Wide-power-range soft switching hybrid control method for wireless charging system of electric vehicle

Abstract

The invention provides a soft switching hybrid control method for a wide power range of an electric vehicle wireless charging system. The method is used for solving the problems of loss increase and transmission efficiency reduction of an existing system. The method comprises the steps of initializing system circuit parameters, system working frequency, an expected current value of system constant-current charging and an expected voltage value of system constant-voltage charging; the charging voltage and the charging current of a system load battery are sampled in real time, and the equivalent internal resistance and the normalized output power of the load battery are calculated; selecting a constant-current or constant-voltage charging mode of the system according to the charging voltage of the load battery, and selecting a full-bridge or half-bridge working mode of the high-frequency inverter according to the selected charging mode and the normalized output power; and calculating the phase angle controlled by the high-frequency inverter and the switching frequency of ZVS realized by the high-frequency inverter in the next control period in different modes, and controlling the high-frequency inverter. According to the invention, energy loss and electromagnetic interference in the electric energy conversion process are reduced, and more stable and reliable wireless charging is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wireless power transmission, and particularly to a soft-switching hybrid control method for wide power range of electric vehicle wireless charging system. BACKGROUND

[0002] The electric vehicle wireless charging (EV-WPT) technology uses electric field, magnetic field and other transmission media to transmit grid power to electric vehicles in a non-electrical contact manner. It has attracted more and more attention due to its high reliability, easy operation and environmental friendliness. In the magnetic field type wireless charging system, when the electric vehicle needs to be charged, the transmitting end power conversion device converts the grid power into high-frequency alternating current, and transmits the power to the receiving coil in the form of alternating magnetic field through the transmitting coil. The receiving coil transmits the power to the on-board power conversion device, which charges the battery load after processing.

[0003] Since the charging process of the EV-WPT system involves multiple conversions and transmissions of electric energy, and the system works in high frequency mode, a large amount of energy loss will be generated in the switching process of the inverter switching device. These losses not only affect the stability of the system operation, but also reduce the transmission efficiency of the system and shorten the service life of the switching device. In the EV-WPT system, the application of soft switching technology can effectively solve these problems. The soft switching technology sets a short dead time, so that the switching device can switch when the voltage or current is close to zero, avoiding the overlap between voltage and current, thereby reducing switching loss and electromagnetic interference, and improving the transmission efficiency and operation stability of the system.

[0004] The current research on the soft switching implementation method of the EV-WPT system mainly focuses on three directions: adding auxiliary circuits, optimizing resonant element parameters, and control strategies. The method of adding auxiliary circuits to achieve ZVS has the advantages of simple design method, high robustness, etc., and to some extent meets the dynamic adjustment demand of the system ZVS range. However, this method increases the system size and cost in practical application, and the voltage and current stress of the device is large, which limits the transmission power level of the system. In the parameter optimization of the resonant element, the relationship between the compensation element parameters and the ZVS operating conditions of the inverter is analyzed, and the parameter configuration is optimized to achieve ZVS. However, this method usually only targets a single parameter, making it difficult to optimize multiple target parameters simultaneously. In addition, when the optimized element parameters drift, the system may lose the soft switching state. Compared with the above two methods of achieving ZVS operation of the inverter, the method of achieving ZVS by control strategy can effectively reduce the system cost and design complexity, and can adjust the output power and ZVS working range in real time according to the actual operation demand of the system. Although the method of achieving ZVS by control strategy can effectively reduce the system cost and design complexity, a single control strategy may cause the system to work in a hard switching state when the output voltage gain range is wide, resulting in increased system loss, severe heating, and reduced transmission efficiency, etc. Therefore, appropriate control strategies need to be adopted to solve these problems. SUMMARY

[0005] The purpose of the present application is to provide a wide power range soft switching hybrid control method for electric vehicle wireless charging system. To solve the technical problems of existing electric vehicle wireless charging process, such as increased system loss, severe heating and reduced transmission efficiency.

[0006] A wide power range soft switching hybrid control method for electric vehicle wireless charging system, the system includes a transmitting end and a receiving end, the transmitting end includes a DC power supply, a high-frequency inverter, a primary side compensation circuit and a primary side coil connected in sequence, the receiving end includes a receiving coil, a secondary side compensation circuit, a rectifier filter circuit and a load battery connected in sequence, the specific steps of the control method are:

[0007] S1: initialize system circuit parameters, system operating frequency f n , the expected current value I0 of the system constant current charging and the expected voltage value U0 of the system constant voltage charging;

[0008] S2: real-time sampling of the charging voltage U b and the charging current I b of the system load battery, and calculating the equivalent internal resistance R b and the normalized output power P L * ;

[0009] S3: selecting system constant current or constant voltage charging mode according to charging voltage U of the load battery b , selecting system constant current or constant voltage charging mode according to charging voltage U of the load battery L * , selecting high-frequency inverter full-bridge or half-bridge working mode according to selected charging mode and normalized output power P

[0010] S4: calculating phase angle of high-frequency inverter controlled in next control cycle and switching frequency of high-frequency inverter realizing ZVS in different modes, and controlling high-frequency inverter.

[0011] Optionally, the initialization of system circuit parameters in step S1 includes DC power supply output voltage, primary side and secondary side coil mutual inductance, primary side compensation circuit parameters and secondary side compensation circuit parameters.

[0012] Optionally, the specific steps of selecting system charging mode and high-frequency inverter working mode in step S3 are as follows:

[0013] S3.1: judging whether charging voltage U of the load battery at current time is greater than or equal to U0, if yes, then system selects constant current output and high-frequency inverter full-bridge working mode, if no, then system selects constant voltage output and goes to step S3.2; b L *

[0014] S3.2: judging whether normalized output power P is greater than or equal to 0.5, if yes, then high-frequency inverter full-bridge working mode is selected, if no, then high-frequency inverter half-bridge working mode is selected.

[0015] Optionally, the specific method of calculating phase angle of high-frequency inverter controlled in next control cycle in step S4 is as follows:

[0016] When system is in full-bridge constant current mode, difference between expected current value I0 and sampled charging current I is calculated, and the difference is input into constant current PI controller to obtain control angle δ2 of high-frequency inverter full-bridge working mode; b

[0017] When system is in full-bridge constant voltage mode, difference between expected voltage value U0 and sampled charging voltage U is calculated, and the difference is input into constant voltage PI controller to obtain control angle δ2 of high-frequency inverter full-bridge working mode; b

[0018] When system is in half-bridge constant voltage mode, difference between expected voltage value U0 and sampled charging voltage U is calculated, and the difference is input into constant voltage PI controller to obtain control angle δ3 of high-frequency inverter half-bridge working mode. b

[0019] ​​​​​Optionally, when the high-frequency inverter is in full-bridge operation, the specific method for calculating the switching frequency of the high-frequency inverter in the next control cycle to realize ZVS is as follows:

[0020] with the charging current I b , the switching frequency f s of the current control cycle, the load battery equivalent internal resistance R b , and the control angle δ2 as inputs, the calculation system calculates the inverter output current i f1,OAVC (t2) for OAVC-VF control, and judges whether the system operating point meets the ZVS operation condition according to the inverter output current i f1,OAVC (t2).

[0021] Optionally, the specific method for judging whether the system operating point meets the ZVS operation condition according to i f1,OAVC (t2) is as follows:

[0022] judging whether (1-η)·i f1,OAVC (t2)>I th is true, where η is a threshold parameter, I th is the threshold current when the switching tube is turned on or turned off:

[0023] If not, decrease f s [m] by Δf, recalculate i f1,OAVC (t2), and judge again whether the ZVS operation condition is met;

[0024] If yes, judge the relationship between f s [m] and f n : if f s [m]>f n , then gradually decrease f s [m] by Δf until its value is equal to f n ; if f s [m]<f n , then gradually increase f s [m] by Δf until its value is equal to f n ; if f s [m]=f n , then let f s [m+1]=f s [m], and control the high-frequency inverter in the next cycle with f s [m+1] and the phase angle δ2.

[0025] Optionally, when the high-frequency inverter is in half-bridge operation, the specific method for calculating the switching frequency of the high-frequency inverter in the next control cycle to realize ZVS is as follows:

[0026] with the charging current I b, the switching frequency f of the current control period s [n], the equivalent internal resistance R of the load battery b and the control angle δ3 as inputs, the calculation system calculates the inverter output current i f1,HB (t0) according to i f1,HB (t0) to determine whether the system operating point meets the ZVS operating condition.

[0027] Optionally, the specific steps for determining whether the system operating point meets the ZVS operating condition according to i f1,HB (t0) are as follows:

[0028] determining whether (1-η)·i f1,HB (t0)<-I th is true, wherein η is a threshold parameter, and I th is the threshold current when the switching tube is turned on or turned off:

[0029] If not, f s [n] is decreased by Δf, i f1,HB (t0) is recalculated, and it is determined again whether the ZVS operating condition is met;

[0030] If yes, it is determined that the relationship between f s [n] and f n is as follows: if f s [n]>f n , f s [n] is gradually decreased by Δf until its value is equal to f n ; if f s [n]<f n , f s [n] is gradually increased by Δf until its value is equal to f n ; if f s [n]=f n , f s [n+1]=f s [n], and the next period of the high-frequency inverter is controlled by f s [n+1] and the phase angle δ3.

[0031] Due to the adoption of the above technical solutions, the present application has the following advantages:

[0032] The present application optimizes the soft switching control method of the EV-WPT system, which is beneficial to reduce the energy loss and electromagnetic interference in the electric energy conversion process, improve the overall efficiency and component life of the system, and realize a more stable and reliable wireless charging process.

[0033] Additional advantages, objects, and features of the application will be apparent from the following specification, taken in conjunction with the accompanying drawings. The above-mentioned and other advantages of the present application can be more fully understood and appreciated by considering the following detailed description in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0034] The drawings accompanying the specification are included as part of, and are to be taken in conjunction with, the disclosure. The drawings illustrate the principles of the present application and, although not to be construed as limiting, enable those skilled in the art to further appreciate the present application.

[0035] Figure 1 The circuit diagram of the electric vehicle wireless charging system of the present application.

[0036] Figure 2 The constant voltage charging phase control schematic diagram of the EV-WPT system of the present application.

[0037] Figure 3 The flow chart of the wide power range soft-switching hybrid control method of the present application.

[0038] Figure 4 The system equivalent circuit diagram under the action of Nth harmonic of the present application.

[0039] Figure 5 The ZVS operation region diagram under the OAVC-VF control of the present application.

[0040] Figure 6 The ZVS optimal operation trajectory diagram under the OAVC-VF control of the present application.

[0041] Figure 7 The ZVS operation region diagram under the HB-VF control of the present application.

[0042] Figure 8 The ZVS optimal operation trajectory diagram under the HB-VF control of the present application.

[0043] Figure 9 The full-bridge inverter output simulation waveform diagram of the present application with the system output power of 11.2kW.

[0044] Figure 10 The inverter output simulation waveform diagram under the OAVC control and OAVC-VF control of the present application.

[0045] Figure 11 The half-bridge inverter output simulation waveform diagram of the present application with the system output power of 5.6kW.

[0046] Figure 12 The inverter output simulation waveform diagram under the HB control and HB-VF control of the present application.

[0047] Figure 13This is a simulation waveform diagram of the inverter output during the switching process of the full-bridge / half-bridge working mode of the present invention.

[0048] Figure 14 This is a simulation waveform of the output voltage / current during the switching process of the full-bridge / half-bridge working mode of the present invention.

[0049] Figure 15 This is a diagram showing the output characteristics of the system in constant current / constant voltage charging mode according to the present invention.

[0050] Figure 16 This is a diagram illustrating the ZVS implementation during the constant current / constant voltage charging process of this invention. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0052] Example 1:

[0053] like Figure 1 The illustrated wireless charging system for electric vehicles includes a transmitter and a receiver. The transmitter includes a DC power supply U connected in sequence. dc High-frequency inverter, primary-side compensation circuit and primary-side coil L p The receiving end includes a secondary coil L connected in sequence. s Secondary-side compensation circuit, rectifier and filter circuit, and load battery R b .

[0054] The primary-side compensation circuit and the secondary-side compensation circuit constitute an LCC-LCC topology. The primary-side compensation circuit includes a primary-side compensation inductor L. f1 Primary-side compensation capacitor C f1 and primary-side compensation capacitor C p The secondary-side compensation circuit includes a secondary-side compensation inductor L. f2 Secondary side compensation capacitor C f2 and secondary side compensation capacitor C s The high-frequency inverter includes four MOSFETs (S1-S4), and the rectifier and filter circuit includes four diodes (D1-D4) and a filter capacitor C. d .

[0055] Figure 1 Chinese R p and R s The primary coil L p and secondary coil L s internal resistance, It outputs high-frequency AC voltage via an inverter. The input voltage at the rectifier terminal. For inverter output current, To compensate for the inductor current at the receiving end, and Primary and secondary winding current, U b and I b are the charging voltage and current of the load battery R b , respectively. Through the analysis of the system, the output power P out of the system is:

[0056]

[0057] where R eq is the equivalent load of the load battery R b , and according to formula (1), under the condition that the system input voltage mutual inductance M and compensation inductance L f1 and L f2 parameters are determined, the output current of the system remains constant, showing the characteristics of decoupling from the load.

[0058] In addition, as the charging process proceeds, the equivalent internal resistance of the load changes constantly, and the constant-current output characteristics of the LCC-LCC compensation topology help the system to achieve constant-current charging when the load changes, and the system output current size can be adjusted by controlling the inverter output voltage, so as to meet the charging needs of different types of electric vehicles. Through the analysis of the charging mode of the system, it is known that the output power of the EV-WPT system has the characteristics of wide range variation, and the output power needs to be adjusted by changing the inverter output voltage during the charging process. However, the traditional phase-shift control will have the problem of too large phase-shift angle under light load working condition, at this time the inverter switch tube loss is large, which reduces the transmission efficiency of the system.

[0059] Analysis of the time-domain model of the LCC-LCC topology of the harmonic:

[0060] In the process of adjusting the output power of the system, the switching current of the inverter is the key index to judge whether the system can realize ZVS operation. However, in the LCC-LCC compensation topology, the switching current contains a large amount of harmonic components, which will affect the ZVS characteristics of the system, and the traditional fundamental approximation method cannot calculate the accurate value. Therefore, this application will consider the influence of harmonic components on the inverter switching current, and derive the time-domain expression of the inverter output current containing harmonic components. Since the parameters of the resonant elements of the LCC-LCC compensation topology are designed at the fundamental frequency, when solving the harmonic components of the inverter output current, the system no longer satisfies the resonance condition, and according to Figure 4 , the equivalent circuit of the system under the action of Nth harmonic can be obtained.

[0061] According to Figure 4 , the receiving end circuit impedance Z s_N of the system under the action of Nth harmonic and the reflection impedance Z ref of the receiving end can be obtained.N and input impedance Z in _ N The expression is:

[0062]

[0063]

[0064]

[0065] The input impedance angle of the system under the influence of the Nth harmonic can be obtained from equation (4). The expression is:

[0066]

[0067] Furthermore, the inverter output current i under the influence of the Nth harmonic can be obtained. f1_N The expression for (t) is:

[0068]

[0069] Based on the principle of circuit superposition, the inverter output current i can be obtained. f1 The time-domain expression for (t) is:

[0070]

[0071] In this embodiment, the system parameters are set as shown in Table 1, where f n is the resonant frequency of the system.

[0072] Table 1 Parameters of EV-WPT System Based on LCC-LCC Topology

[0073]

[0074] In this embodiment, the primary and secondary coils adopt a square coil structure design to improve the system's anti-offset capability and coupling stability. To enhance the system's transmission efficiency, output power level, and magnetic field coupling strength, magnetic cores are laid above the receiving coil and below the transmitting coil, respectively, and magnetic shielding is achieved by adding an aluminum plate. Furthermore, to reduce the weight and size of the vehicle-mounted receiver, the receiver compensation inductor is integrated below the receiving coil.

[0075] Example 2:

[0076] Such as Figure 2 and Figure 3 The method for wide-power-range soft-switching hybrid control of a wireless charging system for electric vehicles, as shown, includes the following steps:

[0077] S1: Initialize system circuit parameters and system operating frequency fn , the expected current value I0 of the system constant current charging and the expected voltage value U0 of the system constant voltage charging;

[0078] In the embodiment, the initialization of the system circuit parameters includes the DC power supply output voltage U dc , the primary side and secondary side coil mutual inductance M, the primary side compensation circuit parameters and the secondary side compensation circuit parameters, and the specific parameters are shown in Table 1.

[0079] S2: Real-time sampling of the charging voltage U b and the charging current I b of the system load battery, and calculating the equivalent internal resistance R b and the normalized output power P L of the load battery. * ;

[0080] In the embodiment, the normalized output power P L * is:

[0081]

[0082] In the formula, P L is the output power of the system, and P f is the transmission power when the system is full load.

[0083] S3: According to the charging voltage U b of the load battery, selecting the system constant current or constant voltage charging mode, and according to the selected charging mode and the normalized output power P L * , selecting the full-bridge or half-bridge working mode of the high-frequency inverter; the specific steps are as follows:

[0084] S3.1: Judging whether the charging voltage U b of the load battery at the current time is greater than the constant voltage U0, if yes, the system selects the constant current output, and selects the full-bridge working mode of the high-frequency inverter; if no, the system selects the constant voltage output, and goes to step S3.2;

[0085] S3.2: Judging whether the normalized output power P L * is greater than 0.5, if yes, selecting the full-bridge working mode of the high-frequency inverter; if no, selecting the half-bridge working mode of the high-frequency inverter.

[0086] In the embodiment, the system first charges the vehicle-mounted battery at a constant current I0, and the vehicle-mounted battery voltage U b increases with the increase of the battery equivalent internal resistance R b . When U b reaches the constant voltage charging value U0, the system enters the constant voltage charging mode. At this time, the battery charging current Ib will gradually decrease with the increase of R b , and the charging process ends when the preset value of the current reduction system is reduced.

[0087] S4: Calculate the phase angle of the high-frequency inverter control in the next control cycle and the switching frequency of the high-frequency inverter to realize ZVS in different modes, and control the high-frequency inverter, the specific steps are:

[0088] S4.1: The specific method for calculating the phase angle of the inverter control in the next control cycle in different modes is:

[0089] When the system is in full-bridge constant-current mode, calculate the difference between the expected current value I0 and the sampled charging current I b , input the difference into the constant-current PI controller to obtain the control angle δ2 of the high-frequency inverter when the full-bridge works;

[0090] When the system is in full-bridge constant-voltage mode, calculate the difference between the expected voltage value U0 and the sampled charging voltage U b , input the difference into the constant-voltage PI controller to obtain the control angle δ2 of the high-frequency inverter when the full-bridge works;

[0091] When the system is in half-bridge constant-voltage mode, calculate the difference between the expected voltage value U0 and the sampled charging voltage U b , input the difference into the constant-voltage PI controller to obtain the control angle δ3 of the high-frequency inverter when the half-bridge works.

[0092] S4.2: The specific method for calculating the switching frequency of the high-frequency inverter to realize ZVS in the next control cycle of the system when the high-frequency inverter works in full-bridge mode is:

[0093] Take the collected charging current I b , the switching frequency f s [m] of the current control cycle, the equivalent internal resistance R b of the load battery, and the control angle δ2 as inputs, calculate the inverter output current i f1,OAVC (t2) of the system controlled by OAVC-VF, and determine whether the system operating point meets the ZVS operating condition according to the inverter output current i f1,OAVC (t2).

[0094] The specific method for determining whether the system operating point meets the ZVS operating condition according to i f1,OAVC (t2) is:

[0095] Determine whether (1-η)·i f1,OAVC (t2)>I th is true, where η is a threshold parameter, I th is the threshold current when the switching tube is turned on or turned off:

[0096] If not, fs [m] Decrease Δf and recalculate i f1,OAVC (t2) and then determine again whether the ZVS operating conditions are met;

[0097] If true, then determine f. s [m] and f n Yes, the relationship is: if f s [m]>f n Then f s [m] Decrease Δf successively until its value equals f. n If f s [m] <f n Then f s [m]Increment Δf successively until its value equals f. n If f s [m]=f n Then let f s [m+1]=f s [m], and with f s [m+1] and phase angle δ2 control the next cycle of the high-frequency inverter.

[0098] In this embodiment, Inverter output current i f1,OAVC The calculation method for (t2) is as follows:

[0099]

[0100] When the control strategy for the full-bridge inverter is OAVC-VF control, then the expression is:

[0101]

[0102] S4.3: When the high-frequency inverter operates in half-bridge mode, the specific method for calculating the switching frequency of the high-frequency inverter to achieve ZVS in the next control cycle of the system is as follows:

[0103] The collected charging current I b The switching frequency f of the current control cycle s [n], Equivalent internal resistance of the load battery R b With the control angle δ3 as input, the inverter output current i of the HB-VF control system is calculated. f1,HB (t0), according to i f1,HB (t0) Determine whether the system operating point meets the ZVS operating conditions.

[0104] According to i f1,HB (t0) The specific steps to determine whether the system operating point meets the ZVS operating conditions are as follows:

[0105] Judgment (1-η)·i f1,HB (t0)<-Ith Whether it holds true, where: η is the threshold parameter, I th Threshold current when the switching transistor is turned on or off:

[0106] If not, f s [n] Decrease Δf and recalculate i f1,HB (t0) and then determine again whether the ZVS operating conditions are met;

[0107] If true, then determine f. s [n] and f n Yes, the relationship is: if f s [n]>f n Then f s [n] Decrease Δf successively until its value equals f. n If f s [n] <f n Then f s [n]Increment Δf successively until its value equals f. n If f s [n] = f n Then let f s [n+1]=f s [n], and with f s [n+1] and phase angle δ3 control the next cycle of the high-frequency inverter.

[0108] In this embodiment, Inverter output current i f1,HB The calculation method for (t0) is as follows:

[0109]

[0110] When the system operates in half-bridge mode HB-VF control, the expression is:

[0111]

[0112] In this embodiment, I th This is the threshold current when the switching transistor is turned on or off, used to discharge the parasitic capacitance of the switching transistor. In practical applications, to prevent two switching transistors on the same bridge arm from conducting simultaneously, a dead time is added. Therefore, I th It can be represented as:

[0113]

[0114] In the formula, t d For dead time, C oss This is the junction capacitance of the switching transistor.

[0115] In this embodiment, the MOSFET used in the high-frequency inverter is model C3M0021120K. According to the datasheet, its junction capacitance C oss The capacitance is 180pF, and the dead time is set to 250ns. Taking the system parameters in Table 1 as an example, the threshold current I can be calculated. th Given a current of 1.32A and a margin of η = 5%, the switching current required for the inverter to achieve ZVS is I. th It is 1.39A.

[0116] In this embodiment, the normalized switching frequency of the system is set to f. s * The expression is:

[0117]

[0118] Based on the above parameters, i is calculated. f1,OAVC (t2), and plot i f1,OAVC (t2) Regarding f s * The three-dimensional relationship between δ2 and δ2 is shown in the figure below. Figure 5 As shown, and plane i is constructed. f1,OAVC (t2) = 1.39A and Figure 5 Intersecting the 3D graphs in (a), we obtain the ZVS operating region under OAVC control as shown below. Figure 5 As shown in (b).

[0119] In full-bridge mode, such as Figure 6 As shown. When the system is at point A1, the switching frequency f s Equal to the system's resonant frequency f n When the control angle δ2 = 0°, the system is in the rated output power state.

[0120] To improve system operating efficiency, the range of switching frequency variation should be as small as possible. Therefore, Figure 6 The red dashed line in the diagram represents the optimal operating trajectory for the inverter to achieve ZVS with minimal switching frequency variation. Figure 6 The optimal operating trajectory of ZVS in the model is: when the system output power P L When a reduction is needed, the switching frequency f s Keeping the control angle constant and increasing it by δ2, the system operating point moves along A1B1. During this process, the system always operates in region 2 and satisfies f s =f n After reaching the critical point B1, if it is necessary to continue reducing P... L Adjusting only δ2 will cause the system to operate along B1C1, in which case the system is operating in region 1. To make the system operate in region 2, f also needs to be adjusted in addition to δ2. sto ensure that the operating point runs along the red dotted line until the output power of the system reaches the desired value.

[0121] Similarly, according to the above parameters, i f1,HB (t0) is calculated, and a three-dimensional relationship diagram of i f1,HB (t0) about f s and δ3 is drawn as shown in Figure 7 , and the plane i f1,HB (t0) = -1.39A intersects the three-dimensional diagram in Figure 7 (a), and the ZVS operating area under HB control is shown in Figure 7 (b).

[0122] In the half-bridge mode, as shown in Figure 8 . Among them, A2 point is the rated operating point of the system in the half-bridge mode, at this time the switching frequency f s is equal to the resonant frequency f n of the system, and the control angle δ3 = 0°. The analysis of the ZVS optimal operating trajectory under HB control is the same as that of OAVC control.

[0123] From the above analysis, it can be seen that when the system output power gain is between 0.5 and 1, the system operates in full-bridge mode, at this time the control strategy of the inverter is OAVC-VF control, and the operating point of the system moves along the red dotted line in Figure 6 . When the system output power gain is between 0 and 0.5, the system operates in half-bridge mode, at this time the inverter adopts HB-VF control, and the operating point of the system moves along the red dotted line in Figure 8 . Then the inverter can realize ZVS operation in a wide power range.

[0124] S5: Determine whether the system charging is completed, if yes, the control is completed, if not, return to step S2.

[0125] In this embodiment, when the system is in constant current charging mode, it is determined that the charging is not completed.

[0126] S6: Simulation verification:

[0127] S6.1: Construct a system simulation model: create a closed-loop control simulation model of the LCC-LCC type EV-WPT system as shown in Figure 2 , and simulate the feasibility and effectiveness of the proposed soft switching hybrid control strategy from three aspects of system ZVS implementation, full-bridge / half-bridge mode switching, and constant current / constant voltage output characteristics. In the simulation model, a variable resistor is used to replace the change process of the equivalent internal resistance of the vehicle-mounted battery. According to the formula resonance working condition, the basic parameters of the simulation model are configured, and the specific simulation parameters are shown in Table 2.

[0128] Table 2 EV-WPT system simulation parameter table

[0129]

[0130] S6.2: System ZVS implementation simulation verification: According to the EV-WPT system simulation model built, the ZVS implementation of the system in a wide power output range is simulated and verified, and the system works in constant voltage mode. As shown in Figure 9 , it can be seen from Figure 9 that the inverter output voltage phase slightly leads the inverter output current phase, the input impedance of the system presents weak inductance, and the inverter realizes ZVS operation.

[0131] In full-bridge mode, the output power level of the system is adjusted by using OAVC control and OAVC-VF control respectively, and the ZVS implementation of the inverter under the two control methods is analyzed, and the output power gain of the system is between 0.5 and 1, as shown in Figure 10 , in which Figure 10 (a), (c) and (e) are OAVC control, Figure 10 (b), (d) and (f) are OAVC-VF control; Figure 10 In (a) and (b), I b = 24.5A, the system outputs 7 / 8P f ; Figure 10 In (c) and (d), I b = 21A, the system outputs 6 / 8P f ; Figure 10 In (e) and (f), I b = 17.5A, the system outputs 5 / 8P f . When the control strategy of the system is OAVC control, it can be seen from Figure 10 (a), (c), (e) that as the control angle δ2 increases, the output power of the system decreases, and the switch tube S2 always works in a non-ZVS state. As shown in Figure 10 (b), (d), (f), by using the OAVC-VF control strategy proposed in the application, the control angle δ2 is adjusted at the same time, and the switching frequency f s is adjusted. The inverter realizes ZVS operation in the output power gain range of 0.5 to 1, and the change range of the switching frequency is small, which is conducive to improving the efficiency of the system.

[0132] When the output power of the system is 5.6kW, the output power gain is 0.5 at this time, the drive signals of the four switch tubes of the full-bridge inverter are adjusted, so that they work in half-bridge mode, and the inverter switching frequency is 85kHz, Figure 11 , from Figure 11It can be seen from (a), (c) and (e) that the phase of the inverter output current lags slightly behind the phase of the inverter output voltage Uinv, and the inverter realizes ZVS operation.

[0133] In the half-bridge mode, the output power level of the system is regulated by HB control and HB-VF control respectively, and the output power gain of the system is between 0 and 0.5. As shown in Figure 12 Figure 12 In (a), (c) and (e), HB control is adopted, Figure 12 In (b), (d) and (f), HB-VF control is adopted. Figure 12 In (a) and (b), I b = 10.5 A, and the system output is 3 / 8P f . Figure 12 In (c) and (d), I b = 7 A, and the system output is 2 / 8P f . Figure 12 In (e) and (f), I b = 3.5 A, and the system output is 1 / 8P f . From Figure 12 (a), (c) and (e), it can be seen that although HB control achieves the purpose of regulating the output power of the system, the switch S1 fails to realize ZVS operation. As shown in Figure 12 (b), (d) and (f), by adopting HB-VF control, ZVS operation of the inverter switches S1 and S2 can be realized at the same time.

[0134] From the above simulation results, it can be seen that the soft-switching hybrid control method proposed in this paper realizes output regulation of the system in a wide power range and ZVS operation of the inverter.

[0135] S6.3: Simulation verification of system full-bridge / half-bridge mode switching: In the constant voltage charging stage, in order to verify the feasibility of the wide power range output control method based on full-bridge / half-bridge mode switching given in this application, the equivalent resistance R b is increased from 28Ω to 33Ω, the full-bridge / half-bridge mode switching process of the system is simulated and verified, and the simulation results are shown in Figure 13 and Figure 14 It can be seen from Figure 13 and Figure 14 that at t = 0.1s, the system switches from the full-bridge working mode to the half-bridge working mode, the output voltage U b remains 400V, and the output current I b decreases from 14.3A to 12.1A.

[0136] ​S6.4: System constant current / constant voltage output characteristic simulation verification: In order to verify that the soft switching hybrid control method proposed in the application can meet the constant current / constant voltage charging requirements of the system vehicle battery, the constant current / constant voltage charging process of the system is simulated by using the method of resistance step change to simulate the change process of the equivalent internal resistance of the vehicle battery. The constant current charging current value of the system is set to 28A, and the constant voltage charging voltage value is 400V, as shown in Figure 15 , the AB segment and the BC segment are the constant current and constant voltage charging stages of the vehicle battery respectively. In the constant current charging stage, the system maintains an output current of 28A, and the equivalent internal resistance R b of the battery changes in a small range of 5Ω-12Ω. The output voltage of the system rises with the increase of the load, and when it increases to 400V, the system charging mode switches to constant voltage charging. R b The change range of the constant voltage stage is 16Ω-80Ω, and in this process, the battery charging current gradually decreases, and when it decreases to the minimum charging current value preset by the system, the system stops charging.

[0137] In addition, take R b =12Ω, R b =16Ω, R b =25Ω and R b =40Ω, the ZVS implementation of the inverter in the constant current / constant voltage charging process is simulated and verified, and the results are shown in Figure 16 (a), (b), (c) and (d) respectively. As shown in Figure 16 (a), (b) and (c), when R b =12Ω, 16Ω and 25Ω, the output power gain range is between 0.5 and 1, and the system works in full-bridge mode, at this time the soft switching control method of the inverter is OAVC-VF control; as shown in Figure 16 (d), when R b increases from 25Ω to 40Ω, the system output power gain is less than 0.5, and the system switches to half-bridge working mode, and the inverter adopts HB-VF control strategy. The simulation results show that the soft switching hybrid control method proposed in the application realizes the constant current / constant voltage output of the system and ensures the ZVS operation of the inverter.

[0138] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the application and not to limit it, although the application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific embodiments of the application can be modified or replaced, without departing from the spirit and scope of the application. Any modification or equivalent replacement, which should be covered within the protection scope of the claims of the application.

Claims

1. A soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles, the system comprising a transmitter and a receiver, the transmitter comprising a DC power supply, a high-frequency inverter, a primary-side compensation circuit, and a primary-side coil connected in sequence, and the receiver comprising a receiving coil, a secondary-side compensation circuit, a rectifier and filter circuit, and a load battery connected in sequence, characterized in that, The specific steps of the control method are as follows: S1: Initialize system circuit parameters and system operating frequency f n The expected current value I0 for constant current charging of the system and the expected voltage value U0 for constant voltage charging of the system; S2: Charging voltage U of the load battery in the real-time sampling system b and charging current I b And calculate the equivalent internal resistance R of the load battery. b and normalized output power P L * ; S3: Based on the charging voltage U of the load battery b Select either constant current or constant voltage charging mode for the system, and adjust the charging mode and normalized output power P accordingly. L * Select the full-bridge or half-bridge operating mode of the high-frequency inverter; S4: When calculating different modes, the phase angle controlled by the high-frequency inverter and the switching frequency of the high-frequency inverter to achieve ZVS in the next control cycle are calculated, and the high-frequency inverter is controlled.

2. The soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles according to claim 1, characterized in that, The initialization of system circuit parameters in step S1 includes the DC power supply output voltage, the mutual inductance of the primary and secondary coils, the primary compensation circuit parameters, and the secondary compensation circuit parameters.

3. The soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles according to claim 1, characterized in that, The specific steps for selecting the system charging mode and the high-frequency inverter operating mode in step S3 are as follows: S3.1: Determine whether the charging voltage U of the load battery at the current moment b <is less than U0. If so, the system selects constant current output and selects the high-frequency inverter to operate in the full-bridge mode; if not, the system selects constant voltage output and proceeds to step S3.2; S3.2: Determine the normalized output power P L * If the value >0.5 is true, then select the high-frequency inverter in full-bridge mode; if not, select the high-frequency inverter in half-bridge mode.

4. The soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles according to claim 1, characterized in that, The specific method for calculating the phase angle of the inverter control in the next control cycle when calculating different modes in step S4 is as follows: When the system is in full-bridge constant current mode, calculate the desired current value I0 and the sampled charging current I. b The difference is input into the constant current PI controller to obtain the control angle δ2 when the high-frequency inverter is in full-bridge operation; When the system is in full-bridge constant voltage mode, calculate the desired voltage value U0 and the sampled charging voltage U. b The difference is input into the constant voltage PI controller to obtain the control angle δ2 when the high-frequency inverter is in full-bridge operation; When the system is in half-bridge constant voltage mode, calculate the desired voltage value U0 and the sampled charging voltage U. b The difference is input into the constant voltage PI controller to obtain the control angle δ3 when the high-frequency inverter half-bridge is working.

5. The soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles according to claim 1, characterized in that, When the high-frequency inverter operates in full-bridge mode, the specific method for calculating the switching frequency of the high-frequency inverter to achieve ZVS in the next control cycle of the system is as follows: The collected charging current I b The switching frequency f of the current control cycle s [m], Equivalent internal resistance of the load battery R b With the control angle δ2 as input, the inverter output current i of the system under OAVC-VF control is calculated. f1,OAVC (t2), based on the inverter output current i f1,OAVC (t2) determines whether the system operating point meets the ZVS operating conditions.

6. The soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles according to claim 5, characterized in that, According to i f1,OAVC (t2) The specific method for determining whether the system operating point meets the ZVS operating conditions is as follows: Judgment (1-η)·i f1,OAVC (t2)>I th Whether it holds true, where: η is the threshold parameter, I th Threshold current when the switching transistor is turned on or off: If not, f s [m] Decrease Δf and recalculate i f1,OAVC (t2) and then determine again whether the ZVS operating conditions are met; If true, then determine f. s [m] and f n Yes, the relationship is: if f s [m]>f n Then f s [m] Decrease Δf successively until its value equals f. n If f s [m] <f n Then f s [m]Increment Δf successively until its value equals f. n If f s [m]=f n Then let f s [m+1]=f s [m], and with f s [m+1] and phase angle δ2 control the next cycle of the high-frequency inverter.

7. The soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles according to claim 1, characterized in that, When the high-frequency inverter operates in half-bridge mode, the specific method for calculating the switching frequency of the high-frequency inverter to achieve ZVS in the next control cycle of the system is as follows: The collected charging current I b The switching frequency f of the current control cycle s [n], Equivalent internal resistance of the load battery R b With the control angle δ3 as input, the inverter output current i of the HB-VF control system is calculated. f1,HB (t0), according to i f1,HB (t0) Determine whether the system operating point meets the ZVS operating conditions.

8. The soft-switching hybrid control method for a wide power range of a wireless charging system for electric vehicles according to claim 7, characterized in that, According to i f1,HB (t0) The specific steps to determine whether the system operating point meets the ZVS operating conditions are as follows: Judgment (1-η)·i f1,HB (t0)<-I th Whether it holds true, where: η is the threshold parameter, I th Threshold current when the switching transistor is turned on or off: If not, f s [n] Decrease Δf and recalculate i f1,HB (t0) and then perform another judgment to determine whether the ZVS running conditions are met; If true, then determine f. s [n] and f n Yes, the relationship is: if f s [n]>f n Then f s [n] Decrease Δf successively until its value equals f. n If f s [n] <f n Then f s [n]Increment Δf successively until its value equals f. n If f s [n] = f n Then let f s [n+1]=f s [n], and with f s [n+1] and phase angle δ3 control the next cycle of the high-frequency inverter.

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