CN114335771A - Balanced discharge method with SOC difference - Google Patents

Abstract

The invention relates to the technical field of lithium battery balanced discharge, and discloses a balanced discharge method with SOC difference, which specifically comprises the following steps: s1: the parallel operation BMSs are communicated with each other, the real-time battery rated capacity (AH _ rate), the residual capacity (AH _ soc), the output current (Io) and the fault state of the parallel operation BMSs are transmitted, and the host synchronously adjusts the adjusting rhythm of the parallel operation BMSs; s2: the average discharge current target value is calculated by the BMS according to the following formula based on the rated capacity (AH _ rate), the residual capacity (AH _ soc) and the output current (Io), and the BMSs report real-time data periodically. According to the parallel operation discharging current equalizing method and device, the output voltage is adjusted to control the current equalizing proportion of parallel operation discharging and whether the SOC is correlated or not, the parallel operation current equalizing strategy is adjusted based on the current data, the correlation of the SOC is increased, the purpose of battery collaborative discharging can be achieved, and the balance discharging function based on the SOC difference is increased on the basis of the parallel operation discharging current equalizing scheme of the DC/DC BMS.

Description

Equilibrium discharge method with SOC difference

technical field

The patent of the present invention relates to the technical field of balanced discharge of lithium batteries, in particular, to a balanced discharge method with SOC difference.

Background technique

We know that when the output power ports of multiple batteries are connected in parallel, there will be high-voltage batteries to charge low-voltage batteries; different management methods for lithium batteries include:

1. Conventional switching BMS, as shown in Figure 1, through the power switch, the charging circuit switch is closed when the battery needs to be charged, the discharge circuit switch is closed when the battery needs to be discharged, and the charging is disconnected when charging or discharging is not allowed. or discharge switch, BMS cannot adjust the output voltage;

2. Referring to Fig. 2, the BMS with PWM control of DC/DC power supply changes realizes the regulation of BUS discharge voltage by changing the PWM of the power conversion circuit.

However, in the case of discharging the load, the higher voltage battery will have a larger discharge current than the lower battery voltage, that is, natural current sharing, and there will be parallel circulating current (mutual charging and discharging) and uneven current discharge problems, which may reduce battery life. The battery life of different batteries is different. For the same lithium battery and the number of battery cells in different strings, the problems of battery circulation and unbalanced discharge are particularly obvious.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a balanced discharge method with SOC difference, by adjusting the output voltage to control the current sharing ratio of the parallel discharge, whether to correlate the SOC, and the strategy of adjusting the parallel current sharing based on the current data, which increases the correlation of the SOC, and can be more efficient. To achieve the purpose of battery coordinated discharge, it aims to solve the problem that in the prior art, in the case of discharging the load, the higher voltage battery will have a larger discharge current than the lower battery voltage, that is, natural current sharing, and parallel circulating current (mutual charging and discharging) and inconsistency. The problem of current sharing and discharge may reduce the battery life, and the battery life in parallel is different.

The present invention is implemented in this way, and the balanced discharge method with SOC difference specifically includes the following steps:

S1: Each parallel BMS communicates with each other, and transmits its own real-time battery rated capacity (AH_rate), remaining capacity (AH_soc), output current (Io), and fault status, and the host synchronously adjusts the adjustment rhythm of each parallel BMS;

S2: Calculate the average discharge current target value based on the rated battery capacity (AH_rate), remaining capacity (AH_soc), and output current (Io) of each BMS using the following formula, and each BMS periodically reports real-time data;

Ibus_delta=Io+AH_soc_x-(∑(Ibus_x)+∑(AH_soc_x–AH_soc_avg))/n(2)

Vset_delta=X*Io_delta (3)

Among them: X: proportional correlation coefficient based on the current difference to adjust the voltage difference;

M: proportional correlation coefficient of battery capacity relative to discharge current;

Ibus_x: The BUS terminal of each BMS is turned on to output current, charging is positive, and discharging is negative;

AH_soc_x: the remaining capacity of each BMS;

AH_soc_avg: the average capacity of each BMS;

Ibus_delta: The difference between the current of a BMS BUS, the average parallel current and the battery capacity;

Vset_delta: The discharge BUS voltage difference that needs to be adjusted in order for a BMS to make its own output current close to the average parallel current;

n: The number of parallel BMSs with discharge capability;

S3: By determining the absolute values of Ibus_delta and Vset_delta, it is determined whether the correlation of the increased SOC has achieved the purpose of coordinated discharge of the battery.

Further, in S3, it is first determined whether the absolute value of Ibus_delta is greater than or equal to 9A, and if so, it is determined whether the Vset_delta1 equation is established by formula (3).

Further, if the formula (3) does not hold, it is judged whether the absolute value of Ibus_delta is greater than or equal to 1A, and if it is greater than or equal to 1A, it is judged whether the equation of Vset_delta12 holds.

Further, the Vset_delta1=X1*Io_delta, the Vset_delta2=X2*Io_delta, where X1=3, X2=1.

Further, if it is first determined that the absolute value of Ibus_delta is less than 9A, it is directly determined that the absolute value of bus_delta is greater than or equal to 1A, and finally it is determined whether the Vset_delta12 equation holds.

Compared with the prior art, the balanced discharge method with SOC difference provided by the present invention has the following beneficial effects:

1. By adjusting the output voltage to control the current sharing ratio of the parallel discharge and whether to correlate the SOC, the strategy of adjusting the parallel current sharing based on the current data increases the correlation of the SOC, and can better achieve the purpose of battery coordinated discharge, making the DC/DC BMS On the basis of the parallel discharge current sharing scheme, the balanced discharge function based on SOC difference is added;

2. This technical solution is applied in the battery parallel/parallel system. It only needs to connect the positive and negative busbars of all batteries and connect the CAN communication lines together to automatically discharge current and equalize. The core idea is to detect each BMS. Output voltage, SOC, number of parallel machines, calculate and adjust the output discharge voltage.

Description of drawings

Fig. 1 is a conventional BMS topology diagram;

Fig. 2 is the topological diagram of BMS with DCDC function;

FIG. 3 is a flow chart of a balanced discharge method with SOC difference proposed by the present invention;

FIG. 4 is a schematic diagram of the wiring of the BMS in parallel in the balanced discharge method with SOC difference proposed by the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The implementation of the present invention will be described in detail below with reference to specific embodiments.

Referring to Figure 3-4, the balanced discharge method with SOC difference specifically includes the following steps:

S1: Each parallel BMS communicates with each other, and transmits its own real-time battery rated capacity (AH_rate), remaining capacity (AH_soc), output current (Io), and fault status, and the host synchronously adjusts the adjustment rhythm of each parallel BMS;

S2: Calculate the average discharge current target value based on the rated battery capacity (AH_rate), remaining capacity (AH_soc), and output current (Io) of each BMS using the following formula. Each BMS periodically reports real-time data, and the period is T(2～ 4 seconds);

Ibus_delta=Io+AH_soc_x-(∑(Ibus_x)+∑(AH_soc_x–AH_soc_avg))/n(2)

Vset_delta=X*Io_delta (3)

Among them: X: proportional correlation coefficient based on the current difference to adjust the voltage difference;

M: proportional correlation coefficient of battery capacity relative to discharge current;

Ibus_x: The BUS terminal of each BMS is turned on to output current, charging is positive, and discharging is negative;

AH_soc_x: the remaining capacity of each BMS;

AH_soc_avg: the average capacity of each BMS;

Ibus_delta: The difference between the current of a BMS BUS, the average parallel current and the battery capacity;

Vset_delta: The discharge BUS voltage difference that needs to be adjusted in order for a BMS to make its own output current close to the average parallel current;

n: The number of parallel BMSs with discharge capability;

S3: By determining the absolute value of Ibus_delta and Vset_delta, determine the correlation of the increased SOC, whether the purpose of battery coordinated discharge is achieved, control the current sharing ratio of parallel discharge by adjusting the output voltage, whether it is related to SOC, and adjust the parallel based on current data. The current sharing strategy increases the correlation of SOC, and can better achieve the purpose of battery coordinated discharge, so that the DC/DC BMS adds a balanced discharge function based on SOC differences on the basis of the parallel discharge current sharing scheme.

In S3 of this embodiment, first determine whether the absolute value of Ibus_delta is greater than or equal to 9A, and if so, determine whether the Vset_delta1 equation is established by formula (3), that is, Vset_delta1=X1*Io_delta, where when the value of Ibus_delta is larger, X1 It is the proportional correlation coefficient of the voltage difference adjusted based on the current difference. If the formula (3) does not hold, it is judged whether the absolute value of Ibus_delta is greater than or equal to 1A. When the value of Ibus_delta is small, X2 is the proportional correlation coefficient for adjusting the voltage difference based on the current difference.

In this embodiment, when Vset_delta1=9A, Vset_delta2=1A, where X1=3, X2=1, so as to determine whether to realize automatic discharge current sharing/balance, the core idea is to detect the output voltage, SOC, parallel connection of each BMS quantity, calculate and adjust the output discharge voltage.

In this embodiment, if it is first determined that the absolute value of Ibus_delta is less than 9A, it is directly determined that the absolute value of bus_delta is greater than or equal to 1A, and finally it is determined whether the Vset_delta12 equation holds.

In this technical solution, the formula (1) is basically the same as the formula or flow chart in Fig. 3, but some parameters, such as X1, X2, M, are changed. This is applied to the battery parallel/parallel system. The positive and negative busbars are connected, and the CAN communication lines are connected together to automatically discharge current sharing/balance. By adjusting the output voltage to control the current sharing ratio of parallel discharge and whether it is related to SOC, the correlation of SOC is increased, and battery coordination can be achieved. For the purpose of discharge, the DC/DC BMS adds a balanced discharge function based on SOC differences on the basis of the parallel discharge current sharing scheme.

Referring to FIG. 4 , in a parallel/parallel system of multiple batteries, it only needs to connect the positive and negative busbars of all batteries, and connect the CAN communication lines together, and the SOC of this technical solution can be correlated to automatically discharge current sharing / balanced.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (5)

1. A balanced discharge method with SOC difference, characterized in that it specifically includes the following steps: S1: Each parallel BMS communicates with each other, and transmits its own real-time battery rated capacity (AH_rate), remaining capacity (AH_soc), output current (Io), and fault status, and the host synchronously adjusts the adjustment rhythm of each parallel BMS; S2: Calculate the average discharge current target value based on the rated battery capacity (AH_rate), remaining capacity (AH_soc), and output current (Io) of each BMS using the following formula, and each BMS periodically reports real-time data;

Ibus_delta=Io+AH_soc_x-(∑(Ibus_x)+∑(AH_soc_x–AH_soc_avg))/n (2) Vset_delta=X*Io_delta (3) Among them: X: proportional correlation coefficient based on the current difference to adjust the voltage difference; M: proportional correlation coefficient of battery capacity relative to discharge current; Ibus_x: The BUS terminal of each BMS is turned on to output current, charging is positive, and discharging is negative; AH_soc_x: the remaining capacity of each BMS; AH_soc_avg: the average capacity of each BMS; Ibus_delta: The difference between the current of a BMS BUS, the average parallel current and the battery capacity; Vset_delta: The discharge BUS voltage difference that needs to be adjusted in order for a BMS to make its own output current close to the average parallel current; n: The number of parallel BMSs with discharge capability; S3: By determining the absolute values of Ibus_delta and Vset_delta, it is determined whether the correlation of the increased SOC has achieved the purpose of coordinated discharge of the battery. 2. The balanced discharge method with SOC difference according to claim 1, wherein in S3, first determine whether the absolute value of Ibus_delta is greater than or equal to 9A, and if so, determine whether the Vset_delta1 equation is established by formula (3). . 3. The balanced discharge method with SOC difference as claimed in claim 2, characterized in that, if the formula (3) is not established, it is judged whether the absolute value of Ibus_delta is greater than or equal to 1A, and if greater than or equal to 1A, it is judged whether the Vset_delta12 equation is established. . 4 . The balanced discharge method with SOC difference according to claim 3 , wherein the Vset_delta1=X1*Io_delta, the Vset_delta2=X2*Io_delta, wherein X1=3, X2=1. 5 . 5. The balanced discharge method with SOC difference according to claim 4, characterized in that, if it is first determined that the absolute value of Ibus_delta is less than 9A, then it is directly determined that the absolute value of bus_delta is greater than or equal to 1A, and finally it is determined whether the Vset_delta12 equation is established.

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