A cascaded discharge self-heating circuit suitable for high-voltage, high-capacity lithium batteries

Abstract

This invention provides a cascaded self-heating circuit suitable for high-voltage, high-capacity lithium batteries. Each heating circuit includes two heating branches: the first heating branch consists of battery pack B1, switching MOSFET V1, current-limiting inductor L, and capacitor C connected in series; the second heating branch consists of battery pack B2, switching MOSFET V2, current-limiting inductor L, and capacitor C connected in reverse series. By controlling the on / off state of switching MOSFET V1 and MOSFET V2, the two battery packs alternately charge the capacitor, consuming energy and generating heat through the battery's internal resistance. This invention uses a capacitor and inductor in series under low-frequency conditions, limiting the peak current while ensuring the effective current value, thereby improving heating efficiency and achieving soft switching. Through the cascading of heating circuits, the purpose of low-temperature heating of high-voltage, high-capacity lithium battery packs is achieved.

Description

Technical Field

[0001] This invention belongs to the field of low-temperature heating systems for lithium batteries, specifically relating to a cascaded discharge self-heating circuit for high-voltage, high-capacity lithium batteries. Background Technology

[0002] The performance of lithium-ion batteries is closely related to ambient temperature, especially low temperatures, which can lead to severe performance degradation and a significant decrease in safety. At low temperatures, the internal chemical reaction processes of lithium-ion batteries slow down, making discharge difficult, significantly reducing capacity, and drastically lowering key performance indicators such as power density and energy density. Therefore, researching efficient, low-cost, safe, and convenient battery preheating methods has significant scientific value and broad application needs.

[0003] Currently, low-temperature preheating of lithium-ion batteries can be categorized into two main types: external heating and internal heating. External heating is easy to implement, but suffers from low heating efficiency and uneven temperature distribution within the battery pack. Internal self-heating does not require external excitation; instead, it involves charging and discharging the battery. However, in low-temperature environments, charging-heating often leads to lithium deposition in the lithium-ion battery, accelerating battery aging. Furthermore, to avoid overcharging and over-discharging, the current amplitude needs to be limited, resulting in low heating efficiency and certain safety hazards. In contrast, discharging-heating virtually eliminates the risk of lithium deposition and has greater application value. Summary of the Invention

[0004] The purpose of this invention is to provide a cascaded discharge self-heating circuit for high-voltage, high-capacity lithium batteries, which is a capacitor-based cascaded low-temperature heating circuit for lithium batteries, in order to solve the problems of low heating efficiency and poor safety performance in the prior art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A cascaded discharge self-heating circuit suitable for high-voltage, high-capacity lithium batteries, wherein a single heating circuit includes a first heating branch and a second heating branch;

[0007] The first heating branch consists of battery pack B1, switching MOSFET V1, current limiting inductor L and capacitor C connected in series; the drain of switching MOSFET V1 is connected to the positive terminal of battery pack B1, and the gate is connected in series with current limiting inductor L and capacitor C and then connected to the negative terminal of battery pack B1.

[0008] The second heating branch consists of battery pack B2, switching MOSFET V2, current limiting inductor L and capacitor C connected in reverse series; the drain of switching MOSFET V2 is connected to the positive terminal of battery pack B2, and the gate is connected in series with current limiting inductor L and capacitor C and then connected to the negative terminal of battery pack B2.

[0009] By turning MOSFET V1 and MOSFET V2 on and off, battery pack B1 or battery pack B2 can charge capacitor C in turn, thus realizing the internal cyclic heating of the battery.

[0010] Furthermore, multiple individual heating circuits are cascaded to achieve low-temperature heating of high-voltage, high-capacity lithium battery packs.

[0011] Furthermore, under low-frequency conditions, the capacitor C of the first heating branch and the current-limiting inductor L are connected in series to limit the peak current while ensuring the effective value of the current, thereby improving the heating efficiency.

[0012] Furthermore, regarding MOSFET selection, the rated voltage U N The theoretical calculation is determined by equation (1);

[0013] (1)

[0014] Among them, U C This is the rated voltage of the capacitor;

[0015] Rated current I N The theoretical calculation is determined by equation (2):

[0016] (2)

[0017] Among them, I MAX This indicates the peak current of the circuit.

[0018] The beneficial effects of this invention are as follows:

[0019] The self-heating discharge circuit of this invention requires no external excitation, has a simple circuit structure, low implementation cost, and a remarkably high heating rate, effectively improving the performance of lithium batteries at low temperatures. Furthermore, the self-heating discharge circuit of this invention virtually eliminates the risk of lithium deposition, reducing the possibility of safety accidents and ensuring safe and stable operation, thus possessing greater application value.

[0020] Under the same heating efficiency, this invention can achieve a lower switching frequency. At low frequencies, the use of a capacitor and inductor in series limits the peak current while ensuring the effective current value, thereby improving heating efficiency. Simultaneously, the lower switching frequency extends the battery discharge time within a single cycle, allowing the circuit to reach a steady state and the line current to reach zero. This enables the MOSFET to turn on and off under zero current conditions, achieving soft switching.

[0021] Because both batteries are heated simultaneously, fewer switching transistors flow through the circuit in the next cycle at the same frequency, resulting in lower line losses. Furthermore, cascading heating circuits can achieve low-temperature heating of high-voltage, high-capacity lithium battery packs. Attached Figure Description

[0022] Figure 1 Topology diagram of a single heating circuit in this invention;

[0023] Figure 2 Cascaded topology of the heating circuit of this invention;

[0024] Figure 3 Schematic diagram of the heating circuit mode 1 of this invention;

[0025] Figure 4 Schematic diagram of the heating circuit mode 2 of this invention;

[0026] Figure 5 Voltage and current waveforms of a single heating circuit in this invention;

[0027] Figure 6 Temperature rise waveform diagram of a single heating circuit in this invention;

[0028] Figure 7 Voltage and current waveforms of the cascaded heating circuit of this invention;

[0029] Figure 8 This invention ignores the equivalent circuit diagram of inductance. Detailed Implementation

[0030] 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 protection scope of the present invention.

[0031] like Figure 1 As shown, the single heating circuit of the cascaded discharge self-heating circuit for the high-voltage, high-capacity lithium battery of the present invention includes a first heating branch and a second heating branch. The first heating branch is composed of battery pack B1, switching MOSFET V1, current-limiting inductor L, and capacitor C connected in series; the second heating branch is composed of battery pack B2, switching MOSFET V2, current-limiting inductor L, and capacitor C connected in reverse series; multiple single heating branches can be cascaded, such as... Figure 2As shown, low-temperature heating of high-voltage, high-capacity battery packs can be achieved. The drain of the switching MOSFET V1 is connected to the positive terminal of battery pack B1, and its gate is connected in series with the current-limiting inductor L and the capacitor C and then connected to the negative terminal of battery pack B1; the drain of the switching MOSFET V2 is connected to the positive terminal of battery pack B2, and its gate is connected in series with the current-limiting inductor L and the capacitor C and then connected to the negative terminal of battery pack B2.

[0032] By switching MOSFET V1 and MOSFET V2 on and off, a group of batteries alternately charges capacitor C, achieving internal cyclic heating of the battery. Under low-frequency conditions, the capacitor C is connected in series with the current-limiting inductor L, limiting the peak current while ensuring the effective current value, thereby improving heating efficiency. Simultaneously, low-temperature heating of high-voltage, high-capacity lithium battery packs can be achieved through cascading heating circuits.

[0033] For MOSFET selection, the rated voltage U N The theoretical calculation is determined by equation (1);

[0034] (1)

[0035] Among them, U C This is the rated voltage of the capacitor.

[0036] Rated current I N The theoretical calculation is determined by equation (2):

[0037] (2)

[0038] Among them, I MAX This indicates the peak current of the circuit.

[0039] The capacitor voltage, current flowing through the battery, and temperature rise curve of the single heating circuit and the cascaded circuit were simulated and verified respectively.

[0040] The circuit diagram for heating circuit mode one is as follows: Figure 3 As shown, MOSFET V1 is in the ON state, and MOSFET V2 is in the OFF state. Battery pack B1 charges capacitor C, and battery pack B1 stores energy in capacitor C. The heating topology is energized along battery pack B1-MOSFET V1-capacitor C. According to KVL's law, we can obtain:

[0041] (3)

[0042] Among them, u R u L u C u BThese represent the voltage across the resistor, inductor, capacitor, and battery, respectively. C represents the capacitance value, R represents the battery internal resistance, L represents the inductance value, and i represents the current flowing through the circuit.

[0043] Given that the initial voltage of capacitor C is u B The direction is opposite to the current flow direction. From the above formula, the capacitor voltage can be calculated as:

[0044] (4)

[0045] Among them, u C u B These represent the voltages on the capacitor and the battery, respectively; among them, the characteristic roots p1 and p2 are only related to the circuit parameters and structure, and are not related to the excitation and initial energy storage.

[0046] The current flowing through the battery is:

[0047] (5)

[0048] Among them, u B The voltage on the battery is represented by C, the capacitance value is represented by i, and the current flowing through the circuit is represented by i. The characteristic roots p1 and p2 are only related to the circuit parameters and structure, and are not related to the excitation and initial energy storage.

[0049] After a period of time, the circuit reaches a steady state, the capacitor voltage equals the battery voltage, and no current flows through the circuit.

[0050] Heating circuit mode two such Figure 4 As shown, MOSFET V2 is in the ON state, and MOSFET V1 is in the OFF state. At this time, battery pack B2 charges capacitor C, and the capacitor voltage undergoes a process of first decreasing and then increasing in the opposite direction. The heating topology is activated along battery pack B2-MOSFET V2-capacitor C, and similarly, the capacitor voltage is:

[0051] (6)

[0052] Among them, u C and u represent the voltages on the capacitor and battery, respectively; among them, the characteristic roots p1 and p2 are only related to the circuit parameters and structure, and are not related to the excitation and initial energy storage.

[0053] The current flowing through the battery is:

[0054] (7)

[0055] Among them, u BThe voltage on the battery is represented by C, the capacitance value is represented by i, and the current flowing through the circuit is represented by i. The characteristic roots p1 and p2 are only related to the circuit parameters and structure, and are not related to the excitation and initial energy storage.

[0056] Through the switching between two sets of interactive modes, current continuously flows through the lithium-ion battery, and heat is generated by energy consumption on the internal resistance for low-temperature heating.

[0057] The heating circuit of this invention was verified as follows:

[0058] Step 1: Simulation of heating with a single heating circuit.

[0059] The heating process was simulated in MATLAB / Simulink with a frequency of 3.3 kHz, a capacitor of 100 μF, an inductor of 500 nH, and a duty cycle of 50%. The simulation results are as follows. Figure 5 , Figure 6 As shown in the figure. Where: U represents the voltage waveform at capacitor C; I represents the current waveform flowing through a single battery; T represents the temperature rise waveform of the battery.

[0060] Step 2: Simulation of heating of cascaded circuit.

[0061] In MATLAB / Simulink, a cascaded three heating circuits are used to simulate the low-temperature heating process in a cascaded configuration. The basic parameter settings are the same as for a single heating circuit. The simulation results are as follows: Figure 7 As shown. Where: U represents the voltage waveform at capacitor C; I1 and I2 represent the current flowing through the two batteries in a single heating circuit. From the results, it can be seen that the waveforms of each heating unit... Figure 1 Therefore, each heating unit can ensure independent operation of its internal heating, and cascade heating is feasible.

[0062] Step 3: Verify the heat consumption of a single battery's internal resistance within one cycle.

[0063] At low frequencies, the effect of inductance on the effective value of the current can be ignored. Considering the internal resistance of the switching transistor, the heating circuit used is as follows: Figure 8 As shown. According to the lumped-parameter thermal model, for low-temperature battery heating, the heating efficiency is mainly related to the heat dissipated across the battery's internal resistance. The calculation formula is:

[0064] (8)

[0065] Where: T represents the period; I represents the current flowing through a single cell; R represents the internal resistance of the cell; r represents the line circuit; U B This indicates the battery voltage.

[0066] Step 4: Line loss verification within one cycle.

[0067] For low-temperature battery heating, the heating efficiency is also related to circuit losses. The calculation formula is as follows:

[0068] (9)

[0069] Where: T represents the period; I represents the current flowing through a single cell; R represents the internal resistance of the cell; r represents the line circuit; U B This indicates the battery voltage.

[0070] The present invention has been described in detail above through specific embodiments and examples, but these are not intended to limit the invention. Those skilled in the art can modify and apply the structure and parameters of the heating system without departing from the principles of the invention, and can also do so according to actual circumstances.

Claims

1. A self-heating circuit suitable for high-voltage and high-capacity lithium batteries, characterized in that: a single heating circuit comprises a first heating branch and a second heating branch; the first heating branch is composed of a battery pack B1, a switch MOSFET V1, a current-limiting inductor L, and a capacitor C connected in series; the drain electrode of the switch MOSFET V1 is connected to the positive electrode of the battery pack B1, and the gate electrode is connected to the current-limiting inductor L and the capacitor C in series and then connected to the negative electrode of the battery pack B1; the second heating branch is composed of a battery pack B2, a switch MOSFET V2, a current-limiting inductor L, and a capacitor C connected in reverse series; the drain electrode of the switch MOSFET V2 is connected to the positive electrode of the battery pack B2, and the gate electrode is connected to the current-limiting inductor L and the capacitor C in series and then connected to the negative electrode of the battery pack B2; by turning on and off the switch MOSFET V1 and the switch MOSFET V2, the battery pack B1 or the battery pack B2 is used to charge the capacitor C alternately, realizing internal cycle heating of the battery; under low-frequency conditions, the capacitor C and the current-limiting inductor L in each of the first heating branch and the second heating branch are connected in series, limiting the peak current while ensuring the effective value of the current.

2. The low temperature heating circuit according to claim 1, wherein: a plurality of single heating circuits are cascaded to realize low-temperature heating of high-voltage and high-capacity lithium battery packs.

3. The low temperature heating circuit according to claim 1, wherein: For the MOSFET selection, the rated voltage U N The theoretical calculation is determined by equation (1); (1) wherein U C is the capacitor rated voltage; Rated current I N The theoretical calculation is determined by equation (2): (2) where I MAX represents the peak current of the circuit.

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