CN116505615A - Distributed dynamic equalizing charge system and method for lithium battery pack - Google Patents
Distributed dynamic equalizing charge system and method for lithium battery pack Download PDFInfo
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- CN116505615A CN116505615A CN202310556255.5A CN202310556255A CN116505615A CN 116505615 A CN116505615 A CN 116505615A CN 202310556255 A CN202310556255 A CN 202310556255A CN 116505615 A CN116505615 A CN 116505615A
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 123
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 123
- 238000000034 method Methods 0.000 title claims abstract description 58
- 238000012546 transfer Methods 0.000 claims abstract description 98
- 230000002457 bidirectional effect Effects 0.000 claims abstract description 37
- 238000002955 isolation Methods 0.000 claims abstract description 10
- 238000005070 sampling Methods 0.000 claims description 5
- 238000004364 calculation method Methods 0.000 claims description 3
- 238000013459 approach Methods 0.000 claims description 2
- 230000002035 prolonged effect Effects 0.000 abstract description 4
- 239000003990 capacitor Substances 0.000 description 3
- 238000013461 design Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000011217 control strategy Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010336 energy treatment Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
- H02J7/0014—Circuits for equalisation of charge between batteries
- H02J7/0019—Circuits for equalisation of charge between batteries using switched or multiplexed charge circuits
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0029—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with safety or protection devices or circuits
- H02J7/00302—Overcharge protection
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Charge And Discharge Circuits For Batteries Or The Like (AREA)
Abstract
The invention relates to a distributed dynamic equalizing charge system and method for a lithium battery pack, and belongs to the technical field of batteries. The charging system comprises a lithium battery pack, an energy transfer circuit, an isolation controller, a control system, a driving circuit and a charging bidirectional switch; the input side of the energy transfer module is connected to the positive and negative ends of the single battery, and the output end of the energy transfer module is connected to the positive and negative ends of the lithium battery pack; the control system controls each energy transfer module through the isolation controller so that the energy of the single battery is transferred to the lithium battery pack; the charging circuit of the lithium battery pack is provided with a charging bidirectional switch, and the control system is matched with the driving circuit to modulate the charging bidirectional switch so as to control the charging energy of the lithium battery pack. When the method is finished, each battery is under the same preset balance condition, the electric performance consistency is similar, the whole service capacity of the lithium battery pack is improved to the maximum extent, and the service life of the battery is prolonged.
Description
Technical Field
The invention belongs to the technical field of batteries, and relates to a distributed dynamic equalizing charge system and method for a lithium battery pack.
Background
In the practical use process of the lithium battery, a plurality of single lithium batteries are generally required to be connected in series and used in groups so as to meet the voltage class and power requirements of different electric equipment. Because of the differences of the battery manufacturing process and the external use environment, the inconsistency phenomenon can occur among the batteries in the lithium battery pack, the available capacity of the lithium battery pack is reduced, the cycle life is shortened and potential safety hazards exist when the lithium battery pack is used in series, and therefore, the lithium battery pack in series is necessary to be subjected to balanced management and safety management.
The current lithium battery pack equalization scheme is divided into passive equalization and active equalization according to different energy treatment modes. The passive equalization is to dissipate the surplus energy of the battery in a mode of connecting dissipation resistors at two ends of the single battery in parallel, and has the advantages of simple structure, easy control, small equalization current, low equalization speed, and heat management safety problem because of a large amount of heat generated by the equalization resistors connected in parallel. The active equalization has the advantages of high energy utilization rate, high equalization speed and the like, and the capacity, the inductance, the transformer and the DC-DC converter are generally utilized to construct an energy transfer circuit to realize the electric quantity transfer among the batteries in the group.
Active equalization can be divided into two main categories, namely centralized equalization and distributed equalization, according to the energy transfer circuit structure. The whole lithium battery pack in the centralized equalization structure is provided with an energy transfer circuit in common, the utilization rate of the energy transfer circuit is high, the circuit design is complex, the overall equalization time can be increased along with the increase of the number of batteries, and the lithium battery pack is suitable for lithium battery packs with fewer strings and is not easy to expand and maintain. Each battery in the distributed equalization structure corresponds to one energy transfer circuit, so that energy transfer can be carried out on multiple single batteries at the same time, the energy transfer rate is high, the control is flexible, various equalization control strategies can be conveniently realized, the expansion is easy, and the equalization method is a common equalization method at present.
The distributed equalization method based on the capacitor takes the capacitor as an energy transfer carrier, realizes electric quantity equalization according to the pressure difference between the single batteries in the group, when the voltage difference between the adjacent batteries is larger, the equalization current is larger, and after each equalization, the capacitor can have residual transfer energy, thereby easily causing the heating problem and having low reliability. The distributed equalization method based on the inductance has controllable equalization current, but can bring about the problem of larger volume of an energy transfer circuit. The distributed balancing method based on the transformer tends to be complex in structure along with the increase of the number of batteries, and the size and the cost of the transformer are increased. The distributed equalization method based on the DC-DC converter can design the converter into the same input and output parameters, so that the converter circuit is simply multiplexed, the operation reliability is higher, the maintenance is convenient, the multiple converters can be operated simultaneously, the equalization rate is high, and the method is wider in engineering application.
In the existing distributed equalization method based on the DC-DC converter, equalization is mostly carried out under the condition of charging a lithium battery pack, and the energy of the single battery which has reached the equalization condition is transferred into the lithium battery pack, but the energy flows into the single battery which has reached the equalization condition in the mode, so that the voltage of the single battery is continuously increased, the potential safety hazard of overcharging the battery exists, meanwhile, the full charge of all batteries cannot be realized, and the available capacity of the lithium battery pack cannot be used to the maximum extent. In addition, the method also has the advantages that the method is communicated with the charger in real time in the equalization process to realize the adjustment of the input energy of the lithium battery pack, so that the electric quantity of each single battery in the pack is consistent when the charging is finished, the control difficulty is increased due to the fact that the method is communicated with the charger in real time, and meanwhile, the control cost is increased.
Disclosure of Invention
Therefore, the invention aims to provide a distributed dynamic equalizing charging system and method for a lithium battery pack, so as to realize the control of charging energy of the lithium battery pack without controlling a charger, and avoid the potential safety hazard of charging the lithium battery pack for a long time without disconnecting the charger. And the dynamic balanced charging of the lithium battery pack can be realized, the electric quantity of the fully charged battery is kept unchanged, the battery which is not fully charged continues to be balanced charged, and when the charging is finished, the whole battery is in a fully charged state, so that the available capacity of the lithium battery pack is increased, and the service life of the battery is prolonged.
In order to achieve the above purpose, the present invention provides the following technical solutions:
the distributed dynamic equalizing charging system for the lithium battery pack comprises the lithium battery pack, an energy transfer circuit, an isolation controller, a control system, a driving circuit and a charging bidirectional switch;
the lithium battery pack is respectively marked as Cell by n 1 、Cell 2 、…、Cell n Is formed by serially connecting single batteries; two ends of each single battery are connected with n energy transfer modules, namely an energy transfer module 1, energy transfer modules 2 and … and an energy transfer module n; n energy transfer modules form an energy transfer circuit;
the input side of the energy transfer module is connected to the positive and negative ends of the single battery, and the output end of the energy transfer module is connected to the positive and negative ends of the lithium battery pack;
the control system controls each energy transfer module through the isolation controller so that the energy of the single battery is transferred to the lithium battery pack;
the charging circuit of the lithium battery pack is provided with a charging bidirectional switch, and the control system is matched with the driving circuit to modulate the charging bidirectional switch so as to control the charging energy of the lithium battery pack.
Optionally, when the charging system does not start the equalization function, the charger charges the lithium battery pack according to a preset condition, the energy transfer circuit does not work, and the charging bidirectional switch is in a full-open state;
when the single batteries in the lithium battery pack reach the balanced starting threshold value, the corresponding single batteries are transferred into the lithium battery pack through the energy transfer circuit, and meanwhile, the input energy is adjusted to be matched with the single battery energy transfer circuit in a mode of controlling the duty ratio of the charging bidirectional switch, so that the balanced variable of the single batteries reaching the threshold value in the lithium battery pack is kept unchanged after the single batteries in the lithium battery pack start the energy transfer circuit, and all the balanced variables of the single batteries approach to be consistent when the balancing is finished;
in the charging process of the lithium battery pack, the end voltage reaction energy of the single battery in the charging process is set, the voltage of the single battery reaches the maximum voltage, namely the battery is fully charged, and the end voltage equalization variable of the battery is selected; at the final stage of charging the power lithium battery pack, controlling the input energy of the lithium battery pack to match with the energy transferred by the single batteries, so that the single battery energy with the end voltage reaching an equalization threshold is not increased, the end voltage is kept unchanged, the energy of other single batteries is continuously increased, the end voltage is increased until reaching the equalization threshold, and finally, the end voltages of all the single batteries reach the equalization threshold, thereby realizing the equalization target that the end voltages of all the single batteries are consistent when the charging is finished;
set up single Cell in lithium Cell group 1 The end pressure of the battery Cell reaches an equilibrium threshold value at first, and the equilibrium is started 1 The energy transfer circuit is started, and energy passes through the energy transfer circuit and is transmitted from the single battery Cell 1 Flowing to the whole group of batteries, and recording the efficiency of all the energy transfer circuits as eta, the following steps are provided:
ΔE’ 1 ＝η·ΔE 1 (1)
in the series lithium battery pack, under the condition that the charging current is the same and the end voltages of the single batteries are not great, the single batteries Cell 1 The input energy is E 1 ：
Set up Cell 1 The energy outflow and the energy input of the battery Cell1 are equal, and the energy is kept unchanged, so that the battery Cell1 has the following structure:
ΔE 1 ＝E 1 (3)
the combined type (1), (2) and (3) are obtained:
E in ＝E-ΔE' 1 ＝nE 1 -ηΔE 1 ＝(n-η)ΔE 1 (4)
by measuring equalizer input energy deltae 1 Obtaining the energy E required to be input by the charger in The method comprises the steps of carrying out a first treatment on the surface of the Adjusting input energy E in The energy of the opened and balanced single battery is kept unchanged in the whole residual charging process; average value of input energy<E in >The calculation formula of (2) is as follows:
in E in For constant input energy over a period of time, T is a PWM period, T on The on time of the charging bidirectional switch in one switching period is set, and D is the on duty ratio of the charging bidirectional switch in one period; controlling the average of the input energy by adjusting the charge switch on timeValue size; the longer the on time, the larger the input energy average value, otherwise, the smaller the input energy average value;
by controlling the energy transfer circuit to enable the switch, the single battery Cell is enabled 1 Is pressed at V ON And V is equal to OFF Wave between, energy is E ON And E is connected with OFF Inter-fluctuation, ensure the energy E input into the single battery Cell1 1_in The method meets the following conditions:
E 1_in ≤ΔE 1 (6)
when the energy transfer circuit of the single battery Cell1 is started under the condition of the formula (6), the energy of the single battery Cell1 is reduced, and the end voltage is reduced; when the single battery Cell 1 When the energy transfer circuit of (a) is turned off, the single battery Cell 1 Is increased, and the end pressure is increased; cell by changing energy transfer circuit enable signal 1 Is pressed at V ON And V is equal to OFF Wave between, energy is E ON And E is connected with OFF Inter-fluctuation;
V ON -V OFF ＜V σ (7)
E ON -E OFF ＜E σ (8)
v in the formulas (7), (8) σ 、E σ When the value is a minimum value, the single Cell is considered to be 1 In the equalization process t 0 ～t m In the process, the terminal voltage is unchanged, the energy is unchanged, and the single battery Cell is realized 1 The energy of (2) is relatively constant during the equalization process;
E n_in ≤ΔE n (9)
under the condition of meeting the formula (9), all the single batteries reach the energy, and the balance of all the single batteries is completed;
the energy transfer circuit consists of a DC-DC converter and is of a two-stage structure formed by a front-stage Boost circuit and a rear-stage flyback circuit; the front-stage Boost circuit initially boosts the single battery to 10V and is used as the input of the back-stage flyback circuit; the back-stage flyback circuit performs circuit isolation and increases the input voltage to the voltage of the lithium battery pack, and combines an intermittent operation flyback boost formula to perform constant power output control, and the maximum rated power is 5W.
The distributed dynamic equalizing charge method of the lithium battery pack based on the system comprises the following steps:
s1: judging whether the lithium battery pack is in a protection state currently or not;
before the charger is connected with the lithium battery pack, the charging bidirectional switch is disconnected, and the charging loop is in an open state; the control system detects the end pressure of each single battery in the battery pack, when any battery is in an under-voltage or over-voltage state, the charging bidirectional switch is always turned off, the lithium battery pack is not charged, and meanwhile, the energy transfer circuit does not work;
s2: lithium battery pack opening charge
After judging that the lithium battery pack does not enter a protection state, opening a charging bidirectional switch to charge the lithium battery pack according to a preset charging multiplying power;
s3: judging whether to start equalizing charge
In the charging process of the lithium battery pack, the control system detects whether the end voltage of a single battery reaches an equilibrium starting threshold, and if the end voltage of a certain single battery reaches the equilibrium starting threshold, S4 is executed; otherwise, keeping the current charging state to continue charging until detecting that the end voltage of a certain battery reaches an equilibrium starting threshold;
s4: equalizing charge
Starting an equalizing charge function; the control system inquires and screens out the single battery which reaches the equilibrium threshold value, starts the energy transfer circuit, inquires the single battery end voltage of the energy transfer circuit, calculates the current single battery end voltage and the single battery end voltage difference value at the last sampling moment, namely the increment of the equilibrium single battery end voltage; if all the end voltage increment of the equalizing single battery is not positive, the duty ratio of the charging switch is increased, and the input energy power is increased; if the end voltage increment of the equalizing single battery is positive, the duty ratio of the charging switch is reduced, and the input energy power is reduced;
s5: judging completion of equalizing charge
Repeating the query and control mode of the S4 until all the single batteries reach the equalization threshold, closing the charging switch and all the energy transfer circuits, and finishing equalization charging when all the single battery end pressures in the lithium battery pack are between the equalization opening threshold and the equalization closing threshold;
s6: completion of charging
And reporting a charging completion signal, recording voltage change data in the complete charging process, and ending the charging.
The invention has the beneficial effects that:
(1) The charging energy of the lithium battery pack is controlled by controlling the on and off time of the charging bidirectional switch without communicating with a charger, thereby simplifying the control.
(2) And each battery in the lithium battery pack is not charged continuously after being fully charged, and other batteries in the lithium battery pack can be charged continuously without being influenced by the balanced batteries. By means of the charging mode, the service life of the battery can be prolonged, and the risk of overcharge of the battery is avoided.
(3) When the method is finished, each battery is under the same preset balance condition, the electric performance consistency is similar, the whole service capacity of the lithium battery pack is improved to the maximum extent, and the service life of the battery is prolonged.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and other advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the specification.
Drawings
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in the following preferred detail with reference to the accompanying drawings, in which:
fig. 1 is a distributed dynamic full-equalizing charge system structure;
FIG. 2 is an energy flow relationship during equalization charge;
FIG. 3 is a cell equalization control diagram;
FIG. 4 is a DC-DC converter energy transfer circuit;
fig. 5 shows the process of equalizing charge of the end voltage of each unit cell.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be noted that the illustrations provided in the following embodiments merely illustrate the basic idea of the present invention by way of illustration, and the following embodiments and features in the embodiments may be combined with each other without conflict.
Wherein the drawings are for illustrative purposes only and are shown in schematic, non-physical, and not intended to limit the invention; for the purpose of better illustrating embodiments of the invention, certain elements of the drawings may be omitted, enlarged or reduced and do not represent the size of the actual product; it will be appreciated by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numbers in the drawings of embodiments of the invention correspond to the same or similar components; in the description of the present invention, it should be understood that, if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc., that indicate an azimuth or a positional relationship based on the azimuth or the positional relationship shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but not for indicating or suggesting that the referred device or element must have a specific azimuth, be constructed and operated in a specific azimuth, so that the terms describing the positional relationship in the drawings are merely for exemplary illustration and should not be construed as limiting the present invention, and that the specific meaning of the above terms may be understood by those of ordinary skill in the art according to the specific circumstances.
Equalizing charge system structure: the structure diagram of the distributed dynamic full-equalizing charging system of the lithium battery pack is shown in figure 1.
The lithium battery pack is respectively marked as Cell by n 1 、Cell 2 、…、Cell n Is formed by serially connecting single batteries. Each power savingThe two ends of the pool are connected with the energy transfer modules, and the number of the energy transfer modules is n. The input side of the energy transfer module is connected to the positive and negative ends of the single batteries, and the output end is connected to the positive and negative ends of the whole group of batteries. The control system controls the normal operation of each energy transfer module through the isolation controller, so that the energy of the single battery is transferred to the lithium battery pack. A charging bidirectional switch is added in a charging loop of the lithium battery pack, and a control system is matched with a driving circuit to modulate the charging bidirectional switch so as to control the charging energy of the lithium battery pack.
Equalizing charge principle: the energy flow relationship during the lithium battery pack equalizing charge is shown in fig. 2.
When the equalization function is not started, the charger charges the lithium battery pack according to the preset, the energy transfer circuit does not work, and the charging bidirectional switch is in a full-open state. When the single batteries in the battery pack reach the balanced starting threshold value, the corresponding single batteries are transferred into the lithium battery pack through the energy transfer circuit, and meanwhile, the input energy is adjusted to be matched with the single battery energy transfer circuit in a mode of controlling the duty ratio of the charging bidirectional switch, so that the balanced variable of the single batteries reaching the threshold value in the lithium battery pack is kept unchanged after the single batteries start the energy transfer circuit, and when the balancing is finished, the balanced variable of all the single batteries is nearly consistent.
In the charging process of the lithium battery pack, the end voltage of the single battery can react with energy, and the set single battery voltage reaches the maximum voltage, namely the battery is fully charged, so that the end voltage equalization variable of the battery is selected. At the end of charging of the power lithium battery pack, the input energy of the lithium battery pack is controlled to be matched with the energy transferred by the single batteries, so that the single battery energy of which the end voltage reaches the balance threshold value is not increased, the end voltage is kept unchanged, the energy of other single batteries is continuously increased, the end voltage rises until reaching the balance threshold value, and finally, the end voltages of all the single batteries reach the balance threshold value, and the balance target of consistency of the end voltages of all the single batteries when the charging is finished is realized.
Now assume that the single Cell in the lithium battery pack 1 The end pressure of (1) first reaches the equalization threshold and equalization is initiated as shown in fig. 2. At this time, cell 1 The energy transfer circuit is started, and energy passes through the energy transfer circuit and is transmitted from the single battery Cell 1 Flowing to the whole group of batteries, and recording the efficiency of all the energy transfer circuits as eta, the following steps are provided:
ΔE’ 1 ＝η·ΔE 1 (1)
in the series lithium battery pack, under the condition that the charging current is the same and the end voltages of the single batteries are not great, the single batteries Cell 1 The input energy is E 1 ：
Assume a Cell 1 The energy outflow is equal to the energy input, and the single battery Cell 1 The energy is kept unchanged. The method can obtain:
ΔE 1 ＝E 1 (3)
the combined type (1), (2) and (3) can be obtained:
E in ＝E-ΔE' 1 ＝nE 1 -ηΔE 1 ＝(n-η)ΔE 1 (4)
by measuring equalizer input energy deltae 1 The energy E required to be input by the charger can be obtained in . Adjusting input energy E in The energy of the single battery which is balanced in opening can be kept unchanged in the whole residual charging process, and the battery is an absolute energy balance. Average value of input energy<E in >The calculation formula of (2) is as follows:
in E in For a short period of time, T is a PWM period, T on The on time of the charging bidirectional switch in one switching period is set, and D is the on duty ratio of the charging bidirectional switch in one period. By adjusting the charge switch on time, the average magnitude of the input energy can be controlled. The longer the on time, the larger the input energy average value, and conversely the smaller the input energy average value. The method is based on the switch of the existing power lithium battery pack management system, and does not require any additional amountThe circuit is additionally arranged, and the charger is not required to be controlled, so that the control of input energy can be realized.
In practical application, the efficiency of each energy transfer circuit is different, the energy of each single battery in the power lithium battery pack is not distributed evenly, and accurate quantitative analysis of the energy of all the single batteries is extremely difficult. The absolute energy balance described above is modified herein to a relative energy balance as shown in fig. 3.
By controlling the energy transfer circuit to enable the switch, the single battery Cell is enabled 1 End pressed at V ON And V is equal to OFF Wave between, energy is E ON And E is connected with OFF Inter-wave. At the moment, only the single battery Cell needs to be input 1 Energy E in (a) 1_in The method meets the following conditions:
E 1_in ≤ΔE 1 (6)
cell unit under the condition of formula (6) 1 When the energy transfer circuit is started, a single battery Cell 1 The energy is reduced and the end pressure is reduced. When the single battery Cell 1 When the energy transfer circuit is closed, the single battery Cell 1 The energy increases and the end pressure increases. Cell can be made by changing the energy transfer circuit enable signal 1 End pressed at V ON And V is equal to OFF Wave between, energy is E ON And E is connected with OFF Inter-wave.
V ON -V OFF ＜V σ (7)
E ON -E OFF ＜E σ (8)
V in the formulas (7), (8) σ 、E σ When the value is a minimum value, it can be considered that the Cell is 1 In the equalization process t 0 ～t m The terminal voltage is approximately unchanged in the process, and the energy is approximately unchanged. Realizing single battery Cell 1 Is relatively constant during the equalization process.
The method can be popularized to all single batteries.
E n_in ≤ΔE n (9)
Under the condition of meeting the formula (9), the energy dynamic matching scheme can ensure that the energy of the single batteries is relatively unchanged in the balancing process, and finally, all the single batteries reach the energy range, so that the balancing of all the single batteries is completed.
The energy transfer circuit composed of the DC-DC converter is shown in fig. 4, and a two-stage structure is composed of a front-stage Boost circuit and a rear-stage flyback circuit. The front-stage Boost circuit initially boosts the single battery to 10V and is used as the input of the back-stage flyback circuit. The back-stage flyback circuit performs circuit isolation and increases the input voltage to the voltage of the lithium battery pack, and combines an intermittent operation flyback boost formula to perform constant power output control, and the maximum rated power is 5W.
The implementation steps of the scheme are as follows:
step 1, judging whether the lithium battery pack is currently in a protection state
Before the charger is connected with the lithium battery pack, the charging bidirectional switch is disconnected, and the charging loop is in an open state. The control system detects the end pressure of each single battery in the battery pack, when any battery is in an under-voltage or over-voltage state, the charging bidirectional switch is always turned off, the lithium battery pack is not charged, and meanwhile, the energy transfer circuit does not work.
Step 2, starting charging of lithium battery pack
And after judging that the lithium battery pack does not enter a protection state, opening a charging bidirectional switch to charge the lithium battery pack according to a preset charging multiplying power.
Step 3, judging whether to start equalizing charge
And (4) detecting whether the end voltage of a single battery reaches an equilibrium starting threshold value by the control system in the charging process of the lithium battery pack, and executing the step (4) if the end voltage of the single battery reaches the equilibrium starting threshold value. Otherwise, the current charging state is kept to continue charging until a certain battery end voltage is detected to reach an equilibrium starting threshold.
Step 4, equalizing charge
And starting an equalizing charge function. The control system inquires and screens out the single battery which reaches the equalization threshold, starts the energy transfer circuit, inquires the single battery end voltage of the energy transfer circuit, calculates the current single battery end voltage and the single battery end voltage difference value at the last sampling moment, namely the increment of the equalization single battery end voltage. If all the end voltage increment of the equalizing single battery is not positive, the duty ratio of the charging switch is increased, and the input energy power is increased; if the end voltage increment of the equalizing single battery is positive, the duty ratio of the charging switch is reduced, and the input energy power is reduced.
Step 5, judging that the equalizing charge is completed
And repeating the inquiry and control mode until all the single batteries reach the equalization threshold value, closing the charging switch and all the energy transfer circuits, wherein the end voltage of all the single batteries in the lithium battery pack is between the equalization opening threshold value and the equalization closing threshold value at the moment, the end voltage difference value is smaller, and the equalization charging is completed.
Step 6, charging is completed
And reporting a charging completion signal, recording voltage change data in the complete charging process, and ending the charging.
The 24 strings of lithium iron phosphate battery packs are taken as experimental objects for case description.
The model of the monomer lithium iron phosphate battery is IFR32135-15Ah.
The specific experimental operation steps are as follows:
step 1, judging whether the lithium battery pack is currently in a protection state
Before the charger is connected with the lithium battery pack, the charging bidirectional switch is disconnected, and the charging loop is in an open state. The control system detects the end pressure of each single battery in the group, when any battery is in an under-voltage (2.0V) or over-voltage (3.7V) state, the charging bidirectional switch is always disconnected, the lithium battery group is not charged, and meanwhile, the energy transfer circuit does not work.
Step 2, starting charging of lithium battery pack
And after judging that the lithium battery pack does not enter a protection state, opening a charging bidirectional switch to charge the lithium battery pack according to a preset charging multiplying power of 0.5C (7.5A).
Step 3, judging whether to start equalizing charge
And (3) detecting whether the end voltage of a single battery reaches an equilibrium starting threshold (3.50V) by the control system in the charging process of the lithium battery pack, and executing the step (4) if the end voltage of a certain single battery reaches the equilibrium starting threshold (3.50V). Otherwise, the current charging state is kept to continue charging until a certain battery end voltage is detected to reach an equilibrium starting threshold (3.50V).
Step 4, equalizing charge
And starting an equalizing charge function. The control system firstly adjusts the charging bidirectional switch to enable the charger to charge the lithium battery pack at a charging multiplying power of 0.1C (1.5A), then inquires and screens out single batteries reaching an equilibrium starting threshold (3.50V), starts an energy transfer circuit, inquires and starts single battery end voltage of the energy transfer circuit, calculates the current single battery end voltage and the single battery end voltage difference value at the last sampling moment, namely, balances single battery end voltage increment. If all the end voltage increment of the equalizing single battery is not positive, the duty ratio of the charging switch is increased, and the input energy power is increased; if the end voltage increment of the equalizing single battery is positive, the duty ratio of the charging switch is reduced, and the input energy power is reduced.
The current battery voltage 1 and the current battery voltage 2 are designed to reach an equilibrium starting threshold (3.50V), the energy transfer circuit 1 and the energy transfer circuit 2 are started to work, and the energy transfer circuit is designed to output with constant power of 5W.
The output gain formula of the front-stage Boost circuit in the energy transfer circuit is as follows:
v in g Is the input voltage of the Boost circuit, V o1 To output voltage D Boost Is the on duty cycle of one switching cycle.
The output gain formula of the post-stage flyback circuit in the energy transfer circuit is as follows:
the available output power P is expressed as:
in which L p Is the exciting inductance of the transformer in the flyback circuit, V o1 For input voltage, T is a switching period, D 1 Is the on duty cycle of one switching cycle.
At the moment, the control system inquires the No. 1 and No. 2 batteries to calculate the end voltage increment of the current single battery and the end voltage increment of the single battery at the last sampling moment, if the end voltage increment is not positive, the duty ratio of a charging switch is increased, and the input energy power is increased; if the end voltage increment of the equalizing single battery is positive, the duty ratio of the charging switch is reduced, and the input energy power is reduced. The remaining batteries continue to charge with the energy transferred in balance.
Step 5, judging that the equalizing charge is completed
And repeating the inquiry and control mode until all the single batteries reach the equalization threshold value, closing the charging switch and all the energy transfer circuits, wherein the end voltage of all the single batteries in the lithium battery pack is between the equalization opening threshold value and the equalization closing threshold value at the moment, the end voltage difference value is smaller, and the equalization charging is completed.
Step 6, charging is completed
And reporting a charging completion signal and ending the charging.
The battery terminal voltage change in the whole charging process is collected, the result is shown in fig. 5, the terminal voltage of each battery is the same when the charging is finished, the terminal voltage range is 39mV, and the balanced charging of the lithium battery pack is completed.
Finally, it is noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the claims of the present invention.
Claims (3)
1. A lithium battery distributed dynamic equalizing charge system is characterized in that: the charging system comprises a lithium battery pack, an energy transfer circuit, an isolation controller, a control system, a driving circuit and a charging bidirectional switch;
the lithium battery pack is respectively marked as Cell by n 1 、Cell 2 、…、Cell n Is formed by serially connecting single batteries; two ends of each single battery are connected with n energy transfer modules, namely an energy transfer module 1, energy transfer modules 2 and … and an energy transfer module n; n energy transfer modules form an energy transfer circuit;
the input side of the energy transfer module is connected to the positive and negative ends of the single battery, and the output end of the energy transfer module is connected to the positive and negative ends of the lithium battery pack;
the control system controls each energy transfer module through the isolation controller so that the energy of the single battery is transferred to the lithium battery pack;
the charging circuit of the lithium battery pack is provided with a charging bidirectional switch, and the control system is matched with the driving circuit to modulate the charging bidirectional switch so as to control the charging energy of the lithium battery pack.
2. The distributed dynamic equalizing charge system of a lithium battery pack according to claim 1, wherein: when the charging system does not start the equalization function, the charger charges the lithium battery pack according to the preset, the energy transfer circuit does not work, and the charging bidirectional switch is in a full-on state;
when the single batteries in the lithium battery pack reach the balanced starting threshold value, the corresponding single batteries are transferred into the lithium battery pack through the energy transfer circuit, and meanwhile, the input energy is adjusted to be matched with the single battery energy transfer circuit in a mode of controlling the duty ratio of the charging bidirectional switch, so that the balanced variable of the single batteries reaching the threshold value in the lithium battery pack is kept unchanged after the single batteries in the lithium battery pack start the energy transfer circuit, and all the balanced variables of the single batteries approach to be consistent when the balancing is finished;
in the charging process of the lithium battery pack, the end voltage reaction energy of the single battery in the charging process is set, the voltage of the single battery reaches the maximum voltage, namely the battery is fully charged, and the end voltage equalization variable of the battery is selected; at the final stage of charging the power lithium battery pack, controlling the input energy of the lithium battery pack to match with the energy transferred by the single batteries, so that the single battery energy with the end voltage reaching an equalization threshold is not increased, the end voltage is kept unchanged, the energy of other single batteries is continuously increased, the end voltage is increased until reaching the equalization threshold, and finally, the end voltages of all the single batteries reach the equalization threshold, thereby realizing the equalization target that the end voltages of all the single batteries are consistent when the charging is finished;
set up single Cell in lithium Cell group 1 The end pressure of the battery Cell reaches an equilibrium threshold value at first, and the equilibrium is started 1 The energy transfer circuit is started, and energy passes through the energy transfer circuit and is transmitted from the single battery Cell 1 Flowing to the whole group of batteries, and recording the efficiency of all the energy transfer circuits as eta, the following steps are provided:
ΔE′ 1 ＝η·ΔE 1 (1)
in the series lithium battery pack, under the condition that the charging current is the same and the end voltages of the single batteries are not great, the single batteries Cell 1 The input energy is E 1 ：
Set up Cell 1 The energy outflow and the energy input of the battery Cell1 are equal, and the energy is kept unchanged, so that the battery Cell1 has the following structure:
ΔE 1 ＝E 1 (3)
the combined type (1), (2) and (3) are obtained:
E in ＝E-ΔE' 1 ＝nE 1 -ηΔE 1 ＝(n-η)ΔE 1 (4)
by measuring equalizer input energy deltae 1 Obtaining the energy E required to be input by the charger in The method comprises the steps of carrying out a first treatment on the surface of the Adjusting input energy E in The energy of the opened and balanced single battery is kept unchanged in the whole residual charging process; average value of input energy<E in >The calculation formula of (2) is as follows:
in E in T is a PWM period for constant input energy over a period of time，t on The on time of the charging bidirectional switch in one switching period is set, and D is the on duty ratio of the charging bidirectional switch in one period; controlling the average value of input energy by adjusting the on time of a charging switch; the longer the on time, the larger the input energy average value, otherwise, the smaller the input energy average value;
by controlling the energy transfer circuit to enable the switch, the single battery Cell is enabled 1 Is pressed at V ON And V is equal to OFF Wave between, energy is E ON And E is connected with OFF Inter-fluctuation, ensure the energy E input into the single battery Cell1 1_in The method meets the following conditions:
E 1_in ≤ΔE 1 (6)
when the energy transfer circuit of the single battery Cell1 is started under the condition of the formula (6), the energy of the single battery Cell1 is reduced, and the end voltage is reduced; when the single battery Cell 1 When the energy transfer circuit of (a) is turned off, the single battery Cell 1 Is increased, and the end pressure is increased; cell by changing energy transfer circuit enable signal 1 Is pressed at V ON And V is equal to OFF Wave between, energy is E ON And E is connected with OFF Inter-fluctuation;
V ON -V OFF ＜V σ (7)
E ON -E OFF ＜E σ (8)
v in the formulas (7), (8) σ 、E σ When the value is a minimum value, the single Cell is considered to be 1 In the equalization process t 0 ～t m In the process, the terminal voltage is unchanged, the energy is unchanged, and the single battery Cell is realized 1 The energy of (2) is relatively constant during the equalization process;
E n_in ≤ΔE n (9)
under the condition of meeting the formula (9), all the single batteries reach the energy, and the balance of all the single batteries is completed;
the energy transfer circuit consists of a DC-DC converter and is of a two-stage structure formed by a front-stage Boost circuit and a rear-stage flyback circuit; the front-stage Boost circuit initially boosts the single battery to 10V and is used as the input of the back-stage flyback circuit; the back-stage flyback circuit performs circuit isolation and increases the input voltage to the voltage of the lithium battery pack, and combines an intermittent operation flyback boost formula to perform constant power output control, and the maximum rated power is 5W.
3. The lithium battery pack distributed dynamic equalizing charge method based on the system of claim 1, which is characterized in that: the method comprises the following steps:
s1: judging whether the lithium battery pack is in a protection state currently or not;
before the charger is connected with the lithium battery pack, the charging bidirectional switch is disconnected, and the charging loop is in an open state; the control system detects the end pressure of each single battery in the battery pack, when any battery is in an under-voltage or over-voltage state, the charging bidirectional switch is always turned off, the lithium battery pack is not charged, and meanwhile, the energy transfer circuit does not work;
s2: lithium battery pack opening charge
After judging that the lithium battery pack does not enter a protection state, opening a charging bidirectional switch to charge the lithium battery pack according to a preset charging multiplying power;
s3: judging whether to start equalizing charge
In the charging process of the lithium battery pack, the control system detects whether the end voltage of a single battery reaches an equilibrium starting threshold, and if the end voltage of a certain single battery reaches the equilibrium starting threshold, S4 is executed; otherwise, keeping the current charging state to continue charging until detecting that the end voltage of a certain battery reaches an equilibrium starting threshold;
s4: equalizing charge
Starting an equalizing charge function; the control system inquires and screens out the single battery which reaches the equilibrium threshold value, starts the energy transfer circuit, inquires the single battery end voltage of the energy transfer circuit, calculates the current single battery end voltage and the single battery end voltage difference value at the last sampling moment, namely the increment of the equilibrium single battery end voltage; if all the end voltage increment of the equalizing single battery is not positive, the duty ratio of the charging switch is increased, and the input energy power is increased; if the end voltage increment of the equalizing single battery is positive, the duty ratio of the charging switch is reduced, and the input energy power is reduced;
s5: judging completion of equalizing charge
Repeating the query and control mode of the S4 until all the single batteries reach the equalization threshold, closing the charging switch and all the energy transfer circuits, and finishing equalization charging when all the single battery end pressures in the lithium battery pack are between the equalization opening threshold and the equalization closing threshold;
s6: completion of charging
And reporting a charging completion signal, recording voltage change data in the complete charging process, and ending the charging.
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