Active battery equalization circuit and equalization method thereof

Abstract

The application provides an active battery equalization circuit and an equalization method thereof, and belongs to the technical field of battery equalization, and comprises a microcontroller, a rectification conversion unit and a CLL-MRC converter, wherein the CLL-MRC converter comprises at least one half-bridge LLC converter, one end of the rectification conversion unit is connected to a power grid, the other end of the rectification conversion unit is connected to one end of the half-bridge LLC converter, the other end of the half-bridge LLC converter is connected to a battery pack through a switch array, and the microcontroller selects unbalanced batteries in the battery pack to the other end of the half-bridge LLC converter through control of the switch array, so that energy transfer between the unbalanced batteries and the power grid or the battery pack is realized; the structure is simple, easy to expand and high in efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery balancing technology, and more particularly to an active battery balancing circuit and its balancing method. Background Technology

[0002] To meet the demands of high-power applications such as electric vehicles, lithium-ion batteries are often connected in series and parallel to form battery packs. However, individual differences in batteries increase with aging, which can easily lead to reduced capacity, shortened lifespan, and even safety hazards such as fire and explosion. Therefore, battery balancing technology is crucial for unlocking battery potential, extending lifespan, and ensuring safety.

[0003] In traditional battery balancing circuits, switches are paired with numerous distributed energy storage components, and each circuit can only connect to a single battery cell at a time. Due to the reliance on a large number of switches and energy storage components, traditional battery balancing circuits suffer from low integration, poor reliability, and high cost. With the development of power electronics technology, battery balancing technology is evolving towards higher frequencies, higher efficiency, and higher power density. However, the switching losses caused by the increase in switching frequency have become a core bottleneck restricting system performance. Against this backdrop, LLC series resonant converters (LLC-SRC), with their soft-switching characteristics of zero-voltage turn-on under full load, require no complex control (only 50% fixed duty cycle frequency modulation), support low-rated voltage components, and have lower controller costs than topologies such as phase-shifted full-bridge converters, are widely used as low-cost, high-efficiency isolated power stages, providing a key solution for upgrading battery balancing technology.

[0004] However, in existing technologies, each battery cell is equipped with an independent converter, and each converter comes with a complete set of power switches. Multi-channel balancing requires multiple times the number of switches. In addition, LLC-SRC has two major design challenges in battery balancing scenarios: (1) To ensure a controllable range, it is necessary to control ,high Caused resonant inductor Containing only alternating current, the change in magnetic flux density ( (1) Extremely high, causing serious core and winding losses, which are difficult to cure even with the use of iron powder cores; (2) Synchronous rectifier (SR) requires millivolt-level precision VDS detection (which can only be achieved by integrated circuits), and low-cost control schemes cannot be adapted, resulting in high cost of SR controller, which contradicts the low-cost requirements of battery balancing system. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to solve the problems of low integration, poor reliability and high cost caused by the reliance on a large number of switches and energy storage components in existing battery equalization circuits.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution: an active battery balancing circuit, comprising: a microcontroller, a rectifier conversion unit, and a CLL-MRC converter. The CLL-MRC converter includes at least one half-bridge LLC converter. One end of the rectifier conversion unit is connected to the power grid, and the other end of the rectifier conversion unit is connected to one end of the half-bridge LLC converter. The other end of the half-bridge LLC converter is connected to the battery pack through a switch array. The microcontroller selects the unbalanced batteries in the battery pack to the other end of the half-bridge LLC converter by controlling the switch array, thereby realizing the energy transfer between the unbalanced batteries and the power grid or the battery pack.

[0007] Beneficial Effects: The active battery balancing circuit proposed in this invention uses a microcontroller to control a switch array to select unbalanced batteries in the battery pack to the other end of a half-bridge LLC converter. It supports the simultaneous selection of multiple adjacent batteries for balancing, overcoming the limitation of traditional battery balancing circuits that can only connect a single battery cell at a time. The use of a CLL-MRC half-bridge resonant topology and power devices achieves soft switching, reducing heat loss. The topology has a wider gain range, and continuous and smooth adjustment of the balancing current is achieved through frequency conversion, eliminating inrush current and improving system reliability and energy transfer efficiency. This balancing circuit eliminates the need for a separate converter for each battery cell, significantly reducing the number of converter switches. The circuit structure is simple, easily expandable, highly efficient, and requires no large amounts of energy storage components, greatly reducing costs.

[0008] Preferably, the CLL-MRC converter includes a transformer, a primary-side circuit, and... A secondary circuit, The battery pack includes Battery cells, Battery cells and Each secondary circuit corresponds to a primary circuit. Each battery cell group includes multiple batteries connected in series. The two ends of each battery are connected to the first and second ports of the secondary circuit through a switching transistor. The unbalanced batteries in each battery cell group transfer energy to the primary circuit through the corresponding secondary circuit.

[0009] Preferably, the primary-side circuit includes a switching transistor. Switching transistor ,inductance ,capacitance Each secondary circuit includes a switching transistor. Switching transistor ,inductance Switching transistor The drain of the transistor is connected to the first port of the rectifier-conversion unit, and the switching transistor is connected to the first port of the rectifier-conversion unit. The sources are respectively connected to the switching transistors. drain, capacitor One end of the capacitor The other end is connected to the inductor. One end of the transformer resonant inductor The same name terminal, inductor The other end, transformer resonant inductor heteronym terminals and switching transistors After the source is connected, it is connected to the second port of the rectifier conversion unit, and the transformer magnetizing inductor The same terminal and the transformer magnetizing inductor After connecting the different-named terminals, they are connected to the inductor. One end, inductor The other end serves as the first port of the secondary circuit, the transformer magnetizing inductance. The opposite terminal is connected to the switching transistor. The drain of the transformer magnetizing inductance The same terminal is connected to the switching transistor. The drain of the switching transistor Source and switch The source terminal is connected to the second port of the secondary circuit, and a capacitor is connected between the first and second ports. .

[0010] Beneficial effects: The CLL-MRC converter of the present invention uses the input-side inductor After being moved to the output rectifier, the resonant inductor ( , , , The inclusion of a DC component reduces flux density variations and losses, while a simple RC circuit is used to detect voltage change rate and control the synchronous rectifier, significantly reducing costs. Addressing the two major drawbacks of LLC-SRC converters, the CLL-MRC converter reconstructs the resonant cavity, eliminating... Parameter constraints reduce magnetic flux fluctuations in the magnetic core and lower magnetic losses; at the same time, the operating range is optimized, eliminating the need for synchronous rectification, eliminating the need for high-precision VDS detection circuits, reducing control hardware costs, and adapting to battery balancing scenarios.

[0011] Preferably, the rectifier conversion unit includes a switching transistor. To the switching transistor ,inductance Switching transistor Source and switch After the drain is connected, it is switched One end connected to the power grid, the switching transistor Source and switch The drain of the switch is connected to the other end of the power grid. Drain and switching transistor The drain is connected to the inductor. One end, inductor The other end is connected to the switching transistor The drain of the transistor is connected to the first port of the rectifier-conversion unit, and the switching transistor is used as the first port. source and switch source and switch The source terminal is connected to serve as the second port of the rectifier conversion unit, and a capacitor is connected between the first port and the second port. .

[0012] Preferably, the circuit also includes a battery management system, which collects the current and voltage of each battery and transmits the current and voltage of each battery to the microcontroller.

[0013] This invention also provides an active battery balancing method. Using the active battery balancing circuit described above, when connected to the power grid, the microcontroller controls the switch array to select the unbalanced battery to the other end of the half-bridge LLC converter, and the unbalanced battery exchanges energy with the power grid; when not connected to the power grid, the microcontroller controls the switch array to select the unbalanced battery to the other end of the half-bridge LLC converter, and the unbalanced battery exchanges energy with the battery pack.

[0014] Preferably, the microcontroller calculates the state of charge (SOC) of each battery and the average SOC of the battery pack based on the current and voltage of each battery. When there is only one unbalanced battery in each battery cell, the microcontroller sorts the unbalanced batteries according to the difference between the SOC of each battery and the average SOC, and turns on the switches at both ends of the unbalanced batteries in sequence according to the sorting. When there are at least two unbalanced batteries in a battery cell, all the unbalanced batteries in a battery cell are regarded as an unbalanced cell, and the unbalanced batteries in the unbalanced cell are connected in series. The microcontroller sorts the unbalanced cells according to the difference between the SOC of the unbalanced cell and the average SOC, and turns on the switches at both ends of the unbalanced cell in sequence according to the sorting.

[0015] Preferably, when connected to the power grid, the energy exchange process between the unbalanced battery and the power grid within one switching cycle includes 12 modes. The six modes in the first half of the cycle are completely symmetrical with the six modes in the second half of the cycle. The six modes in the first half of the cycle include the first mode to the sixth mode in sequence. In the first mode, the secondary circuit and the unbalanced battery transfer energy. In the second mode, the power grid, the secondary circuit, and the unbalanced battery transfer energy respectively. In the third mode, the secondary circuit and the unbalanced battery transfer energy. In the fourth mode, the power grid, the secondary circuit, and the unbalanced battery transfer energy respectively. In the fifth mode, the secondary circuit and the unbalanced battery transfer energy. In the sixth mode, the power grid, the secondary circuit, and the unbalanced battery transfer energy respectively.

[0016] Preferably, when not connected to the power grid, if all unbalanced batteries or all unbalanced units are either undervoltage or overvoltage, the unbalanced batteries or unbalanced units exchange energy with the battery pack; if all unbalanced batteries or all unbalanced units simultaneously contain both undervoltage and overvoltage, the unbalanced batteries with undervoltage exchange energy with the unbalanced batteries with overvoltage, and the unbalanced units with undervoltage exchange energy with the unbalanced units with overvoltage.

[0017] Preferably, all unbalanced batteries or all unbalanced cells simultaneously contain undervoltage and overvoltage. The power grid or battery pack first exchanges energy with the unbalanced batteries with undervoltage, and then exchanges energy with the unbalanced batteries with overvoltage. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] Figure 1 This is a schematic diagram of the active battery balancing circuit provided in Embodiment 1 of the present invention; Figure 2 This refers to the first operating mode of the CLL-MRC converter in the active battery balancing circuit provided in Embodiment 1 of the present invention within one switching cycle. Figure 3 This refers to the second operating mode of the CLL-MRC converter in the active battery balancing circuit provided in Embodiment 1 of the present invention within one switching cycle. Figure 4 This refers to the third operating mode of the CLL-MRC converter in the active battery balancing circuit provided in Embodiment 1 of the present invention within one switching cycle. Figure 5 This refers to the fourth operating mode of the CLL-MRC converter in the active battery balancing circuit provided in Embodiment 1 of the present invention within one switching cycle. Figure 6 This refers to the fifth operating mode of the CLL-MRC converter in the active battery balancing circuit provided in Embodiment 1 of the present invention within one switching cycle. Figure 7 This refers to the sixth operating mode of the CLL-MRC converter in the active battery balancing circuit provided in Embodiment 1 of the present invention within one switching cycle. Figure 8 Within one switching cycle, the active battery balancing circuit provided in Embodiment 1 of the present invention, under the condition of balancing multiple undervoltage batteries, has a CLL... The first typical operating mode of the MRC converter; Figure 9Within one switching cycle, the active battery balancing circuit provided in Embodiment 1 of the present invention, under the condition of balancing multiple undervoltage batteries, has a CLL... The second typical operating mode of the MRC converter.

[0020] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] Example 1 like Figure 1 As shown, this embodiment provides an active battery balancing circuit, including a battery management system, a microcontroller, a rectifier conversion unit, and a CLL-MRC converter. The battery management system includes a voltage monitoring circuit and a current monitoring circuit. The voltage monitoring circuit is used to collect the voltage of each battery in the battery pack, and the current monitoring circuit is used to collect the current of each battery in the battery pack. The battery management system is communicatively connected to the microcontroller to transmit the collected battery voltage and current to the microcontroller. In this embodiment, the microcontroller is a DSP controller. In the microcontroller, the state of charge (SOC) of each battery is calculated. By averaging the SOC of all batteries, the average SOC of the battery pack is calculated. It is then determined whether the difference between the SOC of each battery and the average SOC is greater than the maximum balancing threshold or less than the minimum balancing threshold. If the difference is greater than the maximum balancing threshold or less than the minimum balancing threshold, the battery is considered an unbalanced battery, and the unbalanced batteries need to be balanced.

[0023] The CLL-MRC converter includes a transformer, a primary circuit, and... A secondary circuit, A primary-side circuit and a secondary-side circuit constitute a half-bridge LLC converter. One end of the rectifier unit is connected to the power grid, and the other end is connected to one end of the half-bridge LLC converter. The other end of the half-bridge LLC converter is connected to the battery pack via a switch array. The microcontroller controls the switch array to select the unbalanced battery in the battery pack to the other end of the half-bridge LLC converter, realizing energy transfer between the unbalanced battery and the power grid or battery pack. When connected to the power grid, the unbalanced battery exchanges energy with the grid; when not connected to the power grid, the unbalanced battery exchanges energy with the battery pack, achieving self-balancing. The battery pack that exchanges energy with the unbalanced battery can be other unbalanced batteries (e.g., energy exchange between an undervoltage battery and an overvoltage battery) or other normal batteries.

[0024] In this invention, the battery pack includes Battery cells, Battery cells and Each secondary circuit corresponds one-to-one with the primary circuit, meaning that each battery cell group transfers energy to the primary circuit through its corresponding secondary circuit. Each battery cell group includes multiple batteries connected in series, and the two ends of each battery are connected to the first and second ports of the secondary circuit through a switching transistor, respectively. The unbalanced batteries in each battery cell group transfer energy to the primary circuit through their corresponding secondary circuits.

[0025] See Figure 1 This embodiment uses Taking a value of 3 as an example: the three secondary circuits are the first secondary circuit, the second secondary circuit, and the third secondary circuit. The battery pack consists of three battery units: the first battery unit, the second battery unit, and the third battery unit. The number of batteries in the first battery unit is... The number of batteries in the second battery unit is The number of batteries in the third battery unit is The total number of switches in the switch array is The number of batteries in each battery cell can be the same or different. In this embodiment, the first battery cell, the second battery cell, and the third battery cell have the same number of batteries, that is... Therefore, the total number of batteries in the battery pack is... The total number of switches in the switch array is See also Figure 1 The first battery unit includes a battery. , ... The second battery unit includes a battery. , ... The third battery unit includes a battery. , ... .

[0026] See also Figure 1 The rectifier conversion unit includes switching transistors. Switching transistor Switching transistor Switching transistor Switching transistor ,inductance Switching transistor Source and switch After the drain is connected, it is switched One end connected to the power grid, the switching transistor Source and switch The drain of the switch is connected to the other end of the power grid. Drain and switching transistor The drain is connected to the inductor. One end, inductor The other end is connected to the switching transistor After the drain is connected, it serves as the first port of the rectifier conversion unit and is connected to the switching transistor in the CLL-MRC converter. The drain of the switching transistor source and switch source and switch The source terminal is connected to serve as the second port of the rectifier-conversion unit, which is then connected to the switching transistor in the CLL-MRC converter. A capacitor is connected between the source terminal of the rectifier and the first port of the rectifier. .

[0027] The primary circuit includes the switching transistor. Switching transistor ,inductance ,capacitance Switching transistor The drain of the transistor is connected to the first port of the rectifier-conversion unit, and the switching transistor is connected to the first port of the rectifier-conversion unit. The sources are respectively connected to the switching transistors. drain, capacitor One end of the capacitor The other end is connected to the inductor. One end of the transformer resonant inductor The same name terminal, inductor The other end, transformer resonant inductor heteronym terminals and switching transistors After the source is connected, it is connected to the second port of the rectifier conversion unit. Here, in order to distinguish the three secondary circuits, the switching transistors, inductors and capacitors in each secondary circuit are labeled with different letters. In actual applications, the switching transistors, inductors and capacitors in each secondary circuit can be of the same type.

[0028] The first secondary circuit includes a switching transistor. Switching transistor ,inductance Transformer magnetizing inductance The same terminal and the transformer magnetizing inductor After connecting the different-named terminals, they are connected to the inductor. One end, inductor The other end serves as the first port of the first secondary circuit, and the transformer magnetizing inductance... The opposite terminal is connected to the switching transistor. The drain of the transformer magnetizing inductance The same terminal is connected to the switching transistor. The drain of the switching transistor Source and switch The source terminal is connected to the second port of the first secondary circuit, and a capacitor is connected between the first port and the second port of the first secondary circuit. .

[0029] The second secondary circuit includes a switching transistor. Switching transistor ,inductance Transformer magnetizing inductance The same terminal and the transformer magnetizing inductor After connecting the different-named terminals, they are connected to the inductor. One end, inductor The other end serves as the first port of the secondary circuit, the transformer magnetizing inductance. The opposite terminal is connected to the switching transistor. The drain of the transformer magnetizing inductance The same terminal is connected to the switching transistor. The drain of the switching transistor Source and switch The source terminal is connected to the second port of the secondary circuit, and a capacitor is connected between the first and second ports. .

[0030] The third secondary circuit includes a switching transistor. Switching transistor ,inductance Transformer magnetizing inductance The same terminal and the transformer magnetizing inductor After connecting the different-named terminals, they are connected to the inductor. One end, inductor The other end serves as the first port of the third secondary circuit, and the transformer magnetizing inductance... The opposite terminal is connected to the switching transistor. The drain of the transformer magnetizing inductance The same terminal is connected to the switching transistor. The drain of the switching transistor Source and switch The source terminal is connected to the second port of the third secondary circuit, and a capacitor is connected between the first port and the second port of the third secondary circuit. .

[0031] Example 2 The difference between this embodiment and Embodiment 1 is that this embodiment provides an active battery balancing method, using the active battery balancing circuit of Embodiment 1. When connected to the power grid, the microcontroller controls the switch array to select the unbalanced battery to the other end of the half-bridge LLC converter, and the unbalanced battery exchanges energy with the power grid; when not connected to the power grid, the microcontroller controls the switch array to select the unbalanced battery to the other end of the half-bridge LLC converter, and the unbalanced battery exchanges energy with the battery pack.

[0032] The energy exchange between unbalanced batteries and the power grid or battery pack includes the following scenarios: when the unbalanced battery is undervoltaged, the power grid or battery pack charges the unbalanced battery through a CLL-MRC converter; when the unbalanced battery is overvoltaged, the unbalanced battery discharges to the power grid or battery pack through a CLL-MRC converter. Even when not connected to the power grid and the unbalanced battery is only undervoltaged or overvoltaged, this invention can still achieve energy exchange between the abnormal individual cell and the entire battery pack using a CLL-MRC converter. For example, when a single cell is overvoltaged, the overvoltaged cell transfers excess energy to the entire battery pack; when a single cell is undervoltaged, the battery pack replenishes the undervoltaged cell, achieving balance through energy transfer between the individual cell and the entire pack.

[0033] When the battery pack contains both undervoltage and overvoltage batteries: When connected to the grid, the grid prioritizes charging the undervoltage batteries via a CLL-MRC converter, and then discharges the overvoltage batteries via the same converter; when not connected to the grid (switch...), ... (When disconnected), the overvoltage battery charges the undervoltage battery through the CLL-MRC converter. At this time, energy is transferred inside the battery pack, realizing the self-balancing of the battery pack.

[0034] In this embodiment, the battery pack is divided into three groups of battery cells, each of which includes... When a series of batteries are connected in series, there are several possible scenarios where the batteries become unbalanced: Scenario 1: Only one cell in each battery cell is unbalanced.

[0035] Scenario 2: Two or more cells in each battery cell are unbalanced.

[0036] Scenario 3: The number of battery cells in which only one cell is unbalanced is [number missing]. The number of battery cells in which two or more cells are unbalanced is: , .

[0037] For each of the above situations, the equilibrium process will be described below: Scenario 1: The microcontroller sorts the unbalanced batteries according to the difference between the state of charge (SBC) of each battery and the average SBC value, from largest to smallest. The microcontroller then sequentially turns on the switches at both ends of the unbalanced batteries through the drive circuit, selecting the unbalanced batteries to the input of the CLL-MRC converter in sequence. The input of the CLL-MRC converter can be regarded as the first and second ports of the secondary circuit, prioritizing the balancing of unbalanced batteries with larger differences.

[0038] Scenario 2: Treat all unbalanced cells in a battery cell as an unbalanced cell. The unbalanced cells in the unbalanced cell are connected in series. The microcontroller sorts the unbalanced cells according to the difference between the state of charge of the unbalanced cell and the average state of charge. The cells are sorted from largest to smallest difference. The microcontroller then turns on the switches at both ends of the unbalanced cells in order of sorting, prioritizing the unbalanced cells with larger differences for balancing.

[0039] Case 3: Case 3 can be seen as a special case of Case 2, in which there is only one unbalanced cell in one of the unbalanced cells, and the balancing process is the same as in Case 2.

[0040] Working principle: See Figures 2 to 7 The following section takes grid connection as an example, with the unbalanced battery being an undervoltage battery. It will introduce the balancing process for each battery cell with one unbalanced battery and for each battery cell with more than one unbalanced battery: When the battery in the first battery cell The battery in the second battery unit The battery in the third battery unit If the difference between the battery's state of charge (SOC) and the average SOC of the battery pack is greater than the set maximum balancing threshold or less than the set minimum balancing threshold, the battery... ,Battery ,Battery All three batteries are unbalanced (undervoltage) and require balancing. The half-bridge LLC converters corresponding to each of the three battery cells will operate in charging mode to charge the undervoltage batteries with energy from the grid. ,Battery ,Battery The process of transferring energy from the grid to the battery pack consists of two stages: the first stage involves the grid power being rectified into direct current and then subjected to power factor correction to improve the power factor; the second stage involves the equalization of the bus capacitors. The CLL-MRC converter sequentially supplies power to the battery. ,Battery ,Battery Transfer energy.

[0041] like Figures 2 to 7 As shown, in the first stage of energy transfer, the switching transistors are first... and switching transistor Closed, the power grid flows to the inductor Release energy and switch the tube. When the switch is turned on, current flows through the freewheeling circuit; secondly, the switching transistor... and switching transistor Close, switch transistor and switching transistor Open, power grid and inductor Energy is released to the equalizing bus capacitor. Power factor correction is completed. In the second stage of energy transfer, the bus capacitors are balanced. Energy is transferred to the battery pack via a CLL-MRC converter. The operation of this LLC half-bridge converter is the same for single and multi-cell batteries. In one switching cycle... The CLL-MRC converter contains 12 operating modes, and its operating modes in the upper and lower half-cycles are completely symmetrical. Therefore, only the six modes in the upper half-cycle will be analyzed here, and the other six modes will not be described in detail.

[0042] Figure 2 This represents the first operating mode of the CLL-MRC converter in an active battery balancing circuit within one switching cycle. (Switching transistor) When the transistor is turned off, the resonant current flowing in reverse begins to supply power to the switching transistor. Parasitic capacitance charging, switching transistor The voltage across the drain and source terminals begins to rise slowly; simultaneously, the switching transistor... Parasitic capacitance discharge, switching transistor The voltage across the drain and source terminals drops slowly. During this period, no energy is transferred to the secondary circuit, and the battery... From the output capacitor Provides energy, battery From the output capacitor Provides energy, batteries From the output capacitor Provides energy.

[0043] Figure 3 This represents the second operating mode of the CLL-MRC converter in an active battery balancing circuit within one switching cycle. (Switching transistor) The drain-source voltage is charged to the input voltage, and the switching transistor... The voltage across the terminals drops to zero, and the switching transistor... The conditions for ZVS activation have been met. During this period, the inductor... and capacitor Resonance occurs between them; while the inductor The voltage across the terminals is clamped to n times the output voltage and does not participate in resonance; the inductor... Current on The current increases linearly. However, numerically... The difference between the two currents, which is greater than the resonant current, is used as the primary input current of the transformer. Furthermore, because the primary input current of the transformer... The induced current flows in from the same-name terminal of the transformer, therefore the induced current on the secondary side of the transformer flows out from the same-name terminal in the middle of the center-tapped transformer, and flows through the switching transistor. The body diode is a capacitor. Energy is provided by the unbalanced battery. In the first secondary circuit, the induced current flows from the same-name terminal in the middle of the center-tapped transformer, through the switching transistor. The body diode is a capacitor. and unbalanced batteries Provides energy; in the second secondary circuit, the induced current flows out from the same-name terminal in the middle of the center-tapped transformer and flows through the switching transistor. The body diode is a capacitor. and unbalanced batteries Provides energy; in the third secondary circuit, the induced current flows out from the same-name terminal in the middle of the center-tapped transformer and flows through the switching transistor. The body diode is a capacitor. and unbalanced batteries Provides energy.

[0044] Figure 4 This is the third operating mode of the CLL-MRC converter in the active battery balancing circuit within one switching cycle. (Regarding the battery...) During balancing, the switching transistor and switching transistor Simultaneously activated. (Regarding the battery) During balancing, the switching transistor and switching transistor Simultaneously activated. (Regarding the battery) During balancing, the switching transistor and switching transistor Simultaneous activation. During this period, the resonant current and the excitation current remain in opposite directions (in this embodiment, the resonant current flows through the resonant inductor). , , , The alternating current, of which, and It is the primary resonant inductor of the isolated LLC branch. , , These are the resonant inductances of the three CLL-MRC equalization branches; the magnetizing current is the equivalent magnetizing inductance of the transformer. to The difference between the internal current and the excitation current (which only flows inside the transformer and is not transmitted to the secondary load) further increases, thus increasing the energy transferred to the secondary side. This affects the operating state of the resonant slot network. Figure 1 same.

[0045] Figure 5 This is the fourth operating mode of the CLL-MRC converter in the active battery balancing circuit within one switching cycle. Due to the inductance... Current on Still in the opposite direction, according to Kirchhoff's current law, the input current on the primary side of the transformer... This becomes the sum of the resonant current and the magnetizing current. Therefore, the energy transferred from the input voltage source to the secondary side continues to increase during this time period.

[0046] Figure 6 This is the fifth operating mode of the CLL-MRC converter in the active battery balancing circuit within one switching cycle. At this time, the resonant current is numerically greater than the magnetizing current, and the transformer primary input current... The difference between the two means that the energy transferred from the primary side to the secondary side gradually decreases during this time period.

[0047] Figure 7 This is the sixth operating mode of the CLL-MRC converter in the active battery balancing circuit within one switching cycle. Transformer primary input current. When the voltage drops to zero, energy no longer flows from the primary side to the secondary side. Simultaneously, the inductor... No longer subject to output voltage clamping, inductor and inductor ,capacitance Resonance occurs, inductor and inductor ,capacitance Resonance occurs, inductor and inductor ,capacitance Resonance occurs. Furthermore, current flows through the switching transistor. The current also drops to zero, and the switching transistor... Achieving ZCS turn-off. During this time period, the resonant current value remains approximately constant, and the capacitor... For unbalanced batteries Provides energy.

[0048]

[0049]

[0050] in, It is the modal resonant frequency, determined by... , , The resonant circuit is formed to obtain the corresponding sixth-mode resonant network; The main resonant frequency is determined by , Parallel equivalent inductance and The circuit calculation is the reference resonant frequency for the converter's frequency modulation range design.

[0051] When multiple batteries in the first, second, and third battery units experience undervoltage, see [reference needed]. Figure 8 and Figure 9 When the first battery cell, the second battery cell, and the third battery cell each have When a battery experiences undervoltage, the unbalanced cells in the first battery cell include the battery... ,Battery ,...,Battery The unbalanced cells in the second battery cell include batteries ,Battery ,...,Battery The unbalanced cells in the third battery cell include batteries ,Battery ,...,Battery At this time, in the first battery cell, the battery ,Battery ,...,Battery Together they form the first unbalanced unit, and in the second battery unit, the battery... ,Battery ,...,Battery Together they form the second unbalanced unit, and in the third battery unit, the battery... ,Battery ,...,Battery Together they form the third unbalanced unit. The equilibrium sorting method at this point is: calculate the values ​​in the first, second, and third unbalanced units respectively. The sum of the states of charge (SOCs) of each battery is used to sort the three SOCs from largest to smallest, for example, the first unbalanced cell, the second unbalanced cell, and the third unbalanced cell. The total state of charge of each battery is as follows: , , ,and Therefore, the microcontroller controls the switching transistors in the switch array through the drive circuit, first turning on the switching transistor connected to the first battery cell. , ... All other switches in the switch array are turned off to equalize the first unbalanced cell; then the switch connected to the second battery cell is turned on. , ... All other switches in the switch array are turned off to balance the second unbalanced unit; finally, the switch connected to the third battery unit is turned on. , ... All other switches in the switching array are turned off to balance the third unbalanced unit. During the balancing of each unbalanced unit, the CLL-MRC converter operates in a charging state to charge the undervoltage unbalanced unit with energy from the grid. The energy transfer from the grid to the unbalanced unit also consists of two stages: the first stage involves the grid power being rectified into DC and then undergoing power factor correction to improve the power factor; the second stage involves balancing the bus capacitance. Energy is transferred to the unbalanced cells in the unbalanced unit via a CLL-MRC converter.

[0052] like Figure 8 and Figure 9 As shown, the multi-cell balancing situation also includes 12 modes. Figure 1 , Figure 2 This is a complete mode diagram under the balanced operating condition of a single battery cell. Figure 8 , Figure 9 This demonstration uses two of the most representative modes from the first half of the 12-mode balancing process of multiple undervoltage cells to illustrate the principle of energy transfer from the bus capacitor. The core process of transferring data to multiple cells via CLL-MRC does not completely replicate the single-cell operating conditions. Figure 1 , Figure 2 The timing nodes. In the first stage of energy transfer, the switching transistors are first... and switching transistor Closed, the power grid flows to the inductor Release energy and switch the tube. When the switch is turned on, current flows through the freewheeling circuit; secondly, the switching transistor... and switching transistor Close, switch transistor and switching transistor Open, power grid and inductor Energy is released to the equalizing bus capacitor. Power factor correction is completed. In the second stage of energy transfer, the bus capacitors are balanced. Energy is transferred to the battery pack via a CLL-MRC converter. The operation of this LLC half-bridge converter is the same for both single and multi-cell batteries. Therefore, only the two modes of the first half-cycle will be introduced here.

[0053] The active battery balancing circuit proposed in this invention significantly improves the balancing efficiency of the entire balancing system, offering advantages such as simple structure, flexible control, easy expansion, and high efficiency. Furthermore, it enables the balancing current to operate in a continuously adjustable state, giving the invention superior rapid balancing performance for single or multiple batteries. This invention improves the integration and reliability of the balancing system, solving the problem of balancing long series-connected battery packs in a low-cost, small-volume manner.

[0054] This invention is mainly aimed at balancing individual battery cells in series; an entire parallel module can be used as a balancing unit, with the switching array selecting and participating in the balancing, thereby realizing energy regulation between parallel modules.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An active battery balancing circuit, characterized in that: include: The system comprises a microcontroller, a rectifier conversion unit, and a CLL-MRC converter. The CLL-MRC converter includes at least one half-bridge LLC converter. One end of the rectifier conversion unit is connected to the power grid, and the other end of the rectifier conversion unit is connected to one end of the half-bridge LLC converter. The other end of the half-bridge LLC converter is connected to the battery pack through a switch array. The microcontroller selects unbalanced batteries in the battery pack to the other end of the half-bridge LLC converter by controlling the switch array, thereby realizing the energy transfer between the unbalanced batteries and the power grid or the battery pack.

2. The active battery equalization circuit according to claim 1, characterized in that: The CLL-MRC converter includes a transformer, primary circuit, and... A secondary circuit, The battery pack includes Battery cells, Battery cells and Each secondary circuit corresponds to a primary circuit. Each battery cell group includes multiple batteries connected in series. The two ends of each battery are connected to the first and second ports of the secondary circuit through a switching transistor. The unbalanced batteries in each battery cell group transfer energy to the primary circuit through the corresponding secondary circuit.

3. The active battery equalization circuit according to claim 2, characterized in that: The primary circuit includes the switching transistor. Switching transistor ,inductance ,capacitance Each secondary circuit includes a switching transistor. Switching transistor ,inductance Switching transistor The drain of the transistor is connected to the first port of the rectifier-conversion unit, and the switching transistor is connected to the first port of the rectifier-conversion unit. The sources are respectively connected to the switching transistors. drain, capacitor One end of the capacitor The other end is connected to the inductor. One end of the transformer resonant inductor The same name terminal, inductor The other end, transformer resonant inductor heteronym terminals and switching transistors After the source is connected, it is connected to the second port of the rectifier conversion unit, and the transformer magnetizing inductor The same terminal and the transformer magnetizing inductor After connecting the different-named terminals, they are connected to the inductor. One end, inductor The other end serves as the first port of the secondary circuit, the transformer magnetizing inductance. The opposite terminal is connected to the switching transistor. The drain of the transformer magnetizing inductance The same terminal is connected to the switching transistor. The drain of the switching transistor Source and switch The source terminal is connected to the second port of the secondary circuit, and a capacitor is connected between the first and second ports. .

4. The active battery equalization circuit according to claim 1, characterized in that: The rectifier conversion unit includes switching transistors. To the switching transistor ,inductance Switching transistor Source and switch After the drain is connected, it is switched One end connected to the power grid, the switching transistor Source and switch The drain of the switch is connected to the other end of the power grid. Drain and switching transistor The drain is connected to the inductor. One end, inductor The other end is connected to the switching transistor The drain of the transistor is connected to the first port of the rectifier-conversion unit, and the switching transistor is used as the first port. source and switch source and switch The source terminal is connected to serve as the second port of the rectifier conversion unit, and a capacitor is connected between the first port and the second port. .

5. The active battery equalization circuit according to claim 1, characterized in that: The circuit also includes a battery management system, which collects the current and voltage of each battery and transmits the current and voltage of each battery to the microcontroller.

6. An active battery balancing method, employing the active battery balancing circuit according to any one of claims 1-5, characterized in that: When connected to the grid, the microcontroller controls the switch array to select the unbalanced battery to the other end of the half-bridge LLC converter, and the unbalanced battery exchanges energy with the grid; when not connected to the grid, the microcontroller controls the switch array to select the unbalanced battery to the other end of the half-bridge LLC converter, and the unbalanced battery exchanges energy with the battery pack.

7. The active battery balancing method according to claim 6, characterized in that: The microcontroller calculates the state of charge (SOC) of each battery and the average SOC of the battery pack based on the current and voltage of each battery. When there is only one unbalanced battery in each battery cell, the microcontroller sorts the unbalanced batteries according to the difference between the SOC of each battery and the average SOC, and turns on the switches at both ends of the unbalanced batteries in sequence according to the sorting. When there are at least two unbalanced batteries in a battery cell, all the unbalanced batteries in a battery cell are regarded as an unbalanced cell. The unbalanced batteries in the unbalanced cell are connected in series. The microcontroller sorts the unbalanced cells according to the difference between the SOC of the unbalanced cell and the average SOC, and turns on the switches at both ends of the unbalanced cell in sequence according to the sorting.

8. The active battery balancing method according to claim 6, characterized in that: When connected to the grid, the energy exchange process between the unbalanced battery and the grid within one switching cycle includes 12 modes. The six modes in the first half of the cycle are completely symmetrical with the six modes in the second half of the cycle. The six modes in the first half of the cycle include the first mode to the sixth mode in sequence. In the first mode, the secondary circuit and the unbalanced battery transfer energy. In the second mode, the grid transfers energy to the secondary circuit and the unbalanced battery respectively. In the third mode, the secondary circuit and the unbalanced battery transfer energy. In the fourth mode, the grid transfers energy to the secondary circuit and the unbalanced battery respectively. In the fifth mode, the secondary circuit and the unbalanced battery transfer energy. In the sixth mode, the grid transfers energy to the secondary circuit and the unbalanced battery respectively.

9. The active battery balancing method according to claim 7, characterized in that: When not connected to the power grid, if all unbalanced batteries or all unbalanced units are either undervoltage or overvoltage, the unbalanced batteries or unbalanced units exchange energy with this battery pack; if all unbalanced batteries or all unbalanced units contain both undervoltage and overvoltage, the unbalanced batteries with undervoltage exchange energy with the unbalanced batteries with overvoltage, and the unbalanced units with undervoltage exchange energy with the unbalanced units with overvoltage.

10. The active battery balancing method according to claim 6, characterized in that: All unbalanced batteries or all unbalanced cells simultaneously contain undervoltage and overvoltage. The power grid or battery pack first exchanges energy with the unbalanced batteries with undervoltage, and then exchanges energy with the unbalanced batteries with overvoltage.

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