Voltage calibration method for judging LLC charging and discharging direction

Abstract

According to the voltage calibration method for judging the LLC charging and discharging direction, the battery voltage sampling value and the bus voltage sampling value are calibrated, and even under the conditions that the turn ratios of transformers of all products are slightly different and the actual bus voltage value is difficult to measure, the battery voltage sampling value and the bus voltage sampling value are calibrated; and the charging and discharging directions can be accurately judged according to the calibrated battery voltage sampling value and the calibrated bus voltage sampling value, so that the circuit cost is saved and the calibration difficulty is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy, and particularly relates to a voltage calibration method for judging the charging and discharging directions of LLC. Background Art

[0002] In the prior art, the LLC topology (abbreviated as LLC) is often used as the DC / DC link of energy storage products to perform voltage boosting and bucking. It is necessary to judge the charging and discharging directions of LLC for loop switching, as well as calculate and display the charging and discharging currents and powers. Common methods for judging the charging and discharging directions of LLC are as follows: Method 1: Sample the bus current on the DC bus at the input end of LLC through a Hall sensor, and judge the charging and discharging directions of LLC by judging the positive and negative of the bus current; Method 2: Judge the charging and discharging directions of LLC by judging the magnitude relationship between the product of the sampled battery voltage and the transformer turns ratio and the sampled bus voltage.

[0003] Among them, Method 1 uses a Hall sensor to sample the DC bus current, which will not only increase the circuit cost, but also increase the circuit weight and volume; in Method 2, since the transformer turns ratio of each product is slightly different, and there are also differences between the sampled battery / bus voltage values and the actual values, there may be problems such as misjudgment. Summary of the Invention

[0004] The purpose of the present invention is to provide a voltage calibration method for judging the charging and discharging directions of LLC to solve the problem that the prior art cannot balance cost and accuracy.

[0005] The present invention provides a voltage calibration method for judging the charging and discharging directions of LLC. The method includes: Step 1: Set the battery voltage to the nominal voltage and set LLC to the battery discharging state; Steps 2 to 7: Calibrate the sampled battery voltage value and the sampled bus voltage value according to the true value of the battery voltage, and determine to perform Step 8 or Step 9 according to the calibration result; Step 8: Judge whether LLC is in the charging or discharging state according to the calibrated sampled battery voltage value Vbat_sam and the calibrated sampled bus voltage value Vbus_sam; if Vbus_sam > Vbat_sam * k0 + b3, judge that LLC is in the charging state at this time; if Vbus_sam < Vbat_sam * k0 - b4, then judge that LLC is in the discharging state at this time; where k0 is the turns ratio of the primary and secondary sides of the transformer, and both b3 and b4 are 1% - 10% of the true value of the battery voltage; Step 9: Report an error and notify the maintenance personnel for repair.

[0006] Further, the Steps 2 to 7 are: Step 2: Calculate the difference between the actual battery voltage value and the sampled battery voltage value to obtain the first bias coefficient b1; Step 3: Update the sampled battery voltage value and count the update times M1; Step 4: Determine whether to perform Step 5, return to Step 2, or perform Step 9 according to the ranges of b1 and M1; Step 5: Calculate the difference between the actual battery voltage value * k0 and the sampled bus voltage value to obtain the second bias coefficient b2; Step 6: Update the sampled bus voltage value and count the update times M2; Step 7: Determine whether to perform Step 8, return to Step 5, or perform Step 9 according to the ranges of b2 and M2.

[0007] Further, Steps 2 to 7 are as follows: Step 2: Calculate the difference between the actual battery voltage value * k0 and the sampled bus voltage value to obtain the second bias coefficient b2; Step 3: Update the sampled bus voltage value and count the update times M2; Step 4: Determine whether to perform Step 5, return to Step 2, or perform Step 9 according to the ranges of b2 and M2; Step 5: Calculate the difference between the actual battery voltage value and the sampled battery voltage value to obtain the first bias coefficient b1; Step 6: Update the sampled battery voltage value and count the update times M1; Step 7: Determine whether to perform Step 8, return to Step 5, or perform Step 9 according to the ranges of b1 and M1.

[0008] Further, the actual battery voltage value is obtained by testing with a voltage measuring instrument; the initial sampled battery voltage value and the initial sampled bus voltage value are obtained through their respective voltage sampling circuits.

[0009] Further, Step 4 is specifically as follows: If b1 > V1 or b1 < -V1, and M1 < N1, return to Step 2; If M1 = N1, then jump to Step 9; If -V1 ≤ b1 ≤ V1, perform Step 5; where N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the true battery voltage value.

[0010] Further, the specific content of the 7th step is as follows: If b2 > V2 or b2 < -V2, and M2 < N2, return to the 5th step; If M2 = N2, then jump to the 9th step; If -V2 ≤ b2 ≤ V2, perform the 8th step; Wherein, N2 is a positive integer greater than 2, and the range of V2 is 0.5% - 2.5% of the rated bus voltage.

[0011] Further, the specific content of the 4th step is as follows: If b2 > V2 or b2 < -V2, and M2 < N2, return to the 2nd step; If M2 = N2, then jump to the 9th step; If -V2 ≤ b2 ≤ V2, perform the 5th step; Wherein, N2 is a positive integer greater than 2, and the range of V2 is 0.5% - 2.5% of the rated bus voltage.

[0012] Further, the specific content of the 7th step is as follows: If b1 > V1 or b1 < -V1, and M1 < N1, return to the 5th step; If M1 = N1, then jump to the 9th step; If -V1 ≤ b1 ≤ V1, perform the 8th step; Wherein, N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the true battery voltage.

[0013] The above voltage calibration method for judging the LLC charge and discharge direction can accurately judge the LLC charge and discharge direction without considering the difference in the transformer turns ratio of each product and without measuring the actual bus voltage value on the premise of not increasing the circuit cost, and has the advantages of low cost, high precision, and good efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is the LLC topology diagram of an embodiment of the present invention; Figure 2 It is the flowchart of the voltage calibration method for judging the LLC charge and discharge direction in the first embodiment of the present invention; Figure 3 It is the flowchart of the voltage calibration method for judging the LLC charge and discharge direction in the second embodiment of the present invention.

[0015] The following specific embodiments will further illustrate the present invention in conjunction with the above drawings. SPECIFIC EMBODIMENTS

[0016] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0018] Please refer to Figure 1 , Figure 1 as an LLC topology diagram. Among them, the primary side (left side) of the transformer Tr is connected to the DC bus, the full-bridge and series resonance topology, and the secondary side (right side) of the transformer Tr is connected to the battery through the full-bridge synchronous rectification topology. The turns ratio of the primary and secondary sides of the transformer is k0; C1 and C2 are the primary side capacitor and the secondary side capacitor respectively, which play a role in smoothing and filtering. In some embodiments, C1 and C2 can be removed. Among them, bus represents the DC bus (abbreviated as the bus), Vbus represents the bus voltage, bat represents the battery, and Vbat represents the battery voltage; the full-bridge on the primary side is formed by connecting the switching tubes Q1-Q4 in series in pairs and then in parallel, that is, the switching tubes Q1 and Q2 are in series, and the switching tubes Q3 and Q4 are in series and then in parallel with each other; the series resonance topology is composed of the resonance inductor Lr, the resonance capacitor Cr and the excitation inductor Lm of the transformer Tr in series. The full-bridge rectification topology on the secondary side is formed by connecting the switching tubes Q5-Q8 in series in pairs and then in parallel, that is, the switching tubes Q5 and Q6 are in series, and the switching tubes Q7 and Q8 are in series and then in parallel with each other. In one embodiment, the switching tubes Q1-Q8 are all MOS tubes.

[0019] It should be noted that Figure 1 only an LLC circuit topology is exemplified. In other embodiments, in the LLC topology, the full-bridge on the primary side can be replaced by a half-bridge, and the series resonance topology on the primary side can be replaced by a parallel resonance topology or a series-parallel resonance topology; the full-bridge synchronous rectification topology on the secondary side can be replaced by a half-bridge synchronous rectification topology, or a full-bridge uncontrolled rectification topology, or a half-bridge uncontrolled rectification topology, and so on. Embodiment

[0020] Please refer to Figure 2 , which shows a voltage calibration method for judging the charging and discharging direction of LLC of the present invention. The method includes: Step 1: Set the battery voltage to the nominal voltage and set the LLC to the battery discharge state.

[0021] Understandably, the battery voltage is set to the nominal voltage. A DC source can be used to supply power to the battery in the LLC topology. First, set the DC source to the nominal voltage and connect it across the battery in the LLC topology. Or, first connect the DC source across the battery in the LLC topology and then set the DC source to the nominal voltage. In one embodiment, the nominal voltage is 48V or 24V. In other embodiments, the nominal voltage can be selected as other values according to actual needs.

[0022] Among them, the battery discharge state, that is, the LLC circuit is in the discharge state, means that the battery discharges to the DC bus through the LLC. Or, in other words, the battery charges the DC bus through the LLC. Understandably, the battery charging state, that is, the LLC circuit is in the charging state, means that the DC bus charges the battery through the LLC.

[0023] Step 2: Calculate the difference between the actual battery voltage value Vbat_real and the sampled battery voltage value Vbat_sam, that is, the first bias coefficient b1 = Vbat_real - Vbat_sam.

[0024] In one embodiment, the actual battery voltage value Vbat_real can be obtained by testing with a voltage measuring instrument, and the initial sampled battery voltage value Vbat_sam can be obtained through a battery voltage sampling circuit.

[0025] Among them, both the actual battery voltage value Vbat_real and the sampled battery voltage value Vbat_sam are current values, that is, the current actual battery voltage value and the current sampled battery voltage value respectively.

[0026] Step 3: Update the sampled battery voltage value Vbat_sam and count the update times M1 of the sampled battery voltage value.

[0027] In one embodiment, updating the sampled battery voltage value Vbat_sam, also known as calibrating the sampled battery voltage value Vbat_sam, means adding the current sampled battery voltage value Vbat_sam to the first bias coefficient b1, or in other words, summing the current sampled battery voltage value Vbat_sam and the first bias coefficient b1, and reassigning the sum to the sampled battery voltage value Vbat_sam, thereby updating the sampled battery voltage value Vbat_sam.

[0028] Understandably, count the update times M1 of the sampled battery voltage value. The initial value of the update times M1 is 0. Each time the sampled battery voltage value is updated, the value of M1 is incremented by 1. For example, when the update times of the sampled battery voltage value is 1, M1 = 1; when the update times of the sampled battery voltage value is 2, the value of M1 is 2; when the update times of the sampled battery voltage value is N, M1 = N, where N is a positive integer.

[0029] Step 4: Determine whether to proceed to Step 5, return to Step 2, or proceed to Step 9 based on the range of the first bias coefficient b1 and the number of updates M1 of the battery voltage sampling value.

[0030] If the first bias coefficient b1 is not between ±V1, that is, b1 > V1 or b1 < -V1, and M1 < N1, then return to Step 2. At this time, the battery voltage sampling value Vbat_sam is the updated battery voltage sampling value Vbat_sam obtained through Step 3, where N1 is a positive integer greater than 2, and N1 can be selected according to actual needs, such as 3, 4, 5, or a larger value. Among them, in one embodiment, the range of V1 is 1%Vbat_real~5%Vbat_real, and in another embodiment, the range of V1 is 2%Vbat_real~4%Vbat_real.

[0031] If M1 = N1, then skip to Step 9.

[0032] If the first bias coefficient b1 is between ±V1, that is, -V1 ≤ b1 ≤ V1, proceed to Step 5.

[0033] Step 5: Calculate the difference between the actual battery voltage value Vbat_real*k0 and the bus voltage sampling value Vbus_sam, that is, the second bias coefficient: b2 = Vbat_real*k0 - Vbus_sam.

[0034] In one embodiment, the initial bus voltage sampling value Vbus_sam can be obtained through a bus voltage sampling circuit; among them, the bus voltage sampling value Vbus_sam is the current value, that is, the current bus voltage sampling value. Step 6: Update the bus voltage sampling value Vbus_sam and count the number of updates M2 of the bus voltage sampling value.

[0035] Updating the bus voltage sampling value Vbus_sam, also known as calibrating the bus voltage sampling value Vbus_sam, means adding the current bus voltage sampling value Vbus_sam to the second bias coefficient b2, or in other words, summing the current bus voltage sampling value Vbus_sam and the second bias coefficient b2, and reassigning the sum to the bus voltage sampling value Vbus_sam to update the bus voltage sampling value Vbus_sam.

[0036] Understandably, the update count M2 of the bus voltage sampling value is counted, where the initial value of the update count M2 is 0. Each time the bus voltage sampling value is updated, the value of M2 is incremented by 1. For example, when the update count of the bus voltage sampling value is 1, M2 = 1; when the update count of the bus voltage sampling value is 2, the value of M2 is 2; when the update count of the bus voltage sampling value is M, M2 = M, where M is a positive integer.

[0037] Step 7: Determine to perform Step 8, return to Step 5, or perform Step 9 according to the second bias coefficient b2 and the range of the update count M2 of the bus voltage sampling value.

[0038] If the second bias coefficient b2 is not between ±V2, that is, b2 > V2 or b2 < -V2, and M2 < N2, then return to Step 5. At this time, the bus voltage sampling value Vbus_sam is the bus voltage sampling value Vbus_sam updated through Step 6, where N2 is a positive integer greater than 2, and N2 can be selected according to actual needs, such as taking 3, 4, 5, or a larger value. Among them, in one embodiment, the range of V2 is 0.5%Vbus_rated~2.5%Vbus_rated, and in another embodiment, the range of V2 is 1%Vbus_rated~2%Vbus_rated, and Vbus_rated is the rated bus voltage.

[0039] If M2 = N2, then jump to Step 9.

[0040] If the second bias coefficient b2 is between ±V2, that is, -V2 ≤ b2 ≤ V2, perform Step 8.

[0041] Step 8: Determine whether the LLC is in the charging or discharging state according to the battery voltage sampling value Vbat_sam and the bus voltage sampling value Vbus_sam.

[0042] If Vbus_sam > Vbat_sam * k0 + b3, it is determined that the LLC is in the charging state at this time; if Vbus_sam < Vbat_sam * k0 - b4, it is determined that the LLC is in the discharging state at this time. Among them, the ranges of b3 and b4 are selected according to actual needs. For example, in one embodiment, the value ranges of both b3 and b4 are 1%Vbat_real~10%Vbat_real, and in another embodiment, the value ranges of both b3 and b4 are 2%Vbat_real~5%Vbat_real, and so on.

[0043] Step 9: Report an error to notify the maintenance personnel for repair. Embodiment

[0044] Please refer to Figure 3, which shows a voltage calibration method for judging the charging and discharging direction of LLC of the present invention, The method includes: Step 1: Set the battery voltage to the nominal voltage and set LLC to the battery discharging state.

[0045] It can be understood that when setting the battery voltage to the nominal voltage, a DC source can be used to supply power to the battery in the LLC topology. First, set the DC source to the nominal voltage and connect it to both ends of the battery in the LLC topology. It is also possible to first connect the DC source to both ends of the battery in the LLC topology and then set the DC source to the nominal voltage. In one embodiment, the nominal voltage is 48V or 24V. In other embodiments, the nominal voltage can be selected as other values according to actual needs.

[0046] Among them, the battery discharging state, that is, the LLC circuit is in the discharging state, means that the battery discharges to the DC bus through LLC, or in other words, the battery charges the DC bus through LLC; it can be understood that the battery charging state, that is, the LLC circuit is in the charging state, means that the DC bus charges the battery through LLC.

[0047] Step 2: Calculate the difference between the actual value of the battery voltage Vbat_real*k0 and the sampled value of the bus voltage Vbus_sam, that is, the second bias coefficient: b2 = Vbat_real*k0 - Vbus_sam.

[0048] In one embodiment, the actual value of the battery voltage Vbat_real can be obtained by testing with a voltage measuring instrument, and the initial sampled value of the bus voltage Vbus_sam can be obtained through a bus voltage sampling circuit; among them, the sampled value of the bus voltage Vbus_sam is the current value, that is, the current sampled value of the bus voltage.

[0049] Step 3: Update the sampled value of the bus voltage Vbus_sam and count the update times M2 of the sampled value of the bus voltage.

[0050] Updating the sampled value of the bus voltage Vbus_sam, also known as calibrating the sampled value of the bus voltage Vbus_sam, means adding the current sampled value of the bus voltage Vbus_sam to the second bias coefficient b2, or in other words, summing the current sampled value of the bus voltage Vbus_sam and the second bias coefficient b2, and reassigning the sum to the sampled value of the bus voltage Vbus_sam, thereby updating the sampled value of the bus voltage Vbus_sam.

[0051] Understandably, the update count M2 of the bus voltage sampling value is counted. The initial value of the update count M2 is 0. Each time the bus voltage sampling value is updated, the value of M2 is incremented by 1. For example, when the update count of the bus voltage sampling value is 1, M2 = 1; when the update count of the bus voltage sampling value is 2, the value of M2 is 2; when the update count of the bus voltage sampling value is M, M2 = M, where M is a positive integer.

[0052] Step 4: Determine whether to proceed to Step 5, return to Step 2, or proceed to Step 9 according to the second bias coefficient b2 and the range of the update count M2 of the bus voltage sampling value.

[0053] If the second bias coefficient b2 is not between ±V2, that is, b2 > V2 or b2 < -V2, and M2 < N2, then return to Step 2. At this time, the bus voltage sampling value Vbus_sam is the bus voltage sampling value Vbus_sam updated through Step 6. Here, N2 is a positive integer greater than 2, and N2 can be set according to actual needs, such as taking 3, 4, 5, or a larger value. In one embodiment, the range of V2 is 0.5%Vbus_rated~2.5%Vbus_rated. In another embodiment, the range of V2 is 1%Vbus_rated~2%Vbus_rated, where Vbus_rated is the rated bus voltage.

[0054] If M2 = N2, then jump to Step 9.

[0055] If the second bias coefficient b2 is between ±V2, that is, -V2 ≤ b2 ≤ V2, proceed to Step 5.

[0056] Step 5: Calculate the difference between the actual battery voltage Vbat_real and the battery voltage sampling value Vbat_sam, that is, the first bias coefficient b1 = Vbat_real - Vbat_sam.

[0057] In one embodiment, the initial battery voltage sampling value Vbat_sam can be obtained through a battery voltage sampling circuit.

[0058] Here, the actual battery voltage Vbat_real and the battery voltage sampling value Vbat_sam are both current values, that is, the current actual battery voltage and the current battery voltage sampling value respectively.

[0059] Step 6: Update the battery voltage sampling value Vbat_sam and count the update count M1 of the battery voltage sampling value.

[0060] In one embodiment, updating the sampled battery voltage value Vbat_sam, also known as calibrating the sampled battery voltage value Vbat_sam, means adding the current sampled battery voltage value Vbat_sam to the first bias coefficient b1, or in other words, summing the current sampled battery voltage value Vbat_sam and the first bias coefficient b1, and reassigning the sum to the sampled battery voltage value Vbat_sam, thereby updating the sampled battery voltage value Vbat_sam.

[0061] Understandably, the update count M1 of the sampled battery voltage value is counted, where the initial value of the update count M1 is 0. Each time the sampled battery voltage value is updated, the value of M1 is incremented by 1. For example, when the update count of the sampled battery voltage value is 1, M1 = 1; when the update count of the sampled battery voltage value is 2, the value of M1 is 2; when the update count of the sampled battery voltage value is N, M1 = N, where N is a positive integer.

[0062] Step 7: Determine whether to proceed to Step 8, return to Step 5, or proceed to Step 9 based on the range of the first bias coefficient b1 and the update count M1 of the sampled battery voltage value.

[0063] If the first bias coefficient b1 is not between ±V1, that is, b1 > V1 or b1 < -V1, and M1 < N1, then return to Step 5. At this time, the sampled battery voltage value Vbat_sam is the sampled battery voltage value Vbat_sam updated in Step 3. Here, N1 is a positive integer greater than 2, and N1 can be selected according to actual needs, such as 3, 4, 5, or a larger value. Among them, in one embodiment, the range of V1 is 1%Vbat_real~5%Vbat_real; in another embodiment, the range of V1 is 2%Vbat_real~4%Vbat_real.

[0064] If M1 = N1, then skip to Step 9.

[0065] If the first bias coefficient b1 is between ±V1, that is, -V1 ≤ b1 ≤ V1, proceed to Step 8.

[0066] Step 8: Determine whether the LLC is in a charging or discharging state based on the calibrated sampled battery voltage value Vbat_sam and the calibrated sampled bus voltage value Vbus_sam.

[0067] If Vbus_sam > Vbat_sam * k0 + b3, it is determined that the LLC is in the charging state at this time; if Vbus_sam < Vbat_sam * k0 - b4, it is determined that the LLC is in the discharging state at this time. Here, b3 and b4 are positive numbers, and the ranges of b3 and b4 are selected according to actual needs. For example, in one embodiment, the value ranges of both b3 and b4 are 1%Vbat_real to 10%Vbat_real, and in another embodiment, the value ranges of both b3 and b4 are 2%Vbat_real to 5%Vbat_real, and so on.

[0068] Step 9: Report an error and notify the maintenance personnel for inspection.

[0069] As can be seen from the above, the difference between the first embodiment and the second embodiment is that in the first embodiment, the battery voltage sampling value Vbat_sam is processed, or updated / calibrated, through Steps 2 to 3 first, and then the bus voltage sampling value Vbus_sam is processed, or updated / calibrated, through Steps 5 to 6; while in the second embodiment, the bus voltage sampling value Vbus_sam is processed, or updated / calibrated, through Steps 2 to 3 first, and then the battery voltage sampling value Vbat_sam is processed, or updated / calibrated, through Steps 5 to 6.

[0070] The voltage calibration method for judging the charging and discharging directions of the LLC of the present invention can accurately judge the charging and discharging directions without increasing the circuit cost, without considering the differences in the transformer turns ratios of each product, and without measuring the actual value of the bus voltage, and has the advantages of low cost, high precision, good efficiency, etc. Here, the product refers to a product containing LLC, such as an energy storage product, etc.

[0071] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the patent of the present invention. For those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A voltage calibration method for determining the charging and discharging direction of LLC, characterized in that The method includes: Step 1: Set the battery voltage to the nominal voltage and set the LLC to the battery discharge state; Steps 2 to 7: Calibrate the battery voltage sampling value and the bus voltage sampling value according to the true value of the battery voltage, and determine whether to perform Step 8 or Step 9 according to the calibration result; Step 8: Judge whether the LLC is in the charging or discharging state according to the calibrated battery voltage sampling value Vbat_sam and the calibrated bus voltage sampling value Vbus_sam; if Vbus_sam > Vbat_sam * k0 + b3, it is judged that the LLC is in the charging state at this time; if Vbus_sam < Vbat_sam * k0 - b4, it is judged that the LLC is in the discharging state at this time; where k0 is the turns ratio of the primary and secondary sides of the transformer, and both b3 and b4 are 1% - 10% of the true value of the battery voltage; Step 9: Report an error and notify the maintenance personnel for inspection.

2. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 1, wherein The said Steps 2 to 7 are: Step 2: Calculate the difference between the actual value of the battery voltage and the battery voltage sampling value to obtain the first bias coefficient b1; Step 3: Update the battery voltage sampling value and count its update times M1; Step 4: Determine whether to perform Step 5, return to Step 2, or perform Step 9 according to the range of b1 and M1; Step 5: Calculate the difference between the actual value of the battery voltage * k0 and the bus voltage sampling value to obtain the second bias coefficient b2; Step 6: Update the bus voltage sampling value and count its update times M2; Step 7: Determine whether to perform Step 8, return to Step 5, or perform Step 9 according to the range of b2 and M2.

3. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 1, wherein The said Steps 2 to 7 are: Step 2: Calculate the difference between the actual value of the battery voltage * k0 and the bus voltage sampling value to obtain the second bias coefficient b2; Step 3: Update the bus voltage sampling value and count its update times M2; Step 4: Determine whether to perform Step 5, return to Step 2, or perform Step 9 according to the range of b2 and M2; Step 5: Calculate the difference between the actual value of the battery voltage and the battery voltage sampling value to obtain the first bias coefficient b1; Step 6: Update the battery voltage sampling value and count its update times M1; Step 7: Determine whether to perform Step 8, return to Step 5, or perform Step 9 according to the range of b1 and M1.

4. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 2 or 3, characterized in that, The actual value of the battery voltage is obtained by testing with a voltage measuring instrument; the initial battery voltage sampling value and the initial bus voltage sampling value are obtained through their respective voltage sampling circuits.

5. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 4, characterized in that, The update of the battery voltage sampling value means reassigning the sum of the current battery voltage sampling value and the first bias coefficient b1 to the battery voltage sampling value.

6. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 4, characterized in that The update of the bus voltage sampling value means reassigning the sum of the current bus voltage sampling value and the second bias coefficient b2 to the bus voltage sampling value.

7. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 2, characterized in that The specific content of Step 4 is: If b1 > V1 or b1 < -V1, and M1 < N1, return to the second step; If M1 = N1, then jump to the ninth step; If -V1 ≤ b1 ≤ V1, proceed to the fifth step; Wherein, N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the true value of the battery voltage.

8. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 2, wherein The specific content of the seventh step is as follows: If b2 > V2 or b2 < -V2, and M2 < N2, return to the fifth step; If M2 = N2, then jump to the ninth step; If -V2 ≤ b2 ≤ V2, proceed to the eighth step; Wherein, N2 is a positive integer greater than 2, and the range of V2 is 0.5% - 2.5% of the rated value of the bus voltage.

9. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 3, characterized in that The specific content of the fourth step is as follows: If b2 > V2 or b2 < -V2, and M2 < N2, return to the second step; If M2 = N2, then jump to the ninth step; If -V2 ≤ b2 ≤ V2, proceed to the fifth step; Wherein, N2 is a positive integer greater than 2, and the range of V2 is 0.5% - 2.5% of the rated value of the bus voltage.

10. The voltage calibration method for judging the charging and discharging direction of LLC according to claim 3, characterized in that, The specific content of the seventh step is as follows: If b1 > V1 or b1 < -V1, and M1 < N1, return to the fifth step; If M1 = N1, then jump to the ninth step; If -V1 ≤ b1 ≤ V1, proceed to the eighth step; Wherein, N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the true value of the battery voltage.

Images