Constant voltage charging circuit for lithium battery formation

Abstract

The application discloses a constant-voltage charging circuit for lithium battery formation, comprising a plurality of constant-voltage charging units for formation; all the constant-voltage charging units for formation are connected in series between the positive and negative poles of a DC power supply module; the constant-voltage charging unit for formation comprises a charging control switch, a bypass control circuit and a constant-voltage control circuit; the charging control switch is connected between the positive pole of a battery BAT and the bypass control circuit; the bypass control circuit is connected with the negative pole of the battery BAT; one side of the constant-voltage control circuit is connected with a DC bus, and the other side of the constant-voltage control circuit is connected with the bypass control circuit and the negative pole of the battery BAT. The application can realize accurate control of lithium battery formation, and improves the service life of the battery and the formation efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery charging technology, and in particular to a constant voltage charging circuit for lithium battery formation. Background Technology

[0002] Formation is a crucial step in battery production, significantly impacting battery performance and cycle life. In practical applications, lithium-ion battery cells must be charged and activated after assembly to activate the active materials within the cell and generate the SEI film. Currently, there are three formation processes: series formation, parallel formation, and a hybrid series-parallel formation. Among these, series formation is gaining popularity due to its lower equipment investment and energy costs. Currently, lithium-ion battery formation uses a single-cell formation scheme, where each cell is formed by an independent power source. In contrast, lead-acid battery formation uses a series connection method. Compared to series formation, which requires only one power source to control the formation of a group of cells, resulting in lower equipment costs, lithium-ion batteries are highly sensitive to voltage. Series formation cannot guarantee that the voltage of each cell remains within the same safe voltage range. Therefore, how to achieve series formation for lithium-ion batteries is a pressing technical challenge. Summary of the Invention

[0003] The purpose of this invention is to provide a constant voltage charging circuit for lithium battery formation. This invention enables precise control of lithium battery formation, improving battery life and formation efficiency.

[0004] The technical solution of the present invention is as follows: a constant voltage charging circuit for lithium battery formation, comprising a plurality of formation constant voltage charging units; all formation constant voltage charging units are connected in series between the positive and negative terminals of a DC power module; each formation constant voltage charging unit includes a charging control switch, a bypass control circuit, and a constant voltage control circuit; the charging control switch is connected to the positive terminal of the battery cell BAT and the bypass control circuit; the bypass control circuit is connected to the negative terminal of the battery cell BAT; one side of the constant voltage control circuit is connected to the DC bus, and the other side of the constant voltage control circuit is connected to the bypass control circuit and the negative terminal of the battery cell BAT.

[0005] In the constant voltage charging circuit for lithium battery formation described above, the charging control switch is composed of a PMOS transistor Q1; the drain of the PMOS transistor Q1 is connected to the positive terminal of the battery cell BAT; and the source and gate of the PMOS transistor Q1 are both connected to the bypass control circuit.

[0006] The aforementioned constant voltage charging circuit for lithium battery formation includes a bypass control circuit composed of a PMOS transistor Q2, a magnetic latching relay M1, and a freewheeling diode D1. The source of the PMOS transistor Q2 and one end of the switch of the magnetic latching relay M1 are both connected to the source of the PMOS transistor Q1. The gate of the PMOS transistor Q2 is connected to the negative terminal of the battery cell BAT. The drain of the PMOS transistor Q2 is connected to the gate of the PMOS transistor Q1, the cathode of the freewheeling diode D1, and one end of the inductance of the magnetic latching relay M1. The anode of the freewheeling diode D1 and the other end of the inductance of the magnetic latching relay M1 are connected to the negative terminal of the battery cell BAT. The other end of the switch of the magnetic latching relay M1 is connected to the constant voltage control circuit.

[0007] The aforementioned constant voltage charging circuit for lithium battery formation comprises a constant voltage control circuit consisting of capacitors C1, C2, and C3, diodes D2 and D3, an NMOS transistor Q3, a high-frequency switching transformer T1, a constant voltage control module, and an isolation drive module. One end of capacitor C1, one end of capacitor C2, and one primary side of the high-frequency switching transformer T1 are all connected to the switching terminal of the magnetic latching relay M1. The other end of capacitor C1 is connected to the negative terminal of the battery cell BAT. The other end of capacitor C2 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the high-frequency switching transformer. The other end of the primary side of T1 is connected to the drain of NMOS transistor Q3; the source of NMOS transistor Q3 is connected to the negative terminal of battery cell BAT; the secondary side of the high-frequency switching transformer T1 is connected between the positive and negative terminals of the DC bus, the positive terminal of the DC bus is connected to the cathode of diode D3, and the anode of diode D3 is connected to one end of the secondary side of the high-frequency switching transformer T1; the secondary side of the high-frequency switching transformer T1 is also connected in parallel with capacitor C3 and a constant voltage control module; the output terminal of the constant voltage control module is connected to the isolation drive module, and the isolation drive module is connected to the gate of NMOS transistor Q3.

[0008] The aforementioned charging method for the constant voltage charging circuit used in lithium battery formation involves, after the formation constant voltage charging unit is connected in series to the DC power module and begins operation, the bypass control circuit in the formation constant voltage charging unit continuously monitors whether the cell BAT voltage in the formation constant voltage charging unit has reached the preset charging threshold V. thre If V is not reached thre When the charging control switch is turned on, the DC power module charges the battery cell BAT, and the voltage of the battery cell BAT gradually increases; when the battery cell voltage reaches the preset charging threshold V... threThe bypass control circuit starts working. On the one hand, the charging control switch gradually closes, and the charging current gradually decreases until it reaches zero. On the other hand, the bypass control circuit gradually enters the saturation state from the cutoff state, and the current flowing through the magnetic latching relay coil in the bypass control circuit gradually increases from zero until it reaches the coil operating current. At this time, the normally open contact of the magnetic latching relay closes, and the normally closed contact opens. The open normally closed contact completely disconnects the battery charging circuit and the bypass control circuit, ensuring that the battery cell will not be charged again after it is fully charged, thus ensuring the formation process performance of the battery cell. The closed normally open contact causes the constant voltage control circuit to start working. On the one hand, it ensures that the voltage across the constant voltage charging unit is constant, reducing the current impact on other constant voltage charging units in the circuit. On the other hand, it feeds back the electrical energy absorbed from the DC power module by the constant voltage charging unit to the DC power module, improving the efficiency of the constant voltage charging circuit.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: First, during the cell formation process, the charging current gradually decreases to zero, realizing soft current shutdown, avoiding battery surge current, and improving battery life; Second, after the cell is fully charged, the voltage across the constant voltage charging unit remains constant, reducing current surge to other constant voltage charging units in the circuit; Third, the constant voltage charging unit of the present invention feeds back the electrical energy absorbed from the DC power module to the DC power module, improving the efficiency of the constant voltage charging circuit. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the constant voltage charging circuit provided in the embodiments of this application;

[0011] Figure 2 This is a circuit diagram of the formation constant voltage charging unit provided in an embodiment of this application. Detailed Implementation

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention. The scope of protection of the present invention should include all the contents of the claims, and the following embodiments can enable those skilled in the art to have a more comprehensive understanding of the present invention.

[0013] Example 1: A constant voltage charging circuit for lithium battery formation, such as... Figure 1As shown, it includes several formation constant voltage charging units; all formation constant voltage charging units are connected in series between the positive and negative terminals of the DC power module; each formation constant voltage charging unit includes a charging control switch, a bypass control circuit, and a constant voltage control circuit; the charging control switch is connected to the positive terminal of the battery cell BAT and the bypass control circuit; the bypass control circuit is connected to the negative terminal of the battery cell BAT; one side of the constant voltage control circuit is connected to the DC bus, and the other side of the constant voltage control circuit is connected to the bypass control circuit and the negative terminal of the battery cell BAT. In this embodiment, the formation constant voltage charging unit consists of PMOS transistor Q1, PMOS transistor Q2, NMOS transistor Q3, battery cell BAT, diodes D1, D2, and D3, capacitors C1, C2, and C3, a magnetic latching relay M1 coil and its normally open and normally closed contacts, a high-frequency switching transformer T1, a constant voltage control module, and an isolation drive module, connected as shown in the diagram. Figure 2 As shown, the above electronic components and modules mainly form the following functional circuits:

[0014] Specifically, the charging control switch is composed of a PMOS transistor Q1, controlled by the battery cell BAT voltage; the drain of the PMOS transistor Q1 is connected to the positive terminal of the battery cell BAT; both the source and gate of the PMOS transistor Q1 are connected to the bypass control circuit. Since the gate of the PMOS transistor Q1 is connected to the negative terminal of BAT through the coil of the magnetic latching relay M1, and the source of the PMOS transistor Q1 is connected to the positive terminal of BAT through the normally closed contact of the magnetic latching relay M1, when the BAT voltage does not reach the preset charging threshold V... thre When PMOS transistor Q2 is off, and the gate potential of PMOS transistor Q1 is at the negative terminal of BAT, PMOS transistor Q1 is saturated and turned on, and the DC power module begins to charge BAT. When the voltage of BAT rises to V... thre At this time, PMOS transistor Q2 begins to conduct, moving from the cutoff region to the amplification region. The gate voltage of PMOS transistor Q1 gradually increases, and the conduction level of PMOS transistor Q1 gradually decreases. Consequently, the charging current of the DC power module to BAT gradually decreases until PMOS transistor Q2 saturates and conducts. The saturation of PMOS transistor Q2 causes PMOS transistor Q1 to turn off, reducing the BAT charging current to zero, thus achieving soft-shutdown control during the BAT charging process. Simultaneously, the coil current of the magnetic latching relay M1 increases to its operating current. The corresponding normally open contact closes, causing the constant voltage control circuit to start operating. The normally closed contact opens, completely disconnecting the battery charging circuit and the bypass control circuit, ensuring that the battery is fully charged and no further charging is required, thus guaranteeing the battery's formation process performance.

[0015] The bypass control circuit consists of a PMOS transistor Q2, a magnetic latching relay M1, and a freewheeling diode D1. The source of the PMOS transistor Q2 and one terminal of the switch of the magnetic latching relay M1 are both connected to the source of the PMOS transistor Q1. The gate of the PMOS transistor Q2 is connected to the negative terminal of the battery cell BAT. The drain of the PMOS transistor Q2 is connected to the gate of the PMOS transistor Q1, the cathode of the freewheeling diode D1, and one end of the inductor of the magnetic latching relay M1. The anode of the freewheeling diode D1 and the other end of the inductor of the magnetic latching relay M1 are connected to the negative terminal of the battery cell BAT. The other terminal of the switch of the magnetic latching relay M1 is connected to the constant voltage control circuit. The bypass control circuit is controlled by appropriately selecting the forward voltage of the PMOS transistor Q2. Equal to BAT's preset charging threshold voltage V thre To achieve BAT charging at V thre When the voltage BAT rises, PMOS transistor Q2 turns on and, as BAT increases, transitions from the cutoff region to the amplification region until it saturates and turns on, driving the coil of magnetic latching relay M1 and actuating its normally open and normally closed contacts. The opening of the normally closed contact of M1 turns off PMOS transistors Q1 and Q2, completely disconnecting the BAT charging circuit and ensuring that the cell stops charging once BAT is fully charged, thus maintaining the cell's formation process performance. It also disconnects the M1 coil drive circuit, reducing system power consumption. The closing of the normally open contact of M1 activates the constant voltage control circuit, ensuring a constant voltage across the formation constant voltage charging unit, reducing current surges to other formation constant voltage charging units in the circuit. Furthermore, it feeds back the energy absorbed from the DC power module to the DC power module, improving the efficiency of the formation constant voltage charging circuit. D1 is the freewheeling diode for the M1 coil, providing a freewheeling path for the current flowing through the coil.

[0016] The constant voltage control circuit consists of capacitors C1, C2, and C3, diodes D2 and D3, an NMOS transistor Q3, a high-frequency switching transformer T1, a constant voltage control module, and an isolation drive module. One end of capacitor C1, one end of capacitor C2, and one end of the primary side of the high-frequency switching transformer T1 are all connected to the switching terminal of the magnetic latching relay M1. The other end of capacitor C1 is connected to the negative terminal of the battery cell BAT. The other end of capacitor C2 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the inner side of the primary side of the high-frequency switching transformer T1. The other end is connected to the drain of NMOS transistor Q3; the source of NMOS transistor Q3 is connected to the negative terminal of battery cell BAT; the secondary side of high-frequency switching transformer T1 is connected between the positive and negative terminals of DC bus, the positive terminal of DC bus is connected to the cathode of diode D3, and the anode of diode D3 is connected to one end of the secondary side of high-frequency switching transformer T1; capacitor C3 and constant voltage control module are also connected in parallel on the secondary side of high-frequency switching transformer T1; the output terminal of constant voltage control module is connected to isolation drive module, and isolation drive module is connected to the gate of NMOS transistor Q3. Capacitor C1 is used to stabilize the voltage across the constant voltage charging unit after bypass; capacitor C2, capacitor C3, diode D2, diode D3, high-frequency switching transformer T1, NMOS transistor Q3, constant voltage control module, and isolation drive module constitute a flyback converter. Diode D2 and capacitor C2 are used to absorb voltage and current spikes on the primary side of the high-frequency switching transformer T1; the high-frequency switching transformer T1 provides isolated feedback of electrical energy; capacitor C3 and diode D3 rectify the electrical energy on the secondary side of the high-frequency switching transformer T1; NMOS transistor Q3 is a switching transistor that controls the on / off state of the primary winding coil of the high-frequency switching transformer T1, and is controlled by the isolation drive; the constant voltage control module stabilizes the voltage across C3 by adjusting the duty cycle of the PWM signal in real time, and then controls the voltage across C1 to stabilize at the set value according to the turns ratio of T1; the isolation drive isolates the PWM signal output by the constant voltage control module and drives the on / off control of Q3.

[0017] Example 2: Based on the constant voltage charging circuit for lithium battery formation in Example 1, after the formation constant voltage charging unit is connected in series to the DC power module and starts working, the bypass control circuit in the formation constant voltage charging unit detects in real time whether the cell BAT voltage in the formation constant voltage charging unit reaches the preset charging threshold V. thre If V is not reached thre When the charging control switch is turned on, the DC power module charges the battery cell BAT, and the voltage of the battery cell BAT gradually increases; when the battery cell voltage reaches the preset charging threshold V... threThe bypass control circuit starts working. On the one hand, the charging control switch gradually closes, and the charging current gradually decreases until it reaches zero. On the other hand, the bypass control circuit gradually enters the saturation state from the cutoff state, and the current flowing through the magnetic latching relay coil in the bypass control circuit gradually increases from zero until it reaches the coil operating current. At this time, the normally open contact of the magnetic latching relay closes, and the normally closed contact opens. The open normally closed contact completely disconnects the battery charging circuit and the bypass control circuit, ensuring that the battery cell will not be charged again after it is fully charged, thus ensuring the formation process performance of the battery cell. The closed normally open contact causes the constant voltage control circuit to start working. On the one hand, it ensures that the voltage across the constant voltage charging unit is constant, reducing the current impact on other constant voltage charging units in the circuit. On the other hand, it feeds back the electrical energy absorbed from the DC power module by the constant voltage charging unit to the DC power module, improving the efficiency of the constant voltage charging circuit.

Claims

1. A constant voltage charging circuit for lithium battery formation, characterized in that: It includes several formation constant voltage charging units; all formation constant voltage charging units are connected in series between the positive and negative terminals of the DC power module; each formation constant voltage charging unit includes a charging control switch, a bypass control circuit, and a constant voltage control circuit; the charging control switch is connected to the positive terminal of the battery cell BAT and the bypass control circuit; the bypass control circuit is connected to the negative terminal of the battery cell BAT; one side of the constant voltage control circuit is connected to the DC bus, and the other side of the constant voltage control circuit is connected to the bypass control circuit and the negative terminal of the battery cell BAT; The charging control switch is composed of a PMOS transistor Q1; the drain of the PMOS transistor Q1 is connected to the positive terminal of the battery cell BAT; the source and gate of the PMOS transistor Q1 are both connected to the bypass control circuit. The bypass control circuit consists of a PMOS transistor Q2, a magnetic latching relay M1, and a freewheeling diode D1. The source of the PMOS transistor Q2 and one normally closed switch of the magnetic latching relay M1 are both connected to the source of the PMOS transistor Q1. The gate of the PMOS transistor Q2 is connected to the negative terminal of the battery cell BAT. The drain of the PMOS transistor Q2 is connected to the gate of the PMOS transistor Q1, the cathode of the freewheeling diode D1, and one inductor of the magnetic latching relay M1. The anode of the freewheeling diode D1 and the other inductor of the magnetic latching relay M1 are connected to the negative terminal of the battery cell BAT. The other normally closed switch of the magnetic latching relay M1 is connected to the constant voltage control circuit via the normally open switch of the magnetic latching relay M1.

2. The constant voltage charging circuit for lithium battery formation according to claim 1, characterized in that: The constant voltage control circuit consists of capacitors C1, C2, and C3, diodes D2 and D3, an NMOS transistor Q3, a high-frequency switching transformer T1, a constant voltage control module, and an isolation drive module. One end of capacitor C1, one end of capacitor C2, and one end of the primary side of the high-frequency switching transformer T1 are all connected to the switching terminal of the magnetic latching relay M1. The other end of capacitor C1 is connected to the negative terminal of the battery cell BAT. The other end of capacitor C2 is connected to the cathode of diode D2, and the anode of diode D2 is connected to the cathode of the primary side of the high-frequency switching transformer T1. The other end is connected to the drain of NMOS transistor Q3; the source of NMOS transistor Q3 is connected to the negative terminal of battery cell BAT; the secondary side of high-frequency switching transformer T1 is connected between the positive and negative terminals of DC bus, the positive terminal of DC bus is connected to the cathode of diode D3, and the anode of diode D3 is connected to one end of the secondary side of high-frequency switching transformer T1; capacitor C3 and constant voltage control module are also connected in parallel on the secondary side of high-frequency switching transformer T1; the output terminal of constant voltage control module is connected to isolation drive module, and isolation drive module is connected to the gate of NMOS transistor Q3.

3. The constant voltage charging circuit for lithium battery formation according to claim 1 or 2, characterized in that: After the constant voltage charging unit is connected in series with the DC power module and starts working, the bypass control circuit in the constant voltage charging unit will detect in real time whether the BAT voltage of the battery cell in the constant voltage charging unit has reached the preset charging threshold. If not achieved When the charging control switch is turned on, the DC power module charges the battery cell BAT, and the voltage of the battery cell BAT gradually increases; when the battery cell voltage reaches the preset charging threshold... The bypass control circuit starts working. On the one hand, the charging control switch gradually closes, and the charging current gradually decreases until it reaches zero. On the other hand, the bypass control circuit gradually enters the saturation state from the cutoff state, and the current flowing through the magnetic latching relay coil in the bypass control circuit gradually increases from zero until it reaches the coil operating current. At this time, the normally open contact of the magnetic latching relay closes, and the normally closed contact opens. The open normally closed contact completely disconnects the battery charging circuit and the bypass control circuit, ensuring that the battery cell will not be charged again after it is fully charged, thus ensuring the formation process performance of the battery cell. The closed normally open contact causes the constant voltage control circuit to start working. On the one hand, it ensures that the voltage across the constant voltage charging unit is constant, reducing the current impact on other constant voltage charging units in the circuit. On the other hand, it feeds back the electrical energy absorbed from the DC power module by the constant voltage charging unit to the DC power module, improving the efficiency of the constant voltage charging circuit.

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