A single receiving coil battery balancing control system based on wireless power feedback and its control method

Abstract

The present invention discloses a single-receiving coil battery balancing control system based on wireless power feedback and its control method. The system can feed back the energy stored in the main circuit inductance to the battery side through wireless transmission without affecting the wired output voltage of the system itself, so that all single cells can reuse the same receiving coil / winding in a time-sharing manner, reducing the number of system coils, saving costs and avoiding the cross-coupling problem existing in multiple receiving coils. Under the condition that the cyclic balancing period remains unchanged, the dual control variable balancing method can make the period T of the connection between the i-th series single cell and the receiving coil i The duty cycle D of the switch during the period i Both can change dynamically according to the SOC difference between cells; in addition, after achieving battery balancing, wireless feedback can be automatically stopped, further improving the overall working efficiency of the system.

Description

Technical Field

[0001] The present invention belongs to the field of battery balancing control, and more specifically, relates to a single-receiving coil battery balancing control system based on wireless power feedback that can be used synchronously in charging and discharging states and a control method thereof. Background Art

[0002] Battery energy storage systems, as a crucial component of renewable energy power generation systems, play a key role in achieving energy balance and stable supply. Lithium-ion battery energy storage systems, due to their long lifespan and high energy density, are widely used in new energy vehicles and household appliances. Typically, lithium-ion batteries are connected in series and parallel to meet required voltage and current requirements. However, during actual discharge, due to parameter errors during lithium battery production, battery aging during operation, and varying operating temperatures, it is difficult for lithium batteries in a system to achieve uniform charge and discharge rates. Over time, the state of charge (SOC) of each lithium battery can deviate. Battery systems with unbalanced SOC are prone to overcharge and overdischarge, causing irreversible damage to the batteries, shortening their lifespan, and even causing spontaneous combustion or explosion. To address the overcharge and overdischarge issues caused by unbalanced battery SOC, cell balancing technology has emerged and is rapidly developing. Balancing technology can effectively reduce SOC variations between individual cells in an energy storage system, improving overall system performance and safety.

[0003] The primary goal of cell balancing is to control the battery's SOC and ensure that excess energy is effectively consumed or transferred. Generally, cell balancing methods can be categorized as passive and active. Passive methods use additional resistors to convert excess energy into heat and dissipate it. However, this method is inefficient and can cause system overheating. Unlike passive methods, active methods utilize energy storage elements such as inductors and capacitors to transfer excess energy, achieving higher efficiency. Depending on the energy storage circuit used, active balancing methods can be categorized as switched capacitor, switched inductor, DC-DC converter, transformer, and wireless transmission. While switched capacitor, switched inductor, and DC-DC converter balancing methods have simple operating principles, they often require a large number of switches and complex control methods. In contrast, transformer balancing, due to its inherent isolation and reduced number of switches, has become the mainstream active balancing method.

[0004] However, the presence of the iron core in the transformer not only increases the volume of the system, but also brings hidden dangers such as overheating, oversaturation and short circuit. The emerging wireless transmission type balancing method abandons the transformer core, achieving a smaller volume while achieving higher safety. Patent [1] collects the signals of each battery to control the working mode of the wireless charging circuit connected to the battery, and realizes efficient wireless charging based on the resonance of the coil frequency. Reference [2] proposes a wireless transmission type balancing method with a single transmitting coil and multiple receiving coils. When an external AC power supply is connected to the transmitting coil battery system for charging, no additional control is required. The energy received by each single battery on the receiving side is inversely proportional to its terminal voltage, thereby realizing battery balancing based on terminal voltage. Reference [3] proposes a multi-receiving winding balancing method based on voltage multiplier (VM). The battery string is divided into multiple modules, and each receiving winding charges a module through VM. At the same time, the energy obtained by different receiving windings is also inversely proportional to the voltage of the battery module to which it is connected. Compared with reference [2], fewer receiving windings can be used while realizing the battery.

[0005] Patent [4] switches between the charging mode and the balancing mode of the system through the control of the battery balancing module based on the external AC power supply. The charging mode of the system is to charge the entire battery string, while the balancing mode is to achieve battery balancing by selectively charging one or more batteries with smaller SOC in the battery string. Similarly, document [5], based on the four-switch Buck-Boost converter, transmits the electric energy of different powers output by the converter through the inverter, SS compensation circuit, rectifier and switch array circuit respectively to achieve battery balancing during the battery string charging process. Patent [6] combines the wireless balancing circuit with the inductor-based inductor circuit, uses the inverter circuit to transmit the energy provided by the external DC power supply to the battery string side through a wireless transmission method, and switches the working mode of the wireless charging device according to the status of the battery string.

[0006] References [2], [3] adopted a wireless transmission method using a single transmitting coil and multiple receiving coils, and demonstrated that the energy obtained by a single battery is inversely proportional to its terminal voltage, thus achieving battery balancing based on the battery terminal voltage. However, multiple receiving coils on the receiving side not only occupy a large space and increase the cost of the system, but also have the problem of cross-coupling between the receiving coils [7], [8]. In addition, during coil production, different coils will inevitably have parameter differences, which will affect the final balancing effect in the automatic balancing of multiple receiving winding batteries.

[0007] References [1], [5], and [6] use an external DC source or the battery's own energy to first convert DC into AC through an inverter circuit, and then transmit it to the battery side through a wireless transmission method and a rectifier to perform battery balancing. However, the energy inversion process not only complicates the control method, but the inevitable energy loss during the inversion process also causes a decrease in system efficiency. Similarly, references [2], [3], and [4] rely on an external AC power source and use the AC power source to charge the battery.

[0008] Due to the reliance on external DC or AC sources, the literature [2-5] can only achieve battery balancing during the charging process. Although the literature [1] and [6] can still work in a balanced state, the problem of battery over-discharge during the discharge process cannot be solved well. Therefore, achieving battery balancing during both the charging and discharging processes is an urgent problem to be solved.

[0009] In summary, the current method still has two obvious shortcomings:

[0010] First, most wireless balancing methods can only achieve battery balancing during the charging process. Charging and balancing cannot be performed simultaneously, and they require an external AC or DC power source. This reliance on an external power source limits their applicability and prevents overdischarge issues that may occur during battery discharge.

[0011] Second, many existing wireless transmission-based balancing methods utilize multiple receiving coils. This not only takes up a lot of space but also increases system costs. Furthermore, cross-coupling issues and parameter differences between multiple receiving coils can affect battery balancing.

[0012] References:

[0013] [1] He Zenglong, Bu Xiaoyu, Zheng Zhiyuan, et al., CN103199587A, Method and system for realizing active balancing of new energy vehicle batteries using wireless charging[P]. 2015.

[0014] [2]LIU M,FU M,WANG Y,et al.Battery Cell Equalization via MegahertzMultiple-Receiver Wireless Power Transfer[J].IEEE Transactions on PowerElectronics,2018,33(5):4135-4144.DOI:10.1109 / TPEL.2017.2713407.

[0015] [3]ZHANG P, YU

[0016] [4] Liu Jin, Xu Bin, Liu Lizhou, et al., CN 112421716A, A battery pack balancing control circuit and method based on wireless charger[P]. 2021.

[0017] [5] Jiang Tao. Design of wireless charging and balancing system for series lithium-ion battery packs[D]. Nanjing University of Science and Technology, 2024.

[0018] [6] Huang Linlu, CN 114221452A, A wireless charging device for electric vehicles with battery energy balancing function and its control method [P]. 2022.

[0019] [7]HE

[0020] [8]ZHU C,YU J,GU Y,et al.Analysis and Design of Cost-Effective WPTSystems With Dual Independently Regulatable Outputs for Automatic GuidedVehicles[J].IEEE Transactions on Power Electronics,2021,36(6):6183-6187.DOI:10.1109 / TPEL.2020.3036353.

[0021] Therefore, it is necessary to design a wireless balancing type battery balancing control system and control method using a single transmitting coil and a single receiving coil, which can achieve faster battery balancing during both charging and discharging processes while avoiding the cross-coupling problem existing in the multi-receiving coil balancing method. Summary of the Invention

[0022] (1) Technical issues to be resolved

[0023] Based on the defects mentioned in the above background technology, the present invention discloses a single receiving coil battery balancing control system based on wireless power feedback and its control method. The system can feed back the energy stored in the main circuit inductance to the battery side through wireless transmission without affecting the wired output voltage of the system itself, so that all single cells can reuse the same receiving coil / winding in a time-sharing manner, reducing the number of system coils, saving costs and avoiding the cross-coupling problem existing in multiple receiving coils. In addition, under the condition that the cyclic balancing period remains unchanged, the control method can make the period T of the connection between the i-th single cell and the receiving coil i The duty cycle D of the switch during the period i Both can change dynamically according to the SOC difference between cells; after achieving battery balancing, wireless feedback can automatically stop, further improving the overall working efficiency of the system.

[0024] (2) Technical solution

[0025] The present invention discloses a single receiving coil battery balancing control system based on wireless power feedback. In the original synchronous BUCK converter, the other parts of the circuit are used as the input end of the synchronous BUCK converter, and the battery string is used as the load of the output end of the synchronous BUCK circuit. The two MOS tubes S in the synchronous BUCK converter are connected to the MOSFET. H and S L At the same time, open and close, S H For the original high-voltage side MOS tube, S L To replace the low-voltage side MOS tube of the original diode, and S H and S L They are all MOS tubes with anti-parallel diodes. The battery string consists of n single cells Cell1~Cell n Connect in series in sequence, and the filter inductor L in the synchronous BUCK converter t Replaced with a transmitting coil of the same impedance, the wireless receiving circuit includes an inductor L rThe receiving coil and the uncontrolled rectifier bridge composed of diodes VD1 to VD4 can couple the transmitting coil with the receiving coil for wireless energy transmission. The positive poles of diodes VD3 and VD4 are connected, and the negative poles of VD3 and VD4 are connected to the positive poles of diodes VD2 and VD1 respectively. Finally, the negative poles of VD2 and VD1 are connected together. One end of the receiving coil is connected to the negative pole of VD3, and the other end is connected to the negative pole of VD4.

[0026] 2n connected switches S1~S 2n Used to select specific single cells Cell1~Cell n Connected to the uncontrolled rectifier bridge, for each single cell i , i takes the value of 1 to n, and the switch S is turned on 2i-1 The negative electrode of the battery is connected to the i The positive pole of the switch S 2i Positive electrode and single cell i Connect the negative pole of the switch S 2i-1 With S 2i Share the same driver P i , all even-numbered cells are connected to switch S 2i The negative poles of the batteries are connected together and connected to the positive poles of VD3 and VD4 in the uncontrolled rectifier bridge; all odd-numbered single batteries are connected to switch S 2i-1 The positive poles are connected together and connected to the negative poles of VD1 and VD2 in the uncontrolled rectifier bridge.

[0027] Furthermore, it also includes a balancing switch S F , all odd-numbered cells are connected to switch S 2i-1 The positive poles are connected together with the equalizing switch S F The negative pole of the balancing switch S F The positive pole is connected to the negative pole of VD1 and VD2 in the rectifier bridge.

[0028] Furthermore, it also includes a filter capacitor C L and filter capacitor C H , filter capacitor C H The two ends of the filter capacitor C are connected in parallel with the other ends of the circuit. L The two ends of the battery string are connected in parallel.

[0029] In another aspect, the present invention further discloses a control method for the above-mentioned single-receiving coil battery balancing control system based on wireless power feedback, the control method comprising the following cyclically executed constant current-constant voltage battery string charging method:

[0030] Step 1: Charge the battery string with a constant current, maintaining the set battery string charging current reference value I pack_ref ;

[0031] Step 2: Determine the battery string voltage V pack ≥ Maximum voltage of battery string V pack_max Is it true? If so, go to step 3; if not, go to step 1;

[0032] Step 3: Charge the battery string at a constant voltage to maintain the set battery string charging voltage reference value V pack_ref ;

[0033] Step 4: Determine the battery string current I pack ≥Minimum battery string current I pack_min Is it true? If so, go to step 3; if not, go to step 5;

[0034] Step 5: Stop constant voltage charging of the battery string, and end the battery string charging process.

[0035] Furthermore, the control method includes the following wireless receiving circuit time division multiplexing method:

[0036] Set a fixed cycle period T0, which contains n access times T1 to T n and n dead time T d , access time T i Represents the corresponding single cell Cell i The time of connecting to the wireless receiving circuit in a cycle period T0 is the time of connecting to the wireless receiving circuit. i The corresponding single battery is connected to the switch S 2i-1 and S 2i Conducting, the single cell Cell i When connected to the balancing circuit, different connection time periods do not overlap with each other, that is, at most only one single cell is connected to the balancing circuit at the same time. After each connection time period, a dead zone time T is entered in which all single cell switches are turned off. d , except for n dead time T d The effective cycle period of balanced switch conduction within the cycle period is defined as T valid , as shown in formula (6);

[0037] T valid =T0-nT d (6)

[0038] In a complete cycle, each single battery will be connected to the wireless receiving circuit in turn at the corresponding access time until the next cycle, when the first battery is connected to the wireless receiving circuit again for the next cycle.

[0039] Furthermore, the time for each single battery to access the wireless receiving circuit is adjusted by the access time controller. In the access time controller, the SOC of each single battery is compared with the average SOC value of the battery string. The average SOC value of the battery string is defined as formula (7);

[0040]

[0041] Then, the i-th single cell Cell i SOC value SOC i With SOC ave The error is fed into the periodic PI link, G period (s) and G period (z) represents the continuous periodic PI link and the discrete periodic PI link respectively; the discrete periodic PI link is shown in formula (8);

[0042]

[0043] where K P_period and K I_period are all parameters in the discrete periodic PI link, β i Represents the access time coefficient of the i-th single cell, β i The calculation is shown in formula (9);

[0044] β i =1+(SOC ave -SOC i )×G period (z) (9)

[0045] Finally, the access time of each single battery in the battery string is T1~T n As shown in formula (10);

[0046]

[0047] From formula (10), it is easy to obtain that within a cycle period T0, the on-time of each single battery satisfies (11), and the cycle period T0 can remain constant throughout the entire balancing process;

[0048] T0=T1+T2+…+T n +nT d (11)

[0049] By driving each P i The corresponding access time is T1~T nThe lower the SOC of a single battery, the longer it is connected to the wireless receiving circuit in one cycle, thereby obtaining more feedback energy in the same time. After the battery is balanced, the time that all single batteries are connected to the wireless receiving circuit in one cycle is the same and equal to T valid / n.

[0050] Furthermore, the control method also includes the following balanced switch duty cycle control method:

[0051] In the balancing switch S F In the duty cycle controller, the SOC of each single battery is equal to the maximum SOC of the battery string. max In comparison, SOC max Defined as formula (12)

[0052] SOC max =max(SOC1…SOC n ) (12)

[0053] The SOC and SOC of each single battery max The error between them is fed into the duty cycle PI link, G max (s) and G max (z) represent the continuous controller and discrete controller of the duty cycle PI link respectively. The discrete duty cycle PI link is shown in formula (13);

[0054]

[0055] where K P_max and K I_max These are all parameters in the discrete duty cycle PI link. Through PI control, the duty cycle coefficients α1~α of each single cell are obtained. n ; For the i-th single cell, its duty cycle coefficient α i The calculation is shown in formula (14);

[0056] α i =(SOC max -SOC i )×G max (z) (14)

[0057] Finally, for the i-th single cell, the balancing switch S F Duty cycle D i As shown in formula (15);

[0058] D i =D×α i (15)

[0059] Where D is the reference duty cycle set by the system. The larger the reference duty cycle D is, the smaller the duty cycle coefficient α1~α n , the greater the difference between the duty cycles at different access times ultimately generated by the duty cycle controller will be.

[0060] (3) Beneficial effects

[0061] 1. During the charging and discharging process of the synchronous BUCK converter, the present invention utilizes the current ripple on the inductor and the current ripple on the switches S1 to S2. 2n By using wireless feedback as a battery balancing energy source, the traditional wireless balancing method eliminates the dependence of the external AC source, and at the same time realizes battery balancing during the charging and discharging process. It has wide applicability, and the boost and buck functions of the converter of the present invention are not affected by the battery balancing process based on wireless power feedback, that is, there is independence between the wired output of charging and discharging and the wireless feedback.

[0062] 2. The present invention uses a single receiving coil, which reduces the system footprint while avoiding the cross-coupling problem existing in traditional multi-receiving coil battery balancing systems;

[0063] 3. The present invention also controls the connection time of each battery to the balancing circuit and the duty cycle of the balancing switch during the connection time period. The dual-control variable balancing method adopted greatly shortens the time required for balancing. Through the balancing switch duty cycle controller, wireless feedback is automatically stopped after battery balancing is achieved, further improving system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the technical solutions of the present invention or the prior art, the following briefly introduces the drawings required for the embodiments:

[0065] Figure 1 This is a system structure diagram of a single-receiving coil battery balancing control system based on wireless power feedback in the present invention;

[0066] Figure 2 The inductor L flows through the converter during the charging process of the present invention. t Schematic diagram of the waveform of the current and its AC component;

[0067] Figure 3 The present invention proposes a T-type equivalent circuit diagram of wireless feedback for a wireless power feedback battery balancing system;

[0068] Figure 4 This is the current flow diagram of the system when cell 1 is connected to the balancing circuit during the battery string discharge process, where the switch S in Figure a is L In Figure b, switch S is turned on. L Shutdown;

[0069] Figure 5 This is a flow chart of the constant current-constant voltage battery string charging strategy adopted by the present invention;

[0070] Figure 6 The current flow of the system when cell 1 is connected to the balancing circuit during the battery string charging process, where the switch S in Figure a is H In Figure b, switch S is turned on. H Shutdown;

[0071] Figure 7 The present invention is based on the Figure 1 The structural block diagram of the access time controller in the proposed time-division multiplexing equalization system;

[0072] Figure 8 The present invention is based on the Figure 1 The proposed balancing switch S F The structural block diagram of the duty cycle controller;

[0073] Figure 9 Schematic diagram of the connection time of each single battery and the duty cycle of the balancing switch in an embodiment of the present invention. DETAILED DESCRIPTION

[0074] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0075] The single receiving coil battery balancing system of the present invention is used to achieve balancing of multiple series-connected batteries. Figure 1 As shown in the figure, the rest of the circuit is the input end of the synchronous buck converter, the battery string is the load of the synchronous buck circuit output end, the two MOS tubes in the synchronous buck converter are turned on and off at the same time (ignoring the dead zone), and both MOS tubes are MOS tubes with anti-parallel diodes. First, the battery string consists of n single cells Cell1~Cell n During the battery charging and discharging process, due to parameter errors of lithium batteries, battery aging and different operating temperatures, the charge and discharge rates of each single cell cannot be kept completely consistent. In the long run, each single cell in the battery string will have different SOC. The battery string generally uses a DC-DC converter to complete the charging and discharging operation. Figure 1 In the circuit shown, there are n single cells Cell1~Cell nThe battery string can be charged at a reduced voltage by a synchronous buck converter, or it can be discharged at a increased voltage by a synchronous buck converter.

[0076] The synchronous buck converter includes a switch S H , switch S L , energy storage inductor L t , filter capacitor C L and filter capacitor C H , switch S H and switch S L When a MOS tube with an anti-parallel diode is used, and the MOS tube is preferably an NMOS tube, its drain is regarded as the positive electrode of the switch, and the source is regarded as the negative electrode of the switch, and the switch S H and switch S L The driving signals of the switches S are complementary and at the same time H and switch S L Only one switch can be turned on. Switch S H and switch S L The driving signals are P H and P L , its duty cycle D H and D L The relationship is shown in formula (1).

[0077] D H =1-D L (1)

[0078] Based on the above converter, the present invention makes appropriate improvements to it so that it can achieve battery balancing based on wireless power feedback. t The transmitting coil with the same impedance is used as the transmitting end of wireless power transmission to transmit electrical energy. In order to feed the energy transmitted by the transmitting coil back to the battery side to achieve battery balance, the present invention also adds a time-division multiplexing wireless receiving circuit. The wireless receiving circuit includes an inductor L r The receiving coil is composed of an uncontrolled rectifier bridge composed of diodes VD1~VD4, and the receiving coil L r With the transmitting coil L t The coupling coefficient between them is k. The positive poles of diodes VD3 and VD4 are connected, and the negative poles of VD3 and VD4 are connected to the positive poles of diodes VD2 and VD1 respectively. Finally, the negative poles of VD2 and VD1 are connected together to form an uncontrolled rectifier bridge. One end of the receiving coil is connected to the negative pole of VD3, that is, the positive pole of VD2; the other end is connected to the negative pole of VD4, that is, the positive pole of VD1. The switches S1 to S 2n Used to select a specific single cell battery to connect to the rectifier bridge.

[0079] In order to realize the time-division multiplexing of the equalization circuit, the present invention also adds an access selection circuit. The selection circuit for accessing the wireless receiving circuit includes an equalization switch S F Connect switches S1 to S1 and the single battery 2n , turn on switches S1~S 2n Preferably, NMOS tube, with the i-th single cell Cell i For example, i ranges from 1 to n, and the switch S 2i-1 The negative electrode (ie the source of the NMOS tube) is connected to the single cell Cell i The positive pole of the switch S 2i The positive electrode (ie the drain of the NMOS tube) and the single cell Cell i The negative pole of the switch S 2i-1 With S 2i Share the same driver P i , all even-numbered cells are connected to switch S 2i The negative poles of the batteries are connected together and connected to the positive poles of VD3 and VD4 in the rectifier bridge; all odd-numbered single batteries are connected to switch S 2i-1 The positive poles of the equalizing switch S F The negative pole is connected, and the final balancing switch S F The positive pole is connected to the negative pole of VD1 and VD2 in the rectifier bridge.

[0080] Next, the present invention will prove that the boost and buck functions of the converter are not affected by the battery balancing process based on wireless power feedback. Figure 1 When the other parts of the circuit shown in the figure are used as loads, the system works in the discharge state, that is, the battery string as the main energy storage system is discharged. At this time, the synchronous BUCK converter works as a boost converter. When the switch S L When turned on, the switch S H When the converter is turned off, the inductor L t The current i L_t Switch S L Short circuit, the inductor current increases; when the switch S L When turned off, the switch S H When conducting, the current cannot flow from S H The source of the reverse flow to the drain, at this time the inductor L in the converter t The current i L_t By switching S H The anti-parallel diode supplies power to the external load, and the inductor current decreases. At this time, by adjusting the switch S L Duty cycle D L , the required load voltage can be output to achieve constant voltage discharge.

[0081] Similarly, when Figure 1When the other parts of the circuit are high voltage DC power supplies, the system works in the charging state, that is, the other parts of the circuit charge the battery string. At this time, the synchronous BUCK converter works as a buck converter. When the switch S H When it is on, the switch S L When the converter is turned off, the inductor L t The current i L_t Rising; when switch S H When turned off, the switch S L When the converter is turned on, the inductor L t The current i L_t By switching S L The anti-parallel diode continues to flow, and the inductor current decreases. Therefore, regardless of the charging and discharging process, the inductor current i L_t Can be regarded as a DC component I dc With an AC component i ripple Taking the charging process as an example, the inductor current i L_t Indicated as attached Figure 2 As shown in formula (2).

[0082] i L_t =I dc +i ripple (2)

[0083] When the system is in charging state, switch S H Whether the inductor current rises or falls is determined by whether the switch S L Only the anti-parallel diode works. H When it is turned on, the current flowing through the inductor L t The current i L_t Rising, when S H When shutting down, due to the freewheeling process current i L_t Similarly, during the discharge process, only the switch S L Whether the inductor is on or off determines whether the inductor current rises or falls. L When it is turned on, the current flowing through the inductor L t The current i L_t Rising, when S L When shutting down, due to the freewheeling process current i L_t During wireless feedback, the transmitting coil Tx is connected to the DC-DC converter, while the receiving coil Rx is connected to the single battery through the wireless receiving circuit. t With the receiving coil L r , L t and L r The mutual inductance can be expressed as M, as shown in formula (3).

[0084]

[0085] The two mutually coupled inductors can be equivalent to a T-type circuit, such as Figure 3 As shown. Due to the characteristics of inductance that passes DC and blocks AC, the equivalent inductance will L_t The DC component I dc Short-circuited, so only the AC component i ripple It is wirelessly transmitted to the receiving side, so the wireless power feedback of the system is independent of the DC part of the inductor current.

[0086] At the same time, when the circuit is in steady state, the AC component i ripple It is always equal to 0 in one cycle. When the battery string is charging, the relationship between the current and voltage of other parts of the circuit in the system and the current and voltage of the battery string is shown in formula (4).

[0087]

[0088] When the battery string is discharging, the relationship between the current and voltage of other parts of the circuit in the system and the current and voltage of the battery string is shown in formula (5).

[0089]

[0090] It is easy to obtain that the current and voltage at both ends of the converter are only related to the switch S in the converter. H and switch S L The duty cycle of the driving signal is related to the AC component i with an average value of 0 in steady state. ripple It does not affect the wired output of the converter. However, it should be noted that the adjustment of the duty cycle will not only affect the wired input and output of the converter, but also affect the inductor L t The current i L_t The current ripple in the inductor is i L_t The AC component i ripple Therefore, we can respectively H and switch S L The switching frequency is adjusted to offset this effect, and the adjustment of the switching frequency will not affect the input and output of the converter.

[0091] The present invention will now specifically describe battery balancing during the discharge and charging processes.

[0092] When the system is in the discharge state, Figure 1 The rest of the circuit is specifically represented as the load. As shown in formula (5), during the discharge process, the output voltage is only related to the switch S L Duty cycle D L Through the closed-loop controller, D LThe discharge voltage requirement can be met by controlling the battery string. Taking a battery string composed of three single cells as an example, when cell 1 is connected to the balancing circuit during the discharge process of the battery string, the switch S L The current flow during turn-on and turn-off is shown in the following figure. Figure 4 The orange line represents the current flow of the converter, the blue line represents the current flow of the balancing circuit, and the gray line indicates that no current flows.

[0093] When the system is in charging state, Figure 1 The other parts of the circuit are specifically represented as a high-voltage DC power supply. According to formula (4), during the charging process, the voltage applied to the battery string by the DC-DC converter and the current flowing through the battery string are only related to the switch S H Duty cycle D H Taking a battery string consisting of three single cells as an example, when cell 1 is connected to the balancing circuit during the battery string charging process, the switch S H The current flow during turn-on and turn-off is shown in the following figure. Figure 6 The orange line represents the current flow of the converter, the blue line represents the current flow of the balancing circuit, and the gray line indicates that no current flows.

[0094] It is worth mentioning that because the current direction under the two working conditions of charge and discharge is inconsistent with the normal voltage drop conduction direction of the corresponding MOS tube, in order to ensure the freewheeling current, Figure 4 and Figure 6 Middle switch S H and switch S L An anti-parallel diode is necessary.

[0095] In addition, the present invention also adopts a constant current-constant voltage battery string charging strategy to extend the life of the battery pack. Figure 5 First, the battery string performs constant current charging on the battery, by pack The closed-loop control maintains the constant charging current of the battery string and controls the current battery string voltage V pack Make a judgment, if the battery string voltage V pack Less than the maximum voltage of the battery string V pack_max , then continue to execute the constant current charging strategy; if the battery string voltage V pack Greater than or equal to the maximum battery string voltage V pack_max , then the battery starts to be charged at constant voltage. During the constant voltage charging process, by pack The closed-loop control maintains the constant charging voltage of the battery string and controls the charging current I pack To judge, if the battery string charging current I pack Greater than or equal to the minimum battery string charging current I pack_min, then continue to execute the constant voltage charging strategy; if the battery string charging current I pack Less than the minimum battery string charging current I pack_min , then stop constant voltage charging of the battery and end the battery charging process.

[0096] Figure 5 The constant current-constant voltage battery string charging method in can be described as the following cyclic execution steps 1-5:

[0097] Step 1: Charge the battery string with a constant current, maintaining the set battery string charging current reference value I pack_ref ;

[0098] Step 2: Determine the battery string voltage V pack ≥ Maximum voltage of battery string V pack_max Is it true? If so, go to step 3; if not, go to step 1;

[0099] Step 3: Charge the battery string at a constant voltage to maintain the set battery string charging voltage reference value V pack_ref ;

[0100] Step 4: Determine the battery string current I pack ≥Minimum battery string current I pack_min Is it true? If so, go to step 3; if not, go to step 5;

[0101] Step 5: Stop constant voltage charging of the battery string, and end the battery string charging process.

[0102] Due to the independence between wired output and wireless feedback, the constant current charging strategy and constant voltage charging strategy do not affect the battery balancing algorithm and current flow based on wireless power feedback.

[0103] The present invention describes the current flow when Cell1 is connected to the circuit balancing circuit in the discharge and charge states. However, in order to achieve individual and overall balancing of each single cell in the battery string, all cells need to be connected to the balancing circuit in sequence, and the battery balancing is finally achieved by controlling the energy obtained during the balancing process. On this basis, the present invention intends to adopt a method of time-division multiplexing of wireless receiving circuits. The present invention sets a fixed cycle period T0, which includes n access times T1 to T2 in one cycle period. n and n dead time T d Access time T i Represents the corresponding single cell Cell i The time of connecting to the wireless receiving circuit in a cycle period T0 is the time of connecting to the wireless receiving circuit. i The corresponding single battery is connected to the switch S 2i-1 and S 2i Conducting, the single cell Celli Connect to the balancing circuit. Different connection time periods do not overlap with each other, that is, at most only one single battery can be connected to the balancing circuit at the same time.

[0104] In order to further ensure the decoupling of the balancing process of different single cells and prevent the delay of the switch action from causing any two cells to be in the balancing state at the same time, after each access time period, a dead time T is entered in which all the single cell switches are closed. d Therefore, removing n dead time T d The effective cycle period of balanced switch conduction within the cycle period can be defined as T valid , as shown in formula (6).

[0105] T valid =T0-nT d (6)

[0106] During a complete cycle, each battery cell is connected to the wireless receiving circuit in sequence at a corresponding connection time. Until the next cycle, the first battery cell is connected to the wireless receiving circuit again and the next cycle begins.

[0107] See also Figure 7 As shown, the time for each single battery to access the wireless receiving circuit is adjusted by the access time controller. In the access time controller, the SOC of each single battery is compared with the average SOC value of the battery string. The average SOC value of the battery string is defined as formula (7).

[0108]

[0109] Then, the i-th single cell Cell i SOC value SOC i With SOC ave The error is fed into the periodic PI link, G period (s) and G period (z) represents the continuous periodic PI link and the discrete periodic PI link respectively. Taking the discrete periodic PI link as an example, as shown in formula (8).

[0110]

[0111] where K P_period and K I_period are all parameters in the discrete periodic PI link, β i Represents the access time coefficient of the i-th single cell, β i It can be calculated as shown in formula (9).

[0112] β i =1+(SOC ave -SOCi )×G period (z) (9)

[0113] Finally, the access time of each single battery in the battery string is T1~T n As shown in formula (10).

[0114]

[0115] From formula (10), it is easy to obtain that within a cycle period T0, the connection time of each single battery satisfies (11), and the cycle period T0 can remain constant throughout the entire balancing process.

[0116] T0=T1+T2+…+T n +nT d (11)

[0117] By driving each P i The corresponding access time is T1~T n The lower the SOC, the longer the battery is connected to the wireless receiving circuit in a cycle, thus obtaining more feedback energy in the same time. After the battery is balanced, the time all the batteries are connected to the wireless receiving circuit in a cycle is the same and equal to T valid / n.

[0118] Considering that only controlling the access time cannot automatically stop wireless feedback after the battery is balanced, and the existence of wireless feedback will inevitably consume energy and reduce the charging and discharging efficiency of the system. In order to further improve the overall efficiency of the system and increase the balancing speed of the battery string, the present invention Figure 1 Based on the balanced switch S F The duty cycle controller and with Figure 7 The access time controller constitutes a dual control variable balancing control. When different single cells are connected to the wireless receiving circuit, the balancing switch S F Switching different duty cycles to achieve faster equalization speed and higher efficiency, such as the attached Figure 8 shown.

[0119] In the balancing switch S F In the duty cycle controller, the SOC of each single battery is equal to the maximum SOC of the battery string. max In comparison, SOC max Defined as formula (12)

[0120] SOC max =max(SOC1…SOC n ) (12)

[0121] The SOC and SOC of each single battery max The error between them is fed into the duty cycle PI link, G max (s) and G max (z) represent the continuous controller and discrete controller of the duty cycle PI link respectively. Taking the discrete duty cycle PI link as an example, as shown in formula (13).

[0122]

[0123] where K P_max and K I_max These are all parameters in the discrete duty cycle PI link. Through PI control, the duty cycle coefficients α1 to α n ; For the i-th single cell, its duty cycle coefficient α i It can be calculated as shown in formula (14).

[0124] α i =(SOC max -SOC i )×G max (z) (14)

[0125] Finally, for the i-th single cell, the balancing switch S F Duty cycle D i As shown in formula (15).

[0126] D i =D×α i (15)

[0127] Where D is the reference duty cycle set by the system. The larger the reference duty cycle D is, the smaller the duty cycle coefficient α1~α n , the difference between the duty cycles in different access times ultimately generated by the duty cycle controller will also be greater, thereby further accelerating the balancing speed.

[0128] From formula (14), if a single battery has the maximum SOC value, that is, its SOC value is equal to SOC max If the SOC of each battery cell is equal to the SOC of the battery string, the duty cycle of the balancing switch is also 0 during the access period of the battery cell connected to the balancing circuit. The battery cell does not have any energy feedback during the balancing process. As the balancing process progresses, the SOC values ​​of each battery cell in the battery string are approximately equal and equal to the SOC maxThis means that the duty cycle of all cells is zero, and the balancing switch remains off throughout the cycle. No energy is fed back to the power supply via wireless transmission, automatically stopping the balancing process. This automatic cessation of the balancing process eliminates energy loss during wireless feedback, further improving system efficiency.

[0129] In order to further explain the working principle of the system, Figure 9 A schematic diagram of the access time of each single battery and the duty cycle of the balancing switch is given, where T0 represents a cycle, T1~T n Represent cell1~cell n Access time, T d Indicates the dead time after the access time period ends, D1~D n Respectively represent cell1~cell n The duty cycle of the balanced switch during the access time, T f Represents the balancing switch S F The switching frequency of cell1, cell2 and cell n The respective SOC values ​​satisfy: SOC max >SOC n >SOC2>SOC1.

[0130] According to the SOC value of each single cell, the balancing system controls the corresponding access time of the single cell and the duty cycle of the balancing switch during the access time. The greater the SOC of the single cell, the shorter the corresponding access time will be, and the smaller the duty cycle of the balancing switch during the access time will be. Figure 7-8 The proposed dual control variable balancing method can significantly improve the balancing speed of the system and balance the switch S F The design of the duty cycle controller reduces system losses and further improves system efficiency.

[0131] In summary, compared with the existing technology, the characteristics and innovations of the present invention are:

[0132] 1. The current ripple on the inductor during the charging and discharging process of the converter is fed back to the power supply side through wireless transmission technology, which is used as the energy source for battery balancing, and the battery balancing control during the charging and discharging process is achieved at the same time.

[0133] 2. A single-coil battery balancing system based on time-sharing multiplexing is proposed. Multiple single batteries are connected to the receiving coil at different times, avoiding the cross-coupling problem existing in the multi-receiving coil battery balancing system.

[0134] 3. During the balancing process, not only is the corresponding access time of each single cell controlled based on its SOC, but the duty cycle of the balancing switch is also adjusted according to the SOC of different single cells when they are connected. The dual-control variable balancing method adopted significantly improves the balancing speed of the system.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A single receiving coil battery balancing control system based on wireless power feedback, characterized in that: In the original synchronous BUCK converter, the rest of the circuit is used as the input end of the synchronous BUCK converter, and the battery string is used as the load at the output end of the synchronous BUCK circuit. The two MOS tubes S in the synchronous BUCK converter are H and S L At the same time, open and close, S H For the original high-voltage side MOS tube, S L To replace the low-voltage side MOS tube of the original diode, and S H and S L They are all MOS tubes with anti-parallel diodes. The battery string consists of n single cells Cell1~Cell n Connect in series in sequence, and the filter inductor L in the synchronous BUCK converter t Replaced with a transmitting coil of the same impedance, the wireless receiving circuit includes an inductor L r The receiving coil and the uncontrolled rectifier bridge composed of diodes VD1 to VD4 can couple the transmitting coil with the receiving coil for wireless energy transmission. The positive poles of diodes VD3 and VD4 are connected, and the negative poles of VD3 and VD4 are connected to the positive poles of diodes VD2 and VD1 respectively. Finally, the negative poles of VD2 and VD1 are connected together. One end of the receiving coil is connected to the negative pole of VD3, and the other end is connected to the negative pole of VD4. 2n connected switches S1~S 2n Used to select specific single cells Cell1~Cell n Connected to the uncontrolled rectifier bridge, for each single cell i , i takes the value of 1 to n, and the switch S is turned on 2i-1 The negative electrode of the battery is connected to the i The positive pole of the switch S 2i Positive electrode and single cell i Connect the negative pole of the switch S 2i-1 With S 2i Share the same driver P i , all even-numbered cells are connected to switch S 2i The negative poles of the batteries are connected together and connected to the positive poles of VD3 and VD4 in the uncontrolled rectifier bridge; all odd-numbered single batteries are connected to switch S 2i-1 The positive poles are connected together and connected to the negative poles of VD1 and VD2 in the uncontrolled rectifier bridge.

2. The single receiving coil battery balancing control system based on wireless power feedback according to claim 1, characterized in that: Also includes equalization switch S F , all odd-numbered cells are connected to switch S 2i-1 The positive poles are connected together with the equalizing switch S F The negative pole of the balancing switch S F The positive pole is connected to the negative pole of VD1 and VD2 in the rectifier bridge.

3. The single receiving coil battery balancing control system based on wireless power feedback according to claim 2, characterized in that: Also includes filter capacitor C L and filter capacitor C H , filter capacitor C L The two ends of the filter capacitor C are connected in parallel with the other ends of the circuit. H The two ends of the battery string are connected in parallel.

4. A control method for a single-receiving-coil battery balancing control system based on wireless power feedback according to any one of claims 1 to 3, characterized in that: The control method includes the following cyclic execution of the constant current-constant voltage battery string charging method: Step 1: Charge the battery string with a constant current, maintaining the set battery string charging current reference value I pack_ref ; Step 2: Determine the battery string voltage V pack ≥ Maximum voltage of battery string V pack_max Is it true? If so, go to step 3; if not, go to step 1; Step 3: Charge the battery string at a constant voltage to maintain the set battery string charging voltage reference value V pack_ref ; Step 4: Determine the battery string current I pack ≥Minimum battery string current I pack_min Is it true? If so, go to step 3; if not, go to step 5; Step 5: Stop constant voltage charging of the battery string, and end the battery string charging process.

5. A control method for a single-receiving-coil battery balancing control system based on wireless power feedback according to any one of claims 2 to 3, characterized in that: The control method includes the following wireless receiving circuit time division multiplexing method: Set a fixed cycle period T0, which contains n access times T1 to T n and n dead time T d , access time T i Represents the corresponding single cell Cell i The time of connection with the wireless receiving circuit in a cycle period T, during the access time T i The corresponding single battery is connected to the switch S 2i-1 and S 2i Turn on and connect the single battery i When connected to the balancing circuit, different connection time periods do not overlap with each other, that is, at most only one single cell is connected to the balancing circuit at the same time. After each connection time period, a dead zone time T is entered in which all single cell switches are turned off. d , except for n dead time T d The effective cycle period of balanced switch conduction within the cycle period is defined as T valid , as shown in formula (6); T valid =T0-nT d (6) In a complete cycle, each single battery will be connected to the wireless receiving circuit in turn at the corresponding access time until the next cycle, when the first battery is connected to the wireless receiving circuit again for the next cycle.

6. The control method of the single receiving coil battery balancing control system based on wireless power feedback according to claim 5, characterized in that: The time for each single battery to access the wireless receiving circuit is adjusted by the access time controller. In the access time controller, the SOC of each single battery is compared with the average SOC value of the battery string. The average SOC value of the battery string is defined as formula (7); Then, the i-th single cell Cell i SOC value SOC i With SOC ave The error is fed into the periodic PI link, G period (s) and G period (z) represents the continuous periodic PI link and the discrete periodic PI link respectively; the discrete periodic PI link is shown in formula (8); where K P_period and K I_period are all parameters in the discrete periodic PI link, β i Represents the access time coefficient of the i-th single cell, β i The calculation is shown in formula (9); β i =1+(SOC ave -SOC i )×G period (z) (9) Finally, the access time of each single battery in the battery string is T1~T n As shown in formula (10); From formula (10), it is easy to obtain that within a cycle period T0, the on-time of each single battery satisfies (11), and the cycle period T0 can remain constant throughout the entire balancing process; T0=T1+T2+…+T n +nT d (11) By driving each P i The corresponding access time is T1~T n The lower the SOC of a single battery, the longer it is connected to the wireless receiving circuit in one cycle, thereby obtaining more feedback energy in the same time. After the battery is balanced, the time that all single batteries are connected to the wireless receiving circuit in one cycle is the same and equal to T valid / n.

7. The control method of the single receiving coil battery balancing control system based on wireless power feedback according to claim 6, characterized in that: The control method also includes the following balanced switch duty cycle control method: In the balancing switch S F In the duty cycle controller, the SOC of each single battery is equal to the maximum SOC of the battery string. max In comparison, SOC max Defined as formula (12) SOC max =max(SOC1…SOC n ) (12) The SOC and SOC of each single battery max The error between them is fed into the duty cycle PI link, G max (s) and G max (z) represent the continuous controller and discrete controller of the duty cycle PI link respectively. The discrete duty cycle PI link is shown in formula (13); where K P_max and K I_max These are all parameters in the discrete duty cycle PI link. Through PI control, the duty cycle coefficients α1~α of each single cell are obtained. n ;for The duty cycle coefficient of the i-th single cell is α i The calculation is shown in formula (14); a i =(SOC max -SOC i )×G max (z) (14) Finally, for the i-th single cell, the balancing switch S F Duty cycle D i As shown in formula (15); D i =D×α i (15) Where D is the reference duty cycle set by the system. The larger the reference duty cycle D is, the smaller the duty cycle coefficient α1~α n , the greater the difference between the duty cycles at different access times ultimately generated by the duty cycle controller will be.

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