Efficient and stable wireless charging method and system suitable for pressure-bearing lithium battery

Abstract

The invention provides an efficient and stable wireless charging method suitable for a pressure-bearing lithium battery, and solves the problems that an existing maximum efficiency tracking control method has the defects of being high in time complexity, low in solving speed and low in maximum tracking speed, and the charging process is inaccurate due to the fact that parameters of the pressure-bearing lithium battery are affected by pressure. According to the invention, the improved perturbation observation-golden section algorithm is adopted to realize rapid maximum efficiency tracking and stable control of the pressure-bearing lithium battery. The method comprises the following steps: firstly, comparing a current solution with a previous solution and a next solution, and if the current solution is superior to the previous solution and the next solution at the same time, determining an interval in which an optimal solution is located; secondly, maximum efficiency tracking is carried out through a golden section search algorithm; the time complexity of the golden section search algorithm is generally O (log n), and n is the dimension of a solution space. Therefore, the high-efficiency stability of wireless charging of the pressure-bearing lithium battery can be improved to a certain extent by adopting the perturbation observation-golden section method.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater wireless charging, and in particular relates to an efficient and stable wireless charging method and system suitable for pressurized lithium batteries. Background Art

[0002] Pressure-bearing lithium batteries have the characteristics of directly bearing pressure, changing the internal characteristic parameters of the battery with the change of external pressure, and protecting their own structural components. They are of great significance in the deep-water application of autonomous underwater vehicles (AUVs). They have been put into use, but are restricted by the lack of in-situ and efficient energy replenishment methods. The working time, navigation speed, navigation depth and other indicators of AUVs are almost all affected, which seriously limits the scope and effect of underwater operations. Therefore, underwater wireless power transmission technology with the characteristics of no physical contact, avoiding contact sparks and interface exposure is applied to the energy replenishment of AUVs. The wireless charging system consists of two parts, the transmitter and the receiver. Pursuing the maximum charging efficiency is an important direction. If the maximum efficiency of the system is to be achieved, it is necessary to track and control the maximum efficiency. At present, most of the existing technical solutions send the operating parameters (such as voltage and current) of the receiver to the transmitter through a wireless communication network. The transmitter calculates the optimal DC / DC voltage value through a series of derived formulas to achieve maximum efficiency. This calculation method can obtain accurate maximum efficiency, but it requires wireless communication, which is prone to interference in a strong magnetic field environment such as wireless charging, leading to problems such as packet loss and connection interruption.

[0003] Chinese patent CN111509865B provides a maximum efficiency tracking control method and system for a wireless charging system, and Chinese patent application CN110571899A provides a constant current output control and efficiency improvement method for a wireless power transmission system based on a variable step size perturbation observation method. The above schemes can perform maximum efficiency tracking without the need for wireless communication. However, the above maximum efficiency tracking control methods are all based on the perturbation observation method, which is a greedy algorithm, that is, starting from a point in the solution space, moving to adjacent points until a local optimal solution that cannot be moved is reached. The time complexity of a typical greedy algorithm is usually linear or nearly linear, that is, O(log n), where n is the dimension of the solution space. It has a high time complexity, a slow solution speed, and a low maximum tracking speed. Summary of the invention

[0004] The present invention aims to solve the problems that the parameters of pressurized lithium batteries are affected by pressure, the maximum efficiency tracking control method has high time complexity, slow solution speed and low maximum tracking speed, and provides an efficient and stable wireless charging method suitable for pressurized lithium batteries.

[0005] To achieve the above purpose, the technical solution provided by the present invention is:

[0006] The efficient and stable wireless charging method for pressurized lithium batteries is special in that it includes the following steps:

[0007] Step 1: Determine the stable output voltage range of the primary-side DC-DC converter

[0008] Step 1.1: A pressurized lithium battery is a soft-packaged battery that is directly exposed to seawater and bears the pressure of seawater. As the pressure increases, the internal characteristic parameters of the pressurized lithium battery will change, the resistance will decrease monotonically, and the terminal voltage and actual available capacity will also increase; therefore, it is necessary to obtain the current SOC value SOC of the pressurized lithium battery 0 , Equivalent load resistance R under different pressures Li And the actual available charge C of the pressurized lithium battery with SOC=1 under different pressures i ;

[0009] Step 1.2: Equivalent load resistance R under different pressures Li , the battery charging power P set by the wireless charging system out The voltage gain G set by the wireless charging system determines the stable output voltage range [V inmin , V inmax ];

[0010] Step 2: Determine the best efficiency operating point

[0011] Step 2.1: Optimal solution existence judgment stage

[0012] According to the stable output voltage range of the primary side DC-DC converter determined in step 1, the maximum output voltage V inmax Start by decreasing it twice with its minimum resolution, taking V(1) = V inmax 、V(2)=V inmax -ΔV, V(3)=V(2)-ΔV as input voltage, and calculate the corresponding input power P respectively in (1) P in (2) and P in (3); where ΔV is the minimum resolution of the primary-side DC-DC converter output voltage;

[0013] If P in (1) <P in (2) <P in (3), the maximum output voltage V of the primary side DC-DC converter is inmax The optimal output voltage value for system efficiency is selected, the maximum efficiency tracking is completed, and the process goes to step 3;

[0014] Otherwise, go to step 2.2;

[0015] Step 2.2: Improve the perturbation observation phase

[0016] In the stable output voltage range of the primary side DC-DC converter, the output voltage is in descending order (V inmax -V inmin ) / 10 as the step size ΔV' is gradually reduced (thereby, the optimal solution interval can be determined in 10 times at most), and V(k-1)=V(k-2)-ΔV', V(k)=V(k-1)-ΔV', V(k+1)=V(k)-ΔV' are used as input voltages in turn, and the corresponding input power P is calculated respectively. in (k-1), P in (k) and P in (k+1); the value of k ranges from 2 to 9. During the iteration process:

[0017] If P in (k+1)>P in (k) <P in (k-1), then the optimal output voltage selection range for system efficiency is [V(k+1), V(k-1)], and go to step 2.3;

[0018] If P in (k+1)>P in (k)≥P in (k-1), then the optimal output voltage selection range for system efficiency is [V(k), V(k-1)], and go to step 2.3;

[0019] If there is always P in (k+1) <P in (k) <P in (k-1), until V(k+1)≤V inmin (In actual situations, the minimum output voltage of the primary-side DC-DC converter is V inmin , but in the judgment, it is also possible to perform the next iteration to obtain the calculated value. Therefore, in the judgment process, V(k+1) can be less than V inmin ), then the minimum output voltage V inmin The optimal output voltage value for system efficiency is selected, the maximum efficiency tracking is completed, and the process goes to step 3;

[0020] In the method of the present invention, in order to avoid more judgments, P is not considered. in (k+1)=P in (k) In this way, the judgment logic and process can be simplified;

[0021] Step 2.3: Golden Section Search Phase

[0022] Use the golden section search algorithm to select the optimal output voltage selection value within the optimal output voltage selection range selected in step 2.2, and proceed to step 3;

[0023] Step 3: Determine whether the pressurized lithium battery is fully charged

[0024] The optimal output voltage selected in step 2 is used as the input voltage to charge the pressure-bearing lithium battery, and the SOC value SOC of the pressure-bearing lithium battery is obtained in real time during the charging process. t , until SOC t =1, indicating that the pressure-bearing lithium battery is fully charged and charging stops;

[0025]

[0026] Where t is the charging time, I t is the charging current at time t, C N is the total charge of the battery at normal pressure, ΔC is the error in the actual available charge of the battery caused by pressure change, C i The corresponding value can be selected according to the pressure borne by the pressure-bearing lithium battery, and then ΔC=C i -C N Calculate the difference between the actual available charge of the battery brought about by different pressures and the total charge of the battery under normal pressure.

[0027] At the same time, the present invention provides an efficient and stable wireless charging system suitable for pressurized lithium batteries, which is special in that it includes a transmitting end and a receiving end;

[0028] The transmitting end includes a power supply battery, a primary side controller, a primary side DC-DC converter, an inverter, a primary side compensation network and a primary side coupler;

[0029] The positive and negative electrodes of the power supply battery are connected to the positive and negative input ports of the primary-side DC-DC converter, the output port of the primary-side DC-DC converter is connected to the input port of the inverter, the output port of the inverter is connected to the input port of the primary-side compensation network, and the output port of the primary-side compensation network is connected to the primary-side coupler; wherein the primary-side controller controls the output voltage of the primary-side DC-DC converter through the PWM duty cycle, that is, the maximum efficiency tracking is performed through the input voltage of the wireless charging system inverter;

[0030] The receiving end includes a pressure-bearing lithium battery, a secondary-side controller, a secondary-side DC-DC converter, a rectifier, a secondary-side compensation network, and a secondary-side coupler;

[0031] The output port of the secondary side coupler is connected to the input port of the secondary side compensation network, the output port of the secondary side compensation network is connected to the input port of the rectifier, the high frequency alternating current is converted into direct current after passing through the rectifier, the output port of the rectifier is connected to the input port of the secondary side DC-DC converter, and the output positive and negative ports of the secondary side DC-DC converter are connected to the positive and negative electrodes of the pressure-bearing lithium battery;

[0032] The primary side coupler and the secondary side coupler are coupled after the transmitting end and the receiving end are connected, and the two wirelessly transmit electric energy through electromagnetic induction generated by high-frequency alternating current;

[0033] The secondary-side DC-DC converter controls the output current and voltage according to the load requirements of the pressurized lithium battery, that is, the secondary-side DC-DC converter generates the voltage or current required by the pressurized lithium battery under the control of the secondary-side controller to supply energy to the pressurized lithium battery;

[0034] The primary-side DC-DC converter adopts the above-mentioned efficient and stable wireless charging method to achieve maximum efficiency tracking of the wireless charging system and find the optimal output voltage selection value.

[0035] Furthermore, the driving signal of the inverter is constant, the duty cycle is 50%, and the phase shift angle is 180°.

[0036] Concept and principle of the present invention:

[0037] In view of the problems existing in the prior art, the research team of the present invention conducted an in-depth analysis and found that the internal resistance of the pressurized lithium battery, the actual available charge and other parameters will change with the pressure. At present, there is no wireless charging method that considers the influence of pressure. Therefore, the present invention establishes a parameter library of pressurized lithium batteries under different pressures in advance, including the equivalent load resistance R Li , Actual available charge C i When charging, the stable output voltage range of the primary-side DC-DC converter is determined based on the impact of pressure on battery parameters, and then the optimal efficiency working point is obtained for charging and judging whether it is fully charged.

[0038] In the efficient and stable control of charging efficiency, the traditional perturbation observation method has a high time complexity of the algorithm when executing, which is O(n), and the calculation time is long. The maximum efficiency tracking speed is slow and there will be a three-point oscillation link in the final stage, which is not conducive to the rapid tracking of the maximum efficiency point. At the same time, the theoretical optimal point finally found by the perturbation observation method is in the three-point oscillation area near the actual optimal point. Therefore, the selection of the perturbation step size ΔV needs to balance the convergence speed and oscillation, which is not conducive to the stability of the system. Figure 2As shown in the figure, although increasing the perturbation step size ΔV can increase the maximum efficiency tracking speed, the final three-point oscillation area will be very large; although reducing the perturbation step size ΔV can reduce the three-point oscillation area, it will significantly increase the maximum efficiency tracking time; the operating mechanism of using the existing perturbation observation method for maximum efficiency tracking in the wireless charging system is as follows:

[0039] First, the receiving end maintains the current value or voltage value required by the load under the control of the primary side DC-DC converter (i.e., buck-boost converter). At this time, the output power P of the receiving end is out Then, the output voltage of the primary side DC-DC converter is adjusted based on the disturbance observation algorithm. When the output power of the battery (which is also the input power P of the wireless charging system) is detected, in ) reaches the minimum, the efficiency of the entire system reaches the maximum. When the system is in area A and area C, the input voltage of the inverter can be increased or decreased by the disturbance step ΔV, thereby continuously reducing the input power P in When the system enters zone B, V in The state becomes P 2 , P min and P 4 The three-point oscillation stage between the points, that is, the optimal inverter input voltage for maximum efficiency is found. During operation, the change of the inverter input voltage is controlled by the duty cycle of the primary-side DC-DC converter, and the control method is the fixed-step perturbation observation method described in CN111509865B. It can be seen that if the amplitude of the final three-point oscillation stage is to be avoided, the perturbation step size needs to be reduced; if the speed of maximum efficiency tracking is to be increased, the perturbation step size needs to be increased. Therefore, the selection of the perturbation step size requires a trade-off between the oscillation amplitude and the tracking speed, which is not conducive to the stability of the system.

[0040] Therefore, in order to improve the speed of tracking the maximum efficiency point, the present invention adopts an improved perturbation observation-golden section algorithm to achieve fast maximum efficiency tracking. First, the current solution should be compared not only with the previous solution, but also with the next solution. If the current solution is better than both the previous solution and the next solution, the interval where the optimal solution is located can be determined; secondly, the maximum efficiency tracking is performed through the golden section search algorithm. The time complexity of the golden section search algorithm is usually O(log n), where n is the dimension of the solution space. Since the dimension of the solution space is usually greater than 1, O(log n) < O(n), so the perturbation observation-golden section method can improve the speed of maximum efficiency tracking to a certain extent, thereby improving the charging efficiency of the entire system.

[0041] In the wireless charging method provided by the present invention, the secondary side DC-DC converter is used to adjust the output to maintain a constant output voltage V required by the load. outOr the constant output current I required by the load out The input voltage of the primary side coupler is V in Only the primary side DC-DC converter performs iterative adjustment (reduction or increase), and the control method is to improve the disturbance detection-golden section algorithm until the output power of the input end battery (i.e., the input power P of the wireless power transmission system) reaches in ) reaches the minimum point. For a given output voltage or output current, reaching the minimum input power operating point is equivalent to reaching the maximum energy efficiency operating point (system efficiency η=P out / P in , then when P out unchanged, P in During the whole operation, the driving signal of the inverter is constant, with a duty cycle of 50% and a phase shift angle of 180°, so as to better ensure that the system is in a soft switching state.

[0042] The advantages of the present invention are:

[0043] 1. The transmitting end of the wireless charging system of the present invention includes a power supply battery, a primary side controller, a primary side DC-DC converter, an inverter, a primary side compensation network and a primary side coupler, and the receiving end includes a pressure-bearing lithium battery, a secondary side controller, a secondary side DC-DC converter, a rectifier, a secondary side compensation network and a secondary side coupler; and the secondary side DC-DC converter controls the output current and voltage according to the pressure-bearing lithium battery load requirements, and the primary side DC-DC converter uses the improved disturbance detection-golden section algorithm proposed by the present invention to quickly achieve the maximum efficiency tracking of the wireless charging system. Conventional disturbance observation passes the current solution k only need to be compared with the previous solution k-1, so there will be Figure 2 The three-point oscillation in the final stage shown in range B in the figure; in the improved disturbance observation of the present invention, the current solution k needs to be compared not only with the previous solution k-1, but also with the next solution k+1. After judging the obtained interval, the golden section method is used to optimize the interval; since the golden section method is unique and has low time complexity and fast solution speed, it can quickly track the maximum efficiency and avoid three-point oscillation.

[0044] 2. Compared with the simple disturbance observation method, the disturbance observation-golden section wireless charging method proposed in the present invention can realize the rapid maximum efficiency tracking of the system without communication conditions and avoid the three-point oscillation existing in the disturbance observation method. At the same time, because no communication is required, it also avoids the different degrees of attenuation of electromagnetic waves caused by different underwater environmental temperatures, salinity and conductivity, resulting in long delays and poor stability of the communication system, reducing the cost, volume and complexity of the underwater wireless charging system, and improving its stability. In addition, since the proposed method does not involve mutual inductance, it can be unaffected by the docking situation on the system power transmission to a certain extent, and achieves the maximum efficiency transmission in this docking state, so it is still effective when the coupler is misaligned.

[0045] 3. Compared with conventional wireless charging methods, the wireless charging method for pressurized lithium batteries proposed in the present invention takes into account the impact of pressure on the internal resistance of the battery load, the actual available charge, etc., and improves the accuracy of tracking the optimal efficiency working point and judging the charging status. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the LCC-S compensation wireless charging system without communication proposed by the present invention;

[0047] Figure 2 The operating mechanism of the fixed-step maximum efficiency tracking disturbance observation method in the current wireless charging system;

[0048] Figure 3 This is a flow chart of the wireless charging method of the present invention;

[0049] Figure 4 : is the relationship between the system efficiency of the present invention and the output voltage range of the primary side DC-DC converter; (a) is case A, (b) is case B, and (c) is case C;

[0050] Figure 5 To improve the optimal solution interval iteration process in the disturbance observation phase of the present invention;

[0051] Figure 6 It is the iterative calculation process of the golden section search phase of the present invention;

[0052] Figure 7 To compare the system efficiency when using the perturbation observation-golden section method and when not using this method;

[0053] Figure 8 For comparison between the perturbation observation-golden section method of the present invention and the traditional perturbation observation method, (a) load resistance R = 7.5Ω; (b) load resistance R = 12.5Ω; DETAILED DESCRIPTION

[0054] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0055] In order to achieve efficient and stable charging control under pressure, the wireless charging method for pressurized lithium batteries proposed in the present invention adopts the disturbance observation-golden section algorithm to determine the optimal efficiency working point and achieve stable tracking of the maximum charging efficiency. The method flow chart is as follows: Figure 3 As shown, it includes three steps: determining the stable output voltage range of the primary side DC-DC converter, determining the optimal efficiency working point, and judging whether the battery is fully charged. The specific steps are as follows.

[0056] Step 1: Determine the stable output voltage range of the primary-side DC-DC converter

[0057] Get the current SOC value of the pressurized lithium battery SOC 0 , Equivalent load resistance R under different pressures Li And the actual available charge C of the pressurized lithium battery with SOC=1 under different pressures i ;

[0058] The above SOC value refers to the amount of electricity that can be discharged at a certain temperature and discharge rate when the battery is not damaged.

[0059] Generally, the SOC is expressed as the ratio of the amount of charge that can be discharged by the battery to the rated capacity, as shown in formula (1).

[0060]

[0061] In the formula, C remain is the remaining charge of the battery at a certain discharge rate, C N is the total charge of the battery under normal pressure, that is, the rated capacity of the battery;

[0062] Usually, during the use of the pressurized lithium battery, the battery management system (BMS) is used for real-time management, and the SOC value SOC of the current pressurized lithium battery can be directly obtained. 0 ;

[0063] The pressure-bearing lithium battery is charged under different pressures, and the charging voltage V is set. out , and measure the battery charging current I according to the BMS i , calculate the equivalent load resistance R of the pressure-bearing lithium battery according to formula (2) Li , and finally the equivalent load resistance of the pressurized lithium battery under different pressures is obtained;

[0064]

[0065] At the same time, under different pressures, the pressure-bearing lithium battery with SOC=1 was subjected to a discharge experiment, and the actual available charge C released by the battery when it was completely discharged was recorded. i , and finally the actual available charge of the pressurized lithium battery under different pressures is obtained;

[0066] Step 1.2: Equivalent load resistance R under different pressures Li , the battery charging power P set by the wireless charging system out The voltage gain G set by the wireless charging system determines the stable output voltage range [V inmin , V inmax ]; specifically:

[0067] First, use formula (3) to calculate the charging power P out Equivalent load resistance R under different pressures Li The charging voltage V required by the system out , which is the output voltage of the wireless charging system;

[0068]

[0069] Secondly, use formula (4) to calculate the input voltage V of the wireless charging system inverter in , which is the output voltage of the primary-side DC-DC converter;

[0070]

[0071] Finally, the calculated minimum and maximum values ​​are selected to determine the stable output voltage range of the primary side DC-DC converter as [V inmin , V inmax ].

[0072] Step 2: Determine the best efficiency operating point

[0073] Step 2.1: Optimal solution existence judgment stage

[0074] Since the stable output voltage range of the primary-side DC-DC converter is a finite interval, this interval may be on the left side of the best efficiency point, on the right side of the best efficiency point, or include the best efficiency point, such as Figure 4 Therefore, it is necessary to determine whether the interval of the primary-side DC-DC converter output voltage contains the optimal solution before performing maximum efficiency tracking.

[0075] In the optimal solution existence judgment stage, according to the stable output voltage range of the primary side DC-DC converter determined in step 1, the minimum resolution of the primary side DC-DC converter output voltage is used as the disturbance step ΔV, and the primary side DC-DC converter is adjusted from the maximum output voltage V(1)=V inmax Start by decreasing twice with the minimum resolution, i.e. V(2) = V inmax -ΔV and V(3)=V(2)-ΔV, and calculate the corresponding input power P respectively in (1) P in (2) and P in (3). If P in (1) <P in (2) <P in (3), that is, Figure 4 In case (a) of A, the maximum output voltage of the primary side DC-DC converter is V inmax is the optimal point of system efficiency, the maximum efficiency tracking ends, and the process goes to step 3; otherwise, the process goes to step 2.2;

[0076] Step 2.2: Improve the perturbation observation phase

[0077] In the improved disturbance observation stage, the present invention improves the disturbance observation algorithm so that the current solution P in(k) Not only with the previous solution P in(k-1) Compare with the next solution P in(k+1) In order to increase the speed of maximum efficiency tracking, the step size of voltage change can be larger, that is, V (k) =V (k-1) -n*ΔV, where ΔV is the minimum resolution of the primary-side DC-DC converter output voltage, n*ΔV is ΔV', ΔV' = (V inmax -V inmin ) / 10, then, n=[(V inmax -V inmin ) / 10] / ΔV.

[0078] In the improved disturbance observation stage, if the relationship between the system efficiency and the output voltage range of the primary side DC-DC converter belongs to Figure 4 (b) Case B. In this case, if P in (k+1)>P in (k) <P in (k-1), the interval where the optimal solution is located is [V(k+1), V(k-1)], and go to step 2.3;

[0079] If P in (k+1)>P in (k)≥P in(k-1), the interval where the optimal solution is located is [V(k), V(k-1)], and go to step 2.3;

[0080] Figure 5 The iterative process of improving the optimal solution interval in the disturbance observation phase is shown. During the search process, if there is always P in (k+1) <P in (k) <P in (k-1), until V(k+1)≤V inmin , that is, belongs to Figure 4 In case (c) of C, the minimum output voltage of the primary side DC-DC converter is V inmin The optimal output voltage value for system efficiency is selected, the maximum efficiency tracking is completed, and the process goes to step 3.

[0081] Step 2.3: Golden Section Search Phase

[0082] After improving the perturbation observation phase, the interval where the optimal solution exists is obtained. The next step is to use the golden section search algorithm to find the optimal solution.

[0083] Golden section search is an accurate line search algorithm. When using the golden section search method, the second and third points constitute the golden section points of the initial interval, such as Figure 6 As shown in the figure, when the optimal solution interval is from the first point to the third point, the second point is exactly the golden section point of the new interval; when the optimal solution interval is from the second point to the fourth point, the third point is exactly the golden section point of the new interval. Therefore, the golden section point of the initial interval can be reused in the next iteration, greatly reducing the number of experiments.

[0084] The efficient and stable wireless charging method of the present invention can achieve faster maximum efficiency tracking. This is because in the improved disturbance observation stage, the step size of the voltage change can take a larger value, and the time complexity of the golden section search algorithm is lower than that of the disturbance observation method. In addition, the proposed disturbance observation-golden section method for maximum efficiency tracking can also effectively avoid the three-point oscillation existing in the disturbance observation method.

[0085] Step 3: Determine whether the pressurized lithium battery is fully charged

[0086] The optimal output voltage selected in step 2 is used as the input voltage to charge the pressure-bearing lithium battery, and the SOC value SOC of the pressure-bearing lithium battery is obtained in real time during the charging process. t , until SOC t =1, indicating that the pressure-bearing lithium battery is fully charged and charging stops;

[0087]

[0088] Where t is the charging time, It is the charging current at time t, C N is the total charge of the battery at normal pressure, ΔC is the error in the actual available charge of the battery caused by pressure change, C i The corresponding value can be selected according to the pressure borne by the pressure-bearing lithium battery, and then ΔC=C i -C N Calculate the difference between the actual available charge of the battery brought about by different pressures and the total charge of the battery under normal pressure.

[0089] Figure 7 The curves of system efficiency changing with load resistance, coupling coefficient, and whether the perturbation observation-golden section algorithm is used are shown. It can be seen that the system efficiency decreases with the increase of load resistance, because the efficiency of the wireless charging system is related to the load resistance. When the coupling coefficient k is 0.45 or 0.50, the system efficiency using the perturbation observation-golden section algorithm is higher than the system efficiency when it is not used. Therefore, it can be verified that the perturbation observation-golden section algorithm improves the system efficiency. In addition, it can be proved that the proposed method is still effective when the coupling coefficient changes (i.e., coupler offset).

[0090] In the disturbance observation-golden section algorithm, in the optimal solution existence judgment stage, the voltage V in The step size of the change is the same as that of the traditional P&O method (Perturb and Observe, i.e., the traditional perturbation observation method), i.e., ΔV, where ΔV is the minimum output resolution of the primary-side DC-DC converter. In the improved ramp phase, the voltage V in The step size of the change is (V inmax -V inmin ) / 10 to speed up the maximum efficiency tracking.

[0091] Figure 8 The input power P of the perturbation observation-golden section and traditional perturbation observation methods is shown under the conditions of coupling coefficient k = 0.45, 0.50 and load resistance R = 7.5, 12.5. in The relationship curve with the number of iterations.

[0092] from Figure 8 It can be clearly seen from (a) and (b) that the traditional perturbation observation method will have three-point oscillation in the final stage, while the perturbation observation-golden section method of the present invention can effectively avoid oscillation. Figure 8 Under the same number of iterations, the P of the perturbation observation-golden section method in The value is smaller than that of the traditional perturbation observation method, which means it is more efficient.

[0093] In summary, compared with the traditional wireless charging method, the wireless charging method proposed in the present invention uses pressurized lithium batteries as the charging object for the first time, realizes the rapid maximum efficiency tracking of the system without communication conditions, and avoids the different degrees of attenuation of electromagnetic waves caused by different underwater environmental temperatures, salinity and conductivity, resulting in long delays and poor stability of the communication system, thereby reducing the cost, volume and complexity of the underwater wireless charging system and improving its stability. In addition, since the proposed method does not involve mutual inductance, it is still effective when the coupler is misaligned.

Claims

1. An efficient and stable wireless charging method for pressurized lithium batteries, characterized in that: The following steps are involved: Step 1: Determine the stable output voltage range of the primary-side DC-DC converter Step 1.1: Obtain the current SOC value SOC0 of the pressurized lithium battery and the equivalent load resistance R under different pressures Li And the actual available charge C of the pressurized lithium battery with SOC=1 under different pressures i ; Step 1.2: Equivalent load resistance R under different pressures Li , the battery charging power P set by the wireless charging system out The voltage gain G set by the wireless charging system determines the stable output voltage range [V inmin , V inmax ]; Step 2: Determine the best efficiency operating point Step 2.1: Optimal solution existence judgment stage According to the stable output voltage range of the primary side DC-DC converter determined in step 1, the maximum output voltage V inmax Start by decreasing it twice with its minimum resolution, taking V(1) = V inmax 、V(2)=V inmax -ΔV, V(3)=V(2)-ΔV as input voltage, and calculate the corresponding input power P respectively in (1) P in (2) and P in (3); where ΔV is the minimum resolution of the primary-side DC-DC converter output voltage; If P in (1) <P in (2) <P in (3), the maximum output voltage V of the primary side DC-DC converter is inmax The optimal output voltage value for system efficiency is selected, the maximum efficiency tracking is completed, and the process goes to step 3; Otherwise, go to step 2.2; Step 2.2: Improve the perturbation observation phase In the stable output voltage range of the primary side DC-DC converter, the output voltage is in descending order (V inmax -V inmin ) / 10 as the step size ΔV' is gradually reduced, and V(k-1)=V(k-2)-ΔV', V(k)=V(k-1)-ΔV', V(k+1)=V(k)-ΔV' are used as the input voltages in turn, and the corresponding input powers P are calculated respectively. in (k-1), P in (k) and P in (k+1); the value of k ranges from 2 to 9. During the iteration process: If P in (k+1)>P in (k) <P in (k-1), then the optimal output voltage selection range for system efficiency is [V(k+1), V(k-1)], and go to step 2.3; If P in (k+1)>P in (k)≥P in (k-1), then the optimal output voltage selection range for system efficiency is [V(k), V(k-1)], and go to step 2.3; If there is always P in (k+1) <P in (k) <P in (k-1), until V(k+1)≤V inmin , then the minimum output voltage V of the primary side DC-DC converter inmin The optimal output voltage value for system efficiency is selected, the maximum efficiency tracking is completed, and the process goes to step 3; Step 2.3: Golden Section Search Phase Use the golden section search algorithm to select the optimal output voltage selection value within the optimal output voltage selection range selected in step 2.2, and proceed to step 3; Step 3: Determine whether the pressurized lithium battery is fully charged The optimal output voltage selected in step 2 is used as the input voltage to charge the pressure-bearing lithium battery, and the SOC value SOC of the pressure-bearing lithium battery is obtained in real time during the charging process. t , until SOC t =1, indicating that the pressure-bearing lithium battery is fully charged and charging stops; Where t is the charging time, I t is the charging current at time t, C N is the total charge of the battery at normal pressure, ΔC is the error in the actual available charge of the battery caused by pressure change, ΔC = C i -C N .

2. An efficient and stable wireless charging system for pressurized lithium batteries, characterized by: Includes a transmitter and a receiver; The transmitting end includes a power supply battery, a primary side controller, a primary side DC-DC converter, an inverter, a primary side compensation network and a primary side coupler; The positive and negative electrodes of the power supply battery are connected to the positive and negative input ports of the primary side DC-DC converter, the output port of the primary side DC-DC converter is connected to the input port of the inverter, the output port of the inverter is connected to the input port of the primary side compensation network, and the output port of the primary side compensation network is connected to the primary side coupler; wherein the primary side controller controls the output voltage of the primary side DC-DC converter through the PWM duty cycle; The receiving end includes a pressure-bearing lithium battery, a secondary-side controller, a secondary-side DC-DC converter, a rectifier, a secondary-side compensation network, and a secondary-side coupler; The output port of the secondary side coupler is connected to the input port of the secondary side compensation network, the output port of the secondary side compensation network is connected to the input port of the rectifier, the output port of the rectifier is connected to the input port of the secondary side DC-DC converter, and the positive and negative output ports of the secondary side DC-DC converter are connected to the positive and negative electrodes of the pressure-bearing lithium battery; The primary side coupler and the secondary side coupler are coupled after the transmitting end and the receiving end are connected, and the two wirelessly transmit electric energy through electromagnetic induction generated by high-frequency alternating current; The secondary-side DC-DC converter controls the output current and voltage according to the pressure-bearing lithium battery load requirements; The primary-side DC-DC converter adopts the efficient and stable wireless charging method of claim 1 to achieve maximum efficiency tracking of the wireless charging system and find the optimal output voltage selection value.

3. A wireless charging system according to claim 2, characterized in that: The drive signal of the inverter is constant, the duty cycle is 50%, and the phase shift angle is 180°.

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