LCC-S type wireless charging system receiving end resonance parameter calculation method

Abstract

The application relates to a kind of LCC-S type wireless charging system receiving end resonance parameter calculation methods, belong to wireless charging field.The method takes LCC-S type wireless charging system as the research object, considers the nonlinearity of harmonic and rectification load, analyzes the transmission characteristics of the system, and then proposes the calculation method of load impedance and receiving end series resonance capacitance parameter based on rectification load compensation.The receiving end resonance parameter design method can make the system receiving end loop resonance, and improve the output power of the system.

Description

Technical Field

[0001] This disclosure relates to the field of wireless charging, and in particular to a method for calculating the resonant parameters of the receiver of an LCC-S type wireless charging system. Background Technology

[0002] Due to its advantages such as no need for cable connections, safety and reliability, and flexible power supply, wireless charging technology has become a research hotspot both domestically and internationally in recent years. To ensure the system has high output power and transmission efficiency, the parameters of each resonant element in the compensation network are often designed to bring the system into a resonant state.

[0003] Common compensation networks include four basic types: series-series (SS), series-parallel (SP), parallel-parallel (PP), and parallel-series (PS), as well as higher-order compensation networks such as LCL compensation and LCC compensation. Among these, the LCC-S type compensation network is widely used due to its advantages such as constant transmitting coil current, adjustable system output voltage, and ease of soft-switching. The circuit diagram of an LCC-S wireless charging system is shown below. Figure 1 As shown. MOSFET switches T1-T4 form a full-bridge inverter circuit; L f C f C1 and C2 are the series resonant inductance, parallel resonant capacitor, and series resonant capacitor at the transmitting end, respectively; L1 and L2 are the self-inductances of the transmitting coil and the receiving coil, respectively; M is the mutual inductance between the two coils; C2 is the series resonant capacitor at the receiving end; diodes D1-D4 form an uncontrolled rectifier circuit, C... d R is the DC output filter capacitor, R is the DC side load resistor, and Z is the DC output filter capacitor. o This is the equivalent impedance of a rectifying load. U in_dc U out_dc and I out_dc These represent the DC input voltage, DC output voltage, and DC output current of the system circuit, respectively. in and u out These are the output square wave voltage of the inverter circuit and the input voltage of the rectifier bridge, respectively. in i1 and i2 are the output current, transmitting coil current, and receiving coil current of the inverter circuit, respectively, and u C2 This is the voltage of the series resonant capacitor at the receiving end.

[0004] To power the DC-side load R of the system, a rectifier and filter circuit needs to be added to the front end of the DC-side load. The rectifier and filter circuit and the DC-side load can be considered equivalent to a rectifier load. Currently, the transmission characteristic analysis and resonant element parameter design of the LCC-S wireless charging system are based on the fundamental equivalent method, which equates the rectifier load to a resistance of 8 / π for the DC-side load. 2 The pure resistance is times that of the original resistance. The resonance parameters are usually calculated based on the resonance formula (1).

[0005]

[0006] Some scholars have also used the fundamental equivalent method to treat the rectifier load as a pure resistor, derived the expression for the fundamental input impedance angle of the system, and achieved zero-voltage turn-on of the switching transistor by optimizing the parameters of the series resonant inductor and capacitor at the transmitter (Analysis and Design of an LCC / S Compensated Resonant converter for Inductively Coupled Power Transfer [C]. 2017 IEEE Transportation Electrification Conference and Expo, Asia-Pacific (ITEC Asia-Pacific). 2017, pp. 1-5). In the existing mainstream LCC-S wireless charging system receiver resonant parameter design methods, although the design methods and processes are different, the rectifier load is always based on the fundamental equivalent method (i.e., treating the rectifier load as a DC-side load with a resistance of 8 / π). 2 (times the pure resistance).

[0007] The rectifier load at the receiver end of a wireless charging system has nonlinear characteristics. If the rectifier load is equivalent to a pure resistor based on the fundamental wave equivalent method for transmission characteristic analysis and resonant element parameter design, the system will deviate from the resonant point, resulting in deviations in the system transmission characteristic analysis and reactive power compensation, and reducing the transmission power and efficiency of the wireless charging system.

[0008] Some scholars (for example, a method and system for identifying multiple load parameters in a wireless charging system: CN202011484877, and an impedance matching network optimization method for a wireless power transmission system under maximum efficiency tracking: CN201910628859.X) have considered the nonlinear design system resonance parameters of rectifier loads. However, the calculation of the equivalent impedance of rectifier loads is obtained by directly measuring the input voltage and current of the rectifier bridge and then performing Fourier analysis. However, measurement errors are inevitable, and data acquisition and processing are relatively complicated.

[0009] Therefore, existing research lacks mathematical models for the rectifier load in the system and accurate methods for calculating impedance, which affects the accurate analysis and design of the system's transmission characteristics and resonant component parameters. Summary of the Invention

[0010] In existing technologies, the receiver circuit of wireless charging systems all include a rectifier circuit to convert the alternating current from the receiving coil into direct current for output to the load. This rectified load has non-linear characteristics, and can be equivalent to a pure resistor (i.e., 8 / π of the DC-side load). 2Performing transmission characteristic analysis and resonant element parameter design on the system by a factor of 100 will cause the system to deviate from the resonant point, resulting in deviations in the system transmission characteristic analysis and reactive power compensation, and reducing the transmission power and efficiency of the wireless charging system.

[0011] To address this problem, this invention focuses on an LCC-S type wireless charging system, considering harmonics and the nonlinearity of the rectifier load. It analyzes the system's transmission characteristics and proposes a method for calculating the load impedance and receiver series resonant capacitor parameters based on rectifier load compensation. The proposed receiver resonant parameter design method enables the system's receiver circuit to resonate, thereby improving the system's output power.

[0012] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows.

[0013] In a first aspect, the present invention proposes a method for calculating the resonant parameters of the receiver of an LCC-S type wireless charging system, the method comprising the following steps:

[0014] S100. Based on the nonlinear characteristics of harmonics and rectifying loads, the following parameters are obtained when the receiver circuit resonates: receiver resonant capacitance C2, receiver coil self-inductance L2, and rectifying load fundamental impedance Z. o_1 Satisfaction Relationship:

[0015]

[0016] In the formula: |Z o_1 | represents the amplitude of the fundamental impedance of the rectifier load, and ω represents the switching angular frequency. The fundamental impedance angle of the rectifying load;

[0017] S200. Based on making the receiving end circuit resonant, obtain the expression for the rectifier load impedance value, calculate the amplitude and phase angle of the fundamental impedance of the rectifier load according to the iterative method, and then compensate for it to obtain the parameter value of the receiving end resonant capacitor C2.

[0018] In the above technical solution, step S100 includes:

[0019] Assuming resonant inductance L f and parallel resonant capacitor C f To maintain constant resonance, the fundamental component of the transmitting coil current i1 is obtained. 1_1 Constantly:

[0020]

[0021] Where: u in_1 The inverter circuit outputs a square wave voltage u in fundamental wave component;

[0022] Obtain the fundamental impedance Z of the receiver loop2_1 for:

[0023]

[0024] in:

[0025]

[0026] The fundamental component of the receiving coil current i2 2_1 for

[0027]

[0028] Where: M is the mutual inductance of coils L1 and L2;

[0029] rectifier bridge input voltage u out Fundamental component u out_1 for:

[0030]

[0031] in:

[0032]

[0033] Therefore, when γ = 0, the resonant capacitance C2 at the receiving end satisfies:

[0034]

[0035] In the above technical solution, the fundamental impedance amplitude and phase angle have the following relationship:

[0036]

[0037] In the formula: |Z o_n | represents the amplitude of the nth harmonic impedance of the rectifier load. The phase angle of the nth harmonic impedance of the rectifier load is determined by the square wave voltage u output by the inverter circuit. in and rectifier bridge input voltage u out It is approximated as a square wave, and obtained by analyzing the nth equivalent circuit of the system using the harmonic analysis method; For the fundamental impedance angle of the rectifying load, |Z o_1 | represents the fundamental impedance amplitude of the rectifier load, and R represents the DC-side load resistance.

[0038] In the above technical solution, the expression for the nth harmonic impedance value of the rectifier load is as follows:

[0039] Z o_n =a / / b

[0040] Where " / / " indicates that a is connected in parallel with b;

[0041]

[0042] In the formula: L f M is the series resonant inductance of the transmitting end, and M is the mutual inductance between the transmitting coil L1 and the receiving coil L2.

[0043] In the above technical solution, step S200 includes the following steps:

[0044] The impedance angle of the fundamental impedance of the rectifier load The initial value is 0°;

[0045] S201. The value of the series resonant capacitor C2 at the receiving end is calculated using the following formula:

[0046]

[0047] Based on the expression for the nth harmonic impedance value of the rectifier load, the impedance amplitude and phase angle of each harmonic are obtained;

[0048] Based on the impedance amplitude and phase angle of each harmonic, the fundamental impedance amplitude and phase angle are obtained according to the relationship between the fundamental impedance amplitude and phase angle.

[0049] Determine whether the fundamental impedance angle iteration error meets the set error accuracy requirement. If it does not meet the requirement, return to step S201; otherwise, end the calculation to obtain the rectifier load impedance value and the value of C2.

[0050] In the above technical solution, the error accuracy is set to 1%.

[0051] In a second aspect, a computer-readable storage medium stores a computer program that can be loaded by a processor and executed by any of the methods described above.

[0052] This invention derives the expression for the rectifier load impedance when the receiver circuit of the LCC-S wireless charging system resonates. Based on an iterative method, the fundamental and harmonic impedances of the rectifier load are accurately calculated and compensated. The parameters of the receiver resonant capacitor C2 are then designed accordingly. Compared to designing resonant parameters based on the fundamental equivalent method, this invention puts the receiver circuit in a resonant state. Under the same DC input voltage, the system has a larger DC output voltage and output power, thus improving the system's power transmission capability. Attached Figure Description

[0053] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 The circuit diagram of the LCC-S wireless charging system mentioned in the background technology;

[0055] Figure 2 , one A schematic diagram of the equivalent circuit of the LCC-S type wireless charging system involved in a specific implementation;

[0056] Figure 3 , one A schematic diagram of the nth equivalent circuit of the LCC-S type wireless charging system involved in a specific implementation;

[0057] Figure 4 , one The i2 and u involved in the specific implementation method in and u out Phase relationship diagram;

[0058] Figure 5 , one A flowchart illustrating the iterative calculation process of the rectifying load impedance in one specific implementation. Detailed Implementation

[0059] The LCC-S type wireless charging system involved in this invention, such as Figure 1 As shown, it includes a DC-AC inverter unit, a transmitter resonant unit, a receiver resonant unit, and an AC-DC conversion unit; the DC-AC inverter unit consists of a full-bridge inverter circuit composed of four MOSFET switches T1-T4, which converts the DC input voltage U... in_dc The power is inverted to alternating current, and the transmitting end resonant unit includes a resonant inductor L. f Resonant capacitor C f The resonant capacitor C1 and the resonant inductor are connected at one end between the source of MOSFET switch T1 and the drain of MOSFET T3, and at the other end with the resonant capacitor C1. f One end of the resonant capacitor C1 is connected to the ground, and the other end of the resonant capacitor C1 is connected to one end of the self-inductance L1 of the transmitting coil. f The other end is connected to the resonant capacitor C f The other end is connected to the source of MOSFET switch T2 and the drain of MOSFET T4; the AC-DC conversion unit includes one DC output filter capacitor C. d One DC-side load resistor R, four diodes D1-D4; D1 and D3 are connected in series, then connected in parallel with the series-connected D2 and D4; the series-connected D2 and D4 are connected in parallel with the DC output filter capacitor C. dThe receiver is connected in parallel with the DC-side load resistor R. The receiving end resonant unit consists of the receiving coil self-inductance L2 and the resonant capacitor C2. One end of the receiving coil self-inductance L2 is connected to one end of the resonant capacitor C2, and the other end of the receiving coil self-inductance L2 is connected between D2 and D4. The other end of the resonant capacitor C2 is connected between D1 and D3.

[0060] For the aforementioned LCC-S type wireless charging system, the nonlinear characteristics of harmonics and rectifier loads are considered when analyzing the system's transmission characteristics. When designing the receiver resonance parameters, the expressions for the fundamental and harmonic impedances of the rectifier load when the receiver circuit resonates based on rectifier load compensation are derived. An iterative method is proposed to accurately calculate the rectifier load impedance, and then design the receiver resonance parameters to achieve system receiver circuit resonance and improve the system's output power.

[0061] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0062] I. Analysis of System Transmission Characteristics Considering Harmonic and Rectifying Load Nonlinearity

[0063] Assuming resonant inductance L f and parallel resonant capacitor C f If the resonant frequency is always maintained, then the fundamental component of the transmitting coil current i1 is i 1_1 Constant:

[0064]

[0065] Where: u in_1 The inverter circuit outputs a square wave voltage u in fundamental wave component.

[0066] The fundamental impedance Z of the receiver circuit 2_1 for:

[0067]

[0068] Where: Z o_1 The fundamental impedance of a rectifying load can be expressed as:

[0069]

[0070] |Z o_1 | and These represent the amplitude and impedance angle of the fundamental impedance of the rectifier load, respectively.

[0071] The fundamental component of the receiving coil current i2 2_1 for:

[0072]

[0073] Receiver series resonant capacitor voltage u C2 Fundamental component u C2_1 for:

[0074]

[0075] Combining equation (5), we can see that i 1_1 with u C2_1 The phase difference is the fundamental impedance Z of the receiving end circuit. 2_1 The impedance angle.

[0076] rectifier bridge input voltage u out Fundamental component u out_1 for:

[0077]

[0078] in:

[0079]

[0080] System output power P out_dc for:

[0081]

[0082] Inverter circuit output voltage u in and rectifier bridge input voltage u out Both can be approximated as square wave voltages. If the forward voltage drop of the switching transistor and the diode is ignored, the corresponding fundamental amplitudes are respectively

[0083]

[0084] When γ = 0, that is, when capacitor C2 satisfies:

[0085]

[0086] The receiver circuit resonates fully at the switching frequency, Z 2_1 For pure resistance, i 1_1 with u C2_1 If the fundamental amplitude of the rectifier bridge input voltage is at its maximum, then the system DC output voltage U... out _ dc Maximum, system output power P out_dc The maximum. Therefore, in the parameter design of C2, the self-inductance L2 of the receiving coil and the fundamental impedance Z of the rectifier load should be considered. o_1 Simultaneously, compensation is performed to make the receiving end circuit resonate.

[0087] II. Calculation method for rectifier load impedance and design method for resonance parameters during receiver circuit resonance

[0088] To ensure resonance in the receiver circuit, the fundamental impedance of the rectifier load at this point needs to be obtained first when designing the parameters of the receiver series resonant capacitor C2. This embodiment calculates the rectifier load impedance at receiver circuit resonance and then designs the parameter values ​​of the receiver series resonant capacitor C2.

[0089] exist Figure 1 In the system model shown, the inverter circuit outputs a square wave voltage u. in and rectifier bridge input voltage u out Approximating it as a square wave, and equating it to a square wave voltage source, we can obtain the equivalent circuit of the LCC-S type wireless charging system as follows: Figure 2 As shown.

[0090] Square wave voltage u in and u out Fourier series decomposition, based on harmonic analysis, yields the nth-order equivalent circuit of the system, such as... Figure 3 As shown.

[0091] i in the figure 2_n To receive the nth harmonic component of the coil current i2, u in_n The output voltage u of the inverter circuit in The nth harmonic component, u out_n The nth harmonic component of the rectifier bridge input voltage has the following amplitudes:

[0092]

[0093] The nth harmonic impedance Z of the rectifier load o_n for:

[0094]

[0095] According to the superposition theorem, i 2_n can be derived from u out_n Harmonic components of the receiving coil current under sole action and u in_n The result is obtained by superimposing the harmonic components of the receiving coil current under individual action:

[0096]

[0097] When the receiving circuit resonates at the switching frequency, the rectifier bridge input voltage u can be obtained from equation (7). out The fundamental component is:

[0098]

[0099] At this time u out_1 Advanced u in_1 The phase angle is the fundamental impedance angle of the rectifying load. Then u out_n Advanced u in_n The phase angle is n times. Combining equation (11), we can obtain the amplitude relationship:

[0100]

[0101] Therefore, we can obtain u in_n with u out_n The corresponding vector relationship is:

[0102]

[0103] Substituting equation (16) into equation (13), then Z o_n It can be represented as:

[0104] Z o_n =a / / b (17)

[0105] Where a and b are connected in parallel, and a and b are respectively:

[0106]

[0107] From equations (2) and (5), it can be seen that when the receiving circuit resonates, i 2_1 with u in_1 They are in phase. Simultaneously, the current i2 in the receiving coil of the rectifier bridge circuit is in phase with the input voltage u of the rectifier bridge. out The zero-crossing points are the same. Assume the fundamental component u of the inverter circuit output voltage is... in_1 If the initial phase angle is 0°, then the corresponding phase relationship is as follows: Figure 4 As shown, the following equations can be derived from this:

[0108]

[0109] Where t0 satisfies

[0110] DC output current I in rectifier bridge circuit out_dc The relationship between the fundamental amplitude of the receiving coil current i2 and the fundamental amplitude can be approximated as follows:

[0111]

[0112] Solving equations (19) and (20) together yields:

[0113]

[0114] As can be seen from equations (17), (18), and (21), the harmonic impedance and fundamental impedance of the rectifier load influence each other, making direct solution difficult. This invention employs an iterative method for calculation. First, the initial value of the fundamental impedance angle of the rectifier load is set to 0°. The value of C2 is calculated according to equation (10). The harmonic impedances of each order are obtained according to equations (17) and (18). The harmonic impedances are substituted into equation (21) to obtain the fundamental impedance value. The iteration error of the fundamental impedance angle is then judged to meet the error accuracy requirements. In this embodiment, the upper limit of the iteration error is set to 1%. If it meets the requirements, the iterative calculation ends to obtain the rectifier load impedance value; otherwise, the above iterative process continues. The specific iterative process is as follows: Figure 5 As shown. After the iteration is complete, the value of C2 can be obtained.

[0115] The rectifier load impedance calculation method and resonant parameter design method of the present invention are applicable to wireless charging systems with a series compensation structure at the receiver end. Here, the series compensation at the receiver end is represented by S. Therefore, the method of the present invention is applicable not only to inductor-capacitor-capacitor-series resonant compensation (LCC-S), but also to parallel-series resonant compensation network (PS), inductor-capacitor-inductor-series resonant compensation (LCL-S), inductor-capacitor-capacitor-inductor-series resonant compensation (LCCL-S), etc.

[0116] In summary, this invention derives the expression for the rectifier load impedance when the receiver circuit of the LCC-S wireless charging system resonates. Based on an iterative method, the fundamental and harmonic impedances of the rectifier load are accurately calculated and compensated. The parameters of the receiver resonant capacitor C2 are then designed accordingly. Compared to designing resonant parameters based on the fundamental equivalent method, this invention puts the receiver circuit in a resonant state. Under the same DC input voltage, the system has a larger DC output voltage and output power, thus improving the system's power transmission capability.

[0117] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for calculating the resonant parameters of the receiver in an LCC-S type wireless charging system, characterized in that, The method includes the following steps: S100. Based on the nonlinear characteristics of harmonics and rectifying loads, the following parameters are obtained when the receiver circuit resonates: receiver resonant capacitance C2, receiver coil self-inductance L2, and rectifying load fundamental impedance Z. o_1 Satisfaction Relationship: In the formula: |Z o_1 | represents the amplitude of the fundamental impedance of the rectifier load, and ω represents the switching angular frequency. The fundamental impedance angle of the rectifying load; S200. Based on making the receiving end circuit resonant, obtain the expression for the rectifier load impedance value, calculate the amplitude and phase angle of the fundamental impedance of the rectifier load according to the iterative method, and then compensate for it to obtain the parameter value of the receiving end resonant capacitor C2. The expression for the harmonic impedance value of a rectifying load is as follows: WITH o_n =a∥b In the formula: L f M is the series resonant inductance of the transmitting end, and M is the mutual inductance between the transmitting coil L1 and the receiving coil L2.

2. The method according to claim 1, characterized in that, Step S100 includes: Assuming resonant inductance L f and parallel resonant capacitor C f To maintain constant resonance, the fundamental component of the transmitting coil current i1 is obtained. 1_1 Constantly: Where: u in_1 The inverter circuit outputs a square wave voltage u in fundamental wave component; Obtain the fundamental impedance Z of the receiver loop 2_1 for: in: The fundamental component of the receiving coil current i2 2_1 for Where: M is the mutual inductance of coils L1 and L2; rectifier bridge input voltage u out Fundamental component u out_1 for: in: Therefore, when γ = 0, the resonant capacitance C2 at the receiving end satisfies:

3. The method according to claim 1, characterized in that, The fundamental impedance amplitude and phase angle of a rectifying load have the following relationship: In the formula: |Z o_n | represents the amplitude of the nth harmonic impedance of the rectifier load. The phase angle of the nth harmonic impedance of the rectifier load is determined by the square wave voltage u output by the inverter circuit. in and rectifier bridge input voltage u out It is approximated as a square wave, and obtained by analyzing the nth equivalent circuit of the system using the harmonic analysis method; For the fundamental impedance angle of the rectifying load, |Z o_1 | represents the fundamental impedance amplitude of the rectifier load, and R represents the DC-side load resistance.

4. The method according to claim 1, characterized in that, S200 includes the following steps: The impedance angle of the fundamental impedance of the rectifier load The initial value is 0°; S201. The value of the series resonant capacitor C2 at the receiving end is calculated using the following formula: Based on the expression for the harmonic impedance value of a rectifier load, the impedance amplitude and phase angle of each harmonic are obtained; Based on the impedance amplitude and phase angle of each harmonic, the fundamental impedance amplitude and phase angle are obtained according to the relationship between the fundamental impedance amplitude and phase angle. Determine whether the fundamental impedance angle iteration error meets the set error accuracy requirement. If it does not meet the requirement, return to step S201; otherwise, end the calculation to obtain the rectifier load impedance value and the value of C2.

5. The method according to claim 4, characterized in that, The error accuracy is set to 1%.

6. A computer-readable storage medium, characterized in that: The computer program is stored that can be loaded by a processor and executed according to any one of claims 1 to 5.

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