CN117335530A - Battery equalization method and system - Google Patents

Battery equalization method and system Download PDF

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Publication number
CN117335530A
CN117335530A CN202311487767.7A CN202311487767A CN117335530A CN 117335530 A CN117335530 A CN 117335530A CN 202311487767 A CN202311487767 A CN 202311487767A CN 117335530 A CN117335530 A CN 117335530A
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China
Prior art keywords
battery
transformer
voltage
equalization
parallel
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Chinese (zh)
Inventor
毕闯
刘皓
白金平
陈华伟
赖俊宇
李学生
钟其水
魏明珠
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Yangtze River Delta Research Institute of UESTC Huzhou
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Yangtze River Delta Research Institute of UESTC Huzhou
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Priority to CN202311487767.7A priority Critical patent/CN117335530A/en
Publication of CN117335530A publication Critical patent/CN117335530A/en
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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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
    • B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
    • B60L58/18—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries of two or more battery modules
    • B60L58/22—Balancing the charge of battery modules
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/441—Methods for charging or discharging for several batteries or cells simultaneously or sequentially
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/06—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes without control electrode or semiconductor devices without control electrode
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/538—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration
    • H02M7/53803—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration with automatic control of output voltage or current
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/425—Structural combination with electronic components, e.g. electronic circuits integrated to the outside of the casing
    • H01M2010/4271—Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing
    • 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
    • H02J2207/00—Indexing scheme relating to details of circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J2207/20—Charging or discharging characterised by the power electronics converter

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Electrochemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)

Abstract

The invention belongs to the technical field of power electronics, and discloses a battery equalization method and a system, which combine a center tap push-pull inverter and a voltage amplification rectifier; the alternating conduction of the diodes in the voltage amplification rectifier is controlled by changing the current direction of the transformer, and the voltage equalization is automatically completed. By alternately turning on the IGBTs, the primary side current direction of the transformer is alternated; the primary side current direction alternation of the transformer causes the secondary side current direction alternation, so that a diode connected with the battery in parallel is alternately conducted; the diodes are alternately conducted, and the voltage amplification rectifier on the secondary side of the transformer automatically completes equalization. The invention has simple circuit design, no negative feedback link and no system stability problem. The circuit of the invention is simple, only common devices are needed, and the cost is very low.

Description

Battery equalization method and system
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a battery equalization method and application.
Background
Electric vehicles have attracted considerable attention due to environmental pollution and energy crisis. The lithium battery has the advantages of low self-discharge rate, high battery voltage, high charging efficiency, high energy density and the like, and is considered as a viable energy source of the electric automobile. In order to achieve the power and range required by an electric vehicle, hundreds or thousands of cells are required to be connected in series or in parallel. However, there is an inconsistency in the interior of the battery pack due to manufacturing, environmental, use, and the like. When the battery pack is unbalanced, overcharge or overdischarge may occur. Affecting the performance and life of the battery pack such that the risk of fire or explosion increases dramatically. In addition, when any one of the battery cells in the battery pack reaches the charge-discharge cut-off voltage, the charge-discharge must be stopped, and overcharge and overdischarge are avoided. However, other cells in the battery are not fully charged or fully discharged, which can lead to a decrease in the overall capacity of the battery, creating a "barrel effect". Therefore, in order to prevent the above problems and to improve the service life of the battery pack, it is necessary to employ an equalization method for the series-connected battery pack.
Equalizer can be broadly divided into two categories: passive equalization and active equalization. Passive equalization is a resistive method that consumes excess energy through a power resistor. The advantage of this method is that it is inexpensive and easy to implement. Only one MOSFET and one power resistor are required per cell. Passive methods are currently the most widely used methods in energy storage systems, but are inefficient and generate heat. The active equalization method uses an energy storage element to transfer energy from the high voltage battery to the low voltage battery, which is more energy efficient. Active equalization methods include switched capacitor methods, voltage multiplier methods, transformer-based methods. Among these topologies, transformer-based solutions have the inherent advantage of being easily isolated.
Through the above analysis, the problems and defects existing in the prior art are as follows:
1. the efficiency is low and heat is generated, because the electric resistance can directly convert electric energy into heat energy, and the energy is not effectively utilized;
2. more active devices are used, and the control method is complex;
3. more magnetic elements such as transformer windings are used, and a large amount of space is occupied.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a battery equalization method and application.
The invention is realized in such a way that a battery equalization method is combined with a center tap push-pull inverter and a voltage amplification rectifier; the alternating conduction of two diodes connected with the battery module in parallel in the voltage amplification rectifier is controlled by changing the current direction of the transformer, so that the voltage equalization is automatically completed.
Further, the input port of the center tap push-pull inverter is connected in series and parallel with the battery, and the output alternating-current square wave is rectified by the voltage amplifying rectifier.
Further, by alternately turning on the IGBTs, the primary side current direction of the transformer is alternated.
Further, the alternating primary side current direction of the transformer causes the alternating secondary side current direction to alternately turn on a diode connected in parallel with the battery.
Further, when the upper IGBT is turned on, the current on the secondary side of the transformer flows into the same-name terminal, and the upper diode connected in parallel with the battery is turned on.
Further, when the lower IGBT is conducted, the current on the secondary side of the transformer flows out of the same-name end, and the lower diode connected with the battery in parallel is conducted.
Further, the diodes are alternately conducted, and the voltage amplification rectifier on the secondary side of the transformer automatically completes equalization.
Further, a pair of complementary pulse width modulated signals is used to control all MOSFET switches.
Further, the switching frequency and the duty cycle are fixed.
Another object of the present invention is to provide an application of a battery equalization method, in which the application range is mainly that the battery is connected in series into a circuit, and equalization is automatically completed.
Another object of the present invention is to provide a battery equalization system, comprising:
a center tap push-pull inverter with its input port connected in series-parallel with the battery to output an alternating square wave;
a voltage amplifying rectifier connected to the inverter to rectify the ac square wave output from the inverter;
a control unit configured to alternately control the IGBTs connected to the primary side of the transformer to change the primary side current direction of the transformer;
a set of diodes connected in parallel with the battery, which are alternately turned on in response to the alternation of the primary side current direction of the transformer;
a pair of complementary pulse width modulation signal generators connected to all the MOSFET switches for controlling the on-state of the switches,
the control unit is further configured to enable the current of the secondary side of the transformer to flow into the same-name end when the upper IGBT is conducted, conduct the upper diode connected with the battery in parallel, enable the current of the secondary side of the transformer to flow out of the same-name end when the lower IGBT is conducted, and conduct the lower diode connected with the battery in parallel, so that voltage balancing is automatically completed.
Wherein the control unit is further configured to:
generating a pulse width modulation signal for controlling the IGBT to be alternately conducted based on the voltage information of the battery string;
monitoring the conducting state of a diode connected in parallel with the battery and adjusting the pulse width modulation signal to optimize the voltage equalization efficiency;
automatically activating a voltage equalization process during battery charging to ensure that all battery cells are charged uniformly;
all MOSFET switches are controlled with a pulse width modulated signal of fixed frequency and duty cycle to stabilize the system's operational performance.
In combination with the technical scheme and the technical problems to be solved, the technical scheme to be protected has the following advantages and positive effects:
first, the equalization path of the battery module consists of passive device energy transfer capacitors and rectifying diodes, rather than a complex network requiring a large number of active switches. The input end of the inverter is connected in parallel with the two ends of the battery string, the two IGBTs are symmetrically and alternately conducted to form alternating current on the secondary side of the transformer, and the output alternating current waveform is rectified by the voltage amplifying rectifier. Meanwhile, the charge alternating current characteristic of the voltage amplification rectifier is similar to the working principle of a switched capacitor inverter, and the transfer capacitor is modeled as a resistance element. In a specific embodiment, the last obtained equation shows that the larger the voltage of the module is, the smaller the current flowing into the module in one period is, and finally, the automatic equalization is performed. The active elements and the magnetic elements are very few, and the control method is simple and does not occupy a large volume.
The invention provides a battery balancing method, which utilizes the change of the current direction of a transformer to control the alternate conduction of diodes in a voltage amplification rectifier and finally realizes automatic balancing.
The invention has simple circuit design, no negative feedback link and no system stability problem.
The invention has simple circuit, only needs to use common devices and has very low cost.
(1) The equalization speed is high: can continuously operate under the conditions of static state, charge and discharge.
(2) The control method is simple: only a pair of PWM drive signals of fixed frequency and duty cycle need be provided to the IGBTs.
(3) A simple transformer is used, and the occupied volume is small.
Second, as inventive supplementary evidence of the claims of the present invention, the following important aspects are also presented: the technical scheme of the invention overcomes the technical bias: in the past balancing method, more heat is generated by passive balancing, so that potential safety hazards are caused, and the efficiency is low; active equalization is either a complex active switching network, with many complex devices controlled, or a multi-winding transformer, taking up a lot of space. The invention only needs to open loop control two IGBTs and a simple transformer, has simple control logic and does not occupy a large amount of space.
Thirdly, the battery equalization method provided by the invention brings remarkable technical progress that:
1. efficiency is improved:
the center tap push-pull inverter and the voltage amplification rectifier can be used for efficiently converting energy and transmitting the energy among different batteries, so that the efficiency of the whole equalization process is improved.
2. And (3) accurate control:
the switch of the IGBT is accurately controlled through the complementary PWM signals, so that the accurate control of the current flowing direction in the battery equalization process can be realized, and the energy loss is reduced.
3. Automatic equalization:
the method realizes automatic battery equalization, does not need external control intervention, simplifies operation and reduces maintenance cost.
4. Compatibility and flexibility:
the design allows compatibility with different types and capacities of batteries, making it suitable for a wide range of applications, from portable electronic devices to electric vehicles.
5. Safety:
the balance state of each single battery in the battery pack can be maintained, so that the battery overcharge and overdischarge can be prevented, and the overall use safety is improved.
6. Prolonging the service life of the battery:
the voltage among the battery monomers is balanced, so that the times of over-charge and over-discharge of the battery can be effectively reduced, and the service life of the battery is prolonged.
7. Space and cost are saved:
this approach reduces the need for additional balancing hardware, as the balancing function is integrated in the transformer and inverter, which reduces the number of additional components, saving space and costs.
8. Reliability:
the fixed switching frequency and duty cycle ensures stable operation of the system, reducing potential reliability problems due to dynamic adjustment.
The technical progress provided by the invention improves the overall performance and reliability of the battery management system, and has important significance for improving the performance and service life of batteries in portable electronic products, energy storage systems and electric automobiles.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic circuit diagram provided by an embodiment of the present invention;
fig. 2 is a schematic diagram of a current flow of equalizer state 1 according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of the current flow of equalizer state 2 according to an embodiment of the present invention;
fig. 4 is a diagram of a battery equalization result provided by an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Embodiment one: battery equalization for battery management system of electric automobile
1. Embodiments are described below:
the center tapped push-pull inverter is designed to be integrated with a Battery Management System (BMS) of an electric vehicle.
The input port of the inverter is directly connected in series-parallel with the battery, and cooperates with the BMS to monitor and control the state of the battery.
The BMS acquires voltage information of each cell of the battery using the sensor, and calculates a voltage difference to be adjusted through a control unit.
The control unit sends out PWM signals to enable the IGBT switch to be conducted at proper time, the direction of the primary side current of the transformer is adjusted, and then automatic equalization is achieved in the battery pack.
The whole system can be designed to automatically activate the equalization function during charging of an electric vehicle, ensuring that all battery cells are charged to the same voltage level.
2. The technical effects are as follows:
the implementation method can obviously prolong the service life of the battery of the electric automobile, ensure the voltage balance among the battery monomers after each charging, reduce the energy waste and improve the driving mileage of the whole automobile.
Embodiment two: battery pack equalization in solar energy storage systems
1. Embodiments are described below:
and integrating a center tap push-pull inverter and a voltage amplification rectifier between the solar panel and the energy storage battery pack.
When the solar panel generates electric energy, the inverter regulates the distribution of the electric energy, so that each battery cell in the energy storage battery pack is ensured to uniformly receive charging.
The system can adjust the state of charge of each cell according to the real-time data, and balance the voltage of the battery pack through the change of the secondary side current direction of the transformer.
The control logic may be designed to preferentially ensure equalization of the battery pack and to automatically initiate an equalization procedure when a battery pack voltage imbalance is detected.
2. The technical effects are as follows:
the battery balancing method is applied to the solar energy storage system, so that the efficiency of solar power generation can be maximized, and the energy utilization rate and the battery life of the whole system are improved by effectively balancing the charging state of each single body in the energy storage battery pack.
Both embodiments of the present invention provide specific application scenarios for using a center-tapped push-pull inverter and a voltage-amplifying rectifier for battery equalization while also exhibiting significant technological advances brought by this technical solution.
Aiming at the problems existing in the prior art, the invention provides a battery equalization method and application.
As shown in fig. 1, the embodiment of the invention provides a method for balancing batteries, and designs an actual circuit according to a battery balancing model and principle.
Fig. 1 shows a schematic diagram of a battery equalization circuit. The equalizer combines a center-tapped push-pull inverter and a voltage-amplifying rectifier. The primary side of the transformer is a center-tapped push-pull inverter topology. The input port of the inverter is connected with the battery in series and parallel, and the output alternating square wave is rectified by the voltage amplifying rectifier. The two IGBTs are complementarily conducted, and when the upper IGBT is conducted, secondary side current flows into the same-name end; when the lower IGBT is conducted, the secondary side current flows out of the same-name end. The IGBT symmetrically works under a fixed period and duty cycle by adopting open-loop controlled automatic balance.
The working process is as follows:
each duty cycle was divided into 2 different states for analysis.
State 1: IGBT1 is turned on, and the secondary side current of the transformer flows into the same-name terminal. The upper diode in parallel with the battery is turned on. Fig. 2 shows the current flow. The secondary side voltage equation can be expressed as
V ci,peak And I ci,1 The average value of the transfer capacitor voltage and current during state 1, V Di Is the forward conduction voltage drop of the diode, V Mi Is the terminal voltage of the module, r ci And r Di The equivalent resistances of the transfer capacitor and the diode, respectively.
State 2: IGBT2 is conducted, and the secondary side current of the transformer flows out of the same-name end. The lower diode in parallel with the battery is turned on. Fig. 3 shows the current flow. The equation of state of the circuit in this process is
V ci,valley And I ci,2 The transfer capacitor voltage, current, respectively, are averaged over state 2.
During the stabilization phase, the transfer capacitor maintains charge balance. Thus, it is possible to obtain:
I ci,1 (t 1 -t 0 )＝I ci,2 (t 2 -t 1 )
t 0 is the moment of the start of a cycle, t 1 Is the time t at which state 1 ends in one cycle 2 Is the moment in a cycle when state 2 ends.
By combining the above formulas, it is possible to obtain the time of one cycle of operation:
ΔV ci ＝2V S -2V D -2I ci (r c +r D )-v Mi
I ci is the current flowing into the battery module for one cycle.
From the change in capacitance charge for one cycle, it is possible to obtain:
T s is the switching period of IGBT, f s Is the IGBT switching frequency.
By combining the formulas, when the equalization circuit operates for one period, the following formula can be obtained:
from the above, it can be seen that V Mi The larger the corresponding battery module I ci The smaller the equalization circuit is, the more equalization is automatically accomplished.
According to the battery balancing method provided by the embodiment of the invention, the battery is used as the input of the center tap push-pull inverter, two currents with opposite directions are provided for the secondary side of the transformer through the alternate conduction of the IGBT, and the switching frequency and the duty ratio are fixed.
The secondary side transfer capacitor C of the embodiment of the invention i Small enough that its voltage variation does not have a relatively large effect on the battery voltage. At the switching cycle scale, the change in battery voltage is negligible compared to the change in transfer capacitance voltage. Thus, the battery voltage can be regarded as a constant voltage source.
The invention provides a battery balancing method, and the charge transfer characteristic of a voltage amplification rectifier is similar to that of a switched capacitor converter. Thus, the analysis of such a voltage-amplifying rectifier-based module equalizer is also similar to a switched capacitor converter, which will C i Modeled as resistive elements.
Principle of: the battery is used as the input of the push-pull inverter with the center tap, the complementary conduction of the IGBT above and below the transformer with the center tap is controlled, the current of the secondary side of the transformer flows into the homonymous end and flows out of the homonymous end alternately, the diodes connected with the battery in parallel are caused to conduct alternately up and down, and the balance of the battery is automatically completed through the transfer capacitor.
The specific design is as follows, the capacitance value of the transfer capacitor is 47 mu F, the switching frequency is 200KHz, the IGBT duty ratio is 50% complementary, the turns ratio of the center tap push-pull transformer is 1:1:2, the leakage inductance of each winding is 8.2 mu H, and the magnetizing inductance is 200 mu H.
In order to make the simulation more convenient, M 1 Batteries 1, M having a capacity of 3.5F and an initial voltage of 3.404V 2 Batteries 2, M with a capacity of 3.5F initial voltage 3.464V n-1 Batteries 3, M having a capacity of 3.5F and an initial voltage of 3.564V n Battery 4 with a capacity of 3.5F and an initial voltage of 3.604V was used. The cell balancing results are shown in fig. 4.
The invention provides a battery balancing method, which mainly has the application range of batteries, and can connect the batteries in series into a circuit to automatically complete balancing.
Automatic equalization system based on center-tapped push-pull transformer and voltage-amplifying rectifier:
1, a center tap push-pull inverter and a voltage amplification rectifier are combined; the alternating conduction of two diodes connected with the battery module in parallel in the voltage amplification rectifier is controlled by changing the current direction of the transformer, so that the voltage equalization is automatically completed.
2. In the process of realizing battery equalization, the current and the voltage of each battery in the battery pack need to be monitored in real time through a current sensor and a voltage sensor.
3. The microprocessor is used for processing the data acquired by the sensor, and whether the equalization circuit is required to be in a working state is adjusted according to the processing result so as to realize the real-time equalization of the voltage of the battery pack.
4. Modeling and simulating the work of the whole system in Matlab/Simulink to obtain circuit parameters and obtain ideal waveforms.
The battery balancing method provided by the invention uses the combination of the center tap push-pull inverter and the voltage amplification rectifier, aims to automatically complete the balancing of the battery voltage, and is particularly suitable for the application of battery strings. The working principle thereof is explained in detail below:
1. combination of battery string and center-tapped push-pull inverter:
the battery is connected in series and parallel to the input end of the center tap push-pull inverter. The inverter is responsible for converting the direct voltage from the battery into an alternating square wave signal.
2. Action of the voltage amplifying rectifier:
the output ac square wave is fed into a voltage amplifying rectifier which rectifies the ac square wave into a dc and voltage amplifies it by the action of a transformer.
Alternating turn-on of igbts and change of primary side current direction of transformer:
IGBTs (insulated gate bipolar transistors) are alternately turned on in a complementary manner, which results in the direction of the current on the primary side of the transformer also being alternately changed. Such alternating current on the primary side will produce a corresponding alternating current on the secondary side.
4. The change of direction of the transformer secondary side current and the alternating conduction of the diode:
the alternating of the transformer secondary side current results in alternating conduction of the diodes in parallel with the battery modules. When the upper IGBT turns on, current flows into the same-name terminal of the transformer, causing the upper diode to turn on, allowing current to flow into or out of the parallel cells, depending on the specific voltage difference.
When the lower IGBT turns on, current flows out of the same-name terminal of the transformer, causing the lower diode to turn on, also allowing current to flow into or out of the battery in parallel with it.
5. Mechanism for automatically completing voltage equalization:
as a result of the above-described process, current alternately flows between the battery modules, it is possible to discharge the higher-voltage battery and charge the lower-voltage battery, thereby achieving equalization.
Use of pwm signals:
a pair of complementary Pulse Width Modulation (PWM) signals are used to control all MOSFET (metal oxide semiconductor field effect transistor) switches. These PWM signals ensure that IGBTs can be turned on and off in the correct sequence and duration.
7. Switching frequency and duty cycle:
the switching frequency (i.e. the frequency at which IGBTs turn on and off) and the duty cycle (the ratio of the on time to the total cycle time) are fixed, which means that the system is running at a constant operating point, which can be preset according to design requirements to achieve optimal equalization efficiency.
Through the working principle, the battery equalization system can effectively transmit energy, and the energy is transferred from a high-voltage battery module to a low-voltage module, so that all battery voltages tend to be consistent, the service life of the battery pack is prolonged, and the performance of the battery pack is improved. The resulting equation in the embodiment shows that the greater the module voltage, the less current flows into the module during an equalization period. The IGBT is only required to be alternately conducted by fixing equal periods and duty ratio signals, and after a plurality of periods are circulated, the module voltage automatically reaches balance, and the simulation result of the Simulink verifies the balance effect.
The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.

Claims (10)

1. A battery equalization method is characterized by combining a center tap push-pull inverter and a voltage amplification rectifier; the alternating conduction of the diodes in the voltage amplification rectifier is controlled by changing the current direction of the transformer, and the voltage equalization is automatically completed.
2. The battery equalization method of claim 1, wherein the input port of the center-tapped push-pull inverter is connected in series with the battery, and the output ac square wave is rectified by a voltage amplifying rectifier.
3. The battery equalization method of claim 1, wherein the primary side current direction of the transformer is alternated by alternately turning on the IGBTs.
4. The battery equalization method of claim 1, wherein the alternating primary side current direction of the transformer causes alternating secondary side current direction, alternately turning on a diode in parallel with the battery.
5. The battery equalization method of claim 4, wherein when the upper IGBT is turned on, a secondary side current of the transformer flows into the same name terminal, and the upper diode connected in parallel with the battery is turned on.
6. The battery equalization method of claim 4, wherein when the lower IGBT is turned on, the transformer secondary side current flows out of the same name terminal and the lower diode connected in parallel with the battery is turned on.
7. The battery equalization method of claim 1, wherein the diodes are alternately turned on and the voltage-amplifying rectifier on the secondary side of the transformer automatically performs equalization.
8. The battery equalization method of claim 1, wherein all MOSFET switches are controlled using a pair of complementary pulse width modulated signals; the switching frequency and duty cycle are fixed.
9. A battery equalization system, comprising:
a center tap push-pull inverter with its input port connected in series-parallel with the battery to output an alternating square wave;
a voltage amplifying rectifier connected to the inverter to rectify the ac square wave output from the inverter;
a control unit configured to alternately control the IGBTs connected to the primary side of the transformer to change the primary side current direction of the transformer;
a set of diodes connected in parallel with the battery, which are alternately turned on in response to the alternation of the primary side current direction of the transformer;
a pair of complementary pulse width modulation signal generators connected to all the MOSFET switches for controlling the on-state of the switches,
the control unit is further configured to enable the current of the secondary side of the transformer to flow into the same-name end when the upper IGBT is conducted, conduct the upper diode connected with the battery in parallel, enable the current of the secondary side of the transformer to flow out of the same-name end when the lower IGBT is conducted, and conduct the lower diode connected with the battery in parallel, so that voltage balancing is automatically completed.
10. The battery equalization system of claim 9, wherein the control unit is further configured to:
generating a pulse width modulation signal for controlling the IGBT to be alternately conducted based on the voltage information of the battery string;
monitoring the conducting state of a diode connected in parallel with the battery and adjusting the pulse width modulation signal to optimize the voltage equalization efficiency;
automatically activating a voltage equalization process during battery charging to ensure that all battery cells are charged uniformly;
all MOSFET switches are controlled with a pulse width modulated signal of fixed frequency and duty cycle to stabilize the system's operational performance.
CN202311487767.7A 2023-11-08 2023-11-08 Battery equalization method and system Pending CN117335530A (en)

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