TWI658676B - Novel battery balancer - Google Patents

Abstract

A new type of battery balancer includes: a battery pack including at least one battery cell, each battery cell comprising two secondary batteries; at least one bidirectional step-down voltage boosting circuit, each having two ports to communicate with a group The two secondary batteries of the battery unit are respectively electrically coupled, and two switches are used to control the energy conversion between the two secondary batteries according to two switch control signals; and a control unit for The two open-circuit voltages of the two secondary batteries and a polynomial function formula are used to calculate a duty cycle to determine the duty cycle of the two switch control signals. The polynomial function formula is: Duty (V _OC , ΔV) = 0.03313 (V _OC ) ² + 0.02388 (ΔV) ² -0.2692 (V _OC )-0.352 (ΔV) + 0.07974 (V _OC ) (ΔV) +1.2 where V _OC is the lower one of the two open circuit voltages , ΔV is the voltage difference between the two open circuit voltages, and Duty is the duty cycle.

Description

Novel battery balancer

The present invention relates to a battery balancer, and more particularly to a battery balancer capable of quickly achieving bidirectional energy transmission between two independent batteries included in a plurality of battery cells of a battery pack.

As global warming and the greenhouse effect intensify, issues such as environmental protection and energy conservation and carbon reduction have received great attention from countries around the world, and the development and application of renewable energy and electric vehicles has become an inevitable trend. Since the development of these systems requires the installation of a large number of battery energy storage and power supply systems, the development of rechargeable battery manufacturing materials, charging, power conversion and management technologies has also attracted much attention.

In the past ten years, lithium-ion batteries have become the only option for power supply of mobile devices, and the energy storage devices of electric vehicles' power batteries and renewable energy power generation systems are also mainly equipped with lithium-ion batteries. Lithium compound batteries have a capacity density that is more than double that of nickel-metal hydride batteries or lead-acid batteries, and have a shorter charging time. They also have light weight, small size, thin thickness, long service life, high current discharge resistance, It has no memory effect, high average working voltage, low self-discharge rate, large dimensional change, and good environmental protection. It has been widely used in 3C electronic products, renewable energy power storage systems, electric vehicles and other high-power industries.

Although a series battery pack (Battery Pack) can provide sufficient voltage, in a multi-cell battery pack, in order to shorten the charging time, when the battery pack is charged with a large current, in addition to the danger of explosion, it will also Increasing battery temperature causes problems such as battery aging, capacity degradation, and reduced cycle life. This aging phenomenon is caused by the gradual increase of the internal resistance of the battery caused by the temperature rise due to the excessively fierce electrochemical reaction under the environment of high working current. In addition, due to the different electric and chemical properties of each battery during production, the imbalance of the battery cell will be caused when the series battery pack is charged. As the number of charge and discharge increases, the imbalance of the battery will occur. It is getting more and more serious, which causes the charge and discharge capacity of series battery packs to decrease sharply, which causes safety concerns and shortens battery pack life.

Selecting a good charging method and a suitable charge balancer have a great impact on the life of high-voltage and high-power battery packs. In order to increase the battery energy in a short time, the charging methods of conventional technologies use large charging currents for fast charging. However, such a fast charging method is likely to cause a fierce electrochemical reaction, which causes the internal pressure and temperature of the battery to increase, thereby causing battery damage or aging and shortening the life.

A suitable battery pack balancer can prolong the service life of the battery and improve the reliability, safety and cost-effectiveness of the load. Therefore, in order to maximize the cost-effectiveness of the battery, it is necessary to have a charging strategy that can slow down the aging of the battery and a suitable balancing mechanism, and a charger that can improve the charging efficiency and extend the service life.

The high-voltage, high-efficiency, and long-life battery system includes protection, management, and balancing. Among them, the balance of battery cells is most closely related to battery life. If there is no good balance method, the voltage difference between battery cells in a battery pack will accumulate with time and the gap will increase. The capacity of the entire battery pack will be in operation. During this period, it will also drop rapidly, eventually causing damage to the battery pack.

Cell balancing methods can be divided into three main categories, as described below:

I. Battery screening method: It is to use pre-screened battery cells with similar characteristics to form a battery pack to suppress the imbalance between battery cells. At present, most low-voltage battery packs used in notebooks and other products use this method.

Second, the passive balance method: only applicable to lead-acid and nickel compound batteries, because lead-acid and nickel compound batteries will not cause permanent damage to the battery cell, but the passive balance method directly charges the high-voltage battery cells. Consumption becomes heat dissipation on the passive element, resulting in poor balance efficiency and long balance time.

Third, the active balance method: the use of external circuits to actively transfer the charge between the battery cells to achieve the purpose of power balance. Active balancing method can be used in most modern battery systems, because this balancing mechanism has nothing to do with the characteristics of the battery being balanced. This method is also the only balancing method applicable to lithium compound batteries, because the temperature and voltage of lithium compound batteries must be It is strictly controlled within the safe operating range.

In the active balance method, the charge energy flow can be classified into the following five categories:

(1) Battery cell bypass method: Bypass the current of the battery cell that has reached the upper limit of the voltage.

(2) Cell-to-cell method: The charge of the cell with the highest charge is transferred to the adjacent cell with the lowest charge.

(3) Cell-to-battery method: transfers the charge of the cell with the highest voltage to the entire battery.

(4) Battery pack-to-cell method: It uses an isolated DC-to-DC converter to transfer the charge of the battery pack to a single battery cell.

(5) Cell-to-battery-to-battery method: the charge is first transferred from the set battery cell to the battery pack, and then from the battery pack to the lower-voltage target battery cell, or from the set battery cell To the target cell.

Among them, the cell-to-battery-to-cell method has excellent balance performance and speed because of direct transfer of charge. However, because the reference potential of each battery cell in the battery pack is different, a bidirectional switch or a transformer is required for electrical isolation, and most bidirectional switches must be driven by floating and the voltage stress of the bidirectional switch is high (about the battery Group voltage), making the cost of the balancer higher and increasing the volume. The adjacent cell-to-cell balancing circuit is cost-effective and compact due to the low voltage stress on the switch and the diode. However, the use of a bidirectional switch in a bidirectional charge transfer circuit will increase component costs and control complexity. Therefore, a new battery balancer is urgently needed in the art.

An object of the present invention is to disclose a new type of battery balancer, which realizes bidirectional energy transmission between two independent batteries through an optimized inductive balancing circuit, so as to reduce the number of switches and inductive components, thereby having a smaller size and a lower cost. Inferior advantages.

Another object of the present invention is to disclose a new type of battery balancer, which compensates by using the open-circuit voltage read by the secondary battery in the rest mode to obtain a more accurate estimation of the current remaining battery capacity.

Another object of the present invention is to disclose a new type of battery balancer, which uses curve fitting to obtain an approximate control equation for the relationship between the voltage difference and the duty cycle, so that the system can adjust the on-time duty cycle in real time when the battery voltage changes. Keep the balance current constant.

Another object of the present invention is to disclose a new type of battery balancer, which further includes a LabVIEW human-machine interface to monitor a temperature change value and a voltage change value of the battery pack, so that when the temperature change value or the voltage change value is greater than At a preset threshold value, a protection signal is sent to the microcontroller to disable the two switch control signals to perform balance monitoring and protection on the battery, so that the battery pack can achieve the purpose of safe and fast active balancing.

Yet another object of the present invention is to disclose a new type of battery balancer, which has a faster balancing speed and shortens the balancing time by 27.1% and 18.6%, respectively, compared with the conventional fixed duty cycle method and the duty cycle adjustment method of the conventional technology.

In order to achieve the foregoing object, a new type of battery balancer has been proposed, which has: a battery pack including at least one battery cell, each battery cell including two secondary batteries; at least one bidirectional step-down circuit, each Having two ports to be electrically coupled to the two secondary batteries of a group of the battery cells, and two switches to control energy conversion between the two secondary batteries according to two switch control signals And a control unit for calculating a duty cycle according to the two open circuit voltages of the two secondary batteries and a polynomial function formula to determine the duty cycle of the two switch control signals, the polynomial function formula is: Duty (V _OC , ΔV) = 0.03313 (V _OC ) ² + 0.02388 (ΔV) ² -0.2692 (V _OC )-0.352 (ΔV) + 0.07974 (V _OC ) (ΔV) +1.2

Wherein, V _OC is the lower one of the two open circuit voltages, ΔV is the voltage difference between the two open circuit voltages, and Duty is the duty cycle.

In one embodiment, the two open-circuit voltages are voltages read by the two secondary batteries in a rest mode.

In one embodiment, the bidirectional buck-boost circuit includes a magnetizing inductor.

In one embodiment, the control unit includes a microcontroller to execute a control program to perform the duty cycle calculation.

In one embodiment, the microcontroller includes: a memory to store the control program; an input port to receive the two open-circuit voltages; a pulse width modulation module to generate all the voltages according to the duty cycle. Said two switch control signals; and an output port to output the two switch control signals.

In an embodiment, it further includes a LabVIEW human-machine interface to monitor a temperature change value and a voltage change value of the battery pack to send out when the temperature change value or the voltage change value is greater than a preset threshold. A protection signal is sent to the microcontroller to disable the two switch control signals.

In order to enable your reviewers to further understand the structure, characteristics, and purpose of the present invention, the drawings and detailed description of the preferred embodiments are attached as follows.

Please refer to Figs. 1a to 1b together. Fig. 1a shows a block diagram of one embodiment of the novel battery balancer of the present case, and Fig. 1b shows a block diagram of another embodiment of the novel battery balancer of the present case.

As shown in FIG. 1a, the new battery balancer has a battery pack 100, at least a bidirectional buck-boost circuit 200, and a control unit 300.

The battery pack 100 includes at least one battery cell 110, and each of the battery cells includes two secondary batteries 111 and 112 and each has an open circuit voltage V _OC1 and V _OC2 .

Each of the two-way buck-boost circuits 200 has a first connection port C ₁ , a first switch Q ₁ , a second connection port C _2, and a second switch Q ₂ . Wherein, the first connection port C ₁ and the second connection port C ₂ of one of the bidirectional step-down and step-up circuits 200 and the two secondary batteries 111 and 112 of a group of the battery units 110 are respectively And electrically coupled to control the energy conversion between the two secondary batteries 111 and 112 according to the switch control signals S ₁ and S _{2 of} the first switch Q ₁ and the second switch Q ₂ .

The control unit 300 is configured to perform a duty cycle calculation based on the two open-circuit voltages V _OC1 , V _OC2 and a polynomial function formula of the two secondary batteries to determine the two switch control signals S ₁ , S ₂ Duty cycle.

The polynomial function formula is: Duty (V _OC , ΔV) = 0.03313 (V _OC ) ² + 0.02388 ( ΔV) ² -0.2692 (V _OC )-0.352 (ΔV) + 0.07974 (V _OC ) (ΔV) +1.2

Wherein, V _OC is the lower one of the two open circuit voltages V _OC1 and V _OC2 , ΔV is the voltage difference between the two open circuit voltages V _OC1 and V _OC2 , and Duty is the duty cycle.

The two open-circuit voltages V _OC1 and V _OC2 are the voltages read by the two secondary batteries 111 and 112 in the rest mode; each of the two-way voltage step-down circuits 200 includes, but is not limited to, an excitation inductance.

As shown in FIG. 1 b, the control unit 300 includes, for example, but not limited to, a microcontroller 310 to execute a control program to perform the duty cycle calculation.

The microcontroller 310 includes: a memory 311; a pulse width modulation module 312; an input port P _in ; and an output port P _out .

Responsibility of the pulse width modulation module 312 is used by the system; the memory 311 used for storing the control program; P _in the input port used for receiving the two open-circuit voltage V _OC1, V _OC2 The period Duty generates the two switch control signals S ₁ and S _2. The output port P _out is used to output the two switch control signals S ₁ and S ₂ .

In addition, the new battery balancer may include a LabVIEW human-machine interface 400 to monitor a temperature change value and a voltage change value of the battery pack 100 so that the temperature change value or the voltage change value is greater than a preset valve When the value is reached, a protection signal is sent to the microcontroller 310 to disable the two switch control signals S ₁ and S ₂ .

The principle of the present invention will be described below:

As mentioned earlier, the cell balancing method used in the new type of battery balancer in this case is the active cell balancing method of the battery cell to battery pack to battery cell method, which has excellent balancing performance and speed.

However, the bidirectional charge transfer circuit of the conventional technology increases the component cost and control complexity due to the need to use a bidirectional switch. The unidirectional charge transfer circuit of the conventional technology uses a diode instead of a switch to achieve the purpose of reducing the number of components, but But because the charge can only move in one direction, the equilibrium speed is slow.

Please refer to FIG. 2, which illustrates a schematic diagram of the bidirectional buck-boost circuit in this case.

As shown in the figure, this case uses an optimized inductive balance circuit to reduce the number of switches and inductive components, and has the advantages of smaller size and lower cost. In this case, the conventional technology diode is replaced by the first switch Q ₁ and the second switch Q ₂ ; the load end is replaced by a battery pack to form a bidirectional buck-boost circuit, wherein the first switch Q ₁ and the second switch Q The signal control of ₂ is complementary.

Please refer to FIG. 3a to FIG. 3d together, where FIG. 3a illustrates a schematic diagram of the operation of one embodiment of the bidirectional buck-boost circuit when the battery B _{1 has a} high charge, and FIG. 3b illustrates the battery B _{1 with a} high charge. operation of another embodiment of a schematic bidirectional buck-boost circuit of the embodiment, Figure 3c shows that when the high power battery B _2, a schematic diagram of the operation of one embodiment of a bidirectional buck-boost circuit, shown in FIG 3d which battery power than B ₂ When high, the operation of another embodiment of the bidirectional buck-boost circuit is illustrated.

3a, when the high power battery B _1, Q ₁ turns on the first switch and the second switch Q ₂ is turned off, the energy storage battery B ₁ to the magnetizing inductance L _m; 3b, a first When the switch Q _{1 is} turned off and the second switch Q _{2 is} turned on, the excitation inductance L _{m is} released to the battery B _2. Therefore, the battery B ₁ can transmit energy to the battery B ₂ at the load end through the excitation inductance L _m .

Conversely, when the power of battery B ₂ is high, as shown in FIG. ₃ c, the energy of battery B _{2 is} transferred to battery B ₁ , the second switch Q _{2 is} turned on and the first switch Q _{1 is} turned off, and battery B ₂ stores the energy magnetizing inductance L _m in; shown in FIG. 3d, the second switch Q ₂ is turned off and the first switch Q ₁ turns on, the magnetizing inductance L _m release energy to the battery B _1, B ₂ and therefore the battery can via a magnetizing inductance energy L _{m is} transmitted to the battery B ₁ at the load side. Therefore, the bidirectional buck-boost circuit in this case has a bidirectional battery-to-battery balancing capability.

At present, the battery power estimation is to detect the amount of remaining power in the battery, so that users can know the battery's endurance, so that users can use the battery efficiently and decide when to stop charging and discharging energy to avoid overcharge or overdischarge. Cause battery damage or aging.

Please refer to FIG. 4, which illustrates a schematic diagram of a battery characteristic measurement platform in this case.

As shown in the figure, this measurement platform uses the Bio-Logic multi-functional modular potentiostat for battery analysis, and EC-Lab software for a series of different battery characteristics analysis. Among them, EC-Lab software can perform constant current charge and discharge, constant voltage charge, constant potential AC impedance measurement and other tests; in the restricted part, you can also choose the voltage, current or time limit of each test step; in the data storage part, EC-Lab software can also automatically store parameters such as voltage, current, charging and discharging capacity, and time for each test, and can generate graphics from it.

The battery power estimation method in this case is mainly based on the open circuit voltage method, supplemented by a table lookup method:

In recent years, users have gradually increased the accuracy of battery power estimation. Different battery power estimation methods not only need to consider the differences between different hardware devices, but also are affected by the battery usage conditions.

Known battery power estimation methods include open-circuit voltage method, Coulomb integration method (ampere-hour method), look-up table method, and impedance tracking method. In order to improve the accuracy and achieve the purpose of real-time estimation, more than two types will be used simultaneously. Way to estimate. In addition to selecting a suitable estimation method, compensation for the factors affecting the estimation is also required to obtain a more accurate estimation.

In this case, the LGDS318650 lithium ternary battery was selected in the battery screening part of the experiment. Its specifications are shown in Table 1.

Table 1 Rated Capacity 2200mAh Rated voltage 3.6V Standard charging conditions CC-CV, 1075 mA, 4.2V Cut-off voltage 3V Charging current 2150mA (0.9C) Discharge current 3225mA (1.5C) size 18mm (diameter), 65.05 mm (height) weight 50g Operating temperature -20˚C to + 60˚C Charging temperature 0˚C to + 45˚C Discharge temperature -20˚C to + 60˚C

Before the experiment, all tested batteries must be screened. The screening content includes testing of characteristics such as Open-Circuit Voltage (OCV), internal resistance measurement, battery capacity, and battery weight to select batteries with similar characteristics for screening. test.

Please refer to FIGS. 5a to 5c together, where FIG. 5a shows the relationship between the open circuit voltage and the current remaining capacity percentage, and FIG. 5b shows the relationship between the battery internal resistance and the current remaining capacity percentage. Schematic diagram showing the current remaining battery capacity compensation in this case.

First charge at constant current-constant voltage (CC-CV) and let it stand for one hour to ensure battery stability. The constant-current charging stage is set to 0.5C as the charging current, and the constant voltage is 4.2V and less than 0.05mA to complete charging. Then, discharge the battery at 0.01C for one hour, and then let it stand for one hour to stabilize the battery. You can directly use the measured voltage to find the relationship between the percentage of capacity and the DC internal resistance to the percentage of capacity. After 100 discharge tests, the relationship curves of the open circuit voltage (OCV), the remaining battery capacity (SOC), the battery internal resistance (R), and the remaining battery capacity as shown in Figs. 5a and 5b are established.

When the battery unit is in rest mode, use the data acquisition of LabVIEW software to read the battery voltage. The current remaining capacity of the battery corresponding to the battery is shown in Figure 5a, and the value is accurately estimated to the table interpolation method. The decimal point is the third place, but because the rest mode is short and the battery has not reached a stable state, the measured battery voltage is not the actual open circuit voltage, resulting in the current remaining battery capacity that is not accurate enough.

As shown in FIG. 5c, the two open-circuit voltages of the new battery balancer in this case are the voltages read by the two secondary batteries in the rest mode, and the voltages are used as the judgment capacity to estimate the Correct the current remaining battery capacity to get a more accurate estimate.

Introduction of the measurement monitoring platform and man-machine interface in this case:

The new type of battery balancer in this case further includes a LabVIEW human-machine interface to monitor a temperature change value and a voltage change value of the battery pack, so that when the temperature change value or the voltage change value is greater than a preset threshold, a A protection signal is sent to the microcontroller to disable the two switch control signals.

When the battery pack is balanced, it is necessary to monitor the battery pack for a long time to record the relevant data of the battery. This case uses the LabVIEW software introduced by National Instrument (NI) to implement the monitoring interface. The man-machine interface can simultaneously measure the voltage and temperature of the battery, and can record the voltage and temperature of the battery during equilibrium for a long time and store it in an Excel file.

Among them, LabVIEW can control the data acquisition card (DAQ) produced by American National Instruments. Through this plug-in available data acquisition card to read analog input signals, generate analog output signals, read and generate digital signals Related to scheduling built-in timers to measure frequency and other related applications.

Please refer to FIGS. 6a to 6c together, where FIG. 6a shows a schematic diagram of the measurement monitoring platform of the case, FIG. 6b shows a flow chart of the monitoring program of the measurement monitoring platform of the case, and FIG. 6c shows the flow of the case. Schematic diagram of the main screen of the man-machine interface of the measurement monitoring platform.

As shown in Figure 6a, the measurement platform monitors the battery voltage and temperature for a long time during the balance, and uses the NI USB-6009 data acquisition card to convert the battery voltage into a digital signal, and then displays the value of the digital signal It can be monitored and saved as an Excel file on the human-machine interface. At the same time, it can also estimate the remaining battery capacity based on different voltage conditions through the software, and use the NI USB-6211 data acquisition card to send the corresponding duty cycle analog signal and input / The output signal communicates with the microprocessor.

For battery temperature measurement, the NI USB-9211 data acquisition card is used, and the values are displayed on the man-machine interface for monitoring and saved as an Excel file to achieve the effects of over-temperature and over-voltage protection.

As shown in Figure 6b, in addition to obtaining the battery voltage and temperature per second for display and data storage, the monitoring program also uses the moving average method to process the data to improve the measurement accuracy, and estimates the current battery by the look-up table method. The remaining capacity is used to determine what kind of balance mode is required between the batteries, calculate the maximum and minimum voltage difference and capacity difference, and perform overvoltage and overtemperature protection. The main screen of the human-machine interface of the monitoring platform is shown in Figure 6c.

The balance control law in this case introduces:

The conventional technology uses the energy converter as the charge balance of the battery. However, when the fixed duty cycle method is used as the control strategy, the balance current will be reduced and the balance completion time will be prolonged in the later stage of the balance because the battery voltage difference becomes smaller. In order to reduce the battery voltage difference but still maintain a certain amount of balanced current, some literatures have proposed a method of adjusting the duty cycle, but the effect is limited due to the nonlinear characteristics of the circuit and the battery.

In order to maintain a constant balance current during the battery balancing period to speed up the balancing speed, the balancing algorithm in this case adaptively adjusts the duty cycle according to the difference in the remaining battery capacity during the balancing process to keep the balancing current constant.

As mentioned earlier, the charge transfer between batteries in this case is through a two-way buck-boost balancing circuit. When the battery B _{1 is} higher than battery B ₂ , the circuit is under steady-state operation. Based on the volt-second balance principle, V _B1 can be derived. The relational expression with V _B2 is shown in equation (1).

(1)

Among them, V _B1 is the voltage of battery B ₁ , V _B2 is the voltage of battery B ₂ , and D is the duty cycle.

If the circuit components are in an ideal state and the input power is equal to the output power, the relationship between the voltage and current of the two batteries can be obtained as shown in equation (2).

(2)

Among them, I _B1 is the balanced current of battery B ₁ , I _B2 is the balanced current of battery B ₂ , R is the internal resistance of the battery, and D is the duty cycle.

From the above formula, when the hardware parameters are determined, when the battery balances the battery, the balance current is mainly affected by the voltage of the battery and the duty cycle of conduction. If the on-duty duty cycle of the switch is kept constant during the balancing process, since the voltage difference of the battery will gradually approach, it can be known from equation (2) that the balancing current will be reduced and the speed of the later balancing will be slower.

Another literature proposes a method of changing the duty cycle of the switch to adjust the balancing current in real time to accelerate the balancing time. The relationship between the voltage difference between the batteries and the duty cycle is shown in Equation (3).

(3)

Among them, DV is the voltage difference between battery B ₁ and battery B ₂ .

In this case, the measured battery voltage and the voltage difference between the batteries are substituted into equation (3), and the corresponding ON duty cycle can be obtained to maintain the balanced current. Therefore, when the battery voltage changes, the balanced current can be maintained at a fixed value. about.

Because the circuit has non-ideal characteristics (switching loss, line resistance, etc.), and the non-linear characteristics of the battery will also cause the balance current to not be easily and accurately adjusted based on mathematical formulas, this case divides the relationship of equation (3) into 12 types of batteries State and 12 kinds of voltage difference, actual measurement and optimization are performed for different battery voltages and the corresponding duty cycle of voltage difference.

In order to make this case applicable to all battery voltages and voltage differences in all operating ranges, curve fitting the data in the table to get an approximate control equation of the voltage difference and the duty cycle, the system can measure the lower power The battery voltage and the voltage difference between the two batteries adjust the conduction duty cycle immediately to maintain a constant balance current.

The comparison table of the duty cycle for maintaining a balanced current of 1A is shown in Tables 2 and 3. Among them, the V _B2 meter has a lower battery voltage, and DV = V _B1 -V _B2 is the voltage difference.

Table 2 V _B2 DV = V _B1 -V _B2 3V 3.1V 3.2V 3.3V 3.4V 3.5V D0.1 V 0.667 0.666 0.665 0.662 0.659 0.657 D0.2 V 0.663 0.662 0.661 0.658 0.656 0.654 D0.3 V 0.659 0.656 0.653 0.652 0.651 0.649 D0.4 V 0.654 0.648 0.642 0.641 0.640 0.639 D0.5 V 0.644 0.639 0.634 0.633 0.636 0.631 D0.6 V 0.636 0.632 0.631 0.630 0.626 0.619 D0.7 V 0.629 0.628 0.626 0.624 0.618 0.617 D0.8 V 0.618 0.617 0.616 0.615 0.614 D0.9 V 0.608 0.607 0.604 0.603 D1.0 V 0.606 0.602 0.592 D1.1 V 0.596 0.588 D1.2 V 0.586

table 3 V _B2 DV = V _B1 -V _B2 3.6V 3.7V 3.8V 3.9V 4V 4.1V D0.1 V 0.655 0.654 0.653 0.652 0.651 0.65 D0.2 V 0.652 0.647 0.645 0.642 0.641 D0.3 V 0.646 0.644 0.641 0.64 D0.4 V 0.638 0.637 0.635 D0.5 V 0.627 0.625 D0.6 V 0.618 D0.7 V D0.8 V D0.9 V D1.0 V D1.1 V D1.2 V

Please refer to Figure 7, which shows the curve fitting relationship between the voltage difference and the duty cycle in this case.

As shown in the figure, the cftool function of MATLAB is used to complete the curve fitting in this case, and the relationship obtained is shown in equation (4).

(4)

Among them, V _OC is the lower one of the two open-circuit voltages, Δ V is the voltage difference between the two open-circuit voltages, and Duty is the duty cycle.

Please refer to FIG. 8, which is a schematic diagram showing a judgment flow of the required equilibrium time in this case. As shown in the figure, when the case enters the battery balance, the program will read the duty cycle calculated by LabVIEW according to the balance control method and send it to the microprocessor through the data acquisition card. Then, the input / output port judges and transmits the energy. Direction, transfer the energy of the larger capacity battery to the smaller capacity battery, and then determine the required balance time according to the maximum capacity difference. Among them, DSOC ₁ ＞ DSOC ₂ ＞ DSOC ₃ , Tb ₁ ＞ Tb ₂ ＞ Tb ₃ ＞ Tb ₄ , that is, the equilibrium time required when the power difference is larger is relatively longer. Finally, the pulse width modulation signal is sent for balance. During the balance process, a short rest time is required to shorten the balance time. In this case, a five-second rest state is performed at the end of each balance program, and the battery power measurement is performed. Then perform the next balance cycle judgment. In this case, the LabVIEW human-machine interface is used for real-time monitoring, and when overtemperature and overvoltage occur, a protection signal is sent to the input / output port of the microprocessor to stop the balance.

Experimental results and comparisons of this case and conventional techniques:

In this case, a bidirectional step-down circuit is used as the power stage circuit of the balancer, and a constant balance current method is proposed to overcome the problem of lower balance speed in the later balance. The following will verify the feasibility and correctness of the balance method in this case through experiments, and compare it with the fixed liability cycle method and the liability cycle adjustment method of conventional technology to highlight the performance improvement of this case.

This case actually completed a physical battery balancer for a battery pack composed of four lithium-ion batteries. The battery used in the experiment was LGDS318650 produced by LG. The battery capacity is 2200mAh, the rated voltage is 3.6V, and the fully-charged battery voltage is 4.2. V, cut-off voltage is 3V. In terms of circuit hardware, its design parameters are shown in Table 4. After the non-ideal factors are taken into account in actual experiments, a dead time of about 3% is added to avoid switching on both sides. At the same time, the inductance value of the bidirectional buck-boost circuit is 20mH.

Table 4 parameter name battery voltage Dead time Switching frequency inductance Value 3 ~ 4.2 V 1μs 30 kHz 20 μH

Please refer to FIGS. 9a to 9c together, where FIG. 9a shows the battery voltage balance curve of the case, FIG. 9b shows the voltage difference curve of the case, and FIG. 9c shows the battery temperature curve of the case.

As shown in the figure, it can be known that the system will determine the charge relationship between the batteries at the beginning of the balance. The battery with a higher charge is passed to the battery with a lower charge. The waveform shows that the battery voltage can be effectively brought into uniformity through balancing. From Figure 9b, it is known that the voltage difference between the highest battery voltage and the lowest battery voltage in the battery pack is about 700mV at the beginning. The voltage voltage difference is reduced to within 20mV of the preset value. According to Fig. 9c, it can be known that the temperature rise of the battery can be kept within 1 ^o C during the balance, which can avoid the situation that the excessive temperature rise causes the charge and discharge efficiency to decrease when the battery is balanced. .

The balance results of the conventional technology's fixed duty cycle method, the conventional technology's duty cycle adjustment method, and this case are compared. The battery voltage values of the three methods before and after balancing are shown in Table 5.

table 5 Before balance After balancing battery voltage V _B1 V _B2 V _B3 V _B4 V _B1 V _B2 V _B3 V _B4 Fixed liability cycle 4.17V 3.93V 3.65V 3.45V 3.64V 3.63V 3.63V 3.63V Duty cycle adjustment 4.17V 3.93V 3.64V 3.46V 3.64V 3.63V 3.63V 3.63V This case 4.16V 3.95V 3.65V 3.45V 3.65V 3.64V 3.64V 3.64V

Table 6 shows the remaining battery capacity (SOC) of the three control methods before and after balancing.

Table 6 Before balance After balancing Remaining battery capacity SOC ₁ SOC ₂ SOC ₃ SOC ₄ SOC ₁ SOC ₂ SOC ₃ SOC ₄ Fixed liability cycle 98% 78% 48% 13% 48% 47% 47% 47% Duty cycle adjustment 98% 79% 49% 12% 48% 47% 47% 47% This case 98% 78% 49% 12% 49% 48% 48% 48%

The balance results using the battery capacity (1%) and the battery voltage difference (20mV) as the termination conditions of the balance are shown in Table 7. It can be learned that the battery balance can be achieved by using the battery capacity judgment.

Table 7 1% as the equilibrium termination condition Before balance After balancing (1%) Remaining battery capacity SOC ₁ SOC ₂ SOC ₃ SOC ₄ SOC ₁ SOC ₂ SOC ₃ SOC ₄ This case 98% 78% 49% 12% 48% 47% 47% 47% 20mV as the equilibrium termination condition Before balance After equilibration (20mV) Remaining battery capacity SOC ₁ SOC ₂ SOC ₃ SOC ₄ SOC ₁ SOC ₂ SOC ₃ SOC ₄ This case 98% 78% 49% 12% 49% 48% 47% 47%

The comparison table of the balance results of the fixed liability cycle method of the conventional technology, the liability cycle adjustment method of the conventional technology, and the three balance control methods in this case is shown in Table 8.

Table 8 project Before balance After balancing Battery maximum and minimum voltage difference Total battery remaining capacity Time required for equilibration (1%) Total battery remaining capacity Fixed liability cycle 717mV 237% 96 minutes 189% Duty cycle adjustment 720mV 238% 86 minutes 189% This case 711mV 237% 70 minutes 193%

Please refer to FIG. 10, which is a comparison diagram of the equilibrium time of the three balance control methods.

As shown in the figure, the fixed liability cycle method of the conventional technology, the liability cycle adjustment method of the conventional technology, and the three balance control methods in this case can complete the battery balance. Although the total remaining battery capacity has decreased after the balance, it still has 80% Equilibrium efficiency of more than%; in terms of balancing time, it takes 96 minutes to complete the balance with the fixed liability cycle method of the conventional technology, while reducing the liability cycle adjustment method of the conventional technology to 86 minutes. In this case, the time was shortened to 70 minutes. The fixed liability cycle method and the liability cycle adjustment method of the conventional technology shorten the balance time by 27.1% and 18.6%, respectively.

In summary, the present invention adjusts the on-duty duty cycle of the switch to maintain the balance current constant through actual measurement, so the balancing speed is faster than the fixed duty cycle method and the duty cycle adjustment method of the conventional technology.

With the design disclosed above, the present invention has the following advantages:

1. The present invention discloses a new type of battery balancer, which realizes bidirectional energy transmission between two independent batteries through an optimized inductive balancing circuit, so as to reduce the number of switches and inductive components, and thus has a smaller size and a lower cost. advantage.

2. The present invention discloses a new type of battery balancer, which compensates by using the open circuit voltage read by the secondary battery in the rest mode to obtain a more accurate estimation of the current remaining capacity of the battery.

3. The present invention discloses a new type of battery balancer, which obtains a control equation for the relationship between the approximate voltage difference and the duty cycle by curve fitting, so that the system can adjust the on-time duty cycle to maintain a balanced current when the battery voltage changes. Of constant.

4. The present invention discloses a new type of battery balancer, which further includes a LabVIEW human-machine interface to monitor a temperature change value and a voltage change value of the battery pack, so that the temperature change value or the voltage change value is greater than a preset value. When the threshold value is reached, a protection signal is sent to the microcontroller to disable the two switch control signals to perform balance monitoring and protection on the battery, so that the battery pack can achieve the purpose of safe and rapid active balancing.

5. The present invention discloses a new type of battery balancer, which has a faster balancing speed, which shortens the balancing time by 27.1% and 18.6%, respectively, compared with the fixed duty cycle method and the duty cycle adjustment method of the conventional technology.

The disclosure of the present invention is a preferred embodiment, and any changes or modifications which are derived from the technical idea of the present invention and are easily inferred by those skilled in the art, do not depart from the scope of patent rights of the present invention.

To sum up, the present invention, regardless of the purpose, means and effect, is showing its technical characteristics that are quite different from the conventional ones, and its first invention is practical, and it also meets the patent requirements of the invention. Pray for granting patents at an early date.

100‧‧‧ battery pack

110‧‧‧battery unit

111‧‧‧ secondary battery

112‧‧‧ secondary battery

200‧‧‧Bidirectional lifting circuit

300‧‧‧Control unit

310‧‧‧Microcontroller

311‧‧‧Memory

312‧‧‧Pulse Width Modulation Module

FIG. 1a illustrates a block diagram of an embodiment of the novel battery balancer of the present case. FIG. 1b shows a block diagram of another embodiment of the novel battery balancer of the present case. FIG. 2 is a schematic diagram of a bidirectional buck-boost circuit of the novel battery balancer in this case. FIG. 3a is a schematic diagram illustrating the operation of one embodiment of the bidirectional buck-boost circuit when the battery B1 has a relatively high charge. FIG. 3b is a schematic diagram illustrating the operation of another embodiment of the bidirectional buck-boost circuit when the battery B1 has a relatively high charge. FIG. 3c is a schematic diagram illustrating the operation of one embodiment of the bidirectional buck-boost circuit when the battery B2 has a relatively high charge. FIG. 3d is a schematic diagram illustrating the operation of another embodiment of the bidirectional buck-boost circuit when the battery B2 has a relatively high charge. FIG. 4 is a schematic diagram of a battery characteristic measurement platform in this case. FIG. 5a is a graph showing the relationship between the open circuit voltage and the percentage of the remaining battery capacity. FIG. 5b is a graph showing the relationship between the internal resistance of the battery and the percentage of the remaining battery capacity. FIG. 5c is a schematic diagram of the current remaining battery capacity compensation in this case. Figure 6a is a schematic diagram showing the structure of the measurement monitoring platform in this case. Figure 6b is a schematic flow chart of the monitoring program of the measurement monitoring platform in this case. Figure 6c is a schematic diagram of the main screen of the human-machine interface of the measurement monitoring platform in this case. FIG. 7 is a curve fitting relationship diagram of the lower battery voltage, voltage difference, and duty cycle in this case. FIG. 8 is a schematic diagram showing a determination process of a required equilibrium time in this case. FIG. 9a illustrates a battery voltage balance curve in this case. FIG. 9b is a curve diagram of the voltage difference in this case. FIG. 9c is a graph showing the temperature change of the battery in this case. FIG. 10 is a comparison diagram of equilibrium time of three kinds of balance control methods.

Claims (6)

A new type of battery balancer includes: a battery pack including at least one battery cell, each battery cell comprising two secondary batteries; at least one bidirectional step-down voltage boosting circuit, each having two ports to communicate with a group The two secondary batteries of the battery unit are respectively electrically coupled, and two switches are used to control the energy conversion between the two secondary batteries according to two switch control signals; and a control unit for The two open-circuit voltages of the two secondary batteries and a polynomial function formula are used to calculate a duty cycle to determine the duty cycles of the two switch control signals. The polynomial function formula is: Duty (V _OC , △ V) = 0.03313 (V _OC ) ² +0.02388 (△ V) ² -0.2692 (V _OC ) -0.352 (△ V) +0.07974 (V _OC ) (△ V) +1.2 where V _OC is the comparison of the two open circuit voltages the low open circuit voltage, △ V is the voltage difference between the two open-circuit voltage, duty of the duty cycle. The new type battery balancer according to item 1 of the scope of patent application, wherein the two open-circuit voltages are voltages read by the two secondary batteries in a rest mode. The new type battery balancer according to item 1 of the scope of patent application, wherein the bidirectional buck-boost circuit includes a magnetizing inductance. The new type battery balancer according to item 1 of the patent application scope, wherein the control unit includes a microcontroller to execute a control program to perform the duty cycle calculation. The new type battery balancer according to item 4 of the patent application scope, wherein the microcontroller includes: a memory to store the control program; an input port to receive the two open circuit voltages; a pulse width modulation mode The group generates the two switch control signals according to the duty cycle; and an output port to output the two switch control signals. The new battery balancer according to item 5 of the patent application scope, further comprising a LabVIEW human-machine interface to monitor a temperature change value and a voltage change value of the battery pack, so as to change the temperature change value or the voltage change value. When it is greater than a preset threshold, a protection signal is sent to the microcontroller to disable the two switch control signals.