A voltage calibration method for determining LLC charge and discharge direction

Abstract

The present invention provides a voltage calibration method for determining the LLC charge and discharge direction. By calibrating the battery voltage sampling value and the bus voltage sampling value, even if the transformer turns ratio of each product is slightly different and the actual bus voltage value is difficult to measure, the charge and discharge direction can be accurately determined by the calibrated battery voltage sampling value and bus voltage sampling value, thereby saving circuit costs and reducing calibration difficulty.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a voltage calibration method for determining LLC charge and discharge directions. Background Art

[0002] In existing technologies, LLC topology (LLC for short) is often used as the DC / DC link of energy storage products to increase or decrease voltage. It is necessary to determine the LLC charge and discharge direction to switch loops, as well as to calculate and display the charge and discharge current and power. Common methods for determining LLC charge and discharge direction include:

[0003] Method 1: Use a Hall sensor to sample the bus current on the DC bus at the LLC input end, and determine the LLC charge and discharge direction by judging the positive or negative value of the bus current;

[0004] Method 2: Determine the LLC charge and discharge direction by judging the product of the battery voltage sampling value and the transformer turns ratio, and the relationship between the bus voltage sampling values.

[0005] Among them, method 1 uses a Hall sensor to sample the DC bus current, which not only increases the circuit cost, but also increases the circuit weight and volume; method 2 has slight differences in the transformer turns ratio of each product, and the battery / bus voltage sampling value and actual value are also different, so there may be problems such as misjudgment. Summary of the Invention

[0006] The purpose of the present invention is to provide a voltage calibration method for determining the charge and discharge direction of LLC, so as to solve the problem that the prior art cannot take into account both cost and accuracy.

[0007] The present invention provides a voltage calibration method for determining LLC charge and discharge direction, the method comprising: step 1: setting the battery voltage to a nominal voltage and setting the LLC to a battery discharge state;

[0008] Steps 2 to 7: Calibrate the battery voltage sampling value and bus voltage sampling value based on the actual battery voltage value, and proceed to step 8 or step 9 based on the calibration results;

[0009] Step 8: Determine whether the LLC is in the charging or discharging state based on the calibrated battery voltage sample value Vbat_sam and the calibrated bus voltage sample value Vbus_sam. If Vbus_sam > Vbat_sam* k 0 + b3, the LLC is in the charging state. If Vbus_sam < Vbat_sam* k 0 – b4, the LLC is in the discharging state. k0 is the transformer primary-to-secondary turns ratio, and b3 and b4 are both 1% to 10% of the actual battery voltage value.

[0010] Step 9: Report an error and notify maintenance personnel for repair.

[0011] Furthermore, the steps 2 to 7 are:

[0012] Step 2: Calculate the difference between the actual value of the battery voltage and the sampled value of the battery voltage to obtain a first bias coefficient b1;

[0013] Step 3: updating the battery voltage sampling value and counting the number of updates M1;

[0014] Step 4: Determine whether to proceed to step 5, return to step 2, or proceed to step 9 based on the range of b1 and M1;

[0015] Step 5: Calculate the difference between the actual battery voltage value * k0 and the bus voltage sampling value to obtain a second bias coefficient b2;

[0016] Step 6: Update the bus voltage sampling value and count its update times M2;

[0017] Step 7: Based on the range of b2 and M2, determine whether to proceed to step 8, return to step 5, or proceed to step 9.

[0018] Furthermore, the steps 2 to 7 are:

[0019] Step 2: Calculate the difference between the actual battery voltage value * k0 and the bus voltage sampling value to obtain a second bias coefficient b2;

[0020] Step 3: Update the bus voltage sampling value and count its update times M2;

[0021] Step 4: Determine whether to proceed to step 5, return to step 2, or proceed to step 9 based on the range of b2 and M2;

[0022] Step 5: Calculate the difference between the actual value of the battery voltage and the sampled value of the battery voltage to obtain a first bias coefficient b1;

[0023] Step 6: Update the battery voltage sampling value and count the number of updates M1;

[0024] Step 7: Based on the range of b1 and M1, determine whether to proceed to step 8, return to step 5, or proceed to step 9.

[0025] Furthermore, 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 respective voltage sampling circuits.

[0026] Further, the specific content of the 4th step is as follows:

[0027] If b1 > V1 or b1 < -V1, and M1 < N1, return to the 2nd step;

[0028] If M1 = N1, then jump to the 9th step;

[0029] If -V1 ≤ b1 ≤ V1, perform the 5th step;

[0030] Where, N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the true value of the battery voltage.

[0031] Further, the specific content of the 7th step is as follows:

[0032] If b2 > V2 or b2 < -V2, and M2 < N2, return to the 5th step;

[0033] If M2 = N2, then jump to the 9th step;

[0034] If -V2 ≤ b2 ≤ V2, perform the 8th step;

[0035] Where, 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.

[0036] Further, the specific content of the 4th step is as follows:

[0037] If b2 > V2 or b2 < -V2, and M2 < N2, return to the 2nd step;

[0038] If M2 = N2, then jump to the 9th step;

[0039] If -V2 ≤ b2 ≤ V2, perform the 5th step;

[0040] Where, 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.

[0041] Further, the specific content of the 7th step is as follows:

[0042] If b1 > V1 or b1 < -V1, and M1 < N1, return to the 5th step;

[0043] If M1 = N1, then jump to the 9th step;

[0044] If -V1 ≤ b1 ≤ V1, perform the 8th step;

[0045] Where, N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the true value of the battery voltage.

[0046] The above voltage calibration method for determining LLC charge and discharge direction can accurately determine LLC charge and discharge direction without increasing circuit cost, without considering the difference in transformer turns ratio of each product, and without measuring the actual value of the bus voltage. It has the advantages of low cost, high accuracy, and good efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is an LLC topology diagram according to an embodiment of the present invention;

[0048] Figure 2 This is a flow chart of a voltage calibration method for determining LLC charge and discharge direction according to a first embodiment of the present invention;

[0049] Figure 3 This is a flow chart of a voltage calibration method for determining LLC charge and discharge direction according to a second embodiment of the present invention.

[0050] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0051] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate several embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0053] See also Figure 1 , Figure 1Figure 1 is an LLC topology diagram, in which the primary side (left side) of the transformer Tr is a DC bus-connected full-bridge and series resonant topology, the secondary side (right side) of the transformer Tr is a full-bridge synchronous rectification topology connected to the battery, and the primary-to-secondary turns ratio of the transformer is k0. C1 and C2 are the primary and secondary capacitors, respectively, which act as smoothing filters. In some embodiments, C1 and C2 can be removed. Wherein, bus represents a DC bus (abbreviated as bus), Vbus represents the bus voltage, bat represents a battery, and Vbat represents the battery voltage. The full-bridge on the primary side is formed by connecting switches Q1-Q4 in series in pairs and then in parallel, i.e., switches Q1 and Q2 are connected in series, switches Q3 and Q4 are connected in series and then in parallel. The series resonant topology is formed by connecting a resonant inductor Lr, a resonant capacitor Cr, and the excitation inductor Lm of the transformer Tr in series. The full-bridge rectifier topology on the secondary side is formed by connecting switches Q5-Q8 in series in pairs and then in parallel, i.e., switches Q5 and Q6 are connected in series, switches Q7 and Q8 are connected in series and then in parallel. In one embodiment, switches Q1-Q8 are all MOS tubes.

[0054] It should be noted that Figure 1 This is just an example to illustrate an LLC circuit topology. In other embodiments, in the LLC topology, the full bridge on the primary side can be replaced by a half bridge, and the series resonant topology on the primary side can be replaced by a parallel resonant topology or a series-parallel resonant 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. Example

[0055] See also Figure 2 , shows a voltage calibration method for determining LLC charge and discharge direction of the present invention,

[0056] The method comprises:

[0057] Step 1: Set the battery voltage to the nominal voltage and set the LLC to the battery discharge state.

[0058] It is understood that the battery voltage is set to a nominal voltage. A DC source can be used to power the battery in the LLC topology. The DC source can be first set to the nominal voltage and connected to the battery terminals in the LLC topology. Alternatively, the DC source can be first connected to the battery terminals in the LLC topology and then set to the nominal voltage. In one embodiment, the nominal voltage is 48V or 24V. In other embodiments, the nominal voltage can be other values based on actual needs.

[0059] 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; 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 the LLC.

[0060] 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.

[0061] In one embodiment, the actual battery voltage value Vbat_real can be obtained by testing with a voltage measuring instrument, and the initial battery voltage sampling value Vbat_sam can be obtained by a battery voltage sampling circuit.

[0062] The actual battery voltage value Vbat_real and the sampled battery voltage value Vbat_sam are both current values, namely, the actual battery voltage value and the sampled battery voltage value, respectively.

[0063] Step 3: Update the battery voltage sampling value Vbat_sam and count the number of updates M1 of the battery voltage sampling value.

[0064] In one embodiment, updating the battery voltage sampling value Vbat_sam, also called calibrating the battery voltage sampling value Vbat_sam, refers to adding the current battery voltage sampling value Vbat_sam and the first bias coefficient b1, or summing the current battery voltage sampling value Vbat_sam and the first bias coefficient b1, and reassigning the sum of the two to the battery voltage sampling value Vbat_sam, thereby updating the battery voltage sampling value Vbat_sam.

[0065] It can be understood that the update number M1 of the battery voltage sampling value is counted, where the initial value of the update number M1 is 0, and the value of M1 is increased by 1 each time the battery voltage sampling value is updated. For example, when the update number of the battery voltage sampling value is 1, M1=1; when the update number of the battery voltage sampling value is 2, the value of M1 is 2; when the update number of the battery voltage sampling value is N, M1=N, where N is a positive integer.

[0066] 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 update number M1 of the battery voltage sampling value.

[0067] If the first offset 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. Here, N1 is a positive integer greater than 2, and N1 can be set according to actual needs, such as 3, 4, 5, or a larger value. 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.

[0068] If M1 = N1, then jump to step 9.

[0069] If the first offset coefficient b1 is between ±V1, that is, -V1 ≤ b1 ≤ V1, proceed to step 5.

[0070] 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 offset coefficient: b2 = Vbat_real*k0 - Vbus_sam.

[0071] In one embodiment, the initial bus voltage sampling value Vbus_sam can be obtained through a bus voltage sampling circuit. Here, 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 update times M2 of the bus voltage sampling value.

[0072] 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 offset coefficient b2, or in other words, summing the current bus voltage sampling value Vbus_sam and the second offset coefficient b2, and reassigning the sum to the bus voltage sampling value Vbus_sam, thereby updating the bus voltage sampling value Vbus_sam.

[0073] [[ID=​​​​

[0075] 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 updated bus voltage sampling value Vbus_sam 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.

[0076] If M2 = N2, then jump to step 9.

[0077] If the second bias coefficient b2 is between ±V2, that is, -V2 ≤ b2 ≤ V2, perform step 8.

[0078] 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.

[0079] 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.

[0080] Step 9: Report an error and notify the maintenance personnel for inspection. Embodiment

[0081] Please refer to Figure 3 , which shows a voltage calibration method for determining the charging and discharging directions of LLC in the present invention.

[0082] The method includes:

[0083] Step 1: Set the battery voltage to the nominal voltage and set the LLC to the battery discharging state.

[0084] It is understood that the battery voltage is set to a nominal voltage. A DC source can be used to power the battery in the LLC topology. The DC source can be first set to the nominal voltage and connected to the battery terminals in the LLC topology. Alternatively, the DC source can be first connected to the battery terminals in the LLC topology and then set to the nominal voltage. In one embodiment, the nominal voltage is 48V or 24V. In other embodiments, the nominal voltage can be other values based on actual needs.

[0085] 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; 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 the LLC.

[0086] Step 2: 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.

[0087] In one embodiment, the actual battery voltage value Vbat_real can be obtained by testing with a voltage measuring instrument, and the initial bus voltage sampling value Vbus_sam can be obtained by a bus voltage sampling circuit; wherein, the bus voltage sampling value Vbus_sam is the current value, that is, the current bus voltage sampling value.

[0088] Step 3: Update the bus voltage sampling value Vbus_sam and count the number of updates M2 of the bus voltage sampling value.

[0089] Updating the bus voltage sampling value Vbus_sam, also known as calibrating the bus voltage sampling value Vbus_sam, refers to adding the current bus voltage sampling value Vbus_sam and the second bias coefficient b2, or summing the current bus voltage sampling value Vbus_sam and the second bias coefficient b2, and reassigning the sum of the two to the bus voltage sampling value Vbus_sam, thereby updating the bus voltage sampling value Vbus_sam.

[0090] It can be understood that the update number M2 of the bus voltage sampling value is counted, where the initial value of the update number M2 is 0, and the value of M2 is increased by 1 each time the bus voltage sampling value is updated. For example, when the update number of the bus voltage sampling value is 1, M2=1, when the update number of the bus voltage sampling value is 2, the value of M2 is 2, and when the update number of the bus voltage sampling value is M, M2=M, where M is a positive integer.

[0091] Step 4: Determine to perform Step 5 or return to Step 2, or perform Step 9 according to the range of the second offset coefficient b2 and the number of updates M2 of the bus voltage sampling value.

[0092] If the second offset coefficient b2 is not between ±V2, that is, b2 > V2 or b2 < -V2, and M2 < N2, return to Step 2. At this time, the bus voltage sampling value Vbus_sam is the updated bus voltage sampling value Vbus_sam obtained 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.

[0093] If M2 = N2, jump to Step 9.

[0094] If the second offset coefficient b2 is between ±V2, that is, -V2 ≤ b2 ≤ V2, perform Step 5.

[0095] Step 5: Calculate the difference between the actual battery voltage value Vbat_real and the battery voltage sampling value Vbat_sam, that is, the first offset coefficient b1 = Vbat_real - Vbat_sam.

[0096] In one embodiment, the initial battery voltage sampling value Vbat_sam can be obtained through a battery voltage sampling circuit.

[0097] Here, the actual battery voltage value Vbat_real and the battery voltage sampling value Vbat_sam are both current values, that is, the current actual battery voltage value and the current battery voltage sampling value respectively.

[0098] Step 6: Update the battery voltage sampling value Vbat_sam and count the number of updates M1 of the battery voltage sampling value.

[0099] In one embodiment, updating the battery voltage sampling value Vbat_sam, also known as calibrating the battery voltage sampling value Vbat_sam, means adding the current battery voltage sampling value Vbat_sam to the first offset coefficient b1, or in other words, summing the current battery voltage sampling value Vbat_sam and the first offset coefficient b1, and reassigning the sum to the battery voltage sampling value Vbat_sam, thereby updating the battery voltage sampling value Vbat_sam.

[0100] Understandably, the update count M1 of the battery voltage sampling value is counted. The initial value of the update count M1 is 0. Each time the battery voltage sampling value is updated, the value of M1 is incremented by 1. For example, when the update count of the battery voltage sampling value is 1, M1 = 1; when the update count of the battery voltage sampling value is 2, the value of M1 is 2; when the update count of the battery voltage sampling value is N, M1 = N, where N is a positive integer.

[0101] Step 7: Determine whether to proceed to Step 8, return to Step 5, or proceed to Step 9 based on the first bias coefficient b1 and the range of the update count M1 of the battery voltage sampling value.

[0102] If the first bias coefficient b1 is not between ±V1, that is, b1 > V1 or b1 < -V1, and M1 < N1, return to Step 5. At this time, the battery voltage sampling value Vbat_sam is the battery voltage sampling 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 taking 3, 4, 5, or a larger value. 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.

[0103] If M1 = N1, jump to Step 9.

[0104] If the first bias coefficient b1 is between ±V1, that is, -V1 ≤ b1 ≤ V1, proceed to Step ⑧.

[0105] Step 8: Determine whether LLC is in a charging or discharging state based on the calibrated battery voltage sampling value Vbat_sam and the calibrated bus voltage sampling value Vbus_sam.

[0106] If Vbus_sam > Vbat_sam * k0 + b3, it is determined that LLC is in a charging state at this time; if Vbus_sam < Vbat_sam * k0 - b4, it is determined that LLC is in a 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~10%Vbat_real; in another embodiment, the value ranges of both b3 and b4 are 2%Vbat_real~5%Vbat_real, and so on.

[0107] Step 9: Report an error to notify the maintenance personnel for inspection.

[0108] As can be seen from the above, the difference between Example 1 and Example 2 is that Example 1 first processes the battery voltage sampling value Vbat_sam through steps 2 to 3, or updates / calibrates it, and then processes the bus voltage sampling value Vbus_sam through steps 5 to 6, or updates / calibrates it; while Example 2 first processes the bus voltage sampling value Vbus_sam through steps 2 to 3, or updates / calibrates it, and then processes the battery voltage sampling value Vbat_sam through steps 5 to 6, or updates / calibrates it.

[0109] The voltage calibration method for determining LLC charge and discharge direction of the present invention accurately determines the charge and discharge direction without increasing circuit cost, without considering the differences in transformer turns ratios between products, and without measuring the actual bus voltage value. It has the advantages of low cost, high accuracy, and excellent efficiency. The product refers to a product that includes an LLC, such as an energy storage product.

[0110] The above embodiments merely illustrate several embodiments of the present invention, and while the descriptions thereof are relatively specific and detailed, they are not to be construed as limiting the scope of the present invention. A person skilled in the art would be able to make various modifications and improvements without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A voltage calibration method for determining LLC charge and discharge direction, applied to an LLC topology, wherein the input terminal of the primary circuit is connected to a busbar and the output terminal of the secondary circuit is connected to a battery, characterized in that: The method comprises: 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 bus voltage sampling value based on the actual battery voltage value, and proceed to step 8 or step 9 based on the calibration results; Step 8: Determine whether the LLC is in the charging or discharging state based on the calibrated battery voltage sample value Vbat_sam and the calibrated bus voltage sample value Vbus_sam. If Vbus_sam > Vbat_sam* k 0 + b3, the LLC is in the charging state. If Vbus_sam < Vbat_sam* k 0 – b4, the LLC is in the discharging state. k0 is the transformer primary-to-secondary turns ratio, and b3 and b4 are both 1% to 10% of the actual battery voltage. Step 9: Report an error and notify maintenance personnel for repair.

2. The voltage calibration method for determining LLC charge and discharge direction according to claim 1, characterized in that: The steps 2 to 7 are: Step 2: Calculate the difference between the actual value of the battery voltage and the sampled value of the battery voltage to obtain a first bias coefficient b1; Step 3: updating the battery voltage sampling value and counting the number of updates M1; Step 4: Determine whether to proceed to step 5, return to step 2, or proceed to step 9 based on the range of b1 and M1; Step 5: Calculate the difference between the actual battery voltage value * k0 and the bus voltage sampling value to obtain a second bias coefficient b2; Step 6: Update the bus voltage sampling value and count its update times M2; Step 7: Based on the range of b2 and M2, determine whether to proceed to step 8, return to step 5, or proceed to step 9.

3. The voltage calibration method for determining LLC charge and discharge direction according to claim 1, characterized in that: The steps 2 to 7 are: Step 2: Calculate the difference between the actual battery voltage value * k0 and the bus voltage sampling value to obtain a second bias coefficient b2; Step 3: Update the bus voltage sampling value and count its update times M2; Step 4: Determine whether to proceed to step 5, return to step 2, or proceed to step 9 based on the range of b2 and M2; Step 5: Calculate the difference between the actual value of the battery voltage and the sampled value of the battery voltage to obtain a first bias coefficient b1; Step 6: Update the battery voltage sampling value and count the number of updates M1; Step 7: Based on the range of b1 and M1, determine whether to proceed to step 8, return to step 5, or proceed to step 9.

4. The voltage calibration method for determining LLC charge and discharge direction 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 battery voltage sampling value and the bus voltage sampling value are obtained through their respective voltage sampling circuits.

5. The voltage calibration method for determining LLC charge and discharge direction according to claim 4, characterized in that: The updating of the battery voltage sampling value refers to 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 determining LLC charge and discharge direction according to claim 4, characterized in that: The updating of the bus voltage sampling value refers to 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 determining LLC charge and discharge direction according to claim 2, characterized in that: The fourth step is specifically as follows: 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; Where N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the actual battery voltage value.

8. The voltage calibration method for determining LLC charge and discharge direction according to claim 2, characterized in that: The specific content of the seventh step is: 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; Where N2 is a positive integer greater than 2, and the range of V2 is 0.5% - 2.5% of the rated bus voltage value.

9. The voltage calibration method for determining LLC charge and discharge direction according to claim 3, characterized in that: The specific content of the fourth step is: 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; Where N2 is a positive integer greater than 2, and the range of V2 is 0.5% - 2.5% of the rated bus voltage value.

10. The voltage calibration method for determining LLC charge and discharge direction according to claim 3, characterized in that: The specific content of the seventh step is: 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; Where N1 is a positive integer greater than 2; the range of V1 is 1% - 5% of the actual battery voltage value.

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