FIELD OF INVENTION:
The present invention relates to an improved battery equalizer and a method for equalizing charge on a string of batteries connected in series/ parallel with protection against fault condition due to wrong connection and faulty battery. More particularly, the present invention is directed to the equalization circuitry and method of charge equalization, with the provision for monitoring, control and management for enhancing life of the batteries connected in the string.
PRIOR ART:
Under normal operating conditions, battery charge characteristics depend upon many factors such as: 1. Age of battery: older batteries receive more current than the newer batteries; 2. State of charge: the charge current varies with time during the charging process; 3. Ambient temperature: batteries accept less charge as the temperature drops; 4. Battery construction: details of battery design affect the charging characteristics.
Variations between individual batteries within a single string will often cause overcharging or under charging in one or more of the batteries of the string. Any battery in the series-connected string that once attains an overcharged state tends to persist in that state during charging until battery failure occurs.
Also each type of electrochemical cell has a characteristic "full charge" voltage. A lower cell voltage indicates a state of charge less than "full". To obtain a higher voltage that can be provided from a single cell, cells are connected in series, often with internal or integral connections between the cells, to form a battery which has the desired level of output voltage. Certain types of electrochemical cells, such as rechargeable alkaline manganese, lithium and lithium ion cells have no internal charge control mechanism. Consequently, if charging of such cells is not carefully controlled, over-charge can result in irreversible changes in cell chemistry, performance loss, and in extreme cases, cell venting. The charging of series connected cells of these types is therefore difficult, since cell voltages and capacities may not be equal. As a result, some cells are overcharged.
To address this problem, equalizers have been developed which monitor the voltage across each cell and connect resistors or current sinks across the cell or cells having an excessive voltage to partially discharge the cell and thereby accomplish charge equalization among the cells. However, equalizing the charge on cells in this manner wastes power and also causes undesirable heating of the battery pack since the equalization circuitry is typically physically located in the battery housing. In addition, the rate at which the cells can be equalized and thus the rate at which the cells can be recharged, is limited to the amount of power dissipation that can be tolerated. Also in case if the difference between the two series connected batteries is very large or if any of the batteries is dead, the equalizing current can be extremely high. Also there is no protection for high current that can damage the equalizer itself.
Reference may be made to the following prior arts:
US patent no 5952815 relates to an apparatus and a method for regulating the charge voltage of a number of electrochemical cells connected in series. Equalization circuitry is provided to control the amount of charge current supplied to individual electrochemical cells included within the series string of electrochemical cells without interrupting the flow of charge current through the series string. This invention does not include the fuse protection and fuse blown indication and protection in case the batteries connected are bad.
US patent no 6,031,354 discloses the on-line battery management and monitoring system and method for monitoring a plurality of battery cells identifies. The invention deals with online management, monitoring and controlling of plurality of battery cells. This invention does not include any cell or battery equalizer feature.
US publication no 20020074985 pertains to a voltage equalizer circuit in which each of plural windings P1 to Pn are electromagnetically coupled to each other, each of plural storage elements El to En series are connected to each other, and each of plural first switching elements S1 to Sn are connected to each other in a series connecting manner so
as to constitute a plurality of closed circuits. This invention docs not provide any protection against any wrong wiring and also does not provide any indication of failure.
US patent no 5,982,142 is directed to a three terminal battery equalizer which includes a DC-DC converter having a first filter inductor in the switched, current conducting path connected to the battery ground and a second filter inductor in the switched, current path connected to the non-grounded. This invention does not provide any protection against any wrong wiring and also does not provide any indication of failure.
US patent no 5,594,320 relates to an equalizer for equalizing the charge on several series-connected cells includes a transformer having plural windings on a core corresponding to the number of cells. The windings are tightly coupled to one another. This invention does not include any protection against wrong connection or faulty battery it also does not provide any indication to show if the system is working properly or not.
US patent no 6452363 is directed to the charge equalizer for a string of series-connected batteries. The equalizer includes a shunt path for each of the batteries. The equalizer measures the voltage of each of the batteries of the string and then closes a switch in the shunt path associated with the highest voltage battery for a predetermined time. Then the switches of all of the shunt paths are opened and the cycle is repeated.
US patent no 6452363 and 6,150,795 discloses charge equalizer for a string of series connected batteries in automotive electrical system.
US patent no 5,710,504 relates to a switched capacitor system for automatic battery equalization that can be used with series coupled batteries as well as primary and backup batteries which are alternately couplable to a load. This does not include any protection against a wrong connection or faulty battery. It also does not provide any indication if the system is working properly or not.
US publication no 20080272739 relates to the battery monitoring device of a battery pack. The device, configured for powering a cordless power tool may include an integrated circuit connected to a microprocessor of the pack that is external to the integrated circuit and is connected to each of the N battery cells of the pack.
US publication 20080272739 relates only to the battery monitoring device and does not contain battery equalization.
US publication no 20070171965 relates to an adaptive equalizer which provides receiving symbols to generate an equalizer output. The adaptive equalizer comprises a plurality of tap cells, a coefficient updater, a plurality of multiplexers, a controller and an integrator. Each tap cell generates a filter value from a tap data value and a coefficient.
Publication no W09310589 relates to an apparatus for balancing the state of charge of a plurality of serially connected sub-units of a battery. The apparatus comprises state of charge monitoring means operative to monitor the state of charge reached by each sub-unit.
The following patents talk about battery equalization, but do not provide protection in case of fault condition.
US patent no 6,452,363 relates to a charge equalizer for a string of series-connected batteries. The charge equalizer includes a shunt path for each of the batteries, measures the voltage of each of the batteries of the string and then closes a switch in the shunt path associated with the highest voltage battery for a predetermined time. This patent does not provide protection in case of fault condition.
US patent no 5,528,122 relates to the battery equalizer for equalizing the voltage on series connected batteries. It synchronously switches the opposite ends of a tapped autotransformer in alternately reversing connection to the distally opposite terminals of
the battery by alternately turning transistor switches on and off in alternate pairs while maintaining a center tap of the autotransformer connected to an intermediate terminal of the series batteries.
US publication no 20050140335 relates to the terminal voltage equalization circuit to equalize the terminal voltage of the series of connected battery strings so that each battery in the series of connected battery strings can be equally charged.
US publication no 20070103121 relates to a method and system for battery protection. In some aspects, a battery pack configured to be interfaced with a power tool includes housing a cell, a controller and a circuit. The circuit is operable to enable the controller to operate when the voltage supplied by the cell to the controller is below an operating voltage threshold off the controller.
Publication no EP0652620 relates to the method and device of equalizing the voltage across drive batteries for electric vehicles, connected in series during recharging.
US patent no 4,331,911 relates to equalizer including DC to DC converter which increase the losses in the system and decreases the overall efficiency of the system. Also it does not provide protection in case of fault condition.
US patent no 6,008,623 relates to a charge equalizer by using flyback converter. Thus it will have higher losses.
US patent no 5,666,041 and 5,982,143 relate to the electronic battery equalization circuit that equalizes the voltages of a plurality of series connected batteries in a battery pack. The current waveform is in the shape of a ramp for providing zero current switching.
US patent no 6,801,014 relates to the method and system for equalizing the voltage of batteries in a battery string to a desired voltage. An equal string current is drawn from the
batteries of the battery string and redistributed as a plurality of secondary currents to each battery, depending upon the comparative voltage of the individual batteries.
Publication no WO2007038898 provides an accumulator battery equalizer and an energy balance accumulator battery. The equalizer is equipped between the plates of individual battery cell, at least two of which are connected in series so as to compose an accumulator battery set.
Application no 3389/DELNP/2007 relates to an implementation of a method for cell equalization. The present invention uses other information such as the individual cell state-of-charge (SOC) estimates and individual capacities and/or cell coulombic efficiencies, possibly available from a dual extended Kalman filter.
Reference may be made to an article by "Vanner Incorporated, July 15, 2002". The article explains an efficient and highly reliable method of obtaining a 12 volt DC power source from a 24 volt DC electrical system. The equalizer makes the batteries look like they are in series and parallel at the same time. In addition to providing regulated 12 volt power, the system ensures that battery voltages remain equal. This significantly extends battery life. This module monitors the battery system's voltage and balance and provides fault signals that can be wired to warning lights, buzzers or other control/warning devices.
Reference may be made to an article by "GSL Electronics, 2009". The article explains 12V/ 24V battery equalizer. The unique feature of the equalizer is that they are 12V TRUE battery equalizers designed for centre tapped 12V dual battery systems. This is due to the micro controller measuring both sides of the system and charging the 12V tapped battery so that it is never out of balance.
Reference may be made to an article by "Ming Tang; Stuart, T, IEEE Transactions on Aerospace and Electronic Systems, Vol 36, Issue 1, P(s):201-211, Jan 2000". The article explains a new selective equalizer developed from the earlier ramp equalizer. . A set of
bipolar junction transistors (BJTs) controlled by a microcontroller is used to route equalization current to the lowest voltage batteries. Since only the lowest voltage batteries are connected to the equalizer, the need for uniform transformer leakage inductance is avoided and a lower power level can be used since no excess current flows to the other batteries.
Reference may be made to an article by "A. Hande, T.A. Stuart". The article explains a special round robin (RR) algorithm has been developed to equalize nickel metal hydride (NiMH) battery packs using a new selective equalizer. This algorithm detects batteries either at a very low state of charge (SOC) or at an extremely high SOC. In this system, a set of electromechanical relays are connected in a matrix to route boost current to the weaker batteries. The relay switching is controlled by a 32-bit microcontroller, and the boost current is supplied by a boost charger. Once the RR algorithm detects a weak battery, it schedules the detected battery for a specific boost time.
Reference may be made to an article by "Analytic Systems Ware Ltd, 2002 ". The article explains a battery equalizer that safely permits 12 Volts to be drawn of a 24V battery bank. The unit is connected across the 24V battery bank, and its output is connected to the 12V midpoint of the battery bank.
Reference may be made to an article by "Hot Juice Electric, LLC, 2007-08". The article explains BEQ1, a rugged, simple to use, economical shunt regulator that is designed to keep a series string of AGM batteries equalized by enhancing the recombinant charging phase. The red over temp LED will illuminate if the BEQ1 temperature exceeds 100° C. Once tripped, the over temp circuit reduces the shunt current and is latched on until the voltage drops below the BEQl's set point. This means the charger should be turned down or turned off until the cause of over heating is determined.
None of the above listed prior art describe an equalizer to be connected between power backup/charging system and string of batteries to equalize the battery charge during the
charging of the batteries. Furthermore, there is a need in the prior art for the development of a battery management and monitoring system and a method which function under software control and which provide a user-friendly system. A practical apparatus and method should be capable of equalizing batteries during a charge cycle, during battery discharge, or during idle times. It is very desirable to avoid sensors or a precise control so that simple, reliable and low-cost equalization circuits can be built. A preferred apparatus and method will operate over a wide range of conditions with little or no change.
With all the above discussed restrictions or limitations, it is essential to have improved equalization charging circuitry and method of charge equalization which can enhance the life of the batteries connected in series.
OBJECTS OF THE INVENTION
The primary object of the present invention is to provide an improved battery equalizer and a method for equalizing charge with a means for continuously equalizing the voltages of the individual cells of storage batteries under conditions of service use.
Another object of the present invention is to provide an improved battery equalizer which is used between the power backup/charging system and the battery for equalizing the string of series/ parallel connected batteries.
Yet another object of the present invention is to favorably affect the equality of charge of the cells of a battery that is rapidly being charged partially.
Still another object of the present invention is to provide an improved battery equalizer and a method for equalizing charge in which the power backup/charging system charges the batteries connected in series/parallel through the battery equalizer.
Another object of the present invention is to provide an improved battery equalizer and a method for equalizing charge which is cost effective and increases the life of the batteries.
Still another object of the present invention is to provide an overload detection circuit for detecting an excessive current in the equalizer circuit.
Yet another object of the present invention is to provide a visual indication for a faulty condition.
Still another object of the present invention is to provide a battery equalizer to sense the battery voltages and to provide the indication in case one or more of the connected batteries are out of order.
Still another object of the present invention is to provide an improved battery equalizer which is usable irrespective of the battery technology.
Yet another object of the present invention is to provide an improved battery equalizer which yields a low cost implementation.
A further object of the present invention is to provide an improved battery equalizer which is more accurate and stable.
Another object of the present invention is to provide a battery voltage equalizer which is bidirectional, i.e. it has the capability of transferring energy from whichever battery at the higher voltage to the other battery at lower voltage.
Still another object of the present invention is to provide an equalization process which can be performed during the main charging process or separately.
Still another object of the present invention is to provide a self-limiting and controlled equalization process.
Another object of the present invention is to provide a system and method which in the situation of overcharge or discharge will cut off the power backup/charging system.
Still another object of the present invention is to provide a system and method to control the equalization current by using pulse width modulation.
Yet another object of the present invention is to provide a system and method to enable or disable the equalization process as per user programmable conditions.
SUMMARY
According to this invention, an improved battery equalizer is provided for equalizing charge on a string of batteries connected in series/ parallel as the batteries are being charged/discharged/remain idle as per user's programmable conditions. More particularly, the present invention relates to the equalization charging circuitry and a method of charge equalization, comprising of monitoring & control. The equalizer, according to the present invention, is used between the power backup system and the string of batteries. The batteries are being charged through the equalizer. The cutoff limits are set in the equalizer, which are user settable. If any of the battery from the string reaches to such as but not limited to the overcharge, deep discharge etc, it will cut off the power backup/charging system. The present invention controls the equalization current by using pulse width modulation technique. The invention enables or disables the equalization process as per user programmable conditions.
In another embodiment of the present invention, display device can be liquid crystal display, light emitting diodes or any other display device.
STATEMENT OF INVENTION
According to this invention, there is provided an improved battery equalizer comprising of a control unit signaling a plurality of switches wherein said equalizer is positioned between power backup system and a plurality of batteries connected to current protection unit in which a voltage/temperature sense unit and a PWM driver are controlled by said control unit driving isolated multiple gate output, which is connected to power transfer section.
BREIF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Further objects and advantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein:
Fig 1 shows block diagram of improved battery charge equalizer according to the present invention.
Fig 2 shows switching transformer section of improved battery equalizer.
Fig 3 shows flow chart for improved battery equalizer according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:
Reference may be made to fig 1 which shows block diagram of an improved battery equalizer and fig 2 shows switching transformer according to the present invention. An improved battery equalizer is provided for equalizing charge on a string of batteries connected in series/ parallel as the batteries are being charged/discharged/remain idle as
per user's programmable conditions. The invention provides a method of charge equalization, comprising of monitoring & control. The equalizer is positioned between the power backup system and the string of batteries 1. Said equalizer comprises a control unit 2. The control unit 2, via control lines, provides signals to the plurality of switches. The control unit 2 is microcontroller/DSC based PWM generator cum controller 2. A current protection unit 3 is also attached to the battery bank 1, which provides high current protection to the power supply 4. A PWM driver 5 controlled by main controller 2 drives isolated multiple gate output 6, which is connected to the power transfer section 7. This section is also attached to the current protection unit 3 to protect unit from high current.
A voltage/ temperature sense unit 8 monitored by controller 2, is attached to the battery bank 1 which senses the voltage and temperature rise in order to protect connected battery bank 1 from being overheated. In-circuit program section 9 is to program the controller 2 in circuit from PC/Programmer. A paralleling interface section 10 having connector is provided to receive (Rx) and transmit (Tx) the data messages from one equalizer unit to another. The display 11 unit shows the measured parameters and paralleling interface section 10 is provided to have parallel inter unit monitoring and control of a number of battery equalizer units connected to N number of batteries in series. A buzzer unit 12 is provided which is fully controlled from central controller 2 and alerts by giving continuous beep in case of abnormal conditions. A single unit is provided to fulfill the need of an equalizer and battery desulphator 13. Driver power supply circuit comprising of input which is fed from battery bank connected with the system. A resistive voltage divider network is utilized to get desired voltage output, diodes at input are used to protect the circuit from being damaged in reverse polarity condition and to supply different input supplies for regulator. Diode at output of regulator is a freewheeling diode and capacitors at input/output are used as a filter. The output is then fed to a linear regulator which generates supply and is also fed to driver IC to switch isolated transformer so as to generate multiple gate drive outputs.
In an aspect, the batteries are being charged through the equalizer. The control unit 2 is connected to the charging connect/ disconnect unit 14 which is in connection with the charging/discharging device 15. The cutoff limits are set in the equalizer, which are user settable through display user interface/ communication If any of the battery from the string reaches to such as but not limited to the overcharge, deep discharge etc, it will cut off the power backup/charging system. The present invention controls the equalization current by using pulse width modulation technique. The invention enables or disables the equalization process as per user programmable conditions.
Connect and disconnect unit may be a static/dynamic switch, which disconnects the external equipment in case of above stated conditions and reconnects the equipment after a predefined time. In case abnormal condition still persists then switch gets disconnected once again, finally this gets repeated until a predefined no. of times, switch gets permanently switched off after predefined number of automatic retries and external equipment gets disconnected permanently. This will be operation once again only by resetting the connect and disconnect on/off switch 16.
Equalization of charge on multiple series/ parallel connected batteries is accomplished in accordance with the present invention rapidly and substantially without unnecessary dissipation of power. Equalization is accomplished automatically without requiring comparison of voltages across individual cells or batteries. Further, the present invention supplies current to a cell unit in proportion to the difference in the voltages between cell units so that the lowest charged cell unit receives the greatest charging current from the highest charged cell/ battery unit while cell/ battery units at voltages intermediate the highest and lowest (where more than two cell units are being charged) receive lesser charge currents. Energy is transferred in this manner from the most highly charged cell unit to the cell unit or units having lesser charge. The invention includes such as but not limited to the controller which measures the voltage of the connected batteries and calculates the difference between the batteries.
Fig 3 shows the flow chart according to the present invention. It initializes the controller input/ output and various peripherals, measures the battery voltage and calculates the difference between the connected batteries. If the difference is > max high, the equalization is stopped and indication is given through display. If the difference is > medium high, it sets equalization to variable active time mode. Now it turns off equalization with blanking, measures the battery voltage and calculates the difference between the connected batteries. This process is repeated and then the equalizer checks for the high current and battery discharge/ overcharge condition according to user setting.
The present invention provides another visual indication, in case any of the fuses connected in the wiring blow due to wrong connections or some faulty condition. The equalizer senses the battery voltage and provides the indication in case one or more of the connected batteries are out of order. So that, the voltage difference between any two series connected batteries is greater than a predefined threshold. A customized pulse transformer is designed for isolated driving of connected semiconductor switches.
The present invention also provides blanking pulse during the normal operation so as to measure the battery voltage properly and detect the fuse blown condition. The apparatus controls the equalization process such that the semiconductor devices are not subjected to extremely high temperature in case the charge difference between the connected batteries is large and a large charge transfer takes place to equalize the two batteries. This is done by controlling the on time and off time of the equalization process through the main controller.
In case of large imbalance in the series connected batteries, the main controller regulates the equalization process by controlling the active and inactive time of the equalization. With a large imbalance, the equalizer turns on and then remains off for a certain time period so that the switching devices can be protected from extremely high temperature which could lead to failure of switching devices. The present system and method are usable irrespective of the battery as well as power back up system technology. Voltage
will be matched between adjacent batteries and power backup system regardless of chemistry, manufacturer or capacity. The system and method yield a low cost implementation. Precise equalization is achieved without any requirements for device matching or tight tolerances. This contrasts strongly with active methods that can equalize only if several different circuits match precisely. The concept is modular and extends to arbitrary numbers of batteries. Batteries can be added without any system redesign by providing each additional battery with a module. The process is self-limiting. The battery voltage equalizer is bidirectional. It transfers energy from any battery at a higher voltage to the other battery at a lower voltage.
It is to be noted that the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant embodiments employing the concepts and features of this invention are intended to be within the scope of the present invention, which is further set forth under the following claims: -

WE CLAIM
1. An improved battery equalizer comprising of a control unit signaling a plurality of switches wherein said equalizer is positioned between power backup system and a plurality of batteries connected to current protection unit in whic h a voltage/temperature sense unit and a PWM driver are controlled by said control unit driving isolated multiple gate output, which is connected to power transfer section.
2. An improved battery equalizer as claimed in claim 1, wherein said control unit is microcontroller/DSC based PWM generator cum controller.
3. An improved battery equalizer as claimed in claim 1 or 2, wherein said power transfer section is attached to the current protection unit to protect unit from high current.
4. An improved battery equalizer as claimed in any of the preceding claims, wherein said sense unit is attached to the battery bank.
5. An improved battery equalizer as claimed in any of the preceding claims, wherein said control unit is connected to charging connect/disconnect unit, which is in connection with charging/discharging device.
6. An improved battery equalizer as claimed in any of the preceding claims, wherein the cutoff limits are set in the equalizer, which are user settable through display user interface/communication.
7. An improved battery equalizer as claimed in any of the preceding claims, comprising of in circuit program section to program the control unit and a paralleling interface section having connector such as herein described.
8. An improved battery equalizer as claimed in any of the preceding claims, comprising of display unit indicating the measured parameters and a buzzer unit.
9. An improved battery equalizer as claimed in any of the preceding claims,
wherein the display unit is such as LCD, LED and audio/visual messages are
generated to update user regarding battery bank status.
10. An improved battery equalizer substantially as herein described with reference to the accompanying drawings.