Wireless power transfer system based on variable capacitor control, and secondary-side control method therefor

Abstract

Provided in the present application are a wireless power transfer system based on variable capacitor control, and a secondary-side control method therefor, which system and method are used for solving the problems of a change in an output power and the output stability being low which are caused by a change in a coefficient of mutual induction between a transmitting coil and a receiving coil of existing wireless charging systems. The wireless power transfer system comprises a transmitting end and a receiving end, wherein the transmitting end comprises a primary-side compensation circuit and a transmitting coil L p ; the receiving end comprises a receiving coil L s and a secondary-side compensation circuit; the primary-side compensation circuit and the secondary-side compensation circuit are LCC network compensation structures symmetrically arranged; and the secondary-side compensation circuit comprises a secondary-side compensation capacitor C s , a secondary-side compensation capacitor C f2 and a secondary-side compensation inductor L f2 , and the secondary-side compensation capacitor C f2 is a variable capacitor. In the present application, a variable capacitor is arranged to adjust a secondary-side output power, such that when a coefficient of mutual induction changes, the output power remains unchanged, thereby improving the stability of the output power of a system.

Description

Wireless power transmission system based on variable capacitance control and its secondary side control method TECHNICAL FIELD

[0001] The present application relates to the field of wireless power transmission, and particularly relates to a wireless power transmission system based on variable capacitance control and a secondary side control method thereof. BACKGROUND

[0002] With the rapid growth of economy and population and the rapid development of urbanization, the number of cars is increasing, and the problems of traditional energy shortage and environmental pollution are increasingly prominent, especially the harm of traditional fuel vehicles to the environment and resources. Therefore, it is of great significance to develop electric vehicles (EV), however, there are many limitations in the wired charging of traditional electric vehicles EV, such as easy damage (aging, leakage) of the connection part, easy generation of sparks when plugging, safety hazards, large floor area, high cost of power battery, short driving range and other problems.

[0003] The magnetic coupling wireless charging technology provides a solution to the above charging method, but with the development of wireless charging technology for electric vehicles, the requirement for the output power of the vehicle-mounted end is higher and higher. The system often changes itself due to changes in load, temperature, transmission distance or other interference factors, thereby causing unstable output power. SUMMARY

[0004] The purpose of the present application is to provide a wireless power transmission system based on variable capacitance control and a secondary side control method thereof. To solve the problem that the mutual inductance of the transmitting coil and the receiving coil of the existing wireless charging system changes, resulting in changes in output power and poor output stability.

[0005] A wireless power transmission system based on variable capacitance control, comprising a transmitting end and a receiving end, the transmitting end comprising a direct current power supply, an inverter, a primary side compensation circuit and a transmitting coil connected in sequence , the receiving end comprising a receiving coil , a secondary side compensation circuit, a rectifier filter circuit and a load connected in sequence, the primary side compensation circuit and the secondary side compensation circuit being symmetrically arranged LCC network compensation structure;

[0006] The secondary side compensation circuit comprises a secondary side compensation capacitor , a secondary side compensation capacitor and a secondary side compensation inductor , and the secondary side compensation capacitor is a variable capacitor.

[0007] Optionally, one end of the secondary side compensation capacitor is connected to one end of the receiving coil , and the secondary side compensation capacitor the other end of the auxiliary side compensation capacitor is connected with the other end of the auxiliary side compensation inductor , one end of the auxiliary side compensation inductor is connected with one input end of the rectifier filter circuit, the other end of the auxiliary side compensation capacitor is connected with the other end of the receiving coil and the other input end of the rectifier filter circuit.

[0008] Optionally, the auxiliary side compensation capacitor comprises a first branch and a second branch arranged in parallel, the first branch comprises a switch tube , a diode and a compensation capacitor , one end of the switch tube and the diode are connected in parallel and close to the anode of the diode and are connected in series with the compensation capacitor ;

[0009] the first branch comprises a switch tube , a diode and a compensation capacitor , one end of the switch tube and the diode are connected in parallel and close to the anode of the diode and are connected in series with the compensation capacitor .

[0010] Optionally, the primary side compensation circuit comprises a primary side compensation capacitor , a primary side compensation capacitor and a primary side compensation inductor ;

[0011] one end of the primary side compensation inductor is connected with one output end of the inverter, the other end of the primary side compensation inductor is connected with one end of the primary side compensation capacitor and the primary side compensation capacitor , the other end of the primary side compensation capacitor is connected with one end of the transmitting coil , the other end of the primary side compensation capacitor is connected with the other end of the transmitting coil and the other output end of the inverter.

[0012] Optionally, the output power of the system is:

[0013]

[0014] In the formula, is the inverse output current of the system, is the equivalent resistance of the system, , is the resistance value of the load, is the inductance value of the primary side compensation inductor , is the angular frequency of the system, is the mutual inductance value between the transmitting coil and the receiving coil , is the output current of the secondary side compensation circuit, is the equivalent impedance of the secondary side;

[0015] The impedance value of the equivalent impedance of the secondary side is:

[0016] .

[0017] Optionally, the capacitance value of the secondary side compensation capacitor is:

[0018]

[0019] wherein the capacitance values of the compensation capacitor and the compensation capacitor are both , is the conduction angle of the switch tube and the switch tube .

[0020] Optionally, the mathematical relationship between the system duty cycle D and the conduction angles of the switch tube and the switch tube is:

[0021] .

[0022] Optionally, it further includes a signal collector, a controller and a driver;

[0023] The signal collector is used to collect the output current and the output voltage of the secondary side compensation circuit and transmit them to the controller, and the controller is used to output the secondary side compensation capacitor The control signal of the driver drives the secondary side compensation capacitor according to the control signal The switching tube And the switching tube The conduction angle changes.

[0024] A secondary side control method of a wireless power transmission system based on variable capacitance control, for controlling the above-mentioned wireless power transmission system based on variable capacitance control, the specific steps are:

[0025] S1: initialize the system duty cycle D;

[0026] S2: detect the output current And the output voltage ;

[0027] S3: according to the output current And the output voltage , calculate the output power Of the system at the current time;

[0028] S4: judge Whether the following is true:

[0029] If true, the secondary side output power control is completed, and the control is ended;

[0030] If not, a new duty cycle D is calculated by PI control, the duty cycle D of PWM is adjusted, and step S2 is returned.

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

[0032] 1. The present application adjusts the secondary side output power by setting a variable capacitor, so that when the mutual inductance coefficient changes, the output power remains unchanged, improving the stability of the system output power.

[0033] 2. By adjusting the secondary side compensation capacitor, compared with the primary side control, the secondary side control reduces the interaction and communication demand between the primary side and the secondary side. Reduce the complexity of system design, improve the stability and reliability of the system.

[0034] Other advantages, objects and features of the present application will be explained in the following description, and to some extent, it will be obvious to those skilled in the art based on the following study, or can be taught from the practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the following description. BRIEF DESCRIPTION OF DRAWINGS

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

[0036] Figure 1 is an equivalent circuit diagram of a wireless power transmission system based on variable capacitance control according to the present application.

[0037] Figure 2 is a structural diagram of a secondary side compensation capacitor according to the present application.

[0038] Figure 3 is a flow chart of a secondary side control method according to the present application.

[0039] Figure 4 is a curve diagram of output power varying with a secondary side compensation capacitor according to the present application.

[0040] Figure 5 is a 3D diagram of output power varying with a secondary side compensation capacitor and mutual inductance according to the present application.

[0041] Figure 6 is a curve diagram of mutual inductance varying with time according to the present application.

[0042] Figure 7 is a curve diagram of output power varying with time according to the present application. DETAILED DESCRIPTION

[0043] The present application will be further described below in conjunction with the accompanying drawings and examples.

[0044] Example 1

[0045] A wireless power transmission system based on variable capacitance control as shown in Figure 1, comprising a transmitting end and a receiving end, the transmitting end comprising a DC power supply, an inverter, a primary side compensation circuit and a transmitting coil connected in sequence , the receiving end comprising a receiving coil , a secondary side compensation circuit, a rectifier filter circuit and a load connected in sequence, characterized in that the primary side compensation circuit and the secondary side compensation circuit are symmetrically arranged LCC network compensation structures.

[0046] The secondary side compensation circuit comprises a secondary side compensation capacitor , a secondary side compensation capacitor and a secondary side compensation inductor , the secondary side compensation capacitor is a variable capacitor.

[0047] In this embodiment, as shown in the equivalent circuit diagram of the system in Figure 1, after the DC power supply is inverted by the inverter, an alternating current input voltage is obtained, and the equivalent load of the rectifier filter circuit and the load is .

[0048] In this embodiment, the secondary side compensation capacitor ​​​​The variable capacitor is arranged to adjust the output power of the secondary side, so that the output power remains unchanged when the mutual inductance changes, thereby improving the stability of the system output power.

[0049] As shown in FIG. 1, one end of the secondary side compensation capacitor is connected to one end of the receiving coil , and the other end of the secondary side compensation capacitor is connected to one end of the secondary side compensation capacitor and the secondary side compensation inductor , respectively. The other end of the secondary side compensation capacitor is connected to the other end of the receiving coil and the other input end of the rectifier filter circuit, respectively.

[0050] As shown in FIG. 1, the primary side compensation circuit includes a primary side compensation capacitor , a primary side compensation capacitor and a primary side compensation inductor .

[0051] One end of the primary side compensation inductor is connected to one output end of the inverter, and the other end of the primary side compensation inductor is connected to one end of the primary side compensation capacitor and the primary side compensation capacitor , respectively. The other end of the primary side compensation capacitor is connected to one end of the transmitting coil , and the other end of the primary side compensation capacitor is connected to the other end of the transmitting coil and the other output end of the inverter, respectively.

[0052] In this embodiment, the resonant frequency of the system is , which satisfies the following formula in the primary side resonant state:

[0053]

[0054] The equivalent impedance of the secondary side is:

[0055]

[0056] The reflected impedance is:

[0057]

[0058] The primary input impedance is:

[0059]

[0060] Based on the above analysis, the relevant current expression can be obtained as follows:

[0061]

[0062] The output power of the system for:

[0063]

[0064] In the formula, This is the inverter output current of the system. The equivalent resistance of the system. , Compensating inductor for primary side inductance value, The system angular frequency, For transmitting coil and receiving coil Mutual inductance between them This is the output current of the secondary-side compensation circuit. This is the equivalent impedance of the secondary side.

[0065] From output power It can be seen that, with all other parameters fixed, the output power It is about the mutual inductance coefficient and secondary side compensation capacitor It is a bivariate function. Therefore, it can be adjusted... To adjust the output power .

[0066] As shown in Figures 1 and 2, the secondary compensation capacitor It includes a first branch and a second branch connected in parallel, the first branch including a switching transistor. ,diode and compensation capacitor The switching transistor With diode After parallel connection, close to the diode One end of the anode is connected to the compensation capacitor. Series;

[0067] The first branch includes a switch tube , a diode and a compensation capacitor , the switch tube is connected in parallel with the diode and the end close to the anode of the diode is connected in series with the compensation capacitor .

[0068] In this embodiment, the voltage across the capacitor when the switch tube is off can be seen from the variable capacitor as shown in Fig. 2 ; since the absolute value of the charge charged and discharged by the capacitor in one cycle is the same, we have:

[0069]

[0070] For the charge charged and discharged by the capacitor ( in one cycle), we have:

[0071]

[0072] For the charge charged and discharged by the capacitor ( in one cycle), we have:

[0073]

[0074] Taking the capacitance of the two capacitors , both as C ( ), we have:

[0075]

[0076] In the formula, D is the conduction angle of the switch tube and the switch tube . The relationship between the duty cycle D and the conduction angle

[0077] is:

[0078] From the expression of the equivalent capacitance value of the variable capacitor, we can know that when the conduction angles

[0079] of the switch tube and the switch tube are from 0 ~ , the equivalent capacitance value of the variable capacitor is: The equivalent capacitance value of the switch capacitor changes with the duty cycle D The equivalent capacitance value of the switch capacitor changes with the duty cycle D

[0080] As shown in FIG. 1, the system further comprises a signal collector, a controller and a driver;

[0081] The signal collector is configured to collect the output current and the output voltage of the secondary side compensation circuit and transmit them to the controller, the controller is configured to output a control signal of the secondary side compensation capacitor according to the collected signals, and the driver is configured to drive the switching tubes and the switching tubes of the secondary side compensation capacitor according to the control signal to change the conduction angle of the switching tubes .

[0082] In this embodiment, the driver is a Mosfet driver.

[0083] Embodiment 2

[0084] A secondary side control method of a wireless power transmission system based on variable capacitance control, as shown in FIG. 3, is characterized in that it is used to control the wireless power transmission system based on variable capacitance control as described in Embodiment 1, and the specific steps are as follows:

[0085] S1: initialize the system duty cycle D;

[0086] S2: detect the output current and the output voltage ;

[0087] S3: calculate the output power of the system at the current time according to the output current and the output voltage ;

[0088] S4: determine whether the following condition is met: 0= Pset ;

[0089] If the condition is met, the secondary side output power control is completed, and the control ends.

[0090] If the condition is not met, a new duty cycle D is calculated by PI control, the duty cycle D of the PWM is adjusted, and the step S2 is returned.

[0091] In this embodiment, Pset is the expected output power of the system, the step S2 is completed by the signal collector, and the steps S3 and S4 are completed by the controller and the driver.

[0092] S5: System simulation verification:

[0093] Set the secondary compensation capacitor and time t satisfy:

[0094] (F)

[0095] When the mutual inductance coefficient is constant and F, the output power with the secondary compensation capacitor changes can be observed from the MATLAB and Simulink simulation waveform as shown in Figure 4.

[0096] The amplitude of the Simulink simulation waveform is slightly lower than that of the MATLAB waveform due to the loss of inductance, capacitance and equivalent series impedance. As shown in Figure 4, the trend of the output power with the secondary compensation capacitor changes. When the secondary compensation capacitor starts to increase from 1.0× F, the output power increases first and then decreases, that is, when the mutual inductance coefficient changes, the output power can be maintained constant by adjusting the size of the variable capacitor .

[0097] As shown in Figure 5, when the mutual inductance coefficient changes in the range of H~ H, and the variable capacitor changes in the range of F~ F, the change surface diagram of the system output power . It can be seen that within this change range, the output power increases monotonously with the increase of the mutual inductance coefficient and the variable capacitor .

[0098] According to the operating area defined in Figure 4, the change range of the variable capacitor is F~ F, and the mutual inductance coefficient changes in the sampling time 0~0.2s, and the mutual inductance change curve is shown in Figure 6. As shown in Figure 7, the system output power can be restored to 13KW from the Simulink simulation waveform.

[0099] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit it. Although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or equivalently replaced without departing from the spirit and scope of the present application, and any modification or equivalent replacement should be covered in the protection scope of the claims of the present application.

Claims

1. A wireless power transmission system based on variable capacitance control, comprising a transmitting end and a receiving end, the transmitting end comprising a direct current power supply, an inverter, a primary side compensation circuit and a transmitting coil connected in sequence , the receiving end comprising a receiving coil , a secondary side compensation circuit, a rectification filter circuit and a load connected in sequence, characterized in that The primary side compensation circuit and the secondary side compensation circuit are symmetrically arranged LCC network compensation structures. The secondary side compensation circuit includes a secondary side compensation capacitor secondary side compensation capacitor And secondary side compensation inductance , the secondary side compensation capacitor The variable capacitor is variable.

2. A wireless power transfer system based on variable capacitance control according to claim 1, characterized in that, The secondary side compensation capacitor one end of the receiving coil one end of the secondary side compensation capacitor the other end of the secondary side compensation capacitor and one end of the secondary side compensation inductor the other end of the secondary side compensation inductor one input end of the rectification filter circuit, the other end of the secondary side compensation capacitor the other end of the receiving coil and the other input end of the rectification filter circuit.

3. A wireless power transfer system based on variable capacitance control according to claim 2, characterized in that, The secondary side compensation capacitor The first branch and the second branch are arranged in parallel, the first branch comprises a switch tube , a diode and a compensation capacitor , the switch tube is connected with the diode in parallel, and one end of the diode close to an anode is connected with the compensation capacitor in series; The first branch includes a switch tube diode and compensation capacitor , the switch tube with diode Parallel back diode One end of the anode is connected to a compensation capacitor In series.

4. A wireless power transfer system based on variable capacitance control according to claim 3, characterized in that, The primary side compensation circuit comprises a primary side compensation capacitor , a primary side compensation capacitor and a primary side compensation inductor ; The primary side compensation inductor one end of the primary side compensation inductor is connected with one output end of the inverter the other end of the original side compensation capacitor And the original side compensation capacitor one end of the primary side compensation capacitor the other end of the transmission coil one end of the primary side compensation capacitor the other end of the transmission coil The other end of the variable capacitor and another output end of the inverter are connected.

5. A wireless power transfer system based on variable capacitance control according to claim 4, characterized in that, Output power of the system For: ； In the formulae, for the inverter output current of the system, for the equivalent resistance of the system, ， for the load, Primary side compensated inductance the inductance value of the inductor, for the system corner frequency, for transmitting a coil And receiving coil mutual inductance value between the coils, to compensate for the output current of the secondary side, The secondary side equivalent impedance is equivalent impedance. Impedance value of the secondary side equivalent impedance The conduction angle is conduction angle. 。 6. A wireless power transfer system based on variable capacitance control according to claim 2, characterized in that, Secondary side compensation capacitor The capacitance value of the secondary side compensation capacitor is: ； wherein the compensation capacitor and compensation capacitor the capacitance values of the capacitors are ， For the switch tube and switch tube The signal collector, the controller and the driver are further included.

7. A wireless power transfer system based on variable capacitance control according to claim 5, characterized in that, System duty cycle D and switching transistor and switching transistor conduction angle The mathematical relationship is as follows: 。 8. A wireless power transfer system based on variable capacitance control according to claim 6, characterized in that, The conduction angle is changed. The signal collector is used to collect the output current of the secondary side compensation circuit and output voltage and transmitted to a controller configured to output a secondary side compensation capacitance based on the collected signal a control signal, the driver driving the secondary side compensation capacitor according to the control signal switching transistor and a switch tube The variable capacitor control-based wireless power transmission system of claim 8 is controlled, and the specific steps are as follows:

9. A control method for the secondary side of a wireless power transfer system based on variable capacitance control, characterized by, S1: initializing the system duty cycle D; Whether the following condition is established: S2: detecting the output current and output voltage ； S3: according to the output current and output voltage , the output power of the computing system at the current time ； S4: judging If yes, the secondary side output power control is completed, and the control is ended. If no, a new duty cycle D is calculated by PI control, the duty cycle D of the PWM is adjusted, and the step S2 is returned. ​

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