Lithium battery low-temperature cold start system and control method

Abstract

The present invention relates to the field of lithium batteries, and disclosed are a lithium battery low-temperature cold start system and control method. The system comprises: a lithium battery, a lithium battery voltage compensation unit, a heating element, a switch tube SW1, a diode D1, a rapid self-heating circuit, a diode D2, a load, a temperature measurement module, and a control module; the rapid self-heating circuit comprises an inductor L1, a switch tube SW2, and a current-limiting resistor R2; the temperature measurement module is used for monitoring the temperature of the lithium battery; and the control module is used for outputting a control signal on the basis of the temperature of the lithium battery in the system starting process, so as to control the working states of the switch tube SW1 and the switch tube SW2, thereby sequentially implementing in stages the internal self-heating and current limiting of the lithium battery, boosting output and external auxiliary heating of the lithium battery, and normal output and external auxiliary heating of the lithium battery. The present invention does not require preheating in advance, thereby increasing the lithium battery cold start speed and the battery heating speed, and guaranteeing stable voltage output of a load end and the quick response capability of the system.

Description

A low-temperature cold start system and control method for a lithium battery Technical Field

[0001] The present invention belongs to the field of lithium batteries, and in particular relates to a low-temperature cold start system and a control method for a lithium battery. Background Art

[0002] In recent years, with the advancement of lithium-ion battery technology, hybrid or pure electric vehicles (EVs) have become increasingly popular in automobiles, agricultural machinery, and construction machinery. However, battery systems suffer from poor high-power discharge and starting performance in low-temperature conditions. In cold regions and plateau areas of northern my country, where temperatures can drop below -40°C, these low temperatures increase the polarization resistance of lithium-ion batteries, significantly reduce the voltage output platform, and decrease output power, significantly limiting the full and effective application of electrification.

[0003] When starting construction machinery and large transport vehicles, a large starting current and power are required. At the same time, the load requires a stable voltage output to ensure normal starting. However, under low temperature conditions, the polarization resistance is very large, and the large starting current will cause a large voltage drop in the lithium battery, which cannot provide sufficient power and a stable voltage output platform to start the vehicle. How to quickly and efficiently cold start the battery system is one of the urgent problems to be solved in the application of battery systems in cold regions.

[0004] Currently, a common cold-start solution for lithium batteries is to use a battery heating system to raise the battery temperature. However, this method requires a certain warm-up time, making it difficult to start quickly. Furthermore, in cold conditions, the system automatically dissipates heat, making long-term low-power heating extremely inefficient.

[0005] Therefore, more efficient cold-start methods for lithium batteries are needed, including high-power heating methods to reduce the warm-up time and energy consumption during cold-start, and ensure that the system can quickly provide sufficient power output in low-temperature environments. At the same time, it is also necessary to consider how to ensure the system's stable voltage output capability. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a low-temperature cold start system and control method for lithium batteries. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] In a first aspect, an embodiment of the present invention provides a low-temperature cold start system for a lithium battery, comprising:

[0008] A lithium battery, a lithium battery voltage compensation unit, a heating element, a switch tube SW1, a diode D1, a rapid self-heating circuit, a diode D2, a load, a temperature detection module, and a control module; wherein the rapid self-heating circuit includes an inductor L1, a switch tube SW2, and a current-limiting resistor R2; wherein the resistance of the current-limiting resistor R2 is the ratio of the lithium battery rated voltage to the maximum current limit;

[0009] The temperature detection module is used to monitor the temperature of the lithium battery; the control module is used to output different control signals according to different temperatures during the startup process of the low-temperature cold start system of the lithium battery; the output control signal controls the working status of the switch tube SW1 and the switch tube SW2, and realizes internal self-heating and current limiting of the lithium battery, lithium battery boost output and external auxiliary heating, and normal output of the lithium battery and external auxiliary heating in stages.

[0010] In one embodiment of the present invention, the component connection relationship of the low-temperature cold starting system of the lithium battery includes:

[0011] The positive electrode of the lithium battery is connected to the positive electrode of the diode D1 and the input end of the inductor L1;

[0012] The cathode of the diode D1 is connected to the anode of the lithium battery voltage compensation unit and the anode of the load; and the cathode of the diode D1 is connected to the drain of the switch tube SW1;

[0013] The source of the switch tube SW1 is connected to one end of the heating element, and the other end of the heating element is connected to the negative electrode of the lithium battery and the negative electrode of the load;

[0014] The output end of the inductor L1 is connected to the anode of the diode D2 and the drain of the switch tube SW2;

[0015] The cathode of the diode D2 is connected to the anode of the lithium battery voltage compensation unit and the anode of the load;

[0016] The source of the switch tube SW2 is connected to one end of the current limiting resistor R2, and the other end of the current limiting resistor R2 is connected to the negative electrode of the lithium battery, the negative electrode of the lithium battery voltage compensation unit and the negative electrode of the load;

[0017] The gate of the switch tube SW1 is connected to the control signal S1 output by the control module, and the gate of the switch tube SW2 is connected to the control signal S2 output by the control module.

[0018] In one embodiment of the present invention, the control signal output by the control module includes a high-level signal, a low-level signal and a PWM signal.

[0019] In one embodiment of the present invention, the lithium battery voltage compensation unit includes a supercapacitor.

[0020] In one embodiment of the present invention, the heating element comprises a thermistor.

[0021] In one embodiment of the present invention, the heating element includes a heating and thermal insulation film covering the lithium battery.

[0022] In one embodiment of the present invention, the working principle of realizing internal self-heating and current limiting of a lithium battery includes:

[0023] When the control signal S1 is a low-level signal and the control signal S2 is a high-level signal, the switch tube SW1 is controlled to be turned off and the switch tube SW2 is turned on, so that the self-heating circuit generates an instantaneous short-circuit current that does not exceed the maximum discharge rate of the lithium battery based on the current limiting resistor R2, thereby realizing internal self-heating and current limiting of the lithium battery.

[0024] In one embodiment of the present invention, the working principle of realizing the lithium battery boost output and external auxiliary heating includes:

[0025] When the control signal S1 is a high-level signal and the control signal S2 is a PWM signal, the switch tube SW1 is controlled to be turned on, and the switch tube SW2 is frequently turned on and off to achieve the boost output of the lithium battery. At the same time, the external auxiliary heating during the boost process is achieved by connecting the heating element in parallel.

[0026] In one embodiment of the present invention, the working principle of achieving normal output of the lithium battery and external auxiliary heating includes:

[0027] When the control signal S1 is a high-level signal and the control signal S2 is a low-level signal, the switch tube SW1 is controlled to be turned on and the switch tube SW2 is turned off, thereby realizing conventional external auxiliary heating of the battery, and allowing the lithium battery to output through the diode D1, thereby realizing normal output of the lithium battery, and the lithium battery voltage compensation unit is first discharged to realize external auxiliary heating, and when the discharge voltage of the lithium battery voltage compensation unit is equal to the voltage of the lithium battery, the lithium battery voltage compensation unit and the lithium battery are passively connected in parallel to jointly provide power to the load, and the lithium battery voltage compensation unit acts as a power filter, passively providing power or absorbing excess output power of the lithium battery.

[0028] In a second aspect, an embodiment of the present invention provides a low-temperature cold start control method for a lithium battery, which is applied to the low-temperature cold start system for the lithium battery described in the first aspect. The method includes:

[0029] When the temperature detection module detects that the temperature of the lithium battery is lower than the preset lower temperature limit, the control module outputs a low-level signal to control the switch tube SW1 to turn off, and outputs a high-level signal to control the switch tube SW2 to turn on, thereby achieving internal self-heating and current limiting of the lithium battery;

[0030] When the temperature detection module detects that the temperature of the lithium battery is greater than or equal to the preset lower temperature limit but less than the preset normal temperature start temperature, the control module outputs a PWM signal to control the switch tube SW2 to frequently turn on or off, and outputs a high-level signal to control the switch tube SW1 to turn on, thereby achieving lithium battery boost output and external auxiliary heating;

[0031] When the temperature detection module detects that the temperature of the lithium battery is greater than or equal to the preset normal temperature start-up temperature, the control module outputs a high-level signal to control the switch tube SW1 to turn on, and outputs a low-level signal to control the switch tube SW2 to turn off, thereby achieving normal output of the lithium battery and external auxiliary heating.

[0032] Beneficial effects of the present invention:

[0033] The embodiment of the present invention detects the temperature of the lithium battery and uses a control signal to control the conduction or shutdown of the switch tube SW1 and the switch tube SW2. It can sequentially achieve internal self-heating and current limiting of the lithium battery, boost output of the lithium battery and external auxiliary heating, and normal output of the lithium battery and external auxiliary heating in stages. Compared with the traditional self-heating method of lithium batteries, the present invention does not require preheating in advance and can achieve simultaneous internal and external heating of the lithium battery. It can use a fast self-heating circuit to boost the voltage and compensate the lithium battery voltage. During the lithium battery self-heating process, it can ensure stable voltage output and rapid startup of the system, which can improve the response speed of the entire system and the battery heating speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 shows the discharge characteristic curves of lithium batteries at low and normal temperatures;

[0035] FIG2 is a schematic structural diagram of a low-temperature cold start system for a lithium battery provided by an embodiment of the present invention;

[0036] FIG3 is a main circuit topology diagram of a low-temperature cold start system for a lithium battery according to an embodiment of the present invention;

[0037] FIG4 is a current path diagram of active internal heating of a lithium battery as an example in an embodiment of the present invention;

[0038] FIG5 is a current path diagram of a lithium battery boost auxiliary heating as an example in an embodiment of the present invention;

[0039] FIG6 is a current path diagram of supercapacitor-assisted heating as an example in an embodiment of the present invention;

[0040] FIG7 is a current path diagram of conventional auxiliary heating of a lithium battery as an example in an embodiment of the present invention;

[0041] FIG8 is a schematic flow chart of a low-temperature cold start control method for a lithium battery provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Please refer to Figure 1, which shows the discharge characteristic curves of a lithium battery at different temperatures. It can be seen that at low temperatures, the lithium battery is low in temperature when it starts, and there is a significant voltage drop; as the working time increases, its own temperature rises, and the voltage begins to rise again. A common lithium battery cold start solution is to use a battery heating system to increase the battery temperature, but it requires a certain amount of preheating time, making it difficult to start quickly. At the same time, under cold conditions, the system automatically consumes heat, and long-term low-power heating is extremely inefficient. Therefore, in order to solve the above problems, an embodiment of the present invention provides a low-temperature cold start system and control method for a lithium battery.

[0044] In a first aspect, an embodiment of the present invention provides a low-temperature cold start system for a lithium battery, as shown in FIG2 , which may include:

[0045] A lithium battery, a lithium battery voltage compensation unit, a heating element, a switch tube SW1, a diode D1, a rapid self-heating circuit, a diode D2, a load, a temperature detection module, and a control module; wherein the rapid self-heating circuit includes an inductor L1, a switch tube SW2, and a current-limiting resistor R2;

[0046] Among them, the resistance of the current limiting resistor R2 is the ratio of the rated voltage of the lithium battery to the maximum current limit; those skilled in the art can understand that, through the above setting, the resistance of the current limiting resistor R2 is a very small value, specifically, the resistance of the current limiting resistor R2 is less than 1 ohm, or even less than 0.1 ohm.

[0047] The temperature detection module is used to monitor the temperature of the lithium battery; the control module is used to output different control signals according to different temperatures during the startup process of the low-temperature cold start system of the lithium battery; the output control signal controls the working status of the switch tube SW1 and the switch tube SW2, and realizes internal self-heating and current limiting of the lithium battery, lithium battery boost output and external auxiliary heating, and normal output of the lithium battery and external auxiliary heating in stages.

[0048] Among them, the internal self-heating and current limiting of the lithium battery, the boost output of the lithium battery and the external auxiliary heating, and the normal output of the lithium battery and the external auxiliary heating can be understood as the three stages of the low-temperature cold start process.

[0049] Referring to FIG2 , the connection relationship of the components of the low-temperature cold start system of the lithium battery includes:

[0050] The positive electrode of the lithium battery is connected to the positive electrode of the diode D1 and the input end of the inductor L1;

[0051] The cathode of the diode D1 is connected to the anode of the lithium battery voltage compensation unit and the anode of the load; and the cathode of the diode D1 is connected to the drain of the switch tube SW1;

[0052] The source of the switch tube SW1 is connected to one end of the heating element, and the other end of the heating element is connected to the negative electrode of the lithium battery and the negative electrode of the load;

[0053] The output end of the inductor L1 is connected to the anode of the diode D2 and the drain of the switch tube SW2;

[0054] The cathode of the diode D2 is connected to the anode of the lithium battery voltage compensation unit and the anode of the load;

[0055] The source of the switch tube SW2 is connected to one end of the current limiting resistor R2, and the other end of the current limiting resistor R2 is connected to the negative electrode of the lithium battery, the negative electrode of the lithium battery voltage compensation unit and the negative electrode of the load;

[0056] The gate of the switch tube SW1 is connected to the control signal S1 output by the control module, and the gate of the switch tube SW2 is connected to the control signal S2 output by the control module.

[0057] In the embodiment of the present invention, the heating element can be represented by R1.

[0058] In an optional embodiment, the heating element includes a thermistor, or PTC for short.

[0059] In an optional embodiment, the heating element includes a heating and thermal insulation film covering the lithium battery.

[0060] Alternatively, the heating element in the embodiment of the present invention may be a combination of a thermistor and a heating and heat-insulating film covering the lithium battery. However, it should be noted that the heating element in the embodiment of the present invention is not limited to the above. Any element that can achieve a heating function in a circuit can be included in the protection scope of the heating element in the embodiment of the present invention, and no specific limitation is imposed here.

[0061] In one optional embodiment, the control signal output by the control module includes a high-level signal, a low-level signal, and a PWM (pulse width modulation) signal. In this embodiment of the present invention, the control signal S1 output by the control module is used to control the switch SW1, and the control signal S2 output by the control module is used to control the switch SW2. The control signal S1 can be a high-level signal or a low-level signal, and the control signal S2 can be a high-level signal, a low-level signal, or a PWM signal. It is understood that a PWM signal is composed of periodic high and low levels.

[0062] The embodiment of the present invention sequentially controls the two switching tubes SW1 and SW2 through high and low level signals or PWM signals, thereby realizing rapid heating or heat preservation inside and outside the lithium battery and ensuring stable voltage output and rapid response of the system.

[0063] Among them, the switch tube SW1 is driven and controlled by high and low level signals. It is turned on when the signal is high and turned off when the signal is low. The switch tube SW1 is used to control the external auxiliary heating of the lithium battery; the switch tube SW2 is driven and controlled by PWM signals or high and low level signals. It is turned on when the signal is high and turned off when the signal is low. The switch tube SW2 can not only control the active heating inside the lithium battery, but also control the boost output of the lithium battery, which will be explained in detail later.

[0064] In an optional embodiment, the lithium battery voltage compensation unit includes a supercapacitor, or may also include a low-temperature lithium battery, etc., which is not specifically limited here.

[0065] In order to facilitate understanding of the embodiments of the present invention, the heating element is illustrated as a thermistor and the lithium battery voltage compensation unit is illustrated as a supercapacitor in the following text. Therefore, the low-temperature cold start system of the lithium battery in the embodiment of the present invention can be understood by referring to Figure 3.

[0066] In an optional embodiment, for a low-temperature cold start system of a lithium battery, the working principle of realizing internal self-heating and current limiting of the lithium battery includes:

[0067] When the control signal S1 is a low-level signal and the control signal S2 is a high-level signal, the switch tube SW1 is controlled to be turned off and the switch tube SW2 is turned on, so that the self-heating circuit generates an instantaneous short-circuit current that does not exceed the maximum discharge rate of the lithium battery based on the current limiting resistor R2, thereby realizing internal self-heating and current limiting of the lithium battery.

[0068] Specifically, when the system needs to start quickly, the temperature of the lithium battery itself is relatively low due to being in a cold environment for a long time. Direct startup requires a large current due to the load, and the lithium battery will experience a huge voltage drop, resulting in the system being unable to start normally or reliably. The existing technology usually uses a battery heating system for preheating to increase the temperature of the lithium battery, but it requires a certain preheating time, making it difficult to start quickly. At the same time, under cold conditions, the system automatically consumes heat, and long-term low-power heating will result in extremely low efficiency. In order to avoid extra waiting time, supercapacitors can directly provide starting current, but supercapacitors can only provide instantaneous large current. Long-term large current output will inevitably lead to voltage drop. Therefore, the embodiment of the present invention considers actively self-heating the lithium battery when the temperature of the lithium battery is extremely low and while the supercapacitor provides large current. Since the current limiting resistor R2 in the self-heating circuit is very small, when the switch tube SW2 is turned on, the internal current passing through the lithium battery will be very large in a short time, which is equivalent to the instantaneous short-circuit current. At this time, the lithium battery realizes internal active heating through its own internal resistance heat, that is, the internal self-heating of the lithium battery is realized, realizing a high-power heating method, which can reduce the warm-up time and energy consumption during the cold start of the battery; and the embodiment of the present invention sets the resistance value of the current limiting resistor R2, so that the instantaneous short-circuit current generated does not exceed the maximum discharge rate of the lithium battery, thereby realizing the current limiting function and playing the role of protecting the circuit. The working principle of the circuit at this time can be understood in conjunction with the current path diagram of the active heating of the lithium battery shown in Figure 4; the black bold arrow line represents the current path at this time.

[0069] In an optional embodiment, for a low-temperature cold start system of a lithium battery, the working principle of realizing a lithium battery boost output and external auxiliary heating includes:

[0070] When the control signal S1 is a high-level signal and the control signal S2 is a PWM signal, the switch tube SW1 is controlled to be turned on, and the switch tube SW2 is frequently turned on and off to achieve the boost output of the lithium battery. At the same time, the external auxiliary heating during the boost process is achieved by connecting the heating element in parallel.

[0071] Specifically, after the lithium battery is self-heated, the temperature of the lithium battery rises rapidly, thereby reducing the polarization resistance, resulting in a significant drop in the lithium battery voltage output platform. At this time, the switch tube SW2 can be controlled by the PWM signal to frequently turn on and off to achieve high-power output of the lithium battery boost, thereby effectively ensuring the stable voltage output of the system; at the same time, the switch tube SW1 is turned on and external auxiliary heating is performed through the heating element R1, which can achieve boost auxiliary heating as an external auxiliary heating method for lithium batteries. In addition, the boost output of the lithium battery can further increase the speed of battery heating. The working principle of the circuit at this time can be understood in conjunction with the current path diagram of the lithium battery boost auxiliary heating shown in Figure 5; the black bold arrow line represents the current path at this time.

[0072] In an optional embodiment, for a low-temperature cold start system of a lithium battery, the working principle of achieving normal output of the lithium battery and external auxiliary heating includes:

[0073] When the control signal S1 is a high-level signal and the control signal S2 is a low-level signal, the switch tube SW1 is controlled to be turned on and the switch tube SW2 is turned off, thereby realizing conventional external auxiliary heating of the battery, and allowing the lithium battery to output through the diode D1, thereby realizing normal output of the lithium battery, and the lithium battery voltage compensation unit is first discharged to realize external auxiliary heating, and when the discharge voltage of the lithium battery voltage compensation unit is equal to the voltage of the lithium battery, the lithium battery voltage compensation unit and the lithium battery are passively connected in parallel to jointly provide power to the load, and the lithium battery voltage compensation unit acts as a power filter, passively providing power or absorbing excess output power of the lithium battery.

[0074] Specifically, through the lithium battery boost output and external auxiliary heating, the system can reach a state of full startup at room temperature. At this time, the switch tube SW2 can be turned off to stop the internal heating and boosting work, and the switch tube SW1 is kept on. The lithium battery outputs normally through the diode D1, and the heating element R1 can be used to achieve external auxiliary heating, that is, to achieve conventional external auxiliary heating of the battery. At this time, due to the previous boost, the voltage of the supercapacitor is higher than the voltage of the lithium battery. The supercapacitor will first discharge to provide energy for the load and external auxiliary heating, that is, to achieve the supercapacitor auxiliary heating function. Please refer to the current path diagram of the supercapacitor assisted heating shown in Figure 6 for understanding; when the discharge voltage of the supercapacitor is equal to the voltage of the lithium battery, the two are passively connected in parallel to provide power to the load together. The supercapacitor is now a power filter, passively providing power or absorbing excess output power of the lithium battery, as shown in Figure 7. Figure 7 is a current path diagram of conventional auxiliary heating of a lithium battery as an example in an embodiment of the present invention; Figures 6 and 7 use black bold arrows to indicate the corresponding current paths.

[0075] The low-temperature cold start system for lithium batteries provided in the embodiments of the present invention realizes rapid self-heating of the lithium battery internally by integrating internal self-heating, current limiting and boost output, thereby ensuring stable voltage output at the load end. External auxiliary heating can realize rapid external heating and has a heat preservation function, thereby increasing the internal and external heating speed of the system while ensuring stable voltage output at the load end and the system's rapid response capability.

[0076] Furthermore, when a supercapacitor is used as a lithium battery voltage compensation unit, the external auxiliary heating provided by the system includes three modes: boost auxiliary heating, supercapacitor auxiliary heating and battery conventional auxiliary heating.

[0077] In a second aspect, a low-temperature cold start control method for a lithium battery is applied to the low-temperature cold start system for the lithium battery described in the first aspect. Referring to FIG. 8 , the method may include:

[0078] S100, when the temperature detection module detects that the temperature of the lithium battery is lower than a preset lower temperature limit, the control module outputs a low-level signal to control the switch tube SW1 to turn off, and outputs a high-level signal to control the switch tube SW2 to turn on, thereby achieving internal self-heating and current limiting of the lithium battery;

[0079] The lower limit of the preset temperature may be -40°C, etc., and is not specifically limited here.

[0080] Specifically, when the temperature detection module detects that the temperature of the lithium battery is lower than the preset temperature lower limit, the system starts to work, the control module outputs a low-level signal to control the switch tube SW1 to turn off, and outputs a high-level signal to control the switch tube SW2 to turn on. Since the current limiting resistor R2 is very small, at this time, the lithium battery performs internal rapid self-heating through the rapid self-heating circuit with a current that does not exceed the maximum discharge rate, and the supercapacitor provides the first stage starting power to the load, as shown in Figure 4.

[0081] S200, when the temperature detection module detects that the temperature of the lithium battery is greater than or equal to the preset lower temperature limit but less than the preset normal temperature start temperature, the control module outputs a PWM signal to control the switch tube SW2 to frequently turn on or off, and outputs a high-level signal to control the switch tube SW1 to turn on, thereby achieving lithium battery boost output and external auxiliary heating;

[0082] The preset normal temperature start temperature may be 0°C, etc., and is not specifically limited here.

[0083] Specifically, after the lithium battery is internally heated, the polarization resistance decreases, which can ensure the voltage output power of the lithium battery. When the temperature detection module detects that the temperature of the lithium battery is greater than or equal to the preset temperature lower limit but less than the preset normal temperature starting temperature, the remaining energy of the supercapacitor decreases, and the control module outputs a PWM signal to drive the switch tube SW2 to achieve lithium battery boost output, and then the lithium battery and the supercapacitor jointly provide the second stage starting power. At the same time, the control module outputs a high-level signal to control the switch tube SW1 to turn on, and the lithium battery is boosted and auxiliary heated through the resistance heating element R1, as shown in Figure 5.

[0084] S300, when the temperature detection module detects that the temperature of the lithium battery is greater than or equal to the preset normal temperature start-up temperature, the control module outputs a high-level signal to control the switch tube SW1 to turn on, and outputs a low-level signal to control the switch tube SW2 to turn off, thereby achieving normal output of the lithium battery and external auxiliary heating.

[0085] Wherein, the preset temperature lower limit is lower than the preset normal temperature starting temperature.

[0086] Specifically, when the temperature detection module detects that the internal and external temperatures of the lithium battery have reached the preset normal temperature start-up temperature, the normal voltage platform output of the lithium battery can be guaranteed, and the control module outputs a low-level signal to control the switch tube SW2 to turn off, and the lithium battery outputs normally through the diode D1. The control module outputs a high-level signal to control the switch tube SW1 to turn on, and the heating element R1 is used to achieve conventional auxiliary heating of the battery. At this time, since the voltage of the supercapacitor is higher than the voltage of the lithium battery due to the early boost, the supercapacitor will first discharge to provide energy for the load and external auxiliary heating, realizing supercapacitor auxiliary heating, as shown in Figure 6. Moreover, when the discharge voltage of the supercapacitor is equal to the voltage of the lithium battery, the two are passively connected in parallel to provide power to the load together. At this time, the supercapacitor is a power filter, passively providing power or absorbing excess output power of the lithium battery, as shown in Figure 7.

[0087] The low-temperature cold start control method of a lithium battery provided in an embodiment of the present invention is that when the system needs to start quickly, the temperature of the lithium battery itself is relatively low due to being in a cold environment for a long time. Direct startup requires a large current due to the load, and the lithium battery has a huge voltage drop, resulting in the system being unable to start normally or reliably. First, the lithium battery is actively self-heated. At the same time, in order to avoid spending extra waiting time, a lithium battery voltage compensation unit such as a supercapacitor can directly provide a starting current, but it can only provide a transient large current. Long-term large current output will inevitably cause a voltage drop. During the period when the supercapacitor provides a large current, the lithium battery can achieve internal active heating through a fast self-heating circuit. After the temperature rises rapidly, the polarization resistance decreases. Thereafter, a boosted high-power output is achieved through PWM signal control. After the system is fully started, the switch tube SW2 is controlled to turn off, so that the internal heating stops and the boost work stops. The lithium battery outputs normally through the diode D1, passively connected in parallel with the supercapacitor to provide power to the load, and the switch tube SW1 is controlled to remain on to achieve external auxiliary heating and heat preservation of the lithium battery, thereby maintaining continuous voltage and power output capabilities under low temperature conditions.

[0088] It can be seen that the embodiment of the present invention detects the temperature of the lithium battery and uses a control signal to control the switching tube SW1 and the switching tube SW2 to be turned on or off, which can realize the internal self-heating and current limiting of the lithium battery, the boost output of the lithium battery and external auxiliary heating, and the normal output of the lithium battery and external auxiliary heating in stages. Compared with the traditional self-heating method of the lithium battery, the present invention does not require preheating in advance, can achieve simultaneous heating of the lithium battery internally and externally, can use a fast self-heating circuit to boost the voltage and compensate the lithium battery voltage, ensure stable voltage output and rapid startup of the system during the self-heating process of the lithium battery, and can improve the response speed of the entire system and the battery heating speed.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A low temperature cold start system for a lithium battery, characterized in that: include: A lithium battery, a lithium battery voltage compensation unit, a heating element, a switch tube SW1, a diode D1, a fast self-heating circuit, a diode D2, a load, a temperature detection module and a control module; wherein the fast self-heating circuit includes an inductor L1, a switch tube SW2 and a current limiting resistor R2; wherein the resistance of the current limiting resistor R2 is the ratio of the rated voltage of the lithium battery to the maximum current limit; The temperature detection module is used to monitor the temperature of the lithium battery; the control module is used to output different control signals according to different temperatures during the startup process of the low-temperature cold start system of the lithium battery; the working states of the switch tube SW1 and the switch tube SW2 are controlled by the output control signal, and the internal self-heating and current limiting of the lithium battery, the lithium battery boost output and external auxiliary heating, and the normal output of the lithium battery and external auxiliary heating are realized in stages.

2. The low temperature cold start system of a lithium battery according to claim 1, characterized in that: The component connection relationship of the low temperature cold start system of the lithium battery includes: The positive electrode of the lithium battery is connected to the positive electrode of the diode D1 and the input end of the inductor L1; The cathode of the diode D1 is connected to the anode of the lithium battery voltage compensation unit and the anode of the load; and the cathode of the diode D1 is connected to the drain of the switch tube SW1; The source electrode of the switch tube SW1 is connected to one end of the heating element, and the other end of the heating element is connected to the negative electrode of the lithium battery and the negative electrode of the load; The output end of the inductor L1 is connected to the anode of the diode D2 and the drain of the switch tube SW2; The cathode of the diode D2 is connected to the anode of the lithium battery voltage compensation unit and the anode of the load; The source of the switch tube SW2 is connected to one end of the current limiting resistor R2, and the other end of the current limiting resistor R2 is connected to the negative electrode of the lithium battery, the negative electrode of the lithium battery voltage compensation unit and the negative electrode of the load; The gate of the switch tube SW1 is connected to the control signal S1 output by the control module, and the gate of the switch tube SW2 is connected to the control signal S2 output by the control module.

3. The low temperature cold start system of a lithium battery according to claim 1, characterized in that: The control signal output by the control module includes a high level signal, a low level signal and a PWM signal.

4. The low temperature cold start system of a lithium battery according to claim 1, characterized in that: The lithium battery voltage compensation unit includes a super capacitor.

5. The low temperature cold start system of a lithium battery according to claim 1, characterized in that: The heating element includes a thermistor.

6. The low temperature cold start system of a lithium battery according to claim 1, characterized in that: The heating element comprises a heating and heat-insulating film covering the lithium battery.

7. The low temperature cold start system of a lithium battery according to any one of claims 1 to 6, characterized in that: The working principle of realizing internal self-heating and current limiting of lithium batteries includes: When the control signal S1 is a low-level signal and the control signal S2 is a high-level signal, the switch tube SW1 is controlled to be turned off and the switch tube SW2 is turned on, so that the self-heating circuit generates an instantaneous short-circuit current that does not exceed the maximum discharge rate of the lithium battery based on the current limiting resistor R2, thereby realizing internal self-heating and current limiting of the lithium battery.

8. The low temperature cold start system of a lithium battery according to claim 7, characterized in that: The working principle of realizing lithium battery boost output and external auxiliary heating includes: When the control signal S1 is a high level signal and the control signal S2 is a PWM signal, the switch tube SW1 is controlled to be turned on, and the switch tube SW2 is frequently turned on and off to achieve the boost output of the lithium battery. At the same time, the external auxiliary heating in the boost process is achieved by connecting the heating element in parallel.

9. The low temperature cold start system of a lithium battery according to claim 8, characterized in that: The working principle of achieving normal output of lithium battery and external auxiliary heating includes: When the control signal S1 is a high-level signal and the control signal S2 is a low-level signal, the switch tube SW1 is controlled to be turned on and the switch tube SW2 is turned off to realize conventional external auxiliary heating of the battery, and the lithium battery is output through the diode D1 to realize normal output of the lithium battery, and the lithium battery voltage compensation unit is first discharged to realize external auxiliary heating, and when the discharge voltage of the lithium battery voltage compensation unit is equal to the voltage of the lithium battery, the lithium battery voltage compensation unit and the lithium battery are passively connected in parallel to jointly provide power for the load, and the lithium battery voltage compensation unit acts as a power filter to passively provide power or absorb excess output power of the lithium battery.

10. A low temperature cold start control method for a lithium battery, characterized in that: A low-temperature cold start system for a lithium battery according to any one of claims 1 to 9, the method comprising: When the temperature detection module detects that the temperature of the lithium battery is lower than the preset lower temperature limit, the control module outputs a low-level signal to control the switch tube SW1 to turn off, and outputs a high-level signal to control the switch tube SW2 to turn on, so as to achieve internal self-heating and current limiting of the lithium battery; When the temperature detection module detects that the temperature of the lithium battery is greater than or equal to the preset lower temperature limit, but less than the preset normal temperature start temperature, the control module outputs a PWM signal to control the switch tube SW2 to frequently turn on or off, and outputs a high-level signal to control the switch tube SW1 to turn on, so as to achieve lithium battery boost output and external auxiliary heating; When the temperature detection module detects that the temperature of the lithium battery is greater than or equal to the preset normal temperature starting temperature, the control module outputs a high-level signal to control the switch tube SW1 to turn on, and outputs a low-level signal to control the switch tube SW2 to turn off, thereby achieving normal output of the lithium battery and external auxiliary heating.

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