CN116953544A - Battery pack insulation resistance detection method and system - Google Patents
Battery pack insulation resistance detection method and system Download PDFInfo
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Abstract
The detection circuit is regarded as a first-order RC circuit, after the detection resistor is connected, the first-order RC circuit is waited for a first preset time period and then the second positive voltage and the second negative voltage are acquired after the first-order RC circuit reaches an equilibrium state, so that the detection values of the second positive voltage and the second negative voltage are accurate, the insulation resistance calculated based on the second positive voltage and the second negative voltage is accurate, and the problem of false alarm is avoided. The other detection method provides a prediction method for detecting the voltage when the detection circuit reaches the equilibrium state, so that the third positive voltage and the third negative voltage can be predicted to obtain the equilibrium state before the detection circuit reaches the equilibrium state, and the insulation resistance is calculated based on the third positive voltage and the third negative voltage.
Description
Technical Field
The application relates to the technical field of battery pack insulation detection, in particular to a battery pack insulation resistance detection method and system.
Background
Insulation resistance testing of battery packs is a very important test item. As early as 2015, a technical standard has been proposed to detect the insulation resistance of the positive electrode and the negative electrode of the battery pack to the ground. The detection steps are as follows: (1) As shown in fig. 1, the voltage between the positive electrode and the ground and the voltage between the negative electrode and the ground of the ess (REchargeable Energy Storage System, rechargeable energy storage system, i.e., battery pack) are detected byU 1 Representing the voltage with larger value, adoptingU 1 ' represents a voltage in which the value is small, and the corresponding two insulation resistances are defined asR i1 、R i2 The values are allR i The method comprises the steps of carrying out a first treatment on the surface of the (2) As shown in fig. 2, a known sense resistor is addedR 0 And (3) withR i1 Parallel connection and detectionU 2 AndU 2 'A'; (3) Calculating insulation resistanceR i The method comprises the following steps:
1) Will beR 0 And three voltagesU 1 、U 1 ' sumU 2 Substitution formula (a):
2）R i can be usedR 0 And all four voltage valuesU 1 、U 1 ’、U 2 AndU 2 ' substituted formula (b) to calculate:
the insulation resistance detection method for the battery pack adopts the method provided by the standard at present.
However, the inventor found that when a battery pack is subjected to insulation resistance detection by using one charge-discharge machine several times according to the method provided by the above standard, the detection result is extremely unstable and varies from several tens of kΩ to several hundreds of kΩ, and the industrial personal computer alarms and causes detection interruption when the insulation resistance is lower than 250kΩ, so that a large amount of false alarm information easily occurs in the battery pack insulation resistance detection process.
Furthermore, the inventors have found that, in order to improve the detection efficiency, when two battery packs (BMS 1, BMS 2) are simultaneously subjected to insulation resistance detection by one charge-discharge machine according to the method provided by the above standard, the battery pack is liable to have abnormal waveforms as shown by the graph in fig. 3. In fig. 3, the horizontal direction indicates time, the vertical direction indicates the voltage of the battery pack positive/negative electrode to the ground, the time point in indicates the start of switching in the detection resistor, and the time point out indicates the cut-off detection resistor. And the expected waveforms should be as shown in fig. 4 according to the sensing resistor cut-in and cut-out time of the battery pack BMS 1. As can be seen by comparing fig. 3 and 4, the detected waveform of the battery pack BMS1 is abnormal during a part of the period, and the abnormal condition of the waveform seriously affects the accuracy of the insulation resistance detection.
The two problems are bothered by technicians for a long time, and particularly, the problem of the abnormal waveform limits that one charge-discharge machine can only detect for one battery pack, so that the insulation resistance detection efficiency of the battery pack is difficult to improve.
Disclosure of Invention
The purpose of the specification is to provide a battery pack insulation resistance detection method and system, so as to improve the accuracy of insulation monitoring and solve the problem of false alarm caused by insulation resistance reduction.
A first aspect of the present specification provides a battery pack insulation resistance detection method, including: after the first battery pack is connected to the detection channel of the charging and discharging motor, before the detection resistor is not incorporated, a first positive voltage of the positive electrode of the first battery pack to the ground and a first negative voltage of the negative electrode of the first battery pack to the ground are obtained; if the first positive voltage is larger than the first negative voltage, controlling to connect a detection resistor between the positive electrode of the first battery pack and the ground; if the first positive voltage is smaller than the first negative voltage, controlling to connect a detection resistor between the negative electrode of the first battery pack and the ground; after the detection resistor is connected, at least waiting for a first preset time, acquiring a second positive voltage of the positive electrode of the first battery pack to the ground and a second negative voltage of the negative electrode of the first battery pack to the ground; and calculating a first insulation resistance of the first battery pack positive electrode to the ground and a second insulation resistance of the first battery pack negative electrode to the ground according to the first positive voltage, the first negative voltage, the second positive voltage, the second negative voltage and the detection resistance.
In some embodiments, the first predetermined time period is greater than or equal to 150ms.
In some embodiments, after the first positive voltage and the first negative voltage are obtained, the BMS in the first battery pack sends a closing instruction to the controllable switch, and the controllable switch responds to the closing instruction to execute a closing action so as to enable the detection resistor to be connected into the detection circuit; after sending a closing instruction to the controllable switch, the BMS at least waits for a second preset time period and then acquires the second positive voltage and the second negative voltage; the second predetermined time length is the sum of the first predetermined time length and the action time of the controllable switch.
In some embodiments, in the case of insulation resistance detection of a plurality of battery packs, after the detection circuit of the first battery pack reaches a steady state after the detection resistance is incorporated and the second positive voltage and the second negative voltage are acquired, the detection of the first battery pack is ended, and the detection of the second battery pack is started.
In some embodiments, after the detection resistor is switched in when the first battery pack is detected, the detection of the first battery pack is ended and the detection of the second battery pack is started after at least waiting for a third preset time period; wherein, the value interval of the third preset time length is 7000ms to 13000ms.
In some embodiments, the sampling time interval of the second positive voltage and the second negative voltage is not more than 3ms.
A second aspect of the present specification provides a battery pack insulation resistance detection method, including: after the first battery pack is connected to the detection channel of the charging and discharging motor, before the detection resistor is not incorporated, a first positive voltage of the positive electrode of the first battery pack to the ground and a first negative voltage of the negative electrode of the first battery pack to the ground are obtained; if the first positive voltage is larger than the first negative voltage, controlling to connect a detection resistor between the positive electrode of the first battery pack and the ground; if the first positive voltage is smaller than the first negative voltage, controlling to connect a detection resistor between the negative electrode of the first battery pack and the ground; predicting a third positive voltage of the first battery pack positive electrode to ground and a third negative voltage of the first battery pack negative electrode to ground when the detection circuit reaches a steady state by: acquiring a fourth positive voltage of the first battery pack positive electrode to the ground and a fourth negative voltage of the first battery pack negative electrode to the ground at a first moment, acquiring a fifth positive voltage of the first battery pack positive electrode to the ground and a fifth negative voltage of the first battery pack negative electrode to the ground at a second moment, and acquiring a sixth positive voltage of the first battery pack positive electrode to the ground and a sixth negative voltage of the first battery pack negative electrode to the ground at a third moment; judging whether the detection circuit reaches a stable state according to the fourth positive voltage, the fifth positive voltage and the sixth positive voltage or the fourth negative voltage, the fifth negative voltage and the sixth negative voltage, and predicting the third positive voltage of the first battery pack positive electrode to the ground when the detection circuit reaches the stable state according to the fourth positive voltage, the fifth positive voltage and the sixth positive voltage when the detection circuit reaches the stable state under the condition that the detection circuit does not reach the stable state, and predicting the third negative voltage of the first battery pack negative electrode to the ground when the detection circuit reaches the stable state according to the fourth negative voltage, the fifth negative voltage and the sixth negative voltage; and calculating a first insulation resistance of the first battery pack positive electrode to the ground and a second insulation resistance of the first battery pack negative electrode to the ground according to the first positive voltage, the first negative voltage, the third positive voltage, the third negative voltage and the detection resistance.
In some embodiments, in the case of insulation resistance detection of a plurality of battery packs, after the voltage of the positive electrode of the first battery pack to the ground and the voltage of the negative electrode of the first battery pack to the ground are obtained at the first time, the second time, and the third time, detection of the second battery pack is started before the detection circuit of the first battery pack reaches a stable state.
A third aspect of the present specification provides a battery pack insulation resistance detection system for performing the method of any one of the first aspects; the system comprises: the battery pack is internally provided with a BMS, and the BMS has the insulation detection capability; the industrial personal computer is used for controlling the time for starting insulation detection and the time for ending insulation detection of each battery pack; and one side of the charging and discharging machine is used for being connected with an alternating current power grid, and the other side of the charging and discharging machine is provided with a plurality of battery pack detection channels, and each battery pack detection channel is used for being connected with one battery pack.
A fourth aspect of the present specification provides a computer program product comprising a computer program which, when executed by a processor, implements the steps performed by the BMS or the industrial personal computer in the method according to any of the first aspects.
According to the battery pack insulation resistance detection method and system, the detection circuit is regarded as the first-order RC circuit, and the transient process before the first-order RC circuit reaches the equilibrium state after the detection resistor is connected is considered, so that the second positive voltage of the positive electrode of the first battery pack and the second negative voltage of the first battery pack to the ground are acquired after the first preset time is waited after the detection resistor is connected, the detection values of the second positive voltage and the second negative voltage are accurate, the first insulation resistance of the positive electrode of the first battery pack to the ground and the second insulation resistance of the negative electrode of the first battery pack are accurate based on the accurate second positive voltage and the accurate second negative voltage, and the problems that the insulation resistance value is small, detection is interrupted and false alarm based on the second positive voltage and the second negative voltage are avoided.
The insulation resistance value obtained by the existing insulation resistance detection method is changed between tens of kΩ and hundreds of kΩ, and the insulation resistance values detected by the insulation resistance detection method provided by the specification are all above 1000kΩ, so that the insulation monitoring accuracy is greatly improved, and insulation fault false alarm is avoided.
According to the battery pack insulation resistance detection method and system, the detection circuit is regarded as a first-order RC circuit, a transition process before the first-order RC circuit reaches an equilibrium state after the detection resistor is connected is considered, and a prediction method for detecting the voltage when the detection circuit reaches the equilibrium state is provided based on the transition process, so that a third positive voltage of the first battery pack positive electrode to the ground and a third negative voltage of the first battery pack negative electrode to the ground can be predicted when the detection circuit reaches the equilibrium state, and the first insulation resistance of the first battery pack positive electrode to the ground and the second insulation resistance of the first battery pack negative electrode to the ground can be calculated based on the third positive voltage and the third negative voltage. The scheme not only can obtain more accurate insulation resistance, but also does not need to wait for the detection circuit to reach an equilibrium state after being connected with the detection resistor (the time for the detection circuit to reach the equilibrium state after being connected with the detection resistor is tens of seconds or even twenty seconds), so that the scheme can also shorten the detection time of the insulation resistance and improve the detection efficiency.
Drawings
In order to more clearly illustrate the embodiments of the application or the technical solutions in the prior art, the drawings that are necessary for the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the following description are only some of the embodiments described in the application, and that other drawings can be obtained from these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic circuit diagram of an insulation resistance detection method provided by a detection standard when a detection resistance is not connected;
FIG. 2 is a schematic diagram of an insulation resistance detection method according to the detection standard after the detection resistor is connected;
fig. 3 shows an abnormal waveform that occurs when one charge-discharge machine is used to detect insulation resistance of two battery packs simultaneously;
fig. 4 shows the expected waveforms when two battery packs are simultaneously subjected to insulation resistance detection using one charge-discharge machine;
FIG. 5 is a schematic diagram showing the connection of a battery pack insulation resistance detection system;
fig. 6 shows an equivalent circuit when the charge-discharge motor and one battery pack perform charge-discharge detection;
fig. 7, 8 and 9 are schematic diagrams showing the operation procedure of the insulation resistance detection method;
fig. 10 shows an equivalent circuit of the insulation resistance test after switching in the detection resistor;
fig. 11 shows a flowchart of a battery pack insulation resistance detection method provided in the present specification;
FIG. 12 shows a voltage trend diagram of a first order RC circuit;
fig. 13 shows a flowchart of a battery pack insulation resistance detection method provided in the present specification.
Detailed Description
In order to make the technical solution of the present application better understood by those skilled in the art, the technical solution of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, but not all embodiments of the present application. All other embodiments, based on the embodiments of the application, which would be apparent to one of ordinary skill in the art without undue burden are intended to be within the scope of the application.
The battery pack charge and discharge testing system consists of an industrial personal computer, a charge and discharge machine and a battery pack. As shown in fig. 5, the battery pack is connected to a detection channel of the charge-discharge machine (CH 1 represents one detection channel and CH2 represents another detection channel in fig. 5), and the industrial personal computer is in communication connection with the charge-discharge machine, and can send working instructions to the charge-discharge machine. Meanwhile, the industrial personal computer is also in communication connection with a BMS (Battery Management System ) inside the battery pack so as to perform information interaction with the BMS.
During the charge and discharge test of the battery pack, the BMS inside the battery pack continuously monitors the insulation resistance (direct current resistance value, not alternating current impedance) of the positive electrode and the negative electrode to the ground. In practice, the ground insulation resistance of the test system consisting of the charge-discharge machine and the battery pack is monitored.
The insulation monitoring function of each battery pack is completed under the control of the respective BMS. The work instruction sent by the industrial personal computer to the BMS may include: and (5) forcibly starting insulation detection and forcibly stopping insulation detection. After the industrial personal computer sends a working instruction for forcedly starting insulation detection to the BMS, the battery pack BMS can continuously acquire the positive and negative electrode grounding voltage of the battery pack-access detection resistance-acquire the positive and negative electrode grounding voltage of the battery pack-cut detection resistance, and calculate the insulation resistance of the positive electrode of the battery pack to the ground and the insulation resistance of the negative electrode to the ground according to the acquired voltage data. Each time the cycling is performed, a pair of insulation resistances (a pair of insulation resistances includes a positive to ground insulation resistance, a negative to ground insulation resistance) is measured. After the industrial personal computer sends a working instruction for forcibly stopping insulation detection to the BMS, the circulation process is stopped. Normally, when one battery pack is detected by a charge/discharge machine, the voltage waveform of the positive/negative pole of the battery pack to the ground should be as shown in fig. 4.
The inventors made a large number of assumptions about two problems proposed in the background art, and verified through a large number of calculations, and finally found that a large number of false alarm information-prone problems can be well interpreted based on the following assumptions, and the calculated waveform values are almost identical to the abnormal waveform shown in fig. 3.
The content of this hypothesis is: the Y capacitor in the charge-discharge motor enables the charge-discharge loop of the battery pack to be equivalent to a first-order RC circuit, the time constant of the first-order RC circuit is large and can reach tens or even twenty seconds, namely, the circuit can reach a stable state only after waiting for tens or even twenty seconds, and the circuit voltage data can be changed before the circuit reaches the stable state, so that inaccurate detection is caused.
Fig. 6 shows an equivalent circuit when the charge-discharge motor and one battery pack perform insulation resistance detection, wherein,C YP is the capacitance of the positive electrode of the charge-discharge machine to the ground (common mode filter capacitance),C YN is the capacitance of the charge-discharge machine negative electrode to the ground (common mode filter capacitance),C YP 、C YN (also called as a charging and discharging machine output filter capacitor) to form a Y capacitor;R BP the insulation resistance to ground for the battery pack anode,R BN an insulation resistance to ground for the battery pack negative electrode; R 0 A detection resistor with a known resistance value, for example, a resistance value of 1mΩ; s is S 1 、S 2 For insulation resistance detection switch, the switch can be specificallyA relay or a MOS tube is adopted.
The specific verification process is described below.
The first step of the verification process: and executing the detection operation to acquire detection data.
Specifically, after one battery pack is connected to one detection channel of the charge-discharge machine, the voltage of the positive electrode of the battery pack detected by the BMS to the ground is obtainedU P Voltage of negative pole to groundU N The method comprises the steps of carrying out a first treatment on the surface of the Then according toU P 、U N Is to determine the closure S 1 Or S 2 If (3)U P ＞U N Then close S 1 If (3)U P Less thanU N Then close S 2 The method comprises the steps of carrying out a first treatment on the surface of the Detecting the voltage of the battery pack positive electrode to the ground againU P ' voltage of negative pole to groundU N '. After the detection is finished, S is disconnected 1 Or S 2 Waiting for the next detection.
Fig. 7, 8 and 9 show the operation procedure of the detection method, wherein U represents the voltage of the battery pack,R P indicating the equivalent resistance of the positive electrode of the battery pack and the charge-discharge machine to ground,R N the equivalent resistance of the battery pack and the negative electrode of the charge/discharge machine to ground is shown.
The second step of the verification process: the insulation resistance was calculated.
According to fig. 7, there are:
I. assume thatU P ＞U N
Detection according to FIG. 8U P ’、U N '. Due toC YP 、C YN Is present when S is closed 1 Thereafter, atU P ’、U N The circuit has a transition before the' value stabilizes. At this time, the circuit Is a first order RC network, can be determined by adopting a three-element methodU P ’、U N ' value.
The time constant is:
after the circuit enters a steady state, the equivalent resistance of the positive electrode to the ground can be derived according to the formulas (4), (5), (6) and (7)R P 、R N Is a calculation formula of (2). The process is as follows:
or alternatively, the process may be performed,
the formulas (9) and (11) are equivalent to formulas (a) and (b) in the related art, respectively. The advantage of using the formula (a) in the background art or the formula (9) described above is that no voltage can be usedU N '. Because the resistance value is reduced after the positive electrode is connected with the detection resistor, the resistance value of the negative electrode to the ground is unchanged, so that the voltage of the negative electrode to the groundU N 'rise'.
The three-element method is adopted, and the three-element method can be obtained according to formulas (4) - (8)U P ’、U N The expression of':
wherein t is S 1 Closing (incorporating resistorsR 0 ) After that to the pairU P ’、U N Time interval of 'sampling'.
If equations (9), (10) or (11), (12) are used to calculate before the circuit goes into steady stateR P 、R N Inaccurate results are obtained. Substituting formulas (13) and (14) into formulas (9) to (12) to obtain the following components:
as can be seen from equations (15) and (16), the calculated values of the insulation resistance of the positive and negative electrodes to the groundR P (t)、R N (t) and true valueR P 、R N There is a coefficient that varies with time. the smaller t, the larger the calculation error.
II. Assume thatU P ＜U N
Detection according to FIG. 9U P ’、U N '. Due toC YP 、C YN Is present when S is closed 2 Thereafter, atU P ’、U N The circuit likewise has a transition before the' value stabilizes. According to the method of section I, it is possible to obtain:
meanwhile, there are:
the three-element method is adopted, and the method can be obtained from the formulas (21) to (24)U P ’、U N The expression of':
substituting the formulas (25), (26) into the formulas (17), (18) or (19), (20) can obtain the same results as the formulas (15), (16).
The third step of the verification process: and analyzing the influence of the output filter capacitance of the charge-discharge motor on the insulation detection process according to the calculation formula of the insulation resistance.
When the output end of the charging and discharging motor is provided with the filter device, the capacitance in the filter device can influence the detection result. Especially, the Y capacitance (the filter capacitance of the positive and negative electrodes to the ground, respectively, mainly filters common mode interference) has a larger influence.
Y capacitance pair according to measuring method in technical standard formulated by 2015U 1 、U 1 The' measurement has no effect because the RC network has entered a steady state before the measurement. However, the detection resistor isR 0 After the parallel connection, there is a dynamic process. In the course of the dynamic process, the process is,U 2 、U 2 the' value varies continuously. If pairs are in dynamic process U 2 、U 2 ' measurement is performed, the calculated insulation resistance value is inaccurate. Sampling time (measurementU 2 、U 2 ' time) andR 0 the shorter the interval between the moments in time of the parallel connection, the lower the resistance measurement, and the greater the deviation from the true value.
R 0 And after that, an equivalent circuit of the insulation resistance test is shown in fig. 10. In FIG. 10R 1 、R 2 In fact, the ground insulation resistance of the test system formed by the charging and discharging motor and the battery pack. Based on the above analysis, the equivalent circuit shown in fig. 10 is a first order RC network. The time constant is as follows:
normally, the insulation resistance is far greater than the resistance for measurementR 0 And therefore:
the value of the Y capacitance of the charge-discharge machine for battery pack insulation resistance detection is about 1. Mu.F, if the detection resistance isR 0 And the time constant tau is about 1 second. The first order RC circuit typically requires about 10 times the time constant, i.e. tens of seconds, to reach a substantially steady state.
U 2 、U 2 The expression of' over time is:
bringing the formulae (27), (28) into formula (6) to obtainR 2 The relation of the detected value of (c) with time:
bringing the formulae (10), (11) into formula (7)R 1 The relation of the detected value of (c) with time:
the equations (29) and (30) fundamentally reveal the relationship between the detection value of the insulation resistance and the detection time.
Will beSeen as a calculation coefficient. Calculation of Excel shows that changing the equivalent capacitance is much more pronounced than changing the resistance on the calculated coefficient. This is because of the reductionR 0 While decreasing the time constant τ, +.>But the value of (2) is becoming larger; and the value of the capacitor is reduced, so that only the time constant is reduced, and the transient process is shortened.
Taking the data of a certain channel I as an example, the voltage of the battery pack is 315.508V, and the positive and negative resistances to ground are respectivelyR 1 =30589kΩ、R 2 28738 k Ω (these two values are detected by the BMS when channel one is running alone, and can be considered as the insulation resistance value of channel one positive and negative to ground). Can obtain the parallel detection resistorR 0 After thatU 2 、U 2 The expression of' is:
wherein t is self-parallel upper detection resistorR 0 At the beginning, get toU 2 、U 2 ' time interval for taking measurements.
As can be seen from (31), (32),U 2 、U 2 the' value has a dynamically changing course, the length of which is dependent on the time constant τ. If pairs are in dynamic processU 2 、U 2 ' sampling, the resulting value is not the final value, the resistance value is calculated based on thisR 1 、R 2 Inaccuracy is achieved. The shorter the time interval t, the more inaccurate the measurement. The calculated value of the insulation resistance varies with t, see table one below.
From the above data, it can be seen that: sampling the voltage at the 30ms after the detection resistor is connected, and sending an alarm signal by the equipment if the insulation resistance value obtained by calculation according to the sampled voltage does not meet the insulation requirement; sampling the voltage at the 60ms after the detection resistor is connected, wherein the insulation resistance value obtained by calculation according to the sampled voltage still does not meet the insulation requirement, and the equipment sends an alarm signal; sampling voltage at 500ms after the detection resistor is connected, and calculating that the insulation resistance value obtained according to the sampled voltage exceeds 1MΩ, thereby meeting insulation requirements; the insulation resistance value obtained by sampling the voltage at 5000ms after the detection resistor is connected and calculating according to the sampled voltage also meets the insulation requirement, and is very close to the actual insulation resistance value.
In general, the industrial personal computer alarms and causes detection interruption when the insulation resistance is lower than 250kΩ. From the above table, it can be seen that the calculated value of the insulation resistance at 100ms is about 200kΩ, the calculated value of the insulation resistance at 200ms is about 400kΩ, and the calculated value of the insulation resistance at 150ms is determined to be up to 250kΩ in view of the trend of the calculated value of the insulation resistance, so that if voltage sampling is performed after 150ms has been performed after the detection resistor is connected, false alarm is not necessarily generated.
The problem with the abnormal waveforms mentioned in the background art is mainly due to the doubling of the capacity of the Y-capacitance acting in the charge-discharge machine when the channels are running in parallel, resulting in a doubling of the time constant. That is, after the channels are operated in parallel, it is necessary to wait more time for the detection resistor to reach a steady state after switching on. This results in a smaller t-value forU 2 、U 2 The' sampling probability becomes high, the calculated insulation resistance value becomes unqualified, and thus the false alarm is more frequent.
Since the filter circuit at the output end of the charge-discharge machine cannot be removed and its parameters cannot be adjusted, the detection method of the battery pack must be adjusted in order to solve the problem of the decrease in the detection value of the insulation resistance.
Based on this, the present specification proposes an adjustmentR 0 The time interval after the parallel connection to the detection voltage.
Specifically, the present disclosure provides a method for detecting insulation resistance of a battery pack, as shown in fig. 11, comprising the steps of:
s11: after the first battery pack is connected to the detection channel of the charge-discharge motor, a first positive voltage of the first battery pack positive electrode to the ground and a first negative voltage of the first battery pack negative electrode to the ground are obtained before the detection resistor is not incorporated.
S12: if the first positive voltage is larger than the first negative voltage, controlling to connect a detection resistor between the positive electrode of the first battery pack and the ground; if the first positive voltage is smaller than the first negative voltage, controlling to connect a detection resistor between the negative electrode of the first battery pack and the ground; and after the detection resistor is connected, at least waiting for a first preset time, acquiring a second positive voltage of the first battery pack positive electrode to the ground and a second negative voltage of the first battery pack negative electrode to the ground.
S13: and calculating a first insulation resistance of the first battery pack positive electrode to the ground and a second insulation resistance of the first battery pack negative electrode to the ground according to the first positive voltage, the first negative voltage, the second positive voltage, the second negative voltage and the detection resistance.
The method described in the above steps S11 to S13 will be specifically described below taking the example of insulation detection of the battery pack 1 in fig. 5.
After the battery pack 1 is connected to the charge-discharge machine, the industrial personal computer sends a working instruction for forcibly starting insulation detection to the BMS of the battery pack 1, and the BMS responds to the working instruction and continuously obtains the positive and negative electrode ground voltage of the battery pack, accesses the detection resistor, obtains the positive and negative electrode ground voltage of the battery pack and cuts off the circulation process of the detection resistor.
After the first cycle begins, the RC network has entered a steady state. Before the detection resistor is not connected (i.e., as shown in fig. 6 or 7), in step S11, the BMS obtains a first positive voltage of the positive electrode of the battery pack 1 to the groundU P First negative voltage of negative electrode of battery pack 1 to groundU N . The BMS inside the battery pack 1 monitors the voltage values by itself, and the industrial personal computer only needs to obtain the voltage values from the BMS.
Then, in step S12, the BMS may generate a first positive voltageU P A first negative voltageU N Is to determine the closure S 1 Or S 2 . As shown in fig. 6 and 7, 8 and 9, if the first positive voltageU P Greater than a first negative voltageU N Then control to close S 1 To be connected between the positive electrode of the battery pack 1 and the groundA detection resistor is arranged; if a first positive voltageU P Less than a first negative voltageU N Then control to close S 2 To access the sense resistor at the negative electrode of the battery pack 1. After the detection resistor is connected, at least waiting for a first preset time period and after the RC network enters a stable state, a second positive voltage of the positive electrode of the battery pack 1 to the ground is obtained U P ' second voltage of negative electrode of battery pack 1 to groundU N '. The BMS inside the battery pack 1 monitors the voltage values by itself, and the industrial personal computer only needs to obtain the voltage values from the BMS.
Finally, in step S13, the BMS generates a first positive voltageU P First negative voltage of negative electrode of battery pack 1 to groundU N A second positive voltageU P ' second voltageU N ' calculate a first insulation resistance of the positive electrode of the battery pack 1 to the ground, and a second insulation resistance of the negative electrode of the battery pack 1 to the ground. Specific calculation methods can be referred to in formulas (a) or (b) of the background section.
The value of the first preset time period is influenced by the Y capacitance and the detection resistance inside the charging and discharging machine. In the case where the value of the Y capacitance is about 1 μf and the value of the detection resistance is 1mΩ, the first predetermined time period is greater than or equal to 150ms. For example, the first predetermined time period may be 150ms, 200ms, 250ms, 300ms, 350ms, 400ms, 450m, or 500ms.
In some embodiments, after the first positive voltage and the first negative voltage are obtained, the BMS within the first battery pack sends a closing command to the controllable switch, which performs a closing action in response to the closing command to switch the sense resistor into the sense circuit. After sending a closing instruction to the controllable switch, the BMS at least waits for a second preset time period, and then acquires a second positive voltage and a second negative voltage; the second predetermined time is the sum of the first predetermined time and the action time of the controllable switch.
For example, assume that the time at which the BMS sends the close command ist 0 The actuation time of the controllable switch is Δt, the first predetermined time is 500ms, and then after the BMS sends the close command, it should be aftert=t 0 The second positive voltage and the second negative voltage are obtained at the time of +Δt+500 ms.
In some embodiments, before the battery packs are detected by the charging and discharging motor, the plurality of battery packs are connected to the charging and discharging motor together, so that insulation resistance detection of the plurality of battery packs is realized. In this case, after the detection circuit of the first battery pack reaches a steady state after the detection resistor is incorporated and the second positive voltage and the second negative voltage are acquired, the detection of the first battery pack is ended, and the detection of the second battery pack is started.
For example, as shown in fig. 5, the industrial personal computer may first send a work instruction to forcibly turn on the insulation detection to the BMS1 in the battery pack 1, after the detection circuit of the battery pack 1 reaches a stable state after the detection resistor is incorporated and the BMS acquires the second positive voltage and the second negative voltage, the industrial personal computer may send a work instruction to forcibly stop the insulation detection to the BMS1 and send a work instruction to forcibly turn on the insulation detection to the BMS2 in the battery pack 2 to start the detection of the battery pack 2.
In the case of detecting the insulation resistance of the plurality of battery packs, after the detection resistance is switched in when the first battery pack is detected, the detection of the first battery pack is ended and the detection of the second battery pack is started after waiting at least for a third predetermined period of time. The value of the first preset time period is influenced by the Y capacitance and the detection resistance inside the charging and discharging machine. In the case where the value of the Y capacitance is about 1 μf and the value of the detection resistance is 1mΩ, the value interval of the third predetermined period is 7000ms to 13000ms. For example, the third predetermined time period may be at least one of 7000ms, 8000ms, 9000ms, 10000ms, 11000ms, 12000ms, 13000ms.
For example, as shown in fig. 5, a work order to forcibly turn on the insulation detection may be first transmitted to the BMS1 in the battery pack 1, and after waiting 12000ms after the work order is transmitted, the industrial personal computer may transmit a work order to forcibly stop the insulation detection to the BMS1 and transmit a work order to forcibly turn on the insulation detection to the BMS2 in the battery pack 2 to start the detection of the battery pack 2.
According to the battery pack insulation resistance detection method, the detection circuit is regarded as the first-order RC circuit, and the transient process before the first-order RC circuit reaches the equilibrium state after the detection resistor is connected is considered, so that the second positive voltage of the first battery pack positive electrode to the ground and the second negative voltage of the first battery pack to the ground are acquired after the first preset time is waited after the detection resistor is connected, the detection values of the second positive voltage and the second negative voltage are accurate, the first insulation resistance of the first battery pack positive electrode to the ground and the second insulation resistance of the first battery pack negative electrode to the ground are accurate which are calculated based on the accurate second positive voltage and the accurate second negative voltage, and the problems that the second positive voltage and the second negative voltage are acquired in the transient process, the insulation resistance value is small and the detection is interrupted and the alarm is mistaken are avoided.
The insulation resistance value obtained by the existing insulation resistance detection method is changed between tens of kΩ and hundreds of kΩ, and the insulation resistance values detected by the insulation resistance detection method provided by the specification are all above 1000kΩ, so that the insulation monitoring accuracy is greatly improved, and insulation fault false alarm is avoided.
Due to the presence of the Y capacitance, there is a transition in the detected voltage, which may take a longer time if the voltage is detected after waiting for the voltage to enter a steady state. In practice, since the transient is a first order process, the steady state value of the voltage can be obtained by a predictive method.
As shown in fig. 12, assume that:
the above formula can be rewritten as follows according to the three-element method:
it can be seen that:
in FIG. 12, t1, t2, t3 are equally spaced by a distance ΔT. Then it is possible to obtain:
and
before calculation using the above formula, the closeness of f1, f2, f3 should be determined first. If these three values differ by no few, this indicates that steady state has been reached.
Based on the above prediction method, the present disclosure further provides a method for detecting insulation resistance of a battery pack, as shown in fig. 13, which includes the following steps:
s21: after the first battery pack is connected to the detection channel of the charge-discharge motor, a first positive voltage of the first battery pack positive electrode to the ground and a first negative voltage of the first battery pack negative electrode to the ground are obtained before the detection resistor is not incorporated.
S22: if the first positive voltage is larger than the first negative voltage, controlling to connect a detection resistor between the positive electrode of the first battery pack and the ground; and if the first positive voltage is smaller than the first negative voltage, controlling to connect a detection resistor between the negative electrode of the first battery pack and the ground.
S23: predicting a third positive voltage of the first battery pack positive electrode to ground and a third negative voltage of the first battery pack negative electrode to ground when the detection circuit reaches a steady state by: acquiring a fourth positive voltage of the first battery pack positive electrode to the ground and a fourth negative voltage of the first battery pack negative electrode to the ground at a first moment, acquiring a fifth positive voltage of the first battery pack positive electrode to the ground and a fifth negative voltage of the first battery pack negative electrode to the ground at a second moment, and acquiring a sixth positive voltage of the first battery pack positive electrode to the ground and a sixth negative voltage of the first battery pack negative electrode to the ground at a third moment; judging whether the detection circuit reaches a stable state according to the fourth positive voltage, the fifth positive voltage and the sixth positive voltage or the fourth negative voltage, the fifth negative voltage and the sixth negative voltage, and predicting the third positive voltage of the first battery pack positive electrode to the ground when the detection circuit reaches the stable state according to the fourth positive voltage, the fifth positive voltage and the sixth positive voltage when the detection circuit reaches the stable state under the condition that the detection circuit does not reach the stable state, and predicting the third negative voltage of the first battery pack negative electrode to the ground when the detection circuit reaches the stable state according to the fourth negative voltage, the fifth negative voltage and the sixth negative voltage.
S24: and calculating a first insulation resistance of the first battery pack positive electrode to the ground and a second insulation resistance of the first battery pack negative electrode to the ground according to the first positive voltage, the first negative voltage, the third positive voltage, the third negative voltage and the detection resistance.
The method described in the above steps S21 to S24 will be specifically described below taking the example of insulation detection of the battery pack 1 in fig. 5.
After the battery pack 1 is connected to the charge-discharge machine, the industrial personal computer sends a working instruction for forcibly starting insulation detection to the BMS of the battery pack 1, and the BMS responds to the working instruction and continuously obtains the positive and negative electrode ground voltage of the battery pack, accesses the detection resistor, obtains the positive and negative electrode ground voltage of the battery pack and cuts off the circulation process of the detection resistor.
After the first cycle begins, the RC network has entered a steady state. Before the detection resistor is not connected (i.e., as shown in fig. 6 or 7), in step S21, the BMS obtains a first positive voltage of the positive electrode of the battery pack 1 to the groundU P First negative voltage of negative electrode of battery pack 1 to groundU N . The BMS inside the battery pack 1 monitors the voltage values by itself, and the industrial personal computer only needs to obtain the voltage values from the BMS.
Then, in step S22, the BMS may generate a first positive voltageU P A first negative voltage U N Is to determine the closure S 1 Or S 2 . As shown in fig. 6 and 7, 8 and 9, if the first positive voltageU P Greater than a first negative voltageU N Then control to close S 1 To connect the detection resistor between the positive electrode of the battery pack 1 and the ground; if a first positive voltageU P Less than a first negative voltageU N Then control to close S 2 To access the sense resistor at the negative electrode of the battery pack 1. After the detection resistor is connected, at least waiting for a first preset time period and after the RC network enters a stable state, a second positive voltage of the positive electrode of the battery pack 1 to the ground is obtainedU P ' second voltage of negative electrode of battery pack 1 to groundU N '. The BMS inside the battery pack 1 monitors the voltage values by itself, and the industrial personal computer only needs to obtain the voltage values from the BMS.
Steps S21 and S22 described above are identical to the detection method shown in fig. 11.
In step S23, the BMS obtains the fourth positive voltage p1 of the positive electrode of the battery pack 1 to the ground and the fourth negative voltage n1 of the negative electrode of the battery pack 1 to the ground at time t1, obtains the fifth positive voltage p2 of the positive electrode of the battery pack 1 to the ground and the fifth negative voltage n2 of the negative electrode of the battery pack 1 to the ground at time t2, and obtains the sixth positive voltage p3 of the positive electrode of the battery pack 1 to the ground and the sixth negative voltage n3 of the negative electrode of the battery pack 1 at time t 3.
After these data are acquired, it is judged whether the detection circuit reaches a steady state or not based on the above-described fourth positive voltage p1, fifth positive voltage p2, sixth positive voltage p 3. Of course, it is also possible to determine whether the detection circuit reaches the steady state based on the fourth negative voltage n1, the fifth negative voltage n2, and the sixth negative voltage n3.
In the case of reaching a steady state, it is possible to directly respond to the first positive voltageU P A first negative voltageU N The sixth positive voltage p3 and the sixth negative voltage n3 calculate the first insulation resistance of the positive electrode of the battery pack 1 to the ground and the second insulation resistance of the negative electrode of the battery pack 1 to the ground. Specific calculation methods can be referred to in formulas (a) or (b) of the background section.
Under the condition that the stable state is not reached, a positive voltage predicted value when the detection circuit reaches the stable state can be calculated according to the fourth positive voltage p1, the fifth positive voltage p2 and the sixth positive voltage p3 by adopting the formula (33), and the positive voltage predicted value is taken as a third positive voltage; and calculating a negative voltage predicted value when the detection circuit reaches a stable state according to the fourth negative voltage n1, the fifth negative voltage n2 and the sixth negative voltage n3 by adopting the formula (33), and taking the negative voltage predicted value as a third negative voltage.
In step S24, according to the first positive voltageU P A first negative voltageU N The predicted third positive voltage, the predicted third negative voltage, and the second insulation resistance of the battery pack 1 negative electrode to ground are calculated. Specific calculation methods can be referred to in formulas (a) or (b) of the background section.
In some embodiments, before the battery packs are detected by the charging and discharging motor, the plurality of battery packs are connected to the charging and discharging motor together, so that insulation resistance detection of the plurality of battery packs is realized. In this case, after the first, second, and third time points are obtained, the first battery pack positive electrode-to-ground voltage and the first battery pack negative electrode-to-ground voltage, the detection of the second battery pack is started before the detection circuit of the first battery pack reaches a steady state.
For example, as shown in fig. 5, the industrial personal computer may first send a work instruction for forcibly turning on insulation detection to the BMS1 in the battery pack 1, and after the BMS control incorporates the detection resistor and acquires the fourth positive voltage, the fourth negative voltage, the fifth positive voltage, the fifth negative voltage, the sixth positive voltage, and the sixth negative voltage, the industrial personal computer may send a work instruction for forcibly stopping insulation detection to the BMS1 and send a work instruction for forcibly turning on insulation detection to the BMS2 in the battery pack 2 to start detection of the battery pack 2.
It should be noted that, when the industrial personal computer sends the forced insulation stopping detection to the BMS1, the detection circuit of the battery pack 1 does not reach the equilibrium state yet, that is, after the battery pack 1 stops the insulation detection, the capacitor in the channel CH1 on the charging and discharging machine connected to the battery pack 1 is still in the charging or discharging state. When the battery pack 2 starts to detect, the charge and discharge states of the capacitor on the channel CH1 may affect the voltage value when the battery pack 2 detects, and may not reach the equilibrium state until the battery pack 2 detects, but only affect the initial voltage of the battery pack 2, and may not affect the voltage value when the battery pack 2 detects the equilibrium state of the circuit, so the above prediction method can still determine the positive voltage value and the negative voltage value when the battery pack 2 detects the circuit to be balanced more accurately.
According to the battery pack insulation resistance detection method, the detection circuit is regarded as a first-order RC circuit, a transition process before the first-order RC circuit reaches an equilibrium state after the detection resistor is connected is considered, and a prediction method for detecting the voltage when the equilibrium state is reached is provided based on the transition process, so that a third positive voltage of the first battery pack positive electrode to the ground and a third negative voltage of the first battery pack negative electrode to the ground can be predicted when the detection circuit reaches the equilibrium state before the detection circuit reaches the equilibrium state, and the first insulation resistance of the first battery pack positive electrode to the ground and the second insulation resistance of the first battery pack negative electrode to the ground are calculated based on the third positive voltage and the third negative voltage. The scheme not only can obtain more accurate insulation resistance, but also does not need to wait for the detection circuit to reach an equilibrium state after being connected with the detection resistor (the time for the detection circuit to reach the equilibrium state after being connected with the detection resistor is tens of seconds or even twenty seconds), so that the scheme can also shorten the detection time of the insulation resistance and improve the detection efficiency.
In any one of the above insulation resistance detection methods, a sampling time interval of the second positive voltage and the second negative voltage is not more than 3ms. For example, the sampling time interval is 1ms, 1.5ms, 2ms, etc.
In any one of the above insulation resistance detection methods, before performing the detection, the industrial personal computer transmits program code of any one of the above insulation detection methods to the BMS of the battery pack so that the BMS can perform the above insulation detection method.
In order to avoid confusion between the battery pack insulation resistance detection method provided in the present specification and the detection method of the battery cells in the battery pack, the difference between the battery cell insulation detection and the battery pack insulation resistance detection is described below.
The battery cell is one electric core, and the battery pack is formed by combining a plurality of electric cores (generally more than 100 electric cores) in a serial-parallel connection mode.
The insulation monitoring of the battery unit and the battery pack is to monitor whether the insulation of the positive electrode and the negative electrode of the battery to the shell meets the requirement, namely, whether the resistance of the positive electrode and the negative electrode to the shell is larger than a certain specified value. When the insulation resistance values of the anode and the cathode are different from each other, the smaller one is taken for judgment.
The capacitance of the positive electrode and the negative electrode of the battery cell to the shell is in the order of nano-farads (1 nF), and the value of the capacitance is in the order of micro-farads (mu F) in an RC model circuit adopted by a battery pack testing system. In the RC circuit model for detecting the battery single body and the RC circuit model for detecting the insulation resistance of the battery pack, the capacitance value is 1000 times different and is not in an order of magnitude at all. Therefore, the time of voltage acquisition during measurement has a completely different effect on the measurement accuracy.
The key factors influencing the measurement accuracy of the insulation resistance and the capacitance of the battery cell are still the acquisition accuracy of the voltage, but the factors influencing the acquisition accuracy of the voltage are completely different. In the monitoring of the battery cells, the key factors are the type of the on-off switch and its performance. In the insulation monitoring of the battery pack, the key factor is the time constant of the RC circuit.
In addition, the battery cell has no BMS, and monitoring of its insulation resistance can only be accomplished by the battery cell external device. And the battery pack is internally provided with a BMS which is responsible for monitoring the insulation resistance of the battery pack anode and cathode to the outer shell.
The specification also provides a battery pack insulation resistance detection system for executing the battery pack insulation resistance detection method. As shown in fig. 5, the system includes a battery pack, an industrial personal computer, and a charge-discharge motor.
The battery pack is internally provided with a BMS, and the BMS itself has the capability of insulating detection
The industrial personal computer is used for controlling the time of starting insulation detection and the time of ending insulation detection of each battery pack
One side of the charging and discharging machine is used for being connected with an alternating current power grid, a plurality of battery pack detection channels are arranged on the other side of the charging and discharging machine, and each battery pack detection channel is used for being connected with one battery pack.
The present disclosure also provides a computer program product, which includes a computer program, where the computer program when executed by a processor implements the steps executed by the BMS or the industrial personal computer in the foregoing method for detecting insulation resistance of a battery pack.
The foregoing is merely an example of an embodiment of the present disclosure and is not intended to limit the embodiment of the present disclosure. Various modifications and variations of the illustrative embodiments will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, or the like, which is within the spirit and principles of the embodiments of the present specification, should be included in the scope of the claims of the embodiments of the present specification.
Claims (10)
1. A battery pack insulation resistance detection method, comprising:
after the first battery pack is connected to the detection channel of the charging and discharging motor, before the detection resistor is not incorporated, a first positive voltage of the positive electrode of the first battery pack to the ground and a first negative voltage of the negative electrode of the first battery pack to the ground are obtained;
if the first positive voltage is larger than the first negative voltage, controlling to connect a detection resistor between the positive electrode of the first battery pack and the ground; if the first positive voltage is smaller than the first negative voltage, controlling to connect a detection resistor between the negative electrode of the first battery pack and the ground; after the detection resistor is connected, at least waiting for a first preset time, acquiring a second positive voltage of the positive electrode of the first battery pack to the ground and a second negative voltage of the negative electrode of the first battery pack to the ground;
And calculating a first insulation resistance of the first battery pack positive electrode to the ground and a second insulation resistance of the first battery pack negative electrode to the ground according to the first positive voltage, the first negative voltage, the second positive voltage, the second negative voltage and the detection resistance.
2. The method of claim 1, wherein the first predetermined time period is greater than or equal to 150ms.
3. The method of claim 1, wherein after the first positive voltage and the first negative voltage are obtained, the BMS in the first battery pack sends a closing command to the controllable switch, and the controllable switch performs a closing action in response to the closing command to switch the detection resistor into the detection circuit;
after sending a closing instruction to the controllable switch, the BMS at least waits for a second preset time period and then acquires the second positive voltage and the second negative voltage; the second predetermined time length is the sum of the first predetermined time length and the action time of the controllable switch.
4. The method according to claim 1, wherein in the case of performing insulation resistance detection on the plurality of battery packs, after the detection circuit of the first battery pack reaches a steady state after the detection resistance is incorporated and the second positive voltage and the second negative voltage are acquired, the detection of the first battery pack is ended and the detection of the second battery pack is started.
5. The method of claim 4, wherein after the first battery pack is detected, the detecting resistor is connected, the detecting of the first battery pack is ended and the detecting of the second battery pack is started after at least waiting for a third predetermined period of time; wherein, the value interval of the third preset time length is 7000ms to 13000ms.
6. The method of claim 1, wherein the sampling time interval of the second positive voltage and the second negative voltage is no more than 3ms.
7. A battery pack insulation resistance detection method, comprising:
after the first battery pack is connected to the detection channel of the charging and discharging motor, before the detection resistor is not incorporated, a first positive voltage of the positive electrode of the first battery pack to the ground and a first negative voltage of the negative electrode of the first battery pack to the ground are obtained;
if the first positive voltage is larger than the first negative voltage, controlling to connect a detection resistor between the positive electrode of the first battery pack and the ground; if the first positive voltage is smaller than the first negative voltage, controlling to connect a detection resistor between the negative electrode of the first battery pack and the ground;
predicting a third positive voltage of the first battery pack positive electrode to ground and a third negative voltage of the first battery pack negative electrode to ground when the detection circuit reaches a steady state by: acquiring a fourth positive voltage of the first battery pack positive electrode to the ground and a fourth negative voltage of the first battery pack negative electrode to the ground at a first moment, acquiring a fifth positive voltage of the first battery pack positive electrode to the ground and a fifth negative voltage of the first battery pack negative electrode to the ground at a second moment, and acquiring a sixth positive voltage of the first battery pack positive electrode to the ground and a sixth negative voltage of the first battery pack negative electrode to the ground at a third moment; judging whether the detection circuit reaches a stable state according to the fourth positive voltage, the fifth positive voltage and the sixth positive voltage or the fourth negative voltage, the fifth negative voltage and the sixth negative voltage, and predicting the third positive voltage of the first battery pack positive electrode to the ground when the detection circuit reaches the stable state according to the fourth positive voltage, the fifth positive voltage and the sixth positive voltage when the detection circuit reaches the stable state under the condition that the detection circuit does not reach the stable state, and predicting the third negative voltage of the first battery pack negative electrode to the ground when the detection circuit reaches the stable state according to the fourth negative voltage, the fifth negative voltage and the sixth negative voltage;
And calculating a first insulation resistance of the first battery pack positive electrode to the ground and a second insulation resistance of the first battery pack negative electrode to the ground according to the first positive voltage, the first negative voltage, the third positive voltage, the third negative voltage and the detection resistance.
8. The method according to claim 7, wherein in the case of insulation resistance detection for a plurality of battery packs,
after the first, second and third time voltages of the first battery pack positive electrode to the ground and the first battery pack negative electrode to the ground are obtained, the detection of the second battery pack is started before the detection circuit of the first battery pack reaches a stable state.
9. A battery pack insulation resistance detection system for performing the method of any one of claims 1 to 8; the system comprises:
the battery pack is internally provided with a BMS, and the BMS has the insulation detection capability;
the industrial personal computer is used for controlling the time for starting insulation detection and the time for ending insulation detection of each battery pack;
and one side of the charging and discharging machine is used for being connected with an alternating current power grid, and the other side of the charging and discharging machine is provided with a plurality of battery pack detection channels, and each battery pack detection channel is used for being connected with one battery pack.
10. A computer program product comprising a computer program which, when executed by a processor, implements the steps performed by the BMS or the industrial personal computer in the method according to any of claims 1 to 8.
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