Lithium battery bidirectional pulse rapid charging device at low temperature and control method thereof

Abstract

The invention discloses a bidirectional pulse rapid charging device for a lithium battery at low temperature and a control method thereof, and relates to the technical field of preheating and rapid charging of the lithium battery in a low-temperature environment. The device comprises a charging pile, a main circuit and an electric vehicle / unmanned aerial vehicle. The charging pile comprises a first charging gun; the main circuit comprises a device charging interface, an energy storage inductor, a switch S1, a full-control bridge arm, a device controller and a second charging gun; the electric vehicle / unmanned aerial vehicle comprises a charging interface, a power battery, an internal load and a controller. The bidirectional high-frequency pulse current is generated by controlling the switching of the internal load, the on-off of the switch S1 in the main circuit and the full-control devices Q1 and Q2 in the full-control bridge arm, so that the battery can be charged and preheated at low temperature. The charging efficiency of the lithium battery in the low-temperature environment is improved, reversible lithium precipitation is eliminated through negative pulses, the charging time is remarkably shortened, the service life of the battery is prolonged, and the method is suitable for being widely applied to low-temperature environments such as high altitude and high latitude.

Description

Technical Field

[0001] The present invention relates to the technical field of preheating and fast charging of lithium batteries in low temperature environments, and in particular to a bidirectional pulse fast charging device for lithium batteries in low temperature environments and a control method thereof. Background Art

[0002] With the new energy industry prevalent and the low-altitude economy booming, electric vehicles and unmanned aerial vehicles are favored by the transportation industry. At present, electric vehicles and unmanned spacecraft almost all use lithium-ion batteries as power sources because of their high energy density, light weight, and long cycle life. In high altitudes, high latitudes, or in winter, the performance of lithium-ion batteries will drop significantly due to the lower temperature: when charging lithium batteries, the process of lithium ions being removed from the cathode and embedded in the anode is hindered, resulting in extremely low battery charging efficiency and longer charging time, which amplifies the disadvantages of electric vehicles compared to traditional oil vehicles.

[0003] The existing technologies to solve the short range and slow charging of electric vehicles and unmanned aerial vehicles in low-temperature environments mainly adopt three methods: battery swap mode, charging preheating, and unidirectional pulse charging. The smooth operation of the battery swap mode is based on the wide distribution of battery swap stations, which requires large initial infrastructure investment; in addition, the frozen car chassis still needs to be thawed before swapping batteries in extremely cold environments, which will also consume a lot of time, greatly reducing the advantage of battery swapping over charging. The preheating charging mode has cumbersome steps, complex circuit structure, high extra energy consumption, and long charging time, which seriously affects the charging experience in low-temperature environments. Although the existing unidirectional high-frequency pulse charging can charge with a larger current on the basis of reducing the possibility of lithium plating, the unidirectional pulse cannot eliminate the impact of reversible lithium plating on the battery.

[0004] In addition, charging at low temperatures will also cause lithium deposition near the anode of the lithium battery and generate lithium dendrites, causing the battery life to decay rapidly and even causing an internal short circuit in the battery; the internal resistance of the lithium battery increases at low temperatures, resulting in reduced output power and output efficiency. In fact, lithium deposition reactions are divided into reversible lithium deposition and irreversible lithium deposition. Studies have shown that reversible lithium deposition can be eliminated by discharging lithium batteries, improving electrolytes and electrode materials, and the remaining irreversible lithium deposition is called "dead lithium", which will cause irreversible damage to the battery. The endurance and charging of electric vehicles and unmanned aerial vehicles at low temperatures face huge challenges. How to promote fast charging technology that does not deposit lithium in low temperature environments has become a key issue for major companies.

[0005] Therefore, it is an urgent problem for those skilled in the art to propose a bidirectional pulse fast charging device for lithium batteries at low temperatures and a control method thereof to solve the difficulties existing in the prior art. Summary of the invention

[0006] In view of this, the present invention provides a bidirectional pulse fast charging device for lithium batteries at low temperatures and a control method thereof, which can improve the charging efficiency of lithium batteries in low temperature environments, eliminate reversible lithium deposition through negative pulses, significantly shorten the charging time, and extend the battery life.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A bidirectional pulse fast charging device for lithium batteries at low temperatures, comprising: a charging pile, a main circuit, an electric vehicle / unmanned aerial vehicle;

[0009] The charging pile includes: a first charging gun;

[0010] The main circuit includes: device charging interface, energy storage inductor, switch S1, full-control bridge arm, device controller, and second charging gun;

[0011] Electric vehicles / unmanned aerial vehicles include: charging interface, power battery, internal load and controller;

[0012] The first charging gun is connected to the positive and negative electrodes of the device charging interface of the main circuit;

[0013] One end of the energy storage inductor is connected to the positive pole of the device charging interface, and the other end is connected to the midpoint of the fully controlled bridge arm. The fully controlled bridge arm includes: a first fully controlled device Q1, a second fully controlled device Q2, one end of the switch S1 is connected to the positive pole of the device charging interface, and the other end is connected to the positive pole of the second charging gun and one end of the fully controlled bridge arm at the same time. The other end of the fully controlled bridge arm is connected to the negative pole of the device charging interface and the negative pole of the second charging gun.

[0014] The electric vehicle / unmanned aerial vehicle is connected to the second charging gun via the charging interface, and the positive and negative electrodes of the power battery and both ends of the internal load are connected to the charging port;

[0015] The power battery and internal load are also connected to the controller, and the controller, charging pile, switch S1, and full-control bridge arm are all connected to the device controller;

[0016] The charging device has two modes: normal charging mode and bidirectional pulse fast charging mode.

[0017] The above device may optionally be preset with a mode switching temperature T end , if the battery temperature T is lower than the mode switching temperature T end , the control circuit turns on the bidirectional pulse fast charging mode; if the battery temperature T is higher than or equal to the mode switching temperature T end , the control circuit starts the normal charging mode.

[0018] In the above-mentioned device, optionally, the controller, the charging pile, and the device controller are connected by handshaking through the internal low-voltage bus of the second charging gun, the charging interface and the first charging gun, the device charging interface, and information is transmitted via a low-voltage communication protocol.

[0019] The above-mentioned device can optionally, in the bidirectional pulse fast charging mode, the device controller can communicate via the low-voltage bus to control the charging pile to operate in the constant voltage output mode and connect to the main circuit in the form of a constant voltage source.

[0020] The above device can optionally be configured such that, in the bidirectional pulse fast charging mode, S1 is disconnected, the controller controls the internal load to be switched on, and the device controller controls the fully controlled devices Q1 and Q2 to be alternately turned on to generate a bidirectional pulse current;

[0021] State 1: Q1 is on, Q2 is off, the DC source charges the energy storage inductor, and the energy storage inductor current I L The power battery is in a discharge state, and the current is I Load ;

[0022] State 2: Q1 is off, Q2 is on, and the charging current I Charge The energy storage inductor current I L The current I on the power battery decreases. B For I Charge and I Load The power battery is in a superposition state.

[0023] The above device can optionally switch between state 1 and state 2 by using hysteresis control, with a preset reference current I L_ref and ring width 2H;

[0024] Status I L Rising, when I L ≥I L_ref +H, it switches to state 2, at which time I L Decline, when I L ≤I L_ref -H, switches to state 1.

[0025] In the above device, the controller can optionally collect the state of charge SOC and battery temperature T signals of the power battery in real time, and transmit them to the device controller through the low-voltage bus communication. After receiving the signal, the device controller obtains the optimal amplitude I of the battery charging pulse without lithium precipitation according to the internal preset data table. B_ref , frequency f_ref, duty cycle D; when the loop width becomes larger, the frequency will become lower, and when the loop width becomes smaller, the frequency will become higher;

[0026] By adjusting the reference current I L_refThe given value, loop width 2H, and output voltage of the first charging gun control the amplitude, frequency, and duty cycle of the charging pulse.

[0027] The above-mentioned device can optionally have a controller that collects the state of charge SOC and battery entropy thermal coefficient signals of the power battery in real time. After receiving the signals through low-voltage bus communication, the controller controls the switching selection and power changes of different loads in the vehicle to change the amplitude of positive and negative pulses in pulse charging, thereby changing the heat generation rate and charging speed.

[0028] The above device can optionally be configured such that the controller collects the internal load current I in real time. Load The amplitude signal is transmitted to the device controller through the low-voltage bus communication. After receiving the signal, the device controller L_ref Perform the same direction adjustment to keep the positive pulse amplitude at the optimal amplitude I during the bidirectional pulse charging process. B_ref ; when I Load Rise, I L_ref Also rises; when I Load Descending, I L_ref Also decreased.

[0029] A control method for a bidirectional pulse fast charging device of a lithium battery at low temperature, comprising:

[0030] S1, preset cut-off temperature T end ;

[0031] S2. Read the current power battery temperature T, state of charge SOC, and entropy thermal coefficient;

[0032] S3, the controller selects a suitable internal load to access the circuit;

[0033] S4, judging whether the power battery SOC is less than the charging target value, if so, proceeding to the next step; if not, ending the charging;

[0034] S5: Determine whether the battery temperature T is less than the preset cut-off temperature T end If yes, proceed to the next step; if no, switch to normal charging mode and charge until the end;

[0035] S6, look up the table to obtain the maximum pulse charging heat generation rate I corresponding to the current temperature T and SOC without lithium deposition B_ref , f_ref and duty cycle D;

[0036] S7, Adjustment I L_ref , ring width 2H, output voltage of the first charging gun;

[0037] S8, fast charging in bidirectional pulse fast charging mode;

[0038] S9, read the current internal load current ILoad ;

[0039] S10. Judgment I Load Fluctuation occurs, if so, then according to I Load Adjustment I L_ref , so that the charging current amplitude of the bidirectional pulse charging reaches I B_ref , return to S8; if not, return to S2.

[0040] It can be seen from the above technical solution that, compared with the prior art, the present invention provides a bidirectional pulse fast charging device for lithium batteries at low temperatures and a control method thereof, which have the following beneficial effects: 1) It can not only reduce the possibility of lithium plating, but also eliminate part of the reversible lithium plating phenomenon through discharge pulses, thereby reducing the amount of lithium plating in lithium batteries and extending the cycle life of lithium batteries; 2) The device has a simple structure and can be conveniently integrated into a charging pile or inside a car. For electric vehicles / unmanned aerial vehicles, only a slight adjustment of the load structure is required, and no new components need to be added, so the feasibility is very high; 3) Internal preheating and pulse charging are carried out simultaneously, with high electro-thermal conversion efficiency, avoiding lithium plating, reducing the charging time in low temperature environments, and extending the battery life; 4) The device adjusts the access resistance of different loads or adjusts the load power through user portraits, actual battery SOC, and battery entropy thermal coefficient to ensure that no additional damage is caused to the battery while preheating and fast charging the battery. External damage, while meeting the actual load requirements of users to the greatest extent; 5) Hysteresis negative feedback control, simple structure, strong robustness, through bus communication can be real-time according to the battery temperature, SOC and the internal load of the electric vehicle / unmanned aerial vehicle, flexibly adjust the pulse amplitude, frequency, duty cycle to ensure that the battery obtains the maximum heat generation rate and charging efficiency without lithium precipitation; 6) The device can execute different charging strategies according to the actual ambient temperature; 7) The amplitude of the battery charging pulse can be dynamically maintained stable to avoid causing additional life aging to the battery; 8) The device can shake hands with the DC charging pile and the electric vehicle / unmanned aerial vehicle, adjust the charging strategy through the communication protocol, and adopt the CC-PC charging strategy to shorten the charging time while ensuring the durability of the battery; 9) The DC input part of the device has a variety of power sources and is compatible with a variety of power supply forms. The device has strong environmental adaptability and is suitable for the current energy layout and power distribution environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0042] Figure 1This is an overall circuit diagram of a bidirectional pulse fast charging device for lithium batteries at low temperatures provided by the present invention;

[0043] Figure 2 A schematic diagram of the power flow and communication of a bidirectional pulse fast charging device for lithium batteries at low temperatures provided by the present invention;

[0044] Figure 3 A schematic diagram of a state of a bidirectional pulse fast charging device for lithium batteries at low temperature provided by the present invention;

[0045] Figure 4 A schematic diagram of a second state of a bidirectional pulse fast charging device for lithium batteries at low temperature provided by the present invention;

[0046] Figure 5 A bidirectional pulse current is generated by alternately conducting the full-control devices Q1 and Q2 of a bidirectional pulse fast charging device for lithium batteries at low temperatures provided by the present invention;

[0047] Figure 6 A flow chart of a control method for a bidirectional pulse fast charging device for lithium batteries at low temperatures provided by the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0049] In this application, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0050] Reference Figure 1 As shown, the present invention discloses a bidirectional pulse fast charging device for lithium batteries at low temperatures, comprising: a charging pile, a main circuit, an electric vehicle / unmanned aerial vehicle;

[0051] Further, the charging pile includes: a first charging gun;

[0052] The main circuit includes: device charging interface, energy storage inductor, switch S1, full-control bridge arm, device controller, and second charging gun;

[0053] Electric vehicles / unmanned aerial vehicles include: charging interface, power battery, internal load and controller;

[0054] Furthermore, the first charging gun is connected to the positive and negative electrodes of the device charging interface of the main circuit;

[0055] One end of the energy storage inductor is connected to the positive pole of the device charging interface, and the other end is connected to the midpoint of the fully controlled bridge arm. The fully controlled bridge arm includes: a first fully controlled device Q1, a second fully controlled device Q2, one end of the switch S1 is connected to the positive pole of the device charging interface, and the other end is connected to the positive pole of the second charging gun and one end of the fully controlled bridge arm at the same time. The other end of the fully controlled bridge arm is connected to the negative pole of the device charging interface and the negative pole of the second charging gun.

[0056] The electric vehicle / unmanned aerial vehicle is connected to the second charging gun via the charging interface, and the positive and negative electrodes of the power battery and both ends of the internal load are connected to the charging port;

[0057] The power battery and internal load are also connected to the controller, and the controller, charging pile, switch S1, and full-control bridge arm are all connected to the device controller;

[0058] Furthermore, the charging device has two modes: a normal charging mode and a bidirectional pulse fast charging mode.

[0059] Specifically, in normal charging mode: S1 is closed, Q1 and Q2 are not conducting, which is suitable for charging at room temperature with minimal life attenuation. At the same time, the controller can control whether the internal load is connected to the charging pile according to the user profile and load requirements. In this mode, the charging pile charges the power battery and supplies power to the load at the same time;

[0060] Bidirectional pulse fast charging mode: S1 is disconnected, the internal load is connected to the circuit, and Q1 and Q2 are turned on alternately.

[0061] Furthermore, a mode switching temperature T is preset. end , if the battery temperature T is lower than the mode switching temperature T end , the control circuit turns on the bidirectional pulse fast charging mode; if the battery temperature T is higher than or equal to the mode switching temperature T end , the control circuit starts the normal charging mode.

[0062] Further, see Figure 2 As shown, the controller, the charging pile, and the device controller are connected by handshaking through the internal low-voltage bus of the second charging gun, the charging interface and the first charging gun, the device charging interface, and information is transmitted via the low-voltage communication protocol.

[0063] Furthermore, in the bidirectional pulse fast charging mode, the device controller can control the charging pile to work in the constant voltage output mode through low voltage bus communication and access the main circuit in the form of a constant voltage source;

[0064] The traditional lithium-ion battery charging strategy is CC-CV (constant current-constant voltage) charging, in which the CV part of the charging power accounts for a small part of the total charging power, but it takes a very long time and occupies a large part of the total charging time; the purpose of CV charging is to ensure that the lithium-ion battery does not exceed the upper cut-off voltage during the charging process, thereby achieving the purpose of reducing aging and increasing battery durability; this device uses the CAN communication protocol to handshake the charging pile and electric vehicles / unmanned aerial vehicles, and can replace the CV part with PC (pulse charging), which can improve the battery charging speed while ensuring the durability of the battery, and the structure of this device is only suitable for voltage source access circuits.

[0065] Further, see Figure 3 , Figure 4 and Figure 5 As shown, in the bidirectional pulse fast charging mode, S1 is disconnected, the controller controls the internal load to be turned on, and the device controller controls the full-control devices Q1 and Q2 to be turned on alternately to generate a bidirectional pulse current;

[0066] State 1: Q1 is on, Q2 is off, the DC source charges the energy storage inductor, and the energy storage inductor current I L The power battery is in a discharge state, and the current is I Load ;

[0067] State 2: Q1 is off, Q2 is on, and the charging current I Charge The energy storage inductor current I L The current I on the power battery decreases. B For I Charge and I Load The power battery is in a superposition state.

[0068] During the fast charging process, the battery is also preheating internally, the temperature rises, and gradually gets rid of the low temperature environment. This is more streamlined than the traditional external heating strategy and has a higher electrical-heat conversion efficiency;

[0069] The Load in the circuit is the load inside the electric vehicle / unmanned aerial vehicle, which should not be too large, otherwise I Load >I Charge , which will result in superposition of I BIt is still negative, and the battery is still in a discharge state, and the charging purpose cannot be achieved at this time; the negative pulse of this device is mainly to eliminate the reversible lithium plating phenomenon to reduce the battery's life attenuation during fast charging at low temperatures, so the negative pulse amplitude does not need to be too large, which also makes the circuit conditions easier to achieve and the feasibility is very high.

[0070] Furthermore, the switching between state 1 and state 2 adopts hysteresis control, and a reference current I is preset. L_ref and ring width 2H;

[0071] Status I L Rising, when I L ≥I L_ref +H, it switches to state 2, at this time I L Decline, when I L ≤I L_ref -H, switches to state 1.

[0072] Specifically, the opening and closing of the fully controlled devices Q1 and Q2 are controlled by hysteresis loop. The specific principle of hysteresis loop control is: set I L_ref and hysteresis loop width 2H, when the circuit is working I L with I L_ref The error current ΔI is obtained by making a difference L It is always in the hysteresis loop with H and -H as the upper and lower limits; when ΔI L <-H, enter state 1; when ΔI L >H, enter state 2; the two states switch alternately to generate high-frequency pulses; the switching frequency of Q1 and Q2 can be controlled by controlling the size of the loop width 2H. The larger 2H is, the smaller the switching frequency f_ref is, and the smaller 2H is, the larger the switching frequency f_ref is.

[0073] Furthermore, the controller collects the state of charge SOC and battery temperature T signals of the power battery in real time, and transmits them to the device controller through low-voltage bus communication. After receiving the signal, the device controller obtains the optimal amplitude I of the battery charging pulse without lithium precipitation according to the internal preset data table. L_ref , frequency f_ref, duty cycle D;

[0074] Specifically, during the charging process of lithium-ion batteries in a low-temperature environment, bidirectional pulse current flows through the battery, and the battery will generate heat due to the existence of internal resistance, so that the temperature gradually rises; under the premise of ensuring that lithium is not precipitated, in order to ensure the maximum heat generation rate and charging rate, the amplitude, frequency, and duty cycle of the charging current allowed to pass also gradually change; a data table is preset inside the device controller, and the controller obtains the temperature T, state of charge SOC, and battery current I of the internal batteries of electric vehicles and unmanned aerial vehicles in real time through the communication protocol. B , and transmit the signal to the device controller, which can realize IL_ref , f_ref, D is adjusted dynamically;

[0075] When the loop width increases, the frequency becomes lower, and when the loop width decreases, the frequency becomes higher;

[0076] By adjusting the reference current I L_ref The given value, loop width 2H, and output voltage of the first charging gun control the amplitude, frequency, and duty cycle of the charging pulse;

[0077] Specifically, the device controller can control the output voltage of the first charging gun and the reference current IL_ref to control the duty cycle D and amplitude of the charging pulse. The larger the output voltage, the larger the duty cycle, and the smaller the duty cycle, the smaller the duty cycle.

[0078] Furthermore, the controller collects the state of charge SOC and battery entropy thermal coefficient signals of the power battery in real time. After receiving the signals through the low-voltage bus communication, the controller controls the switching selection and power size change of different loads in the vehicle to change the positive and negative pulse amplitudes in the pulse charging, thereby changing the heat generation rate and charging speed:

[0079] When the SOC is high, it is preferred to operate at a large load and full power, because the charging pile can supply part of the power to the load, which is very economical.

[0080] When the SOC is low, it is preferred to operate with a small load and low power; because if it is still operated with a large load and high power, it may cause I Load >I Charge , which will result in superposition of I B If the value is still negative, the battery is still in a discharge state. At this time, the charging purpose cannot be achieved, and the battery will be over-discharged beyond the lower cut-off voltage, causing additional life aging;

[0081] When the entropy thermal coefficient of the battery is positive, high load operation is preferred; when the entropy thermal coefficient is positive, the reversible heat term is exothermic, the battery generates heat relatively quickly, and the circuit can support high load operation;

[0082] When the battery entropy thermal coefficient is negative, it is preferred to operate at a small load; when the entropy thermal coefficient is negative, the reversible heat term is endothermic, the battery generates heat relatively slowly, and can only support small load operation.

[0083] Furthermore, the controller collects the internal load current I in real time. Load The amplitude signal is transmitted to the device controller through the low-voltage bus communication. After receiving the signal, the device controller L_ref Perform the same direction adjustment to keep the positive pulse amplitude at the optimal amplitude I during the bidirectional pulse charging process. B_ref ; when I Load Rise, I L_ref Also rises; when I Load Descending, IL_ref Also decreased.

[0084] Specifically, the amplitude of the bidirectional pulse I B It is dynamically stable. The internal load of the electric vehicle / unmanned aerial vehicle in the circuit usually has a variable power due to its working characteristics or the switching of different loads. When the internal load power changes or the battery SOC increases during charging, the internal load current I Load In order to control the amplitude stability of the bidirectional pulses in fast charging to maintain the safety of the charging device and not cause additional damage to the battery, the controller can collect I Load The information is transmitted to the device controller, and the device controller responds accordingly. L_ref The same direction adjustment: when I Load When rising, I L_ref Also need to rise together, when I Load When descending, I L_ref It also needs to be reduced in a coordinated manner in order to maintain I B The positive pulse amplitude maintains dynamic stability

[0085] Reference Figure 6 As shown, a control method for a bidirectional pulse fast charging device of a lithium battery at low temperature comprises:

[0086] S1, preset cut-off temperature T end ;

[0087] S2. Read the current power battery temperature T, state of charge SOC, and entropy thermal coefficient;

[0088] S3, the controller selects a suitable internal load to access the circuit;

[0089] S4, judging whether the power battery SOC is less than the charging target value, if so, proceeding to the next step; if not, ending the charging;

[0090] S5: Determine whether the battery temperature T is less than the preset cut-off temperature T end If yes, proceed to the next step; if no, switch to normal charging mode and charge until the end;

[0091] S6, look up the table to obtain the maximum pulse charging heat generation rate I corresponding to the current temperature T and SOC without lithium deposition B_ref , f_ref and duty cycle D;

[0092] S7, Adjustment I L_ref , ring width 2H, output voltage of the first charging gun;

[0093] S8, fast charging in bidirectional pulse fast charging mode;

[0094] S9, read the current internal load current I Load ;

[0095] S10. Judgment I Load Fluctuation occurs, if so, then according to I Load Adjustment I L_ref , so that the charging current amplitude of the bidirectional pulse charging reaches I B_ref , return to S8; if not, return to S2.

[0096] In a specific embodiment,

[0097] In the bidirectional pulse fast charging mode, the frequency f_ref of the bidirectional pulse can be flexibly adjusted to maintain the optimal frequency range of the environment while ensuring that lithium is not deposited;

[0098] When the ambient temperature is not extreme, the device can appropriately increase the frequency to the kilohertz level to improve charging efficiency, but the heat generation will be reduced due to the reduction of the internal resistance of the battery at high frequencies, which will sacrifice the preheating rate;

[0099] When the ambient temperature is extremely low, the device can reduce the frequency to hundreds of hertz, sacrificing charging efficiency to increase the preheating rate.

[0100] The power source of the charging pile can be flexibly allocated, not limited to the power grid, but can be distributed power sources in the microgrid, including but not limited to wind power, photovoltaics, hydrogen energy, natural gas, and other energy storage devices such as energy storage power stations, electric vehicles used as power sources in vehicle-grid interaction, etc. These electric energies are gathered in the DC bus and sent to the charging pile, and then input into the charging gun at a suitable voltage through the voltage regulation module.

[0101] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0102] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A bidirectional pulse fast charging device for lithium batteries at low temperature, characterized in that: include: Charging piles, main circuits, electric vehicles / unmanned aerial vehicles; The charging pile includes: a first charging gun; The main circuit includes: device charging interface, energy storage inductor, switch S1, full-control bridge arm, device controller, and second charging gun; Electric vehicles / unmanned aerial vehicles include: charging interface, power battery, internal load and controller; The first charging gun is connected to the positive and negative electrodes of the device charging interface of the main circuit; One end of the energy storage inductor is connected to the positive pole of the device charging interface, and the other end is connected to the midpoint of the fully controlled bridge arm. The fully controlled bridge arm includes: a first fully controlled device Q1, a second fully controlled device Q2, one end of the switch S1 is connected to the positive pole of the device charging interface, and the other end is connected to the positive pole of the second charging gun and one end of the fully controlled bridge arm at the same time. The other end of the fully controlled bridge arm is connected to the negative pole of the device charging interface and the negative pole of the second charging gun. The electric vehicle / unmanned aerial vehicle is connected to the second charging gun via the charging interface, and the positive and negative electrodes of the power battery and both ends of the internal load are connected to the charging port; The power battery and internal load are also connected to the controller, and the controller, charging pile, switch S1, and full-control bridge arm are all connected to the device controller; The charging device has two modes: normal charging mode and bidirectional pulse fast charging mode.

2. A low temperature lithium battery bidirectional pulse fast charging device according to claim 1, characterized in that: Preset mode switching temperature T end , if the battery temperature T is lower than the mode switching temperature T end , the control circuit turns on the bidirectional pulse fast charging mode; if the battery temperature T is higher than or equal to the mode switching temperature T end , the control circuit starts the normal charging mode.

3. A low temperature lithium battery bidirectional pulse fast charging device according to claim 1, characterized in that: The controller, the charging pile, and the device controller are connected by handshaking through the internal low-voltage bus of the second charging gun, the charging interface and the first charging gun, the device charging interface, and information is transmitted via a low-voltage communication protocol.

4. A low temperature lithium battery bidirectional pulse fast charging device according to claim 3, characterized in that: In the bidirectional pulse fast charging mode, the device controller communicates through the low-voltage bus to control the charging pile to operate in the constant voltage output mode and connect to the main circuit in the form of a constant voltage source.

5. A low temperature lithium battery bidirectional pulse fast charging device according to claim 1, characterized in that: In the bidirectional pulse fast charging mode, S1 is disconnected, the controller controls the internal load to be turned on, and the device controller controls the full-control devices Q1 and Q2 to be turned on alternately to generate a bidirectional pulse current; State 1: Q1 is on, Q2 is off, the DC source charges the energy storage inductor, and the energy storage inductor current I L The power battery is in a discharge state, and the current is I Load ; State 2: Q1 is off, Q2 is on, and the charging current I Charge The energy storage inductor current I L The current I on the power battery decreases. B For I Charge and I Load The power battery is in a superposition state.

6. A low temperature lithium battery bidirectional pulse fast charging device according to claim 5, characterized in that: The switch between state 1 and state 2 adopts hysteresis control, and a reference current I is preset. L_ref and ring width 2H; Status I L Rising, when I L ≥I L_ref +H, it switches to state 2, at which time I L Decline, when I L ≤I L_ref -H, switches to state 1.

7. A low temperature lithium battery bidirectional pulse fast charging device according to claim 5, characterized in that: The controller collects the state of charge SOC and battery temperature T signals of the power battery in real time and transmits them to the device controller through low-voltage bus communication. After receiving the signal, the device controller obtains the optimal amplitude I of the battery charging pulse without lithium deposition according to the internal preset data table. B_ref , frequency f_ref, duty cycle D; When the loop width increases, the frequency becomes lower, and when the loop width decreases, the frequency becomes higher; By adjusting the reference current I L_ref The given value, loop width 2H, and output voltage of the first charging gun control the amplitude, frequency, and duty cycle of the charging pulse.

8. A low temperature lithium battery bidirectional pulse fast charging device according to claim 5, characterized in that: The controller collects the state of charge (SOC) and battery entropy thermal coefficient signals of the power battery in real time. After receiving the signals through low-voltage bus communication, the controller controls the switching selection and power changes of different loads in the vehicle to change the amplitude of positive and negative pulses in pulse charging, thereby changing the heat generation rate and charging speed.

9. A low temperature lithium battery bidirectional pulse fast charging device according to claim 5, characterized in that: The controller collects the internal load current I in real time Load The amplitude signal is transmitted to the device controller through the low-voltage bus communication. After receiving the signal, the device controller L_ref Perform the same direction adjustment to keep the positive pulse amplitude at the optimal amplitude I during the bidirectional pulse charging process. B_ref ; when I Load Rise, I L_ref Also rises; when I Load Descending, I L_ref Also decreased.

10. A control method for a bidirectional pulse fast charging device for lithium batteries at low temperatures, applied to a bidirectional pulse fast charging device for lithium batteries at low temperatures as claimed in any one of claims 1 to 9, comprising: S1, preset cut-off temperature T end ; S2. Read the current power battery temperature T, state of charge SOC, and entropy thermal coefficient; S3, the controller selects a suitable internal load to access the circuit; S4, judging whether the power battery SOC is less than the charging target value, if so, proceeding to the next step; if not, ending the charging; S5: Determine whether the battery temperature T is less than the preset cut-off temperature T end If yes, proceed to the next step; if no, switch to normal charging mode and charge until the end; S6, look up the table to obtain the maximum pulse charging heat generation rate I corresponding to the current temperature T and SOC without lithium deposition B_ref , f_ref and duty cycle D; S7, Adjustment I L_ref , ring width 2H, output voltage of the first charging gun; S8, fast charging in bidirectional pulse fast charging mode; S9, read the current internal load current I Load ; S10. Judgment I Load Fluctuation occurs, if so, then according to I Load Adjustment I L_ref , so that the charging current amplitude of the bidirectional pulse charging reaches I B_ref , return to S8; if not, return to S2.

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