CN115047347A - Method for judging residual electric quantity of underwater vehicle battery under dynamic load current - Google Patents

Abstract

The invention relates to a method for judging the remaining power of an underwater vehicle battery under dynamic load current. A plurality of battery cells of the same type as the cells in the lithium battery pack to be tested are selected, divided into several equal parts, and discharged to the cut-off voltage. ; Take the average value of the three available quantities of electricity measured at their respective magnifications as the available quantity of electricity at the corresponding magnification; The current-k function corresponds to the law, and the instantaneous capacity that is finally consumed: Calculate the remaining power of the battery when the current I changes dynamically. Since the present invention fully considers the variable of the load current, the obtained residual power of the battery is more accurate.

Description

Method for judging the remaining power of underwater vehicle battery under dynamic load current

technical field

The invention belongs to a method for judging the remaining power of an underwater vehicle battery, and relates to a method for judging the remaining power of an underwater vehicle battery under a dynamic load current.

Background technique

Electric powered underwater vehicle has great advantages over thermal powered underwater vehicle in terms of structure and performance. In recent years, the development speed is very fast. Therefore, the research of power battery is very important for the development and application of underwater vehicle. Compared with other secondary batteries, lithium-ion batteries have high energy density, high working voltage, low self-discharge rate, convenient use and maintenance, and no memory effect. All devices use lithium-ion batteries as their power source devices.

Compared with the relatively mature battery heat production and temperature field analysis, the current research to determine the influence of temperature on the discharge performance of battery cells is relatively weak. In many applications, predicting the state of charge (SOC) of a battery is critical. Many engineers base their SOC prediction methods on Peukert's equation, which studies the available discharge capacity of lead-acid batteries when they are discharged at a constant current. However, this equation has great limitations, unless the battery is discharged at a constant current and constant temperature, the Peukert equation cannot be used to accurately predict the remaining capacity. In many practical situations, batteries are discharged at different currents through a wide variety of temperatures. Many times the Peukert equation is used in power monitoring and supply systems; however, the drawbacks associated with more drastic changes in the discharge environment challenge this model. Since the average discharge current cannot accurately characterize the records of the battery discharge process, and it is impossible to ensure that the temperature of the battery remains constant during the discharge process, the error introduced by establishing the average current model may be quite large, and a real-time state-based model needs to be introduced. Equivalent charge loss to assess the state of charge of the battery.

SUMMARY OF THE INVENTION

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a method for judging the remaining power of the underwater vehicle battery under the dynamic load current, a method for predicting the remaining power of the lithium battery pack for the underwater vehicle which is different from the existing evaluation method. The method of battery power is used to overcome the disadvantage that the existing evaluation method can only roughly estimate the remaining battery power, but cannot accurately evaluate it.

Technical solutions

A method for determining the remaining power of an underwater vehicle battery under a dynamic load current, characterized in that the steps are as follows:

Step 1: Select multiple battery cells with the same type as the cells in the lithium battery pack to be tested, divide them into several equal parts, and discharge them to the cut-off voltage; take the average value of the three available powers measured at their respective rates as the corresponding rate available power;

Step 2: Calculate the magnification compensation coefficient under different currents

Among them: Q ₀ represents the dischargeable capacity of the battery at a current of 1C rate, and Q _I represents the dischargeable capacity of the battery at the current I

Step 3: Complement the discrete current-k function by using the function fitting method to obtain the corresponding law of the continuous current-k function, and the instantaneous capacity that is finally consumed:

ΔQr=ΔQ·k(I)

The effective power that changes from time t1 to time t2:

Step 4: Calculate the remaining capacity of the battery when the current I changes dynamically:

Take the battery from the time of full charge as the starting point of integration, and integrate the effective capacity consumed by the battery,

The available power Q ₀ of the battery under the 1C rate is used as the nominal capacity, and the remaining power of the battery under the dynamic load is calculated, namely

Q _r =Q ₀ -ΔQ.

The plurality of battery cells is 27, divided into 9 parts on average, and different loads are adopted at 9 different magnifications: 1/20C, 1/10C, 1/5C, 1/2C, 1C, 2C, 5C, 10C, 20C A discharge experiment was performed on the battery.

beneficial effect

A method for judging the remaining power of an underwater vehicle battery under a dynamic load current proposed by the present invention is to select a plurality of battery cells of the same type as the cells in the lithium battery pack to be tested, divide them into several equal parts, and discharge them until the voltage; take the average value of the three available powers measured at their respective rates as the available power at the corresponding rate; calculate the rate compensation coefficients under different currents, and fill in the discrete current-k functions with the function fitting method to obtain a continuous The current-k function corresponds to the law, and the instantaneous capacity that is finally consumed: Calculate the remaining power of the battery when the current I changes dynamically.

The present invention has the following technical effects:

1. Most of the methods in the prior art are based on the simple ampere-hour integration method, while the present invention provides a method combining current load variables, through which the remaining capacity of the battery under dynamic load current can be calculated.

2. Compared with the existing method of calculating the remaining power by using simple ampere-hour integration, the present invention fully considers the variable load current, and the obtained battery remaining power is more accurate.

Description of drawings

Figure 1: Schematic diagram of the test flow

Figure 2: Example graph of battery available capacity as a function of current rate

Detailed ways

The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

The method for predicting the inconsistency of lithium battery packs for underwater vehicles provided by the present invention comprises the following steps:

Step 1: In order to observe the effect of temperature and discharge rate on the capacity and energy of the battery, select the battery cells of the same type as those in the lithium battery pack to be tested, and conduct discharge experiments under different load currents. 9 different rates (1/20C, 1/10C, 1/5C, 1/2C, 1C, 2C, 5C, 10C, 20C) are used for battery discharge experiments, and the discharge data are recorded to obtain the battery discharge capacity under different load currents ;

To improve the Peukert equation, this paper proposes an improved method to define the usable capacity of a battery. This paper defines the usable capacity of the battery as the discharge of the battery from a fully charged state at a certain rate. When the output voltage of the battery is lower than the cut-off voltage, it is regarded as the end of the discharge, and the power released in this process is the available power of the battery. Since this assumption involves an absolute maximum remaining capacity, the maximum remaining capacity of the battery reaches zero when the depth of discharge of the battery reaches 100%, and can never go below this zero value. In order to consider the influence of various discharge standards, the conditions of the discharge program affect the discharge rate as follows.

是电池在t时刻的有效电量，

表示电池在t+1时刻的有效电量，ΔQ_r代表。如前所述，这种情况下每个时间内单位电池的损失电量会受电池的放电电流(I) 和电流倍率(I)的影响:in

is the effective charge of the battery at time t,

Indicates the effective power of the battery at time t+1, and ΔQ _r represents. As mentioned earlier, the power loss per unit of battery in this case will be affected by the battery's discharge current (I) and current rate (I):

ΔQ _r =k(I)·ΔQ (2)

From the discharge experiment data of the empirical battery, it is planned to conduct the battery discharge experiment at 9 different rates (1/20C, 1/10C, 1/5C, 1/2C, 1C, 2C, 5C, 10C, 20C). And record the discharge data to obtain the battery discharge amount under different load currents, so as to calculate the rate compensation coefficient under different currents;

Among them, Q ₀ represents the dischargeable capacity of the battery at the current of 1C rate, and Q _I represents the dischargeable capacity of the battery at the current I. The function of the coefficient k is to combine the reduced effective capacity with the measurable charge obtained by multiplying the actual current by the time. The value of k is related to the discharge current and the current magnification. Finally, the discrete current-k function is complemented by the function fitting method, and the corresponding law of the continuous current-k function can be obtained. Therefore, the final consumed instantaneous capacity form is as follows:

ΔQr=ΔQ·k(I) (4)

And the effective power that changes from time t1 to time t2

Therefore, the remaining capacity of the battery can be calculated more accurately when the current I changes dynamically.

Take the battery from the time of full charge as the starting point of integration, and integrate the effective capacity consumed by the battery,

The available power Q ₀ of the battery under the 1C rate is used as the nominal capacity, and the remaining power of the battery under the dynamic load can be calculated, namely

Q _r =Q ₀ -ΔQ.

Claims (2)

1. a method for judging the residual power of an underwater vehicle battery under dynamic load current is characterized in that the steps are as follows: Step 1: Select multiple battery cells of the same type as the cells in the lithium battery pack to be tested, divide them into several equal parts, and discharge them to the cut-off voltage; take the average value of the three available amounts of electricity measured at their respective rates as the corresponding rate available power; Step 2: Calculate the magnification compensation coefficient under different currents

Among them: Q ₀ represents the dischargeable capacity of the battery at a current of 1C rate, and Q _I represents the dischargeable capacity of the battery at the current I Step 3: Complement the discrete current-k function by using the function fitting method to obtain the corresponding law of the continuous current-k function, and the instantaneous capacity that is finally consumed: ΔQr=ΔQ·k(I) The effective power that changes from time t1 to time t2:

Step 4: Calculate the remaining capacity of the battery when the current I changes dynamically: Take the battery from the time of full charge as the starting point of integration, and integrate the effective capacity consumed by the battery,

The available power Q ₀ of the battery under the 1C rate is used as the nominal capacity, and the remaining power of the battery under the dynamic load is calculated, namely Q _r =Q ₀ -ΔQ. 2. The method for judging the remaining power of an underwater vehicle battery under dynamic load current according to claim 1, characterized in that: the plurality of battery cells is 27, divided into 9 parts on average, and different loads are taken at 9 Different rates: 1/20C, 1/10C, 1/5C, 1/2C, 1C, 2C, 5C, 10C, 20C for battery discharge experiments.

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