFI are found to be low current consuming applications. Audio and video applications such as video players, internet browsing are found to be medium current consuming applications. Audio and video processing such as gaming and multimedia processing are found to be high current consuming applications. The State of charge and the remaining time for which the portable device can be operated are decided based on the classification of current consumption of applications. The charging of the system is done using a charger, which ensures that proper regulation is done. However, in the event of over voltage, charger is disconnected from the battery pack with the controls from microcontroller. Similarly, during discharge as the voltage is measured, it is ensured that voltage is above the under voltage limit. If it is below the under voltage limit, the user gets a prompt displaying under voltage and battery gets disconnected from the load. If the voltage is above the under voltage limit, then the state of charge and time remaining are measured using the data from voltage, current and load type. This process is continuously done.
The state of charge estimation flowchart is shown in Fig 10. The voltage is initially measured as soon as the system is switched on. The initial voltage is used for State Of Charge estimation using open circuit voltage method. The open circuit voltage method matches the state of charge SOC with that of open circuit voltage. The SOC is calculated using a voltage-SOC lookup table which is obtained from a battery voltage discharge curve. Then the current and application types are monitored. The current flowing in and out of the battery is used for State Of Charge estimation. The State of charge and the remaining time. for which the portable device can be operated are decided based on the classification of current consumption of applications. Based on the classification of applications, State of charge and estimated time remaining are related by a linear relationship. For example, a portable device can perform text processing for 4 hours after fully charged condition. After operating for 1 hour, the state of charge will be 75% and time remaining is 2 hours. Now, if the user switches to a media player, a fully charged battery can deliver for two hours and fifty minutes. But, with only 75% remaining, the media player can be operated only for 120 minutes and the revision of state of charge is only 70% of the original capacity. Thus the traditional SOC estimation in terms of time remaining calculation using Coulomb counting method is found to be 5% more erroneous than our system. With the knowledge about the power consumed by these loads, the State of Charge values and time remaining estimation are updated in accordance with the usage of programs. Thus, time remaining estimation becomes more accurate compared to the existing state of charge algorithm. Thus, the proposed battery management system becomes more accurate and gives the end user a more accurate picture of the amount of charge left and the time for which the load can be operated.

Fig 11 shows the Time remaining for various applications vs. State of charge for text processing applications. The values of time remaining are estimated based on the experimental set up.

Fig 12 shows the smart configurable battery management system with adjustable features incorporated using a suitable interface. The user interface enables one to select the rechargeable battery as per the application requirements. The user / manufacturer can specify \ the voltage and capacity either by mentioning the cell voltage and capacity along with the series parallel configuration details or the user / manufacturer can specify the battery voltage and capacity. The user / manufacturer can include any of the three protection features of over' voltage, under voltage and over temperature protection along with the limits for each feature. The end user / manufacturer can view the life cycle number, which is the number of charge and discharge cycles that the device is used for. Each battery pack is rated for specific number of charge / discharge cycles. Thus, the life cycle number displays the number of cycles that device has been used compared to that of the defined number of cycles. This information can be pushed automatically into the cloud using the microcontroller which is interfaced with the battery management system. The algorithm running at the cloud can monitor the life cycle.of the battery pack and whenever it reaches a critical threshold limit (set by the manufacturer), it can alert the battery manufacturer and the user for subsequent replacement strategy of . batteries. There is also a provision for memory effect warning system. Memory effect is observed in nickel cadmium batteries in which the batteries have to be charged and discharged completely. If this is not done properly, due to memory effect, existing capacity is reduced in: Nickel cadmium batteries. The end user / manufacturer can also choose the parameters that he/she wants to see in the display as the device is under operation such as voltage, current, temperature, State of Charge, and Life cycle number. Since, the work is mainly aimed towards ; portable device application; the user can get to choose the application he intends to use. The state of charge remaining in the battery can be chosen either by the Coulomb counting method or the application based State of Charge estimation incorporated in the present invention.

7. Claims

1. Conventionally the BMS is attached at the device end (such as laptops, tablets, smart phones). In the proposed system, we interface the BMS with the battery pack and it can be.. oversized and configured by the battery supplier.

2. The proposed electronics in the BMS monitors the number of charge / discharge cycles of the batteries. Whenever it reaches an upper critical value, it alerts the user / manufacturer for battery replacement. For this purpose, the BMS is interfaced with the cloud server via. a wireless interface

3. The proposed BMS displays time remaining depending on the type of load. Hence a.user will know how long he can operate the device under low, medium and high load conditions.

4. The proposed BMS system continuously monitors the temperature of the battery pack in two stahes. In the first stage, when temperature reaches a threshold (upper) value it initially gives a warning and in the second stage, the system disconnects the charger and load automatically.

5. If the measured voltage of BMS is greater than set maximum value, then the proposed system gives a warning and disconnects the charger from battery. If the voltage is less than the set minimum voltage limit, then an alert is given and the BMS disconnects load from battery.

6. In the proposed BMS if charging current is more than discharging current, then State of Charge is measured using Open Circuit Voltage method, otherwise we identify the type of load ( low, medium and high) and adjust the SOC values using instantaneous values of current, voltage and temperature and estimate the time remaining accurately.

7. The battery management system also provides the function of cell balancing. The individual cell voltages are monitored and the differences in cell voltages are kept minimal.

8. The envisaged system provides an option to the user / manufacturer to decide what alert parameters need to be displayed on the display system.