IPT system parameter design method based on circuit parameter matching

Abstract

The invention provides an IPT system parameter design method based on circuit parameter matching, and is used for solving the problem of high circuit parameter design complexity caused by a large number of compensation circuit parameters in an existing IPT system. The method comprises the following specific steps: setting a transmission demand parameter of an IPT system and a coupler size parameter, and calculating a single-turn coupling self-inductance parameter and a single-turn coupling mutual inductance of a coil; selecting an independent parameter influencing the variable loss of the system, and calculating the value of the independent parameter by taking the minimum total loss of the system as an optimization condition; calculating the mutual inductance, the number of turns and the self-inductance value of the coil according to the independent parameters and the transmission demand parameters; and calculating a compensation capacitance parameter of the system compensation circuit according to the number of turns of the coil, the transmission demand parameter and the resonance condition, and selecting a proper actual compensation capacitance value. According to the method, the power loss is modeled, and the independent parameters are selected, so that decoupling of the circuit parameters in the power loss is realized. And the complexity of circuit parameter design is greatly reduced.

Description

Technical Field

[0001] The invention relates to the field of wireless power transmission, and in particular to an IPT system parameter design method based on circuit parameter matching. Background Art

[0002] Wireless power transfer (WPT) using electromagnetic fields over a distance of several hundred millimeters has been a hot research topic in recent years. According to the transmission type, WPT systems can be divided into two categories: magnetic field wireless power transfer (IPT) and capacitive wireless power transfer (CPT). Compared with the CPT system that uses electric field coupling between plates to transfer power, the IPT system that uses magnetic field coupling between coils to transfer power is relatively mature in many applications, such as consumer electronics, medical equipment, industrial applications, and electric vehicles.

[0003] The IPT system using high-order compensation circuit has good transmission performance and anti-offset performance, but it also increases the number of circuit parameters. Appropriate circuit parameter matching can effectively improve system efficiency. However, a large number of circuit parameters increase the complexity of the design, making it difficult to optimize all circuit parameters at the same time. Traditionally, the circuit parameters of the IPT system are designed based on experience, requiring a large number of experiments, and the performance of the designed systems varies greatly. In order to improve system performance, existing studies have proposed many parameter optimization design methods, which can be divided into two categories: numerical methods and analytical methods.

[0004] The numerical method obtains matching circuit parameters by scanning the circuit parameters or randomly sampling within the parameter value range, and then iteratively optimizes them. This is a commonly used circuit parameter design method in the IPT system. In the existing literature, the Pareto optimal frontier of transmission efficiency is derived by scanning the relevant size parameters, thereby optimizing the geometric structure of the coupler of the IPT system. After determining the coupling parameters, the compensation parameters are scanned in the existing literature to obtain the minimum total coupler loss, but they do not consider the converter loss and compensation loss. In order to minimize the total loss of the resonant circuit, the compensation parameters are scanned in the existing literature, but the core loss and harmonic loss are not considered. In addition, there are studies in the existing literature that use GA, PSO, ANN, NLP and other intelligent algorithms to optimize circuit parameters. In these intelligent algorithms, in order to simplify the calculation, harmonic loss or core loss is always ignored, so these methods are only local optimization of the IPT system rather than global optimization. In addition, the numerical method cannot reveal the optimal matching relationship between circuit parameters, and requires a large number of simulations of nonlinear core loss, which makes the parameter design process more complicated.

[0005] The analytical method obtains the matching relationship between circuit parameters by solving the analytical equation between power loss and circuit parameters. However, for IPT systems with more circuit parameters, the relationship between power loss and circuit parameters is more complicated, making it difficult to solve the multivariable analytical equation of power loss. Existing analytical methods can only solve the derivative of a single variable to obtain the analytical relationship between efficiency and a single variable, and the remaining system parameters are assumed to be known. These studies select and optimize the input-output voltage ratio, current ratio, output load and compensation inductance respectively to obtain the most matching output voltage, current, load and compensation inductance. These methods are only local optimization methods because these matching circuit parameters are obtained when the coupling parameters are given, without considering the core loss and higher harmonic loss. Due to the complexity of the power loss expression, there is currently no analytical method that can clearly derive the optimal efficiency of a multivariable IPT system. Summary of the invention

[0006] The purpose of the present invention is to provide an IPT system parameter design method based on circuit parameter matching, which is used to solve the technical problem that the number of high-order compensation circuit parameters in the existing IPT system is large, resulting in high complexity and large amount of calculation in circuit parameter design.

[0007] A parameter design method for an IPT system based on circuit parameter matching, the IPT system includes a DC power supply, a full-bridge inverter, a DLCC compensation circuit, a coupler, a rectifier and a load, the coupler includes a primary coil and a secondary coil, and the parameter design method includes the following specific steps:

[0008] S1: Set the transmission requirement parameters of the IPT system according to actual needs;

[0009] S2: Set the coupler size parameters, calculate the single-turn coupled self-inductance parameters of the primary coil and the secondary coil, and the single-turn coupled mutual inductance of the primary coil and the secondary coil;

[0010] S3: Select independent parameters that affect the variable loss of the system, and calculate the value of the independent parameters with the minimum total loss of the system as the optimization condition;

[0011] S4: Calculate the mutual inductance of the primary coil and the secondary coil, the number of turns of the primary coil and the secondary coil, and the self-inductance value according to the independent parameters and the transmission requirement parameters;

[0012] S5: Calculate the compensation capacitor parameters of the system compensation circuit according to the number of coil turns, transmission requirement parameters and resonance conditions, and select a suitable actual compensation capacitor value.

[0013] Optionally, the IPT system transmission requirement parameters in step S1 include DC input voltage, DC output voltage, transmission power, resonant frequency, transmission distance and coil size parameters.

[0014] Optionally, the coupler size parameters in step S2 include the coupler core length, core thickness, coil thickness, coil-to-core spacing, and coil internal side length parameters;

[0015] After the size of the coupler is determined, the single-turn coupled self-inductance parameters of the primary coil and the secondary coil, and the single-turn coupled mutual inductance of the primary coil and the secondary coil are obtained by simulation calculation.

[0016] Optionally, in step S3, the independent parameters affecting the variable loss of the system include the product of the number of turns of the primary coil and the current of the primary coil, the inductance value of the primary compensation inductor, and the inductance value of the secondary compensation inductor.

[0017] Optionally, in step S3, the total system loss is equal to the sum of the constant full-bridge converter loss under the fundamental wave and three variable losses affected by three independent parameters, wherein the full-bridge converter loss includes the full-bridge inverter loss and the rectifier loss;

[0018] The minimum values ​​of the three variable losses and their corresponding three independent parameter values ​​are calculated respectively to obtain the optimized three independent parameter values.

[0019] Optionally, the specific method for calculating the mutual inductance between the primary coil and the secondary coil in step S4 is:

[0020] The system transmission power P is:

[0021] P=8M 23 V in V out / π 2 ωL1L4

[0022] Where M 23 is the mutual inductance between the primary coil and the secondary coil, V in is the DC input voltage, V out is the DC output voltage, ω is the system angular frequency, L1 and L4 are the inductance values ​​of the primary and secondary compensation inductors respectively;

[0023] The mutual inductance between the primary coil and the secondary coil is calculated according to the transmission power parameter set in step S1 and the primary compensation inductance and the secondary compensation inductance parameters calculated in step S3.

[0024] Optionally, the specific steps of calculating the number of turns of the primary coil and the secondary coil and the self-inductance value in step S4 are:

[0025] The mutual inductance between the primary and secondary coils is equal to the product of the number of turns of the primary coil, the number of turns of the secondary coil and the single-turn coupled mutual inductance of the primary coil and the secondary coil. The self-inductance of the primary and secondary coils is equal to the product of the square of the number of turns of the coil and the single-turn coupled self-inductance parameter of the coil.

[0026] The number of turns of the primary coil and the secondary coil is calculated by the mutual inductance between the primary coil and the secondary coil calculated in step S4.1 and the single-turn coupled mutual inductance of the primary coil and the secondary coil calculated in step S2; the self-inductance values ​​of the primary coil and the secondary coil are calculated respectively by the single-turn coupled self-inductance parameters of the primary coil and the secondary coil calculated in step S2 and the number of turns of the primary coil and the secondary coil.

[0027] Optionally, the system resonance condition in step S5 is:

[0028] The values ​​of parameters 1 / (L1C1), 1 / (L4C4), 1 / ((L2-L1)C2) and 1 / ((L3-L4)C3) are all equal to the system angular frequency, where: L1 and L4 are the inductance values ​​of the primary and secondary compensation inductors respectively, L2 and L3 are the self-inductance values ​​of the primary and secondary coils respectively, C1 and C2 are the capacitance values ​​of the first and second primary compensation capacitors respectively, and C3 and C4 are the capacitance values ​​of the first and second secondary compensation capacitors respectively.

[0029] Optionally, the parameter design method further includes:

[0030] S6: Determine whether the system transmission power meets the power requirement. If yes, go to step S7. If no, return to step S5 to reselect the actual compensation capacitor value and continue to iterate and update the system parameters.

[0031] S7: Determine whether the system transmission efficiency meets the efficiency requirements. If so, output that the system parameter design is completed. If not, return to step S2 and reset the coupler size parameters, and continue to iterate and update the system parameters.

[0032] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0033] This application models the power loss of the entire system, analyzes the corresponding relationship between power loss and circuit parameters, selects key variables as independent parameters according to the characteristics of the loss, and realizes the decoupling of circuit parameters from power loss. Thus, the multivariable optimization problem of optimizing system transmission efficiency is transformed into multiple single variable optimization problems, and the optimal circuit parameters can be easily derived. This method greatly reduces the design complexity of circuit parameters, and for the first time obtains the analytical solution of the circuit parameters of the IPT system with high-order compensation.

[0034] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings of the present invention are as follows.

[0036] Figure 1 FIG. 4 is a schematic diagram of the structure of an IPT system with a DLCC compensation circuit according to the present invention.

[0037] Figure 2 This is an equivalent circuit model diagram of the IPT system under the fundamental wave of the present invention.

[0038] Figure 3 This is an equivalent circuit model diagram of the IPT system under high-order harmonics of the present invention.

[0039] Figure 4 The figure is a flow chart of the IPT system parameter design method based on circuit parameter matching of the present invention.

[0040] Figure 5 It is a schematic diagram of the structure of the coupler of the present invention.

[0041] Figure 6 This is a power loss diagram of the independent parameter N2I2 of the present invention at different values.

[0042] Figure 7 This is a power loss diagram of the present invention under different values ​​of independent parameters L1 and L4.

[0043] Figure 8 Graph showing the number of coil turns and THD at different values ​​of the independent parameters L1 and L4 of the present invention.

[0044] Fig. 9 This is a transmission efficiency diagram of the IPT system under different output powers with different coil turns of the present invention.

[0045] Fig.10 This is the output result diagram of the simulation experiment of the present invention.

[0046] Fig.11 The figure is a relationship diagram between DC-DC efficiency and output power under different output voltages of the present invention.

[0047] Fig.12 Graph showing the relationship between DC-DC efficiency and transmission power corresponding to different offset conditions under rated load resistance of the present invention.

[0048] Fig.13 This is a distribution diagram of power loss in the simulation experiment of the present invention.

[0049] In the figure: L2 is the primary coil; L3 is the secondary coil; D1 is the primary magnetic core; D2 is the secondary magnetic core. DETAILED DESCRIPTION

[0050] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0051] Embodiment 1:

[0052] like Figure 1 The IPT system with a DLCC compensation circuit shown in FIG. 1 includes a primary circuit and a secondary circuit. The primary circuit includes a DC power supply V in , a full-bridge inverter, a primary compensation circuit and a primary coil L2, and the secondary circuit includes a secondary coil L3, a secondary compensation circuit, a rectifier and a load connected in sequence.

[0053] The primary compensation circuit and the secondary compensation circuit are bilateral LCC (DLCC) type compensation circuits, the primary compensation circuit includes a primary compensation inductor L1, a primary first compensation capacitor C1 and a primary second compensation capacitor C2, the secondary compensation circuit includes a secondary compensation inductor L3, a secondary first compensation capacitor C3 and a secondary second compensation capacitor C4, the full-bridge inverter includes 4 switching tubes S1-S4, the rectifier includes 4 diodes D1-D4; a primary magnetic core D1 is provided on one side of the primary coil L2, and a secondary magnetic core D2 is provided on one side of the secondary coil L3. The primary coil L2, the primary magnetic core D1, the secondary coil L3 and the secondary magnetic core D2 constitute as follows Figure 5 Coupler shown.

[0054] In this embodiment, the IPT system using the DLCC compensation circuit can achieve ZPA at the inverter output and CC output at the rectifier input. The full-bridge inverter converts the DC voltage into AC voltage, and the corresponding fundamental wave and higher harmonics can be obtained by decomposing it through Fourier decomposition. Both the fundamental wave and the higher harmonics will cause losses in the resonant circuit and the converter. Therefore, the modeling of the IPT system needs to consider the influence of both the fundamental wave and the higher harmonics.

[0055] 1. Analysis of the impact of fundamental wave:

[0056] Using the fundamental wave analysis method and ignoring all parasitic parameters, the equivalent circuit model of the IPT system with DLCC compensation can be obtained as follows: Figure 2 shown. Figure 2 Medium:U AB and U ab is the equivalent AC voltage source, U 23 and U 32 It is the induced voltage source on the primary coil L2 and the secondary coil L3, which is induced by the current I3 and I2 on the primary coil L2 and the secondary coil L3 respectively. According to circuit theory, the current and voltage in the equivalent circuit can be:

[0057]

[0058] In formula (1), M 23is the mutual inductance of the primary coil L2 and the secondary coil L3; ω is the system angular frequency.

[0059] According to formula (1), the system transmission power can be deduced as:

[0060] P=-U ab I4=M 23 U AB U ab / ωL1L4=8M 23 V in V out / π 2 ωL1L4 (2)

[0061] exist Figure 1 and Figure 2 The fundamental voltage will cause losses in the full-bridge inverter, resonant tank and magnetic coupler. The loss of the full-bridge converter at the fundamental voltage is P loss,con,FH Including conduction loss P loss,inv,con , switching loss P loss,inv,sw and diode loss P loss,rec , which can be described as:

[0062] P loss,con,FH =P loss,inv,con +P loss,inv,sw +P loss,rec (3)

[0063] in:

[0064]

[0065] In the formula, R ds is the on-resistance of the full-bridge inverter switch tube, θ is the phase angle, e sw-on and e sw-off are the turn-on and turn-off energy losses of the full-bridge inverter switch tube, Q RR 、V R and I R are the reverse recovery charge of the rectifier diode, the reference voltage and current, V f is the threshold voltage of the diode.

[0066] Inductor loss P loss,Li and capacitance loss P loss,Cj It can be described by reactive power and its quality factor:

[0067] P loss,LC,FH =P loss,Li +P loss,Cj i,j=1,2,3,4 (5)

[0068] in:

[0069]

[0070] In the formula, Q Li and Q Cj (i,j=1,2,3,4) is the reactive power of inductance and capacitance, and is the quality factor.

[0071] The remaining losses of the coupler are core loss and shield loss. The core loss P core It can be expressed as:

[0072] P loss,core =C m f α B β (7)

[0073] Where: C m , α, and β are the three Steinmetz coefficients of the core material. B is the magnetic flux density. When the size of the coupler is determined, the core loss and shielding loss are mainly determined by the magnetic field. However, due to the uneven distribution of the magnetic field inside the coupler, it is difficult to accurately calculate the core loss. Therefore, in previous literature, the core loss and shielding loss are mostly obtained through simulation. Since both the core loss and the shielding loss are caused by the magnetic field, they can be regarded as functions of the magnetic field. To simplify the analysis, this application only considers the core loss.

[0074] 2. Analysis of the impact of high-order harmonics:

[0075] In practical applications, the high-order harmonic voltages generated by the switching action can be filtered through the resonant circuit. Their influence on the coupled inductance is small and can be ignored when analyzing the transmission power. The equivalent high-order harmonic circuit model is as follows: Figure 3 As shown, the high-order harmonics only act on the circuit loop composed of L1, C1 and inverter (L4, C4 and rectifier). Through Fourier decomposition, the high-order harmonic voltage U AB-HH and U ab-HH The root mean square value of is:

[0076]

[0077] In formula (8), N is the harmonic order, and the corresponding harmonic current can be derived as:

[0078]

[0079] The harmonic current passes through L1, C1 and the inverter (L4, C4 and rectifier), causing harmonic losses in L1, C1 and the inverter (L4, C4 and rectifier). As mentioned above, in the DLCC compensated IPT system, the transmitted power is mainly determined by the fundamental voltage. However, the power loss is caused by both the fundamental and higher harmonic voltages. In order to maximize the system efficiency, all losses in the IPT system need to be considered.

[0080] exist Figure 3 In the circuit, there are two high-order harmonic current loops, which cause harmonic losses in the circuit components L1, L4, C1, C4 and the inverter / rectifier. Li,N (Q Cj,N )and are the Nth-order reactive power and quality factor of inductors L1 and L4 (capacitors C1 and C4), respectively. The high-order harmonic losses on the inductors and capacitors are:

[0081]

[0082] in:

[0083]

[0084] Similar to the fundamental voltage, the high-order harmonic voltage will also introduce conduction loss P in the full-bridge inverter. inv,con,N , P loss,rec,N and switching loss P inv，sw，N Considering the orthogonality between harmonic voltages, the harmonic loss P of the full-bridge inverter is loss,con,HH It can be described as:

[0085]

[0086] Where:

[0087]

[0088] From the above loss description, it can be seen that the loss in the IPT system depends on the transmission requirements (P, V in 、V out ), coupling parameters (L2, L3, M 23 ) and compensation parameters (L1, L4, C1~C4). Since the core loss and high-order harmonic loss are nonlinear, the loss optimization of the IPT system is a nonlinear, multivariable, and complex optimization problem. It is difficult to directly minimize the total system loss to obtain the optimal parameter relationship while maintaining the transmission requirements.

[0089] Embodiment 2:

[0090] like Figure 4The IPT system parameter design method based on circuit parameter matching is used to design the parameters of the IPT system described in Example 1, and the specific steps are as follows:

[0091] S1: Set the transmission requirement parameters of the IPT system according to actual needs. The transmission requirement parameters of the IPT system include the DC input voltage V in , DC output voltage V out , transmission power P, resonant frequency f, transmission distance d 12 and coil size parameters;

[0092] In this embodiment, the application of wireless charging in electric vehicles is used as an example. The transmission distance, transmission power, coil size, etc. of wireless charging are determined according to actual needs. The basic requirements are shown in Table 1. Input and output voltage V in and V out Both are set to 500V and the transmission power is set to 10kW. To meet the operation requirements of electric vehicles, the transmission distance is set to 175mm. According to the installation requirements of electric vehicles, square coils with a primary coil L2 and a secondary coil L3 of 600mm are selected here.

[0093] Table 1 System operation requirements

[0094]

[0095]

[0096] S2: Set the coupler size and calculate the single-turn coupled self-inductance parameter L of the primary coil L2 20 , and the single-turn coupled self-inductance parameter L of the secondary coil L3 30 , and the coupling mutual inductance M between the primary coil L2 single turn and the secondary coil L3 single turn 230 , and the coupling coefficient k;

[0097] In this embodiment, the primary coil L2, the secondary coil L3, and the mutual inductance M of the primary coil L2 and the secondary coil L3 are 23 Described as:

[0098]

[0099] In formula (14), N2 and N3 are the number of turns of the primary coil L2 and the secondary coil L3 respectively.

[0100] In this embodiment, in this study, the square coil and the magnetic core are set to the same size. Figure 5The relevant dimensions are shown in Table 2. In practical applications, shielding plates are often used to block the spread of electromagnetic fields to the surrounding environment, which will produce certain eddy current losses. Since both shielding loss and core loss are caused by the magnetic field and are functions of the B field, in order to simplify the analysis, only the core loss is considered here without considering the shielding plate.

[0101] Table 2 Coupler dimensions

[0102]

[0103] After determining the coupler dimensions shown in Table 2, the coupling inductance L of the single-turn coupler can be obtained through finite element simulation. 20 , L 30 and M 230 . Self-inductance coefficient L 20 , L 30 About 0.69μH, mutual inductance coefficient M 230 About 0.25μH. The remaining parameter to be determined is the number of coil turns.

[0104] S3: Select independent parameters that affect the system variable loss and use the total system loss P loss,total Minimum is the optimization condition, and the value of the independent parameter is calculated;

[0105] In this embodiment, as mentioned above, the relationship between the circuit parameters in the power loss is complex, and it is extremely difficult to directly solve the three independent parameters of the primary compensation inductor L1, the primary coil L2, the secondary coil L3 and the secondary compensation inductor L4. A possible solution is to find new parameter variables to decouple the circuit parameters. From (1)-(13), it can be seen that, except for the core loss, the losses of the converter and the resonant slot can be described as functions of the circuit parameters. In order to achieve parameter decoupling, it is necessary to find a new independent variable that can characterize the core loss. As mentioned above, the core loss is proportional to the ampere-turns of the coil and can be expressed as:

[0106] B2∝N2I2,B3∝N3I3(15)

[0107] In formula (15), B2 and B3 are the magnetic flux generated by the primary coil L2 and the secondary coil L3 respectively; then from formula (14), it can be seen that the system's transfer power can be expressed as:

[0108] P=ωM 230 N2I2N3I3 (16)

[0109] From equations (15) and (16), it can be seen that N2I2 (or N3I3) can be regarded as the characteristic parameter of the core loss, and the total core loss can be expressed as a function of N2I2:

[0110] P loss,core=f(N2I2) (17)

[0111] Since N2I2 (or N3I3) is independent of any two parameters in (L1, L2, L3, L4), they can be regarded as independent circuit parameters. N2I2, L1 and L4 are selected as the three independent parameters of the DLCC compensation IPT system. The total system loss P loss,total It can be described as a function of the following three independent parameters: the product of the number of primary coil turns and the primary coil current N2I2, the inductance value L1 of the primary compensation inductor, and the inductance value L4 of the secondary compensation inductor:

[0112]

[0113] To simplify the analysis, the quality factors of the coupled inductors (compensation inductors or capacitors) are set equal, where:

[0114]

[0115] From equation (18), it can be seen that, given the transmission demand, the total loss of the IPT system mainly consists of two parts: the constant converter loss under the fundamental wave and the variable loss affected by three independent parameters. According to the selected independent parameters (N2I2, L1 and L4), the total system loss can be clustered into three losses containing only a single independent parameter. The total loss can be simplified as:

[0116] P loss,total =P loss,con,FH +P loss (N2I2)+P loss (L1)+P loss (L4) (20)

[0117] Where:

[0118]

[0119] Through the above analysis, minimizing the loss of a multivariable nonlinear system is transformed into minimizing three losses involving only a single parameter, which can be easily achieved by taking the derivative of a single parameter among the three losses. The loss P in formula (20) is loss (L1) and P loss (L4) are the quadratic and cubic functions of L1 and L4 respectively. Using the corresponding root-finding formula, P can be easily found. loss (L1) and P loss (L4) and the associated values ​​of L1 and L4. It should be noted that the loss P loss (N2I2) includes core loss P loss,core(N2I2), due to the uneven distribution of the magnetic field, its accurate expression is difficult to obtain. Therefore, the core loss P of this application is loss,core (N2I2) is obtained through finite element simulation. With the determined core loss P loss,core (N2I2), by taking the derivative of the parameter N2I2, we can get the loss P loss The minimum value of (N2I2). The minimum total system loss and the values ​​of the related independent parameters N2I2, L1 and L4 are obtained.

[0120] S4: Calculate the mutual inductance M between the primary coil and the secondary coil based on the independent parameters, transmission requirement parameters, and equations (2), (15), and (16): 23 , as well as the number of turns N2, N3 of the primary coil and the secondary coil and the self-inductance values ​​L2, L3;

[0121] S5: Calculate the compensation capacitor parameters of the system compensation circuit according to the number of coil turns, transmission requirement parameters and resonance conditions, and select a suitable actual compensation capacitor value.

[0122] In this embodiment, the resonance condition is expressed as:

[0123] ω=1 / (L1C1)=1 / (L4C4)=1 / ((L2-L1)C2)=1 / ((L3-L4)C3) (23)

[0124] The circuit parameters after system optimization are shown in Table 3.

[0125] Table 3 Circuit parameters

[0126]

[0127] S6: Determine whether the system transmission power meets the power requirement. If yes, go to step S7. If no, return to step S5 to reselect the actual compensation capacitor value and continue to iterate and update the system parameters.

[0128] S7: Determine whether the system transmission efficiency meets the efficiency requirements. If so, output that the system parameter design is completed. If not, return to step S2 and reset the coupler size parameters, and continue to iterate and update the system parameters.

[0129] S8 simulation verification:

[0130] According to the determined circuit parameters, the transmission performance of the IPT system was simulated and experimentally verified. The simulation and experimental results are consistent with the theoretical analysis. A 10kw experimental prototype was built and experimental results under different offset conditions were obtained. The results show that after optimizing the circuit parameters, the dc-dc efficiency of the prototype can reach 97% when the air gap is 170mm.

[0131] S8.1 simulation verification:

[0132] Based on the proposed parameter design method, the transmission performance of the IPT system with different coil turns is simulated using LTspice software. The output voltage is set to 500V, and the output power increases with the increase of input voltage. The simulated dc-dc efficiency at different output powers is shown in Fig. 9 As shown in the figure. The transmission efficiency increases with the increase of output power and reaches the maximum value at the rated output power. When the number of coil turns is set to 10, the rated transmission power is close to 10kW and the dc-dc efficiency is about 97%. When the number of coil turns increases from 10 to 30, the dc-dc efficiency at the rated output power decreases from 97% to 95.9%. The change in transmission efficiency is mainly caused by P loss (L1) and P loss (L4) caused by changes, such as Figure 7 shown.

[0133] S8.2 Experimental verification:

[0134] According to the optimized circuit parameters in Table 3, a 10kW prototype was built. The inductive coupler was wound with multiple 0.1mm, 550-strand Litz wires. The resonant capacitor was made of a film capacitor. The actual circuit parameters are shown in Table 4. The full-bridge inverter consists of four SiC transistors (IMZ120R045M1) and the rectifier consists of four SiC diodes (IDW40G120C5B). To ensure that the system works in the ZVS state, the values ​​of inductors L1, L4 and capacitors C2, C3 are appropriately adjusted.

[0135] The experimental results are as follows Fig.10 , 11 , as shown in 12, Fig.10 (a) is the output voltage and current waveform of the full-bridge inverter. Fig.10 (b) is the system output power and efficiency results. Fig.10 In the process, the output voltage and current of the full-bridge inverter are basically consistent, reaching the ZVS state, ensuring the high transmission performance of the system. The transmission power at the rated input and output voltage is about 10kW, and the dc-dc efficiency is about 97%.

[0136] The transmission performance of the system at different output voltages is as follows: Fig.11 As shown. When the output voltage is set to 500V, the DC efficiency increases with the increase of output power and reaches the maximum value at the rated output power. At the rated transmission power of 10 kilowatts, the maximum transmission efficiency of 97% is achieved. When the output voltage is set to 400V (or 300V), the DC-DC efficiency first increases with the increase of output power, reaches the maximum value, and then decreases. The maximum value is about 97%. The experimental results are consistent with the analysis of this application.

[0137] In this application, the rated output load resistance of the system is about 25Ω. Under the rated load, the transmission performance of the system under different offset distance conditions is tested. The results are shown in Fig.12 As shown. When the coupler is aligned, the dc-dc efficiency increases with the increase of output power, reaching a maximum value of 97% at a rated output power of 10kW. When the offset distance is 150mm, the output power drops from 10kW to 5kW, and the dc-dc efficiency drops from 97% to 96.6%, which has good anti-offset performance.

[0138] To illustrate the unique contribution of this paper, a comprehensive comparison of IPT systems with DLCC compensation using different parameter optimization design methods is conducted in this paper, as shown in Table 5. Using the proposed optimization design method, the designed IPT prototype has good transmission performance and can transmit about 10kW of power over a distance of 175-mm with a DC-DC efficiency of 97%. It should be pointed out that it is unfair to simply compare the efficiency because it is affected by many factors. To this end, the quality factor WPTFOM of the WPT system is introduced to evaluate the transmission performance of the IPT system with similar configuration (the operating frequency is about 85kHz, and optimizing the system efficiency is the main goal). In WPTFOM, the transferred power P, efficiency η, air gap d, and coupler area S are considered and defined as:

[0139]

[0140] As shown in Table 4, the WPTFOM value of the IPT system designed by the parameter design method of this application is much higher than that of other IPT systems with similar configurations. In addition, the characteristics of the parameter design method proposed in this application and the existing optimization methods are also compared in Table 4. The main difference is that the optimization method proposed in this application takes into account all losses in the IPT system and obtains the analytical solution of the global optimal circuit parameters of the high-order compensation IPT system for the first time.

[0141] Table 4 Performance comparison of existing IPT systems with DLCC compensation circuits

[0142]

[0143] In order to better reflect the effectiveness of the parameter design method described in this application under different coupling coefficients, the optimal transmission efficiency of the IPT system under different coupling coefficients k is also calculated. The results are shown in Table 5. It can be seen that using the method proposed in this article, the efficiency of the IPT system under different coupling coefficients is higher than that of the existing IPT system with similar coupling coefficients.

[0144] Table 5 IPT system performance under different coupling coefficients

[0145]

[0146] By calculating the power loss of the inverter, rectifier, inductor and capacitor, the power loss distribution of the actual components of the system is obtained, such as Fig.13 As shown. The main part of the loss is the loss of the coupling inductor, compensation capacitor and converter, accounting for about 90.1% of the total loss. In addition, the loss P corresponding to the variables N2I2, L1 and L4 in Equation 20 and Equation 21 is also calculated. loss (N2I2),P loss (L1) and P loss (L4), accounting for approximately 45.6%, 8.7% and 8.6% of the total losses respectively.

[0147] The above experiments verify that the IPT system designed by the parameter design method proposed in this application can achieve a dc-dc efficiency of 97% when the output power is 10kW, and has good anti-offset performance. The simulation and experimental results are consistent with the theoretical analysis, verifying the effectiveness of the proposed method.

[0148] In summary, this application proposes a parameter design method for an IPT system from the perspective of global loss minimization. The fundamental wave and higher harmonics are considered when designing the coupling inductor and compensation parameters. First, the total power consumption of the system and its relationship with the circuit parameters are analyzed. By selecting three independent variables, the total loss of the IPT system is converted into three losses containing only a single variable, and the theoretical maximum system efficiency can be easily derived. Based on this method, the complexity of the parameter design process can be simplified, and the optimal matching relationship between electrical parameters can be revealed. At the same time, the transmission performance of the IPT system after parameter optimization is analyzed and compared with the existing system. The results verify the effectiveness of the proposed parameter design method.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for designing IPT system parameters based on circuit parameter matching, wherein the IPT system comprises a DC power supply, a full-bridge inverter, a DLCC compensation circuit, a coupler, a rectifier and a load, wherein the coupler comprises a primary coil and a secondary coil, and wherein: The specific steps of the IPT system parameter design method are: S1: Set the transmission requirement parameters of the IPT system according to actual needs; S2: Set the coupler size parameters, calculate the single-turn coupled self-inductance parameters of the primary coil and the secondary coil, and the single-turn coupled mutual inductance parameters of the primary coil and the secondary coil; S3: Select independent parameters that affect the variable loss of the system, and calculate the value of the independent parameters with the minimum total loss of the system as the optimization condition; S4: Calculate the mutual inductance between the primary coil and the secondary coil, the number of turns of the primary coil and the secondary coil, and the self-inductance value according to the independent parameters and the transmission requirement parameters; S5: Calculate the compensation capacitor parameters of the system compensation circuit according to the number of coil turns, transmission requirement parameters and resonance conditions, and select a suitable actual compensation capacitor value.

2. The IPT system parameter design method based on circuit parameter matching according to claim 1, characterized in that: The IPT system transmission requirement parameters in step S1 include DC input voltage, DC output voltage, transmission power, resonant frequency, transmission distance and coil size parameters.

3. The IPT system parameter design method based on circuit parameter matching according to claim 1, characterized in that: In step S2, the coupler size parameters include the coupler core length, core thickness, coil thickness, coil-to-core spacing, and coil internal side length parameters; After the size of the coupler is determined, the single-turn coupled self-inductance parameters of the primary coil and the secondary coil, and the single-turn coupled mutual inductance of the primary coil and the secondary coil are obtained by simulation calculation.

4. The IPT system parameter design method based on circuit parameter matching according to claim 1 or 3, characterized in that: In step S3, the independent parameters affecting the variable loss of the system include the product of the number of turns of the primary coil and the current of the primary coil, the inductance value of the primary compensation inductor, and the inductance value of the secondary compensation inductor.

5. The IPT system parameter design method based on circuit parameter matching according to claim 4, characterized in that: In step S3, the total system loss is equal to the sum of the constant full-bridge converter loss under the fundamental wave and the three variable losses affected by three independent parameters, wherein the full-bridge converter loss includes the full-bridge inverter loss and the rectifier loss; The minimum values ​​of the three variable losses and their corresponding three independent parameter values ​​are calculated respectively to obtain the optimized three independent parameter values.

6. The IPT system parameter design method based on circuit parameter matching according to claim 4, characterized in that: The specific method for calculating the mutual inductance between the primary coil and the secondary coil in step S4 is: The system transmission power P is: P=8M 23 V in V out / p 2 ωL1L4 Where M 23 is the mutual inductance between the primary coil and the secondary coil, V in is the DC input voltage, V out is the DC output voltage, ω is the system angular frequency, L1 and L4 are the inductance values ​​of the primary and secondary compensation inductors respectively; The mutual inductance between the primary coil and the secondary coil is calculated according to the transmission power parameter set in step S1 and the primary compensation inductance and the secondary compensation inductance parameters calculated in step S3.

7. The IPT system parameter design method based on circuit parameter matching according to claim 6, characterized in that: The specific steps of calculating the number of turns of the primary coil and the secondary coil and the self-inductance value in step S4 are: The mutual inductance between the primary and secondary coils is equal to the product of the number of turns of the primary coil, the number of turns of the secondary coil and the single-turn coupled mutual inductance of the primary coil and the secondary coil. The self-inductance of the primary and secondary coils is equal to the product of the square of the number of turns of the coil and the single-turn coupled self-inductance parameter of the coil. The number of turns of the primary coil and the secondary coil is calculated by the mutual inductance between the primary coil and the secondary coil calculated in step S4.1 and the single-turn coupled mutual inductance of the primary coil and the secondary coil calculated in step S2; the self-inductance values ​​of the primary coil and the secondary coil are calculated respectively by the single-turn coupled self-inductance parameters of the primary coil and the secondary coil calculated in step S2 and the number of turns of the primary coil and the secondary coil.

8. The IPT system parameter design method based on circuit parameter matching according to claim 7, characterized in that: The system resonance condition in step S5 is: The values ​​of parameters 1 / (L1C1), 1 / (L4C4), 1 / ((L2-L1)C2) and 1 / ((L3-L4)C3) are all equal to the system angular frequency, where: L1 and L4 are the inductance values ​​of the primary and secondary compensation inductors respectively, L2 and L3 are the self-inductance values ​​of the primary and secondary coils respectively, C1 and C2 are the capacitance values ​​of the first and second primary compensation capacitors respectively, and C3 and C4 are the capacitance values ​​of the first and second secondary compensation capacitors respectively.

9. The IPT system parameter design method based on circuit parameter matching according to claim 1, characterized in that: The IPT system parameter design method also includes: S6: Determine whether the system transmission power meets the power requirement. If yes, go to step S7. If no, return to step S5 to reselect the actual compensation capacitor value and continue to iterate and update the system parameters. S7: Determine whether the system transmission efficiency meets the efficiency requirements. If so, output that the system parameter design is completed. If not, return to step S2 and reset the coupler size parameters, and continue to iterate and update the system parameters.

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