Power receiving device in a wireless power transmission system

Abstract

In improving the power reception efficiency of wireless power transmission systems, optimizing the operation of rectifier circuits using MPPT control presents challenges depending on the magnitude of the received power, such as increasing the size of the circuit and imposing high voltage resistance requirements on the rectifier and charge control circuits. Furthermore, even if optimal operation of the rectifier circuit can be achieved, optimizing the charging of the energy storage elements remains difficult. Moreover, even with power transmission using retrodetective methods, measures are needed to ensure that the power is received without loss by the receiving antenna and to prevent a decrease in power reception efficiency. [Solution] Prioritizing the optimization of the rectifier circuit's operation, the charging current control unit sequence-controls the charging current of the linear charging control unit to maintain the burst mode operation of the buck-boost converter. Furthermore, the antenna system for receiving circularly polarized high-frequency power is arranged and grouped along the rotation direction of the circular polarization to connect the output voltages from each rectifier circuit in parallel without coupling loss and output them to the charging control unit.

Description

Technical Field

[0001] The present invention relates to a charging control technique and an antenna system arrangement for a power receiving device with high power receiving efficiency in a wireless power transmission system.

Background Art

[0002] In a wireless power transmission system, in order to increase the received power, countermeasures are required for the entire system, the power transmission device, and the power receiving device respectively. However, the entire system is restricted by applications and use cases, and the power transmission device is subject to various regulations, so its degree of freedom is small.

[0003] For example, as a countermeasure in the power transmission device, there is an improvement in the gain of the power transmission antenna. One of them is a power transmission technology using a retrodirective method that performs power transmission toward the power receiving antenna, which is also the power transmission target, by a focus beam adjusted to an optimal phase based on the amplitude and phase of the beacon signal from the power receiving antenna. By this, an improvement in gain and thus an optimization of the power receiving efficiency are achieved (see Patent Documents 3 and 4).

[0004] On the other hand, as countermeasures for improving the power receiving efficiency in the power receiving device, which has a relatively large degree of freedom, there are an improvement in the gain of the power receiving antenna, an improvement in the efficiency of the rectifier circuit, an improvement in the efficiency of the charging control circuit, and an improvement in the efficiency of DC / DC.

[0005] For example, regarding the improvement of the efficiency of the rectifier circuit, it is known that the efficiency of the rectifier circuit is maximized by using MPPT control (Maximum Power Point Tracking control) or a technique similar thereto (see Patent Documents 1, 2, and 4).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] However, even in the case of power transmission using a retrodetective-type focused beam, the area of ​​the receiving antenna is small relative to the beam width, and the gain decreases depending on the beam angle. Therefore, it is necessary to receive the transmitted power without any loss and to prevent a decrease in receiving efficiency caused by variations in the received power between antennas.

[0008] Furthermore, while MPPT control commonly uses an open-circuit voltage reference method due to its low cost and simple control, it still presents problems such as the need for larger circuits depending on the magnitude of the received power, high voltage withstand voltage requirements for rectifier and charge control circuits, and the necessity of using half the voltage required by existing standards.

[0009] Furthermore, the applicant came to recognize that while MPPT control can optimize the operation of the rectifier circuit, it is difficult to simultaneously optimize the charging efficiency to the energy storage element. [Means for solving the problem]

[0010] Therefore, in the present invention, in a power receiving device for a wireless power transmission system that charges an energy storage element 5 and supplies power to a load 6 via a power receiving antenna 2, a rectifier circuit 3, and a charge control unit 4 as illustrated in Figure 1, the step-up / step-down converter constituting the charge control unit 4 is set to burst mode operation for high efficiency under light load conditions, prioritizing the optimal operation of the rectifier circuit 3. Similarly, the linear charge control unit constituting the charge control unit 4 is set to CC-CV mode (Constant Current - Constant Voltage mode). Furthermore, the charge current control unit constituting the charge control unit monitors the output voltage of the step-up / step-down converter and controls the charge current using sequence control such as the hill-climbing method or binary search method so that the output voltage maintains a set value that maximizes charging efficiency.

[0011] Furthermore, in the power receiving antenna system, a power receiving antenna that also serves as a beacon signal transmitter is placed in the center, and multiple dedicated power receiving antennas are positioned around it to improve power receiving efficiency, especially when the received high-frequency power is circularly polarized, and to suppress electromagnetic coupling.

[0012] Furthermore, the power from two or more adjacent receiving antennas, which are continuously aligned in the rotational direction of the circular polarization, was combined at high frequency by a coupler and output to the rectifier circuit 3. In this way, the output of each rectifier circuit, including the rectifier circuit of the centrally located receiving antenna, could be made roughly uniform, and these were further coupled in parallel without coupling loss and output to the charging control unit. [Effects of the Invention]

[0013] As a result, in a 1W class wireless power transmission system receiving device, optimal charging efficiency and optimal operation of the rectifier circuit were achieved without using MPPT control, a conventional technology that requires the construction of large circuits, and without limitations such as high voltage withstand requirements. [Brief explanation of the drawing]

[0014] [Figure 1] Schematic diagram of the wireless power transmission system according to the present invention [Figure 2] State of the focus beam in the retro-detective method [Figure 3] Block diagram of the constituent devices in Embodiment 1 [Figure 4] Comparison graph of the efficiency of the buck-boost converter in both the PMW / burst modes [Figure 5] Control sequence using the hill-climbing method in the charging current control unit [Figure 6] Control sequence using the binary search method in the charging current control unit [Figure 7] Diagram of the total power reception efficiency from the input of the rectifier circuit to the energy storage element [Figure 8] Diagram comparing the efficiency of the rectifier circuit based on the input and output power of the rectifier circuit [Figure 9] Block diagram of the constituent devices in Embodiment 2

MODE FOR CARRYING OUT THE INVENTION

[0015] Examples of embodiments according to the present invention will be described below with reference to the drawings, but the present invention is not limited to these examples. In the description of the following examples and the drawings referred to, descriptions of detailed components and the like that can be supplemented by those skilled in the art are omitted.

EXAMPLE

[0016] FIG. 1 is a schematic diagram of the wireless power transmission system in the first embodiment, and FIG. 3 is a block diagram of the main devices constituting the power reception device thereof.

[0017] The power transmission technology used in the first embodiment uses the retro-detective method disclosed in Patent Document 3. The high-frequency power emitted as a circularly polarized high-frequency beam from the power transmission antenna is received by the circularly polarized power reception antennas A1 to A9 that maintain consistency with it. The circularly polarized antenna is known for reducing the influence of environmental factors.

[0018] Here, the receiving antenna A5 serves both to receive high-frequency power from the transmitting antenna and to emit a beacon signal B for the transmitting device to detect its own position, and is located in the center of the receiving antennas A1 to A9. In addition, a square notched pin-fed circularly polarized patch antenna (element) was used for the antenna itself, but it is also possible to use a rectangular dual-pin fed circularly polarized patch antenna or a PCB inverted F antenna, and is not limited to these.

[0019] Furthermore, as shown in Figure 2, the circularly polarized high-frequency beam emitted from the power transmission antenna is a focused beam directed towards the beacon signal generation area. In this case, the electric field strength shows a distribution that decreases as it moves away from the centrally located power receiving antenna A5. Therefore, the other eight power receiving (dedicated) antennas (A1-A4, A6-A9) are arranged to surround power receiving antenna A5 and to suppress electromagnetic coupling between the antennas.

[0020] The high-frequency power received by each dedicated receiving antenna is grouped by high-frequency couplers C1 to C4 before rectification. This is done to reduce coupling losses by making the input power from each rectifier circuit R1 to R5 roughly equal, which is then coupled in parallel (DC combined) by a DC combiner DC before input to the charge control unit CH located in the subsequent stage.

[0021] Specifically, the power-receiving antennas were grouped together in the following order: A1-A2, A3-A6, A9-A8, A7-A4, etc., with adjacent antennas aligned along the rotation direction of the circular polarization (left-hand circular polarization in this embodiment 1). The high-frequency power from each grouped power-receiving antenna is coupled in high-frequency couplers C1-C4, as shown in Figure 3, and input to the respective rectifier circuits R1-R4.

[0022] On the other hand, the ungrouped receiving antenna A5 is input to the rectifier circuit R5 via the high-frequency switch S for beacon transmission. Here, each rectifier circuit is of the voltage doubler type. Subsequently, the DC power output from each rectifier circuit R1 to R5 is coupled in parallel by a DC combiner DC and input to the charge control unit CH.

[0023] The charging control unit CH, as shown in Figure 3, consists of a step-up / step-down converter BC, a linear charging control unit LC, and a charging current control unit CC.

[0024] Here, the linear charge control unit LC can arbitrarily set the charging current and charging voltage using CC-CV mode.

[0025] In the buck-boost converter BC, as shown in the graph on the right of Figure 4, the output voltage was set to 4.7[V] (indicated as 5[V] in Figure 4) so ​​that it operates in burst mode when the LOAD CURRENT is in the range of 1 to 300[mA]. ​​In other words, the power range input from the buck-boost converter BC to the linear charge control unit LC is assumed to be 4.7[mW] to 1.4[W]. This value was set considering the charging voltage specification (4.2[V]) of the typical energy storage element Bt downstream of the linear charge control unit LC and the load Lo.

[0026] The charging current control unit CC employs a sequence control method known as the hill-climbing method, as shown in Figure 5. Here, a threshold value slightly lower than the BC set output voltage of 4.7[V] is separately defined, and the output voltage from the buck-boost converter BC (BC output voltage) is monitored continuously. If the BC set output voltage exceeds the threshold value, the charging current value of the linear charging control unit LC is increased; if it falls below the threshold value, constant current control is performed to decrease the charging current value so that the BC set output voltage is maintained.

[0027] As a result, the buck-boost converter BC will not transition to PWM mode operation due to an overload condition (BC input power < (load power + loss)), but will maintain a light load condition (BC input power ≥ (load power + loss)) and continue burst mode operation.

[0028] In this embodiment 1, the sequence shown in Figure 5 employs the hill-climbing method, but it is also possible to use the binary search method shown in Figure 6, and the embodiment is not limited to these.

[0029] Through the above control, instead of prioritizing efficiency improvement by optimizing the operation of each rectifier circuit R1 to R5 using general MPPT control, the control first enables optimal charging of the energy storage element Bt. As a result, this leads to optimal operation of the rectifier circuit, and furthermore, without requiring a larger circuit or high voltage withstand voltage requirements for the rectifier circuit and charging control unit, we were able to achieve an improvement in the total power reception efficiency from the input to the rectifier circuit to the energy storage element Bt, as shown in Figure 7.

[0030] Figure 7 compares the total power reception efficiency from the inputs to each rectifier circuit R1 to R5 to the energy storage element Bt in this embodiment 1, with the case where a boost-buck charge control with MPPT is used instead of the charge control unit CH that constitutes this embodiment 1. In the figure, "Boost-buck converter + linear charge control (setting 1) and (setting 2)" represent the efficiency when the charge control unit CH is used. Note that two types, setting 1 and setting 2, are plotted due to the difference in the settable current values.

[0031] On the other hand, for cases using MPPT-equipped buck-boost charging control, two types of MPPT control were plotted: MPPT control targeting 50% of the open-circuit voltage (OV50% control), and MPPT control based on the maximum power point measured by temporarily disconnecting the MPPT-equipped buck-boost charging control unit from the rectifier circuit output and attaching a fixed resistor to the rectifier circuit output (ZMPPT control).

[0032] These data show that neither OV50% control nor ZMPPT control provides a stable total power receiving efficiency. This is likely because, in either MPPT control case, the system prioritizes optimizing the load at the output of each rectifier circuit R1 to R5, thus failing to optimize the charging of the energy storage element Bt.

[0033] Furthermore, Figure 8 plots the efficiency of the rectifier circuit based on input and output power under various conditions (Setting 1, Setting 2, OV50%, ZMPPT) as shown in Figure 7. The solid gray line represents the optimal efficiency of the rectifier circuit alone. In other words, if each plotted line is close to the efficiency of this rectifier circuit alone, it can be said that it is operating optimally. The efficiency based on the input and output voltage from the rectifier circuit under OV50% control and ZMPPT control is plotted as dotted and dashed lines, respectively.

[0034] Furthermore, since the MPPT-equipped buck-boost charge control IC has a withstand voltage of 5.5[V], a separate external circuit is built to prevent input voltages exceeding 5[V]. Therefore, the rectified voltage in OV50% control is limited to approximately 3[V] within the circuit, while ZMPPT allows MPPT control up to 4.5[V]. However, in both cases, the circuit is limited at 5V, after which MPPT control becomes ineffective. A decrease in efficiency can be observed in the region where MPPT control is ineffective.

[0035] Based on the above, it can be seen that in the case of control by the step-up / step-down converter BC and the charge control unit CH with a linear charge control unit LC in Example 1, stable operation is maintained while keeping the total power reception efficiency from the input to the rectifier circuit to the energy storage element Bt at nearly 50%. Furthermore, it can be confirmed that even when MPPT operation is not actively performed, each rectifier circuit R1 to R5 is operated optimally, similar to MPPT. In contrast, in the case of MPPT control, the load of the rectifier circuit is prioritized for optimization control, resulting in insufficient charging of the energy storage element Bt, and consequently, a stable total power reception efficiency cannot be maintained. [Examples]

[0036] Figure 9 is a block diagram showing the components in the embodiment of this second example. The difference in components from the first example is in the section from the receiving antennas A1 to A5 to the rectifier circuits R1 to R5, while the section from the DC combiner DC to the load Lo is the same as in the first example.

[0037] The power transmission technology used in this embodiment 2 is the same retrodetective method as in embodiment 1. High-frequency power emitted as a circularly polarized high-frequency beam from the power transmission antenna is received by circularly polarized receiving antennas A1 to A5, which maintain compatibility with the beam.

[0038] Here, the receiving antenna A3 serves both to receive high-frequency power from the transmitting antenna and to emit a beacon signal B for the transmitting device to detect its own position, and is located in the center of the receiving antennas A1 to A5. In addition, a square notched pin-fed circularly polarized patch antenna (element) was used for the antenna itself, but as in Example 1, it is also possible to use a rectangular dual-pin fed circularly polarized patch antenna or a PCB inverted F antenna, and is not limited to these.

[0039] Furthermore, as shown in Figure 2, the circularly polarized high-frequency beam emitted from the power transmission antenna is focused toward the beacon signal generation area, and therefore its electric field strength shows a distribution that decreases as it moves away from the centrally located power receiving antenna A3. For this reason, the other four power receiving (dedicated) antennas (A1-A2, A4-A5) are arranged to surround power receiving antenna A3 and to suppress electromagnetic coupling between the antennas.

[0040] In this embodiment 2, since implementation using a small power receiving device is assumed, the number of power receiving antennas is not increased, and therefore no grouping is performed.

[0041] The high-frequency power received by each dedicated power receiving antenna is input to the subsequent rectifier circuits R1 to R5 and rectified. The rectified DC power is then combined in parallel (DC synthesis) and input to the step-up / step-down converter BC of the charge control unit CH. The components from this point onward are the same as in Example 1 as described above. However, in Example 2, the sequence control shown in Figure 6 was performed using the so-called binary search method.

[0042] Here, the charging current control unit CC continuously monitors the output voltage from the buck-boost converter BC. If this value exceeds a separately defined "threshold" as in Example 1, and the current charging current of the linear charging control unit LC has not reached the maximum value of the range that should be controlled for optimal charging, the charging current is increased to an intermediate value between the current charging current and the maximum value. Conversely, if the value falls below the threshold, and the current has not reached the minimum value of the range that should be controlled, the charging current is decreased to an intermediate value between the current charging current and the minimum value.

[0043] These controls ensure that the output voltage of the buck-boost converter BC maintains the BC set output voltage, allowing the burst mode to continue and enabling optimal charging of the energy storage element Bt. This, in turn, leads to optimal operation of the rectifier circuit, and furthermore, without requiring a larger circuit or high voltage withstand voltage requirements for the rectifier circuit and charge control unit CH, it achieves an improvement in the overall power receiving efficiency of the power receiving device. [Industrial applicability]

[0044] The power receiving device of the present invention can be applied to various electronic devices that utilize wireless power transmission, and can be used in mobile devices and terminals in particular where power receiving efficiency is required. [Explanation of Symbols]

[0045] 1. Power transmission equipment 2. Receiving antenna (indicated as A in this embodiment) 3. Rectifier circuit (indicated as R in this embodiment) 4. Charging control unit (indicated as CH in this embodiment) 5. Energy storage element (indicated as Bt in the embodiment) 6. Load (in this example, sign Lo) A1-A9 Receiving antennas (antennas) B. Beacon signal (generator + control unit) BC Step-up / Step-down Converter Bt energy storage element C1~C4 High frequency coupler CC Charging Current Control Unit CH Charging Control Unit DC DC combiner Lo load LC Linear Charging Control Unit R1~R5 Rectifier circuit S High-Frequency Switch

Claims

1. A power receiving device in a wireless power transmission system, which receives high-frequency power with a power receiving antenna system, charges a power storage element with the DC power output through a rectifier circuit via a charge control unit consisting of a step-up / step-down converter, a linear charge control unit, and a charge current control unit, and supplies it to a load via a voltage regulator, The linear charging control unit allows for arbitrary setting of the charging current and charging voltage in CC-CV mode. The buck-boost converter operates in burst mode at a set output voltage, which is determined based on the charging voltage set in the linear charging control unit. The charging current control unit monitors the output voltage of the buck-boost converter and controls the charging current of the linear charging control unit so that the monitored output voltage maintains the set output voltage, in order to maintain the burst mode operation. A power receiving device characterized by the following.

2. In the power receiving device according to claim 1, The charging control unit prioritizes controlling the charging current of the linear charging control unit by the charging current control unit over optimizing the rectifier circuit for maximum power operation. A power receiving device characterized by the following.

3. In the power receiving device according to claim 2, The control of the charging current of the linear charging control unit by the charging current control unit is a sequence control that adjusts the charging current according to the output voltage of the buck-boost converter monitored by the charging current control unit and the set output voltage. A power receiving device characterized by the following.

4. In the power receiving device according to any one of claims 1 to 3, The power receiving antenna system consists of a first circularly polarized antenna located in the center and a plurality of second circularly polarized antennas arranged in a circle around it, aligned with the direction of rotation of the polarization plane. The first circularly polarized antenna combines the functions of receiving high-frequency power emitted from the power transmission device and transmitting beacon signals. These multiple second circularly polarized antennas function to receive high-frequency power emitted from the power transmission equipment. The configuration is such that, among the multiple second circularly polarized antennas, the high-frequency power received by two or more adjacent circularly polarized antennas, which are arranged in a continuous line along the rotation direction of the polarization plane, is coupled and then input to a rectifier circuit, resulting in the output power from each of the rectifier circuits being approximately equal. A power receiving device characterized by the following.

5. In the power receiving device according to claim 4, The DC power output from each rectifier circuit is combined in parallel by a DC combiner, thereby minimizing losses. A power receiving device characterized by the following.

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