Control strategy for pre-charging and power-on of power battery

Abstract

The invention discloses a control strategy for pre-charging and electrifying a power battery. The control strategy comprises the following steps: calculating a capacitance * resistance limit range value and a sampling precision limit range value; collecting a plurality of groups of pre-charging proportions Kn, and calculating the sampling precision xK in combination with the sampling frequency; judging xK, and if xK is out of tolerance, recording a sampling precision out-of-tolerance fault; calculating an actual capacitance * resistance value RC; judging the RC, and if the RC is out of tolerance, recording capacitance or resistance out-of-tolerance faults; calculating a pre-charging proportion Kx with xK, and taking the pre-charging proportion Kx as a judgment basis for successful pre-charging; whether the pre-charging proportion collected within the allowable time tA reaches Kx or not is judged, and if the pre-charging proportion does not reach Kx, the actual pre-charging time tR and the allowable time tA are calculated; if tR is less than or equal to tA, reporting a pre-charging timeout fault and other reasons; if tR is greater than tA, reporting a pre-charging timeout fault, and recording the fault; and disconnecting the main negative (positive) relay. When the relay is pulled in after pre-charging is completed, large impact is avoided, the service life of the relay is prolonged, meanwhile, faults can be recorded, and positioning and overhauling are convenient.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy vehicle batteries, and in particular relates to a control strategy for pre-charging a power battery. Background Art

[0002] At present, the traditional pre-charging control strategy makes judgments based on the pre-charging ratio. However, there are errors or out-of-tolerances in the pre-charging ratio when it is collected. When the actual pre-charging ratio is less than the set threshold, the traditional judgment logic cannot identify the sampling accuracy out-of-tolerance. At this time, the pre-charging can be completed normally, but when the pre-charging is completed and the main relay is energized, it will be greatly impacted, resulting in a reduction in the life of the relay; when the actual pre-charging ratio is greater than the set threshold, it will cause a pre-charging timeout fault.

[0003] In addition, during the pre-charging process, due to the tolerances of capacitance, resistance, and sampling accuracy, the pre-charging fault cannot be accurately diagnosed and located, making it difficult to troubleshoot. Summary of the invention

[0004] The purpose of the present invention is to provide a control strategy for pre-charging and powering up a power battery, which can avoid large impacts when the pre-charging is completed and the relay is energized, thereby extending the service life of the relay, and can also record faults for easy positioning and maintenance.

[0005] To achieve the above object, the present invention provides a control strategy for pre-charging a power battery, comprising the following steps:

[0006] 1) Close the pre-charge relay;

[0007] 2) Close the main negative (positive) relay;

[0008] 3) Calculate the capacitance × resistance limit range values ​​RCmax and RCmin, and set the capacitance multiplied resistance threshold for subsequent judgment; calculate the sampling accuracy limit range values ​​xAmin and xAmax, and set the sampling accuracy threshold for subsequent judgment;

[0009] 4) Collect multiple sets of pre-charge ratios Kn, combine the sampling frequency t, and calculate the sampling accuracy xK;

[0010] 5) Determine whether the pre-charge ratio sampling accuracy xK exceeds the tolerance. If xAmin≤xK≤xAmax, it is determined to be within the tolerance. Otherwise, it exceeds the tolerance and the sampling accuracy exceeds the tolerance fault is recorded;

[0011] 6) Calculate the actual capacitance × resistance value RC;

[0012] 7) Determine whether the actual capacitance × resistance value RC is out of tolerance. If RCmin≤RC≤RCmax, it is judged to be within tolerance. Otherwise, it is out of tolerance and the capacitance or resistance out of tolerance fault is recorded;

[0013] 8) Calculate the pre-charging ratio Kx with sampling accuracy xK and use it as the basis for judging whether the pre-charging is successful;

[0014] 9) Whether the pre-charge ratio collected within the allowed time tA reaches Kx, if it reaches, the pre-charge is successful and the main positive (negative) relay is closed; if it does not reach, the actual pre-charge time tR and the allowed time tA are calculated;

[0015] 10) If tR≤tA, report pre-charge timeout fault, other reasons; if tR>tA, report pre-charge timeout fault, recorded fault; disconnect the main negative (positive) relay;

[0016] 11) Disconnect the pre-charge relay.

[0017] As a further solution of the present invention: the calculation formula of the capacitance × resistance limit range RCmax and RCmin in step 3) is:

[0018] RCmax=R n ×1+x R ×1+a×10 -6 ×T max -20×C×10 -6 ×1+x C 1

[0019] RCmin=R n ×1-x R ×1+a×10 -6 ×T min -20×C×10 -6 ×1-x C 2

[0020] Among them: RCmax [Ω·μF]: the theoretical maximum value of the product of capacitance and resistance; RCmin [Ω·μF]: the theoretical minimum value of the product of capacitance and resistance; R n [Ω]: pre-charge resistance value; x R [%]: Pre-charge resistance accuracy; a[ppm / ℃]: Pre-charge resistance temperature coefficient; C[μF]: Capacitance; x C [%]: Capacitance accuracy; T max [℃]: Maximum ambient temperature; T min [℃]: minimum ambient temperature;

[0021] xAmin and xAmax are obtained by calculating formulas (3) and (4):

[0022]

[0023] Among them: xAmin[%]: minimum allowable deviation; xAmax[%]: maximum allowable deviation; x[%]: controller sampling accuracy.

[0024] As a further solution of the present invention: in step 4), the multiple groups of pre-charge ratios Kn include the pre-charge ratio K1 collected for the first time, the pre-charge ratio K2 collected for the second time, and the pre-charge ratio K3 collected for the third time. The sampling accuracy xK is calculated by deriving formula (7) through actual capacitance × resistance formula (5) and (6):

[0025]

[0026] Wherein: RC[Ω·μF]: actual capacitance-resistance product value; xK[%]: pre-charge ratio sampling accuracy; K1[%]: pre-charge ratio collected for the first time; K2[%]: pre-charge ratio collected for the second time; K3[%]: pre-charge ratio collected for the third time; t[ms]: sampling frequency.

[0027] As a further solution of the present invention: Step 8) is calculated as shown in formula (8):

[0028]

[0029] Among them: Kx[%]: pre-charge ratio with sampling accuracy; xK[%]: pre-charge ratio sampling accuracy; K[%]: pre-charge ratio setting threshold.

[0030] As a further solution of the present invention: in step 9), the actual pre-charging time tR is shown in formula (9), and the calculation of the allowed time tA is shown in formula (10):

[0031]

[0032] Where: tR [ms]: actual pre-charge time calculation value; RC [Ω·μF]: actual capacitance-resistance product value (see formula (3)); Kx [%]: pre-charge ratio with sampling accuracy (see formula (8));

[0033]

[0034] Wherein: tA[ms]: maximum allowable pre-charge time; Rn[Ω]: pre-charge resistor value; xR[%]: pre-charge resistor accuracy; a[ppm / ℃]: pre-charge resistor temperature coefficient; C[μF]: capacitance; xC[%: capacitance accuracy; x[%]: pre-charge ratio sampling accuracy; Tmax[℃]: maximum ambient temperature; K[%]: pre-charge ratio setting threshold.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] A pre-charging ratio with sampling accuracy is introduced to judge whether the pre-charging is successful. Even if the accuracy exceeds the tolerance, correction can be made to ensure that the actual pre-charging ratio is consistent with the set pre-charging ratio. At this time, the main relay will not be greatly impacted when it is powered on.

[0037] Calculate the product of capacitance and resistance to determine whether the capacitance and resistance are within the specified value range. If they exceed the specified value, the fault will be recorded for subsequent fault reporting;

[0038] The actual pre-charge time is calculated by combining the actual capacitance, resistance and sampling accuracy. If the time exceeds the allowed time, a pre-charge time fault will be reported, and the recorded fault will be reported at the same time for troubleshooting.

[0039] Even if the sampling accuracy, capacitance, and resistance are out of tolerance, if the pre-charging can be completed within the specified time, no fault will be reported and the pre-charging can be completed normally, thus improving the system fault tolerance. By introducing a pre-charging ratio threshold with precision as a judgment condition, when the pre-charging is completed and the relay is energized, a large impact can be avoided and the life of the main relay can be guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A flow chart of the control strategy for pre-charging the power battery of the present invention;

[0041] Figure 2 This is the pre-charging curve diagram under normal conditions of the traditional method;

[0042] Figure 3 This is a pre-charging curve diagram under normal circumstances using the strategy of the present invention;

[0043] Figure 4 To adopt the strategy of the present invention Figure 3 Corrected pre-charge curve diagram;

[0044] Figure 5 It is a pre-charging curve diagram when the pre-charging ratio collected under the condition of excessive sampling accuracy is greater than the actual pre-charging ratio;

[0045] Figure 6 It is a pre-charging curve diagram when the pre-charging ratio collected under the condition of excessive sampling accuracy is less than the actual pre-charging ratio;

[0046] Figure 7 This is the pre-charge curve diagram when the capacitance and resistance are out of tolerance;

[0047] Figure 8 To adopt the strategy of the present invention Figure 7 Corrected pre-charge curve. DETAILED DESCRIPTION

[0048] The present invention will be further described below by way of examples.

[0049] like Figure 1 As shown, a control strategy for pre-charging a power battery is characterized by comprising the following steps:

[0050] 1) Close the pre-charge relay;

[0051] 2) Close the main negative (positive) relay; ① Positive pre-charge: close the main negative relay; ② Negative pre-charge: close the main positive relay; the brackets represent the negative pre-charge situation;

[0052] 3) Calculate the capacitance × resistance limit range values ​​RCmax and RCmin, and set the capacitance multiplied resistance threshold for subsequent judgment; calculate the sampling accuracy limit range values ​​xAmin and xAmax, and set the sampling accuracy threshold for subsequent judgment;

[0053] Furthermore, the calculation formulas for the capacitance × resistance limit range values ​​RCmax and RCmin in step 3) are:

[0054] RCmax=R n ×1+x R ×1+a×10 -6 ×T max -20×C×10 -6 ×1+x C 1

[0055] RCmin=R n ×1-x R ×1+a×10 -6 ×T min -20×C×10 -6 ×1-x C 2

[0056] Among them: RCmax [Ω·μF]: the theoretical maximum value of the product of capacitance and resistance; RCmin [Ω·μF]: the theoretical minimum value of the product of capacitance and resistance; R n [Ω]: pre-charge resistance value; x R [%]: Pre-charge resistance accuracy; a[ppm / ℃]: Pre-charge resistance temperature coefficient; C[μF]: Capacitance; x C [%]: Capacitance accuracy; T max [℃]: Maximum ambient temperature; T min [℃]: minimum ambient temperature;

[0057] xAmin and xAmax are obtained by calculating formulas (3) and (4):

[0058]

[0059] Among them: xAmin[%]: minimum allowable deviation; xAmax[%]: maximum allowable deviation; x[%]: controller sampling accuracy;

[0060] 4) Collect multiple sets of pre-charge ratios Kn, combine the sampling frequency t, and calculate the sampling accuracy xK;

[0061] Furthermore, in step 4), the multiple groups of pre-charge ratios Kn (n is a natural number, indicating the nth acquisition) include the pre-charge ratio K1 acquired for the first time, the pre-charge ratio K2 acquired for the second time, and the pre-charge ratio K3 acquired for the third time. The sampling accuracy xK is calculated by deriving formula (7) from the actual capacitance × resistance formula (5) and (6):

[0062]

[0063] When the natural number n is equal to 1:

[0064]

[0065] When the natural number n is equal to 2:

[0066]

[0067] Let formula (5) = formula (6), and derive formula (7):

[0068]

[0069] Where: RC[Ω·μF]: actual capacitance-resistance product value; xK[%]: pre-charge ratio sampling accuracy; K1[%]: pre-charge ratio collected for the first time; K2[%]: pre-charge ratio collected for the second time; K3[%]: pre-charge ratio collected for the third time; t[ms]: sampling frequency (sampling time interval);

[0070] 5) Determine whether the pre-charge ratio sampling accuracy xK exceeds the tolerance. If xAmin≤xK≤xAmax, it is determined to be within the tolerance. Otherwise, it exceeds the tolerance and the sampling accuracy exceeds the tolerance fault is recorded;

[0071] 6) Calculate the actual capacitance × resistance value RC. Since capacitance and resistance have tolerances and are not consistent for each product, the actual capacitance × resistance value of the current product can be calculated according to formula (5).

[0072] 7) Determine whether the actual capacitance × resistance value RC is out of tolerance. If RCmin≤RC≤RCmax, it is judged to be within tolerance. Otherwise, it is out of tolerance and the capacitance or resistance out of tolerance fault is recorded;

[0073] 8) Calculate the pre-charge ratio Kx with sampling accuracy xK, and use it as the basis for judging the success of pre-charge, so that the actual pre-charge ratio can be the same as the theoretical pre-charge ratio design threshold K, ensuring the life of the relay;

[0074] Furthermore, the calculation method of step 8) is shown in formula (8):

[0075]

[0076] Among them: Kx[%]: pre-charge ratio with sampling accuracy; xK[%]: pre-charge ratio sampling accuracy; K[%]: pre-charge ratio setting threshold;

[0077] 9) Whether the pre-charge ratio collected within the allowed time tA reaches Kx, if it reaches, the pre-charge is successful and the main positive (negative) relay is closed; if it does not reach, the actual pre-charge time tR and the allowed time tA are calculated;

[0078] Furthermore, the actual pre-charge time tR in step 9) is shown in formula (9), and the calculation of the allowed time tA is shown in formula (10):

[0079]

[0080] Where: tR [ms]: actual pre-charge time calculation value; RC [Ω·μF]: actual capacitance-resistance product value (see formula (3)); Kx [%]: pre-charge ratio with sampling accuracy (see formula (8));

[0081]

[0082] Where: tA[ms]: maximum allowable pre-charge time; Rn[Ω]: pre-charge resistor value; xR[%]: pre-charge resistor accuracy; a[ppm / ℃]: pre-charge resistor temperature coefficient; C[μF]: capacitance; xC[%: capacitance accuracy; x[%]: pre-charge ratio sampling accuracy; Tmax[℃]: maximum ambient temperature; K[%]: pre-charge ratio setting threshold;

[0083] 10) If tR≤tA, it means that the actual pre-charge time meets the maximum pre-charge time requirement. In this case, the pre-charge ratio has not been reached, resulting in failure, and a pre-charge timeout fault is reported. Other reasons; if tR>tA, it means that the actual time theoretical calculation will lead to a timeout. This result may be caused by excessive capacitance, resistance or acquisition accuracy. A pre-charge timeout fault is reported and a recorded fault is recorded; disconnect the main negative (positive) relay;

[0084] 11) Disconnect the pre-charge relay.

[0085] There may be a situation where the capacitance and resistance are out of tolerance or the sampling accuracy is out of tolerance, but the pre-charging is still successful, because tA is the time calculated under all extreme conditions. However, in actual situations, although there are out-of-tolerance situations, not all parameters are in extreme conditions, so the influence of each other is reduced, and there will be a single out-of-tolerance and successful pre-charging. In this case, the fault will not be reported, and the system fault tolerance will be improved. The final judgment condition is the corrected pre-charging ratio. Therefore, the pre-charging ratio ensures that even if there is an out-of-tolerance sampling accuracy, the actual pre-charging ratio can still be guaranteed to be the same as the set pre-charging ratio threshold K, ensuring that the main relay will not be subjected to a greater impact. Traditionally, if the sampling accuracy is out of tolerance, the actual pre-charging ratio is much smaller than the collected pre-charging ratio. At this time, the main relay will be greatly impacted, and the fault cannot be identified.

[0086] Here is an example:

[0087] 1. Under normal circumstances:

[0088]

[0089] According to formula (1) and formula (2), RCmax and RCmin are calculated, RCmax = 0.25704, RCmin = 0.14744; assuming that the actual capacitance × resistance = 0.2;

[0090] like Figure 2 As shown, it can be seen from the curve that due to the existence of sampling tolerance, when the BMS collects 97%, it is determined that the pre-charging is successful, but the actual pre-charging ratio is only 95.46%. At this time, the impact voltage received by the relay = 500×(1-95.46%)=22.7V. If the sampling accuracy is worse, the impact voltage received by the relay will be greater, which will greatly reduce the life of the relay. Therefore, the present invention can effectively avoid this situation. The following is an example of the application effect of the present invention.

[0091] like Figure 3 As shown, the pre-charge ratio K1 collected for the first time is 4.96%, the pre-charge ratio K2 collected for the second time is 9.67%, the pre-charge ratio K3 collected for the third time is 14.15%, and the sampling time interval is 10ms; xK is calculated according to formula (7) = 98.41%; xAmin is calculated according to formula (3) = 98.02%; xAmax is calculated according to formula (4) = 102.02%; through step 5), it is determined that the sampling accuracy meets the requirements; RC is calculated according to formula (5) = 0.2; through step 7), it is determined that the capacitance × resistance meets the requirements; through formula (8), the pre-charge ratio Kx with accuracy xK is calculated = 98.56%, and Kx is used as the judgment condition for successful pre-charge; the corrected pre-charge curve is as follows Figure 4 shown.

[0092] By comparing before and after correction, when pre-charging is successful, the actual pre-charging ratio can be guaranteed to be 97%. At this time, the impulse voltage received by the relay = 500 × (1-97.00%) = 15V. The actual pre-charging ratio is controlled at 97% through the correction strategy, ensuring the life of the relay; tR = 701.31ms is calculated by formula (9); tA = 1173.53ms is calculated by formula (10); and it is determined by step 14 that the requirements are met.

[0093] 2. When the sampling accuracy exceeds the tolerance:

[0094] 2.1. When the collected pre-charging ratio is greater than the actual pre-charging ratio (tolerance x is assumed to be 2%);

[0095] like Figure 5 As shown in the curve, if the traditional pre-charging success judgment is used, when the actual pre-charging ratio is 93.20%, the BMS can collect 97.00%, and the pre-charging is judged to be successful. The impact voltage received by the relay = 500×

[0096] (1-93.20%)=34V; through the strategy of the present invention, the corrected pre-charging ratio is 100.96%. When 100.96% is collected, the pre-charging is determined to be successful. The actual pre-charging ratio is 97%. At this time, the impact voltage received by the relay = 500×(1-97%)=15V. At the same time, the pre-charging time will not time out.

[0097] 2.2. When the collected pre-charging ratio is less than the actual pre-charging ratio (tolerance x is assumed to be -1.5%);

[0098] like Figure 6 As shown, it can be seen from the curve in the figure that if the traditional pre-charging success judgment is followed, the BMS can only collect 97.00% when the actual pre-charging ratio is 99.95%. At this time, the actual pre-charging time has exceeded the allowed pre-charging time (1538.23ms>tA=1173.53ms), resulting in pre-charging failure; through the strategy of the present invention, the corrected pre-charging ratio is 94.13%. When 94.13% is collected, the pre-charging is judged to be successful, and the actual pre-charging ratio is 97%. The impact voltage received by the relay = 500×(1-97%) = 15V. At the same time, the pre-charging time will not time out. While ensuring the life of the main relay, the pre-charging can still be successful even if the sampling accuracy exceeds the tolerance.

[0099] 3. When the capacitance and resistance are out of tolerance;

[0100] like Figure 7As shown, it is assumed that the real capacitance × resistance = 0.35; the pre-charge ratio K1 collected for the first time = 3.23%, the pre-charge ratio K2 collected for the second time = 6.35%, the pre-charge ratio K3 collected for the third time = 9.37%, and the sampling time interval is 10ms.

[0101] According to formula (1) and formula (2), RCmax=0.25704, RCmin=0.14744 are calculated; according to formula (7), xK=101.61% is calculated; according to formula (3), xAmin=98.02% is calculated; according to formula (4), xAmax=102.02% is calculated. Through step 5), it is determined that the sampling accuracy meets the requirements; according to formula (5), RC=0.3 is calculated; through step 7), it is determined that the capacitance × resistance does not meet the requirements, and the sampling accuracy out-of-tolerance fault is recorded at this time; through formula (8), the pre-charge ratio Kx with accuracy xK is calculated to be 95.46%, and Kx is used as the judgment condition for successful pre-charge; the corrected pre-charge curve is as follows Figure 8 shown.

[0102] pass Figure 8 The middle curve shows that if the traditional pre-charging success judgment is used, the BMS can only collect 97.00% when the actual pre-charging ratio is 98.56%. At this time, the actual pre-charging time has exceeded the allowed pre-charging time (1273.10ms>

[0103] tA=1173.53ms), resulting in pre-charging failure; through the strategy of the present invention, when the BMS collects 95.46% pre-charging ratio, the pre-charging is determined to be successful, the actual pre-charging ratio is 97%, the impulse voltage received by the relay=500×(1-97%)=15V, and the actual pre-charging time is 1051.97ms<tA=1173.53ms, and the pre-charging will not time out. While ensuring the life of the main relay, even if the capacitor and resistor are out of tolerance, the pre-charging can still be successful. If the tolerance is too much, it will cause a timeout. At this time, the capacitor and resistor out-of-tolerance fault can also be reported to accurately determine the fault type.

Claims

1. A control strategy for pre-charging a power battery, characterized in that: The following steps are involved: 1) Close the pre-charge relay; 2) Close the main negative (positive) relay; 3) Calculate the capacitance × resistance limit range values ​​RCmax and RCmin, and set the capacitance multiplied resistance threshold for subsequent judgment; calculate the sampling accuracy limit range values ​​xAmin and xAmax, and set the sampling accuracy threshold for subsequent judgment; 4) Collect multiple sets of pre-charge ratios Kn, combine the sampling frequency t, and calculate the sampling accuracy xK; 5) Determine whether the pre-charge ratio sampling accuracy xK exceeds the tolerance. If xAmin≤xK≤xAmax, it is determined to be within the tolerance. Otherwise, it exceeds the tolerance and the sampling accuracy exceeds the tolerance fault is recorded; 6) Calculate the actual capacitance × resistance value RC; 7) Determine whether the actual capacitance × resistance value RC is out of tolerance. If RCmin≤RC≤RCmax, it is judged to be within tolerance. Otherwise, it is out of tolerance and the capacitance or resistance out of tolerance fault is recorded; 8) Calculate the pre-charging ratio Kx with sampling accuracy xK and use it as the basis for judging whether the pre-charging is successful; 9) Whether the pre-charge ratio collected within the allowed time tA reaches Kx, if it reaches, the pre-charge is successful and the main positive (negative) relay is closed; if it does not reach, the actual pre-charge time tR and the allowed time tA are calculated; 10) If tR≤tA, report pre-charge timeout fault, other reasons; if tR>tA, report pre-charge timeout fault, recorded fault; disconnect the main negative (positive) relay; 11) Disconnect the pre-charge relay.

2. A control strategy for pre-charging a power battery according to claim 1, characterized in that: In step 3), the calculation formula for the capacitance × resistance limit range RCmax and RCmin is: RCmax=R n ×(1+x R )×[1+a×10 -6 ×(T max -20)]×C×10 -6 ×(1+x C ) (1) RCmin=R n ×(1-x R )×[1+a×10 -6 ×(T min -20)]×C×10 -6 ×(1-x C ) (2) Among them: RCmax [Ω·μF]: the theoretical maximum value of the product of capacitance and resistance; RCmin [Ω·μF]: the theoretical minimum value of the product of capacitance and resistance; R n [Ω]: pre-charge resistance value; x R [%]: Pre-charge resistance accuracy; a[ppm / ℃]: Pre-charge resistance temperature coefficient; C[μF]: Capacitance; x C [%]: Capacitance accuracy; T max [℃]: Maximum ambient temperature; T min [℃]: minimum ambient temperature; xAmin and xAmax are obtained by calculating formulas (3) and (4): Among them: xAmin[%]: minimum allowable deviation; xAmax[%]: maximum allowable deviation; x[%]: controller sampling accuracy.

3. A control strategy for pre-charging a power battery according to claim 2, characterized in that: In step 4), the multiple groups of pre-charge ratios Kn include the pre-charge ratio K1 collected for the first time, the pre-charge ratio K2 collected for the second time, and the pre-charge ratio K3 collected for the third time. The sampling accuracy xK is calculated by deriving formula (7) through the actual capacitance × resistance formula (5) and (6): Wherein: RC[Ω·μF]: actual capacitance-resistance product value; xK[%]: pre-charge ratio sampling accuracy; K1[%]: pre-charge ratio collected for the first time; K2[%]: pre-charge ratio collected for the second time; K3[%]: pre-charge ratio collected for the third time; t[ms]: sampling frequency.

4. A control strategy for pre-charging a power battery according to claim 3, characterized in that: Step 8) The calculation method is shown in formula (8): Among them: Kx[%]: pre-charge ratio with sampling accuracy; xK[%]: pre-charge ratio sampling accuracy; K[%]: pre-charge ratio setting threshold.

5. A control strategy for pre-charging a power battery according to claim 4, characterized in that: The actual pre-charge time tR in step 9) is shown in formula (9), and the calculation of the allowable time tA is shown in formula (10): Where: tR [ms]: actual pre-charge time calculation value; RC [Ω·μF]: actual capacitance-resistance product value (see formula (3)); Kx [%]: pre-charge ratio with sampling accuracy (see formula (8)); Wherein: tA[ms]: maximum allowable pre-charge time; Rn[Ω]: pre-charge resistor value; xR[%]: pre-charge resistor accuracy; a[ppm / ℃]: pre-charge resistor temperature coefficient; C[μF]: capacitance; xC[%: capacitance accuracy; x[%]: pre-charge ratio sampling accuracy; Tmax[℃]: maximum ambient temperature; K[%]: pre-charge ratio setting threshold.

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