Switched capacitor compensation control method for dual-load wireless power transmission system

Abstract

The invention discloses a switched capacitor compensation control method of a dual-load wireless electric energy transmission system, which realizes optimization of wireless electric energy transmission efficiency under various working conditions. According to load states and mutual inductance coefficients under different conditions, synchronous control is carried out on a secondary side compensation switch capacitor and a primary side LCC structure switch capacitor by detecting double-load current, so that an input impedance angle is reduced while double loads reach target output power, and the overall transmission efficiency of the system is improved; and analyzing a transmission efficiency curve of the system under different load power distributions so as to meet the power distribution requirement of the optimal transmission efficiency. By collecting the input voltage and the load current of each converter, the size of the switched capacitor can be adjusted, the steps are simple, the power transmission and the efficiency optimization are greatly improved, the constant current control can be realized by the same method, the given parameters of the system are easy to set, and the system has good economy and practicability.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission, and particularly to a switched-capacitor compensation control method for a dual-load wireless power transmission system. Background Art

[0002] Compared with the traditional wired charging method, wireless charging technology has the advantages of charging safety, timeliness, simplicity, etc. At present, the charging efficiency of magnetic-coupled resonant electric vehicle charging is 85% - 90%, and a single-load system is adopted. However, the single-load system also has some deficiencies: firstly, the uniqueness of the load makes the utilization rate of the whole system relatively low; secondly, there are limitations in position, and the receiving coil and the transmitting coil can only be coaxial to achieve the highest transmission efficiency.

[0003] In the existing technology, only the power distribution without considering the magnetic coupling between the secondary coils is achieved, and no further research is carried out on the basis of the cross-coupling in the secondary side. Summary of the Invention

[0004] In order to make up for the deficiencies of the existing technology, the embodiments of the present application propose a switched-capacitor compensation control strategy for a dual-load wireless power transmission system under cross-coupling effect, which realizes flexible power allocation for wireless charging of new energy electric vehicle batteries while enhancing the anti-offset ability, thereby improving the power transmission ability of the system. The full-resonance control technology of the one-to-two wireless power transmission system is a new technology derived based on the wireless power transmission technology, mainly applied to electric vehicles, to achieve the ability of one charging pile to supply power to two new energy vehicles at the same time. The dual-load wireless charging technology is based on a vertical charging pile. For a new energy vehicle with back-mounted wireless charging, the charging pile can achieve double-sided wireless charging, save the number of charging piles, reduce the cost of building wireless charging piles, and provide a better charging experience for users, realizing the mutual benefit and win-win situation of the State Grid and new energy vehicle users.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] A switched-capacitor compensation control method for a dual-load wireless power transmission system, comprising the following steps:

[0007] Step 1, construct a circuit topology structure diagram of a three-coil wireless power transmission system;

[0008] Step 2, obtain the output voltage U dc1 , and output it to the primary high-frequency inverter module, and the high-frequency inverter outputs an 80 kHz AC square wave to the primary coil;

[0009] Step 3, calculate the load impedance value through the voltage and current of the secondary load;

[0010] Step 4: Given the expected output powers of two sides, construct a control equation set for the charging current of the load battery;

[0011] Step 5: Improve the overall efficiency of the system by controlling the primary-side switched capacitor C 1 to improve the overall efficiency of the system.

[0012] As a further technical solution of the present invention: The specific steps of Step 1 include:

[0013] Step 1.1: Construct the circuit topology of the dual-load wireless power transfer system, which specifically includes: a DC power supply (1), a primary-side high-frequency inverter module (2), a transmitting coil module (3), a receiving coil module (4), a secondary-side rectifier module (5), a battery load (6), a primary-side switched capacitor (7), a secondary-side 1 switched capacitor (8), and a secondary-side 2 switched capacitor (9);

[0014] Among them, the DC power supply (1) is connected to the input end of the primary-side high-frequency inverter module (2), the output end of the high-frequency inverter (2) is connected to the input end of the transmitting coil module (3), the output end of the transmitting coil module (3) is disposed opposite to the input end of the receiving coil module (4), the output end of the receiving coil module (4) is connected to the input end of the secondary-side rectifier module (5), the output end of the secondary-side rectifier module (5) is connected to the system battery load (6), the primary-side switched capacitor (7) is connected in series in the primary-side LCC topology, and the secondary-side 1 switched capacitor (8) and the secondary-side 2 switched capacitor (9) are connected in series in the secondary-side topology as compensation capacitors;

[0015] Step 1.2: Control the primary-side DC power supply (1) to obtain a suitable output voltage, obtain a high-frequency voltage with a zero phase through the high-frequency inverter (2), obtain the input voltage of the transmitting coil module (3) output to the receiving coil module (4) through the topological compensation coil structure, the secondary-side rectifier module (5) converts the high-frequency alternating current into direct current, and the secondary-side battery load (6) is connected to the output of the secondary-side rectifier module (5) to absorb power;

[0016] Step 1.3: The primary-side switched capacitor (7), the secondary-side 1 switched capacitor (8), and the secondary-side 2 switched capacitor (9) are used as compensation capacitors for the transmitting coil module (3) and the receiving coil module (4). By controlling the first switch tube S x and the second switch tube S yKeep the on-off state with a certain duty cycle, change the equivalent capacitance of the primary-side switching capacitor (7), secondary-side 1 switching capacitor (8), and secondary-side 2 switching capacitor (9) to obtain a suitable capacitance value. Change the capacitance values of the secondary-side 1 switching capacitor (8) and secondary-side 2 switching capacitor (9) to obtain the target output current. Change the capacitance value of the primary-side switching capacitor (7) to change the reactive power of the one-to-two wireless power transfer system;

[0017] Step 1.4: Determine the equivalent circuit of the one-to-two wireless power transfer system. According to Kirchhoff's voltage and current laws, obtain a system of equations regarding the input impedance and the relationships between the output power, voltage magnitude, and phase.

[0018] As a further technical solution of the present invention: The specific steps of step 2 include:

[0019] Step 2.1: Control the first switch tube S in the primary-side switching capacitor (7), secondary-side 1 switching capacitor (8), and secondary-side 2 switching capacitor (9) of the primary and secondary sides x and the second switch tube S y to keep the on-off state with a certain duty cycle, turn on the voltage source and determine whether the system is working properly;

[0020] Step 2.2: Obtain the output voltage U dc1 and output current I dc1 of the DC power supply (1). After passing through the high-frequency inverter, obtain an AC square wave with an amplitude of U dc1 , and the phase is considered zero. According to Fourier decomposition, the decomposition formula of this voltage is

[0021] (k is odd, ω is the angular frequency);

[0022] Step 2.3: The obtained high-frequency voltage passes through the LCC resonant topology compensation circuit and reaches the transmitting coil. According to Kirchhoff's voltage theorem, the following specific equations are obtained;

[0023]

[0024] Let L p , C p resonate, and the resonant frequency is:

[0025]

[0026] Simplify the above formula and solve for the current output to the primary-side transmitting coil as:

[0027] I 1 =-jωC p U in

[0028] In the above formula, Lp represents the compensation inductor of the resonant topology; C p represents the parallel compensation capacitor of the resonant topology; U in represents the fundamental component of U ac1 ; I in is the input current I ac1 's fundamental component.

[0029] As a further technical solution of the present invention: The specific steps of step 3 include:

[0030] Step 3.1: Select a suitable power supply voltage U in and the parallel compensation capacitor C of the resonant topology p , to obtain a suitable output current I 1 to the primary side transmitting coil;

[0031] Step 3.2: The two secondary receiving coil modules obtain a suitable current through the primary side transmitting coil. However, there is also mutual inductance between the two secondary receiving coils, and the currents among the three coils are coupled. The specific current equations of the two secondary sides are as follows:

[0032] a = jωM 12

[0033] b = jωM 13

[0034]

[0035] e = jωM 23

[0036] According to Kirchhoff's voltage theorem, the currents output to the two secondary side transmitting coils are solved as:

[0037]

[0038] Among them, C 2 represents the series compensation capacitor of the secondary coil 2 resonant topology, that is, the secondary side 1 switching capacitor (8); R 2 represents the parasitic resistance of the secondary coil 2; R eq2 represents the battery load 2; C 3 represents the series compensation capacitor of the secondary coil 3 resonant topology, that is, the secondary side 2 switching capacitor (9); R 3 represents the parasitic resistance of the secondary coil 3; R eq3 represents the battery load 3; I 2 represents the current flowing through the secondary coil 2, I 3 represents the current flowing through the secondary coil 3; M 12 represents the mutual inductance between coil 1 and 2, M 13Denote the mutual inductance between coils 1 and 3. Since the two secondary coils are relatively close, the mutual inductance M of the two secondary coils is considered. 23 .

[0039] As a further technical solution of the present invention: Step 4 specifically includes:

[0040] Step 4.1: Under the condition that the battery load impedance and the mutual inductance of each side are uncontrollable, by changing the series compensation capacitors C 2 and C 3 of the resonance topology of the secondary coil 2, the method of controlling the current has been given in Step 3.2:

[0041] I 2 = f(C 2 , C 3 )

[0042] i 3 = H(C 2 , C 3 )

[0043] Solve the equations of C 2 and C 3 with respect to I 2 and I 3 by the iterative method:

[0044]

[0045] Step 4.2: By controlling the first switching tube S x and the second switching tube S y of the primary side switching capacitor (7), the secondary side 1 switching capacitor (8), and the secondary side 2 switching capacitor (9) to be kept in the on-off state with a certain duty cycle, the capacitance value equation of the capacitor is as follows:

[0046]

[0047] where C eq is the total capacitance value of the switching capacitor, C a is the fixed capacitor, C b is the series capacitor, and β is the switching conduction angle;

[0048] Step 4.3: Control the magnitudes of the secondary coil currents i 2 and i 3 to change the power distribution of the load batteries 2 and 3. The specific power calculation is as follows:

[0049] P out2 = I 2 2 R eq2

[0050] Pout3 = I 3 2 R eq3

[0051] In the above formula, P out1 represents the power received by the battery load 1, and P out2 represents the power received by the battery load 2.

[0052] As a further technical solution of the present invention: the specific steps of step 5 include:

[0053] Step 5.1: When the output power remains unchanged, the overall efficiency of the system is related to the input power. For the input impedance, assuming U in is at zero phase, then there is the following equation:

[0054] P in = U in I in cosΦ

[0055]

[0056] P cu = I in 2 Z in cosΦ = I in 2 R in

[0057]

[0058] where P cu is the system loss, Z in is the input impedance, R in is the input resistance, cosΦ is the power factor, and η% is the system efficiency;

[0059] Step 5.2: Control the power factor to be maximum, at this time the system efficiency is the highest; U in is at zero phase, then by controlling the first switching tube S x1 and the second switching tube S y1 of the primary side switched capacitor (7) to be turned on and off at a certain duty cycle, changing the value of C 1 , so that the imaginary part of I in is zero. According to Kirchhoff's voltage theorem, the primary side input current is solved:

[0060]

[0061] From the above formula, the vector expression is obtained:

[0062] I in = I′in +I c1

[0063] Wherein, I' in has a fixed magnitude and phase, and I C1 is a pure imaginary number with an adjustable magnitude, and I in has a minimum value, at which time I in is perpendicular to I C1 and perpendicular to U in to make the input reactive power zero;

[0064] From the vector expression, the topological loop vector diagram of the uncontrolled C 1 is obtained, as shown in Figure 16 shown;

[0065] Control the value of C1 to make the power factor angle maximum, and the specific equation is:

[0066]

[0067] Obtain the topological loop vector diagram when the power factor angle is maximum: as shown in Figure 17 shown; Obtain the relationship between each vector from the vector diagram, and through C 1 adjust the phase of I in to achieve the maximum efficiency of the system.

[0068] As a further technical solution of the present invention: during the operation of the system, the state of the battery changes continuously with the charging degree. In order to charge the battery at a certain appropriate power, constant current charging is adopted. The charging battery only uses current control to make the output current stable. The charging battery collects the magnitude of the current on the secondary side through the signal acquisition circuit and the sending module, compares it with the magnitude of the rated charging current, and through PID control, gives the excitation pulses of the corresponding trigger angles of the three switched capacitors to control the magnitude of the output current.

[0069] As a further technical solution of the present invention: the setting of the charging battery power magnitude needs to collect the magnitude of the equivalent load voltage drop on the battery, that is, the product of the equivalent load voltage drop and the current. After comparing it with the ideal received power, the desired input power is obtained, that is, the output voltage is obtained by detecting the load voltage drop of the secondary rectifier bridge, and the received power of the system is obtained by collecting the magnitude of the current of the receiving coil circuit. By adjusting the excitation pulses of the switched capacitors, the ideal input power can be obtained.

[0070] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0071] The present invention provides a one-to-two wireless power transmission method under cross-coupling effect, and proposes a topology structure and parameter configuration method for dual wireless charging under cross-coupling effect, realizing the control of charging current and the transmission and distribution of different powers between batteries, and saving the cost of charging piles. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 It is the system topology diagram of the present invention;

[0073] Figure 2 It is the equivalent load R of the present invention L2 is 15Ω, R L3 is 20Ω, the power distribution diagram of the secondary side 1 transmitting 4451W;

[0074] Figure 3 It is the equivalent load R of the present invention L2 is 15Ω, R L3 is 20Ω, the power distribution diagram of the secondary side 2 transmitting 1853W;

[0075] Figure 4 It is the equivalent load R of the present invention L2 is 15Ω, R L3 is 20Ω, the primary side power transmission diagram for power distribution;

[0076] Figure 5 It is the equivalent load R of the present invention L2 is 20Ω, R L3 is 25Ω, the secondary side 1 power transmission diagram;

[0077] Figure 6 It is the equivalent load R of the present invention L2 is 20Ω, R L3 is 25Ω, the secondary side 2 power transmission diagram.

[0078] Figure 7 It is the equivalent load R L2 is 20Ω, R L3 is 25Ω, the primary side power transmission diagram.

[0079] Figure 8 It is the equivalent load R L2 is 18Ω, R L3 is 22Ω, the secondary side 1 power transmission diagram.

[0080] Figure 9 It is the equivalent load R L2 is 18Ω, R L3 is 22Ω, the secondary side 2 power transmission diagram.

[0081] Figure 10 It is the equivalent load R L2 is 18Ω, RL3 Primary side power transmission diagram when it is 22Ω.

[0082] Figure 11 Comparison of power transmission conditions in two simulations.

[0083] Figure 12 Comparison diagram of variable adjustment in two simulations.

[0084] Figure 13 Secondary side current control flow chart.

[0085] Figure 14 For the secondary side C 2 and C 3 Switching capacitor control diagram.

[0086] Figure 15 For the primary side C 1 Switching capacitor control diagram.

[0087] Figure 16 Topological loop vector diagram when C1 is not controlled.

[0088] Figure 17 Topological loop vector diagram when the power factor angle is maximum.

[0089] Figure 18 For I 2 、I 3 and C 2 Surface diagram;

[0090] Figure 19 For I 2 、I 3 and C 3 Surface diagram;

[0091] Figure 20 For C 1 Regarding different C 2 、C 3 Value surface diagram.

[0092] Figure 21 System efficiency vs. I 2 and I 3 Variation relationship diagram.

[0093] Figure 1 In: 1 - DC power supply, 2 - Primary side high-frequency inverter module, 3 - Transmitting coil module, 4 - Receiving coil module, 5 - Secondary side rectifier module, 6 - Battery load, 7 - Primary side switching capacitor, 8 - Secondary side 1 switching capacitor, 9 - Secondary side 2 switching capacitor. Specific implementation method

[0094] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0095] As Figure 1-21 shown, a switched-capacitor compensation control strategy for a dual-load wireless power transfer system based on variable loads, the method specifically includes the following steps:

[0096] Step 1, construct a circuit topology diagram of a three-coil wireless power transfer system;

[0097] Referring to Figure 1 the circuit topology diagram of the dual-load wireless power transfer system considering the cross-coupling effect shown, the circuit topology specifically includes: a DC power supply 1, a primary high-frequency inverter module 2, a transmitting coil module 3, a receiving coil module 4, a secondary rectifier module 5, a battery load 6, a primary switched capacitor 7, a secondary 1 switched capacitor 8, and a secondary 2 switched capacitor 9;

[0098] Among them, the DC power supply 1 is connected to the input end of the primary high-frequency inverter module 2, the output end of the high-frequency inverter 2 is connected to the input end of the transmitting coil module 3, the output end of the transmitting coil module 3 is oppositely arranged with the input end of the receiving coil module 4, the output end of the receiving coil module 4 is connected to the input end of the secondary rectifier module 5, the output end of the secondary rectifier module 5 is connected to the system battery load 6, the primary switched capacitor 7 is connected in series in the primary LCC topology, and the secondary 1 switched capacitor 8 and the secondary 2 switched capacitor 9 are connected in series in the secondary topology as compensation capacitors;

[0099] The primary DC input voltage V dc of the system is 628.3V, the amplitude of the transmitting coil current I 1 is 28.15A, the secondary output currents I 2 and I 3 are 18.47A and 14.26A respectively, and the secondary output voltages U 2 and U 3 are 277V and 285.1V respectively. The driving frequency of the system is 80 kHz. The transmitting coil L 1 , the receiving coil L 2 , and the receiving coil L 3 are wound with Litz wire to reduce the resistance value of the coil. The inductance values are all 100 μH, and the mutual inductance value M between L 1 and L 2 and L 3 is 30 μH, and the mutual inductance value between L 2 and L 3The mutual inductance value M between 23 is 10 μH, and the compensation inductor L p has an inductance value of 56.5 μH, and the compensation capacitor C p has a magnitude of 70 nF, and C 2 has an initial value set to 39.6 nF, and C 3 has an initial value set to 39.6 nF. Even when the two secondary coils are in the full resonance state, C 1 is set to 113 nF. The filter capacitors are all 2 μF and can meet the filtering requirements.

[0100] Step 2: Obtain the output voltage U of the DC power supply 1 dc1 and output it to the primary high-frequency inverter module. The high-frequency inverter outputs an 80 kHz AC square wave to the primary coil. The specific steps are as follows:

[0101] Step 2.1: Control the first switching tube S in the primary-side primary switching capacitor 7, the secondary-side 1 switching capacitor 8, and the secondary-side 2 switching capacitor 9 x and the second switching tube S y to maintain an on-off state with a certain duty cycle, such that β 2 is 113°, β 3 is 113°, β 1 is 120.7°, and let the system work in the full resonance state, which is also the initial state of the system. Turn on the voltage source and determine whether the system is working properly;

[0102] Step 2.2: Obtain the output voltage U dc1 and output current I dc1 , obtain an AC square wave through the high-frequency inverter, and the amplitude is U dc1 , and the phase can be considered zero. According to Fourier decomposition, the decomposition formula of this voltage can be obtained as

[0103] (k is odd, ω is the angular frequency);

[0104] From the above formula, U in = 800sinωt can be obtained, and the current transmitted to the primary transmitting coil through the topological compensation structure is:

[0105]

[0106] The detection end samples the values of U in and I 1 .

[0107] Step 3: Calculate the load impedance value based on the voltage and current of the secondary-side load. The two receiving coil modules on the secondary side obtain an appropriate current through the primary-side transmitting coil. However, there is also mutual inductance between the two secondary-side receiving coils, and the currents among the three coils are coupled. The specific process is as follows:

[0108] The primary side gives a voltage pulse for ten cycles, and the measured secondary-side output currents I 2 and I 3 are 18.47 A and 14.26 A respectively, and the secondary-side output voltages U 2 and U 3 are 277 V and 285.1 V respectively. The equivalent resistance values of the load, R 2 and R 3 are 15 Ω and 20 Ω respectively

[0109] Step 4: Given the expected output powers of the two secondary sides, construct the control of the load battery charging current. Through the above theoretical analysis, the specific equations that can be constructed are as follows:

[0110] Assume that the expected output powers P out2 is 4451 W and P out3 is 1853 W. Then the magnitudes of the currents that need to be constructed are:

[0111]

[0112] It is easy to obtain that the magnitudes of I 2 and I 3 are 24.36 A and 13.61 A respectively, and the values of C 2 and C 3 can be solved inversely, that is, through the formula:

[0113]

[0114] On the premise of Step 1, I 2 , I 3 and C 2 , C 3 satisfy Figure 18 and Figure 19 surface plots:

[0115] From this, it can be obtained that C 2 is 30 nF and C 3 is 50 nF.

[0116] Control the first switching tube S 2 in the secondary-side 1 switched capacitor C x2 and the second switching tube S y2 to keep the on-off state with a certain duty cycle, and control the first switching tube S 3 in the secondary-side 2 switched capacitor Cx3 and the second switching transistor S y3 keeps the on-off state with a certain duty cycle, C 2 and C 3 values can be obtained through the following formula:

[0117]

[0118] In the above formula, according to C 2 、C 3 values, their respective conduction angles can be obtained, β 2 = 90°, β 3 = 133.4°

[0119] Among them, C a is a fixed capacitor, C b is a series capacitor, and their values are both 50 nF.

[0120] Step 5, improve the overall system efficiency by controlling the primary-side switched capacitor C 1 :

[0121]

[0122] To make the system efficiency transmission reach the optimum, on the premise of step 1, a surface plot of C 1 with respect to different C 2 、C 3 values is given, as shown in Figure 20 .

[0123] Under this expected load power distribution, the system transmission efficiency is as follows:

[0124]

[0125] The system efficiency varies with I 2 and I 3 as shown in the relationship diagram of Figure 20 :

[0126] Among them, the fixed capacitor C 1 of the primary-side switched capacitor C a1 and the series capacitor C b1 are both 220 nF, the conduction angle β 1 is 100.6°, P cu is the system loss, Z in is the input impedance, R in is the input resistance, cosΦ is the power factor, η% is the system efficiency; controlling the power factor to be the maximum, the system efficiency is the highest at this time; U in is zero phase, then by controlling C 1 to make I inThe imaginary part is zero, and the maximum efficiency of the system can be achieved.

[0127] To verify the correctness of the theory, three simulations were conducted in total.

[0128] The first simulation was to verify the power distribution in the specific implementation scheme. The control methods of the second and third simulations were the same as the first one, and the purpose was to achieve constant current control.

[0129] In the first simulation, β 2 was 90°, β 3 was 133.4°, the conduction angle β 1 of the primary side switching capacitor C 1 was 108.5°, and considering all the parasitic resistances in the circuit, the obtained results are as Figure 2 , Figure 3 , Figure 4 shown.

[0130] Among them, the equivalent battery loads of the secondary side are 15Ω and 20Ω respectively, the secondary side output currents are 17.3A and 9.2A respectively, and the power output from the primary side is 6855W. As Figure 4 shown, the power received by the secondary side 1 is 4592W, as Figure 2 shown, the power received by the secondary side 2 is 1765W, as Figure 4 shown. From this, the transmission efficiency of the entire system can be calculated as 92.74%.

[0131] In the second simulation, β 2 was 114°, β 3 was 114°, the conduction angle of the primary side switching capacitor C 1 was 108.5°, and considering all the parasitic resistances in the circuit, the obtained results are as Figure 5 , Figure 6 , Figure 7 shown.

[0132] Among them, the equivalent battery loads of the secondary side are 20Ω and 25Ω respectively, the secondary side output DC currents are 12.08A and 10.51A respectively, and the power output from the primary side is 8855W. As Figure 7 shown, the power received by the secondary side 1 is 4318W, as Figure 5 shown, the power received by the secondary side 2 is 3634W, as Figure 6 shown. From this, the transmission efficiency of the entire system can be calculated as 89.8%.

[0133] In the third simulation, β 2 was 114°, β 3 was 133°, the primary side switching capacitor C 1The conduction angle is 146°, and all parasitic resistances in the circuit are considered, then the obtained results are as Figure 8 , Figure 9 , Figure 10 shown.

[0134] Among them, the equivalent battery loads of the secondary part are 18Ω and 22Ω respectively, the secondary output DC currents are 12.42A and 11.26A respectively, and the power output on the primary side is 7015W. As Figure 10 shown, the power received by secondary 1 is 3140W, as Figure 8 shown, the power received by secondary 2 is 3091W, as Figure 9 shown. From this, the transmission efficiency of the entire system can be calculated as 88.82%.

[0135] Among them Figure 11 , Figure 12 are the summary classification diagrams of the above figures respectively, Figure 13 , Figure 14 are the primary and secondary side switched-capacitor control diagrams respectively. The results obtained by simulation have a small error from the theoretical analysis, and the theory can be considered correct. (Remark: Since the energy of the secondary battery should not be released too much, the power level is small).

[0136] Based on considering the cross-coupling of the secondary coil, the present invention proposes a flexible charging technology based on switched-capacitor control, which can achieve the distribution of the target power, realize safer and more reliable charging of the battery. When the battery state is different, the charging current can be regulated by the secondary compensation switched capacitor to achieve constant current charging of the battery, and switched-capacitor control is added to the LCC topology structure on the primary side of the system to further optimize the transmission efficiency of the system.

[0137] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0138] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment have been appropriately combined to form other embodiments that are easy for those skilled in the art to understand.

Claims

1. A switch capacitor compensation control method for a dual-load wireless power transmission system, characterized in that: The following steps are involved: Step 1, construct a circuit topology diagram of a three-coil wireless power transmission system; Step 2: Get the output voltage U of the DC power supply dc1 , and output it to the primary high-frequency inverter module, and the high-frequency inverter outputs 80kHz AC square wave to the primary coil; Step 3, calculating the load impedance value through the voltage and current of the secondary load; Step 4: Given the expected output power of the two secondary sides, a load battery charging current control equation group is constructed; Step 5: Improve the overall efficiency of the system by controlling the primary switching capacitor C1.

2. The switch capacitor compensation control method of a dual-load wireless power transmission system according to claim 1, characterized in that: The step 1 specifically includes: Step 1.1, constructing a circuit topology structure of a dual-load wireless power transmission system, wherein the circuit topology structure specifically includes: a DC power supply, a primary high-frequency inverter module, a transmitting coil module, a receiving coil module, a secondary rectifier module, a battery load, a primary switching capacitor, a secondary 1 switching capacitor, and a secondary 2 switching capacitor; Wherein, the DC power supply is connected to the input end of the primary high-frequency inverter module, the output end of the high-frequency inverter is connected to the input end of the transmitting coil module, the output end of the transmitting coil module is arranged opposite to the input end of the receiving coil module, the output end of the receiving coil module is connected to the input end of the secondary rectifier module, the output end of the secondary rectifier module is connected to the system battery load, the primary switch capacitor is connected in series in the primary LCC topology, and the secondary 1 switch capacitor and the secondary 2 switch capacitor are connected in series in the secondary topology as compensation capacitors; Step 1.2, control the primary DC power supply to obtain a suitable output voltage, obtain a high-frequency voltage with a phase of zero through the high-frequency inverter, and output the input voltage of the receiving coil module to the transmitting coil module through the topology compensation coil structure. The secondary rectifier module converts the high-frequency AC power into DC, and the secondary battery load is connected to the output of the secondary rectifier module to absorb power; Step 1.3, the primary switch capacitor, the secondary switch capacitor 1, and the secondary switch capacitor 2 are used as compensation capacitors for the transmitting coil module and the receiving coil module. By controlling the first switch tube S in the primary switch capacitor, the secondary switch capacitor 1, and the secondary switch capacitor 2, x And the second switch tube S y Maintaining the on-off state with a certain duty cycle, changing the size of the equivalent capacitance of the primary switch capacitor, the secondary 1 switch capacitor, and the secondary 2 switch capacitor to obtain a suitable capacitance value, changing the capacitance value of the secondary 1 switch capacitor and the secondary 2 switch capacitor to obtain the target output current, and changing the capacitance value of the primary switch capacitor to change the reactive power of the one-to-two wireless power transmission system; Step 1.4, determine the equivalent circuit of the one-to-two wireless power transmission system, and obtain a set of equations about the input impedance and the relationship between the output power and the voltage magnitude and phase according to Kirchhoff's voltage-current law.

3. The switch capacitor compensation control method of a dual-load wireless power transmission system according to claim 1, characterized in that: The step 2 specifically includes: Step 2.1: Control the first switch tube S in the primary switch capacitor of the primary side, the secondary side 1 switch capacitor, and the secondary side 2 switch capacitor x And the second switch tube S y Maintain the on-off state with a certain duty cycle, turn on the voltage source and determine whether the system is working properly; Step 2.2: Get the output voltage U of the DC power supply dc1 and output current I dc1 , an AC square wave is obtained through a high-frequency inverter, and the amplitude is U dc1 , the phase is considered to be zero, and the decomposition formula of the voltage is obtained according to Fourier decomposition: Step 2.3: The obtained high frequency voltage reaches the transmitting coil through the LCC resonant topology compensation circuit. According to Kirchhoff's voltage theorem, the following specific equation is obtained; Another L p , C p Resonance, the resonant frequency is: By simplifying the above formula, the current output to the primary transmitting coil is solved as: I1=-jωC p IN in In the above formula, L p Represents the compensation inductance of the resonant topology; C p Represents the parallel compensation capacitor of the resonant topology; U in Indicates U ac1 The fundamental component of in is the input current I ac1 fundamental wave component.

4. The switch capacitor compensation control method of a dual-load wireless power transmission system according to claim 1, characterized in that: The step 3 specifically includes: Step 3.1: Select the appropriate power supply voltage U in The parallel compensation capacitor C of the resonant topology p , get a suitable output current I1 to the primary transmitting coil; Step 3.2: The two receiving coil modules on the secondary side obtain a suitable current through the primary transmitting coil. However, there is also mutual inductance between the two secondary receiving coils, and the currents between the three coils are coupled. The specific current equations of the two secondary sides are as follows: a=jωM 12 b=jωM 13 e=jωM 23 According to Kirchhoff's voltage theorem, the current output to the two secondary transmitting coils is: Wherein, C2 represents the series compensation capacitor of the secondary coil 2 resonant topology structure, that is, the secondary side 1 switch capacitor; R2 represents the parasitic resistance of the secondary coil 2; R eq2 represents battery load 2; C3 represents the series compensation capacitor of the resonant topology structure of the secondary coil 3, that is, the secondary 2 switch capacitor; R3 represents the parasitic resistance of the secondary coil 3; R eq3 represents the battery load 3; I2 represents the current flowing through the secondary coil 2, and I3 represents the current flowing through the secondary coil 3; M 12 represents the mutual inductance between coils 1 and 2, M 13 Represents the mutual inductance between coils 1 and 3. Since the two secondary coils are close to each other, the mutual inductance M of the two secondary coils is considered. 23 .

5. The switch capacitor compensation control method of a dual-load wireless power transmission system according to claim 4, characterized in that: The step 4 specifically includes: Step 4.1: When the battery load impedance and the mutual inductance of each side cannot be adjusted, the method of controlling the current by changing the series compensation capacitors C2 and C3 of the resonant topology of the secondary coil 2 has been given in step 3.2: I2=f(C2,C3) I3=h(C2,C3) Solve the equations of C2 and C3 with respect to I2 and I3 by iteration: Step 4.2: By controlling the first switch tube S in the primary switch capacitor, the secondary switch capacitor 1, and the secondary switch capacitor 2 x And the second switch tube S y To maintain the on-off state with a certain duty cycle, the capacitance equation of the capacitor is as follows: Among them, C eq is the total capacitance of the switch capacitor, C a is a fixed capacitor, C b is the series capacitor, β is the switch conduction angle; Step 4.3: Control the secondary coil currents i2 and i3 to change the power distribution of load battery 2 and load battery 3. The specific power calculation is as follows: P out2 =I2 2 R eq2 P out3 =I3 2 R eq3 In the above formula, P out1 Indicates the power received by battery load 1, P out2 Indicates the power received by battery load 2.

6. The switch capacitor compensation control method of a dual-load wireless power transmission system according to claim 1, characterized in that: The step 5 specifically includes: Step 5.1: When the output power is constant, the overall efficiency of the system is related to the input power. For the input impedance, assume that U in is zero phase, then we have the following equation: P in =U in I in cosΦ P cu =I in 2 Z in cosΦ=I in 2 R in Where P cu is the system loss, Z in is the input impedance, R in is the input resistance, cosΦ is the power factor, and η% is the system efficiency; Step 5.2: Control the power factor to the maximum, at which point the system efficiency is the highest; U in If the phase is zero, the first switch tube S of the primary switch capacitor is controlled x1 And the second switch tube S y1 Keep the on / off state at a certain duty cycle, and change the value of C1 so that I in The imaginary part of is zero. According to Kirchhoff's voltage theorem, the primary input current is solved as: The vector expression is obtained from the above formula: I in =I′ in +I c1 Among them, I' in The size and phase of I C1 is a pure imaginary number, with adjustable size, I in There is a minimum value, at which I in with I C1 Vertical, with U in Vertical, so that the input reactive power is zero; From the vector expression, we can get the topological loop vector diagram when C1 is not controlled. Control the value of C1 to maximize the power factor angle. The specific equation is: The topological loop vector diagram when the power factor angle is the largest is obtained: the relationship between the various vectors is obtained from the vector diagram, and the relationship between C1 and I in Phase adjustment to achieve maximum efficiency of the system.

7. The switch capacitor compensation control method of a dual-load wireless power transmission system according to claim 1, characterized in that: During the operation of the system, the state of the battery changes continuously with the degree of charging. In order to meet the charging of the battery with a certain appropriate power, constant current charging is adopted. The charged battery only adopts current control to make the output current stable. The charging battery collects the current size of the secondary side through the signal acquisition and transmission module, and compares it with the rated charging current size. Through PID control, the excitation pulses of the corresponding trigger angles are given to the three switch capacitors to control the output current size.

8. The switch capacitor compensation control method of a dual-load wireless power transmission system according to claim 1, characterized in that: The power setting of the rechargeable battery requires the acquisition of the size of the equivalent load voltage drop on the battery, that is, the product of the equivalent load voltage drop and the current. After comparing it with the ideal receiving power, the desired input power is obtained, that is, the output voltage is obtained by detecting the load voltage drop of the secondary side rectifier bridge, and the receiving power of the system is obtained by acquiring the current size of the receiving coil circuit. The excitation pulse of the switching capacitor is adjusted to obtain the ideal input power.

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