A new energy battery pre-charge control and short circuit detection system and method

Abstract

The present invention relates to the technical field of new energy batteries, and in particular to a new energy battery pre-charging control and short-circuit detection system and method. First, the B+ terminal and the B-terminal of a BMS are connected to the B+ terminal and the B-terminal of a battery respectively, the P-terminal of the BMS is connected to the P-terminal of a battery pack, a load C is connected between the P+ terminal and the P-terminal of the battery pack, the longest pre-charging time is set by the BMS, the BMS is powered on, and the BMS enters a pre-charging state. The BMS detects the voltage of the P-terminal and judges the pre-charging state of the load C according to the voltage condition, thereby realizing the function of detecting whether a short circuit is present in the pre-charging stage and reliably pre-charging loads of different capacitance values. After a certain pre-charging time, it is detected whether the voltage of the P-terminal drops. If the voltage of the P-terminal drops, it indicates that the load C is pre-charged normally. If the voltage of the P-terminal does not drop, it indicates that the P+ terminal and the P-terminal are short-circuited, and the system enters a short-circuit fault state, thereby avoiding the short-circuit current impact generated when the charge and discharge MOS is turned on when the pre-charging ends, and extending the life of the BMS.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and in particular relates to a new energy battery pre-charging control and short-circuit detection system and method. Background Art

[0002] New energy battery pre-charging is the preliminary charging of large-capacity capacitors in high-voltage circuits through a pre-charging resistor before powering on or charging the power battery system of an electric vehicle, so as to reduce the current shock that may be generated when powering on directly, protect circuit components and improve safety.

[0003] At present, the pre-charging method of new energy batteries is usually to have a fixed or adjustable pre-charging time before turning on the charging and discharging MOS. After the pre-charging is completed, the charging and discharging MOS is turned on and the battery is connected to the external load.

[0004] However, this method has the following defects:

[0005] 1. During the pre-charging stage, it is impossible to detect whether there is an external short circuit. The short circuit alarm can only be issued when the short circuit current is detected and the protection is triggered at the end of the pre-charging. The BMS board will be subjected to a short circuit current impact, and there is a certain probability that components will be damaged.

[0006] 2. When there is a large capacitor outside, the capacitor cannot be fully charged. After the pre-charge is completed and the MOS is turned on normally, there may still be a large current. If the capacitor is continuously charged, overcurrent protection or even short-circuit protection failure may occur;

[0007] Therefore, we need to propose a new energy battery pre-charging control and short-circuit detection system and method to solve the above-mentioned defects, so that it can detect whether there is a short circuit during the pre-charging stage and reliably pre-charge loads of different capacitance values. Summary of the invention

[0008] In view of the above problems, the present invention provides a new energy battery pre-charging control and short-circuit detection system, including a BMS. The BMS includes a single-chip microcomputer and a current sampling unit, a voltage sampling unit, a power supply unit, a MOS unit, a pre-charging resistor and a charging current limiting module connected to the single-chip microcomputer. The current sampling unit is connected to the MOS unit, and the MOS unit is connected to the charging current limiting module. The MOS unit is used to control the on-off of the current loop, and the voltage sampling unit feeds back the P-terminal voltage of the BMS to the single-chip microcomputer in real time.

[0009] Furthermore, the current sampling unit includes a sampling resistor for collecting current, one end of the sampling resistor is connected to the negative electrode of the battery, and the other end of the sampling resistor is connected to the MOS unit.

[0010] Furthermore, the MOS unit includes a pre-charge resistor R, a pre-charge MOS and a charging MOS connected to the P-end of the BMS, which are connected in sequence. A discharge MOS is connected between the sampling resistor and the charging MOS. The charging current limiting module is connected between the pre-charge MOS and the P-end of the BMS. After the BMS is powered on, it first enters the pre-charge state, the charging MOS and the pre-charge MOS are turned on, and the discharge MOS and the charging current limiting module are turned off, so as to discharge the external load C with a small current.

[0011] Based on the above-described new energy battery pre-charge control and short circuit detection system, the present invention also provides a new energy battery pre-charge control and short circuit detection method, comprising the following steps:

[0012] S1. Connect the B+ and B- terminals of the BMS to the B+ and B- terminals of the battery respectively, connect the P- terminal of the BMS to the P- terminal of the battery pack, and connect the load C between the P+ and P- terminals of the battery pack;

[0013] S2. Set the longest pre-charge time through BMS, power on the BMS, and put the BMS into the pre-charge state;

[0014] S3. The P-terminal voltage is monitored in real time by the BMS, and the pre-charge status of the load C is determined according to the voltage. There are two situations:

[0015] S31, when the pre-charging time reaches the set maximum pre-charging time, the pre-charging ends and enters the normal state;

[0016] S32. After a certain period of precharging, check whether the voltage at the P-terminal has dropped. If the voltage at the P-terminal has dropped, it means that the load C is precharged normally, and enter S31. If the voltage at the P-terminal has not dropped, it means that the P+ terminal and the P-terminal are short-circuited, and enter the short-circuit fault state.

[0017] Furthermore, when the load C is normally charged, the battery charges the load C through the pre-charging resistor R. The charging time is determined by the pre-charging resistor R and the load C. The calculation formula of the load voltage is as follows:

[0018] Vc(t)=Vi*(1-e^(-t / τ)), where: τ=RC, Vi is the battery voltage, and Vc is the value of the voltage of load C changing with time t.

[0019] Furthermore, in step S3, the BMS monitors the voltage of load C by calculating the difference between the P+ terminal voltage and the P- voltage. The voltage of load C gradually increases over time, and the P- voltage gradually decreases. When the P- terminal voltage is less than a certain threshold, it is considered that the load voltage is basically close to the battery voltage, then the pre-charge state is exited and the normal state is entered; when the P- terminal voltage is always equal to the P+ terminal voltage and does not decrease over time, it is judged that the load is short-circuited, then the short-circuit protection state is entered.

[0020] Furthermore, when judging the pre-charging state of the load C, the following process is included:

[0021] A1. First, set the maximum duration of the pre-charge state to T1, the detection delay time of the short-circuit fault to T2, the voltage threshold of the short-circuit fault to V1, the voltage threshold for exiting the pre-charge to V2, and the pre-charge starts;

[0022] A2. When the pre-charging time reaches the longest duration T1 of the pre-charging state, the pre-charging ends and the system works normally.

[0023] A3. When the pre-charge time does not reach the maximum duration T1 of the pre-charge state, it is determined whether the pre-charge time reaches the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the voltage threshold V1 of the short-circuit fault;

[0024] A4. When the pre-charging time reaches the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the short-circuit fault voltage threshold V1, the pre-charging ends and the short-circuit fault is reported;

[0025] A5. When the pre-charge time does not reach the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the short-circuit fault voltage threshold V1, it is determined whether the P-terminal voltage is less than the pre-charge exit voltage threshold V2;

[0026] A6. When the voltage at the P-terminal is less than the voltage threshold V2 for exiting pre-charging, the pre-charging ends and the system operates normally.

[0027] A7. When the P-terminal voltage is greater than or equal to the voltage threshold V2 for exiting pre-charge, enter step A2.

[0028] Furthermore, in step A1, when setting the maximum duration T1 of the pre-charging state, due to the power limitation of the pre-charging resistor R, the maximum duration T1 of the pre-charging state needs to be extended so that the average power of the pre-charging resistor R during the pre-charging period is less than the rated power of the pre-charging resistor R.

[0029] Furthermore, during the pre-charging period, monitor whether the voltage of P- drops to V2. If the voltage of P- drops to V2, it means that the load C has been pre-charged and the voltage of load C is equal to the battery voltage, then the pre-charging is ended. If the voltage of P- does not drop to V2, it means that the load C has not been pre-charged, then the load C continues to be pre-charged until the voltage of P- drops to V2.

[0030] The beneficial effects of the present invention are:

[0031] The present invention detects the voltage of the negative electrode P-terminal of the battery through the BMS, and judges the pre-charging state of the load C according to the voltage condition, thereby realizing the function of detecting whether there is a short circuit in the pre-charging stage and reliably pre-charging loads with different capacitance values. After a certain period of pre-charging, it detects whether the voltage of the P-terminal has dropped. If the voltage of the P-terminal has dropped, it indicates that the load C is pre-charged normally. If the voltage of the P-terminal has not dropped, it indicates that the P+ terminal and the P-terminal are short-circuited, and a short-circuit fault state is entered, thereby avoiding the short-circuit current impact generated when the charge and discharge MOS is turned on when the pre-charging ends, and prolonging the life of the BMS.

[0032] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 A flowchart according to an embodiment of the present invention is shown;

[0035] Figure 2 A block diagram of a BMS system according to an embodiment of the present invention is shown;

[0036] Figure 3 A schematic diagram of a BMS current loop according to an embodiment of the present invention is shown;

[0037] Figure 4 A voltage variation curve diagram according to an embodiment of the present invention is shown;

[0038] Figure 5 A graph showing the relationship between voltage and current over time during a short circuit according to an embodiment of the present invention is shown;

[0039] Figure 6A flow chart of pre-charging state determination according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0041] The embodiment of the present invention provides a new energy battery pre-charge control and short circuit detection system, such as Figure 2-3 As shown, the BMS includes a single-chip microcomputer and a current sampling unit, a voltage sampling unit, a power supply unit, a MOS unit, a pre-charging resistor and a charging current limiting module connected to the single-chip microcomputer. The current sampling unit is connected to the MOS unit, and the MOS unit is connected to the charging current limiting module. The MOS unit is used to control the on-off of the current loop, and the voltage sampling unit feeds back the P-terminal voltage of the BMS to the single-chip microcomputer in real time.

[0042] The sampling unit comprises a sampling resistor for collecting current, one end of the sampling resistor is connected to the negative electrode of the battery, and the other end of the sampling resistor is connected to the MOS unit.

[0043] The MOS unit includes a pre-charge resistor R, a pre-charge MOS and a charging MOS connected to the P-end of the BMS, which are connected in sequence. A discharge MOS is connected between the sampling resistor and the charging MOS. The charging current limiting module is connected between the pre-charge MOS and the P-end of the BMS. After the BMS is powered on, it first enters the pre-charge state, the charging MOS and the pre-charge MOS are turned on, and the discharge MOS and the charging current limiting module are turned off, and the external load C is discharged with a small current to make the external load voltage rise to be close to the battery voltage. The current loop is as follows Figure 3 shown.

[0044] Based on the above-described new energy battery pre-charge control and short circuit detection system, the present invention also provides a new energy battery pre-charge control and short circuit detection method, such as Figure 1-6 As shown, the following steps are included:

[0045] S1, connect the B+ and B- terminals of the BMS to the B+ and B- terminals of the battery respectively, connect the P- of the BMS to the P- of the battery pack, and connect the load C between the P+ and P- terminals of the battery pack;

[0046] S2. Set the longest pre-charge time through BMS, power on the BMS, and put the BMS into the pre-charge state;

[0047] When the load C is normally charged, the battery charges the load C through the pre-charging resistor R. The charging time is determined by the pre-charging resistor R and the load C. The larger the external load is, the longer the charging time is required. The calculation formula of the load voltage is as follows:

[0048] Vc(t)=Vi*(1-e^(-t / τ)), where: τ=RC, Vi is the battery voltage, Vc is the value of the voltage of load C changing with time. For example, when R=23.5 ohms, C=50000uF, it takes about 5.4 seconds for Vc to increase from 0 to 99% of Vi. Its voltage curve is as follows Figure 4 shown.

[0049] S3. The P-terminal voltage is monitored in real time by the BMS, and the pre-charge status of the load C is determined according to the voltage. There are two situations:

[0050] S31, when the pre-charging time reaches the set maximum pre-charging time, the pre-charging ends and enters the normal state;

[0051] S32. After a certain period of precharging, check whether the voltage at the P-terminal has dropped. If the voltage at the P-terminal has dropped, it means that the load C is precharged normally, and enter S31. If the voltage at the P-terminal has not dropped, it means that the P+ terminal and the P-terminal are short-circuited, and enter the short-circuit fault state.

[0052] When the BMS monitors the voltage of load C, it calculates the difference between the voltage at the P+ terminal and the voltage at the P- terminal. The voltage of load C gradually increases over time, and the voltage at the P- terminal gradually decreases. When the voltage at the P- terminal is less than a certain threshold, the pre-charge state is exited and the normal state is entered. When the voltage at the P- terminal is always equal to the voltage at the P+ terminal and does not decrease over time, it is judged that the load is short-circuited, and the short-circuit protection state is entered.

[0053] The voltage sampling unit processes the P-voltage and collects it through the microcontroller. By monitoring the voltage at the P-terminal, the BMS can control the end time of pre-charging, so that the pre-charging state is exited when the load voltage is greater than a certain threshold (such as 99% of the battery voltage). The pre-charging stage is shorter when the external capacitance is small, and longer when the external capacitance is large, thus having a strong adaptability to the capacitance value of the external capacitance.

[0054] When the positive and negative electrodes of the battery are short-circuited, the voltage at the P- terminal is always equal to the voltage at the P+ terminal and will not decrease over time, and the pre-charge current remains basically unchanged. Based on this, the BMS determines the fault and enters the short-circuit protection state. This avoids the short-circuit current impact generated when the charge and discharge MOS is turned on at the end of pre-charge, and prolongs the life of the BMS. The relationship between the voltage and current changes over time during the short circuit period is as follows Figure 5 shown.

[0055] When judging the pre-charge status of load C, if Figure 6 As shown, the following process is included:

[0056] A1. First, set the maximum duration of the pre-charge state to T1, the detection delay time of the short-circuit fault to T2, the voltage threshold of the short-circuit fault to V1, the voltage threshold for exiting the pre-charge to V2, and the pre-charge starts;

[0057] When setting the maximum duration T1 of the pre-charging state, due to the power limitation of the pre-charging resistor R, the maximum duration T1 of the pre-charging state needs to be extended so that the average power of the pre-charging resistor R during the pre-charging period is less than the rated power of the pre-charging resistor R.

[0058] A2. When the pre-charging time reaches the longest duration T1 of the pre-charging state, the pre-charging ends and the system works normally.

[0059] A3. When the pre-charge time does not reach the maximum duration T1 of the pre-charge state, it is determined whether the pre-charge time reaches the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the voltage threshold V1 of the short-circuit fault;

[0060] A4. When the pre-charging time reaches the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the short-circuit fault voltage threshold V1, the pre-charging ends and the short-circuit fault is reported;

[0061] A5. When the pre-charge time does not reach the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the short-circuit fault voltage threshold V1, it is determined whether the P-terminal voltage is less than the pre-charge exit voltage threshold V2;

[0062] A6. When the voltage at the P-terminal is less than the voltage threshold V2 for exiting pre-charging, the pre-charging ends and the system operates normally.

[0063] A7. When the P-terminal voltage is greater than or equal to the voltage threshold V2 for exiting pre-charge, enter step A2.

[0064] Among them, the maximum duration of the pre-charge state is T1: This parameter is configurable. The time for the external capacitor to charge to 99% is about 5.4 seconds when the capacitance is 50,000 uF, and about 16.2 seconds when the capacitance is 150,000 uF. Therefore, this parameter can be set to about 5~15 seconds, which can meet the general pre-charge requirements. When the external capacitance is greater than 150,000 uF, T1 can be changed to a larger value. Considering the power limit of the pre-charge resistor, it may be turned on for a while and then turned off for a while during the pre-charge period, so that the average power of the pre-charge resistor will not cause it to burn out, so T1 needs to be lengthened accordingly.

[0065] Short circuit fault detection delay T2: This parameter can be set to about 3 seconds. After the pre-charge begins, under normal circumstances, the P- / P+ pressure difference will gradually increase with the increase of Vc. After T2 time, the pressure difference is significantly greater than the V1 threshold. In the case of a short circuit, the P- / P+ pressure difference is always 0.

[0066] Voltage threshold V1 for short-circuit fault: This parameter can be set to about 2 V. If the P- / P+ voltage difference is still less than V1 after T2 time from the start of pre-charging, a short-circuit fault is considered to occur.

[0067] The voltage threshold V2 for exiting pre-charge: This parameter can be set to about 2V. When the P- voltage is less than V2, it means that Vc is basically full and the pre-charge can be ended and normal operation can be started. The smaller the value, the more fully the external capacitor is charged, and the smaller the current at the moment of starting normal operation.

[0068] During the pre-charging period, monitor whether the voltage of P- drops to V2. If the voltage of P- drops to V2, it means that the load C has been pre-charged and the voltage of load C is equal to the battery voltage, then the pre-charging is ended; if the voltage of P- does not drop to V2, it means that the load C has not been pre-charged, then the load C continues to be pre-charged until the voltage of P- drops to V2.

[0069] In summary, the BMS detects the voltage of the negative electrode P-terminal of the battery and judges the pre-charge state of the load C according to the voltage condition, thereby realizing the function of detecting whether there is a short circuit in the pre-charge stage and reliably pre-charging loads of different capacitance values. After a certain period of pre-charging, it detects whether the voltage of the P-terminal has dropped. If the voltage of the P-terminal has dropped, it means that the load C is pre-charged normally. If the voltage of the P-terminal has not dropped, it means that the P+ terminal and the P-terminal are short-circuited, and the short-circuit fault state is entered, thereby avoiding the short-circuit current impact generated when the charge and discharge MOS is turned on at the end of pre-charging, thereby extending the life of the BMS.

[0070] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A new energy battery pre-charge control and short circuit detection system, characterized in that: The BMS includes a single-chip microcomputer and a current sampling unit, a voltage sampling unit, a power supply unit, a MOS unit, a pre-charging resistor and a charging current limiting module connected to the single-chip microcomputer. The current sampling unit is connected to the MOS unit, and the MOS unit is connected to the charging current limiting module. The MOS unit is used to control the on-off of the current loop. The voltage sampling unit feeds back the P-terminal voltage of the BMS to the single-chip microcomputer in real time. The sampling unit includes a sampling resistor for collecting current, one end of the sampling resistor is connected to the negative electrode of the battery, and the other end of the sampling resistor is connected to the MOS unit; The MOS unit includes a pre-charge resistor R, a pre-charge MOS and a charging MOS connected to the P-terminal of the BMS, which are connected in sequence. A discharge MOS is connected between the sampling resistor and the charging MOS. The charging current limiting module is connected between the pre-charge MOS and the P-terminal of the BMS. After the BMS is powered on, it first enters the pre-charge state, the charging MOS and the pre-charge MOS are turned on, and the discharge MOS and the charging current limiting module are turned off, so as to discharge the external load C with a small current. When judging the pre-charge state of load C, the following process is included: A1. First, set the maximum duration of the pre-charge state to T1, the detection delay time of the short-circuit fault to T2, the voltage threshold of the short-circuit fault to V1, the voltage threshold for exiting the pre-charge to V2, and the pre-charge starts; When the maximum duration T1 of the pre-charging state is set, due to the power limitation of the pre-charging resistor R, the maximum duration T1 of the pre-charging state needs to be extended so that the average power of the pre-charging resistor R during the pre-charging period is less than the rated power of the pre-charging resistor R; A2. When the pre-charging time reaches the longest duration T1 of the pre-charging state, the pre-charging ends and the system works normally. A3. When the pre-charge time does not reach the maximum duration T1 of the pre-charge state, it is determined whether the pre-charge time reaches the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the voltage threshold V1 of the short-circuit fault; A4. When the pre-charging time reaches the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the short-circuit fault voltage threshold V1, the pre-charging ends and the short-circuit fault is reported; A5. When the pre-charge time does not reach the short-circuit fault detection delay time T2, and the voltage difference between the P-terminal and the P+terminal is less than the short-circuit fault voltage threshold V1, it is determined whether the P-terminal voltage is less than the pre-charge exit voltage threshold V2; A6. When the voltage at the P-terminal is less than the voltage threshold V2 for exiting pre-charging, the pre-charging ends and the system operates normally. A7. When the P-terminal voltage is greater than or equal to the voltage threshold V2 for exiting pre-charge, enter step A2.

2. A new energy battery pre-charge control and short circuit detection method, The new energy battery pre-charge control and short circuit detection system according to claim 1 is characterized in that: The steps include: S1. Connect the B+ and B- terminals of the BMS to the B+ and B- terminals of the battery respectively, connect the P- terminal of the BMS to the P- terminal of the battery pack, and connect the load C between the P+ and P- terminals of the battery pack; S2. Set the longest pre-charge time through BMS, power on the BMS, and put the BMS into the pre-charge state; S3. The P-terminal voltage is monitored in real time by the BMS, and the pre-charge status of the load C is determined according to the voltage. There are two situations: S31, when the pre-charging time reaches the set maximum pre-charging time, the pre-charging ends and enters the normal state; S32. After a certain period of precharging, check whether the voltage at the P-terminal has dropped. If the voltage at the P-terminal has dropped, it means that the load C is precharged normally, and enter S31. If the voltage at the P-terminal has not dropped, it means that the P+ terminal and the P-terminal are short-circuited, and enter the short-circuit fault state.

3. A new energy battery pre-charge control and short circuit detection method according to claim 2, characterized in that: When the load C is normally charged, the battery charges the load C through the pre-charging resistor R. The charging time is determined by the pre-charging resistor R and the load C. The calculation formula of the load voltage is as follows: Vc(t)=Vi*(1-e^(-t / τ)), where: τ=RC, Vi is the battery voltage, and Vc is the value of the voltage of the load C changing with time t.

4. A new energy battery pre-charge control and short circuit detection method according to claim 3, characterized in that: In step S3, the BMS monitors the voltage of load C by calculating the difference between the P+ terminal voltage and the P- voltage. The voltage of load C gradually increases over time, and the P- voltage gradually decreases. When the P- terminal voltage is less than a certain threshold, it is considered that the load voltage is basically close to the battery voltage, then the pre-charge state is exited and the normal state is entered; when the P- terminal voltage is always equal to the P+ terminal voltage and does not decrease over time, it is judged that the load is short-circuited, then the short-circuit protection state is entered.

5. A new energy battery pre-charge control and short circuit detection method according to claim 4, characterized in that: During the pre-charging period, monitor whether the voltage of P- drops to V2. If the voltage of P- drops to V2, it means that the load C has been pre-charged and the voltage of load C is equal to the battery voltage, then the pre-charging is ended; if the voltage of P- does not drop to V2, it means that the load C has not been pre-charged, then the load C continues to be pre-charged until the voltage of P- drops to V2 or the pre-charging time reaches T1.

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