Patent Application
20170155261
This application claims the benefit under 35 U.S.C. §119(a) of Chinese Patent Application No. CN 201510856770.0, filed on Nov. 30, 2015, the disclosure of which is incorporated herein by reference in its entirety.
The present disclosure relates generally to a system and method for protecting a battery pack.
In the field of power tools, battery packs are common power supply devices, which can improve convenience and movability of the power tool.
In order to prevent the battery pack from damage due to over discharge, the battery pack has an over discharge protecting module. The currently known protecting module determines the capacity of the battery pack based on a terminal voltage of the battery pack. When the terminal voltage detected is less than a constant value, the power is cut off.
However, the terminal voltage of the battery pack may be affected by an internal resistance of cells, so that the voltage detected may not reflect the real capacity of the battery pack, especially in low temperatures. When in low temperatures, the internal resistance of cells increases greatly. Thus, known determining methods have large error. Because the protecting module may misjudge the capacity, the battery pack may not supply power even it still has remaining considerable capacity.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In one aspect of the disclosure, a method is provided for protecting a battery pack. The method includes discharging the battery pack, detecting the temperature T of the battery pack, detecting the discharge current I of the battery pack, detecting the discharge voltage U1 of the battery pack, obtaining an internal resistance R according to the temperature T or the discharge voltage U1, calculating a capacity voltage U2 according to an equation U2=U1+IR, determining whether the capacity voltage U2 is less than a preset threshold, and, if yes, limiting discharging.
In another aspect of the disclosure, a system is provided for protecting a battery pack. The system includes a temperature detection module for detecting the temperature of the battery pack, a current detection module for detecting the current of the battery pack, a voltage detection module for detecting the voltage of the battery pack, and a control module being capable of making the battery pack discharge. When the battery pack is discharged, the current detection module detects the discharge current of the battery pack, the voltage detection module detects the discharge voltage of the battery pack and, the control module calculates a capacity voltage U2 according to an equation U2=U1+IR and then controls the battery pack to discharge or not through comparing the capacity voltage U2 and a preset threshold, wherein R is an internal resistance and the control module obtains the internal resistance R according to a detection result of the temperature detection module or the voltage detection module.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the scope of the invention hereinafter claimed, its application, or uses.
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Specifically, the voltage detection module 13 detects the voltage between a positive terminal B+ and a negative terminal B- of the battery pack 102.
In the combination 100, when the battery pack 102 is controlled to be discharged by the control module 14, the current detection module 12 detects the discharge current of the battery pack 102, the voltage detection module 13 detects the discharge voltage of the battery pack 102, and the control module 14 calculates a capacity voltage U2 according to an equation: U2=U1+IR. Then the battery pack 102 is controlled to be discharged or not by the control module 14 through comparing the capacity voltage U2 and a preset threshold. When the capacity voltage U2 is less than the preset threshold, the battery pack 102 is stopped discharging. In the equation, R is an internal resistance, which is obtained by the control module 14 through the detection result of the temperature detection module 11 or the current detection module 12.
The internal resistance R of the cells can be affected greatly by the temperature of the battery pack 102 and the capacity of the cells in a limiting case. For example, when the capacity of the cells is close to being fully discharged and close to 50%, the internal resistance R of the cells is different even in the same temperature. On the other hand, when the temperature is low and high, the internal resistance R of the cells is different even when the capacity of the cells is the same 50%.
Alternatively, the internal resistance R can be obtained according to the detection results of the temperature detection module 11 and the current detection module 12 jointly. It is noted that, the term ‘the internal resistance R obtained by the control module 14 through the detection result of the temperature detection module 11 or the current detection module 12’ should be comprehended as obtaining the internal resistance R according to at least one of the detection result of the temperature detection module 11 and the current detection module 12. Obtaining the internal resistance R according to the detection results of the temperature detection module 11 and the current detection module 12 jointly is one situation of the term.
Preferably, if the temperature detected is in a preset range, the internal resistance R can be obtained only according to the detection result of the voltage detection module. On the other hand, if the capacity of the cells is in a preset range, the internal resistance R can be obtained only according to the detection result of the temperature detection module.
A real capacity of the cells is unknown when the internal resistance R has not been obtained. So the internal resistance R can be obtained according to the two detection results of the temperature detection module and the current detection module and the single detection result of the temperature detection module alternately, which can reduce the power consumption caused by detection.
Specifically, the control module 14 can control a switch 16 in the discharge circuit of the battery pack 102 so as to control the battery pack 102 to discharge or not.
A motor 15 is arranged in the discharge circuit of the battery pack 102, which acts as an electrical device.
The temperature detection module 11 can be disposed in the battery pack 102 as shown in
The current detection module 12, the voltage detection module 13 and the control module 14 in
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S401. discharging the battery pack;
S402. detecting the temperature T, the discharge current I and the discharge voltage U1 of the battery pack;
S403. obtaining the internal resistance R according to the temperature T and the discharge current I of the battery pack;
S404. calculating the capacity voltage U2 according to the equation U2=U1+IR;
S405. determining whether the capacity voltage U2 is less than the preset threshold U, if yes, turning to S406, if no, returning to S401; and
S406. stopping discharging.
Further, the internal resistance R is stored in a corresponding control module. The corresponding control module can find the corresponding internal resistance R according to a data combination of the discharge voltage U1 and the temperature T and a corresponding relationship.
Here, the corresponding relationship can be an equation or relationships in other methods.
Specifically, the corresponding relationship is a one to one correspondence. That is, one data combination of the discharge voltage U1 and the temperature T corresponds to one internal resistance R.
However, the internal resistance R can be obtained only according to the discharge voltage U1 or the temperature T as mentioned above.
Otherwise, the switch 16 for controlling on/off in the discharge circuit can be disposed in the battery pack. Or, there may be several switches, some switches are disposed in the power tool and other switches are disposed in the battery pack, so that the battery pack is multi-protected.
The above illustrates and describes basic principles, main features and advantages of the present invention. Those skilled in the art should appreciate that the above embodiments do not limit the claimed invention in any form. Technical solutions obtained by equivalent substitution or equivalent variations all fall within the scope of the claimed invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201510856770.0 | Nov 2015 | CN | national |
