Modular battery equalizer based on asymmetric duty ratio and phase shift combined modulation

Abstract

The invention is suitable for the technical field of battery equalization, and provides a modular battery equalizer based on asymmetric duty ratio and phase shift joint modulation, the modular battery equalizer comprises a module side multi-winding transformer and M battery equalization structures, and each battery equalization structure comprises a first inductor, a first capacitor, a first switch tube, a second switch tube, a second capacitor and a battery equalization module; one end of a winding in the module side multi-winding transformer is connected with a first end of a first inductor, the other end of the winding is connected with a first end of a first capacitor, and a second end of the first inductor is connected with a source electrode of a first switch tube and a drain electrode of a second switch tube. The drain electrode of the first switch tube is connected with the first end of the second capacitor and the first end of the battery equalization module. The source electrode of the second switch tube is connected with the second end of the first capacitor, the second end of the second capacitor and the second end of the battery equalization module. According to the invention, the equalization speed of the battery equalizer can be improved while devices are reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of battery balancing, and in particular, relates to a modular battery equalizer based on asymmetric duty cycle and phase shift joint modulation. Background Art

[0002] At present, lithium-ion batteries are widely used in energy storage systems and electric vehicles due to their advantages such as high power density, long cycle life, and low self-discharge rate. The terminal voltage of lithium-ion battery cells commonly used in life is limited. When used in large-capacity, high-voltage applications, it is often necessary to connect multiple battery cells in series and parallel to form a battery pack. However, the manufacturing process errors in the battery production process cause differences between battery cells. As the number of uses increases, the battery pack is repeatedly charged and discharged, and the energy mismatch problem gradually becomes prominent. If no balancing measures are taken, the differences between the series-connected battery cells in the battery pack will become larger and larger as the work progresses, and explosions or fires may occur. The use of battery equalizers is beneficial to alleviate the energy imbalance problem between battery cells, so as to extend the application life of the series battery pack.

[0003] Typically, battery balancers are classified into two methods: dissipative and non-dissipative. Dissipative methods use dissipative components, such as resistors, to convert excess energy in high-voltage batteries into heat for heat dissipation. The mismatched energy in this method is wasted, reducing the available capacity of the battery pack. In addition, the excess heat generated may accelerate the aging of nearby batteries. Non-dissipative methods transfer the mismatched energy in high-voltage batteries to low-voltage batteries, and they enable more efficient and rapid energy balancing. Based on the balancing mode, non-dissipative methods can be divided into five categories: adjacent cell-to-cell (AC2C), direct cell-to-cell (DC2C), cell-to-cell pack (C2P), pack-to-cell (P2C), and any cell-to-any cell (AC2AC). In the first four methods, energy is only transferred between individual cells. When the balancer balances the target cell, other cells need to wait for balancing, resulting in a slower balancing speed when all cells need to be balanced. Compared with the other four methods, the AC2AC type battery balancer has a more flexible energy transfer path and a faster balancing speed.

[0004] AC2AC battery equalizers are divided into two categories: inductor-based and DC-DC converter-based. In order to reduce the number of passive components and provide the possibility of soft switching, some scholars have proposed an equalizer based on a multi-winding transformer. The balancing current of this traditional AC2AC battery equalizer depends on the voltage difference between the batteries. As the voltage balancing progresses, the voltage difference gradually decreases, and the balancing current also decreases accordingly, resulting in a slow balancing speed. In order to achieve a faster balancing speed, some scholars have proposed a fast equalizer whose balancing current is not limited by the voltage difference. In the topology of this equalizer, each battery requires two corresponding switching tubes and a low-frequency passive component (inductor). Voltage balancing between any batteries can be achieved through phase shift modulation. And the balancing current is independent of the battery voltage difference, so it will not decrease as the voltage balancing progresses, thereby increasing the balancing speed. The disadvantage of this equalizer is that it requires a large number of switching devices and passive components, and the cost is high. Summary of the invention

[0005] The embodiment of the present application provides a modular battery equalizer based on asymmetric duty cycle and phase shift joint modulation, which can solve the problem that the battery equalizer requires many components and has a slow equalization speed.

[0006] The embodiment of the present application provides a modular battery balancer based on asymmetric duty cycle and phase shift joint modulation, including a module-side multi-winding transformer and M battery balancing structures, the battery balancing structure including a first inductor, a first capacitor, a first switch tube, a second switch tube, a second capacitor and a battery balancing module;

[0007] Among them, one end of a winding in the module-side multi-winding transformer is connected to the first end of the first inductor, the other end of the winding is connected to the first end of the first capacitor, the second end of the first inductor is respectively connected to the source of the first switch tube and the drain of the second switch tube, the drain of the first switch tube is respectively connected to the first end of the second capacitor and the first end of the battery balancing module, and the source of the second switch tube is respectively connected to the second end of the first capacitor, the second end of the second capacitor and the second end of the battery balancing module;

[0008] The switch tubes in the battery balancing module are modulated based on asymmetric duty cycle and phase shift.

[0009] Optionally, the battery balancing module includes a battery-side multi-winding transformer and N / 2 battery modules, the battery module includes a second inductor, a third switch tube, a fourth switch tube, a first battery and a second battery connected in series, one end of a winding in the battery-side multi-winding transformer is connected to the first end of the second inductor, the other end of the winding is respectively connected to the source of the third switch tube and the drain of the fourth switch tube, the second end of the second inductor is respectively connected to the negative electrode of the first battery and the positive electrode of the second battery, the drain of the third switch tube is connected to the positive electrode of the first battery, and the source of the fourth switch tube is connected to the negative electrode of the second battery;

[0010] The positive electrode of the first battery of the first battery module among the N / 2 battery modules is connected to the first end of the second capacitor in the battery balancing structure to which the battery balancing module belongs, and the negative electrode of the second battery of the N / 2th battery module among the N / 2 battery modules is connected to the second end of the first capacitor in the battery balancing structure to which the battery balancing module belongs;

[0011] The positive electrode of the first battery of the first battery module in the Mth battery balancing structure is connected to the negative electrode of the second battery of the Nth battery module in the M-1th battery balancing structure, where M is an integer greater than or equal to 2.

[0012] Optionally, the balancing among the M battery balancing structures is achieved by controlling the first switch tube and the second switch tube in each battery balancing structure.

[0013] Optionally, the balancing in the battery balancing structure is achieved by controlling the third switch tube and the fourth switch tube in each battery module.

[0014] Optionally, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are all MOSFET transistors.

[0015] Optionally, when N is 4, the battery balancing module is equivalent to a DAB converter.

[0016] Optionally, when N is an integer greater than 4, the battery balancing module is equivalent to a MAB converter.

[0017] The above solution of the present application has the following beneficial effects:

[0018] In the embodiment of the present application, the battery equalizer realizes battery pack balancing through modular design by M battery balancing structures, which greatly reduces the amount of calculation and control complexity when only a single multi-winding transformer is used to connect the battery pack, and each additional battery balancing structure only requires the corresponding addition of two switch tubes and inductors. Compared with the traditional fast equalizer, the modular battery equalizer of the present application requires fewer devices, achieving a more compact size and low cost. In addition, a more flexible balancing path is provided through the internal balancing of the battery balancing structure and the balancing between the battery balancing structures, thereby improving the balancing speed of the battery equalizer.

[0019] Other beneficial effects of the present application will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A schematic diagram of the structure of a modular battery equalizer based on asymmetric duty cycle and phase shift joint modulation provided in an embodiment of the present application;

[0022] Figure 2 A topological diagram of a modular battery equalizer provided in one embodiment of the present application;

[0023] Figure 3 A structural diagram of an internal equalizer of a battery equalization structure provided in an embodiment of the present application;

[0024] Figure 4 A waveform diagram of an equalizer containing four batteries provided in an embodiment of the present application;

[0025] Figure 5 A working mode diagram of internal balancing of a battery balancing structure provided in an embodiment of the present application;

[0026] Figure 6 A disassembled diagram of the working principle of a battery module provided in one embodiment of the present application;

[0027] Figure 7 A schematic diagram of a balancing strategy within a battery balancing structure provided in an embodiment of the present application;

[0028] Figure 8 A working mode diagram of balancing between battery balancing structures provided in one embodiment of the present application;

[0029] Fig. 9 A working state diagram of balancing between battery balancing structures provided in an embodiment of the present application;

[0030] Fig.10 N is a simulation experiment dc =N c Equilibrium diagram at ;

[0031] Fig.11 N is a simulation experiment dc >N c Equilibrium diagram at ;

[0032] Fig.12 N is a simulation experiment dc <N c Equilibrium status diagram. DETAILED DESCRIPTION

[0033] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0034] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.

[0035] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0036] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.

[0037] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0038] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0039] In view of the problem that the current battery equalizer requires many components and has a slow balancing speed, the embodiment of the present application provides a modular battery equalizer based on asymmetric duty cycle and phase shift joint modulation. The battery equalizer realizes battery pack balancing through modular design and M battery balancing structures, which greatly reduces the amount of calculation and control complexity when only a single multi-winding transformer is used to connect the battery pack. Moreover, each additional battery balancing structure only requires two switches and inductors to be added accordingly. Compared with the traditional fast equalizer, the modular battery equalizer of the present application requires fewer components, achieving a more compact size and low cost. In addition, a more flexible balancing path is provided through internal balancing of the battery balancing structure and balancing between battery balancing structures, thereby improving the balancing speed of the battery equalizer.

[0040] The modular battery equalizer based on asymmetric duty cycle and phase shift joint modulation provided by the present application is exemplarily described below in conjunction with specific embodiments.

[0041] like Figure 1 to Figure 2 As shown, the modular battery balancer based on asymmetric duty cycle and phase shift joint modulation provided in the embodiment of the present application includes a module-side multi-winding transformer and M battery balancing structures, and the specific structures of each battery balancing structure are the same.

[0042] Specifically, the battery balancing structure includes a first inductor, a first capacitor, a first switch tube, a second switch tube, a second capacitor and a battery balancing module. Among them, one end of a winding in the multi-winding transformer on the module side is connected to the first end of the first inductor, the other end of the winding is connected to the first end of the first capacitor, the second end of the first inductor is respectively connected to the source of the first switch tube and the drain of the second switch tube, the drain of the first switch tube is respectively connected to the first end of the second capacitor and the first end of the battery balancing module, and the source of the second switch tube is respectively connected to the second end of the first capacitor, the second end of the second capacitor and the second end of the battery balancing module.

[0043] like Figure 1 to Figure 2 As shown, the module-side multi-winding transformer includes M windings (i.e. Figure 1The windings T1, T2, ..., T M ), each winding corresponds to a battery balancing structure. Specifically, the battery balancing structure corresponding to winding T1 (ie, the first battery balancing structure) is composed of a first inductor L1, a first capacitor C 12 , the first switch tube S 1A , the second switch tube S 1B , the second capacitor C 11 and battery balancing module ( Figure 1 The battery balancing structure corresponding to the winding T2 (i.e., the second battery balancing structure) is composed of the first inductor L2, the first capacitor C 22 , the first switch tube S 2A , the second switch tube S 2B , the second capacitor C 21 and battery balancing module ( Figure 1 The module 2) in the winding T M The corresponding battery balancing structure (i.e., the Mth battery balancing structure) is composed of the first inductor L M , the first capacitor C M2 , the first switch tube S MA , the second switch tube S MB , the second capacitor C M1 and battery balancing module ( Figure 1 It is composed of module M).

[0044] In some embodiments of the present application, Figure 2 As shown, the battery balancing module includes a battery-side multi-winding transformer and N / 2 battery modules, and the specific structures of each battery module are the same.

[0045] Specifically, the battery module includes a second inductor, a third switching tube, a fourth switching tube, a first battery and a second battery connected in series, one end of a winding in a multi-winding transformer on the battery side is connected to the first end of the second inductor, the other end of the winding is respectively connected to the source of the third switching tube and the drain of the fourth switching tube, the second end of the second inductor is respectively connected to the negative electrode of the first battery and the positive electrode of the second battery, the drain of the third switching tube is connected to the positive electrode of the first battery, and the source of the fourth switching tube is connected to the negative electrode of the second battery.

[0046] The positive electrode of the first battery of the first battery module among the N / 2 battery modules is connected to the first end of the second capacitor in the battery balancing structure to which the battery balancing module (referring to the battery balancing module to which the N / 2 battery modules belong) belongs, and the negative electrode of the second battery of the N / 2th battery module among the N / 2 battery modules is connected to the second end of the first capacitor in the battery balancing structure to which the battery balancing module (referring to the battery balancing module to which the N / 2 battery modules belong) belongs.

[0047] The positive electrode of the first battery of the first battery module in the Mth battery balancing structure is connected to the negative electrode of the second battery of the Nth battery module in the M-1th battery balancing structure, where M is an integer greater than or equal to 2.

[0048] like Figure 2 As shown, the battery side multi-winding transformer N / 2 windings (i.e. Figure 2 The winding T 11 , T 12 ,…,T 1N / 2 ). Specifically, winding T 11 The corresponding battery module (i.e., the first battery module) is connected by the second inductor L 11 , the third switch tube S 11 , the fourth switch tube S 12 , the first battery B connected in series 11 and the second battery B 12 Composition, winding T 12 The corresponding battery module (i.e., the second battery module) is connected by the second inductor L 12 , the third switch tube S 13 , the fourth switch tube S 14 , the first battery B connected in series 13 and the second battery B 14 Composition, winding T 1N / 2 The corresponding battery module (i.e., the N / 2th battery module) is connected by the second inductor L 1N / 2 , the third switch tube S 1N-1 , the fourth switch tube S 1N , the first battery B connected in series 1N-1 and the second battery B 1N constitute.

[0049] like Figure 2 As shown, the battery side multi-winding transformer N / 2 windings (i.e. Figure 2 The winding T M1 , T M2 ,…,T MN / 2 ). Specifically, winding T M1 The corresponding battery module (i.e., the first battery module) is connected by the second inductor L M1 , the third switch tube S M1 , the fourth switch tube S M2 , the first battery B connected in series M1 and the second battery B M2 Composition, winding T M2 The corresponding battery module (i.e., the second battery module) is connected by the second inductor L M2 , the third switch tube S M3 , the fourth switch tube S M4, the first battery B connected in series M3 and the second battery B M4 Composition, winding T MN / 2 The corresponding battery module (i.e., the N / 2th battery module) is connected by the second inductor L MN / 2 , the third switch tube S MN-1 , the fourth switch tube S MN , the first battery B connected in series MN-1 and the second battery B MN It is understandable that, since the specific structures of the battery balancing structures are the same, Figure 2 Only part of the battery balancing structure is shown.

[0050] It should be noted that the battery pack to be balanced in the embodiment of the present application includes M*N batteries, which are divided into M battery balancing structures. Each battery balancing structure only requires 2 additional power switch tubes (i.e., the first switch tube and the second switch tube) to achieve modularization. Each battery balancing structure contains N batteries, N power switches (i.e., the third switch tube and the fourth switch tube in the N / 2 battery modules), N / 2 inductors and a multi-winding transformer. Compared with the traditional fast equalizer, the device achieves a more compact size and low cost.

[0051] At the same time, since the balancing current and transmission power of the modular battery balancer are controllable, fast and accurate AC2AC balancing can be achieved, which is suitable for fast balancing of long series battery packs.

[0052] In practical applications, the balancing between the M battery balancing structures is achieved by controlling the first switch tube and the second switch tube in each battery balancing structure, and the balancing within the battery balancing structure is achieved by controlling the third switch tube and the fourth switch tube in each battery module. Among them, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube can all be MOSFET transistors. When N is 4, the battery balancing module is equivalent to a DAB converter. When N is an integer greater than 4, the battery balancing module is equivalent to a MAB converter.

[0053] In some embodiments of the present application, the switch tube in the above-mentioned battery balancing module is modulated based on asymmetric duty cycle and phase shift, so as to maintain the stability of the balancing current by adjusting the duty cycle and phase shift angle, thereby achieving faster balancing.

[0054] The control process of the modular battery equalizer is exemplarily described below.

[0055] The balancing between the battery balancing structures is achieved by controlling the first switch tube and the second switch tube in each battery balancing structure. It should be noted that the control method of the switch tubes in each battery balancing structure is the same. 1A , the second switch tube S1B As an example, the control process is exemplarily described. Specifically, the first switch tube S 1A , the second switch tube S 1B The control process is as follows: In one cycle T, the complementary symmetrical PWM drive signal controls S 1A First conduction 50% cycle, S 1B Shut down; then switch to S 1B On 50% cycle, S 1A It can be understood that the control is achieved by inputting a PWM drive signal to the corresponding switch tube.

[0056] The balancing in the battery balancing structure is achieved by controlling the third switch tube and the fourth switch tube in each battery module in the battery balancing structure. It should be noted that the control method of the switch tubes in each battery module is the same. Here, the third switch tube S in the first battery module of the first battery balancing structure is used. 11 , the fourth switch tube S 12 As an example, the control process is exemplified. Specifically, the third switch tube S 11 , the fourth switch tube S 12 The control process is as follows: according to the voltage of the two batteries and the given balancing current, the duty cycle D1 is determined. In a cycle T, the time period from 0 to D1T, the PWM drive signal is used to control S 11 On, S 12 Shutdown; D1T~T period, control S through PWM drive signal 11 Shutdown, S 12 It can be understood that the control is achieved by inputting a PWM drive signal to the corresponding switch tube. V1 is the first battery B in the battery module 11 The voltage of the second battery B in the battery module is V2. 12 The voltage of the winding is R, which is the equivalent line resistance of the winding in actual work. L1 is a given balancing current.

[0057] The working principle of the modular battery equalizer of the present application is exemplarily described below in conjunction with specific embodiments.

[0058] For ease of understanding, here we take 4 batteries as an example to analyze the internal balanced mode of the battery balancing structure. The analysis method is the same for other 4-battery cases. When four batteries are balanced, two half-bridge structures consisting of two batteries can be equivalent to a DAB converter, such as Figure 3 (a). Before the analysis, the following assumptions are made: 1. V n (n=1,2,3,4) is battery B nThe initial voltage of the battery, and it satisfies the conditions of V1>V2>V3>V4; 2. L ki , L m and R i They are the leakage inductance, magnetizing inductance and equivalent resistance of the multi-winding transformer, n E is the original-to-secondary turns ratio, ideally 1; 3, G sn It is switch S n The driving signal of G s1 duty cycle to drive switches S1 and S2, D2 is G s3 The duty cycle of switches S3 and S4 is used to drive switches S3 and S4. It's G s1 and G s3 The angle between the center lines of g1 is the current flowing inside half-bridge structure 1 (B1 and B2), i g2 L is the current flowing inside half-bridge structure 2 (B3 and B4). k1 is the sum of the external inductance L1 and the leakage inductance of the connected winding, L k2 It is the sum of the external inductance L2 and the leakage inductance of the connected winding.

[0059] According to the operation of the switch tube, the internal equalizer of the module (i.e., the battery balancing structure) can be divided into four working states, and its waveform is as follows: Figure 4 As shown, the working status is as follows Figure 5 As shown:

[0060] Working state 1: During [t0-t1], S1 and S4 are turned on. Current i g1 It increases linearly due to positive voltage, i g2 Due to the negative voltage, it decreases linearly, and the expression is shown in formula (1). The working state is as follows Figure 5 (a) shown.

[0061]

[0062] Working state 2: During [t1-t2], S1 and S3 are turned on. Current i g1 It increases linearly due to positive voltage, i g2 Due to the negative voltage, it decreases linearly, and the expression is shown in formula (2). The working state is as follows Figure 5 (b) as shown.

[0063] Working state 3: During [t2-t3], S2 and S3 are turned on. Current i g1 It decreases linearly due to negative voltage, i g2 Due to the positive voltage, it increases linearly, and the expression is shown in formula (3). The working state is shown in the figure Figure 5 (c) as shown.

[0064] Working state 4: During [t3-t4], S2 and S4 are turned on. Current i g1 It decreases linearly due to positive voltage, i g2 Due to the positive voltage, it increases linearly, and the expression is shown in formula (4). The working state is shown in the figure Figure 5 (d) as shown.

[0065] Since the battery has capacitance characteristics in long-term operation, the following formula can be obtained from equations (1)-(4) and the ampere-second characteristic:

[0066]

[0067]

[0068] Among them I D3 is the balancing current of the third battery, A=V1+V2, B=V3+V4, C=V2-V4, F=V1+V4, G=2πf s (L k1 +L k2 ), H = 8π 2 f s (L k1 +L k2 ), the balancing current of the remaining batteries can be obtained in the same way, f s is the designed switching frequency, is the offset between the duty cycle center lines of the two switching tubes that control the opening and closing of the half-bridge structure, such as Figure 4 As indicated in the markings.

[0069] When the number of cells in the balancer is greater than four, multiple half-bridge structures can be equivalent to a MAB converter, such as Figure 3 As shown in (b), according to the existing literature (RW De Doncker, DM Divan and MH Heraluwala, "A three-phase soft-switched high power density DC / DC converter for high power applications," IEEE Trans. Ind. Appl., vol. 27, no. 1, pp. 63–73, Jan.-Feb. 1991.), each half-bridge structure can be equivalent to a voltage source connected to an inductor (such as Figure 3 (c)). In order to analyze the transmission power between ports, only two ports i and j are selected for analysis. At this time, the ΔMAB equivalent power flow model (as shown in Figure 3 (d)), the equivalent inductance between the two ports (L ij) and the current flowing through the leakage inductance are shown as follows:

[0070]

[0071] Among them, L ij is the equivalent inductance between port i and port j, i i is the total current at port i, i ij is the current flowing from port i to port j. N / 2-1 is the total current of port N / 2-1, L kN / 2-1 is the equivalent inductance of port N / 2-1, V N / 2-1 ′ is the equivalent voltage source of port N / 2-1, i N / 2 is the total current of port N / 2, L kN / 2 is the equivalent inductance of port N / 2, V N / 2 ′ is the equivalent voltage source of port N / 2, i1 is the total current of port 1, L k1 is the equivalent inductance of port 1, V1′ is the equivalent voltage source of port 1, i2 is the total current of port 2, L k2 is the equivalent inductance of port 2, V2′ is the equivalent voltage source of port 2, L m is the magnetizing inductance; i i is the total current at port i, V i ′ is the equivalent voltage source of port i, i i1 is the current flowing from port i to port 1, L i1 is the equivalent inductance between port i and port 1, i i(N / 2) is the current flowing from port i to port N / 2, L i(N / 2) is the equivalent inductance between port i and port N / 2, i ij is the current flowing from port i to port j, L ij is the equivalent inductance between port i and port j, i j is the total current at port j, V j ′ is the equivalent voltage source at port j, i j1 is the current flowing from port j to port 1, L j1 is the equivalent inductance between port j and port 1, i j(N / 2) is the current flowing from port j to port N / 2, L j(N / 2) is the equivalent inductance between port j and port N / 2.

[0072] The following uses four batteries as an example to explain the working principle of internal balancing of the battery balancing structure:

[0073] 1. When the target battery (i.e. the battery to be balanced) is in a group (i.e. in a battery module) (B1 and B2 are the target batteries, such as Figure 6 (a), or B3 and B4 are target batteries (such as Figure 6 (b) shows that energy balance can be achieved through the Buck-Boost converter structure consisting of two batteries and an excitation inductor. There is no energy transfer between the two groups, that is, the phase shift angle is 0°. Through the modal analysis of the two switches in the Buck-Boost converter, it can be found that the half-bridge structure 1 (i.e. Figure 6 (a) shows the structure) and the duty cycle D1 of the half-bridge structure 2 (i.e. Figure 6 The duty cycle D2 of the structure shown in (b) can be automatically adjusted according to the voltage of the two batteries:

[0074]

[0075] The magnetizing inductance of the transformer is significantly higher than the leakage inductance, so the leakage inductance can be ignored. In equation (9), I L1 and I L2 are the average currents flowing through the excitation inductances in the half-bridge structure 1 and the half-bridge structure 2 respectively, and R is the equivalent line resistance of the winding in actual work.

[0076] 2. When the target battery (i.e. the battery to be balanced) is located in different groups (i.e. not in the same battery module, B1 and B4 are located in group 1 and group 2 respectively, such as Figure 6 (c)), the DAB converter composed of two batteries works to achieve energy balance. The energy transfer current of the DAB converter is shown in equation (6).

[0077] When the number of batteries is greater than or equal to six, the balancing of the batteries within the group is the same as the above analysis, and the balancing between groups must be combined with the current formula (8) in the MAB converter.

[0078] The following is an explanation of the balancing strategy within the battery balancing structure.

[0079] From the above analysis, we can see that the realization of battery voltage balancing is divided into two parts: intra-group balancing and inter-group balancing. Therefore, the battery current can also be divided into two parts:

[0080]

[0081] Among them, I Bn is the balancing current flowing through each battery (i.e., I Bx ,I By ), which can be set according to the maximum charge and discharge current of the battery (it can be less than the maximum charge and discharge current), and is a known number during calculation; I kn is the internal current of the half-bridge structure i, reflecting the energy transfer of the Buck-Boost structure and is only affected by the duty cycle; I Dn It is the current on the leakage inductance, reflecting the energy transfer in the DAB converter, which is determined by the phase shift angle and the duty cycle.

[0082] This application adopts the balancing method of "balancing the batteries with the largest and smallest terminal voltages, and leaving the other batteries idle". The balancing process is as follows Figure 7 As shown, where N c 、N dc 、N s are the number of batteries charged, discharged and at rest, respectively, I charging is the charging current, I discharging is the discharge current, I is the balancing current given in the DSP control program, which can be adjusted according to actual conditions, and D n is the duty cycle of the half-bridge structure n, is the phase shift angle between half-bridge structure i and half-bridge structure j, N is the number of batteries in the entire battery string (i.e., battery pack), E n is the terminal voltage of the nth battery. The half-bridge structure i and the half-bridge structure j are two different half-bridge structures among the multiple half-bridge structures.

[0083] The equilibrium strategy can be expanded into the following steps:

[0084] 1. Determine the charge and discharge current based on the number of batteries to be charged and discharged. First, calculate the average voltage of multiple batteries, and define the batteries that exceed the average voltage as high-voltage batteries, that is, batteries that must be discharged; and define the batteries that are less than the average voltage as low-voltage batteries, that is, batteries that must be charged. The discharge current of the battery with a higher voltage and the charging current of the battery with a lower voltage are as follows:

[0085]

[0086] 2. Any two adjacent batteries can form a Buck-Boost converter through switches and a common winding. By generalizing equation (9), the duty cycle calculation formula can be obtained as follows:

[0087]

[0088] Where x and y are the odd and even cells in group i, respectively. Li is the average current flowing through the magnetizing inductor in the Buck-Boost converter.

[0089] 3. Based on the transmission current distribution of the battery, the transmission current between each two battery groups can be determined. Combining the duty cycle obtained in the above formula and the known battery voltage, the phase shift angle can be determined through formulas (6) and (8).

[0090] The following is an explanation of the balancing between battery balancing structures.

[0091] The balance between modules (i.e., battery balancing structure) is based on the switch S 1A and S 1BThe action can also be divided into four stages. Its analysis is similar to the working principle of the internal equalizer of the above module. The working states are as follows: Figure 8 As shown. Figure 8 As shown in (a), in working state 1, the module with a higher total voltage (i.e., the battery balancing module) stores energy in the inductor; Figure 8 As shown in (b), in working state 2, the high voltage module (i.e., the battery balancing module) continues to charge the inductor, and the inductor discharges to the low voltage module (i.e., the battery balancing module); Figure 8 As shown in (c), in working state 3, the inductor continues to discharge to the low voltage module (i.e., the battery balancing module); Figure 8 As shown in (d), in working state 4, the energy in the inductor circulates between the switch tubes, thereby realizing the charging process of the module with higher total voltage to the module with lower total voltage.

[0092] Taking a balancer containing 8 batteries (divided into 2 modules (i.e., battery balancing structure), each module has 4 batteries) as an example, combined with the working principles of the above-mentioned module internal balancer and inter-module balancer, the balancing process is as follows: Fig. 9 As shown. First, the module (i.e., battery balancing structure) is balanced internally. The buck-boost converter is used to realize the energy transmission within the group, and the DAB converter is used to realize the energy transmission between groups. The two realize the balance within the module. At the same time, the energy transmission from the high-voltage module to the low-voltage module is realized through the inter-module balancer. In this balancing method, the balance within the group, the balance between the groups, and the balance between the modules occur simultaneously, providing a flexible balance path and achieving a faster balance speed.

[0093] The simulation results of the internal balance of the battery balance structure using 4 batteries as an example are as follows: Figures 10 to 12 As shown, Fig.10 , 11 , 12 respectively show N dc =N c 、N dc >N c 、N dc <N c The balancing status and the balancing current changes of each battery are shown in Figure 1. As the balancing process proceeds, the voltage difference between the batteries gradually decreases, and finally the battery balancing is achieved. The balancing results of four batteries prove the effectiveness of the battery balancer. Figures 10 to 12 In the graph, the horizontal axis is time, the vertical axis is battery voltage, B1 is the voltage change curve of the first battery, B2 is the voltage change curve of the second battery, B3 is the voltage change curve of the third battery, and B4 is the voltage change curve of the fourth battery. av is the average voltage of the four batteries, which is the final balanced voltage expected to be achieved.

[0094] In summary, the modular battery equalizer of the present application has the following advantages:

[0095] 1. By jointly modulating the asymmetric duty cycle and the phase shift angle, the battery balancing current is controllable, thereby ensuring that as the balancing process proceeds, the voltage difference decreases, but the balancing current remains unchanged. That is, compared with the traditional AC2AC equalizer, the equalizer proposed in this application can maintain the stability of the balancing current under different voltage difference conditions by adjusting the duty cycle and the phase shift angle, thereby achieving faster balancing.

[0096] Second, a more flexible balancing path is provided through internal balancing of modules and balancing between modules, achieving a higher balancing speed.

[0097] 3. The equalizer is modularly designed to greatly reduce the amount of calculation and control complexity when connecting a battery pack with only a single multi-winding transformer. Each additional module only requires the addition of two power switches and inductors, which reduces the cost of multi-module operation and is more suitable for long series battery packs.

[0098] 4. Multiple working modes: According to actual needs, the charging and discharging mode of any battery to any battery can be realized, and the transmission path is flexible.

[0099] The above is a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles described in the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A modular battery equalizer based on asymmetric duty cycle and phase shift joint modulation, characterized in that: It includes a module-side multi-winding transformer and M battery balancing structures, wherein the battery balancing structure includes a first inductor, a first capacitor, a first switch tube, a second switch tube, a second capacitor and a battery balancing module; One end of a winding in the module-side multi-winding transformer is connected to the first end of the first inductor, the other end of the winding is connected to the first end of the first capacitor, the second end of the first inductor is respectively connected to the source of the first switch tube and the drain of the second switch tube, the drain of the first switch tube is respectively connected to the first end of the second capacitor and the first end of the battery balancing module, and the source of the second switch tube is respectively connected to the second end of the first capacitor, the second end of the second capacitor and the second end of the battery balancing module; The switch tube in the battery balancing module is modulated based on asymmetric duty cycle and phase shift.

2. The modular battery equalizer according to claim 1, characterized in that: The battery balancing module includes a battery-side multi-winding transformer and N / 2 battery modules, wherein the battery module includes a second inductor, a third switch tube, a fourth switch tube, a first battery and a second battery connected in series, one end of a winding in the battery-side multi-winding transformer is connected to the first end of the second inductor, the other end of the winding is respectively connected to the source of the third switch tube and the drain of the fourth switch tube, the second end of the second inductor is respectively connected to the negative electrode of the first battery and the positive electrode of the second battery, the drain of the third switch tube is connected to the positive electrode of the first battery, and the source of the fourth switch tube is connected to the negative electrode of the second battery; The positive electrode of the first battery of the first battery module among the N / 2 battery modules is connected to the first end of the second capacitor in the battery balancing structure to which the battery balancing module belongs, and the negative electrode of the second battery of the N / 2th battery module among the N / 2 battery modules is connected to the second end of the first capacitor in the battery balancing structure to which the battery balancing module belongs; The positive electrode of the first battery of the first battery module in the Mth battery balancing structure is connected to the negative electrode of the second battery of the Nth battery module in the M-1th battery balancing structure, where M is an integer greater than or equal to 2.

3. The modular battery equalizer according to claim 1, characterized in that: The balancing among the M battery balancing structures is achieved by controlling the first switch tube and the second switch tube in each battery balancing structure.

4. The modular battery equalizer according to claim 2, characterized in that: The balancing in the battery balancing structure is achieved by controlling the third switch tube and the fourth switch tube in each battery module.

5. The modular battery equalizer according to claim 2, characterized in that: The first switch tube, the second switch tube, the third switch tube and the fourth switch tube are all MOSFET transistors.

6. The modular battery equalizer according to claim 2, characterized in that: When N is 4, the battery balancing module is equivalent to a DAB converter.

7. The modular battery equalizer according to claim 2, characterized in that: When N is an integer greater than 4, the battery balancing module is equivalent to a MAB converter.

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