CN104937810A - A wireless power receiving device capable of improving efficiency and power transfer by modulating the effective load resistance of the receiving end - Google Patents

Abstract

The present invention relates to a wireless power receiving device capable of improving power transmission by modulating an effective load resistance at a receiving end and a wireless power transmission system using the device. A receiving unit of the wireless power receiving device receives power from a wireless power transmission device. A rectifying circuit unit rectifies a current output from the receiving unit and outputs the rectified current. A load resistance modulation unit receives a control signal having a duty cycle, controls a current provided from the rectifying circuit unit according to the received control signal to change the size of the effective load resistance, and increases the size of the equivalent resistance to improve efficiency.

Description

A wireless power receiving device capable of improving efficiency and power transfer by modulating the effective load resistance of the receiving end

technical field

The present invention relates to a wireless power transmission system, and more particularly to a wireless power receiving device that improves power transmission by modulating the effective load resistance of a receiving end.

Background technique

A wireless power transmission system generally includes a transmitting device DC power supply, a transmitting device resonant inverter, a transmitting resonator, a receiving resonator, a rectifying circuit unit, and a power converter. To provide high efficiency within the constraints of low coupling and small resonators, the load resistance of the receiving device needs to be optimized accordingly.

In addition to efficiency, the ability to transmit more power than is required by the receiving device is also required. In particular, when there is a long distance between the transmitting device and the receiving device, it is difficult to provide sufficient power to the receiving device. In addition to distance, load resistance also affects power transfer. Therefore, in order to transmit desired power to the receiving device with high efficiency, it is necessary to select the load resistance appropriately.

The problem is that it is difficult to change the load resistance freely. Load resistance is determined by the power requirements of the devices actually consuming power and is not a system design variable. When an impedance conversion circuit is used, it is possible to convert the effective load resistance observed from the receiving resonator and improve performance.

However, a typical impedance transformation circuit already has a fixed transformation ratio, and the impedance transformation ratio cannot be changed freely.

In this case, there is a limit that performance can be optimized under the condition of a certain distance or a certain load current, but when the distance changes or the load current changes, the performance drops and the system becomes unstable.

The power conversion circuit at the rear of a typical receiving device only has the function of limiting power when receiving more power than required. Thus, when the received power is smaller than the required power, it is practically difficult to sufficiently supply the desired power to the load resistor.

In US patent application US2010/0277003A1 entitled "Adaptive Impedance Tuning in Wireless Power Transfer", the purpose of changing the resistance of a receiving device by using a DC-DC inverter is to control power, not to increase efficiency. This patent application claims different control methods and output/input power sensing methods for increasing or decreasing output power. However, its purpose is power transfer control rather than increasing efficiency. This patent application describes that the efficiency does not have to be increased when the transmitted power is increased by using these methods.

Instead, the aim of this patent application is to increase the efficiency of the resonator with the aid of a power conversion circuit, rather than to control the power. Even if the proposed receiving device receives the same power at the same distance, since the receiving device operates in a state where its reflection resistance has been amplified, the receiving device has high efficiency. The addition of the proposed load resistance modulation unit provides higher efficiency than without the addition of the proposed load resistance modulation unit.

Contents of the invention

technical problem

The purpose of the present invention is to provide a wireless power transfer system that improves power transfer by modulating the effective load resistance of the receiving end, which can solve the following limitations: in the case of a specific distance or a specific load current, it can optimize performance, but when the distance changes or the load current changes, since the typical impedance transformation circuit used in a typical wireless power transmission system cannot freely change the impedance transformation ratio, and already has a fixed transformation ratio, the performance drops, and the system becomes Get unstable.

Technical solutions

In order to achieve the above object, the present invention provides a wireless power receiving device, which includes: a receiving unit that receives power from a power transmission device; a rectifying circuit unit that rectifies the current output from the receiving unit, and outputting the rectified current; and a load resistance modulation unit that receives a control signal having a duty ratio, adjusts the current provided from the rectification circuit unit according to the received control signal to change the magnitude of the effective load resistance, and Increase the size of the reflective resistor to improve efficiency.

Beneficial effect

According to the present invention, there is an advantage that the efficiency and output power of the entire system can be increased by changing the effective load resistance in the direction of increasing the loaded Q value of the receiving device and by increasing the reflection resistance reflected to the transmitting device.

In addition, since the reflection resistance can be increased when there is a long distance between the wireless power transmitting device and the wireless power receiving device, and thus the output power decreases to less than or equal to the power required by the load resistor, there are cases where a longer distance can be maintained under the same efficiency and output power advantages.

Description of drawings

Figures 1(a) and 1(b) show the correlation between a series receiving resonator and a reflection resistor.

Figures 2(a) and 2(b) show the correlation between receiving resonators and reflection resistors connected in parallel.

FIG. 3 is a block diagram of a wireless power transfer system according to an embodiment of the present invention.

FIG. 4 is an example of a rectification circuit diagram in FIG. 3 .

FIG. 5 shows a first modulation circuit (boost type modulation circuit) of the first embodiment of the load resistance modulation unit of the present invention.

FIG. 6 shows the second modulation circuit (boost type modulation circuit) of the second embodiment of the load resistance modulation unit of the present invention.

FIG. 7 shows a third modulation circuit (SEPIC type modulation circuit) of the third embodiment of the load resistance modulation unit of the present invention.

FIG. 8 shows a fourth modulation circuit (buck type modulation circuit) of the fourth embodiment of the load resistance modulation unit of the present invention.

FIG. 9 shows a fifth modulation circuit (flyback modulation circuit receiving a pulsating DC voltage input) of a fifth embodiment of the load resistance modulation unit of the present invention.

FIG. 10 shows a sixth modulation circuit (buck-boost-cascade type modulation circuit) of the sixth embodiment of the load resistance modulation unit of the present invention.

11(a) and 11(b) are examples of equivalently performing series or parallel conversion of the receiving unit by modulating the load resistance in order to increase the reflection resistance when the receiving unit of the present invention includes a series resonant structure and a parallel resonant structure.

FIG. 12 is a flow chart of the operation method of the wireless power receiving device in FIG. 3 .

FIG. 13 is a flowchart of a method of operation of the wireless power transfer system in FIG. 3 .

Fig. 14(a) is a graph of the transmission power with respect to the distance between the wireless power transmitting device and the wireless power receiving device in the present invention and the prior art, and Fig. 14(b) is the transmission power according to the present invention and the prior art A graph of power versus distance between the transmitting device and the receiving device. ("Load Modulation" represents the invention and "Rectifier Only" represents prior art.)

Figure 15(a) is a graph of efficiency versus distance when the output is 21.6W according to the present invention and the prior art, and Figure 15(b) is when the output is 10.9W in the present invention and the prior art A plot of efficiency versus distance for . ("Modulated load" represents the invention and "Rectifier only" represents prior art.)

Detailed ways

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, detailed descriptions related to known functions or structures will be omitted in order to unnecessarily obscure the subject matter of the present invention.

Since the present invention can be variously modified and have several embodiments, specific embodiments will be shown in the drawings and will be described in detail in this application or application. However, it is not intended to limit the present invention to specific embodiments, and it should be understood that the present invention covers all modifications, equivalents, and/or alternatives falling within the spirit and scope of the present invention.

When it is mentioned that any element is "connected" or "accessed" to another element, it will be understood that the former may be directly connected or accessed with the latter or another element may be present therebetween. Conversely, when any element is referred to as being 'directly connected' or 'directly accessed' to another element, it will be understood that there may be no other element in between. Other expressions used to describe the relationship between elements, such as "between," "directly between," or "adjacent to," and "directly adjacent to," should also interpreted in the same way.

The terms used in the present invention are used to describe specific embodiments only, and are not intended to limit the present invention. The terms of a singular form include plural forms unless otherwise specified. It should be understood that in the present invention, the term "comprises" or "has" indicates the existence of features, numbers, steps, operations, elements, components or combinations thereof, but does not exclude one or more other features, numbers, steps , operations, elements, components, or the presence or addition of combinations thereof.

Hereinafter, the present invention will be described in more detail by referring to the accompanying drawings.

Before describing the present invention, the magnitude of the equivalent resistance in the wireless power transmission device can be represented by the following equation 1:

[Formula 1]

R _reflected = k ² ω ₀ L ₁ Q _RX .

In this example, k represents the coupling coefficient between the transmitting coil in the transmitting device and the receiving resonator in the receiving device, L1 represents the inductance _of the transmitting coil, and Q _RX represents the loaded Q value (loaded-Q) of the receiving resonator , ω ₀ is the resonant frequency of the resonator and the switching frequency of the inverter, and the influence of the coupling between the transmitting coil and the receiving device is represented by a single equivalent resistance _Rreflected .

Because the influence of the receiving device is reflected to the transmitting coil, the equivalent resistance R _reflected is called the reflection resistance.

As shown in FIGS. 1( a ) to 2 ( b ), the reflection resistance R _reflected is connected in series with the parasitic resistance R _{TX parasitic} of the transmission coil L ₁ . Therefore, the condition for high efficiency and high output is to increase the reflective resistance R _reflected .

The reflected resistance depends on Q _RX determined by the load resistance of the receiving resonator (see Equation 1).

In the case of a series resonant receiving device, the loaded Q value and reflected resistance increase as the load resistance _RL decreases (see Figure 1), and in the case of a parallel resonant receiving device, the loaded Q value and reflected resistance R _reflected increase with the load resistance _RL increases with increasing (see Figure 2).

Therefore, the present invention changes the magnitude of the effective load resistance and the reflection resistance of the receiving resonator through the load resistance modulation circuit, so as to increase the efficiency of the transmission power and the transmission power.

FIG. 3 is a block diagram of a wireless power transfer system according to an embodiment of the present invention. FIG. 4 is an example of a circuit diagram of the rectifier in FIG. 3 .

As shown in FIG. 3 , the wireless power transmission system 300 of the present invention includes a wireless power transmission device 100 and a wireless power receiving device 200 .

The wireless power transmission device 100 transmits power. The wireless power transmission device 100 includes a DC power supply and a transmission resonance unit, and plays _a role of transmitting power generated from the DC power supply to the outside via the inductor L1 in the transmission resonance unit.

In order to improve the transmission efficiency of wireless power, the wireless power receiving device 200 adjusts the size of the reflection resistance.

More specifically, the wireless power receiving device 200 includes a receiving unit 120 , a rectifying circuit unit 130 , and a load resistance modulating unit 140 .

The receiving unit 120 receives power from the wireless power transmitting device.

The rectification circuit unit 130 rectifies the current output from the receiving unit 120 and outputs the rectified current.

The load resistance modulation unit 140 receives the control signal including the duty ratio, adjusts the current supplied from the rectification circuit unit 130 according to the received control signal CNT to change the size of the effective load resistance, and adjusts the size of the reflection resistance in the power transmission device , in order to improve efficiency.

The control signal CNT controls the operation of the load resistance modulation unit 140, specifically, the control signal CNT is a pulse signal with a fixed or variable duty cycle, which regularly turns on/off the switching devices in the load resistance modulation unit 140 .

The receiving unit 120 may be configured in a structure in which the inductor L and the capacitor C are connected in series, in parallel, or in both series and parallel. A more specific description is provided with reference to FIG. 10 below.

Next, referring to FIG. 4 , the rectification circuit unit 130 includes a first rectification unit 131 , a second rectification unit 132 , and a rectification circuit unit output filter 133 . The rectification circuit unit 130 receives the rectified current from the reception unit 120 and provides the received current to the load resistance modulation unit 140 .

The first rectification unit 131 includes two diodes D connected in series via the first node N1, the second rectification unit 132 includes two diodes D connected in series via the second node N2, and the first rectification unit 131 and the second rectification unit 132 connected in parallel. In addition, the rectification circuit unit 130 is connected in parallel with the rectification circuit unit output filter C.

The alternating current supplied from the receiving unit 120 is output as direct current in the output filter C of the rectifying circuit unit 130 via the rectifying device (diode) of the first rectifying unit 131 .

The load resistance modulation unit 140 functions to adjust the current supplied from the rectification circuit unit 130 to change the magnitude of the load resistance _RL . More specifically, it adjusts the current supplied from the rectification circuit unit 130 so as to increase or decrease the magnitude of the effective load resistance.

FIG. 5 shows the first modulation circuit (boost type modulation circuit) of the first embodiment of the load resistance modulation unit of the present invention.

More specifically, as shown in FIG. 5, the load resistance modulation unit 140 is different according to the connection structure of the inductor L and the capacitor C in the receiving unit 120. In the case of a series connection structure, the load resistance modulation unit 140 includes a first A modulation circuit 210, a second modulation circuit 220, or a third modulation circuit 230, and in the case of a parallel connection structure, the load resistance modulation unit 140 includes a fourth modulation circuit 240, a fifth modulation circuit 250, or a sixth modulation circuit 260.

The first modulation circuit 210 may be a boost circuit including an inductor 211 , a first switching device 212 , a second switching device 213 , and a capacitor 214 .

More specifically, one end of the inductor 211 is connected to the rectification unit, and the other end thereof is connected to the third node N3. The drain terminal of the first switching device 212 is connected to the third node N3, and the source terminal thereof is connected to the fourth node N4. One end of the second switching device 213 is connected to the third node N3, and the other end thereof is connected to the fifth node N5.

The control signal CNT is a pulse signal, which is supplied to the gate terminal of the first switching device 212 . The duty cycle of the control signal CNT may have a fixed value or vary according to the output voltage of the load resistor.

The first switching device 212 and the second switching device 213 are turned on alternately.

When the first switching device 212 is turned on, the current flowing in the inductor 211 is gradually accumulated. The current flowing in the inductor is gradually accumulated through the first switching device 212 and the rectification circuit unit 130 .

When the first switching device 212 is turned off, the voltage of the third node N3 increases, and once the voltage is equal to or higher than the threshold voltage of the second switching device 213, the second switching device 213 is turned on. Thus, the current flowing in the inductor 211 is supplied to the load resistor _RL .

As the proportion (eg, duty cycle) of the first switching device 212 being turned on during the entire switching cycle increases, the gradually accumulated current increases, the resistance input to the modulator 210 decreases, and because the input to the first modulation circuit The 210 resistor is the effective load resistor, so the reflected resistance increases.

Thus, the first modulating circuit 210 adjusts the current according to the duty ratio of the control signal CNT (pulse signal), so that the input resistance is reduced compared to a typical load resistance to increase the reflection resistance in the wireless power transmission device 100 . Therefore, wireless power transmission efficiency and transmission power increase.

FIG. 6 shows the second modulation circuit (boost type modulation circuit) of the second embodiment of the load resistance modulation unit of the present invention.

As shown in FIG. 6 , the second modulation unit 220 is a circuit diagram representing an example of a step-up type circuit receiving a pulsating DC current.

More specifically, the second modulation circuit 220 includes a first switching device 221 , a second switching device 222 , and a capacitor 223 .

The drain terminal of the first switching device 221 is connected to the third node N3, the gate terminal thereof is connected to the control unit 170, and the source terminal thereof is connected to the fourth node N4.

One end of the second switching device 222 is connected to the third node N3, and the other end thereof is connected to the fifth node N5. The capacitor 223 is connected in parallel with the second switching device 222 .

The second modulation circuit 222 is a circuit obtained by removing the rectification circuit unit output filter C of the power receiving circuit and the inductor of the load resistance modulation unit in the first modulation circuit 210 .

Thus, when the first switching device 221 is turned on, the amplitude of the resonance current at the receiving unit slowly increases. In this case, when the turn-on portion (eg, turn-on time portion) of the first switching device 221 is long, a gradual accumulation of current occurs in the receiving unit 120 . Thus, effective load resistance at the receiving unit 120 decreases, and reflection resistance increases.

FIG. 7 shows a third modulation circuit (SEPIC type modulation circuit) of the third embodiment of the load resistance modulation unit of the present invention.

As shown in FIG. 7, the third modulation circuit 230 is a circuit representing an example of a SEPIC type conversion circuit receiving a pulsating DC current. More specifically, the third modulation circuit 230 includes a first switching device 231, a second switching device 234, a A capacitor 232 , a second capacitor 235 , and an inductor 233 .

The drain terminal of the first switching device is connected to the third node N3, the gate terminal thereof is connected to the control unit, and the source terminal thereof is connected to the fourth node N4.

One end of the first capacitor 232 is connected to the third node N3, and the other end thereof is connected to the fifth node N5. One end of the inductor 233 is connected to the fifth node N5, and the other end thereof is connected to the sixth node N6. The second switching device 234 is a diode, one end thereof is connected to the sixth node N6, and the other end thereof is connected to the seventh node N7. One end of the second capacitor 235 is connected to the seventh node N7, and the other end thereof is connected to the eighth node N8.

In this example, when the first switching device 231 receives the control signal CNT and is activated, the current supplied to the third node N3 and the receiving unit 120 increases. In this case, the inductor connected to the sixth node N6 has a state where the current gradually accumulates, and thus supplies the current I _LS to the fifth node N5.

Then, when the first switching device 231 is turned off, the voltage supplied to the fifth node N5 corresponding to the current I _CS + I _SL increases to be greater than the threshold voltage of the second switching device 234 . Then, the second switching device 234 is turned on, and thus, the current supplied to the fifth node N5 increases.

Thus, by adjusting the effective load resistance at the load resistance modulation unit 140, the magnitude of the load resistance _RL at the receiving unit 120 can be increased or decreased. According to this principle, reflection resistance can be reduced or increased.

FIG. 8 shows a fourth modulation circuit (step-down modulation circuit) of the fourth embodiment of the load resistance modulation unit of the present invention.

As shown in FIG. 8 , the fourth modulation unit 240 is a circuit diagram representing an example of a step-down conversion circuit for increasing input resistance.

More specifically, the fourth modulation unit includes a first switching device 241 , a second switching device 242 , an inductor 243 , and a capacitor 244 .

The drain terminal of the first switching device 241 is connected to the rectification circuit unit 130, the gate terminal thereof is connected to the control unit 170, and the drain terminal thereof is connected to the third node N3. The second switching device 242 may be a diode, one end thereof is connected to the third node N3, and the other end thereof is connected to the fourth node N4. One end of the inductor 243 is connected to the third node N3, and the other end thereof is connected to the fifth node N5. One end of the capacitor 244 is connected to the third node N3, and the other end thereof is connected to the sixth node N6, so that the capacitor is connected in parallel with the inductor.

When the first switching device 241 receives the control signal (pulse signal) and turns on, the effective load resistance is fixed. If the first switching device 241 is turned off, the current decreases, the effective load resistance increases, and thus there is a larger reflection resistance in the wireless power transmission device.

A high reflection resistance increases efficiency and power, and thereby increases power delivered to the wireless power receiving device and power transfer efficiency.

FIG. 9 shows a fifth modulation circuit (a flyback modulation circuit receiving a pulsating DC voltage input) of a fifth embodiment of the load resistance modulation unit of the present invention.

As shown in FIG. 9, the fifth modulation circuit 250 is a circuit diagram representing an example of a flyback modulation circuit that receives a pulsating DC voltage input.

More specifically, the fifth modulation circuit 250 includes a flyback transformer 253, a first switching device 254, a second switching device 255, and a capacitor 256, wherein, in the flyback transformer 253, the first inductor 251 and the second inductor The coils in 252 are wound in the opposite direction.

For reference, the flyback transformer 253 is formed in such a manner that a coil in the first inductor 251 is wound in an opposite direction to a coil in the second inductor 252 and supplies current using a corresponding counter electromotive force.

One end of the first inductor 251 is connected to the third node N3 and the other end thereof is connected to the source terminal of the first switching device 254 . A source terminal of the first switching device 254 is connected to the other end of the first inductor 251, a control signal is supplied to a gate terminal of the first switching device, and a drain terminal of the first switching device is connected to the fourth node N4.

One end of the second inductor 252 is connected to one end of the diode, and the other end thereof is connected to one end of the capacitor 256 . Capacitor 256 is connected in parallel with the diode.

When the turn-off portion of the first switching device 254 becomes longer as the turn-off ratio of the control signal (pulse signal) supplied to the fifth modulation circuit 250 increases, from the first inductor 251 to the second inductor The current of 252 decreases, and the resonance voltage of receiving unit 120 increases. As a result, the effective load resistance increases.

Thus, the receiving unit 120 causes reflection resistance in the wireless power transmission device to become high. A high reflection resistance increases power transfer efficiency and power, and thus power transferred to the wireless power receiving device and power transfer efficiency increase.

FIG. 10 shows a sixth modulation circuit (buck-boost-cascade type modulation circuit) of the sixth embodiment of the load resistance modulation unit of the present invention.

The sixth modulation circuit 260 is a circuit diagram representing an example of a buck-boost-cascade type circuit receiving a pulsating DC voltage input.

More specifically, the sixth modulation circuit 260 includes a first switching device 261 , a second switching device 262 , an inductor 263 , a third switching device 264 , a fourth switching device 265 , and a capacitor C.

A source terminal of the first switching device 261 is connected to the rectification circuit unit 130, a control signal is supplied to a gate terminal of the first switching device, and a drain terminal of the first switching device is connected to the third node N3.

One end of the inductor 263 is connected to the third node N3, and the other end thereof is connected to the fifth node N5. One end of the second switching device 262 is connected to the third node N3, and the other end thereof is connected to the fourth node N4. A source terminal of the third switching device is connected to the fifth node N5, a gate terminal thereof is connected to the control unit 170, and a drain terminal thereof is connected to the sixth node N6. One end of the capacitor 267 is connected to the seventh node N7, and the other end thereof is connected to the eighth node N8.

In this example, the first and third switching devices 261 and 264 simultaneously receive the control signal CNT (the same pulse signal) to perform on/off operations.

Therefore, when the first and third switching devices 261 and 264 are turned on, the current on the inductor gradually accumulates. When the gradual accumulation time (for example, the on-time portion) is short, it frequently occurs that the resonance voltage of the receiving unit 120 is gradually accumulated.

As a result, the effective load resistance at the receiving unit 120 increases and the reflective resistance in the transmitting device correspondingly increases. Therefore, the power output from the wireless power transmission device 100 and the power transmission efficiency can be increased.

11( a ) and FIG. 11( b ) are examples of equivalently performing series or parallel conversion on the receiving device to increase reflection resistance by modulating the load resistance when the receiving unit of the present invention includes a series resonant structure and a parallel resonant structure.

Referring to FIG. 11( a ), the power receiving device includes both series and parallel resonant structures composed of C _2A and C _2B .

if Then the effect of C _2B is ignored and the circuit becomes series resonant. In this case, when the load resistance modulation unit controls the current to reduce the effective load resistance, the loading Q value and the reflection resistance can be increased.

if A transition to a series resonant structure is then performed, and the load resistance changes to the inverse such that scaling is performed (e.g., ). Thus, as the load resistance _RL increases, the converted load resistance decreases and the load Q value increases. Therefore, when the load resistance modulation unit controls the current to increase the effective load resistance, it is possible to increase the reflection resistance.

Referring to FIG. 11( b ), the power receiving device also includes both series and parallel resonant structures composed of C _2A and C _2B .

if Then the effect of C _2B is ignored and the circuit becomes series resonant. In this case, when the load resistance modulating unit controls the current to increase the effective load resistance, the loading Q value and the reflection resistance can be increased.

if Then the receiving unit is converted into a parallel resonance structure, and the load resistance is changed into an inverse number, thereby performing scaling. (For example, ).

Thus, as the load resistance decreases, the converted load resistance increases and the load Q increases. Thus, when the load resistance modulation unit controls the current to reduce the effective load resistance, it is possible to increase the reflection resistance.

FIG. 12 is a flow chart of the operation method of the wireless power receiving device in FIG. 3 .

As shown in FIG. 12 , the operation method S10 of the wireless power receiving device includes a receiving step S11 , a rectifying step S12 , and a load resistance changing step S13 .

The receiving step S11 is a step in which the receiving unit receives power from the wireless power transmission device 100 .

The rectification step S12 is a step in which the rectification circuit unit rectifies the current generated by using the received power.

The load resistance changing step S13 is the following steps: the load resistance modulating unit 140 receives a control signal with a duty cycle, adjusts the current according to the control signal CNT to change the effective load resistance, and adjusts the reflective resistance to improve efficiency.

The duty cycle may be a fixed or variable duty cycle, and the rectifying step S12 may include a step of generating a pulsating DC current.

FIG. 13 is a flowchart of a method of operation of the wireless power transfer system in FIG. 3 .

As shown in FIG. 13 , the operation method S100 of the wireless power transmission system includes a transmitting step S110 , a receiving step S120 , a rectifying step S130 , and a load resistance changing step S140 .

The transmitting step S11 is a step in which the wireless power transmitting device 100 transmits power.

The receiving step S120 is a step in which the wireless power receiving device 200 receives the transmitted power.

The rectification step S130 is a step in which the wireless power reception device 200 rectifies the current generated by using the received power.

The load resistance changing step S140 is the following steps: the wireless power receiving device 200 receives the control signal CNT with a duty ratio, adjusts the current according to the control signal CNT to change the size of the effective load resistance, and adjusts the size of the reflection resistance accordingly to improve power transfer efficiency.

Fig. 14(a) is a graph of the transmission power of the present invention and the prior art with respect to the distance between the transmitting device and the receiving device, and Fig. 14(b) is a graph of the transmission power of the present invention and the prior art with respect to A graph of the distance between the transmitting device and the receiving device.

As shown in FIG. 14(a) and FIG. 14(b), it can be seen that in the prior art, the longer the distance, the lower the transmission power and system efficiency. On the contrary, it can be seen that the present invention has distance-independent and constant transmission power and efficiency via the load resistance modulation unit.

Figure 15(a) is a graph of efficiency versus distance for the present invention and the prior art when outputting 21.6W, and Figure 15(b) is the efficiency for the present invention and prior art when outputting 10.9W Graph versus distance.

In this way, the present invention can receive the output voltage of the receiving device as feedback to adjust the magnitude (value) of the reflection resistance. In addition, constant power can be provided even when there is a long distance. Conversely, when there are long distances and the output power before the power converter drops to less than or equal to the power actually required by the load resistor, the prior art has been unable to provide power.

However, due to the invention's ability to increase the reflected resistance, transmission can be maintained even at longer distances when there is a long distance and the output power before the power converter drops to less than or equal to the power actually required by the load resistor The output power required by the device.

Although the present invention has been described using specific embodiments and drawings, the present invention is not limited thereto, and within the technical spirit of the present invention and the equivalent scope of the following claims, those skilled in the art to which the present invention belongs can make modifications and changes .

Explanation of reference signs

100: wireless power transmission device

120: receiving unit

130: Rectifier circuit unit

140: Load resistance modulation unit

200: wireless power receiving device

210: The first modulation circuit

220: Second modulation circuit

230: The third modulation circuit

240: The fourth modulation circuit

250: fifth modulation circuit

260: The sixth modulation circuit

300: Wireless Power Transfer System

Claims (12)

1. A wireless power receiving device, comprising: a receiving unit that receives power from the power transfer device; a rectification circuit unit which rectifies the current output from the receiving unit and outputs the rectified current; and a load resistance modulation unit that receives a control signal having a duty ratio, adjusts the current supplied from the rectification circuit unit according to the received control signal to change the magnitude of effective load resistance, and increases the magnitude of reflection resistance to improve efficiency . 2. The wireless power receiving apparatus according to claim 1, wherein the duty cycle is a fixed or variable duty cycle. 3. The wireless power receiving device according to claim 1 or 2, wherein the receiving unit includes an inductor and a capacitor connected in series. 4. The wireless power receiving device according to claim 3, wherein the load resistance modulation unit adjusts the current supplied from the rectification circuit unit to reduce the magnitude of the effective load resistance. 5. The wireless power receiving device according to claim 4, wherein the load resistance modulating unit is a step-up modulation circuit or a step-up-step-down modulation circuit. 6. The wireless power receiving device according to claim 4, wherein the load resistance modulation unit is a SEPIC type modulation circuit. 7. The wireless power receiving device according to claim 1 or 2, wherein the receiving unit includes an inductor and a capacitor connected in parallel. 8. The wireless power receiving device according to claim 7, wherein the load resistance modulation unit adjusts the current supplied from the rectification circuit unit to increase the magnitude of the effective load resistance. 9. The wireless power receiving device according to claim 8, wherein the load resistance modulation unit is a buck modulation circuit or a buck-boost modulation circuit. 10. The wireless power receiving device according to claim 8, wherein the load resistance modulation unit is a buck-boost-cascade modulation circuit. 11. The wireless power receiving device according to claim 1 or 2, wherein the receiving unit includes an inductor and two capacitors, wherein each of the two capacitors is in a series-parallel configuration or a parallel- A series structure is connected to the inductor. 12. The wireless power receiving device according to claim 11, wherein the load resistance modulating unit is a modulation circuit for modulating the effective load resistance to increase a loading Q value of the wireless power receiving device.