Lithium battery pack charging equalization circuit

Abstract

The invention relates to the technical field of battery pack management, in particular to a lithium battery pack charging equalization circuit, which comprises a basic Zeta converter, n-1 interstage capacitors CVB, n-1 output expansion units and n lithium ion batteries, and is characterized in that the basic Zeta converter comprises an inductor L1, an inductor Lin, a capacitor C1, a capacitor Ci1, a switch S1 and a diode D1; each output expansion unit is composed of an inductor L2, a capacitor C2, a capacitor Ci2 and a diode D2, the n-1 inter-stage capacitors CVB and the output expansion units are installed in a one-to-one correspondence mode, the two ends of one inter-stage capacitor CVB are connected with the capacitor Ci1 and the capacitor Ci2 respectively, and the two ends of the remaining n inter-stage capacitors CVB are connected with the capacitors Ci2 in the two adjacent output expansion units. According to the invention, voltage sharing among the battery units is realized through the inter-stage capacitors, complicated sampling and control algorithms are not needed, the voltage deviation is effectively reduced, the battery equalization precision is improved, equalization of the battery pack is realized through the switch, and the control difficulty and cost of the circuit are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery pack management, and particularly to a charging equalization circuit for a lithium battery pack. Background Art

[0002] As the core energy storage carrier for power grids, electric vehicles, and energy storage systems, lithium-ion batteries have inherent deviations in key parameters such as initial capacity, internal resistance, and self-discharge rate among individual cells due to inconsistent production processes and uneven distribution of raw materials during the manufacturing stage. With the increase in the cycling time, such initial deviations are exponentially amplified under the influence of external conditions such as temperature fluctuations, further exacerbating the differentiation of the energy state inside the battery pack, and ultimately triggering the "short board effect" - that is, overcharging or over-discharging of individual cells. This not only significantly reduces the overall available capacity and cycling life of the battery pack, but also may cause serious safety hazards such as battery swelling, electrolyte leakage, and even thermal runaway explosion due to local thermal runaway;

[0003] Since a lithium battery energy storage system usually contains a large number of individual cells and has a complex series-parallel topology structure, once the equalization function fails, it will lead to a rapid decay of the battery pack capacity, and the battery replacement cost generated due to deteriorated consistency in the later stage will increase significantly. Especially under extreme temperature conditions, the differences in battery internal resistance and polarization voltage are further enlarged, which not only exacerbates the equalization demand of the system, but also poses more stringent requirements on the dynamic response characteristics, control accuracy, and thermal management design of the equalization circuit. The common battery equalization technologies in engineering are mainly divided into two types: passive equalization and active equalization.

[0004] There are inconsistencies among existing different battery cells, which will reduce the capacity utilization rate of the battery pack. At the same time, it will also cause overcharging and over-discharging of the battery, accelerate battery aging, and endanger the safety of the battery system. Passive equalization will result in large battery energy loss, and the high-temperature environment caused by improper heat dissipation treatment will damage battery performance; Therefore, it does not meet the existing needs, and for this reason, we propose a charging equalization circuit for a lithium battery pack. Summary of the Invention

[0005] The purpose of the present invention is to provide a charging equalization circuit for a lithium battery pack to solve the problems mentioned in the above background art, where there are inconsistencies among existing different battery cells, which will reduce the capacity utilization rate of the battery pack, and at the same time, it will also cause overcharging and over-discharging of the battery, accelerate battery aging, endanger the safety of the battery system, passive equalization will result in large battery energy loss, and the high-temperature environment caused by improper heat dissipation treatment will damage battery performance.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A charging equalization circuit for a lithium battery pack includes a basic Zeta converter, n - 1 inter-stage capacitors C VB, n - 1 output expansion units and n lithium - ion batteries. The basic Zeta converter includes an inductor L1, an inductor L in , a capacitor C1, a capacitor C i1 , a switch S1 and a diode D1;

[0007] Each of the output expansion units is composed of an inductor L2, a capacitor C2, a capacitor C i2 and a diode D2. n - 1 of the inter - stage capacitors C VB are installed corresponding to the output expansion units one by one. One of the inter - stage capacitors C VB has its two ends respectively connected to the capacitor C i1 and the capacitor C i2 ; the remaining n inter - stage capacitors C VB have their two ends both connected to the capacitor C i2 in two adjacent output expansion units;

[0008] The n lithium - ion batteries are installed corresponding to the capacitor C1 and n - 1 capacitors C2 one by one. The positive and negative electrodes of one of the lithium - ion batteries are respectively connected to the two ends of the capacitor C1, and the positive and negative electrodes of the remaining n - 1 lithium - ion batteries are respectively connected to the two ends of the n - 1 capacitors C2. The negative electrodes of every two adjacent lithium - ion batteries are connected to the positive electrodes, and the n lithium - ion batteries are connected in series.

[0009] Preferably, the gate of the switch S1 is connected to a controller. The duty cycle of the gate of the switch S1 floats between 0 and 1. The drain of the switch S1 is connected to the positive electrode of a DC input source u in . The source of the switch S1 is respectively connected to the inductor L in and the capacitor C i1 . The end of the capacitor C i1 far from the source of the switch S1 is respectively connected to the cathode of the diode D1 and the inductor L1. One end of the inductor L1 is connected to the capacitor C1, and the end of the capacitor C1 far from the inductor L1 is respectively connected to the anode of the diode D1, the inductor L in and the cathode of the DC input source u in .

[0010] Preferably, one end of the capacitor C i2 is respectively connected to the cathode of the diode D2 and the inductor L2. One end of the inductor L2 is connected to the capacitor C2, and the end of the capacitor C2 far from the inductor L2 is connected to the anode of the diode D2.

[0011] Preferably, when n = 4, the switch S1 is in the closed state. The inductor L in is charged through the positive electrode of the DC input source u in . The diode D1 and three diodes D2 are reverse - biased and cut off. The DC input source uin Through the DC input source U in , the inter-stage capacitor C VB , the capacitor C i2 and the inductor L2 form a loop to charge one of the inter-stage capacitors C VB , and the other two said inter-stage capacitors C VB are charged through the power supply, and the four said lithium-ion batteries form a lithium-ion battery pack.

[0012] Preferably, when n is 4, the switch S1 is in the off state, the diode D1 and three diodes D2 are conducting, and one of the said inter-stage capacitors C VB discharges through the loop composed of the inter-stage capacitor C VB , the inductor L in , the inductor L2 and the capacitor C i2 , and the two said inter-stage capacitors C VB are both in the discharge state.

[0013] Preferably, when the SOC of one of the lithium-ion batteries in the lithium-ion battery pack is higher than the average value, the initial voltage U B1 > U B2 , when the switch S1 is in the off state, the diode D1 is in the non-conducting state through one of the inter-stage capacitors C VB and maintains the discharge of the inter-stage capacitor C VB , and when the voltage U CVB of the inter-stage capacitor C VB rises to be equal to the output voltage U B , the diode D1 conducts.

[0014] Preferably, the relationship between the voltage ripple of the inter-stage capacitor C VB and the equalization deviation is:

[0015]

[0016] where ΔU is the voltage deviation between adjacent battery cells, and ΔV pp is the peak value of the voltage ripple of the inter-stage capacitor C VB , V peak is the peak voltage of the inter-stage capacitor C VB during the off stage of the switch S1, and V avg is the average voltage of the inter-stage capacitor C VB ;

[0017] The relationship between the capacitance value of the capacitor and the ripple is:

[0018]

[0019] where I charge is the charging current, Toff is the switch-off time, and CVB is the inter-stage capacitance C VB value;

[0020] When the capacitance value range of the output capacitor C1 is between 100 μF and 1000 μF, the output voltage ripple satisfies Δvout < 0.02 V.

[0021] Preferably, the capacitor voltage ripple ΔU VB and the inter-stage capacitance C VB relationship is:

[0022]

[0023] The voltage deviation Δu is:

[0024]

[0025] When the capacitance value range of the three inter-stage capacitances C VB is between 220 μF and 1000 μF, the peak-to-peak voltage ripple ΔV pp ≤0.04 V, and the voltage deviation ΔU of the four lithium-ion batteries ≤0.02 V.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. Through the fixed duty cycle in-phase control strategy, the present invention only requires a low-cost MCU to drive, reducing the cost of the drive circuit. The inter-stage capacitance directly reuses the energy storage capacitor in the Zeta converter topology, eliminating the need to add multiple additional inductors, reducing the bill of materials cost, and significantly optimizing the hardware cost and complexity;

[0028] 2. The single-switch architecture of the present invention avoids the risks of multi-switch timing conflicts and device failures, significantly improving the system reliability; for each additional battery section, only one output expansion unit and one inter-stage capacitance need to be added, and the hardware complexity increases linearly. Moreover, the inter-stage capacitance automatically balances the energy of adjacent batteries through charge sharing, without the need for closed-loop control, supporting the mixing of new and old batteries or batteries with different capacities. The dynamic charge distribution mechanism effectively improves the SOC balancing speed by 30%, adapting to battery aging and inconsistency scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the circuit schematic diagram of the present invention;

[0030] Figure 2 is the schematic diagram of the equalization circuit of the lithium-ion battery pack of the present invention;

[0031] Figure 3 is the simulation diagram of the equalization circuit of the lithium-ion battery pack of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0033] Please refer to Figure 1 , an embodiment provided by the present invention: a lithium battery pack charging equalization circuit, including a basic Zeta converter, n - 1 inter - stage capacitors C VB , n - 1 output expansion units and n lithium - ion batteries. The basic Zeta converter includes an inductor L1, an inductor L in , a capacitor C1, a capacitor C i1 , a switch S1 and a diode D1. The gate of the switch S1 is connected to a controller, and the duty cycle of the gate of the switch S1 floats between 0 and 1. The drain of the switch S1 is connected to the positive pole of a DC input source u in , the source of the switch S1 is respectively connected to the inductor L in and the capacitor C i1 , one end of the capacitor C i1 far from the source of the switch S1 is respectively connected to the cathode of the diode D1 and the inductor L1. One end of the inductor L1 is connected to the capacitor C1, and the end of the capacitor C1 far from the inductor L1 is respectively connected to the anode of the diode D1, the inductor L in and the cathode of the DC input source u in , using the basic Zeta converter as the basic circuit carrier of the lithium battery pack;

[0034] Each output expansion unit is composed of an inductor L2, a capacitor C2, a capacitor C i2 and a diode D2. The n - 1 inter - stage capacitors C VB and the output expansion units are installed in one - to - one correspondence. The two ends of one of the inter - stage capacitors C VB are respectively connected to the capacitor C i1 and the capacitor C i2 . The two ends of the remaining n inter - stage capacitors C VB are both connected to the capacitor C i2 in the adjacent two output expansion units. One end of the capacitor C i2 is respectively connected to the cathode of the diode D2 and the inductor L2. One end of the inductor L2 is connected to the capacitor C2, and the end of the capacitor C2 far from the inductor L2 is connected to the anode of the diode D2. The n lithium - ion batteries are installed in one - to - one correspondence with the capacitor C1 and the n - 1 capacitors C2. The positive and negative poles of one of the lithium - ion batteries are respectively connected to the two ends of the capacitor C1, and the positive and negative poles of the remaining n - 1 lithium - ion batteries are respectively connected to the two ends of the n - 1 capacitors C2. The negative poles of every two adjacent lithium - ion batteries are connected to the positive poles, and the n lithium - ion batteries are connected in series. Through the multiple output expansion units and the basic Zeta converter, the corresponding number of lithium - ion batteries can be stably connected and balanced.

[0035] Please refer to Figure 2 , when n is 4 and the switch S1 is in the closed state, the inductor L in is charged through the DC input source u in from the positive terminal. The diode D1 and the three diodes D2 are reverse-biased and cut off. The DC input source u in charges one of the inter-stage capacitors C in through the DC input source U VB , the inter-stage capacitor C i2 , and the inductor L2 in a loop formed by the capacitor C VB . The other two inter-stage capacitors C VB are charged through the power supply. When the switch S1 is in the open state, the diode D1 and the three diodes D2 conduct. One of the inter-stage capacitors C VB discharges through the loop formed by the inter-stage capacitor C VB , the inductor L in , the inductor L2, and the capacitor C i2 . The two inter-stage capacitors C VB are both in the discharge state. The capacitor C1 and the three capacitors C2 supply energy to the lithium-ion battery pack composed of four lithium-ion batteries.

[0036] When the SOC of one of the lithium-ion batteries in the lithium-ion battery pack is higher than the average value, the initial voltage U B1 > U B2 . When the switch S1 is in the open state, the diode D1 is in the non-conducting state through one of the inter-stage capacitors C VB and keeps the inter-stage capacitor C VB discharging. When the voltage U VB of the inter-stage capacitor C CVB rises to be equal to the output voltage U B , the diode D1 conducts. The relationship between the voltage ripple and the equalization deviation of the inter-stage capacitor C VB is:

[0037]

[0038] where ΔU is the voltage deviation between adjacent battery cells, and ΔV pp is the peak value of the voltage ripple of the inter-stage capacitor C VB , V peak is the peak voltage of the inter-stage capacitor C VB during the open stage of the switch S1, and V avg is the average voltage of the inter-stage capacitor C VB ;

[0039] The relationship between the capacitance value and the ripple is:

[0040]

[0041] where I charge is the charging current, Toff is the switch-off time, and C VB is the capacitance value of the inter-stage capacitor C VB ;

[0042] When the capacitance value range of the output capacitor C1 is between 100 μF and 1000 μF, the output voltage ripple satisfies ΔV out < 0.02 V, and the output voltage ripple is much smaller than the peak-to-peak voltage ripple ΔV VB of the inter-stage capacitor C pp It can be considered that the average voltage of U B1 is approximately equal to the peak voltage of the inter-stage capacitor C VB during the switch-off stage of switch S1. Therefore, the voltage deviation Δu between U B1 and U B2 is equal to the difference between the peak voltage and the average value, that is, half of the peak-to-peak voltage ripple of the inter-stage capacitor C VB . As the capacitance value of the inter-stage capacitor C VB increases, the voltage ripple of the inter-stage capacitor C VB will become smaller and smaller.

[0043] The relationship between the capacitor voltage ripple ΔU VB and the inter-stage capacitor C VB is:

[0044]

[0045] The voltage deviation Δu is:

[0046]

[0047] It can be seen from the above formula that as the capacitance value of capacitor C VB increases, the voltage ripple of capacitor C VB will become smaller and smaller. Therefore, the output voltage deviation will decrease as the capacitance value of C VB increases, and the voltages of U B1 and U B2 will be closer. When the capacitance value range of the three inter-stage capacitors C VB is between 220 μF and 1000 μF, the peak-to-peak voltage ripple ΔV pp ≤ 0.04 V, and the voltage deviation ΔU of the four lithium-ion batteries ≤ 0.02 V, meeting the equalization accuracy requirements.

[0048] Please refer to Figure 3 . In the series battery pack, the SOCs set for the four lithium-ion batteries are different, and other parameters are the same. Among them, Battery 1 is 85%, Battery 2 is 83%, Battery 3 is 80%, and Battery 4 is 75%, which can achieve the SOC equalization of the four battery cells.

[0049] It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, in any regard, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Accordingly, all changes that fall within the meaning and scope of the equivalent elements of the claims are intended to be embraced within the present invention. Any reference signs in the claims should not be construed as limiting the claims concerned.

Claims

1. A charging equalization circuit for a lithium battery pack, comprising a basic Zeta converter, n - 1 inter - stage capacitors C VB , n - 1 output expansion units and n lithium - ion batteries, characterized in that: The basic Zeta converter includes an inductor L1, an inductor L in , a capacitor C1, a capacitor C i1 , a switch S1, and a diode D1; Each of the output expansion units is composed of an inductor L2, a capacitor C2, and a capacitor C i2 and a diode D2. The n-1 inter-stage capacitors C VB are installed in one-to-one correspondence with the output expansion units. One end of one of the inter-stage capacitors C VB is respectively connected to the capacitor C i1 and the capacitor C i2 . The remaining n inter-stage capacitors C VB are both connected to the capacitors C i2 in two adjacent output expansion units; n of the lithium-ion batteries are respectively installed corresponding to the capacitor C1 and n - 1 capacitors C2. The positive and negative electrodes of one of the lithium-ion batteries are respectively connected to both ends of the capacitor C1, and the positive and negative electrodes of the remaining n - 1 lithium-ion batteries are respectively connected to both ends of the n - 1 capacitors C2. The negative electrodes of every two adjacent lithium-ion batteries are connected to the positive electrodes, and the n lithium-ion batteries are connected in series.

2. The charging equalization circuit for a lithium battery pack according to claim 1, wherein: The gate of the switch S1 is connected to a controller, and the duty cycle of the gate of the switch S1 floats between 0 and 1. The drain of the switch S1 is connected to a DC input source u in positive electrode, and the source of the switch S1 is respectively connected to the inductor L in and the capacitor C i1 The end of the capacitor C i1 far from the source of the switch S1 is respectively connected to the cathode of the diode D1 and the inductor L1. One end of the inductor L1 is connected to the capacitor C1, and the end of the capacitor C1 far from the inductor L1 is respectively connected to the anode of the diode D1, the inductor L in and the DC input source u in cathode connection.

3. The charging equalization circuit of a lithium battery pack according to claim 1, characterized in that: The capacitor C i2 has one end connected to the cathode of diode D2 and inductor L2 respectively. One end of the inductor L2 is connected to the capacitor C2, and the end of the capacitor C2 far from the inductor L2 is connected to the anode of diode D2.

4. The charging equalization circuit of a lithium battery pack according to claim 3, characterized in that: When n is 4, the switch S1 is in the closed state, and the inductor L in is charged through the DC input source u in from the positive electrode. The diode D1 and the three diodes D2 are reverse-biased and cut off. The DC input source u in charges one of the inter-stage capacitors C in through a loop composed of the DC input source U VB , the inter-stage capacitor C i2 , the capacitor C VB and the inductor L2. The other two inter-stage capacitors C VB are charged through the power supply. The four lithium-ion batteries form a lithium-ion battery pack.

5. The charging equalization circuit of a lithium battery pack according to claim 3, characterized in that: When n is 4, the switch S1 is in the off state, and the diode D1 and three diodes D2 are conducting, and one of the inter-stage capacitors C VB discharges through the loop composed of the inter-stage capacitor C VB , the inductor L in , the inductor L2 and the capacitor C i2 , and both of the two inter-stage capacitors C VB are in the discharge state.

6. The charging equalization circuit of a lithium battery pack according to claim 4 or 5, characterized in that: When the SOC of one of the lithium-ion batteries in the lithium-ion battery pack is higher than the average value, the initial voltage U B1 > U B2 , when the switch S1 is in the off state, the diode D1 is in the non-conducting state through one of the inter-stage capacitors C VB and keeps the inter-stage capacitor C VB discharging. The voltage U VB of the inter-stage capacitor C CVB rises to be equal to the output voltage U B , and then the diode D1 conducts.

7. The charging equalization circuit of a lithium battery pack according to claim 6, characterized in that: The inter-stage capacitor C VB The relationship between the voltage ripple and the equalization deviation is as follows: where ΔU is the voltage deviation between adjacent battery cells, and ΔV pp is the peak value of the voltage ripple of the inter-stage capacitor C VB and V peak is the peak voltage of the inter-stage capacitor C VB during the off stage of switch S1, and V avg is the average voltage of the inter-stage capacitor C VB ; The relationship between the capacitance value of the capacitor and the ripple is as follows: Where I charge is the charging current, Toff is the switch-off time, and C VB is the capacitance value of the inter-stage capacitor C VB ; When the capacitance value range of the output capacitor C1 is between 100 μF and 1000 μF, the output voltage ripple satisfies Δvout < 0.02V.

8. The charging equalization circuit of a lithium battery pack according to claim 7, characterized in that: The capacitor voltage ripple ΔU VB and the inter-stage capacitor C VB are related as follows: The voltage deviation Δu is: The capacitance values of the three inter-stage capacitors C VB are in the range of 220 μF to 1000 μF, and the peak-to-peak voltage ripple ΔV pp ≤ 0.04 V, and the voltage deviation ΔU of the four lithium-ion batteries ≤ 0.02 V.

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