Multi-parameter online identification energy efficiency improvement method for underwater wireless transmission system

Abstract

The invention discloses an underwater wireless transmission system multi-parameter online identification energy efficiency improvement method, which comprises the following steps: firstly, constructing a topological graph of an underwater wireless power transmission system, when the system works normally, acquiring voltage U1 and current I1 of a transmitting coil, and calculating input impedance; determining an equivalent circuit, and establishing an equation of a mutual inductor M, a bridging capacitor Ce and an equivalent load RLe through the voltage U1 and the current I1; and solving the mutual inductance M, the bridging capacitor Ce and the equivalent load RLe to realize multi-parameter identification. According to the technology, the driving frequency of a system does not need to be changed, a complex circuit does not need to be added, and the identification requirements of mutual inductance, bridging capacitance and load can be rapidly and accurately met. Afterwards, the working state of the system is judged according to the obtained bridging capacitance value, the method can accurately control the power and efficiency of the system, and the stability and reliability of the charging process are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless power transmission, and specifically relates to a method for online identification of multiple parameters and energy efficiency improvement of an underwater wireless transmission system. Background Art

[0002] Autonomous Underwater Vehicles (AUVs) play an important role in both military and civilian applications such as ocean hydrological exploration and underwater mine hunting. However, their endurance is limited, requiring frequent recovery for charging, and limited by their load capacity, it is difficult to realize the advantages of unmanned and intelligent operation. The emergence of wireless power transmission technology provides an effective solution to this problem, which can effectively avoid problems such as electric leakage and water seepage, and promote the wide application of AUVs.

[0003] In the background of actual engineering applications, due to the wave fluctuations, the coils of the wireless power transmission system are misaligned during transmission, which causes changes in the mutual inductance and bridging capacitance between the two coils of the system. Due to the change of the energy receiving device, the load changes. The changes in mutual inductance, bridging capacitance and load will affect the transmission performance of the system, reduce the service life of the working equipment, reduce the transmission efficiency and power during charging, and cause instability and unreliability during the charging process. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for online identification of multiple parameters and energy efficiency improvement of an underwater wireless transmission system. This method can accurately control the power and efficiency of the system, and improve the stability and reliability of the charging process.

[0005] To achieve the above purpose, a method for online identification of multiple parameters and energy efficiency improvement of an underwater wireless transmission system of the present invention includes the following steps:

[0006] Step 1, construct a topology diagram of an underwater wireless power transmission system, including: a DC power supply, a DC-AC converter, a transmitting coil, a receiving coil, an AC-DC converter, and an equivalent load of a charging device; the DC power supply is connected to the input end of the DC-AC converter, the output end of the DC-AC converter is connected to the input end of the transmitting coil, the output end of the transmitting coil is disposed opposite to the input end of the receiving coil, the output end of the receiving coil is connected to the input end of the AC-DC converter, and the output end of the AC-DC converter is connected to the equivalent load of the charging device;

[0007] Step 2, when the system is operating normally, obtain the voltage U1 and current I1 of the transmitting coil, and calculate the input impedance;

[0008] Step 3, determine the equivalent circuit, the equivalent circuit includes the voltage U1, and one end of the voltage U1 is sequentially connected in series with the parasitic resistance R1 of the primary compensation capacitor, and the primary transmitting coil compensation capacitor C P, the compensation capacitor C of the primary side transmitting coil P The other end of is divided into two paths. One path is successively connected in series with the equivalent inductance L of the primary side transmitting coil P , the parasitic resistance R of the primary side transmitting coil P , the parasitic resistance R of the primary side transmitting coil P The other end of is divided into two paths. One path is connected to the voltage U1 to form the first mesh. The other path of the compensation capacitor C of the primary side transmitting coil P is connected in series with the bridging capacitor C e , the other end of the bridging capacitor C e is divided into two paths. One path is successively connected in series with the equivalent inductance L of the secondary side transmitting coil S , the parasitic resistance R of the secondary side transmitting coil S , the parasitic resistance R of the secondary side transmitting coil S The other end of is divided into two paths. One path is connected in series with the bridging capacitor C e ' and then connected to the other path of the parasitic resistance R of the primary side transmitting coil P to form the second mesh; The other path of the bridging capacitor C e is successively connected in series with the compensation capacitor C of the secondary side transmitting coil S , the parasitic resistance R2 of the secondary side compensation capacitor, and the equivalent load R of the system Le , and finally connected to the other path of the parasitic resistance R of the secondary side transmitting coil S to form the third mesh; Establish equations for the mutual inductance M, the bridging capacitor C e and the equivalent load R Le through the voltage U1 and the current I1;

[0009] Step Four, according to the voltage U1 and the current I1 obtained in Step Two, substitute them into the system of equations in Step Three to solve for the mutual inductance M, the bridging capacitor C e and the equivalent load R Le , to achieve multi-parameter identification;

[0010] Step Five, after identifying the value of the bridging capacitor C e of the system, according to the magnitude of the value of the bridging capacitor C e of the system, analyze what working state the system is in, and achieve targeted energy efficiency optimization for each working state; The working states include: the working state of the capacitive decoupling underwater wireless power transmission system and the working state of the capacitive coupling underwater wireless power transmission system; The energy efficiency optimization includes constant current output characteristic optimization and maximum efficiency and output power point tracking.

[0011] As a further solution of the present invention: The voltage U1 and the current I1 in the above Step Two respectively represent the voltage vector and the current vector of the transmitting coil (3) during normal operation.

[0012] As a further solution of the present invention: In the above Step Three, solve for the mutual inductance M, the bridging capacitor C eand the equivalent load R Le The equations are as follows:

[0013] The equation for solving the single variable mutual inductance M is as follows:

[0014]

[0015] Z2 = -R p -jωL p +jωM (4)

[0016] Z3 = -jωM (5)

[0017]

[0018] Z5 = -R s -jωL s +jωM (7)

[0019]

[0020] Where j is the imaginary unit, ω is the system driving angular frequency, Z1, Z2, Z3, Z4, Z5 and Z6 are the impedances corresponding to the currents in each mesh of the equivalent circuit, and T1 is an intermediate variable;

[0021] The single variable bridging capacitor C e The solution is as follows:

[0022]

[0023] T2 = MωB - L p C + jD + E (10)

[0024]

[0025] Where T 2、 A, B, C, D and E are intermediate variables;

[0026] The single variable equivalent load R Le The solution is as follows:

[0027]

[0028] T3 = B1 - 2Z2Z3Z5 + Z1Z4Z5 + C1 (13)

[0029]

[0030] Where T 3、 A1, B, C1, D1 and E1 are intermediate variables;

[0031] Multiple variables: mutual inductance M, bridging capacitor C e, Equivalent load R Le Solution of:

[0032] Transform Equation (15) to obtain Equation (17):

[0033]

[0034] Construct the function as Equation (17):

[0035]

[0036] In the formula, T is an intermediate variable. For the function Γ, the parameter region where the optimal solution appears may not be within the numerical range that conforms to the actual engineering situation. Therefore, it is necessary to constrain the ranges of the variables M, C e and R Le ; Set the ranges of M, C e and R Le as shown in Equation (18):

[0037]

[0038] Optimize the objective function to obtain the minimum value of the equation and the corresponding variables as shown in Equation (19). At this time, the corresponding Μ1, C e1 and R Le1 are the solutions corresponding to the Equation (19),

[0039] Γ(M1, C e1 , R Le1 ) = min{Γ(M, C e , R Le )} = 0 (19).

[0040] As a further solution of the present invention:

[0041] The DC-AC converter (2) adopts a single-phase full-bridge inverter circuit. During the process of mutual inductance M identification, the output frequency of the DC-AC converter (2) remains fixed, and the output voltage is a square wave with a fixed duty cycle. The output voltage satisfies the formula where U ab is the fundamental effective value of the output voltage of the DC-AC converter (2), and V DC is the output DC voltage value of the DC power supply (1);

[0042] The transmitting coil (3) includes a transmitting coil L P and a compensation capacitor C P connected in series; One end of the compensation capacitor C P is connected to an output end of the DC-AC converter (2), and the other end of the compensation capacitor C P is connected to the transmitting coil LP is connected to one end; the transmitting coil L P The other end is connected to another output end of the DC-AC converter (2);

[0043] The receiving coil (4) includes a transmitting coil L connected in series with each other S and a compensation capacitor C S ; The compensation capacitor C S One end is connected to an input end of the AC-DC converter (5), and the compensation capacitor C S The other end is connected to one end of the transmitting coil L S is connected to one end; the transmitting coil L S The other end is connected to another input end of the AC-DC converter 5;

[0044] The AC-DC converter (5) includes a single-phase uncontrolled rectifier circuit and a filter capacitor C filter , The single-phase uncontrolled rectifier circuit is connected in parallel with the filter capacitor C filter ; The single-phase uncontrolled rectifier circuit includes four uncontrolled diodes. Two uncontrolled diodes form a bridge arm. There are a total of two bridge arms, and the two bridge arms are connected in parallel.

[0045] As a further solution of the present invention: The multi-parameter online identification energy efficiency improvement method is applied to four working modes. Working mode one is when the bridging capacitor C e and the equivalent load R Le are known, according to formulas (3)-(8), the expression of the mutual inductance M can be solved as (1) and (2); Performing mathematical analysis on equations (1) and (2), solving the system of equations (1) can obtain the complex solutions a1 and a2 of the mutual inductance M with the negative roots omitted. Since the imaginary parts of a1 and a2 are much smaller than the real parts, they can be ignored, and it is considered that the real parts of a1 and a2 are the solution values of the mutual inductance M; At the same time, considering that the actual mutual inductance is positive, taking the positive solutions of a1 and a2, the solution of the mutual inductance M can be obtained; Working mode two is when the mutual inductance M and the equivalent load R Le are known, according to formulas (3)-(8), the expression of the bridging capacitor C e can be solved as (9), (10) and (11). Performing mathematical analysis on equations (9), (10) and (11), the solution of the bridging capacitor C e can be obtained; Working mode three is when the mutual inductance M and the bridging capacitor C e are known, according to formulas (3)-(8), the expression of the equivalent load R Le can be solved as (12), (13) and (14). Performing mathematical analysis on equations (12), (13) and (14), the solution of the equivalent load R Le can be obtained; Working mode four is to use the mutual inductance M, the bridging capacitor C e and the equivalent load R LeThe recognition problem is transformed into the problem of optimizing the above parameter values, and the problem of solving the non-linear equation is transformed into the numerical optimization problem of the function to realize the mutual inductance M, the bridging capacitance C e and the equivalent load R Le for simultaneous identification of multiple parameters.

[0046] As a further solution of the present invention: the transmission characteristic equation of the capacitive decoupled underwater wireless power transmission system includes:

[0047]

[0048] Z2 = -R p -jωL p +jωM (21)

[0049] Z3 = -jωM (22)

[0050]

[0051] Z5 = -R s -jωL s +jωM (24)

[0052]

[0053] P out = |I3| 2 R Le (28)

[0054]

[0055] where I1, I2 and I3 are the currents of each mesh respectively, P out is the output power of the system, η is the coil efficiency of the system, Z in is the input impedance. According to equations (20)-(25), the impedance of each element of the impedance matrix can be obtained, and then according to equations (26) and (27), the mesh currents of the capacitive decoupled underwater wireless power transmission system are solved. At this time, I2 is set to 0 to realize the decoupling of the bridging capacitance of the system, and then the output characteristics of the system are solved according to equations (28) to (30);

[0056] The transmission characteristic equation of the capacitive coupled underwater wireless power transmission system includes:

[0057]

[0058] Z2 = -R p -jωL p +jωM (32)

[0059] Z3 = -jωM (33)

[0060]

[0061] Z5 = -R s -jωL s +jωM (35)

[0062]

[0063] P out = |I3| 2 R Le (39)

[0064]

[0065] According to equations (31)-(36), the impedances of each element of the impedance matrix can be obtained. Then, according to equations (37) and (38), the mesh currents of each mesh of the capacitive-coupled underwater wireless power transmission system are solved. At this time, the formula for I2 is derived and substituted into the system to realize the cross-connected capacitance coupling of the system. Then, according to equations (39) to (41), the output characteristics of the system are solved;

[0066] According to the output characteristic formula of the capacitive-decoupled underwater wireless power transmission system, the constant current output of the system is realized. When the constant current output is achieved, the output current expression of the system is:

[0067]

[0068] According to the output characteristic formula of the capacitive-coupled underwater wireless power transmission system, the maximum efficiency and output power tracking of the system are realized; at this time, the output power and coil efficiency expressions of the system are:

[0069] P out = |I3| 2 R Le (43)

[0070]

[0071] Compared with the existing technology, the present invention provides a method for improving the energy efficiency of online identification of multiple parameters of an underwater wireless transmission system. By obtaining the input voltage U1 and current I1 of the system, the mutual inductance M, cross-connected capacitance C e and equivalent load R LeThis technology can quickly and accurately meet the identification requirements of mutual inductance, bridging capacitance, and load without changing the driving frequency of the system or adding complex circuits. Subsequently, based on the magnitude of the calculated bridging capacitance value, the operating state of the system is determined. Constant-current optimization is performed on the capacitive decoupling underwater wireless power transmission system, and maximum efficiency and maximum output power point tracking optimization are carried out on the capacitive coupling underwater wireless power transmission system to more specifically achieve system-level energy efficiency optimization analysis. This method can accurately control the power and efficiency of the system, improving the stability and reliability of the charging process. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 is the topology diagram of the underwater wireless power transmission system of the present invention.

[0073] Figure 2 is the equivalent circuit diagram of the topology diagram of the underwater wireless power transmission system of the present invention.

[0074] Figure 3 is the single-parameter identification flowchart of the present invention.

[0075] Figure 4 is the multi-parameter identification flowchart of the present invention.

[0076] Figure 5 is the parameter identification diagram of the mutual inductance between the system coils of the present invention under various working conditions.

[0077] Figure 6 is the parameter identification diagram of the bridging capacitance between the system coils of the present invention under various working conditions.

[0078] Figure 7 is the parameter identification diagram of the load of the system of the present invention under various working conditions.

[0079] Figure 8 is the solution diagram of the maximum efficiency and maximum output power load curve of the capacitive coupling wireless power transmission system of the present invention.

[0080] Figure 9 is the constant current output characteristic curve diagram of the capacitive decoupling wireless power transmission system of the present invention.

[0081] In the figure: 1. DC power supply, 2. DC-AC converter, 3. Transmitting coil, 4. Receiving coil, 5. AC-DC converter, 6. Equivalent load of the charging device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0082] The present invention will be further described below with reference to the accompanying drawings.

[0083] As Figure 1 shown, a method for improving the energy efficiency of multi-parameter online identification of an underwater wireless transmission system includes the following steps:

[0084] Step 1: Construct the topology diagram of the underwater wireless power transmission system, including: DC power supply 1, DC-AC converter 2, transmitting coil 3, receiving coil 4, AC-DC converter 5, and charging device equivalent load 6; the DC power supply 1 is connected to the input end of the DC-AC converter 2, the output end of the DC-AC converter 2 is connected to the input end of the transmitting coil 3, the output end of the transmitting coil 3 is arranged opposite to the input end of the receiving coil 4, the output end of the receiving coil 4 is connected to the input end of the AC-DC converter 5, and the output end of the AC-DC converter 5 is connected to the charging device equivalent load 6;

[0085] Step 2: When the system is operating normally, obtain the voltage U1 and current I1 of the transmitting coil 3, and calculate the input impedance;

[0086] Step 3: Determine the equivalent circuit, as shown in Figure 2 the equivalent circuit includes voltage U1, one end of voltage U1 is sequentially connected in series with the primary compensation capacitor parasitic resistance R1, the primary transmitting coil compensation capacitor C P , the other end of the primary transmitting coil compensation capacitor C P is divided into two paths, one path is sequentially connected in series with the primary transmitting coil equivalent inductance L P , the primary transmitting coil parasitic resistance R P , the other end of the primary transmitting coil parasitic resistance R P is divided into two paths, one path is connected to voltage U1 to form the first mesh, the other path of the primary transmitting coil compensation capacitor C P is connected in series with the bridging capacitor C e , the other end of the bridging capacitor C e is divided into two paths, one path is sequentially connected in series with the secondary transmitting coil equivalent inductance L S , the secondary transmitting coil parasitic resistance R S , the other end of the secondary transmitting coil parasitic resistance R S is divided into two paths, one path is connected in series with the bridging capacitor C e ' and then connected to the other path of the primary transmitting coil parasitic resistance R P to form the second mesh; the other path of the bridging capacitor C e is sequentially connected in series with the secondary transmitting coil compensation capacitor C S , the secondary compensation capacitor parasitic resistance R2, the equivalent load R of the system Le , and finally connected to the other path of the secondary transmitting coil parasitic resistance R S to form the third mesh; since the bridging capacitor C e and the bridging capacitor C e ' are of comparable size, so only the bridging capacitor C e needs to be solved. According to Kirchhoff's law, establish the mutual inductance M and the bridging capacitor C through voltage U1 and current I1e and the equivalent load R Le of the equations;

[0087] Step 4: Substitute the voltage U1 and current I1 obtained in Step 2 into the system of equations in Step 3 to solve for the mutual inductance M, the bridging capacitor C e and the equivalent load R Le , to achieve multi-parameter identification.

[0088] The voltage U1 and current I1 in Step 2 respectively represent the voltage vector and current vector of the transmitting coil 3 during normal operation.

[0089] In Step 3, to solve for the mutual inductance M, the bridging capacitor C e and the equivalent load R Le the equations are as follows:

[0090] The equation for solving the single variable mutual inductance M is as follows:

[0091]

[0092] Z2 = -R p -jωL p +jωM (4)

[0093] Z3 = -jωM (5)

[0094]

[0095] Z5 = -R s -jωL s +jωM (7)

[0096]

[0097] where j is the imaginary unit, ω is the system driving angular frequency, Z1, Z2, Z3, Z4, Z5 and Z6 are Figure 2 the impedances corresponding to the currents in each mesh in

[0098] The solution for the single variable bridging capacitor C e is as follows:

[0099]

[0100] T2 = MωB - L p C + jD + E (10)

[0101]

[0102] where T 2、 A, B, C, D and E are intermediate variables.

[0103] Single-variable equivalent load R Le is solved as follows:

[0104]

[0105] T3 = B1 - 2Z2Z3Z5 + Z1Z4Z5 + C1 (13)

[0106]

[0107] In the formula, T 3、 A1, B1, C1, D1, and E1 are intermediate variables.

[0108] Multiple variables: mutual inductance M, shunt capacitance C e , equivalent load R Le is solved as follows:

[0109] Transform equation (15) to obtain equation (17):

[0110]

[0111] Construct a function as in equation (17):

[0112]

[0113] In the formula, T is an intermediate variable. For the function Γ, the parameter region where the optimal solution appears may not be within the numerical range that conforms to the actual engineering situation. Therefore, it is necessary to constrain the ranges of the variables M, C e and R Le . Constrain the ranges of M, C e and R Le as shown in equation (18).

[0114]

[0115] Among them, the maximum and minimum values of each parameter depend on the parameter fluctuation limit value in the actual engineering situation. Optimize the objective function to obtain the minimum value of the equation and the corresponding variables as shown in equation (19). At this time, the corresponding Μ1, C e1 and R Le1 are the solutions corresponding to equation (19).

[0116] Γ(M1, C e1 , R Le1 ) = min{Γ(M, C e , R Le )} = 0 (19)

[0117] The DC-AC converter 2 adopts a single-phase full-bridge inverter circuit. During the process of mutual inductance M identification, the output frequency of the DC-AC converter 2 remains fixed, and the output voltage is a square wave with a fixed duty cycle. The output voltage satisfies the formula where U ab is the effective value of the fundamental wave of the output voltage of the DC-AC converter 2, in V DC is the output DC voltage value of the DC power supply 1.

[0118] The transmitting coil 3 includes a transmitting coil L P and a compensation capacitor C P connected in series; one end of the compensation capacitor C P is connected to an output end of the DC-AC converter 2, and the other end of the compensation capacitor C P is connected to one end of the transmitting coil L P ; the other end of the transmitting coil L P is connected to the other output end of the DC-AC converter 2.

[0119] The receiving coil 4 includes a transmitting coil L S and a compensation capacitor C S connected in series; one end of the compensation capacitor C S is connected to an input end of the AC-DC converter 5, and the other end of the compensation capacitor C S is connected to one end of the transmitting coil L S ; the other end of the transmitting coil L S is connected to the other input end of the AC-DC converter 5.

[0120] The AC-DC converter 5 includes a single-phase uncontrolled rectifier circuit and a filter capacitor C filter , and the single-phase uncontrolled rectifier circuit is connected in parallel with the filter capacitor C filter ; the single-phase uncontrolled rectifier circuit includes four uncontrolled diodes, with two uncontrolled diodes forming one arm, a total of two arms, and the two arms are connected in parallel.

[0121] The multi-parameter online identification energy efficiency improvement method is applied to four working modes. Working mode one is when the bridging capacitor C e and the equivalent load R Le are known, and according to formulas (3)-(8), the expression of the mutual inductance M can be solved as (1) and (2); performing mathematical analysis on formulas (1) and (2) and solving the system of equations, the complex solutions a1 and a2 of the mutual inductance M with the negative roots omitted can be obtained. Since the imaginary parts of a1 and a2 are much smaller than the real parts, they can be ignored, and it is considered that the real parts of a1 and a2 are the solution values of the mutual inductance M; at the same time, considering that the actual mutual inductance is positive, taking the positive solutions of a1 and a2, the solution of the mutual inductance M can be obtained; working mode two is when the mutual inductance M and the equivalent load R LeWhen known, the bridging capacitor C can be solved according to formulas (3)-(8). e The expressions of C are (9), (10) and (11). By performing mathematical analysis on equations (9), (10) and (11), the solution of the bridging capacitor C can be obtained. e Operating mode three is that when the mutual inductance M and the bridging capacitor C e are known, the equivalent load R can be solved according to formulas (3)-(8). Le The expressions of R are (12), (13) and (14). By performing mathematical analysis on equations (12), (13) and (14), the solution of the equivalent load R can be obtained. Le Operating mode four is to transform the identification problem of the mutual inductance M, the bridging capacitor C e and the equivalent load R Le into a problem of optimizing the above parameter values, and transform the problem of solving the nonlinear equation into a numerical optimization problem of a function to realize the simultaneous identification of multiple parameters of the mutual inductance M, the bridging capacitor C e and the equivalent load R Le .

[0122] Step five, after identifying the value of the bridging capacitor C e in the identification system, analyze what working state the system is in according to the magnitude of the value of the system bridging capacitor C e to achieve the targeted performance energy efficiency optimization of each working state. The working states include: the working state of the capacitive decoupling underwater wireless power transmission system and the working state of the capacitive coupling underwater wireless power transmission system. The energy efficiency optimization includes the optimization of the constant current output characteristic and the tracking of the maximum efficiency and output power point.

[0123] The transmission characteristic equations of the capacitive decoupling underwater wireless power transmission system include:

[0124]

[0125] Z2 = -R p -jωL p +jωM (21)

[0126] Z3 = -jωM (22)

[0127]

[0128] Z5 = -R s -jωL s +jωM (24)

[0129]

[0130] P out = |I3| 2 R Le (28)

[0131]

[0132] Where I1, I2, and I3 are the currents of each mesh, respectively, and P out is the output power of the system, η is the coil efficiency of the system, and Z in is the input impedance. According to Equations (20)-(25), the impedances of each element of the impedance matrix can be obtained. Then, according to Equations (26) and (27), the currents of each mesh of the capacitive decoupled underwater wireless power transmission system are solved. At this time, I2 is set to 0 to achieve the cross-connected capacitance decoupling of the system. Then, according to Equations (28) to (30), the output characteristics of the system are solved.

[0133] The transmission characteristic equations of the capacitive coupled underwater wireless power transmission system include:

[0134]

[0135] Z2 = -R p -jωL p +jωM (32)

[0136] Z3 = -jωM (33)

[0137]

[0138] Z5 = -R s -jωL s +jωM (35)

[0139]

[0140] P out = |I3| 2 R Le (39)

[0141]

[0142] According to Equations (31)-(36), the impedances of each element of the impedance matrix can be obtained. Then, according to Equations (37) and (38), the currents of each mesh of the capacitive coupled underwater wireless power transmission system are solved. At this time, the formula for I2 is derived and substituted into the system to achieve the cross-connected capacitance coupling of the system. Then, according to Equations (39) to (41), the output characteristics of the system are solved.

[0143] According to the output characteristic formula of the capacitive decoupled underwater wireless power transmission system, the constant current output of the system is realized. When the constant current output is achieved, the output current expression of the system is:

[0144]

[0145] According to the output characteristic formula of the capacitive coupling underwater wireless power transmission system, the maximum efficiency and output power tracking of the system are realized. At this time, the expressions of the output power and coil efficiency of the system are as follows:

[0146] P out =|I3| 2 R Le (43)

[0147]

[0148] That is, after identifying the parameters of the bridging capacitor, according to the size of the bridging capacitor of the coupler, the system will be in different working states. Working state 1: When the bridging capacitor is very small, the transmission characteristics of the system are decoupled into a non-capacitive-coupled wireless power transmission system. At this time, the working characteristics approach those in air, and the system energy efficiency optimization goal is the constant current output of the system. Working state 2: When the bridging capacitor cannot be ignored, the transmission characteristics of the system show a trend of first increasing and then decreasing with the load. The energy efficiency optimization goal changes to finding the maximum efficiency point and the maximum output power point. The online mutual inductance identification method of the underwater wireless power supply system based on the relay coil is applied to the underwater AUV wireless power transmission.

[0149] Embodiment:

[0150] Step 1: Construct the circuit topology structure diagram of the underwater wireless power transmission system as shown in Figure 1 including a DC power supply 1, a DC-AC converter 2, a transmitting coil 3, a receiving coil 4, an AC-DC converter 5, and a charging device equivalent load 6; the DC power supply 1 is connected to the input end of the DC-AC converter 2, the output end of the DC-AC converter 2 is connected to the input end of the transmitting coil 3, the output end of the transmitting coil 3 is oppositely arranged with the input end of the receiving coil 4, the output end of the receiving coil 4 is connected to the input end of the AC-DC converter 5, and the output end of the AC-DC converter 5 is connected to the charging device equivalent load 6.

[0151] The DC input voltage V of the system DC is 50V, the driving frequency of the system is 92.8 kHz, the transmitting coil L P , the receiving coil L S are both wound with Litz wire to reduce the resistance value of the coil, and the inductance values are both 86.5 uH. The compensation capacitors C P , C S are both 34 nF. At a high frequency of 92.8 kHz, the resistance R of the transmitting coil P is 0.33 W, the resistance R of the receiving coil S = 0.45 W, and the parasitic resistances R1 and R2 of the compensation capacitor of the transmitting coil and the compensation capacitor of the receiving coil are 0.1 W. In this embodiment, it is assumed that the transmitting coil L Pand the mutual inductance M between the relay coil L S is 34.335 uH, and the equivalent bridging capacitance C e between the transmitting coil and the receiving coil L = 2.5426 nF, and the system load R Le = 50 W, then the equivalent load R

[0152] Step 2: When the system is operating normally, obtain the voltage U1 and current I1 of the transmitting coil 3, and calculate the input impedance;

[0153] Step 3: Determine the equivalent circuit, as Figure 2 shown. According to Kirchhoff's law, establish equations for the mutual inductance M, the bridging capacitance C e and the equivalent load R Le using the voltage U1 and current I1; solve for the single variable mutual inductance M according to formulas (1)-(8); solve for the single variable bridging capacitance C e according to formulas (9)-(11), and solve for the single variable equivalent load R Le according to formulas (12)-(14); the solutions for the multiple variables M, C e and R Le are based on equations (15)-(18);

[0154] Step 4: Substitute the voltage U1 and current I1 obtained in Step 2 into the system of equations in Step 3 to obtain the mutual inductance M in Working Mode 1, the bridging capacitance C e in Working Mode 2, the load R Le in Working Mode 3, and the M, C e and R Le in Working Mode 4, to achieve the identification of multiple parameters. The implementation process refers to Figure 3 and Figure 4 . The specific method is as follows:

[0155] Working Mode 1: According to the obtained voltage U1 and current I1, calculate Z1, Z2, Z3, Z4, Z5, Z6, and T1 in formulas (2)-(8). Then substitute these parameters into formula (1) to obtain the mutual inductance M.

[0156] Working Mode 2: According to the obtained voltage U1 and current I1, calculate Z1, Z2, Z3, Z4, Z5, Z6, T2, A, B, C, D, and E in formulas (3)-(8), (10), and (11). Then substitute these parameters into formula (9) to obtain the bridging capacitance C e .

[0157] Operating mode three: According to the obtained voltage U1 and current I1, calculate Z1, Z2, Z3, Z4, Z5, Z6, T3, A1, B1, C1, D1, and E1 in formulas (3)-(8), (13), and (14). Then substitute these parameters into formula (12) to obtain the load R Le .

[0158] Operating mode four: According to the obtained voltage U1 and current I1, calculate Z1, Z2, Z3, Z4, Z5, Z6, and T in formulas (2)-(8). Then substitute these parameters into formulas (17) and (19) to obtain the mutual inductance M, the bridging capacitor C e and the load R Le .

[0159] In this example, the mutual inductance M obtained through operating mode one is 34.3352 uH, with an error of 0.0005% from the set value of 34.335 uH. The bridging capacitor C e obtained through operating mode two is 2.46648 nF, with an error of 2.9937% from the set value of 2.5426 nF. The mutual inductance R Le obtained through operating mode three is 44.937 Ω, with an error of 0.126% from the set value of 45 Ω. The mutual inductance M obtained through operating mode four is 34.3301 uH, C e is 2.4480 nF, and R Le is 44.9857 Ω. The errors from the set values are 0.0001%, 9.46%, and 0.0003% respectively. The recognition results are for reference Figures 5 to 7 . By comparing the experimental values with the assumed values, it can be found that the errors are small, fully demonstrating that the method used in the present invention is feasible and effective.

[0160] Step five: After identifying the value of the bridging capacitor of the system, analyze what working state the system is in according to the size of the system bridging capacitor value, and realize the targeted energy efficiency optimization of each working state. According to formulas (20)-(25), the impedance of each element of the impedance matrix can be obtained. Then, according to formulas (26) and (27), the mesh currents of each network of the capacitive decoupled underwater wireless power transmission system are solved. At this time, set I2 to 0 to realize the decoupling of the bridging capacitor of the system. Then, according to formulas (28) to (30), the output characteristics of the system are solved. According to formulas (31)-(36), the impedance of each element of the impedance matrix can be obtained. Then, according to formulas (37) and (38), the mesh currents of each network of the capacitive coupled underwater wireless power transmission system are solved. At this time, deduce the formula of I2 and substitute it into the system to realize the coupling of the bridging capacitor of the system. Then, according to formulas (39) to (41), the output characteristics of the system are solved.

[0161] According to the bridging capacitor obtained in step 4, it can be found that the system should be in the working state of the capacitive-coupled underwater wireless power transmission system at this time. Therefore, the transmission characteristics of the system are optimized according to the energy efficiency optimization goal of maximum power and maximum efficiency tracking.

[0162] Based on Figure 8 It can be known that the output power of the system shows an increasing trend according to the identified value of the bridging capacitor. Therefore, when the load corresponding to the maximum power is 100 ohms at this time, and the maximum efficiency is 94.86501%, which appears when the load is 19 ohms. Therefore, the energy efficiency optimization goal of the system should be to pursue the maximum efficiency. The load should be set to 19 ohms.

[0163] After setting the bridging capacitor to 0 nF, the system is in the working state of the capacitive-decoupled underwater wireless power transmission system. At this time, the energy efficiency optimization goal is to achieve a constant current output of the system. After that, according to Figure 9 , it can be found that after adjusting the working frequency of the system, the system realizes a constant current output under load fluctuations.

[0164] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An online identification energy efficiency improvement method for multi-parameters of an underwater wireless transmission system, characterized in that, It includes the following steps: Step 1: Construct a topology diagram of an underwater wireless power transmission system, including: a DC power supply (1), a DC-AC converter (2), a transmitting coil (3), a receiving coil (4), an AC-DC converter (5), and a charging device equivalent load (6); the DC power supply (1) is connected to the input end of the DC-AC converter (2), the output end of the DC-AC converter (2) is connected to the input end of the transmitting coil (3), the output end of the transmitting coil (3) is arranged opposite to the input end of the receiving coil (4), the output end of the receiving coil (4) is connected to the input end of the AC-DC converter (5), and the output end of the AC-DC converter (5) is connected to the charging device equivalent load (6); Step 2: When the system is operating normally, obtain the voltage U1 and current I1 of the transmitting coil (3), and calculate the input impedance; Step 3, determine the equivalent circuit. The equivalent circuit includes voltage U1. One end of voltage U1 is successively connected in series with the primary compensation capacitor parasitic resistor R1 and the primary transmitting coil compensation capacitor C P and the other end of the primary transmitting coil compensation capacitor C P is divided into two paths. One path is successively connected in series with the primary transmitting coil equivalent inductance L P and the primary transmitting coil parasitic resistor R P . The other end of the primary transmitting coil parasitic resistor R P is divided into two paths. One path is connected to voltage U1 to form the first mesh. The other path of the primary transmitting coil compensation capacitor C P is connected in series with the bridging capacitor C e . The other end of the bridging capacitor C e is divided into two paths. One path is successively connected in series with the secondary transmitting coil equivalent inductance L S and the secondary transmitting coil parasitic resistor R S . The other end of the secondary transmitting coil parasitic resistor R S is divided into two paths. One path is connected in series with the bridging capacitor C e ' and then connected to the other path of the primary transmitting coil parasitic resistor R P to form the second mesh; The other path of the bridging capacitor C e is successively connected in series with the secondary transmitting coil compensation capacitor C S , the secondary compensation capacitor parasitic resistor R2, and the equivalent load R of the system Le , and finally connected to the other path of the secondary transmitting coil parasitic resistor R S to form the third mesh; Establish equations for the mutual inductance M, the bridging capacitor C e and the equivalent load R Le through voltage U1 and current I1; Step 4: Substitute the voltage U1 and current I1 obtained in Step 2 into the system of equations in Step 3 to solve for the mutual inductance M, the bridging capacitor C e and the equivalent load R Le , to achieve multi-parameter identification; Step 5, after identifying the value of the cross-connecting capacitor C of the recognition system e , according to the magnitude of the value of the cross-connecting capacitor C e of the system, analyze what working state the system is in, and achieve targeted energy efficiency optimization for each working state; the working states include: the working state of the capacitive decoupling underwater wireless power transmission system and the working state of the capacitive coupling underwater wireless power transmission system; the energy efficiency optimization includes the optimization of the constant current output characteristic and the tracking of the maximum efficiency and output power point.

2. The multi-parameter online identification energy efficiency improvement method for an underwater wireless transmission system according to claim 1, wherein The voltage U1 and current I1 in Step 2 respectively represent the voltage vector and current vector of the transmitting coil (3) during normal operation.

3. An energy efficiency improvement method for online multi-parameter identification of an underwater wireless transmission system according to claim 1, characterized in that, In the third step described above, solve for the mutual inductance M, the shunt capacitance C e and the equivalent load R Le The equations are as follows: The equation for solving the single variable mutual inductance M is as follows: Z2 = -R p -jωL p +jωM (4) Z3 = -jωM (5) Z5 = -R s -jωL s +jωM (7) In the formula, j is the imaginary unit, ω is the system driving angular frequency, Z1, Z2, Z3, Z4, Z5, and Z6 are the impedances corresponding to the currents in each mesh of the equivalent circuit, and T1 is an intermediate variable; Single-variable bridging capacitor C e is solved as follows: T2 = MωB - L p C + jD + E (10) where, T 2、 A, B, C, D and E are intermediate variables; Single-variable equivalent load R Le is solved as follows: T3 = B1 - 2Z2Z3Z5 + Z1Z4Z5 + C1 (13) where, T 3、 A1, B1, C1, D1 and E1 are intermediate variables; Multiple variables: mutual inductance M, shunt capacitance C e , equivalent load R Le Solution for: Transform Equation (15) to obtain Equation (17): Construct a function as in Equation (17): where T is an intermediate variable. For the function Γ, the parameter region where the optimal solution appears may not be within the numerical range that conforms to the actual engineering situation. Therefore, it is necessary to constrain the ranges of the variables M, C e and R Le ; the ranges of M, C e and R Le are set as shown in Equation (18): Optimize the objective function to obtain the minimum value of the equation and the corresponding variables as shown in Equation (19). At this time, the corresponding Μ1, C e1 and R Le1 are the solutions corresponding to Equation (19). Γ(M1, C e1 , R Le1 ) = min{Γ(M, C e , R Le )} = 0 (19).

4. An online multi-parameter identification energy efficiency improvement method for an underwater wireless transmission system according to claim 1, characterized in that The DC-AC converter (2) adopts a single-phase full-bridge inverter circuit. During the process of mutual inductance M identification, the output frequency of the DC-AC converter (2) remains fixed, and the output voltage is a square wave with a fixed duty cycle. The output voltage satisfies the formula where U ab is the fundamental effective value of the output voltage of the DC-AC converter (2), in V DC is the output DC voltage value of the DC power supply (1); The transmitting coil (3) includes a transmitting coil L connected in series with each other P and a compensation capacitor C P ; One end of the compensation capacitor C P is connected to an output end of the DC-AC converter (2), and the other end of the compensation capacitor C P is connected to one end of the transmitting coil L P ; The other end of the transmitting coil L P is connected to the other output end of the DC-AC converter (2); The receiving coil (4) includes a transmitting coil L connected in series with each other S and a compensation capacitor C S ; One end of the compensation capacitor C S is connected to an input terminal of the AC-DC converter (5), and the other end of the compensation capacitor C S is connected to one end of the transmitting coil L S ; The other end of the transmitting coil L S is connected to the other input terminal of the AC-DC converter (5); The AC-DC converter (5) includes a single-phase uncontrolled rectifier circuit and a filter capacitor C filter , the single-phase uncontrolled rectifier circuit is in parallel with the filter capacitor C filter ; the single-phase uncontrolled rectifier circuit includes four uncontrolled diodes, two uncontrolled diodes form a bridge arm, there are two bridge arms in total, and the two bridge arms are in parallel.

5. An energy efficiency improvement method for online identification of multiple parameters of an underwater wireless transmission system according to claim 1, characterized in that, The multi-parameter online identification energy efficiency improvement method is applied to four working modes. Working mode 1: When the bridging capacitor C e and the equivalent load R Le are known, according to formulas (3)-(8), the expression of the mutual inductance M can be solved as (1) and (2); performing mathematical analysis on equations (1) and (2), the complex solutions a1 and a2 of the mutual inductance M with the negative roots omitted can be obtained from the system of equations (1). Since the imaginary parts of a1 and a2 are much smaller than the real parts, they can be ignored, and it is considered that the real parts of a1 and a2 are the solution values of the mutual inductance M; at the same time, considering that the actual mutual inductance is positive, taking the positive solutions of a1 and a2, the solution of the mutual inductance M can be obtained. Working mode 2: When the mutual inductance M and the equivalent load R Le are known, according to formulas (3)-(8), the expression of the bridging capacitor C e can be solved as (9), (10), and (11). Performing mathematical analysis on equations (9), (10), and (11), the solution of the bridging capacitor C e can be obtained. Working mode 3: When the mutual inductance M and the bridging capacitor C e are known, according to formulas (3)-(8), the expression of the equivalent load R Le can be solved as (12), (13), and (14). Performing mathematical analysis on equations (12), (13), and (14), the solution of the equivalent load R Le can be obtained. Working mode 4: The identification problem of the mutual inductance M, the bridging capacitor C e and the equivalent load R Le is transformed into the problem of optimizing the above parameter values, and the problem of solving the non-linear equation is transformed into the numerical optimization problem of the function to realize the simultaneous identification of multiple parameters of the mutual inductance M, the bridging capacitor C e and the equivalent load R Le .

6. An energy efficiency improvement method for online identification of multiple parameters of an underwater wireless transmission system according to claim 1, characterized in that In Step 5, the transmission characteristic equation of the capacitive decoupled underwater wireless power transmission system includes: Z2 = -R p -jωL p +jωM (21) Z3 = -jωM (22) Z5 = -R s -jωL s +jωM (24) P out = |I3| 2 R Le (28) where I1, I2, and I3 are the currents of each mesh, and P out is the output power of the system, η is the system coil efficiency, and Z in is the input impedance. According to equations (20)-(25), the impedances of each element of the impedance matrix can be obtained. Then, according to equations (26) and (27), the currents of each mesh of the capacitive decoupled underwater wireless power transmission system are solved. At this time, I2 is set to 0 to achieve capacitive decoupling of the system. Then, the output characteristics of the system are solved according to equations (28) to (30); The transmission characteristic equation of the capacitive coupled underwater wireless power transmission system includes: Z2 = -R p -jωL p +jωM (32) Z3 = -jωM (33) Z5 = -R s -jωL s +jωM (35) P out = |I3| 2 R Le (39) According to Equations (31)-(36), the impedances of each element of the impedance matrix can be obtained. Then, according to Equations (37) and (38), the mesh currents of the capacitive coupled underwater wireless power transmission system are solved. At this time, the I2 formula is derived and substituted into the system to achieve the cross-connected capacitance coupling of the system. Then, the output characteristics of the system are solved according to Equations (39) to (41); According to the output characteristic formula of the capacitive decoupled underwater wireless power transmission system, a constant current output of the system is achieved. During the constant current output, the output current expression of the system is: According to the output characteristic formula of the capacitive coupled underwater wireless power transmission system, the maximum efficiency and output power tracking of the system are achieved; at this time, the output power and coil efficiency expressions of the system are:

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