Power transmission equipment, power transmission system, and power transmission method

Abstract

To provide a power transmission device, a power transmission system, and a power transmission method, capable of preventing an error detection of a full charging, caused by a factor other than a charging control regardless of a charging state of a secondary battery at a time of starting charging, appropriately stopping radio power transmission to a power reception device from the power transmission device without performing a communication between the power transmission device and the power reception device.SOLUTION: A power transmission device comprises a power supply part, a power transmission part, and a processing part. The power supply part supplies first power to the power transmission part. The power transmission part transmits power supplied from the power supply part to the power reception device in radio. The processing part determines that a charger operated by the power received by the power reception device is in execution of a constant voltage charging, in the case where an inclination of a graph indicating a time change in second power obtained by reflecting the first power in a circuit on a rear stage side of the power supply part is a positive and the graph is convex upward.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a power transmission device, a power transmission system, and a power transmission method.

Background Art

[0002] There is a technology called wireless power transmission that wirelessly transmits power from a power transmission device to a power reception device. The power reception side may have a charging function for charging a secondary battery. In this case, if the charging is completed, it is better for the power transmission device to stop power transmission to the power reception device for reasons such as preventing overcharging and suppressing power consumption. For this reason, a conventional power reception device includes communication means for notifying the power transmission device that the charging is completed. In addition, a conventional power transmission device includes communication means for receiving a notification from the power reception device. However, mounting communication means on the power reception device and the power transmission device leads to an increase in the cost of the power reception device and the power transmission device and an increase in the size of the devices. Note that the power reception side includes a power reception device and a device that operates with the power supplied from the power reception device.

[0003] Patent Document 1 discloses a method in which a power transmission device detects the completion of charging without communicating with a power reception device.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the method described in Patent Document 1, it is detected that the charger has shifted from constant current charging to constant voltage charging. Therefore, in the method described in Patent Document 1, for example, when charging is started without performing rapid charging such as constant current charging because the secondary battery is close to full charge, it becomes impossible to detect, and there is a possibility that the completion of charging cannot be determined.

[0006] Furthermore, in wireless power transmission, reflected power can fluctuate over time due to factors such as misalignment of the coupler. However, the method described in Patent Document 1 cannot distinguish whether the fluctuation in reflected power is due to the designed charging control or to factors other than the charging control. Therefore, the method described in Patent Document 1 may falsely detect a full charge.

[0007] The problem that the present invention aims to solve is to provide a power transmission device, a power transmission system, and a power transmission method that can prevent false detection of full charge due to factors other than charge control, regardless of the charge state of the secondary battery at the start of charging, and that can appropriately stop wireless power transmission from the power transmission device to the power receiving device without communication between the power transmission device and the power receiving device when charging on the power receiving side is complete. [Means for solving the problem]

[0008] The power transmission device of the embodiment comprises a power supply unit, a power transmission unit, and a processing unit. The power supply unit supplies a first power to the power transmission unit. The power transmission unit wirelessly transmits the power supplied from the power supply unit to the power receiving device. The processing unit determines that a charger operating with the power received by the power receiving device is performing constant voltage charging if the slope of the graph showing the time change of a second power, which is the first power reflected by a circuit downstream of the power supply unit, is positive and the graph is convex upwards. [Effects of the Invention]

[0009] The present invention prevents false detection of full charge due to factors other than charge control, and when charging on the receiving side is complete, it can appropriately stop wireless power transmission from the power transmission device to the power receiving device without communication between the power transmission device and the power receiving device. [Brief explanation of the drawing]

[0010] [Figure 1] A diagram showing an overview of the power transmission system according to the first embodiment. [Figure 2]Figure 1 shows a power transmission system and a block diagram illustrating an example of the main circuit configuration of the components included in the power transmission system. [Figure 3] A flowchart showing an example of processing by the processor of the power transmission device in Figure 2 according to the first embodiment. [Figure 4] A diagram showing an example of the waveform of the output power (forward wave) of the power supply according to the first embodiment. [Figure 5] A diagram showing various waveforms when a charger is charging a battery. [Figure 6] A diagram showing various waveforms when a charger is charging a battery. [Figure 7] A diagram showing an overview of the power transmission system according to the third embodiment. [Figure 8] Figure 7 is a block diagram showing an example of the circuit configuration of the main components of the power transmission system and its constituent elements. [Figure 9] A flowchart showing an example of processing by the power transmission device's processor according to the first embodiment in Figure 8. [Figure 10] A diagram showing various waveforms when a misalignment occurs in the power receiving coupler. [Modes for carrying out the invention]

[0011] Several embodiments of power transmission systems will be described below with reference to the drawings. Note that the scale of the parts in the drawings used in the following description of embodiments may be appropriately changed. Also, for illustrative purposes, some components may be omitted from the drawings used in the following description of embodiments. Furthermore, in the drawings and this specification, the same reference numerals indicate the same elements.

[0012] [First Embodiment] The configuration of the power transmission system 1 according to the first embodiment will be described using Figures 1 and 2. Figure 1 is a diagram showing an overview of the power transmission system 1 according to the first embodiment. Figure 2 is a block diagram showing an example of the main circuit configuration of the power transmission system 1 and the components included in the power transmission system 1 according to the first embodiment. The power transmission system 1 is a system that wirelessly transmits power from the power transmission device 100 to the power reception device 210. The power transmission system 1 includes, as an example, the power transmission device 100 and the cart 200.

[0013] The power transmission device 100 is a device that wirelessly transmits power to the power reception device 210 of the cart 200. The power transmission device 100 is fixed to the ground G such as the floor, for example. The power transmission device 100 is embedded under the ground G, for example. Alternatively, the power transmission device 100 may be on the ground G. The power transmission device 100 includes, as an example, a power transmission coupler 110, a power source 120, a control unit 130, and a power detection unit 140.

[0014] The power transmission coupler 110 wirelessly transmits power to the power reception coupler 211 of the power reception device 210. The method of power transmission from the power transmission coupler 110 to the power reception coupler 211 is, for example, electric field coupling, magnetic field coupling, or other power transmission methods. Also, the method of power transmission from the power transmission coupler 110 to the power reception coupler 211 may be electric field resonance, which is a type of electric field coupling. Also, the method of power transmission from the power transmission coupler 110 to the power reception coupler 211 may be magnetic field resonance, which is a type of magnetic field coupling. Note that the power transmission coupler 110 is an example of a power transmission unit that wirelessly transmits the power supplied from the power source 120 to the power reception device 210.

[0015] The power transmission coupler 110 that transmits power by electric field coupling includes, for example, a pair of two power transmission electrodes. The power transmission coupler 110 that transmits power by electric field resonance includes, for example, a pair of two power transmission electrodes and a resonance coil. The power transmission coupler 110 that transmits power by magnetic field coupling includes, for example, a power transmission inductor. The power transmission coupler 110 that transmits power by magnetic field resonance includes, for example, a power transmission inductor and a resonance inductor or capacitor.

[0016] The power supply 120 is, for example, a high-frequency power supply. The power supply 120 supplies AC power to the power transmission coupler 110. In the case of the power transmission device 100 using the electric field resonance or magnetic field resonance method, the power supply 120 supplies AC power with the same frequency as the resonance frequency to the power transmission coupler 110. Note that the power supply 120 is an example of a power supply unit that supplies power to the power transmission coupler 110.

[0017] The control unit 130 is a computer that performs processes such as calculations and controls necessary for the operation of the power transmission device 100. As an example, the control unit 130 includes a processor 131, a ROM (read-only memory) 132, a RAM (random-access memory) 133, and an auxiliary storage device 134. And a bus 135 or the like connects these respective units.

[0018] The processor 131 is the central part of the control unit 130 and performs various calculations and processing. The processor 131 is, for example, a CPU (central processing unit), MPU (micro processing unit), SoC (system on a chip), DSP (digital signal processor), GPU (graphics processing unit), ASIC (application specific integrated circuit), PLD (programmable logic device), or FPGA (field-programmable gate array). Alternatively, the processor 131 is a combination of several of these. Furthermore, the processor 131 may also be a combination of these with hardware accelerators. The processor 131 controls each part to realize various functions of the power transmission device 100 based on programs such as firmware, system software, and application software stored in the ROM 132 or auxiliary storage device 134. The processor 131 also executes processing described later based on the said program. Note that part or all of the said program may be incorporated into the circuit of the processor 131. The processor 131 is also an example of a processing unit.

[0019] ROM132 and RAM133 are the main memory of the control unit 130. ROM132 is a non-volatile memory used exclusively for reading data. ROM132 stores, for example, firmware from the aforementioned programs. ROM132 also stores data used by the processor 131 for various processing tasks. RAM133 is memory used for reading and writing data. RAM133 is used as a work area to store data that the processor 131 temporarily uses when performing various processes. RAM133 is typically volatile memory.

[0020] The auxiliary storage device 134 is an auxiliary storage device of the control unit 130. The auxiliary storage device 134 is, for example, an EEPROM (electric erasable programmable read-only memory), an HDD (hard disk drive), or flash memory. The auxiliary storage device 134 stores, for example, system software and application software from the above-mentioned programs. The auxiliary storage device 134 also stores data used by the processor 131 in performing various processes, data generated by processing by the processor 131, and various setting values.

[0021] Bus 135 includes a control bus, an address bus, and a data bus, and transmits signals exchanged between the various parts of the control unit 130.

[0022] The power detection unit 140 detects forward wave power and reflected wave power. Forward wave power is the power of the forward wave input from the power supply 120 to the power transmission coupler 110. Reflected wave power is the power of the reflected wave that is reflected by the circuit downstream of the power supply 120. This downstream circuit is a circuit to which power output from the power supply 120 is input directly or indirectly via other circuits. This downstream circuit includes, for example, the power transmission coupler 110, the power receiving device 210, and the load 230. Of these, the power transmission coupler 110 mainly reflects the forward wave. Reflected waves are generated, for example, by mismatch between the transmitting side impedance and the receiving side impedance. If the difference between these impedances is small, the reflected power is small, and if the difference in impedance is large, the reflected power is large. In the case of constant current charging, the value of the reflected power is constant. In an impedance matching state (a state in which the difference between the transmitting side and the receiving side impedance is small), rapid charging using constant current charging, etc., is possible.

[0023] The cart 200 is a cart for transporting goods, such as a shopping cart. The cart 200 includes, for example, a power receiving device 210, a cart section 220, and a load 230. Note that the cart 200 and the power receiving device 210 are examples of power receiving devices.

[0024] The power receiving device 210 is a device that receives power wirelessly transmitted from the power transmitting device 100. The power receiving device 210 includes, as an example, a power receiving coupler 211, a rectifier 212, a charger 213, and a battery 214.

[0025] The power receiving coupler 211 receives power wirelessly from the power transmission coupler 110 of the power transmission device 100. The power receiving coupler 211 is an example of a power receiving unit that receives power from the power transmission coupler 110.

[0026] The power receiving coupler 211, which receives power by electric field coupling, is equipped with, for example, a pair of power receiving electrodes. The power receiving coupler 211, which receives power by electric field resonance, includes, for example, a pair of power receiving electrodes and a resonant coil. The power receiving coupler 211, which receives power through magnetic field coupling, includes, for example, a power receiving inductor. The power receiving coupler 211, which receives power by magnetic field resonance, includes, for example, a power receiving inductor and a resonance inductor or capacitor.

[0027] The rectifier unit 212 is a circuit that rectifies the AC power output by the power receiving coupler 211 into DC power and outputs it to the charger 213. The rectifier unit 212 is an example of a power supply unit that supplies power received by the power receiving coupler 211 to the charger 213.

[0028] The charger 213 charges the battery 214 using the power received by the power receiving coupler 211. The charger 213 charges the battery 214 using a charging method that combines rapid charging and constant voltage charging, such as constant-current, constant voltage charging (CCCV (constant-current, constant voltage) charging). If the remaining charge of the battery 214 is less than a predetermined level, the charger 213 rapidly charges the battery 214. That is, the charger 213 rapidly charges the battery 214 while the voltage of the battery 214 is less than a predetermined voltage V1. Then, if the remaining charge of the battery 214 is above a predetermined level, the charger 213 charges the battery 214 at a constant voltage. That is, the charger 213 constantly charges the battery 214 at a constant voltage while the voltage of the battery 214 is V1 or higher. When charging by CCCV, the charger 213 rapidly charges by, for example, constant-current charging.

[0029] Battery 214 is a secondary battery that is charged by the power received by the power receiving coupler 211. Battery 214 is a secondary battery that is charged by the charger 213. Battery 214 is also a power source that supplies power to the load 230, etc.

[0030] The cart section 220 has general functions of a shopping cart, for example. For example, the cart section 220 can carry shopping baskets, for example. The cart section 220 is equipped with baskets on which goods can be placed. The cart section 220 is also equipped with wheels for movement.

[0031] Load 230 consumes power output by battery 214. Load 230 is a powered device, such as a tablet terminal. The tablet terminal notifies the user of the cart 200 of various information related to shopping, for example. The tablet terminal also registers items to be placed in the cart 200 for purchase, for example.

[0032] The operation of the power transmission system 1 according to the first embodiment will be described below with reference to Figure 3 and other figures. Note that the processing described below is just an example, and various processes that can obtain similar results can be used as appropriate. Figure 3 is a flowchart showing an example of processing by the processor 131 of the power transmission device 100 according to the first embodiment. The processor 131 executes the processing shown in Figure 3 based on a program stored, for example, in the ROM 132 or auxiliary storage device 134. The processor 131 starts the processing shown in Figure 3, for example, when the power transmission device 100 is started up.

[0033] In step ST11, the processor 131 starts standby operation. Standby operation is an operation to detect that the power receiving coupler 211 of the power receiving device 210 is in a position to receive power transmitted from the power transmitting coupler 110 of the power transmitting device 100. During standby operation, the processor 131 controls the power supply 120 to output a waveform as shown in period D1 of Figure 4. Figure 4 is a diagram showing an example of the output power (forward wave) waveform of the power supply 120 according to the first embodiment. Period D1 is the period during which the standby operation is performed. During standby operation, the power supply 120 repeatedly turns the output of power P1 on and off. Power P1 is less power than power P2, which is the power transmitted from the power transmitting device 100 to the power receiving device 210. In order to reduce power consumption during standby operation, it is better if power P2 is as small as possible within the range that the power receiving coupler 211 can detect. In addition, during standby operation, the processor 131 monitors the forward wave power and reflected wave power using the power detection unit 140. The closer the power receiving coupler 211 is to a position with high power receiving efficiency, the smaller the ratio of reflected wave power to forward wave power (hereinafter referred to as the "power ratio"). That is, (power ratio) = (reflected wave power) ÷ (forward wave power). Note that power P1, i.e., forward wave power during standby operation, is an example of the third power. Also, reflected wave power during standby operation is an example of the fourth power.

[0034] In step ST12, the processor 131 determines whether the power ratio is less than a predetermined threshold TH1. Threshold TH1 is a threshold used to determine whether or not to start power transmission from the power transmission device 100 to the power receiving device 210. Threshold TH1 is set in advance by, for example, the designer or manager of the power transmission system 1. If the power ratio is greater than or equal to threshold TH1, the processor 131 determines No in step ST12 and repeats the process in step ST12. Conversely, if the power ratio is less than threshold TH1, the processor 131 determines Yes in step ST12 and proceeds to step ST13. Figure 4 shows the time t1 as the point in time when the processor 131 determines that the power ratio is less than threshold TH1.

[0035] In step ST13, the processor 131 begins transmitting power from the power transmission coupler 110 to the power receiving coupler 211 via wireless power transmission. For this purpose, the processor 131 terminates its standby operation. After the processor 131 has performed standby operation for a predetermined period, it begins power transmission operation. Figure 4 shows the time t2 as the point when the standby operation terminates and standby operation begins. Figure 4 also shows the time t3 as the point when the standby operation terminates and power transmission operation begins. Furthermore, the period D2 shown in Figure 4 is the period during which standby operation is performed. The period D3 is the period during which power transmission operation is performed.

[0036] During standby operation, the processor 131 controls the power supply 120 so that the forward wave power becomes zero. Standby operation is, for example, the time spent waiting for a person to leave the cart 200. Alternatively, the processor 131 may skip standby operation and transition directly from standby operation to power supply operation.

[0037] The processor 131 controls the power supply 120 so that the forward wave power becomes power P2 during power transmission. Power transmission is the operation to transmit power from the power transmission coupler 110 to the power receiving coupler 211. Power P2, i.e., the forward wave power during power transmission, is an example of the first power. The reflected wave power during power transmission is an example of the second power.

[0038] In step ST14, the processor 131 determines whether the power ratio is outside a predetermined range. This predetermined range is, for example, a range greater than or equal to threshold TH2. Threshold TH2 may be the same value as threshold TH1 or a different value. Threshold TH2 is, for example, a value greater than threshold TH1. Threshold TH2 is set in advance by, for example, the designer or manager of the power transmission system 1. If the processor 131 does not determine that the power ratio is outside the predetermined range, it determines No in step ST14 and proceeds to step ST15.

[0039] In step ST15, the processor 131 determines whether the reflected wave power is an abnormal value. For example, the processor 131 determines that the reflected wave power is an abnormal value if it is greater than or equal to a predetermined threshold TH3. The threshold TH3 is set in advance by, for example, the designer or manager of the power transmission system 1. The threshold TH3 is a threshold for detecting when the reflected wave power is abnormally high. For example, the reflected wave power may become an abnormal value if the position of the receiving coupler 211 is misaligned with that of the transmitting coupler 110, or if there is foreign matter between the transmitting coupler 110 and the receiving coupler 211. If the processor 131 does not determine that the reflected wave power is an abnormal value, it determines No in step ST15 and proceeds to step ST16.

[0040] In step ST16, the processor 131 determines whether the traveling wave power is an abnormal value. For example, the processor 131 determines that the traveling wave power is an abnormal value if it is greater than or equal to a predetermined threshold TH4 or less than a predetermined threshold TH5. Thresholds TH4 and TH5 are set in advance by, for example, the designer or manager of the power transmission system 1. Threshold TH4 is a threshold for detecting when the traveling wave power is abnormally high. Threshold TH4 is, for example, a value greater than power P2. Threshold TH5 is a threshold for detecting when the traveling wave power is abnormally low. Threshold TH5 is, for example, a value less than power P2. For example, if there is an abnormality in the electrical circuit in the power transmission device 100, or if there is an abnormality in the power supply 120, the traveling wave power may be an abnormal value. If the processor 131 does not determine that the traveling wave power is an abnormal value, it determines No in step ST16 and proceeds to step ST17.

[0041] In step ST17, the processor 131 determines whether the charger 213 of the power receiving device 210 is performing constant voltage charging. The determination method will be explained using Figure 5.

[0042] Figure 5 shows various waveforms when the charger 213 charges the battery 214. Graphs (a) to (d) in Figure 5 show the waveforms when the charger 213 rapidly charges the battery 214 until time t11, and then charges the battery 214 with constant voltage charging from time t11. Waveform W1 is a graph showing the time change of the charging current when the charger 213 charges the battery 214. Waveform W2 is a graph showing the time change of the charging voltage when the charger 213 charges the battery 214. Waveform W3 is a graph showing the time change of the reflected wave power. Waveform W4 is a graph showing the rate of change of the reflected wave power over time. In other words, waveform W4 is a graph showing the first derivative of waveform W3. Waveform W5 is a graph showing the slope of the rate of change of the reflected wave power over time. In other words, waveform W5 is a graph showing the second derivative of waveform W3.

[0043] During constant voltage charging, the output power of the charger 213 decreases in a shape similar to waveform W1, so the reflected wave power has a positive slope (derivative) and is convex upwards, as shown in waveform W3. When the slope of waveform W3 is positive, the value of waveform W4 is positive. That is, when the slope of waveform W3 is positive, the first derivative of waveform W3 is positive. When waveform W3 is convex upwards, the slope of waveform W4 is negative. That is, when waveform W3 is convex upwards, the second derivative of waveform W3 is negative. In waveform W5, the state of being negative continues after time t11. Based on the above, the processor 131 determines that the charger 213 is performing constant voltage charging if the duration of the state in which the slope of waveform W3 is positive and waveform W3 is convex upwards is greater than or equal to a predetermined threshold TH6. The threshold TH6 is set in advance, for example, by the designer or manager of the power transmission system 1. Alternatively, the processor 131 may determine that the charger 213 is performing constant voltage charging, regardless of the duration, if the slope of waveform W3 is positive and the waveform W3 is convex upwards. If the processor 131 does not determine that the charger 213 is performing constant voltage charging, it determines No in step ST17 and proceeds to step ST18.

[0044] In step ST18, the processor 131 determines whether the elapsed time of the timer is equal to or greater than time Tp. The timer and time Tp will be described later. If the elapsed time of the timer is less than time Tp or the timer is stopped, the processor 131 determines No in step ST18 and returns to step ST14. Thus, the processor 131 enters a standby state in which it repeats steps ST14 to ST18 until it determines that the power ratio is outside a predetermined range, that the reflected wave power is an abnormal value, that the forward wave power is an abnormal value, that the charger 213 is performing constant voltage charging, or that the elapsed time of the timer is equal to or greater than time Tp.

[0045] If the processor 131 determines that the charger 213 is performing constant voltage charging while in the standby state of steps ST14 to ST18, it determines Yes in step ST17 and proceeds to step ST19. In step ST19, the processor 131 calculates the estimated time Tp until the battery 214 is fully charged. The calculation formula and threshold for calculating time Tp do not necessarily need to be set so that the battery charge rate is 100%, but can be set considering the balance between the charge rate and overcharge prevention. For example, the processor 131 considers the battery 214 to be fully charged when the rate of change of reflected wave power over time falls below R1. Therefore, the processor 131 calculates the estimated time Tp as the estimated time until the rate of change of reflected wave power over time falls below R1. For example, the processor 131 calculates the estimated time Tp using the rate of change of reflected wave power over time and at least one of the said rate of change. The processor 131 calculates the estimated time Tp using, for example, a predetermined calculation formula or a table. For example, an auxiliary storage device 134 stores the table. The processor 131 also starts a timer in step ST19. This timer is used to determine when time Tp has elapsed. Figure 4 shows the timer start time as time t4.

[0046] After the processor 131 determines the estimated time Tp (after it has determined that the charger 213 is performing constant voltage charging), it skips the processing of step ST17 until it stops power transmission (until it performs the processing of step ST21). If it skips, the processor 131 proceeds to step ST18 if it determines No in step ST16, for example.

[0047] In step ST20, the processor 131 terminates the power transmission operation and starts intermittent operation. Intermittent operation is an operation to prevent sudden cessation of power transmission. Therefore, the power transmitted during intermittent operation is smaller than the power transmitted during power transmission operation. During intermittent operation, the processor 131 controls the power supply 120 to output a waveform as shown in period D4 of Figure 4. Period D4 is the period during which intermittent operation is performed. During intermittent operation, the power supply 120 repeatedly turns the output of power P2 on and off. In Figure 4, time t6 is shown as the point in time when the power transmission operation terminates and intermittent operation begins. After processing in step ST20, the processor 131 returns to step ST14. Note that the power transmission device 100 does not have to perform intermittent operation. In this case, the processor 131 of the power transmission device 100 does not perform the processing in step ST20, and returns to step ST14 after processing in step ST19.

[0048] If the processor 131 determines that the elapsed time of the timer is equal to or greater than time Tp while in the standby state of steps ST14 to ST18, it determines Yes in step ST18 and proceeds to step ST21. For example, if the timer measurement time is equal to or greater than time Tp, the processor 131 determines that the battery 214 is fully charged.

[0049] In step ST21, the processor 131 performs a charging completion process to complete the charging. As part of the charging completion process, the processor 131 terminates the power transmission or intermittent operation and stops the power transmission from the power transmission coupler 110 to the power reception coupler 211. That is, the processor 131 stops the power transmission from the power transmission coupler 110 to the power reception coupler 211 by controlling the power supply 120 to stop the power output. In Figure 4, the time t7 is shown as the point in time when the intermittent operation ends. The processor 131 also stops and resets the timer as part of the charging completion process. After the processing in step ST21, the processor 131 returns to step ST11. Figure 4 shows that time t8 represents the point in time when the standby operation restarts in step ST11 after the processing in step ST21.

[0050] If the processor 131 determines that the power ratio is outside a predetermined range while in the standby state of steps ST14 to ST18, it determines Yes in step ST14 and proceeds to step ST22. Also, if the processor 131 determines that the reflected wave power is an abnormal value while in the standby state of steps ST14 to ST18, it determines Yes in step ST15 and proceeds to step ST22. Also, if the processor 131 determines that the forward wave power is an abnormal value while in the standby state of steps ST14 to ST18, it determines Yes in step ST16 and proceeds to step ST22.

[0051] In step ST22, the processor 131 performs a charging stop process to stop charging due to an abnormality. As part of the charging stop process, the processor 131 terminates the power transmission or intermittent operation and stops the power transmission from the power transmission coupler 110 to the power reception coupler 211. That is, the processor 131 stops the power transmission from the power transmission coupler 110 to the power reception coupler 211 by controlling the power supply 120 and stopping the power output. In addition, as part of the charging stop process, the processor 131 stops the timer and resets the timer. After processing in step ST22, the processor 131 returns to step ST11.

[0052] According to the power transmission system 1 of the first embodiment, the power transmission device 100 and the power receiving device 210 do not communicate with each other. Therefore, the power transmission device 100 and the power receiving device 210 of the first embodiment do not require any configuration for communication between the power transmission device 100 and the power receiving device 210. Furthermore, according to the power transmission system 1 of the first embodiment, the power transmission device 100 determines that the charger 213 is performing constant voltage charging when the slope of the waveform W3 is positive and the waveform W3 is convex upwards. Therefore, even if the charger 213 starts constant voltage charging without going through rapid charging, the power transmission device 100 of the first embodiment can appropriately stop power transmission when charging by the charger 213 is completed. For example, the charger 213 starts constant voltage charging without going through rapid charging if the voltage of the battery 214 is initially above voltage V1.

[0053] As an example, Figure 6 shows various waveforms when the charger 213 starts constant voltage charging without going through rapid charging. Figure 6 is a diagram showing various waveforms when the charger 213 charges the battery 214. Time t21 in Figure 6 indicates the time when the charger 213 starts charging the battery 214. Time t22 indicates the time when the power transmission from the power transmission coupler 110 to the power reception coupler 211 is stopped. Waveforms W11 to W14 show the waveforms from time t21 to time t22. Waveform W11 is a graph showing the time change of the charging current when the charger 213 charges the battery 214. Waveform W12 is a graph showing the time change of the charging voltage when the charger 213 charges the battery 214. As can be seen from waveform W12, the charger 213 is performing only constant voltage charging. Waveform W13 shows the time change of reflected wave power. Waveform W14 is a graph showing the time rate of change of reflected wave power. In other words, waveform W14 is a graph showing the first derivative of waveform W13. For comparison, waveforms W1 to W3 are also shown as dashed lines in Figure 6. Even in such cases, the processor 131 can determine that the slope of waveform W3 is positive and that waveform W3 is convex upwards, and therefore can detect that the charger 213 is performing constant voltage charging.

[0054] Furthermore, according to the power transmission system 1 of the first embodiment, the power transmission device 100 determines that the charger 213 is performing constant voltage charging when the slope of the waveform W3 is positive and the waveform W3 is convex upwards. Therefore, the power transmission device 100 of the first embodiment does not mistakenly detect that the battery is fully charged when a misalignment occurs between the power receiving coupler 211 and the power transmission coupler 110.

[0055] As an example, Figure 10 shows various waveforms when a displacement occurs in the power receiving coupler 211. Figure 10 is a diagram showing various waveforms when a displacement occurs in the power receiving coupler 211. Waveform W21 is a graph showing the time change of reflected wave power when a displacement occurs in the power receiving coupler 211. Waveform W22 is a graph showing the time change of reflected wave power when a displacement occurs in the power receiving coupler 211. Waveform W23 is a graph showing the time rate of change of reflected wave power when a displacement occurs in the power receiving coupler 211. The time t31 shown in Figure 10 is the time when the power receiving coupler 211 began to move. The time t32 is the time when the movement of the power receiving coupler 211 stopped. That is, it is assumed that the power receiving coupler 211 was displaced by moving in a direction that lowers the power receiving efficiency from time t31 to time t32.

[0056] The waveform W21 has a positive slope but is not convex upwards. Therefore, the power transmission device 100 does not determine that the charger 213 is performing constant voltage charging.

[0057] Furthermore, waveform W23 has a short period of negative value and is impulsive. In contrast, waveform W5 in Figure 5 remains negative after time t11. This also shows that the waveform does not become convex upwards due to misalignment of the power receiving coupler 211.

[0058] Furthermore, according to the power transmission system 1 of the first embodiment, the power transmission device 100 determines that the charger 213 is performing constant voltage charging when the slope of the waveform W3 is positive and the time for which the waveform W3 is convex upwards continues for a threshold TH6 or longer. This prevents the power transmission device 100 of the first embodiment from making a false determination in cases where, for some reason, the slope of the waveform W3 is positive and the waveform W3 is convex upwards for only a moment.

[0059] Furthermore, according to the power transmission system 1 of the first embodiment, if the power transmission device 100 determines that the charger 213 is performing constant voltage charging, it calculates time Tp and stops power transmission when time Tp has elapsed. As a result, the power transmission device 100 of the first embodiment can appropriately stop power transmission when charging by the charger 213 is complete.

[0060] Furthermore, according to the power transmission system 1 of the first embodiment, the power transmission device 100 starts transmitting power when the power ratio falls below the threshold TH1 during standby operation. In this way, the power transmission device 100 of the first embodiment can start transmitting power when the position of the power receiving coupler 211 relative to the power transmission coupler 110 is in an appropriate position.

[0061] Furthermore, according to the power transmission system 1 of the first embodiment, the power transmission device 100 stops power transmission when the power ratio is outside a predetermined range. This allows the power transmission device 100 of the first embodiment to stop power transmission in cases such as when there is a malfunction in the power transmission system 1.

[0062] Furthermore, according to the power transmission system 1 of the first embodiment, the power transmission device 100 stops transmitting power when the traveling wave power is at an abnormal value. As a result, the power transmission device 100 of the first embodiment can stop transmitting power in cases such as when there is a malfunction in the power transmission system 1.

[0063] Furthermore, according to the power transmission system 1 of the first embodiment, the power transmission device 100 stops power transmission if the reflected wave power is at an abnormal value. This allows the power transmission device 100 of the first embodiment to stop power transmission in cases such as when there is a malfunction in the power transmission system 1.

[0064] [Second Embodiment] The configuration of the power transmission system 1b according to the second embodiment will be described using Figures 7 and 8. Figure 7 is a diagram showing an overview of the power transmission system 1b according to the second embodiment. Figure 8 is a block diagram showing an example of the main circuit configuration of the power transmission system 1b and its components according to the second embodiment. Note that the differences between the second embodiment and the first embodiment will be described.

[0065] The power transmission system 1b includes, as an example, a power transmission device 100b, a cart 200, and a vehicle stop detection device 300. In other words, the power transmission system 1b includes a power transmission device 100b in place of the power transmission device 100. Furthermore, the power transmission system 1b includes a vehicle stop detection device 300 in addition to the components of the power transmission system 1.

[0066] The power transmission device 100b includes, as an example, a power transmission coupler 110, a power supply 120, a control unit 130, a power detection unit 140, and a detection interface 150. In other words, the power transmission device 100b includes the detection interface 150 in addition to the components of the power transmission device 100.

[0067] The detection interface 150 is an interface for the power transmission device 100b to receive signals output by the vehicle stop detection device 300. The power transmission device 100b communicates with the vehicle stop detection device 300 via the detection interface 150. This communication may be wired or wireless.

[0068] The stop detection device 300 detects when the cart 200 has stopped at a predetermined position. The predetermined position is a position in which the power receiving device 210 can receive power transmitted from the power transmitting device 100b. The stop detection device 300 includes, as an example, a switch 301 and an output unit 302.

[0069] Switch 301 is, for example, a momentary push-button switch. For instance, when a part of the cart 200 presses switch 301, switch 301 turns on. Then, when the cart 200 moves away from switch 301, switch 301 turns off. In this way, switch 301 detects when the cart 200 has stopped at a predetermined position and when it has moved away from that predetermined position.

[0070] Preferably, the switch 301 is designed so that other carts and objects other than carts cannot press the switch 301. For example, the switch 301 includes multiple push-button switches or other switches that correspond to the shape of the cart 200. That is, each switch is arranged so that all the switches included in the switch 301 are pressed when the cart 200 is in a predetermined position. The switch 301 turns on, for example, when all of the multiple switches included in the switch 301 are pressed simultaneously. In such a case, since objects other than the cart 200 have a different shape from the cart 200, it is difficult for them to press all the switches simultaneously. With this mechanism, the vehicle stop detection device 300 can use the switch 301 to determine whether the object in a predetermined position is the cart 200 or an object other than the cart 200. Alternatively, the switch 301 may have a shape that makes it difficult to press unless it is the cart 200. The cart 200 may also have a protrusion or other feature that matches the shape of the switch 301, allowing it to press the switch 301. Even in such cases, the vehicle stop detection device 300 can similarly use the switch 301 to determine whether the object at a predetermined position is the cart 200 or an object other than the cart 200.

[0071] The output unit 302 outputs a detection signal in response to the switch 301 being turned on. The detection signal indicates that the cart 200 has been detected to have stopped at a predetermined position. The detection signal is received by the detection interface 150 of the power transmission device 100b. The detection interface 150 outputs a signal to the processor 131 indicating that the detection signal has been received. The processor 131 receives this signal as input.

[0072] The stop detection device 300 may also detect that the cart 200 has stopped at a predetermined position using sensors other than the switch 301. For example, the stop detection device 300 may detect that the cart 200 has stopped at a predetermined position using a camera, radar, LIDAR (light detection and ranging), infrared sensor, ultrasonic sensor, ToF (time of flight) sensor, inductive, capacitive, or magnetic proximity sensor, or other sensors. The output unit 302 outputs a detection signal when these sensors detect that the cart 200 has stopped at a predetermined position. In this case as well, it is preferable that the stop detection device 300 is structured so as not to detect carts other than the cart 200 or objects other than carts. For example, the stop detection device 300 includes a plurality of sensors for detecting the cart 200, according to the shape of the cart 200. That is, each sensor is arranged so that all of these sensors detect the cart 200 when the cart 200 is in a predetermined position. The vehicle stop detection device 300 determines that the cart 200 is in a predetermined position when all of the multiple sensors used to detect the cart 200 detect the cart 200. In such a case, it is difficult to have all the sensors simultaneously detect objects other than the cart 200 because their shapes are different from those of the cart 200.

[0073] Furthermore, the vehicle stop detection device 300 may use sensors other than the switch 301 to determine whether an object at a predetermined location is a cart 200 or an object other than a cart 200. For example, the vehicle stop detection device 300 may distinguish between a cart 200 and an object other than a cart 200 by, for example, image recognition, communication with the cart 200, or reading information specific to the cart 200, such as reading a barcode attached to the cart 200.

[0074] The operation of the power transmission system 1b according to the second embodiment will be described below with reference to Figure 9 and other figures. Note that the processing content in the following description of operation is just an example, and various processing that can obtain similar results can be used as appropriate. Figure 9 is a flowchart showing an example of processing by the processor 131 of the power transmission device 100 according to the second embodiment. The processor 131 executes the processing shown in Figure 9 based on a program stored, for example, in the ROM 132 or auxiliary storage device 134. The processor 131 starts the processing shown in Figure 9, for example, when the power transmission device 100 is started up.

[0075] In step ST31, the processor 131 determines whether or not the cart 200 has stopped at the predetermined position. For example, if the detection interface receives a detection signal, the processor 131 determines that the cart 200 has stopped at the predetermined position. If the cart 200 has not stopped at the predetermined position, the processor 131 determines No in step ST31 and repeats the process of step ST31. On the other hand, if the cart 200 has stopped at the predetermined position, the processor 131 determines Yes in step ST31 and proceeds to step ST11.

[0076] In the second embodiment, the processor 131 returns to step ST31 after processing in step ST21 and step ST22.

[0077] The power transmission system 1b of the second embodiment provides the same effects as the power transmission system 1 of the first embodiment. Furthermore, the power transmission system 1b of the second embodiment also provides the following effects. According to the power transmission system 1b of the second embodiment, the power transmission device 100b detects that the cart 200 has stopped at a predetermined position using the cart stop detection device 300. Once the power transmission device 100b detects that the cart 200 has stopped at the predetermined position, it starts a standby operation. Therefore, the power transmission device 100b of the second embodiment can reduce power consumption compared to the case where the standby operation is continuously performed regardless of the position of the cart 200.

[0078] Furthermore, according to the power transmission system 1b of the second embodiment, the power transmission device 100b starts a standby operation when it detects that the cart 200 has stopped at a predetermined position. Then, the power transmission device 100b starts transmitting power when the power ratio falls below the threshold TH1 during the standby operation. In this way, the power transmission device 100b starts transmitting power after two stages of operation: an operation to detect that the cart has stopped, and an operation to determine that the power ratio has fallen below the threshold TH1. Therefore, the power transmission device 100b of the second embodiment can prevent the transmission of power from starting when there is a foreign object other than the cart 200 at the predetermined position, more effectively than in the case of a single-stage operation.

[0079] The above embodiment can also be modified as follows: In the above embodiment, the processor 131 determines time Tp and uses a timer to determine that time Tp has elapsed. Alternatively, the processor 131 may determine a time after time Tp from the current time (hereinafter referred to as the "estimated time"). Then, if the current time is after the estimated time, the processor 131 determines that the battery 214 is fully charged and determines Yes in step ST18.

[0080] In the above embodiment, the processor 101 of the power transmission device 100 starts intermittent operation when it determines that the charger 213 is performing constant voltage charging. However, the processor 101 may also start intermittent operation when the time obtained by subtracting the timer time from time Tp is less than or equal to the threshold TH7. Figure 4 shows time t5 as the point in time when the time obtained by subtracting the timer time from time Tp is less than or equal to the threshold TH7.

[0081] The power transmission device 100b of the second embodiment may start transmitting power without performing a standby operation. In this case, if the processor 131 of the power transmission device 100b determines Yes in step ST31, for example, it proceeds to step ST13. In this case, the power transmission device 100b can reduce power consumption compared to when it performs a standby operation. The power transmitted at this point is an example of the first power as described above.

[0082] In the above embodiment, the case in which the cart 200 is equipped with a power receiving device 210 was described as an example. However, other vehicles such as automobiles, motorcycles, electric bicycles, railway vehicles, or other vehicles may also be equipped with a power receiving device 210. Alternatively, vehicles other than automobiles, drones, or robots may be equipped with a power receiving device 210. Furthermore, the power receiving device 210 may be something that a person or other person carries by hand.

[0083] The charger and battery may be located within a device connected to the power receiving device. In this case, the power receiving device outputs power received from the power transmitting device 100 to the device. The device then charges using this power. The load 230 may be the device itself. The power transmitting device 100 can operate in the same manner as in the above embodiment even when the charger is located outside the power receiving device.

[0084] The processor 131 may implement some or all of the processing implemented by the program in the above embodiment through the hardware configuration of the circuit.

[0085] The program that implements the processing of the embodiment is transferred, for example, while stored in the device. However, the device may be transferred without the program stored in it. Alternatively, the program may be transferred separately and written to the device. This transfer of the program can be achieved, for example, by recording it on a removable storage medium or by downloading it via a network such as the Internet or a LAN (local area network).

[0086] The embodiments of the present invention have been described above, but these are merely examples and do not limit the scope of the invention. Embodiments of the present invention can be implemented in various ways without departing from the spirit of the invention. [Explanation of Symbols]

[0087] 1,1b Power transmission system 100,100b Power transmission equipment 110 Power transmission coupler 120 Power supply 130 Control Unit 131 Processors 132 ROM 133 RAM 134 Auxiliary storage 135 Bus 140 Power detection unit 150 detection interfaces 200 carts 210 Power receiving device 211 Power receiving coupler 212 Rectifier 213 Charger 214 batteries 220 Cart Section 230 load 300 Stop detection device 301 Switch 302 Output section

Claims

1. A power supply unit that supplies first power to the power transmission unit, The power transmission unit wirelessly transmits the power supplied from the power supply unit to the power receiving device, A power transmission device comprising: a processing unit that determines that a charger operating with power received by the power receiving device is performing constant voltage charging when the slope of a graph showing the time change of a second power, which is reflected by a circuit downstream of the power supply unit from the first power, is positive and the graph is convex upwards; and

2. The power transmission device according to claim 1, wherein the processing unit determines that the charger is performing constant voltage charging when the slope of the graph is positive and the graph remains convex upward for a predetermined period of time or longer.

3. The power transmission device according to claim 1, wherein the processing unit determines that the charger is performing constant voltage charging, determines the estimated time until charging by the charger is completed, and stops the transmission of power by the power transmission unit once the estimated time has elapsed.

4. The power transmission device according to claim 1, wherein the processing unit causes the power supply unit to supply a third power less than the first power, and when the ratio of the third power to the fourth power, which is the third power reflected by a circuit downstream of the power supply unit, falls below a predetermined threshold, the processing unit causes the power supply unit to start supplying the first power.

5. The power transmission device according to claim 4, wherein the processing unit causes the power supply unit to start supplying the third power when it receives a signal from a sensor that detects that the power receiving device is in a predetermined position.

6. The power transmission device according to claim 1, wherein the processing unit, upon receiving a signal from a sensor that detects that the power receiving device is in a predetermined position, causes the power supply unit to begin supplying the first power.

7. The power transmission device according to claim 1, further comprising a sensor for detecting that the power receiving device is in a predetermined position and that the power receiving device has moved away from the predetermined position.

8. The power transmission device according to any one of claims 5 to 7, wherein the sensor has a shape or structure corresponding to the shape of the power receiving device.

9. The power transmission device according to claim 1, wherein the processing unit stops transmitting power by the power transmission unit when the ratio of the second power to the first power falls outside a predetermined range.

10. The power transmission device according to claim 1, wherein the processing unit stops transmitting power by the power transmission unit when the first power is of an abnormal value.

11. The power transmission device according to claim 1, wherein the processing unit stops the transmission of power by the power transmission unit when the second power is of an abnormal value.

12. Including power transmission equipment and power receiving equipment, The aforementioned power transmission device is A power supply unit that supplies first power to the power transmission unit, The power transmission unit wirelessly transmits the power supplied from the power supply unit to the power receiving device, The device comprises a processing unit that determines that a charger operating with power received by the power receiving device is performing constant voltage charging if the slope of the graph showing the time change of the second power, which is the first power reflected by the circuit downstream of the power supply unit, is positive and the graph is convex upwards, The power receiving device is A power receiving unit that receives power from the aforementioned power transmission unit, A power transmission system comprising: a supply unit that supplies power received by the power receiving unit to the charger.

13. The aforementioned processing unit, The power supply unit is instructed to supply a third power less than the first power, and when the ratio of the third power to the fourth power reflected by the circuit downstream of the power supply unit falls below a predetermined threshold, the power supply unit is instructed to start supplying the first power. The power transmission system according to claim 12, wherein if it is determined that the charger is performing constant voltage charging, the estimated time until charging by the charger is completed is determined, and if the estimated time has elapsed, the power transmission unit stops transmitting power.

14. The power transmission system according to claim 12 or 13, wherein the processing unit, upon receiving a signal from a sensor that detects the power receiving device being in a predetermined position, causes the power supply unit to start supplying the first power or a third power less than the first power.

15. The first power is supplied to the power transmission section. The power supplied to the power transmission unit is transmitted wirelessly from the power transmission unit to the power receiving device. A power transmission method in which, if the slope of a graph showing the time change of a second power, which is reflected by a circuit downstream of the power supply unit from the first power, is positive and the graph is convex upward, it is determined that a charger operating with power received by the power receiving device is performing constant voltage charging.

16. A third power less than the first power is supplied to the power transmission unit, and when the ratio of the fourth power, which is the third power reflected by the circuit downstream of the power supply unit, to the third power falls below a predetermined threshold, the supply of the first power is started. The power transmission method according to claim 15, wherein if it is determined that the charger is performing constant voltage charging, the estimated time until charging by the charger is completed is determined, and if the estimated time has elapsed, the power transmission is stopped.

17. The power transmission method according to claim 15 or claim 16, wherein when the power receiving device detects that it is in a predetermined position, the supply of the first power or a third power less than the first power is started.

Images