Wireless power transmission system for optimal power transmission and optimal resonant frequency control method thereof

Abstract

The present invention relates to a design of a wireless power transmission system and an optimal resonant frequency control method applied to the system, and provides a wireless power transmission system and an optimal resonant frequency control method applied to the system, by designing the power transmission part to match the frequency control range and designing the quality factor of the resonance unit of the power receiving part to be low, the difference of the power receiving performance in the control frequency range is small, and even if the resonance frequency of the wireless power transmission system arranged in a metal environment changes, the wireless power transmission system can still work normally. Power can be stably received, and a system frequency can be easily and quickly controlled to search for and find an optimal resonant frequency.

Description

Technical Field

[0001] The present invention relates to a wireless power transmission system and an optimal resonant frequency control method of the system. More specifically, the present invention relates to a wireless power transmission system for optimal power transmission and an optimal resonant frequency control method applied to the wireless power transmission system, the wireless power transmission system can stably receive power and can easily, quickly and effectively control the system frequency to search for the optimal resonant frequency. Background Art

[0002] Wireless power transmission refers to a technology that supplies power to home appliances or electric vehicles wirelessly instead of using traditional wired power lines. The advantage is that devices that require power can be charged wirelessly without connecting them to a power outlet using a power line. Therefore, related research is actively underway.

[0003] Wireless power transmission technologies mainly include magnetic induction, magnetic resonance and microwave. The magnetic induction method is a technology that uses magnetic induction coupling between two adjacent coils. The distance between the two power transmission and receiving coils is within a few centimeters, and the transmission efficiency is greatly affected by the arrangement conditions of the two coils. The magnetic resonance method is a technology that transmits non-radiative magnetic field energy between two resonators separated from each other through resonant coupling. Even if the distance between the power transmission and receiving coils is about 1m to 2m, wireless power transmission can be performed. Compared with the magnetic induction method, the advantages are that the wiring of the two coils is more flexible and the relay method can be used to expand the range of wireless charging. The microwave method is a technology that transmits power by radiating ultra-high frequency electromagnetic waves such as microwaves through antennas. It can perform long-distance wireless power transmission, but safety issues caused by electromagnetic waves need to be considered.

[0004] The wireless power transmission system is composed of a wireless power transmitting device that transmits power wirelessly and a wireless power receiving device that receives the power wirelessly. Generally, when the wireless power transmitting device and the wireless power receiving device have the same resonant frequency, maximum power transmission can be performed in the wireless power transmission system.

[0005] That is, the magnetic resonance type wireless power transmission system can maximize the transmission efficiency by the magnetic resonance effect even when the coupling between the power transmission unit and the power reception unit coil is small. However, there is a problem that the transmission efficiency drops sharply when the resonance condition is not satisfied.

[0006] In addition, at present, the magnetic induction method is mainly promoted for commercialization in small household appliances (mobile phones, headphones, tablets, etc.), while the magnetic resonance method is applied and tried in products that require large gaps and high power (automobiles, large household appliances, motors, etc.).

[0007] Compared with wired transmission methods, wireless power transmission technology is widely used in products ranging from small household appliances with low power to product groups with high power such as electric vehicles due to its high convenience and safety compared to wired transmission methods, and many products have been launched on the market.

[0008] However, although the magnetic induction method has many commercial applications, there are limitations in increasing the transmission distance. Moreover, although the power transmission distance is relatively long, the magnetic resonance method can ensure high transmission efficiency through the resonance phenomenon, but the transmission efficiency varies greatly depending on whether the resonance conditions are met.

[0009] In particular, the resonance conditions for the power transmission unit and the power receiving unit can be derived from mathematical theoretical solutions. However, when the positions of the power transmission unit and the power receiving unit and the distance between the power transmission unit and the power receiving unit change, the coupling effect will change and the conditions will change accordingly. In the case of the magnetic resonance method, when the resonance conditions are not met, the transmission efficiency will drop sharply. Therefore, a system and method are needed that can search for the optimal resonance frequency for optimal power transmission according to the change in the transmission distance.

[0010] Although this type of magnetic resonance power transmission has difficulties in terms of wired power supply or battery replacement, it has great application necessity and possibility for power transmission between two objects that require power and are arranged at a close distance.

[0011] In addition, in this magnetic resonance type power transmission, a phenomenon occurs in which the physical resonance frequency of the power transmission unit changes depending on whether a metal substance exists near the power transmission unit or the distance between the metal substance and the power transmission unit when a metal substance exists.

[0012] In particular, in an environment where a metal substance exists near the power transmission unit and the distance to the metal substance continuously changes, the resonance frequency may continuously change, and in this case, stable power transmission may become difficult.

[0013] Therefore, there is a need for a wireless power system that can maintain wireless power transmission performance even if a metal substance exists near a power transmission unit of the wireless power transmission system or the resonance frequency changes according to a change in the distance from the metal substance. Summary of the invention

[0014] Technical Problems to be Solved by the Invention

[0015] The problem to be solved by the present invention is to provide a wireless power transmission system and an optimal resonant frequency control method applied to the system, which is set in an environment where metal materials exist in the vicinity of the wireless power transmission surface (defined as the direction in which the power transmitting part and the power receiving part face each other to transmit wireless power) (hereinafter referred to as the "metal environment"), and can stably receive power even if the resonant frequency changes, and can easily and quickly control the system frequency to search for and find the optimal resonant frequency.

[0016] In addition, the problem to be solved by the present invention is to provide a wireless power transmission system and an optimal resonant frequency control method applied to the system, which can not only improve the stability and efficiency of wireless power transmission by minimizing the influence of the metal environment, but also make the circuit design of the power receiving unit easier by making it easier to select components.

[0017] In addition, the problem to be solved by the present invention is to provide a wireless power transmission system for efficient and optimal power transmission and an optimal resonant frequency control method applied to the system, which can be applied to various systems or household appliances in an environment where the resonant frequency changes due to a metal environment or an environment where the power transmission distance changes.

[0018] Technical Solution

[0019] To solve the above problems, the present invention can provide a wireless power transmission system for optimal power transmission, wherein a metal object is provided near a power transmission unit thereof and resonant inductive coupling is utilized, and the wireless power transmission system comprises: a power transmission unit, comprising a direct current / alternating current (AC / DC) conversion circuit, a direct current / radio frequency (DC / RF) conversion circuit, a matching circuit, a power transmission coil, a control circuit, and a communication circuit, and the power transmission unit is used to transmit power; and a power receiving unit, comprising a power receiving coil, a matching circuit, a rectification circuit, a stabilization circuit, a direct current / direct current (DC / DC) conversion circuit, a control circuit, and a communication circuit, and the power receiving unit receives power from the power transmission unit, the system being configured to control the received power of the power receiving unit by controlling the frequency of the transmitted power of the power transmission unit, and designing the resonant unit of the power receiving unit in such a manner that a quality factor value Q defined by the following mathematical formula 1 of the resonant unit composed of the power receiving coil and the matching circuit of the power receiving unit is less than a preset value,

[0020] Mathematical formula 1:

[0021]

[0022] The quality factor Q is the full width at half maximum (FWHM), which is defined as the frequency (f) at which the maximum power transmission / reception performance value exhibited at the resonant frequency is half the value of the resonant frequency. 2 , f 1 ) width.

[0023] In addition, the power transmission unit is installed under the vehicle wheel arch, the power receiving unit is installed inside the vehicle tire arranged on the wheel arch side and supplies power to the sensor module installed inside the tire, and the metal object can be arranged in an area other than the space where the power transmission unit transmits wireless power to the power receiving unit.

[0024] In addition, the sensor module may be an acceleration sensor, a temperature sensor or an air pressure sensor.

[0025] Here, the quality factor Q of the resonance unit of the power receiving unit may be set to be less than 100, and the quality factor Q of the resonance unit composed of the power transmission coil and the matching circuit of the power transmission unit may be set to be greater than 100.

[0026] In this case, the quality factor Q of the resonance unit of the power receiving unit and the quality factor Q of the resonance unit composed of the power transmission coil and the matching circuit of the power transmission unit may be set to be less than 100.

[0027] In addition, a shield member made of a ferrite material may be attached between the metal object and the power transmission portion.

[0028] In addition, in order to solve the above-mentioned problem, the present invention can provide a frequency control method for optimal power transmission, by which the wireless power transmission system for optimal power transmission is controlled, the method comprising: step (a), calculating the application range of the system resonance frequency change value of the power transmission unit constituting the wireless power transmission system; step (b), setting the starting value of the driving resonance frequency of the power transmission unit, and driving the power transmission unit at the starting value of the resonance frequency; step (c), driving the power transmission unit and measuring the output voltage of the power receiving unit to compare with a predetermined power receiving unit voltage reference value; and step (d), when the output voltage of the power receiving unit is greater than the voltage reference value, driving the power transmission unit in such a manner that the driving resonance frequency of the power transmission unit is sequentially increased or decreased until the resonance frequency at the moment when the output voltage of the power receiving unit is less than the voltage reference value is determined as the optimal resonance frequency, thereby determining the optimal resonance frequency.

[0029] In addition, the method may further include: step (e), driving the power transmission unit in reverse from the optimal resonant frequency determined in step (d) in such a manner that the driving resonant frequency of the power transmission unit is sequentially driven downward or upward to measure the output voltage of the power receiving unit and the deviation of the output voltage; and step (f), comparing the output deviation with a predetermined deviation reference.

[0030] Here, if the output deviation is larger than the reference deviation, the steps (b) and following steps of resetting the initial value and driving the power transmission unit at the resonant frequency initial value are repeated.

[0031] In this case, in step (b) of driving the transmission unit according to the frequency in sequence from the resonant frequency starting value, the transmission current value is measured together, and in step (c), the output current of the receiving unit is also measured together, and in the process of comparing the output voltage of the receiving unit with a predetermined receiving unit voltage reference value, it is determined whether the transmission efficiency of the transmission unit is maximized.

[0032] Beneficial Effects

[0033] According to the wireless power transmission system for optimal power transmission of the present invention and the optimal resonance frequency control method using the same, a wireless power transmission system and an optimal resonance frequency control method applied to the system are provided, which can stably receive power even if the resonance frequency of the wireless power transmission system set in a metal environment changes by designing the quality factor Q of the resonance unit of the power receiving part to be low, and can easily and quickly control the system frequency to search for and find the optimal resonance frequency.

[0034] In addition, according to the wireless power transmission system for optimal power transmission of the present invention and the optimal resonance frequency control method using the same, not only can the stability and efficiency of wireless power transmission be improved by minimizing the influence of the metal environment, but also the circuit design of the power receiving unit can be facilitated by easily selecting components.

[0035] In addition, according to the wireless power transmission system for optimal power transmission of the present invention and the optimal resonant frequency control method using the same, a wireless power transmission system for effectively transmitting optimal power and an optimal resonant frequency control method applied to the system are provided, which can be applied to environments with varying power transmission distances or various systems or household appliances by quickly and effectively searching the frequency control variable range and controlling the system frequency within the searched frequency variable range. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram showing a block diagram configuration of a wireless power transmission system using resonant inductive coupling disposed in an area where a metal object is disposed according to an embodiment of the present invention.

[0037] Figure 2 A schematic diagram showing a detailed block diagram configuration of a first system as a wireless power transmission system using resonant inductive coupling and disposed in an area where a metal object is disposed according to an embodiment of the present invention is shown.

[0038] Figure 3 A schematic diagram showing a detailed block diagram configuration of a second system as a wireless power transmission system using resonant inductive coupling and disposed in an area where a metal object is disposed according to an embodiment of the present invention is shown.

[0039] Figure 4 A graph defining and illustrating a quality factor value Q applied to a wireless power transmission system according to an embodiment of the present invention is shown.

[0040] Figure 5 A diagram for explaining a design of a power receiving unit Rx matching a target reception power in a wireless power transmission system according to an embodiment of the present invention is shown.

[0041] Figure 6 A schematic diagram and a graph showing the inductance change of a coil in a metal environment of a wireless power transmission system using resonant inductive coupling disposed in an area where a metal object is disposed according to another embodiment of the present invention are shown.

[0042] Figure 7 and Figure 8 The detailed process of the optimal resonant frequency control method of the wireless power transmission system for optimal power transmission according to the embodiment of the present invention is shown.

[0043] Fig. 9 A graph showing changes in the resonant frequency of a power transmission coil in a metallic environment applied to the optimal resonant frequency method according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0044] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may also be implemented in other forms. However, the embodiments introduced herein are provided to make the disclosed contents thorough and complete and to fully convey the inventive ideas to those of ordinary skill in the art. The same reference numerals throughout the specification represent the same constituent elements.

[0045] Figure 1 An example of a wireless power transmission system using resonant inductive coupling provided in a region where a metal object is provided according to an embodiment of the present invention is shown.

[0046] Figure 1In order to supply wireless power to a sensor module installed in a vehicle tire, the wireless power transmission system shown can have a power transmission unit on the vehicle wheel arch side and a power receiving unit inside the tire to supply the power required by the sensor module (e.g., an air pressure sensor) that can be installed inside the tire.

[0047] The wireless power transmission system can adopt the following method, that is, the transmission part constituting the wireless power transmission system can be installed on the inner circumference side of the wheel cover, and the receiving part is installed on the inner circumference of the tire, so that when the tire rotates one circle, the receiving part passes through the position opposite to the transmission part once and supplies wireless power at this moment.

[0048] The wheel cover is generally made of a metal material extending from a side body of a vehicle and may form a mounting space for mounting a wheel and a tire, and may generally be provided with a mudguard or the like made of a non-metal material.

[0049] The power transmission unit constituting the wireless power transmission system of the present invention needs to be arranged along the tire direction, so the power transmission unit can be installed between the frame of the wheel house and the fender or installed outside the fender along the tire direction or the axle direction.

[0050] Furthermore, the power receiving unit constituting the wireless power transmission system of the present invention is attached to the inner peripheral surface of a tire or the like, and transmits power wirelessly, thereby being able to supply power to a sensor module or the like.

[0051] This wireless power transmission system is provided with metal objects such as wheel house frames around it, and the distance between the power transmission unit and the power reception unit may be continuously changed according to the specifications of the tires, the road conditions, the suspension operation, and the like.

[0052] Therefore, in a wireless power transmission system, the resonant frequency of the system continuously changes depending on the presence of metal objects located nearby other than the direction in which power is transmitted to the power receiving unit, the distance between the power transmitting unit and the power receiving unit, etc. However, in conventional ordinary wireless power transmission systems, it is difficult to ensure stable wireless power transmission efficiency due to the use of a fixed resonant frequency.

[0053] Therefore, the technical problem of the wireless power transmission system of the present invention is to provide a wireless power transmission system for supplying power to a sensor module such as an air pressure sensor arranged inside a vehicle tire, wherein a power transmission unit 100 is arranged close to the vehicle wheel arch frame, and automatically searches for and controls the resonant frequency that changes according to the influence of a metal object 10 constituting the vehicle wheel arch frame, so as to be able to effectively transmit power to a power receiving unit 200, and even if the resonant frequency of the power transmission unit is changed to be different from the original due to the surrounding metal environment, power can be stably received by the pre-designed quality factor value Q of Rx described later.

[0054] That is, the present invention provides a wireless power transmission system, which can not only automatically search for the changed resonant frequency and effectively set the variable range of the control frequency, but also set the power receiving unit resonance unit 210 to have a low Q (performance index) value, so that the optimal resonant frequency for stable and optimal power transmission can be searched in a special environment where the resonant frequency changes due to the influence of the metal object 10 in a wireless power transmission system for supplying power in a metal environment where the metal object 10 is provided, and the power receiving unit 200 required must be a small size in order to be installed inside the tire. A specific description will be given.

[0055] Figure 2 A schematic diagram of a detailed block diagram configuration of a system (first system) that is a wireless power transmission system utilizing resonant inductive coupling and is disposed in an area where a metal object is provided according to an embodiment of the present invention, and that searches for optimal transmission efficiency by controlling the system frequency with a preset receiving voltage reference value or a receiving current reference value.

[0056] Figure 2 The system according to an embodiment of the present invention shown can be a wireless power transmission system, which is installed on the side of the wheel house frame of the vehicle made of metal material, and automatically searches for the resonant frequency that changes in the metal environment through feedback of the reference voltage value or the reference current value measured by the voltmeter 245 and the ammeter 244 of the power receiving unit. At this time, the resonance unit 210 of the power receiving unit 200 is intentionally designed to have a low Q value to ensure that even if the resonant frequency fluctuates within the entire operating range of the resonant frequency of the transmission unit, there is no large difference in the power receiving performance. Then, the frequency is searched as the resonant frequency with the best transmission efficiency when the received receiving voltage value is above the preset receiving voltage reference value while the frequency is controlled within the preset control frequency variable range based on the searched resonant frequency.

[0057] More specifically, if Figure 2 As shown, the system according to an embodiment of the present invention may include: a power transmission unit 100, which is installed on the wheel cover side; and a power receiving unit 200, which is arranged in a tire sensor module arranged inside the tire and receives the power transmitted from the above-mentioned power transmission unit 100 through the magnetic resonance effect.

[0058] The power transmission unit 100 may include: an AC / DC conversion circuit 110, which converts an AC input current into a DC; a DC / RF conversion circuit 120, which converts the DC converted by the DC conversion circuit into a radio frequency; a control circuit 150, which controls the resonant frequency when converting the DC into radio frequency power; a resonance unit 130, which includes a matching circuit 135 for magnetic resonance coupling and a power transmission coil connected to the matching circuit 135; and a communication circuit 160, which is used to send and receive voltage or current signals.

[0059] The power receiving unit 200 may include: a resonance unit 210, including a power receiving coil and a matching circuit 215, wherein the power receiving coil is coupled with the aforementioned power transmission coil within a certain power transmission distance and has a preset Q value; a rectifier circuit 220, which rectifies the high-frequency received power signal at the rear end of the resonance unit 210; a voltage stabilizing circuit 240, which is used to stabilize the rectified output voltage at the rear end of the rectifier circuit 220; a DC / DC conversion circuit 240, which outputs a predetermined voltage by stabilization at the rear end of the voltage stabilizing circuit 230; a control circuit 250, which receives a current signal from the above-mentioned rectifier circuit 220 and measures a voltage and / or current signal at the output end of the DC / DC conversion circuit 250, and then generates a feedback control signal; and a communication circuit 250, which sends a feedback control signal to the communication circuit 160 of the power transmitting unit 100.

[0060] like Figure 2 As shown, the system according to the embodiment of the present invention provides a wireless power transmission system, in which, when the frequency is changed within a preset range, the power transmission unit transmits power and sets the frequency with the maximum transmission current as the resonant frequency, and sets the resonance unit 210 of the power receiving unit 200 so that the Q value has a preset value (low Q value), and then the system frequency is changed within a preset frequency variable range based on the set resonant frequency by the control circuit of the power transmission unit 100, and at the same time, the output voltage V is measured by the voltmeter 245 at the output end of the DC / DC conversion circuit 240 of the power receiving unit 200, and the resonant frequency at which the measured output voltage value is a preset judgment voltage value is determined as the optimal resonant frequency.

[0061] Figure 3 A schematic diagram showing a detailed block diagram configuration of a system (second system) that controls system frequency and calculates and searches for power transmission efficiency as a wireless power transmission system using resonant inductive coupling provided in an area where a metal object is provided according to an embodiment of the present invention.

[0062] As another embodiment of the present invention, a wireless power transmission system can also be applied, and the position where the output voltage in the system is measured is connected to the wireless power transmission system. Figure 2 The illustrated embodiment is configured differently, namely, the stabilized output voltage Vr is measured between the stabilization circuit 230 and the DC / DC conversion circuit 240, and the resonant frequency when the measured stabilized output voltage Vr is above a preset reception voltage reference value is determined as the optimal resonant frequency.

[0063] That is, the stabilization circuit 230 can be provided between the rectifier circuit 220 and the DC / DC conversion circuit 240 of the power receiving unit 200 to improve the output stability, and prevent the risk of device damage caused by the drastic fluctuation of the output voltage value due to the load change at the output end and ensure the system stability. As described above, the stable output voltage value Vr measured between the stabilization circuit 230 and the DC / DC conversion circuit 240 is used as the output voltage value, so that a wireless power transmission system with more stable optimal transmission efficiency can be provided.

[0064] In addition, the reception voltage reference value for the measured stable output voltage value Vr may be greater than the reception voltage reference value for the DC output voltage value V measured at the output terminal. This is because the stable output voltage has a characteristic of increasing or decreasing in proportion to the amount of received power.

[0065] in addition, Figure 3 The second system according to the embodiment of the present invention shown can be a wireless power transmission system, which is installed on the side of the wheel house frame of the vehicle, and automatically searches for the changing resonant frequency in the metal environment through the transmission current measurement of the transmission unit 100, and sets the resonance unit 210 of the receiving unit 200 to have a preset low Q (Low Q) value, and then controls the frequency within a preset control frequency range based on the searched resonant frequency. At the frequency when the received receiving voltage value is above the preset receiving voltage reference value, the power transmission efficiency is calculated by the input current value, the output voltage value Vr, and the output current value A, and the resonant frequency corresponding to the maximum value is searched as the frequency with the best transmission efficiency.

[0066] Here, the resonance unit 210 of the power receiving unit 200 may be an LC resonance unit including a power receiving coil and a matching circuit, and is intentionally designed to have a low Q value to ensure that there is no large difference in power reception performance even if the resonance frequency changes within the entire operating range of the power transmitting unit resonance frequency.

[0067] More specifically, in the second system according to the embodiment of the present invention, the system frequency can be changed within a preset frequency variable range by the control circuit 150 of the power transmission unit 100, while measuring the input current value of the power transmission unit 100 and the output voltage value V at the output end of the DC / DC conversion circuit 240 of the power receiving unit 200, and if the measured output voltage value is greater than the preset reception voltage reference value, the power transmission efficiency is calculated in the system frequency by the input current value, the output voltage value, and the output current value, and the resonant frequency corresponding to the maximum value is determined as the optimal resonant frequency.

[0068] In addition, as another embodiment of the present invention, it can be a wireless power transmission system, which changes the system frequency within a preset frequency variable range through the control circuit 150 of the power transmission unit 100, and at the same time measures the input current value of the power transmission unit 100 and the stable output voltage value Vr between the stabilization circuit 230 and the DC / DC conversion circuit 240 of the power receiving unit 200, and if the measured stable output voltage value Vr is greater than the preset reception voltage reference value, the power transmission efficiency is calculated in the system frequency through the input current value, the output current value A and the stable output voltage value Vr, and the resonant frequency corresponding to the maximum value is determined as the optimal resonant frequency.

[0069] Figure 4 A diagram defining and illustrating a quality factor value Q applied to a wireless power transmission system according to an embodiment of the present invention is shown, Figure 5 A diagram for explaining a design of the power receiving unit 200 matching the target reception power in the wireless power transmission system according to the embodiment of the present invention is shown.

[0070] In the embodiment of the present invention, in order to solve the problem that in the wireless power transmission system applied to the tire sensor of a vehicle, the resonance frequency changes at any time due to the influence of the metal object 10 such as the vehicle frame located at the rear end of the power transmission unit 100, so that the power cannot be stably received from the power receiving unit 200, it is necessary to design a resonance unit 210 of the power receiving unit 200 so that the Q value of the resonance unit 210 of the power receiving unit 200 has a preset low value (low Q value) so that the power can be stably received in a wide range. The definition of the Q value is as follows: Figure 4 shown.

[0071] That is, the Q value can be defined as the full width at half maximum (FWHM), which is defined as the frequency (f) at which the maximum power transmission and reception performance value exhibited at the resonant frequency is half the value divided by the resonant frequency. 2 , f 1 ) width. As shown in the following mathematical formula 1.

[0072] Mathematical formula 1

[0073]

[0074] For example, if the resonant frequency is 200kHz and f 1 =199kHz and f 2 =201kHz, then Q=200kHz / (201kHz-199kHz)=100.

[0075] Reference Figure 5, using Q defined in this manner, a method for designing the power receiving unit 200 corresponding to the target reception power of the wireless power transmission system according to the embodiment of the present invention will be described in detail.

[0076] Under the condition that the transmission distance between the power transmission unit 100 and the power reception unit 200 is fixed and the resonant frequency is f1 and does not change, the design of the power reception unit 200 optimizes the efficiency by designing the impedance so that at the resonant frequency f 1 The target reception power at the maximum value is received at the RC circuit (such as Rx1 (high Q value)), so the Rx circuit does not receive excessive power in any case, so that the circuit can be used stably. However, as a disadvantage, if the resonance frequency becomes f differently from the design intention, 2 , the problem of receiving power not reaching the target may occur.

[0077] Considering that this is the condition for the resonant frequency to change, if using Figure 5 Rx shown 2 Design, then even if the frequency is f 1 ~f 2 The receiving target has no problem receiving power, but at the resonance frequency f 1 The circuit may receive too much power, causing the circuit to heat up or the voltage to rise and exceed the withstand voltage limit of the circuit components, resulting in component damage. In addition, in order to design a reliable circuit, there is a problem that expensive components with high withstand voltage and high heat resistance must be used.

[0078] Therefore, in an embodiment of the present invention, a method and a system thereof are proposed, which searches for a range of resonance frequency changes in a metal environment such as a metal object 10 (e.g., a tire sensor of a vehicle), and accordingly generates a signal with the resonance frequency of the metal object 10 being detected. Figure 5 The Rx3 method shown in the figure designs the Rx with a low Q value. If the resonant unit 210 of the power receiving unit 200 is designed in this way, even if the frequency is f 1 ~f 2 The received power varies within a certain range, so there is little heat generation and no circuit failure. Therefore, it is easy to select components, making the circuit design of the power receiving unit 200 easy and having high circuit stability.

[0079] In addition, in the tire industry, the weight of the built-in sensor module for passenger car tires is limited to 15-20g or less, and 25g for trucks. From the perspective of tire dynamics, local loads in the tire may cause tire vibration, so the weight of the sensor module is limited.

[0080] When designing an Rx (receiving) module that satisfies these conditions, the size of the wireless power coil also needs to be minimized, and the diameter is limited to about 85 mm or less. In addition, the Q value of the resonance unit 210 including the receiving coil is preferably limited to less than 100 to ensure that even if the control resonance frequency of the transmission unit fluctuates within a relatively wide frequency control range, the power receiving performance based on it should not have a large deviation.

[0081] In addition, the quality factor Q of the power receiving resonance unit 210 can be set to be less than 100, and the quality factor Q of the power transmitting resonance unit 130 can be set to be greater than 100. This setting can be applied to a system including the power transmitting resonance unit 130 and the power receiving resonance unit 210 for a long-distance smart tire with a large power transmission distance.

[0082] In addition, in a wireless power transmission system provided with a resonance unit for a general household appliance with a relatively short transmission distance, the Q value of the resonance units 130 and 210 of the power transmission unit 100 and the power reception unit 200 can be set to be less than 100. The Q value of the resonance unit applied to the above system is the Q value of the resonance unit composed of the power transmission or reception coil and the capacitor of each matching circuit.

[0083] Figure 6 A schematic diagram and a graph showing the change in inductance of a coil in a metal environment of a wireless power transmission system using resonant inductive coupling disposed in an area with a metal object according to another embodiment of the present invention are shown. If the inductance of the coil changes, the physical resonant frequency of the resonant unit changes.

[0084] Figure 6 Part (a) shows a schematic diagram showing a separation distance of a metal object 10 from a wireless power transmission system in a metal environment, Figure 6 Part (b) of FIG. 1 is a graph showing the inductance of the power transmission coil according to the separation distance between the metal object 10 and the power transmission coil. Figure 6 Part (c) is a graph showing the rate of change of inductance according to the separation distance between the metal object 10 and the power transmission coil.

[0085] like Figure 6 As shown in part (a) of FIG. 1 , in a wireless power transmission system using resonant inductive coupling and arranged in a region having a metal object 10 according to an embodiment of the present invention, different from Figure 1An embodiment of the present invention proposes a structure in which an electromagnetic wave shielding component made of ferrite material is attached to the rear end of the transmission unit 100, so that in order to reduce or eliminate the influence of the inductance change of the transmission coil of the transmission unit 100 caused by the reflection of electromagnetic waves generated in the transmission coil by a metal object 10 such as a vehicle frame at the rear end of the transmission unit 100, an electromagnetic wave shielding component made of ferrite material is attached between the transmission unit 100 (transmission coil) and the metal object 10 to minimize the influence of the metal environment.

[0086] Here, ferrite is a high-frequency magnetic material that has a strong magnetic property of exhibiting spontaneous magnetization at room temperature and is used for high resistance, and is a material of industrial importance. In addition, ferrite is generally an ionic compound having a spinel structure, and can be formed by combining iron oxide as a main component with various metal compounds. Ferrite having such a spinel structure is widely used as an electromagnetic wave absorbing material and an electromagnetic wave shielding material.

[0087] In the embodiment of the present invention, in order to minimize the influence of the metal environment such as the metal object 10 located at the rear end of the power transmission coil, as shown in FIG. Figure 6 As shown, an electromagnetic wave shielding member made of a ferrite material can be attached to the rear end of the power transmission unit 100 between the power transmission unit 100 and the metal object 10, so that the influence of the metal environment such as the vehicle frame is minimized. In the case of the power transmission unit, the fluctuation of the coil inductance can also be minimized by the ferrite shield, thereby minimizing the fluctuation range of the system (=physical) resonant frequency of the power transmission unit due to the metal environment. Only when the fluctuation range of the resonant frequency of the power transmission unit is limited as much as possible so as to keep it within the frequency range where the power receiving performance of the power receiving unit changes little, the system design can be easily realized.

[0088] Furthermore, electromagnetic wave shielding can be enhanced by providing a ferrite shielding member at the rear end of the power receiving coil disposed inside the tire.

[0089] In order to observe the influence of the inductance of the power transmission coil of the wireless power transmission system in such a metal environment, the inductance and the inductance change rate of the power transmission coil according to the separation distance between the power transmission coil and the metal object 10 were measured experimentally, and the inductance change rate of the power transmission coil according to the separation distance between the power transmission coil and the metal object 10 was measured. Figure 6 The graphs C and CF are shown in parts (b) and (c) of FIG. 1 and 1. ...c) of FIG. 1 and 1. The graphs C and CF are shown in parts (c) of FIG. 1 and 1.

[0090] First, it can be seen that when the distance between the metal object 10 and the power transmission coil is within about 40 mm, the inductance and inductance change rate of the power transmission coil are large. When the power transmission coil is closer to the metal object 10, the inductance becomes significantly smaller. It can be seen that due to the influence of the metal object 10, the inductance decreases and its change increases, resulting in a problem of reduced efficiency and stability of power transmission. In addition, it can be seen from Figure 6 It is clearly seen in parts (b) and (c) that when a ferrite shielding member is attached to the rear end of the power transmission coil, the inductance of the power transmission coil and its rate of change will not change significantly relatively even if the distance to the metal object 10 changes.

[0091] As described above, according to the wireless power transmission system using resonant inductive coupling provided in the area where the metal object 10 is provided according to the embodiment of the present invention, an electromagnetic wave shielding member such as a ferrite material must be provided in the power transmission unit 100 to minimize the frequency fluctuation range caused by the metal environment as much as possible, so that a wireless power system that can be stably operated in the metal environment can be designed. If the frequency fluctuation range of the power transmission unit is not limited and becomes too large, even if the power receiving unit is designed to have a low Q value, the frequency range for smoothly receiving wireless power is wider than that of a coil with a high Q value, but it is still limited, so that beyond this range, the power reception effect is not good. In addition, if the power receiving unit is designed to have a too low Q value, there is also a problem that the wireless power reception performance itself deteriorates. Therefore, the Q value of the power receiving unit cannot be too low, and should be a value within the range of a minimum of 30 to a maximum of 90. On the other hand, if the Q value of the power receiving unit is too large (above 100), the reception efficiency at the resonant frequency is good, but there is a problem that the reception performance changes sharply even if the frequency changes slightly due to the metal environment.

[0092] Figure 7 and Figure 8 The detailed process of the optimal resonant frequency control method of the wireless power transmission system for optimal power transmission according to the embodiment of the present invention is shown.

[0093] In implementation Figure 7 and Figure 8 Before the resonant frequency control method is implemented, first, the application range of the system resonant frequency change value of the power transmitting unit caused by the surrounding metal environment except for the wireless power transmission direction is calculated, and within this frequency range, the resonant circuit of the power receiving unit is designed to have a low Q value so that the output voltage of the power receiving unit is higher than the reference value.

[0094] like Figure 7As shown, in the optimal resonant frequency control method of the wireless power transmission system for optimal power transmission according to an embodiment of the present invention, the system is set in an area with a metal object 10, and a method for searching, maintaining and controlling the optimal resonant frequency is proposed in the frequency control method for optimal power transmission of the wireless power transmission system using resonant inductive coupling of the power transmitting unit 100 and the power receiving unit 200, so that the power receiving unit stably outputs a voltage above a reference value.

[0095] The control range is determined by the frequency range that fits the pre-designed characteristics of the resonant circuits in the power transmission and receiving units. Figure 5 As shown in the figure, the lowest frequency in the control frequency range is defined as the lower frequency limit, and the highest frequency is defined as the upper frequency limit. Figure 5 If f 1 to f 2 Defined as the control range, then f 1 is the lower frequency limit, f 2 is the upper frequency limit.

[0096] The upper and lower frequency limits are defined before implementing the control algorithm by first identifying the effect of the frequency fluctuation range on the metal surrounding the power transmission unit. Figure 7 and Figure 8 The embodiments of the frequency upward search control are shown in FIG. The upward control is a method of searching for the optimal resonance frequency by increasing the frequency by one control unit starting from the frequency lower limit value. Figure 7 The optimum frequency is the last frequency at which the output voltage of the power receiving unit exceeds the judgment reference value.

[0097] Specifically, Figure 7 The frequency control method for optimal power transmission of the wireless power transmission system shown in the figure can first calculate the application range of the change value of the system resonant frequency of the power transmission part due to the surrounding metal environment other than the wireless power transmission direction (step S110), and set the resonant frequency starting value (step S120). As described above, in the case of downward control, the starting frequency can be the upper limit of the frequency range of the resonant frequency change value. However, as Figure 7 As shown, when searching with upward control, the starting frequency can be the lower frequency limit value.

[0098] Therefore, the power transmission unit can be driven sequentially according to the frequency (step S130), and the output voltage of the power receiving unit can be measured (step S140), and the output voltage of the power receiving unit can be compared with the reference value (step S150). When the output voltage of the power receiving unit is still high, the power transmission unit can be driven by sequentially controlling upward and increasing the frequency by one control unit (step S160).

[0099] If the output voltage of the power receiving unit decreases as a result of comparing the output voltage of the power receiving unit with the reference value (step S150), the resonant frequency immediately before it is determined to be the optimal resonant frequency, and the search for the optimal resonant frequency is completed. Therefore, the power transmitting unit is driven at the previous resonant frequency by reducing the frequency by one unit in the reverse direction (step S170), and the output voltage of the power receiving unit is measured (step S180), and the deviation of the output voltage of the power receiving unit is measured (step S190) and compared with the reference deviation (step S200). If the output deviation is larger than the reference deviation, the steps following the step of setting the resonant frequency start value (step S120) are repeated. If the output deviation is smaller than the reference deviation, the resonant frequency search step is terminated, and wireless power is transmitted at the optimal resonant frequency, while returning to the state of receiving the output voltage of the power receiving unit (step S180).

[0100] Figure 8 As a method of searching for the optimum frequency, a frequency search that satisfies all transmission efficiencies in addition to the output voltage is shown by further measuring the power transmission unit current and the power reception unit current.

[0101] Will surround Figure 7 The differences in the methods shown are explained. Figure 8 The optimal resonance frequency control method of the wireless power transmission system for optimal power transmission shown includes a step of measuring a transmission current and a step of calculating a transmission efficiency in a control step.

[0102] Specifically, in the step of sequentially driving the transmission unit according to the frequency from the starting value resonance frequency set in the step of setting the resonance frequency starting value (step S320) (step S330), the transmission current value is measured (step S340), and the receiving unit current is measured in addition to the receiving unit output voltage (step S350), and in the step of comparing the receiving unit output voltage with the reference value, in addition to the voltage reference value, it can also be determined whether the transmission efficiency is the maximum (step S370). That is, Figure 8 When the output voltage of the power receiving unit exceeds the reference value, the transmission efficiency of the optimum resonance frequency is at a frequency of a local maximum.

[0103] If the output voltage of the power receiving unit is less than the reference value or the power transmission efficiency is not the maximum value, the steps below the step of setting the starting value of the resonant frequency are repeated to search upward. If the output voltage of the power receiving unit is greater than the reference value and the power transmission efficiency is also the maximum value, the driving state of the power transmitting unit is maintained at the resonant frequency (step S390), the output voltage and current of the power receiving unit are received (step S400), and the deviation of the output voltage and output current of the power receiving unit is measured (step S410).

[0104] Similarly, the output deviation of the output voltage and current of the power receiving unit is measured (step S410) and compared with the reference deviation (step S420). If the output deviation is greater than the reference deviation, the steps below the step of setting the resonant frequency starting value (step S320) are repeated. If the output deviation is less than the deviation reference, the resonant frequency search step is terminated, wireless power is transmitted at the optimal resonant frequency, and the state of receiving the output voltage and output current of the power receiving unit (step S400) is restored.

[0105] same, Figure 8 The control method shown can also be a downward search control. In this case, the method starts with the lower limit value of the frequency range as the starting frequency and reduces the starting frequency by one control unit to search for the optimal resonance frequency.

[0106] Fig. 9 A method for designing a range of control frequency (in other words, upper and lower limits of frequency control) for expected fluctuations in consideration of the setting conditions of a power transmission coil in a metal environment according to an embodiment of the present invention is described. Generally, as the physical frequency of a wireless power system increases, the size or number of components decreases, making it easier to configure a resonant circuit. Therefore, it is advantageous to select the upper limit of the control frequency as the maximum value in the legally permitted frequency band. In this embodiment, the wireless power permitted frequency band is 110 to 205 kHz, so the upper limit of the frequency control range is determined to be 205 kHz, and the lower limit of the frequency control is designed. The application object is a power transmission unit that supplies power to a tire sensor wirelessly, which is provided on a wheel housing, and a vehicle metal frame is provided on the back of the wheel housing within 30 to 60 mm according to the setting position. Therefore, this is an environment in which the resonant frequency changes due to the metal frame of the vehicle when the power transmission unit is provided.

[0107] like Fig. 9 As shown, when the power transmission unit 100 designed to have a resonant frequency of 199kHz is located in a metal environment without considering the metal environment, the system resonant frequency can be found by monitoring the current of the power transmission unit 100 according to the distance from the metal object 10. That is, when the consumption current of the power transmission unit according to the change of the control frequency is measured in the setting environment without a metal object and the distance between the metal object 10 and the power transmission unit 100 is 60mm and 30mm respectively, and is represented in a graph, it can be clearly seen that the frequency corresponding to the maximum power transmission consumption current is the resonant frequency. Therefore, as described above, by monitoring the power transmission current, the frequency representing the maximum power transmission current can be quickly and effectively confirmed as the resonant frequency. Here, the front of the power transmission coil is defined as the wireless power transmission direction. The metal frame is located on the back.

[0108] Initially, the physical resonant frequency of the power transmission unit was designed to be 199kHz regardless of the metal environment, but based on the results of this experiment, it can be expected that the resonant frequency will be between the minimum value of 201kHz and the maximum value of 204kHz when installed on the fender. Therefore, the control frequency range must include these two frequency ranges to achieve stable and effective control. In addition, considering the frequency band used in the state without a metal environment, the frequency control lower limit is set to 199kHz.

[0109] The frequency control uses the frequency band on either side of the left or right side based on the system resonant frequency to form a consistent functional relationship. Usually, the frequency band on the right side of the resonant frequency is used. If the lower limit of the frequency range is determined to be 199kHz and the upper limit is determined to be 205kHz, then within this range, whether there is no metal environment or the metal environment is within the range of 30 to 60mm, it is within the range of wireless power transmission, so it can be used.

[0110] As described above, considering the frequency fluctuation caused by the metal environment, the power transmission unit is designed so that the fluctuation range of the physical resonance frequency of the power transmission unit has a predetermined frequency range. However, it is known that the resonance frequency is 204kHz when the surrounding metal is close to 30mm.

[0111] In this case, the actual frequency control range is between 204kHz and 205kHz, which is only about 1kHz. Therefore, in order to further increase this frequency range, the design of the power transmission unit needs to be modified. For example, in this case, in order to have a control range of at least 3kHz, the design needs to be changed so that the resonant frequency of the power transmission unit when the surrounding metal is close to 30mm is 202kHz.

[0112] Thus, when there is no metal around, the resonant frequency will also fluctuate when the surrounding metal is close to 60mm. Therefore, the control lower limit value is changed accordingly to determine the frequency application range.

[0113] After designing the power transmission unit in this way, it is necessary to design the Q value of the power reception unit so that there is no difference in the power reception performance within the frequency operating range. Figure 5 As shown, if the frequency control lower limit value is f1 and the frequency control upper limit value is f2, the Q value of the power receiving unit is determined so as to ensure that there is no large deviation in the reception performance between the frequencies f1 and f2.

[0114] If the Q value is too low, the reception performance itself deteriorates, and if the Q value is too large, the received power deviation depending on the frequency becomes too large, so the circuit must operate in a wide power range, making it difficult to select components and making the component price expensive. Therefore, it is necessary to select the Q value appropriately to optimize performance and price.

[0115] If the Q value is less than 30, the reception performance is poor, and if it is more than 100, the value becomes too large, and even a slight change in frequency will increase the deviation of the reception performance. Therefore, the Q value is determined by defining the difference between the maximum and minimum reception performances within the range. For example, if the difference between the maximum reception performance and the minimum reception performance is designed to be within 25% within the above frequency control range, the desired power reception performance in the above system can be obtained by determining the Q value to be about 50.

Claims

1. A wireless power transmission system for optimal power transmission, wherein a metal object is provided near a power transmission part thereof and resonant inductive coupling is used, characterized in that: include: a power transmission unit, comprising an AC / DC conversion circuit, a DC / RF conversion circuit, a matching circuit, a power transmission coil, a control circuit, and a communication circuit, and the power transmission unit is used to transmit electric power, and a power receiving unit including a power receiving coil, a matching circuit, a rectifying circuit, a stabilizing circuit, a DC / DC conversion circuit, a control circuit, and a communication circuit, and the power receiving unit receives electric power from the power transmitting unit; The system is configured to control the reception power of the power receiving unit by controlling the frequency of the transmission power of the power transmitting unit; The resonant unit of the power receiving unit is designed so that the quality factor Q defined by the following mathematical formula 1 of the resonant unit composed of the power receiving coil and the matching circuit of the power receiving unit is smaller than a preset value. Mathematical formula 1: The quality factor value Q is the full width at half maximum, which is defined as a value obtained by dividing the resonance frequency by the width of the frequency (f2, f1) at half the maximum power transmission / reception performance value exhibited at the resonance frequency.

2. The wireless power transmission system for optimal power transmission according to claim 1, characterized in that The power transmission unit is installed under a wheel house of the vehicle, and the power reception unit is installed inside a vehicle tire provided on the wheel house side and supplies power to a sensor module installed inside the tire. The metal object is disposed in a region other than a space in which the power transmission unit transmits wireless power to the power reception unit.

3. The wireless power transmission system for optimal power transmission according to claim 2, characterized in that The sensor module is an acceleration sensor, a temperature sensor or an air pressure sensor.

4. The wireless power transmission system for optimal power transmission according to claim 1, characterized in that The quality factor Q of the resonance unit of the power receiving unit is set to be less than 100, and the quality factor Q of the resonance unit composed of the power transmission coil and the matching circuit of the power transmission unit is set to be greater than 100.

5. The wireless power transmission system for optimal power transmission according to claim 1, characterized in that The quality factor Q of the resonance unit of the power receiving unit and the quality factor Q of the resonance unit composed of the power transmission coil and the matching circuit of the power transmission unit are both set to be less than 100.

6. The wireless power transmission system for optimal power transmission according to claim 1, characterized in that A shield member made of a ferrite material is attached between the metal object and the power transmission portion.

7. A frequency control method for optimal power transmission, wherein the method controls the wireless power transmission system for optimal power transmission according to any one of claims 1 to 6, characterized in that: include: Step (a), calculating an application range of a system resonant frequency variation value of a power transmission unit constituting the wireless power transmission system; Step (b), setting a starting value of a driving resonance frequency of the power transmission unit, and driving the power transmission unit at the starting value of the resonance frequency; Step (c), driving the power transmission unit and measuring the output voltage of the power reception unit to compare with a predetermined power reception unit voltage reference value; as well as Step (d), when the output voltage of the power receiving unit is greater than the voltage reference value, driving the power transmitting unit in such a manner that the driving resonant frequency is sequentially increased or decreased until the resonant frequency at the moment when the output voltage of the power receiving unit is less than the voltage reference value is determined as the optimal resonant frequency, thereby determining the optimal resonant frequency.

8. The frequency control method for optimal power transmission according to claim 7, characterized in that: Also includes: Step (e), driving the power transmission unit in reverse from the optimal resonance frequency determined in step (d) in such a manner that the driving resonance frequency of the power transmission unit is sequentially downward or upward to measure the output voltage of the power reception unit and the deviation of the output voltage; as well as Step (f), comparing the output deviation with a predetermined deviation reference.

9. The frequency control method for optimal power transmission according to claim 8, characterized in that: If the output deviation is larger than the reference deviation, the steps (b) and below of resetting the initial value and driving the power transmission unit at the resonant frequency initial value are repeated.

10. The frequency control method for optimal power transmission according to claim 7, characterized in that: In step (b) of sequentially driving the transmission unit according to the frequency from the starting value of the resonant frequency, the transmission current value is measured, and in step (c), the output current of the receiving unit is also measured, and in the process of comparing the output voltage of the receiving unit with a predetermined voltage reference value of the receiving unit, it is determined whether the transmission efficiency of the transmission unit is maximized.

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