Lithium ion battery SOC active equalization circuit

Abstract

A lithium ion battery SOC active equalization circuit comprises an n-winding flyback converter, (n-1) bridging capacitors and n lithium ion batteries, and the n-winding flyback converter comprises two power switches S1 and S2, an input capacitor Cin, an active clamping capacitor Cs, an excitation inductor Lm and a transformer T; and a first output diode D1 and a first output capacitor C1. A second output diode D2 and a second output capacitor C2; ,...; an nth output diode Dn; and an nth output capacitor Cn. On the basis of transformer type equalization, a multi-winding transformer equalization topological structure is adopted, and the SOC equalization of the series battery pack is realized by adding bridging capacitors among windings. Compared with a traditional multi-winding transformer equalization structure, equalization of the battery pack is achieved only through two switches, the control difficulty and cost of the circuit are reduced, the problem of terminal voltage imbalance caused by the cross adjustment rate during multi-winding output of the transformer is solved, voltage deviation is effectively reduced, and the battery equalization precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery balancing, and particularly to an active balancing circuit for the state of charge (SOC) of a lithium-ion battery. Background Art

[0002] To meet the performance requirements of energy storage systems, lithium-ion batteries are usually used in groups. However, there are inconsistencies among different battery cells, such as differences in performance like capacity, internal resistance, and voltage. These differences will reduce the capacity utilization rate of the battery pack, and at the same time, they will also cause overcharging and over-discharging of the battery, accelerating battery aging and endangering the safety of the battery system. The current battery balancing technology is most remarkable in optimizing the inconsistency effect. The battery balancing technology is mainly divided into passive balancing and active balancing. Passive balancing, also known as energy-consuming balancing, means that all the excess energy of the battery cell is consumed in the form of heat. However, this method will cause large energy loss of the battery, and the high-temperature environment caused by improper heat dissipation treatment will damage the battery performance. Active balancing, as a non-energy-consuming balancing, means that energy is transferred through energy storage elements, thereby reducing the inconsistency of the battery pack and achieving the balance of battery energy.

[0003] Due to its high energy utilization rate and flexible energy transfer, active balancing is a hot topic in battery balancing technology. For example, the patent document with the application publication number CN113489083A discloses a hierarchical balancing control method for a lithium-ion battery pack based on a buck-boost converter. This method adds multiple energy storage inductance elements, diodes, and balancing control switches on the basis of the lithium-ion battery pack. By controlling the closing of the switch, the single battery with higher energy storage stores the excess energy in the corresponding inductor, and then controls the switch to turn off, and transfers the energy in the inductor to the single battery with lower energy storage, forming the balancing control of the series lithium-ion battery pack. In addition, two adjacent single batteries are formed into a small module, and then the adjacent small modules are formed into a large module, and each level is balanced through logical control to achieve three-level balancing control. The balancing control method proposed in this patent can not only achieve the balance between two adjacent single batteries, but also indirectly achieve the balance between two non-adjacent single batteries through the balancing control between adjacent modules, shortening the energy transmission path and improving the efficiency of the battery pack balancing system. However, the balancing circuit adopted by this control method includes multiple control switches, and the logical control is very complex. Summary of the Invention

[0004] To address the deficiencies of existing battery pack balancing technologies, the present invention proposes a lithium-ion battery SOC active balancing circuit, which consists of a multi-winding flyback converter and multiple bridging capacitors. Based on transformer-based balancing, this balancing circuit adopts a multi-winding transformer balancing topology and achieves the SOC balancing of a series battery pack by adding bridging capacitors between the windings. Compared with the traditional multi-winding transformer balancing structure, it realizes the balancing of a lithium-ion battery pack using only two switches, reducing the control difficulty and cost of the circuit, and avoiding the problem of unbalanced terminal voltages caused by the cross-regulation rate when the transformer has multiple windings output, effectively reducing the voltage deviation and improving the balancing accuracy of the lithium-ion battery pack.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A lithium-ion battery SOC active balancing circuit includes an n-winding flyback converter, (n - 1) bridging capacitors, and n lithium-ion batteries, where:

[0007] An n-winding flyback converter includes two power switches S 1 、S 2 , an input capacitor C in , an active clamp capacitor C s , an exciting inductor L m , and a transformer T; and:

[0008] The first output diode D 1 , the first output capacitor C 1 ; the second output diode D 2 , the second output capacitor C 2 ;...; the nth output diode D n , the nth output capacitor C n ;

[0009] The connection form of the n-winding flyback converter is as follows:

[0010] The upper end of the exciting inductor L m is respectively connected to the input end of the primary winding L p of the transformer T, one end of the active clamp capacitor C s , and one end of the input capacitor C in ;

[0011] The lower end of the exciting inductor L m is respectively connected to the output end of the primary winding L p of the transformer T, the source of the power switch S 1 , and the drain of the power switch S 2 ;

[0012] The other end of the active clamp capacitor C s is connected to the power switch S 1Drain; Power switch S 2 The source is connected to the input capacitor C in The other end;

[0013] The secondary winding L of transformer T s1 The upper end is connected to the diode D 1 Anode, diode D 1 The cathode is connected to the capacitor C 1 The upper end, capacitor C 1 The lower end is connected to the secondary winding L of transformer T s1 The lower end;

[0014] The secondary winding L of transformer T s2 The upper end is connected to the diode D 2 Anode, diode D 2 The cathode is connected to the capacitor C 2 The upper end, capacitor C 2 The lower end is connected to the secondary winding L of transformer T s2 The lower end;

[0015] ... And so on,

[0016] The secondary winding L of transformer T sn The upper end is connected to the diode D n Anode, diode D n The cathode is connected to the capacitor C n The upper end, capacitor C n The lower end is connected to the secondary winding L of transformer T sn The lower end.

[0017] (n - 1) The connection form between the bridging capacitors and each output winding is as follows:

[0018] Capacitor C vb1 The upper end is connected to the diode D 1 The anode and the secondary winding L of transformer T s1 The intersection of the upper end, capacitor C vb1 The lower end is connected to the diode D 2 The anode and the secondary winding L of transformer T s2 The intersection of the upper end;

[0019] Capacitor C vb2 The upper end is connected to the diode D 2 The anode and the secondary winding L of transformer T s2 The intersection of the upper end, capacitor C vb2 The lower end is connected to the diode D 3 The anode and the secondary winding L of transformer T s3 The upper end intersection;

[0020] Capacitor C vb3 The upper end is connected to the diode D 3 The anode and the secondary winding L of transformer Ts3 The intersection point at the upper end, capacitor C vb3 The lower end is connected to diode D 4 The anode is connected to the secondary winding L of transformer T s4 The intersection point at the upper end.

[0021] And so on.

[0022] Capacitor C vb(n-1) The upper end is connected to diode D n-1 The anode is connected to the secondary winding L of transformer T s(n-1) The intersection point at the upper end, capacitor C vb(n-1) The lower end is connected to diode D n The anode is connected to the secondary winding L of transformer T sn The intersection point at the upper end;

[0023] Among n lithium-ion batteries:

[0024] Lithium-ion battery B 1 The positive electrodes are respectively connected to diode D 1 The cathode and capacitor C 1 The upper end, lithium-ion battery B 1 The negative electrodes are respectively connected to diode D 2 The cathode and capacitor C 1 The lower end;

[0025] Lithium-ion battery B 2 The positive electrodes are respectively connected to diode D 2 The cathode and capacitor C 2 The upper end, lithium-ion battery B 2 The negative electrodes are respectively connected to diode D 3 The cathode and capacitor C 2 The lower end;

[0026] And so on.

[0027] Lithium-ion battery B n-1 The positive electrodes are respectively connected to diode D n-1 The cathode and capacitor C n-1 The upper end, lithium-ion battery B n-1 The negative electrodes are respectively connected to diode D n The cathode and capacitor C n-1 The lower end;

[0028] Lithium-ion battery B n The positive electrodes are respectively connected to diode D n The cathode and capacitor C n The upper end, lithium-ion battery B n The negative electrode is connected to capacitor C n The lower end.

[0029] Battery pack B 1 and B 2, ……, B n At the same time, as the input source of the converter, the lithium-ion battery B 1 The positive electrodes are respectively connected to the secondary winding L of the transformer T s1 upper end and the input capacitor C in upper end; The lithium-ion battery B n The negative electrodes are respectively connected to the source of the power switch S 2 and the lower end of the input capacitor C in lower end.

[0030] The power switch S 1 , S 2 The gates are connected to the controller, and its duty cycle can vary between 0 and 0.5 and the phases are interleaved.

[0031] A lithium-ion battery SOC active equalization circuit containing 4 lithium-ion batteries, the circuit includes a 4-winding flyback converter, 3 bridging capacitors, and 4 lithium-ion batteries, where:

[0032] A 4-winding flyback converter includes 2 power switches S 1 , S 2 , the input capacitor C in , the active clamp capacitor C s , the excitation inductor L m , the transformer T; and:

[0033] The first output diode D 1 , the first output capacitor C 1 ; The second output diode D 2 , the second output capacitor C 2 ; The third output diode D 3 , the third output capacitor C 3 ; The fourth output diode D 4 , the fourth output capacitor C 4 ;

[0034] The connection form of the 4-winding flyback converter is as follows:

[0035] The upper end of the excitation inductor L m is respectively connected to the input end of the primary winding L of the transformer T p , one end of the active clamp capacitor C s , one end of the input capacitor C in ;

[0036] The lower end of the excitation inductor L m is respectively connected to the output end of the primary winding L of the transformer T p , the source of the power switch S 1 , the drain of the power switch S 2 ;

[0037] Active clamping capacitor C s The other end is connected to the power switch S 1 Drain; power switch S 2 The source is connected to the input capacitor C in The other end;

[0038] The secondary winding L of transformer T s1 The upper end is connected to diode D 1 Anode, diode D 1 The cathode is connected to capacitor C 1 The upper end, capacitor C 1 The lower end is connected to the secondary winding L of transformer T s1 The lower end;

[0039] The secondary winding L of transformer T s2 The upper end is connected to diode D 2 Anode, diode D 2 The cathode is connected to capacitor C 2 The upper end, capacitor C 2 The lower end is connected to the secondary winding L of transformer T s2 The lower end;

[0040] The secondary winding L of transformer T s3 The upper end is connected to diode D 3 Anode, diode D 3 The cathode is connected to capacitor C 3 The upper end, capacitor C 3 The lower end is connected to the secondary winding L of transformer T s3 The lower end;

[0041] The secondary winding L of transformer T s4 The upper end is connected to diode D 4 Anode, diode D 4 The cathode is connected to capacitor C 4 The upper end, capacitor C 4 The lower end is connected to the secondary winding L of transformer T s4 The lower end;

[0042] The connection forms between 3 bridging capacitors and each output winding are as follows:

[0043] Capacitor C vb1 The upper end is connected to diode D 1 The intersection of the anode and the secondary winding L of transformer T s1 The upper end of capacitor C vb1 The lower end is connected to diode D 2 The intersection of the anode and the secondary winding L of transformer T s2 The upper end;

[0044] Capacitor C vb2 The upper end is connected to diode D 2The intersection of the anode and the secondary winding L of the transformer T s2 The upper end, capacitor C vb2 The lower end is connected to the diode D 3 The intersection of the anode and the secondary winding L of the transformer T s3 The upper end intersection;

[0045] Capacitor C vb3 The upper end is connected to the diode D 3 The intersection of the anode and the secondary winding L of the transformer T s3 The upper end, capacitor C vb3 The lower end is connected to the diode D 4 The intersection of the anode and the secondary winding L of the transformer T s4 The upper end intersection.

[0046] Among the 4 lithium-ion batteries:

[0047] Lithium-ion battery B 1 The positive electrodes are respectively connected to the diode D 1 The cathode, capacitor C 1 The upper end, lithium-ion battery B 1 The negative electrodes are respectively connected to the diode D 2 The cathode, capacitor C 1 The lower end;

[0048] Lithium-ion battery B 2 The positive electrodes are respectively connected to the diode D 2 The cathode, capacitor C 2 The upper end, lithium-ion battery B 2 The negative electrodes are respectively connected to the diode D 3 The cathode, capacitor C 2 The lower end;

[0049] Lithium-ion battery B 3 The positive electrodes are respectively connected to the diode D 3 The cathode, capacitor C 3 The upper end, lithium-ion battery B 3 The negative electrodes are respectively connected to the diode D 4 The cathode, capacitor C 3 The lower end;

[0050] Lithium-ion battery B 4 The positive electrodes are respectively connected to the diode D 4 The cathode, capacitor C 4 The upper end, lithium-ion battery B 4 The negative electrode is connected to the capacitor C 4 The lower end.

[0051] Lithium-ion battery B 1 The positive electrodes are respectively connected to the input capacitor C in The upper end, the first output capacitor C 1 The upper end is connected; lithium-ion battery B4 The negative electrode is respectively connected to the input capacitor C in lower end and the power switch S 2 source electrode.

[0052] During a switching cycle, there is always a loop L s1 →C vb1 →L S2 →C 2 loop. According to the volt-second balance of the inductor, the average voltage across the inductor L s1 and L S2 is 0, and since the number of turns of the secondary winding of the transformer is equal, U Ls1 and U Ls2 are equal in magnitude and opposite in direction in the loop, so the average voltage u vb1 of the capacitor C vb1 is equal to the average voltage u 2 of the capacitor C c2 ; similarly, the voltage u vb2 of C vb3 is equal to the voltage u 3 of the capacitor C c3 , and the voltage u vb3 of the capacitor C vb3 is equal to the voltage u c4 of the capacitor C c4 .

[0053] When the switch S 2 conducts, the switch S 1 turns off, and the diodes D 1 , D 2 , D 3 , D 4 turn off. The lithium-ion battery pack transfers energy to the primary side winding of the transformer through series connection, and the current flows into the primary side winding L p of the transformer at the same-name terminal. The current in the primary coil L p rises, and the energy stored in the transformer increases. The capacitors C 1 , C 2 , C 3 , C 4 supply power to the load; the current in the secondary side winding of the transformer flows out of the reference point, and there is a loop C vb1 →L s1 →C 2 →L S2 →C vb1

[0054] When the switch S 2 turns off, the switch S 1 turns on; the exciting inductor L m continues to conduct current through the switch S 1 , and the current flows out of the primary side winding L pHomonymous terminal, transformer secondary coil L s1 , L s2 , L s3 and L s4 The voltage is positive at the top and negative at the bottom, charging the output capacitor C 1 , C 2 , C 3 , C 4 and lithium-ion battery B 1 , B 2 , B 3 , B 4 Charging. Assume that the voltage of lithium-ion battery B 1 is higher than that of lithium-ion battery B 2 . Due to the effect of the bridging capacitor C vb1 , the diode D 1 in the lightly loaded path does not conduct initially, and the current first charges the capacitor C vb1 until the voltage of the capacitor C vb1 rises to be equal to U B1 , and then the diode D 1 starts to conduct. Assume that the output capacitor is large enough, and the output voltage ripple is much smaller than the voltage ripple of the capacitor C vb1 . It can be approximately considered that the average voltage of U B1 is approximately equal to the peak voltage of the capacitor C vb1 during the switch-off stage.

[0055] U B1 and U B2 The voltage deviation Δu is equal to the difference between the peak voltage and the average voltage of C vb1 , that is, half of the peak-to-peak voltage ripple of the capacitor C vb1 .

[0056] Obviously, through the above analysis, it can be seen that the introduction of the auxiliary capacitor C vb1 can greatly reduce the inter-terminal voltage deviation caused by battery imbalance. Assume that C vb1 is large enough and Δu Cp is small enough. All the unbalanced charges ΔQ approximately flow into the capacitor C vb1 , and then the capacitor voltage ripple Δu vb and the capacitor C vb have the following relationship:

[0057]

[0058] In summary, as the capacitance value of the capacitor C vb1 increases, the voltage ripple of the capacitor C vb1 will become smaller and smaller. Therefore, the output voltage deviation will become smaller as the capacitance value of C vb1 increases, and U B1 and U B2The voltages will be closer.

[0059] The lithium-ion battery equalization mechanism with n outputs is similar to the above analysis and will not be described here. When the capacitors C vb1 , C vb2 , C vb3 , C vb4 , C vb5 , C vb6 are large enough, the voltages of each lithium-ion battery cell are equal.

[0060] Assume that the SOC of the single lithium-ion B 1 in the lithium-ion group is higher than the average value. When the power switch S 1 is turned on, lithium-ion B 1 is connected in series with lithium-ions B 2 , B 3 , B 4 , and the excess energy is transferred to the primary side winding of the transformer. After the switch is turned off again, the secondary side windings L s2 , L s3 , L s4 are respectively connected in parallel with lithium-ions B 2 , B 3 , B 4 , and the energy stored in the transformer is transmitted to lithium-ions B 2 , B 3 , B 4 , so that part of the energy of the series battery pack can be transmitted to the lithium-ion monomers with lower energy, achieving the SOC equalization of the lithium-ion group.

[0061] The technical effects of an SOC active equalization circuit for lithium-ion batteries according to the present invention are as follows:

[0062] 1) By connecting a bridging capacitor between adjacent output windings of a flyback converter, the present invention achieves the effect of automatically equalizing the output voltages of a multi-output converter, improving the battery equalization degree.

[0063] 2) The circuit topology of the equalization circuit of the present invention is simple, using only two switches, reducing the difficulty of the control system design. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The present invention will be further described below in conjunction with the drawings and examples;

[0065] Figure 1 is the circuit schematic diagram of the present invention;

[0066] Figure 2 is the circuit schematic diagram for achieving the SOC equalization of a series battery pack of four single lithium-ion batteries according to the present invention;

[0067] Figure 3This is a simulation diagram for achieving balance in a series battery pack of four lithium-ion battery cells in the present invention. Detailed implementation

[0068] As Figure 2 shown, a battery SOC active balancing circuit includes a 4-winding flyback converter, 3 bridging capacitors, and 4 lithium-ion batteries, where:

[0069] A 4-winding flyback converter includes 2 power switches S 1 , S 2 , an input capacitor C in , an active clamp capacitor C s , an exciting inductor L m , and a transformer T; and:

[0070] The first output diode D 1 , the first output capacitor C 1 ; the second output diode D 2 , the second output capacitor C 2 ; the third output diode D 3 , the third output capacitor C 3 ; the fourth output diode D 4 , the fourth output capacitor C 4 ;

[0071] The connection form of the 4-winding flyback converter is as follows:

[0072] The upper end of the exciting inductor L m is respectively connected to the input end of the primary winding L p of the transformer T, one end of the active clamp capacitor C s , and one end of the input capacitor C in ;

[0073] The lower end of the exciting inductor L m is respectively connected to the output end of the primary winding L p of the transformer T, the source of the power switch S 1 , and the drain of the power switch S 2 ;

[0074] The other end of the active clamp capacitor C s is connected to the drain of the power switch S 1 ; the source of the power switch S 2 is connected to the other end of the input capacitor C in ;

[0075] The upper end of the secondary winding L s1 of the transformer T is connected to the anode of the diode D 1 , and the cathode of the diode D 1 is connected to the upper end of the capacitor C 1 ;1 The lower end is connected to the secondary winding L of transformer T s1 Lower end;

[0076] The secondary winding L of transformer T s2 The upper end is connected to diode D 2 Anode, diode D 2 The cathode is connected to capacitor C 2 Upper end, capacitor C 2 The lower end is connected to the secondary winding L of transformer T s2 Lower end;

[0077] The secondary winding L of transformer T s3 The upper end is connected to diode D 3 Anode, diode D 3 The cathode is connected to capacitor C 3 Upper end, capacitor C 3 The lower end is connected to the secondary winding L of transformer T s3 Lower end;

[0078] The secondary winding L of transformer T s4 The upper end is connected to diode D 4 Anode, diode D 4 The cathode is connected to capacitor C 4 Upper end, capacitor C 4 The lower end is connected to the secondary winding L of transformer T s4 Lower end;

[0079] The connection forms between three bridging capacitors and each output winding are as follows:

[0080] Capacitor C vb1 The upper end is connected to diode D 1 The intersection of the anode and the secondary winding L of transformer T s1 Upper end of capacitor C vb1 The lower end is connected to diode D 2 The intersection of the anode and the secondary winding L of transformer T s2 Upper end;

[0081] Capacitor C vb2 The upper end is connected to diode D 2 The intersection of the anode and the secondary winding L of transformer T s2 Upper end of capacitor C vb2 The lower end is connected to diode D 3 The intersection of the anode and the secondary winding L of transformer T s3 Upper end intersection;

[0082] Capacitor C vb3 The upper end is connected to diode D 3 The intersection of the anode and the secondary winding L of transformer T s3 Upper end of capacitor C vb3 The lower end is connected to diode D4 The upper intersection point of the anode and the secondary winding L of the transformer T s4

[0083] Among the 4 lithium-ion batteries:

[0084] Lithium-ion battery B 1 The positive electrodes are respectively connected to the cathode of the diode D 1 and the upper end of the capacitor C 1 For lithium-ion battery B 1 The negative electrodes are respectively connected to the cathode of the diode D 2 and the lower end of the capacitor C 1

[0085] Lithium-ion battery B 2 The positive electrodes are respectively connected to the cathode of the diode D 2 and the upper end of the capacitor C 2 For lithium-ion battery B 2 The negative electrodes are respectively connected to the cathode of the diode D 3 and the lower end of the capacitor C 2

[0086] Lithium-ion battery B 3 The positive electrodes are respectively connected to the cathode of the diode D 3 and the upper end of the capacitor C 3 For lithium-ion battery B 3 The negative electrodes are respectively connected to the cathode of the diode D 4 and the lower end of the capacitor C 3

[0087] Lithium-ion battery B 4 The positive electrodes are respectively connected to the cathode of the diode D 4 and the upper end of the capacitor C 4 For lithium-ion battery B 4 The negative electrode is connected to the capacitor C 4 at the lower end.

[0088] Lithium-ion battery B 1 The positive electrodes are respectively connected to the upper end of the input capacitor C in and the upper end of the first output capacitor C 1 For lithium-ion battery B 4 The negative electrodes are respectively connected to the lower end of the input capacitor C in and the source electrode of the power switch S 2

[0089] During a switching cycle, there is always a loop L s1 →C vb1 →L S2 →C 2 loop. According to the volt-second balance of the inductor, the inductor L s1 and L S2 ​​​​​The average voltage at both ends is 0, and since the number of turns in the secondary winding of the transformer is equal, U Ls1 and U Ls2 are equal in magnitude and opposite in direction in the circuit. Therefore, the average voltage u vb1 across capacitor C vb1 is equal to the average voltage u 2 across capacitor C c2 ; similarly, the voltage u vb2 across C vb3 is equal to the voltage u 3 across capacitor C c3 , the voltage u vb3 across capacitor C vb3 is equal to the voltage u c4 across capacitor C c4 .

[0090] When switch S 2 conducts, switch S 1 turns off, and diodes D 1 , D 2 , D 3 , D 4 turn off. The lithium-ion battery pack transfers energy to the primary side winding of the transformer through series connection, and the current flows into the primary side winding L p at the same name terminal. The current in the primary coil L p rises, and the energy stored in the transformer increases. Capacitors C 1 , C 2 , C 3 , C 4 supply power to the load; the current in the secondary side winding of the transformer flows out of the reference point, and there is a loop C vb1 →L s1 →C 2 →L S2 →C vb1

[0091] When switch S 2 turns off, switch S 1 turns on; the exciting inductor L m continues to flow current through switch S 1 . The current flows out of the primary side winding L p at the same name terminal. The voltages of the secondary coils L s1 , L s2 , L s3 and L s4 are positive at the top and negative at the bottom, charging the output capacitors C 1 , C 2 , C 3 , C 4 and the lithium-ion batteries B 1 , B 2 , B 3 , B 4Charging. Assume a lithium-ion battery B 1 has a voltage higher than that of the lithium-ion battery B 2 . Due to the effect of the bridging capacitor C vb1 , the diode D in the lightly loaded path 1 does not conduct current initially and first charges the capacitor C vb1 until the voltage of the capacitor C vb1 rises to be equal to U B1 , at which point the diode D 1 starts to conduct. Assume the output capacitor is large enough such that the output voltage ripple is much smaller than the voltage ripple of the capacitor C vb1 . It can be approximately considered that the average voltage of U B1 is approximately equal to the peak voltage of the capacitor C vb1 during the switch-off stage.

[0092] The voltage deviation Δu between U B1 and U B2 is equal to the difference between the peak voltage and the average voltage of C vb1 , that is, half of the peak-to-peak voltage ripple of the capacitor C vb1 .

[0093] Obviously, from the above analysis, it can be seen that the introduction of the auxiliary capacitor C vb1 can greatly reduce the inter-terminal voltage deviation caused by battery imbalance. Assume C vb1 is large enough and Δu Cp is small enough, then all the unbalanced charge ΔQ approximately flows into the capacitor C vb1 . Furthermore, the relationship between the capacitor voltage ripple Δu vb and the capacitor C vb is as follows:

[0094]

[0095] In summary, as the capacitance value of the capacitor C vb1 increases, the voltage ripple of the capacitor C vb1 becomes smaller and smaller. Therefore, the output voltage deviation will decrease as the capacitance value of C vb1 increases, and the voltages of U B1 and U B2 will be closer.

[0096] The lithium-ion battery equalization mechanism with n-way outputs is similar to the above analysis and will not be elaborated here. When the capacitors C vb1 , C vb2 , C vb3 , C vb4 , C vb5 , C vb6 are large enough, the voltages of each lithium-ion battery cell are equal.

[0097] Assume that the state of charge (SOC) of the individual lithium-ion B in the lithium-ion battery pack 1 is higher than the average value. When the power switch S 1 is turned on, lithium-ion B 1 is connected in series with lithium-ion B 2 , B 3 , B 4 to transfer the excess energy to the primary side winding of the transformer. After the switch is turned off again, the secondary side windings L s2 , L s3 , L s4 are respectively connected in parallel with lithium-ion B 2 , B 3 , B 4 to transfer the energy stored in the transformer to lithium-ion B 2 , B 3 , B 4 . Thus, part of the energy of the series battery pack can be transferred to the lithium-ion monomers with lower energy, achieving the SOC balance of the lithium-ion battery pack.

[0098] It can be seen from Figure 3 that the actually set SOCs of the three battery packs are different, and other parameters are the same. Among them, the SOC of battery B 1 is 90%, the SOC of battery B 2 is 88%, the SOC of battery B 3 is 86%, and the SOC of battery B 4 is 84%. Through the converter proposed in the present invention, the battery unit with a higher SOC can transfer energy to the battery unit with a lower SOC, and finally the SOCs of the four battery units reach equilibrium.

Claims

1. A lithium-ion battery SOC active equalization circuit, characterized in that: It includes an n-winding flyback converter, (n-1) cross-connected capacitors, and n lithium-ion batteries, where: An n-winding flyback converter consists of two power switches S1 and S2, an input capacitor C in , active clamp capacitor C s , magnetizing inductance L m , transformer T; and: The first output diode D1, the first output capacitor C1; the second output diode D2, the second output capacitor C2; ...; the nth output diode D n , the nth output capacitor C n ; The connection form of the n-winding flyback converter is as follows: Excitation inductance L m The upper end is connected to the primary winding L of the transformer T p Input terminal, active clamp capacitor C s One end, input capacitor C in one end; Excitation inductance L m The lower ends are connected to the primary winding L of the transformer T p Output terminal, source of power switch S1, drain of power switch S2; Active clamp capacitor C s The other end is connected to the drain of power switch S1; the source of power switch S2 is connected to the input capacitor C in The other end; transformer T secondary winding L s1 The upper end is connected to the anode of diode D1, the cathode of diode D1 is connected to the upper end of capacitor C1, and the lower end of capacitor C1 is connected to the secondary winding L of transformer T s1 lower end; Transformer T secondary winding L s2 The upper end is connected to the anode of diode D2, the cathode of diode D2 is connected to the upper end of capacitor C2, and the lower end of capacitor C2 is connected to the secondary winding L of transformer T s2 lower end; ... and so on. Transformer T secondary winding L sn The upper end is connected to a diode D n Anode, diode D n Cathode connection capacitor C n Upper end, capacitor C n The lower end is connected to the secondary winding L of the transformer T sn lower end; The connection between the (n-1) jumper capacitors and each output winding is as follows: Capacitor C vb1 The upper end is connected to the anode of diode D1 and the secondary winding L of transformer T. s1 The upper intersection point, capacitor C vb1 The lower end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The intersection point at the upper end; Capacitor C vb2 The upper end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The upper intersection point, capacitor C vb2 The lower end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 Upper intersection point; Capacitor C vb3 The upper end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 The upper intersection point, capacitor C vb3 The lower end is connected to the anode of diode D4 and the secondary winding L of transformer T. s4 Upper intersection point; ... and so on. Capacitor C vb(n-1) The upper end is connected to a diode D n-1 Anode and transformer T secondary winding L s(n-1) The upper intersection point, capacitor C vb(n-1) The lower end is connected to a diode D n Anode and transformer T secondary winding L sn Upper intersection point; Among n lithium-ion batteries: The positive electrode of the lithium-ion battery B1 is connected to the cathode of the diode D1 and the upper end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the cathode of the diode D2 and the lower end of the capacitor C1; The positive electrode of the lithium-ion battery B2 is connected to the cathode of the diode D2 and the upper end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the cathode of the diode D3 and the lower end of the capacitor C2; ... and so on. Lithium-ion battery B n-1 The positive pole is connected to the diode D n-1 Cathode, capacitor C n-1 Top, lithium-ion battery B n-1 The cathode is connected to diode D n Cathode, capacitor C n-1 lower end; Lithium-ion battery B n The positive pole is connected to the diode D n Cathode, capacitor C n Top, lithium-ion battery B n Negative connection capacitor C n lower end; The positive electrode of the lithium-ion battery B1 is connected to the secondary winding L of the transformer T s1 The upper and input capacitors C in Upper connection: Lithium-ion battery B n The negative electrode is connected to the source of the power switch S2 and the input capacitor C in Lower end connection.

2. The lithium-ion battery SOC active equalization circuit according to claim 1, characterized in that: The gates of the power switches S1 and S2 are connected to a controller, and the duty cycle thereof can be varied between 0 and 0.5 with staggered phases.

3. A lithium-ion battery SOC active equalization circuit containing four lithium-ion batteries, characterized in that: The circuit includes a 4-winding flyback converter, 3 cross-capacitors, and 4 lithium-ion batteries, among which: A 4-winding flyback converter consists of two power switches S1 and S2, an input capacitor C in , active clamp capacitor C s , magnetizing inductance L m , transformer T; and: A first output diode D1, a first output capacitor C1; a second output diode D2, a second output capacitor C2; a third output diode D3, a third output capacitor C3; a fourth output diode D4, a fourth output capacitor C4; The connection form of the 4-winding flyback converter is as follows: Excitation inductance L m The upper end is connected to the primary winding L of the transformer T p Input terminal, active clamp capacitor C s One end, input capacitor C in one end; Excitation inductance L m The lower ends are connected to the primary winding L of the transformer T p Output terminal, source of power switch S1, drain of power switch S2; Active clamp capacitor C s The other end is connected to the drain of power switch S1; the source of power switch S2 is connected to the input capacitor C in The other end; Transformer T secondary winding L s1 The upper end is connected to the anode of diode D1, the cathode of diode D1 is connected to the upper end of capacitor C1, and the lower end of capacitor C1 is connected to the secondary winding L of transformer T s1 lower end; Transformer T secondary winding L s2 The upper end is connected to the anode of diode D2, the cathode of diode D2 is connected to the upper end of capacitor C2, and the lower end of capacitor C2 is connected to the secondary winding L of transformer T s2 lower end; Transformer T secondary winding L s3 The upper end is connected to the anode of diode D3, the cathode of diode D3 is connected to the upper end of capacitor C3, and the lower end of capacitor C3 is connected to the secondary winding L of transformer T. s3 lower end; Transformer T secondary winding L s4 The upper end is connected to the anode of diode D4, the cathode of diode D4 is connected to the upper end of capacitor C4, and the lower end of capacitor C4 is connected to the secondary winding L of transformer T s4 lower end; The connection between the three jumper capacitors and each output winding is as follows: Capacitor C vb1 The upper end is connected to the anode of diode D1 and the secondary winding L of transformer T. s1 The upper intersection point, capacitor C vb1 The lower end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The intersection point at the upper end; Capacitor C vb2 The upper end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The upper intersection point, capacitor C vb2 The lower end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 Upper intersection point; Capacitor C vb3 The upper end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 The upper intersection point, capacitor C vb3 The lower end is connected to the anode of diode D4 and the secondary winding L of transformer T. s4 Upper intersection point; Of the 4 lithium-ion batteries: The positive electrode of the lithium-ion battery B1 is connected to the cathode of the diode D1 and the upper end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the cathode of the diode D2 and the lower end of the capacitor C1; The positive electrode of the lithium-ion battery B2 is connected to the cathode of the diode D2 and the upper end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the cathode of the diode D3 and the lower end of the capacitor C2; The positive electrode of the lithium-ion battery B3 is connected to the cathode of the diode D3 and the upper end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the cathode of the diode D4 and the lower end of the capacitor C3; The positive electrode of the lithium-ion battery B4 is connected to the cathode of the diode D4 and the upper end of the capacitor C4, and the negative electrode of the lithium-ion battery B4 is connected to the lower end of the capacitor C4; The positive electrode of the lithium-ion battery B1 is connected to the input capacitor C in The upper end of the first output capacitor C1 is connected; the negative electrode of the lithium-ion battery B4 is connected to the input capacitor C in The lower end and the source of the power switch S2 are connected.

4. The lithium-ion battery SOC active equalization circuit comprising four lithium-ion batteries according to claim 3, characterized in that: In one switching cycle, there is a loop L s1 →C vb1 →L S2 →C2 loop, according to the volt-second balance of inductance, the inductance L s1 and L S2 The average voltage across the two ends is 0, and since the number of turns of the secondary winding of the transformer is equal, U Ls1 and U Ls2 In the loop, the magnitudes are equal and the directions are opposite, so the capacitance C vb1 Average voltage u vb1 and the average voltage u of capacitor C2 c2 Equal; similarly, C vb2 The voltage u vb3 Equal to the voltage u of capacitor C3 c3 , capacitor C vb3 The voltage u vb3 Equal to capacitance C c4 The voltage u c4 .

5. A lithium-ion battery SOC active equalization circuit comprising four lithium-ion batteries according to claim 4, characterized in that: When switch S2 is turned on, switch S1 is turned off, diodes D1, D2, D3, and D4 are turned off, and the lithium-ion battery pack transfers energy to the primary winding of the transformer through series connection, and the current flows into the primary winding L of the transformer. p Same name end, primary coil L p As the current rises, the transformer energy storage increases, and capacitors C1, C2, C3, and C4 supply power to the load; the transformer secondary winding current flows out of the reference point, and there is a loop C vb1 →L s1 →C2→L S2 →C vb1 .

6. The lithium-ion battery SOC active equalization circuit containing four lithium-ion batteries according to claim 5, characterized in that: When switch S2 is turned off, switch S1 is turned on; the magnetizing inductance L m After the switch S1 continues to flow, the current flows out of the primary winding L of the transformer p Same name end, transformer secondary coil L s1 , L s2 , L s3 and L s4 The voltage is positive at the top and negative at the bottom, charging the output capacitors C1, C2, C3, C4 and the lithium-ion batteries B1, B2, B3, B4; assuming that the voltage of lithium-ion battery B1 is higher than that of lithium-ion battery B2, due to the cross-connected capacitor C vb1 The role of the lightly loaded diode D1 is that it does not conduct current at first and first supplies the capacitor C vb1 Charge until the capacitor C vb1 Rise to U B1 When the output voltage is equal to C, the diode D1 starts to conduct; assuming that the output capacitor is large enough, the output voltage ripple is much smaller than the capacitor C vb1 The voltage ripple can be approximately considered as U B1 The average voltage is approximately equal to the capacitance C vb1 Peak voltage during the switch off phase; U B1 and U B2 The voltage deviation Δu is equal to C vb1 The difference between the peak voltage and the average voltage, that is, the capacitance C vb1 Half of the peak-to-peak voltage ripple.

7. A lithium-ion battery SOC active equalization circuit comprising four lithium-ion batteries according to claim 6, characterized in that: Auxiliary capacitor C vb1 The introduction of can greatly reduce the inter-electrode voltage deviation caused by battery imbalance; assuming C vb1 is large enough, Δu Cp When the value is small enough, all the unbalanced charge ΔQ will flow into the capacitor C. vb1 Then, the capacitor voltage ripple Δu can be obtained vb and capacitor C vb The relationship is as follows: With the capacitor C vb1 As the capacitance increases, the capacitor C vb1 The voltage ripple will become smaller and smaller, so the output voltage deviation will increase with C vb1 As the capacitance increases, U B1 with U B2 The voltages will be closer.

8. A lithium-ion battery SOC active equalization circuit containing four lithium-ion batteries according to claim 7, characterized in that: The SOC of the single lithium ion B1 in the lithium ion group is higher than the average value. When the power switch S1 is turned on, the lithium ion B1 is connected in series with the lithium ions B2, B3, and B4 to transfer the excess energy to the primary winding of the transformer. After the switch is turned off again, the secondary winding L s2 , L s3 , L s4 They are connected in parallel with lithium ion batteries B2, B3, and B4 respectively, and the energy stored in the transformer is transmitted to lithium ion batteries B2, B3, and B4, so that part of the energy of the series battery pack can be transmitted to the lithium ion monomers with lower energy, achieving SOC balance of the lithium ion pack.

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