An equalization circuit for a plurality of lithium battery packs connected in series

Abstract

The application relates to a kind of equalization circuits of multiple lithium battery groups in series, the negative pole of lithium battery group is connected with the negative pole of voltage sampling unit, the negative pole of capacitor C3 and the negative pole of winding L1, the positive pole of lithium battery group 1 is connected with the anode of diode of photoelectric coupler G1 and G2, the positive pole of voltage sampling unit, the positive pole of capacitor C3, the cathode of rectifier diode D1, the anode of rectifier diode D1 is connected with the positive pole of winding L1, the cathode of diode of photoelectric coupler G1 and G2 is connected with two enable ends of voltage sampling unit, the power supply positive pole and negative pole of equalization driving unit are connected with the cathode and anode of voltage stabilizing diode D5 in voltage dividing circuit in parallel, the output end of equalization driving unit 31 is connected with the gate of field effect transistor T1, the source of field effect transistor T1 is connected with the positive pole of winding L5, the negative pole of winding L5 is connected with the positive pole of total lithium battery group, the application effectively solves the capacity difference problem existing between series lithium battery groups, can make the voltage of lithium battery group equal, so that lithium battery group capacity is fully utilized.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to an equalization circuit for multiple lithium battery packs connected in series. Background Technology

[0002] Lead-acid batteries typically have a single cell voltage of 12V. In energy storage applications, it's common to use four 12V batteries of the same capacity connected in series. However, in the current transition from lead to lithium, there's significant market potential for replacing lead-acid batteries with four 12.8V lithium iron phosphate batteries. While 12.8V lithium battery packs generally have internal balancing circuits, there are inherent capacity and voltage differences before they leave the factory. These differences become increasingly pronounced during use. Sometimes, purchased lithium batteries may not be from the same batch or even the same company, leading to even greater capacity and voltage variations. Furthermore, buying two batteries last year, using them for a while, and then buying two more this year for simultaneous use can result in significant capacity and voltage differences. Series-connected lithium battery packs exhibit a "weakest link" effect: charging is based on the highest voltage lithium battery, while discharging is based on the lowest voltage lithium battery. Therefore, voltage balancing between lithium battery packs is crucial. Summary of the Invention

[0003] To overcome the above-mentioned technical problems, the present invention provides an equalization circuit for multiple lithium battery packs connected in series, and a method for using multiple lithium battery packs in series, thereby solving the problem that the capacity of lithium battery packs cannot be fully utilized due to differences in capacity and voltage in these applications.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] An equalization circuit for multiple lithium battery packs connected in series includes several lithium battery packs, several voltage sampling units, an equalization current conversion circuit, a voltage divider circuit, an equalization switch unit, and a charger. The lithium battery packs are connected in series. The equalization current conversion circuit includes an equalization drive unit, a field-effect transistor T1, an equalization rectifier transformer composed of a winding L5 in a magnetic core connected in series with several windings L1 on the other side and a rectifier diode D1, and a filter circuit composed of several capacitors C3 connected in series. The negative terminal of each lithium battery pack is connected to the negative terminal of the voltage sampling unit, the negative terminal of capacitor C3, and the negative terminal of winding L1. The positive terminal of the equalization drive unit is connected to the anode of the diode in optocouplers G1 and G2, the positive terminal of the voltage sampling unit, the positive terminal of capacitor C3, and the cathode of rectifier diode D1. The anode of rectifier diode D1 is connected to the positive terminal of winding L1. The cathode of the diode in optocouplers G1 and G2 is connected to the two enable terminals of the voltage sampling unit. The positive and negative terminals of the power supply of the equalization drive unit are connected in parallel with the cathode and anode terminals of Zener diode D5 in the voltage divider circuit. The output terminal of equalization drive unit 31 is connected to the gate of field-effect transistor T1. The source of field-effect transistor T1 is connected to the positive terminal of winding L5. The negative terminal of winding L5 is connected to the positive terminal of the total lithium battery pack.

[0006] Furthermore, the voltage divider circuit consists of a Zener diode D5, a resistor R22, and the drain and source of a field-effect transistor T2 connected in series, which are then connected in parallel to the negative and positive terminals of the total lithium battery pack. The gate of the field-effect transistor T2 is connected to the equalization switch unit.

[0007] Furthermore, the equalization switch unit is equipped with transistors G1S, G3S, G5S, G7S, G2S, G4S, G6S, G8S and resistors R20 and R21 in the optocoupler. Transistors G1S, G3S, G5S and G7S in the optocoupler are the transistor parts in optocoupler G1 in the four voltage sampling units (2). Their collectors are connected in series with resistor R20, and their emitters are connected in series with resistor R21 and connected to the gate of T2 in the voltage divider circuit. The other end of resistor R20 is connected to the positive terminal of the total lithium battery pack, and the other end of resistor R21 is connected to the negative terminal of the total lithium battery pack. Transistors G2S, G4S, G6S and G8S in the optocoupler are the transistor parts in optocoupler G2 in the four voltage sampling units (2). Their series connection is connected in parallel with resistor R21.

[0008] Furthermore, the voltage sampling unit includes resistors R1 to R6, capacitors C1 to C2, and voltage regulator chips IC1 to IC2. Resistors R1 and R2 are connected in series, and resistor R1 is connected in parallel with capacitor C1. The connection line between resistors R1 and R2 and the positive terminal of capacitor C1 are connected to the reference terminal of voltage regulator chip IC1. The cathode of voltage regulator chip IC1 is connected to resistor R5, and the other end of resistor R5 is connected to the cathode of diode in optocoupler G1. Resistors R3 and R4 are connected in series, and resistor R3 is connected in parallel with capacitor C2. The connection line between resistors R3 and R4 and the positive terminal of capacitor C2 are connected to the reference terminal of voltage regulator chip IC2. The cathode of voltage regulator chip IC2 is connected to resistor R6, and the other end of resistor R6 is connected to the cathode of diode in optocoupler G2.

[0009] Furthermore, the equalization drive unit includes a switching power supply chip IC9, resistors R24 to R27, capacitors C13 to C15, and a rectifier diode D6. The switching power supply chip IC9 is connected to resistors R27, R25, R24, C13, C14, and C15 respectively. Resistor R25 and rectifier diode D6 are connected in parallel. The anode of rectifier diode D6 is connected to resistor R26. Resistor R25 is connected to the gate of field-effect transistor T1. Resistor R24 ​​is connected to the drain of field-effect transistor T1. A current sampling resistor R23 is connected in series between the drain of field-effect transistor T1 and the negative terminal of the total lithium battery pack.

[0010] Furthermore, after winding L1 and rectifier diode D1 are connected in series, capacitor C3 is connected to both ends to form an equalization charging unit, which is connected in parallel to the positive and negative terminals of the lithium battery pack. After several equalization charging units are connected in series, their two ends are connected to the positive and negative terminals of the total lithium battery pack, respectively.

[0011] Furthermore, a capacitor C16, a resistor R28, and a rectifier diode D7 are installed between the two ends of winding L5 to form a peak voltage absorption circuit, protecting T1 from overvoltage damage. The equalization current conversion circuit 3 is also equipped with a filter capacitor C17.

[0012] The current circuit diagram describes a lithium battery pack with a total voltage of 51.2V, consisting of four 12.8V lithium battery packs connected in series. This invention can also be applied to 24V and 36V lead-to-lithium conversion applications, as well as to the series application of ternary lithium battery packs, sodium battery packs, and solid-state battery packs.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] It solves the problem of capacity differences in lithium battery packs, avoids the "weakest link" effect caused by capacity differences, and enables voltage balance between lithium battery packs, so that the capacity of lithium battery packs can be fully utilized. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the circuit structure of the present invention.

[0016] Figure 2 This is a schematic diagram of the detailed circuit structure of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] This invention provides an equalization circuit for multiple lithium battery packs connected in series, and a method for using multiple lithium battery packs connected in series, thereby solving the problem that the capacity of lithium battery packs cannot be fully utilized due to differences in capacity and voltage in these applications.

[0019] Specifically, an equalization circuit for multiple lithium battery packs connected in series includes several lithium battery packs 1, several voltage sampling units 2, an equalization current conversion circuit 3, a voltage divider circuit 4, an equalization switch unit 5, and a charger 6. The several lithium battery packs 1 are connected in series. The equalization current conversion circuit 3 includes an equalization drive unit 31, a field-effect transistor T1, an equalization rectifier transformer composed of windings L5 in a magnetic core 32 connected in series with several windings L1 on the other side and rectifier diodes D1, and a filter circuit composed of several capacitors C3 connected in series. The negative terminal of the lithium battery pack 1 is connected to the negative terminal of the voltage sampling unit 2, the negative terminal of the capacitor C3 and the negative terminal of the windings L1. The positive terminal of lithium battery pack 1 is connected to the anode of the diode in optocouplers G1 and G2, the positive terminal of voltage sampling unit 2, the positive terminal of capacitor C3, and the cathode of rectifier diode D1. The anode of rectifier diode D1 is connected to the positive terminal of winding L1. The cathodes of the diodes in optocouplers G1 and G2 are connected to the two enable terminals of voltage sampling unit 2. The positive and negative terminals of the power supply of equalization drive unit 31 are connected in parallel with the cathode and anode terminals of Zener diode D5 in voltage divider circuit 4. The output terminal of equalization drive unit 31 is connected to the gate of field-effect transistor T1. The source of field-effect transistor T1 is connected to the positive terminal of winding L5. The negative terminal of winding L5 is connected to the positive terminal of the total lithium battery pack.

[0020] The voltage divider circuit 4 consists of a Zener diode D5, a resistor R22, and the drain and source of a field-effect transistor T2 connected in series, which are then connected in parallel to the negative and positive terminals of the total lithium battery pack. The gate of the field-effect transistor T2 is connected to the equalization switch unit 5.

[0021] The equalization switch unit is equipped with transistors G1S, G3S, G5S, G7S, G2S, G4S, G6S, G8S and resistors R20 and R21 in the optocoupler. Transistors G1S, G3S, G5S and G7S in the optocoupler are the transistor parts in optocoupler G1 in the four voltage sampling units (2). Their collectors are connected in series with resistor R20 and their emitters are connected in series with resistor R21. They are also connected to the gate of the field effect transistor T2 in the voltage divider circuit. The other end of resistor R20 is connected to the positive terminal of the total lithium battery pack and the other end of resistor R21 is connected to the negative terminal of the total lithium battery pack. Transistors G2S, G4S, G6S and G8S in the optocoupler are the transistor parts in optocoupler G2 in the four voltage sampling units (2). Their series connection is connected in parallel with resistor R21.

[0022] The voltage sampling unit 2 includes resistors R1 to R6, capacitors C1 to C2, and voltage regulator chips IC1 to IC2. Resistors R1 and R2 are connected in series, and resistor R1 is connected in parallel with capacitor C1. The connection line between resistors R1 and R2 and the positive terminal of capacitor C1 are connected to the reference terminal of voltage regulator chip IC1. The cathode of voltage regulator chip IC1 is connected to resistor R5, and the other end of resistor R5 is connected to the cathode of diode in optocoupler G1. Resistors R3 and R4 are connected in series, and resistor R3 is connected in parallel with capacitor C2. The connection line between resistors R3 and R4 and the positive terminal of capacitor C2 are connected to the reference terminal of voltage regulator chip IC2. The cathode of voltage regulator chip IC2 is connected to resistor R6, and the other end of resistor R6 is connected to the cathode of diode in optocoupler G2.

[0023] The equalization drive unit 31 includes a switching power supply chip IC9, resistors R24 to R27, capacitors C13 to C15, and a rectifier diode D6. The switching power supply chip IC9 is connected to resistors R27, R25, R24, C13, C14, and C15 respectively. Resistor R25 and rectifier diode D6 are connected in parallel. The anode of rectifier diode D6 is connected to resistor R26. Resistor R25 is connected to the gate of field-effect transistor T1. Resistor R24 ​​is connected to the drain of field-effect transistor T1. A current sampling resistor R23 is connected in series between the drain of field-effect transistor T1 and the negative terminal of the total lithium battery pack.

[0024] After winding L1 and rectifier diode D1 are connected in series, capacitor C3 is connected to both ends to form an equalization charging unit, which is connected in parallel to the positive and negative terminals of the lithium battery pack. After several equalization charging units are connected in series, their two ends are connected to the positive and negative terminals of the total lithium battery pack.

[0025] A capacitor C16, a resistor R28, and a rectifier diode D7 are installed between the two ends of winding L5 to form a peak voltage absorption circuit, which protects T1 from overvoltage damage. The equalization current conversion circuit 3 is also equipped with a filter capacitor C17.

[0026] When the lithium battery pack has not reached its equalization voltage, all optocouplers are blocked. The total voltage of the series-connected lithium battery pack cannot be connected to the equalization drive circuit through resistor R20, and the equalization current conversion stops working. During charging, the lithium battery pack voltage rises. The set equalization charging voltage for lithium battery pack 1 (approximately 13.8V for 4 series lithium iron phosphate batteries, about 95% of the current total capacity) is then reached. Specifically, the voltage at the connection point of resistors R1 and R2 in one of the four voltage sampling units 2 first reaches 2.5V, turning on the voltage regulator IC1. The LED in optocoupler G1 generates current through the voltage regulator IC1, and the transistors G1S, G3S, and G4S in the optocoupler... At least one of the transistors 5S and G7S is conducting. The total voltage flows through resistor R20, the optocoupler's transistors G1S, G3S, G5S, or G7S, and resistor R21 to form a current. The voltage drop across resistor R21 turns on MOSFET T2. MOSFET T2's drain follows its gate, generating an output voltage. This voltage is regulated by Zener diode D5 through resistor R22, supplying power to the switching power supply chip IC9. This generates a pulse voltage that is transmitted to MOSFET T1 through resistor R25. The total lithium battery pack voltage forms a loop through winding L5, MOSFET T1, and resistor R23. As the current increases, the voltage drop across resistor R23 also increases, feeding back to the switch through resistor R24. When the power supply chip IC9 reaches a certain threshold, the switching power supply chip IC9 shuts off its output, the MOSFET T1 turns off, and the current in winding L5 is interrupted. The electrical energy stored in winding L5 generates a flyback voltage. This voltage is transmitted to the four identical windings L1 through the core of the equalizing transformer, and then rectified by four rectifier diodes D1 to charge the four lithium battery packs. This cycle repeats. According to the working principle of the flyback converter, the lithium battery pack with the lowest voltage receives the largest charging current, allowing the lower-voltage lithium battery pack to receive more charging power, thus achieving voltage balance among the four lithium battery packs. Balance cannot continue indefinitely as it will consume power. When the equalization charging voltage is reached (for four series lithium iron phosphate batteries...), the equalization charging will stop. (Around 14.3V, which is more than 99% of the current total capacity of the lithium battery pack). That is, when the voltage at the connection point of the four sets of resistors R3 and R4 is greater than 2.5V, the four voltage regulator chips IC2 are turned on. The light-emitting diodes in the four optocouplers G2 form current through the four voltage regulator chips IC2, and their transistors G2S, G4S, G6S, and G8S are all turned on. The total voltage of the lithium battery pack is short-circuited through resistor R20 and the voltage at the gate of the field-effect transistor T2 through the transistors G7S, G5S, G3S, and G1S in optocoupler G1. The drain output of the field-effect transistor T2 is zero, the switching power supply chip IC9 does not receive the power supply voltage and stops working, and the equalization ends.

[0027] Taking a total voltage of 51.2V as an example, the total voltage is divided across resistor R21 through resistor R20 and the conducting optocoupler. It can be set to around 35V, and the Zener diode D5 is selected to be 15V.

[0028] The equalizer can also be connected to an external charger 6 to charge lithium battery packs that have not reached the starting equalization charging voltage, and to replenish the power loss during the equalization process. It can also provide the power required for the equalization process of 2-cell and 3-cell lithium battery packs.

[0029] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A balancing circuit for multiple lithium battery packs connected in series, characterized in that: The application relates to a lithium battery equalization charging device, which comprises a plurality of lithium battery groups (1), a plurality of voltage sampling units (2), an equalization current conversion circuit (3), a voltage dividing circuit (4), an equalization switch unit (5) and a charger (6). The lithium battery groups (1) are connected in series. The equalization current conversion circuit (3) comprises an equalization driving unit (31), a field effect transistor T1, an equalization rectifier transformer composed of a winding L5 in a magnetic core (32) and a plurality of windings L1 on the other side and a rectifier diode D1 connected in series and then connected in series, and a filter circuit composed of a plurality of capacitors C3 connected in series. The negative pole of the lithium battery group (1) is connected with the negative pole of the voltage sampling unit (2), the negative pole of the capacitor C3 and the negative pole of the winding L1. The positive pole of the lithium battery group (1) is connected with the anode of the diode in the optical coupler G1 and G2, the positive pole of the voltage sampling unit (2), the positive pole of the capacitor C3 and the cathode of the rectifier diode D1. The anode of the rectifier diode D1 is connected with the positive pole of the winding L1. The cathodes of the diodes in the optical couplers G1 and G2 are connected with the two enable ends of the voltage sampling unit (2). The positive and negative poles of the equalization driving unit (31) are connected in parallel with the cathode and anode of the voltage stabilizing diode D5 in the voltage dividing circuit (4). The output end of the equalization driving unit (31) is connected with the gate of the field effect transistor T1. The source of the field effect transistor T1 is connected with the positive pole of the winding L5. The negative pole of the winding L5 is connected with the positive pole of the total lithium battery group. The voltage dividing circuit (4) is composed of the voltage stabilizing diode D5, the resistor R22, the drain and source of the field effect transistor T2 connected in series and connected in parallel with the negative and positive poles of the total lithium battery group. The gate of the field effect transistor T2 is connected with the equalization switch unit (5). The equalization switch unit (5) is provided with the optical coupler triodes G1S, G3S, G5S, G7S, G2S, G4S, G6S, G8S and the resistors R20 and R21. The optical coupler triodes G1S, G3S, G5S and G7S in the optical coupler are respectively the triode parts in the optical coupler G1 in the four voltage sampling units (2). The collector and the emitter of the triode parts connected in parallel are connected with the resistor R20 and the resistor R21 respectively. The gate of the field effect transistor T2 in the voltage dividing circuit (4) is connected with the resistor R20 and the resistor R21. The other end of the resistor R20 is connected with the positive pole of the total lithium battery group. The other end of the resistor R21 is connected with the negative pole of the total lithium battery group. The optical coupler triodes G2S, G4S, G6S and G8S in the optical coupler are respectively the triode parts in the optical coupler G2 in the four voltage sampling units (2). The triode parts connected in series are connected with the resistor R21 in parallel.

2. The balancing circuit for a plurality of lithium battery packs connected in series according to claim 1, wherein: The voltage sampling unit (2) comprises resistors R1-R6, capacitors C1-C2 and voltage stabilizing chips IC1-IC2, the resistor R1 and R2 are connected in series, the resistor R1 is connected with the capacitor C1 in parallel, the connection line of the resistor R1 and R2 and the positive pole of the capacitor C1 are connected with the reference end of the voltage stabilizing chip IC1, the cathode of the voltage stabilizing chip IC1 is connected with the resistor R5, the other end of the resistor R5 is connected with the diode cathode in the photo-coupler G1, the resistor R3 and R4 are connected in series, the resistor R3 is connected with the capacitor C2 in parallel, the connection line of the resistor R3 and R4 and the positive pole of the capacitor C2 are connected with the reference end of the voltage stabilizing chip IC2, the cathode of the voltage stabilizing chip IC2 is connected with the resistor R6, the other end of the resistor R6 is connected with the diode cathode in the photo-coupler G2.

3. The balancing circuit for a plurality of lithium battery packs connected in series according to claim 1, wherein: The equalization driving unit (31) comprises a switching power supply chip IC9, resistors R24-R27, capacitors C13-C15 and a rectifier diode D6, the switching power supply chip IC9 is connected with the resistor R27, the resistor R25, the resistor R24, the capacitor C13, the capacitor C14 and the capacitor C15 respectively, the resistor R25 and the rectifier diode D6 are connected in parallel, the anode of the rectifier diode D6 is connected with the resistor R26, the resistor R25 is connected with the gate of the field effect transistor T1, the resistor R24 is connected with the drain of the field effect transistor T1, the current sampling resistor R23 is connected in series between the drain of the field effect transistor T1 and the negative pole of the total lithium battery group.

4. The balancing circuit for a plurality of lithium battery packs connected in series according to claim 1, wherein: The winding L1 and the rectifier diode D1 are connected in series, and the two ends are connected with the capacitor C3 respectively, to form an equalization charging unit, which is connected in parallel between the positive pole and the negative pole of the lithium battery group, and a plurality of equalization charging units are connected in series, and the two ends are connected with the positive pole and the negative pole of the total lithium battery group respectively.

5. The balancing circuit for a plurality of lithium battery packs connected in series according to claim 1, wherein: The winding L5 is provided with the capacitor C16, the resistor R28 and the rectifier diode D7 between the two ends, and the equalization current conversion circuit (3) is further provided with the filter capacitor C17.

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