CN115549264A

CN115549264A - Battery management system and charge equalization control method

Info

Publication number: CN115549264A
Application number: CN202211392331.5A
Authority: CN
Inventors: 何亮明
Original assignee: Jiaxing Sustainable New Energy Co ltd
Current assignee: Jiaxing Sustainable New Energy Co ltd
Priority date: 2022-11-08
Filing date: 2022-11-08
Publication date: 2022-12-30

Abstract

The invention relates to a battery management system and a charging equalization control method, which comprise a battery monitoring and protecting unit, a charging and discharging control switch and driving unit, a passive equalization unit and a trickle charging unit. The battery monitoring and protecting unit outputs a battery protecting signal through real-time detection and judgment of battery state parameters, and the battery protection comprises overcharge, overdischarge and overcurrent protection. The charging and discharging control switch and the driving unit timely turn off the charging and discharging of the battery pack after receiving the battery protection signal, and the passive equalization unit enables the battery to independently discharge after meeting a certain condition. In the charging process, when the charging control switch is disconnected due to battery protection, the trickle charging unit generates a charging current with a small value, so that the battery which is not fully charged can be continuously charged with the small current, and the fully charged battery bypasses the charging current through the passive equalizing unit.

Description

Battery management system and charging equalization control method

Technical Field

The invention relates to a battery management system and a charging equalization control method, in particular to a battery management system and a charging equalization control method which are used for realizing long-time equalization of a battery by combining trickle charging and passive equalization technologies, prolonging the cycle life of a battery pack, effectively controlling the cost and being particularly suitable for the cost-sensitive field of electric light vehicles and the like.

Background

The Battery Management System (BMS) ensures that each parameter of the battery is within a safety range by monitoring various state parameters of the battery, and avoids safety risks such as overcharge, overdischarge or overheating of the battery. In general, parameters such as the capacity and the internal resistance of each battery in a series battery pack are slightly different, or the state of charge (SOC) of each battery is different due to self-discharge. Most of the BMS solutions that exist today stop the discharge of the entire battery pack when a certain battery in the battery pack is discharged, although other batteries may not be completely discharged; or when one of the batteries in the battery pack is fully charged, the entire battery pack is stopped from being charged, although the other batteries may not be fully charged. Thus, there is a significant "tub effect" that reduces the actual usable capacity of the battery pack.

To reduce the effects of cell inconsistencies, active or passive equalization techniques may be used. The active equalization is fast in speed and strong in performance, but power devices such as a large-capacity capacitor, an inductor or a transformer need to be used, the circuit is complex, the control difficulty is high, the reliability is poor, and the cost is high. The passive balancing only needs one small electronic switch and a load resistor, the circuit is simple, the cost is low, and the passive balancing method is a mainstream balancing mode which is applied in a large batch at present. Due to the heat dissipation limitation, the passive equalization current is small, the equalization speed is slow, and a long time is needed. However, most of the existing solutions can not satisfy the above conditions. And in the charging process, when certain battery voltage reaches the equalizing voltage, the passive equalizing circuit corresponding to the battery is started. When a certain battery voltage reaches the overcharge voltage, the entire battery charging process has to be switched off (in this case even the passive equalization is switched on, since the charging has stopped). For lithium iron phosphate batteries with fast charging speed or flat voltage curves, the time from equalizing voltage to overcharging voltage of the battery is very short (sometimes only a few minutes), so that the passive equalization time is very short. On the other hand, due to the limitation of material characteristics and process, the lithium iron phosphate battery has poor consistency, high self-discharge and large voltage difference between batteries after long-term use, and the effective capacity of the battery pack is remarkably reduced. Therefore, while maintaining the advantages of simple passive equalization circuit, reliable technology and cost, it is urgently needed to further improve the utilization efficiency.

One existing hardware BMS solution is shown in fig. 1. Each string of batteries of the battery pack uses a single-section protection IC to realize overcharge, overdischarge and overcurrent protection of the single battery, and a special single-section balancing IC is used to realize passive balance control of the single battery. The overcharge, overdischarge and overcurrent protection signals of each battery string are cascaded through a triode to form a logic OR gate, and the logic OR gate is output to a drive circuit of the charge and discharge control switch. The scheme avoids the problem of common-mode high voltage, and the single-section protection and balance control IC is relatively simple in design and has been widely applied in the field of consumer electronics for a long time, so that the scheme has a remarkable cost advantage. In addition, the scheme is convenient to expand, and the existing product can change the string into a low string in a high string mode and is very flexible. Another existing BMS solution, the basic principle is shown in fig. 2. A multi-string integrated protection IC can manage 2-20 strings of batteries and has the functions of battery overcharge, overdischarge, overcurrent, overheat, sampling line disconnection detection, passive balance control and the like. The scheme has high integration level, saves a large number of resistors, capacitors and triodes, but has poor expansibility and insufficient flexibility, and the number of the battery packs is limited by the problem of common mode high voltage. The two schemes do not overcome the defect that the passive equalization time is too short, and the equalization performance is superior to that of the lithium iron phosphate battery or the fast-charging lithium iron phosphate battery.

In order to solve the problem of too short passive equalization time, patent CN216819469U provides a trickle equalization device for series battery, in which an external equalization manager determines the equalization time by adding a delay control unit. In theory, this scheme can be balanced without limitation. The main defects of the method are that the implementation difficulty of the external equalization manager is high and the cost is high. For the lithium iron phosphate battery, in the voltage range of a battery platform, the electric quantity cannot be simply identified through voltage, and then specific equalization time is calculated. When equalization is started, how long equalization is needed? The SOC can only be indirectly calculated by means of current integration and capacity estimation, which often exceeds the price bearing range of application fields such as consumer electronics and two-wheeled electric vehicles.

Compared with the prior art, the invention mainly has the following three advantages. Firstly, the passive equalization time is long and the equalization performance is strong. Equalization charging can continue as long as the charger is connected and there is an output voltage (BMS charging control switch is not affected after disconnection). For the maintenance of old batteries, the equalizing charge can be carried out for a plurality of days, and the difference of dozens of AH electric quantity of the batteries can be overcome after the equalizing charge is accumulated. Secondly, the circuit is simple and is beneficial to controlling the cost. The trickle charging unit can be realized by common diodes, and passive equalization control and overcharge protection signal multiplexing save a special equalization control IC. Therefore, the invention not only does not increase the additional cost, but also can reduce the overall cost. Finally, the design idea of charging trickle and passive equalization is combined, so that the application range is wide, and the expandable space is large. The intelligent BMS is not only suitable for a hardware BMS scheme formed by single-section protection IC cascade or multi-string integrated protection ICs, but also can be expanded to a software intelligent BMS, even a complex BMS such as an electric automobile and the like.

Disclosure of Invention

The invention aims to provide a battery management system which comprises a battery monitoring and protecting unit, a charging and discharging control switch and driving unit, a passive equalizing unit and a trickle charging unit. The battery monitoring and protecting unit outputs a battery protecting signal through real-time detection and judgment of battery state parameters. The battery protection comprises overcharge, overdischarge and overcurrent protection, and the charge and discharge control switch and the drive unit timely turn off the charge and discharge of the battery pack after receiving the battery protection signal. The passive equalization unit enables the battery to independently discharge after meeting certain conditions. In the charging process, when the charging control switch is disconnected due to battery protection, the trickle charging unit generates a charging current with a small value, so that the battery which is not fully charged can be continuously charged with the small current, and the fully charged battery bypasses the charging current through the passive equalizing unit.

The battery can be various rechargeable storage batteries such as a lithium ion battery, a sodium ion battery, a solid-state battery, a lithium metal battery, a nickel-hydrogen battery, a nickel-cadmium battery and the like.

The charge and discharge control switch can use a relay, a triode, a MOSFET, an IGBT and other switching devices, and can be further implemented by connecting a plurality of switching devices in series or in parallel in order to meet the requirements on current and voltage parameters or reliability.

In a preferred embodiment, the trickle charge unit comprises a controllable switch SW2 and a trickle circuit, which switches the switch SW2 on when the battery needs to be trickle charged and off otherwise.

The controllable switch SW2 can use devices such as a triode, a low-power MOSFET or an IGBT and the like and is controlled by a battery management system, and the trickle circuit can generate milliampere or ampere current matched with passive balance current in a larger voltage range.

In a preferred embodiment, the trickle charge unit comprises a diode D1 and a resistor RL connected in series, the negative pole of the diode D1 being connected to the charger negative pole interface.

The diode D1 can use a general diode to avoid turning on the trickle circuit when the discharge control switch is turned off. The resistor RL needs to select a power resistor with an appropriate resistance value.

In a preferred embodiment, the trickle charging unit comprises a diode D1 and a constant current source connected in series, and the cathode of the diode D1 is connected to the charger cathode interface.

The constant current source can use one constant current diode or constant current triode, and can also use a plurality of constant current diodes or constant current triodes to carry out series-parallel connection to realize current expansion or voltage boosting.

In a preferred embodiment, the charge and discharge control switch employs a relay, and the trickle charge unit is connected in parallel with the relay.

When the charge and discharge control switch comprises a main positive relay and a main negative relay, the trickle charge unit only needs to be connected with one of the relays in parallel.

In a preferred embodiment, the battery monitoring and protecting unit comprises a cascade single-section protecting IC, and the battery overcharge protection and the passive equalization opening are controlled by the same output signal of the single-section protecting IC.

In a preferred embodiment, the charge and discharge control switch comprises two N-type MOSFETs connected in series, and the charge and discharge same-port connection method is adopted. One end of the trickle charge unit is connected with the negative electrode interface of the charger, and the other end of the trickle charge unit is connected with the drain electrode of the charge switch SWC or the source electrode of the discharge switch SWD or the negative electrode B-of the battery pack.

In a preferred embodiment, the charge and discharge control switch comprises two N-type MOSFETs connected in parallel, and a charge and discharge differential connection method is adopted. One end of the trickle charging unit is connected with the negative electrode interface of the charger, and the other end of the trickle charging unit is connected with the drain electrode of the charging switch SWC or the negative electrode B-of the battery pack.

In a preferred embodiment, the battery monitoring and protecting unit comprises a plurality of strings of integrated protection ICs, and has an overheat protection or sampling line disconnection detection function.

Another object of the present invention is to provide a charge equalization control method for a battery management system, comprising the steps of:

the battery monitoring and protecting unit detects the state information of each string of batteries of the battery pack in real time;

when the voltage of the battery is greater than the equalizing voltage or the overcharge voltage, starting the passive equalizing function of the battery;

when any battery in the battery pack enters a protection state, the battery pack charging control switch is turned off, and the trickle charging unit is turned on;

the operation continues until the external charger is removed, or the trickle charge unit is turned off when all the batteries are fully charged.

Drawings

Fig. 1 shows a battery management system with a cascade of single protection ICs.

Fig. 2 shows a battery management system of a multi-string integrated protection IC.

Fig. 3 shows a functional block diagram of a battery management system provided by the present invention.

Fig. 4 is a schematic diagram of a charging trickle unit implemented by using a controllable switch according to the present invention.

Fig. 5 is a schematic diagram illustrating a charging trickle cell implemented by using a diode and a resistor according to the present invention.

Fig. 6 shows a schematic diagram of a charging trickle unit implemented by using a diode and a constant current source according to the present invention.

Fig. 7 shows a battery management system based on a MOSFET device and a charging/discharging same-interface connection method provided by the present invention.

Fig. 8 shows a battery management system based on a MOSFET device and a charging/discharging different port connection method provided by the present invention.

Fig. 9 shows another battery management system based on MOSFET device and charging/discharging same interface connection provided by the present invention.

Detailed Description

In order to make the objects, technical solutions and advantageous technical effects of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

As shown in fig. 3, the present invention provides a battery management system, which includes a battery monitoring and protecting unit 301, a charging and discharging control switch and driving unit 302, a passive equalizing unit 303, and a trickle charging unit 304. The battery monitoring and protecting unit 301 detects state information such as voltage, current or temperature of each battery in real time, and when the battery is found to be overcharged, overdischarged, overcurrent or overheated, a battery protecting signal is output to the charging and discharging control switch and driving unit 302, so that the charging and discharging function of the battery pack is turned off in time. The passive equalization unit 303 discharges a small current through a load resistor after the battery voltage satisfies a certain condition. When the charging control switch is turned off due to the fact that a certain string of single batteries reaches the overcharge protection voltage in the charging process, the charging trickle unit 304 can generate a charging current with a small value in a large voltage range, so that other batteries which are not fully charged can be charged with small current continuously, and the fully charged batteries bypass the charging current through the passive equalization unit 303, and overcharge is avoided.

The battery monitoring and protecting circuit 301 is connected with the positive and negative electrodes of each string of single batteries of the battery pack through voltage sampling lines. The battery passive equalization circuit is connected with the anode and the cathode of each string of single batteries of the battery pack through a battery equalization line. When the passive equalization current is small, the battery equalization line and the voltage sampling line can be multiplexed. In addition, the battery monitoring and protecting circuit 301 may be implemented by a pure hardware circuit, such as a single battery protecting IC or a plurality of strings of integrated protecting ICs, or may be implemented by using embedded software or upper computer software such as a high-performance computing system after ADC sampling conversion. Accordingly, the battery passive equalization and trickle charge starting mode can be realized in a pure hardware mode, such as a voltage comparator or a diode, and can also be realized by combining software. It should be noted that the trickle-charge current value must be less than the passively equalized current value. Therefore, the battery which enters the overcharge protection state can completely bypass the trickle charge current through the passive equalizing circuit, and the damage of the battery due to overcharge is avoided.

The trickle charge unit 304 corresponds to a second current branch of the battery pack charge-discharge control switch. During the charging process, when the charging control switch of the main circuit is turned off, the trickle charging unit 304 will generate a small current, so that the battery pack can continue to trickle charge. The passive equalization unit 303 is equivalent to a second current branch of the battery, and starts passive equalization to bypass a redundant charging current when the battery charging reaches a certain condition. Ensuring that the battery is not overcharged and simultaneously not influencing the charging of other batteries. Therefore, the passive equalization can be continuously performed as long as the external charger is connected and has the output voltage. By combining the strategy of trickle charge and passive equalization, the equalization time is greatly prolonged, and the problem of poor effect of the traditional passive equalization due to small current and short time is solved.

The voltage platform of the lithium iron phosphate battery is flat, most of the capacity is concentrated on about 3.2V, and the low-voltage part and the high-voltage part of a charging curve are very steep. If the cell is charged at 0.5C rate, the cell goes from 3.45V equalization voltage to 3.65V overcharge voltage, which may last only a few minutes. Due to the limitation of heat dissipation, the passive equalization generally has a small current which is often less than one ampere or even only dozens of milliamperes. At this time, even if the passive balance is started, the capacity is only dozens of mAH calculated according to the balance current of 100mA, and the balance effect is very good. Especially for the battery pack with larger capacity, the battery pack is almost negligible. The battery management system provided by the invention combines trickle charge and passive equalization strategies, the battery equalization time is determined by an external charger, and the effect is improved greatly. For example, in the field of common electric bicycles, the battery can be fully charged within 5 to 6 hours after charging at 0.2 ℃. The general user is used to charge overnight, which means that there are 6-7 hours of equalization time, which is several tens times longer than the conventional passive equalization scheme. For the UPS battery of the base station, the battery is in a floating charge state for a long time, and the chargers are connected on line for most of time. The trickle charge balancing method and the trickle charge balancing device can continuously perform trickle charge and have better effect.

As shown in fig. 4, the charge trickle unit is composed of a controllable switch SW2 and a trickle circuit. When the battery needs to be trickle charged, the switch SW2 is turned on, and otherwise, the switch is turned off. The controllable switch SW2 can be a triode or a low-power MOSFET, and devices such as an IGBT can be selected in a high-voltage scene. In order to minimize the cost, the charging trickle circuit may be composed of a diode D1 and a load resistor RL as shown in fig. 5. The general diodes have rich models and low price. The load resistor RL plays a role in current limiting and also has the advantage of low cost. In consideration of the limit situation, the voltage change range at two ends of the resistor RL is very large, and the value of RL is difficult to take. On one hand, when the voltage at two ends of the RL is larger, the resistance value of the RL must be larger in order to ensure that the trickle charge value does not exceed the passive balanced current value; on the other hand, when the voltage across RL is small, the resistance of RL has to be made small to avoid the trickle charge value being too small to affect the equalization effect. The two are difficult to be compatible, and the practical application scene of the scheme is limited.

As shown in fig. 6, the charge trickle unit includes a diode D1 and a constant current source CD1. The constant current source can use a constant current diode or a constant current triode, and can also use a plurality of constant current diodes or constant current triodes to carry out series-parallel connection for current expansion and pressurization. The constant current source is applied, and the value problem of load resistance is solved. In addition, a constant current diode with the current level of tens of milliamperes is not high in price, and the cost of the whole battery management system is low.

As shown in fig. 7, the present invention provides a battery management system based on MOSFET devices and charging and discharging same-port connection method, and a single-protection IC cascade connection mode is used to realize overcharge, overdischarge, and overcurrent protection of a battery. Taking the battery BC1 as an example, the single-node protection IC BH1 supplies power after being filtered by the resistor R11 and the resistor C11 through the battery BC 1. The pin 1 of BH1 outputs an overdischarge protection signal, which is output to a driving circuit of the discharge control switch SWD through a logic or gate formed by a resistor R12 and a PNP transistor Q11. The 3 pin of BH1 outputs overcharge protection signal, constitutes logical OR gate output to the drive circuit of charge control switch SWC through resistance R13 and PNP triode Q12. The current detecting resistor RC and the filter circuits R1 and C1 form a current sampling circuit, and an overcurrent protection signal is generated to control a charge and discharge switch through the input of a pin 2 of BH 1. The load resistor R15 and the PNP triode Q13 form a passive balanced discharge loop which is controlled by a 3-pin overcharge protection signal of BH 1. Namely, after the battery is over-charged and protected, the passive equalization is started. The invention has abundant equalization time, so that passive equalization is not started in advance during charging, and the equalization performance is not influenced. Compared with the prior scheme of fig. 1, the scheme does not need to use a special balance control IC, and is beneficial to further reducing the cost.

As shown in fig. 7, the charging trickle unit can be regarded as a two-terminal circuit module, one terminal of which is connected to the battery module negative electrode Pack-, and the other terminal is connected to the drain of the charging switch SWC or the source of the discharging switch SWD or the battery Pack negative electrode B-. In essence, the three have similar electrical performance. Since the discharge switch SWD is normally in an on state during charging, the source and the drain are short-circuited. Even if the discharge switch SWD is not turned on, its parasitic diode allows the charging current to smoothly pass. The current detection resistor RC is generally in the milliohm level, and the influence of small current such as trickle charge is almost negligible.

As shown in fig. 8, since the charging interface of the battery is separated from the discharging interface, one end of the charging trickle unit is connected to the negative interface of the battery charger and the other end is connected to the drain of the charging switch SWC or the negative B-of the battery pack. The charging current of a general battery is far smaller than the discharging current, and the charging switch and the discharging switch can be respectively designed according to different charging and discharging overcurrent performances required by the battery by using the charging and discharging different-port connection method, so that the cost is further controlled.

As shown in fig. 9, the present invention provides a battery management system based on a multi-string integrated protection IC. The multi-string integrated protection IC has high integration level and rich functions, is suitable for 2-20 strings of battery packs, and has the functions of overcharge, overdischarge, overcurrent, overheat, sampling line disconnection detection protection, passive balance control and the like. For a large battery pack with more battery strings, the large battery pack can be further expanded through a plurality of multi-string integrated protection IC cascades.

The invention also provides a charging balance control method of the battery management system, which comprises the following specific steps:

(1) During the charging process, the battery monitoring and protecting unit detects the state information of each string of batteries of the battery pack in real time, such as the voltage, the current, the temperature, the state of a sampling line and the like of the batteries.

(2) And when a certain battery meets a certain condition, starting the passive equalization function of the battery. This condition may be set to be greater than the equalization voltage or the battery enters overcharge protection.

(3) When one of the batteries enters a protection state, the charging control switch is turned off, and the trickle charging unit is turned on. For example, when the battery reaches an overcharge protection voltage or enters an overheat protection state, the battery pack main circuit charging switch must be turned off.

(4) The operation continues until the external charger is removed, or the trickle charge unit is turned off when all the batteries are fully charged. The trickle charge has a small current value and generates little heat, so that the device can be operated for a long time. When the external charger is removed, the trickle charge can be naturally stopped. If the conditions allow, the trickle charge can be stopped after all the batteries are fully charged, so that a little electric energy is saved.

In conclusion, the design idea of trickle charge and passive equalization is combined, so that the battery equalization time can be greatly prolonged, and the equalization performance can be improved. Moreover, the trickle charge unit is simple to implement, does not influence other circuits in the battery management system, and is convenient for application and expansion, including but not limited to the complicated BMS in the fields of hardware protection boards, intelligent software protection boards, electric vehicles, energy storage systems and the like. The battery management system provided by the invention can obviously solve the industrial difficulties of self-discharge, rapid charge equalization maintenance and the like of the lithium iron phosphate battery without changing the conventional matched charger and increasing extra cost, and has outstanding application value.

Claims

1. A battery management system is characterized by comprising a battery monitoring and protecting unit, a charge and discharge control switch and driving unit, a passive equalizing unit and a trickle charging unit; the battery monitoring and protecting unit outputs a battery protecting signal through real-time detection and judgment of battery state parameters, the battery protection comprises overcharge, overdischarge and overcurrent protection, and the charge and discharge control switch and the driving unit timely turn off the charge and discharge of the battery pack after receiving the battery protecting signal; the battery is independently discharged after meeting a certain condition through the passive equalization unit, and in the charging process, when the charging control switch is disconnected due to battery protection, the trickle charging unit generates a charging current with a small numerical value, so that the battery which is not fully charged can be continuously charged with small current, and the fully charged battery bypasses the charging current through the passive equalization unit.

2. A battery management system according to claim 1, wherein said trickle charge unit comprises a controllable switch SW2 and trickle circuit; when the battery needs to be trickle charged, the switch SW2 is turned on, and otherwise, the switch is turned off.

3. The battery management system of claim 1, wherein said trickle charge unit comprises a diode D1 and a resistor RL connected in series, the negative terminal of said diode D1 being connected to the charger negative terminal interface.

4. The battery management system of claim 1, wherein said trickle charge unit comprises a diode D1 and a constant current source connected in series, the negative terminal of said diode D1 being connected to the negative terminal of the charger interface.

5. The battery management system according to claim 1, wherein the charge and discharge control switch is a relay, and the trickle charge unit is connected in parallel with the relay.

6. The battery management system according to claim 1, wherein the battery monitoring and protecting unit comprises a cascaded single-cell protection IC, and the battery overcharge protection and the passive equalization turn-on are controlled by the same output signal of the single-cell protection IC.

7. The battery management system of claim 6, wherein the charge and discharge control switch comprises two N-type MOSFETs connected in series, using a charge and discharge common port connection; one end of the trickle charge unit is connected with the negative electrode interface of the charger, and the other end of the trickle charge unit is connected with the drain electrode of the charge switch SWC or the source electrode of the discharge switch SWD or the negative electrode B-of the battery pack.

8. The battery management system according to claim 6, wherein the charge and discharge control switch comprises two N-type MOSFETs connected in parallel, and adopts a charge and discharge differential connection method; one end of the trickle charging unit is connected with the negative electrode interface of the charger, and the other end of the trickle charging unit is connected with the drain electrode of the charging switch SWC or the negative electrode B-of the battery pack.

9. The battery management system of claim 1, wherein the battery monitoring and protection unit comprises a plurality of strings of integrated protection ICs with over-temperature protection or sampling line drop detection functions.

10. A charge equalization control method for a battery management system, for implementing the battery management system according to any one of claims 1 to 9, comprising:

when the voltage of the battery is greater than the equalizing voltage or the overcharging voltage, starting the passive equalizing function of the battery;

when any battery in the battery pack enters a protection state, the charging control switch is turned off, and the trickle charging unit is turned on;

the operation continues until the external charger is removed or the trickle charge unit is turned off when all batteries are fully charged.