This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2018-168939, filed on Sep. 10, 2018, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate to a power transmission device and a power reception device.
In a wireless power transmission system, power is wirelessly transmitted from a power transmission device to a power reception device. The power transmission device radiates a magnetic field generated by a coil to a space, and the power reception device couples the magnetic field to a coil, thereby receiving the power. In such wireless power transmission, it is necessary to suppress intensity of the magnetic field (radiation magnetic field) radiated from the power transmission device, to not more than values conforming to laws and regulations represented by Radio Act.
There is a technology in which a frequency is modulated (swept) within a preset frequency range to disperse the intensity of the radiation magnetic field on a time axis in order to suppress the intensity of the radiation magnetic field. In the technology, however, there is an issue that ripple of a receiving voltage occurs on the power reception device side. Occurrence of the ripple causes increase of a load to an electric circuit and decrease of a battery lifetime.
There is a technology in which amplitude of an input voltage on power transmission side is controlled to follow the modulation of the frequency in order to reduce variation of the receiving voltage on power reception side. In the technology, however, it is necessary to separately provide a table of relationship data between the frequency and the amplitude of the input voltage, or to feed back a state of the receiving voltage, etc. on the power reception side to the power transmission side at high speed. This complicates the system configuration.
According to one embodiment, a power transmission device includes an inverter, a first control circuit and a power transmission resonator.
The inverter includes a first arm and a second arm that are connected in parallel, the first arm including series connection of first and second switching devices, and the second arm including series connection of third and fourth switching devices.
The first control circuit controls first to fourth switching signals to be supplied to the first to fourth switching devices, to generate AC power from the inverter.
The power transmission resonator couples a magnetic field corresponding to the AC power to a coil of a power reception unit to transmit the AC power. The power transmission resonator includes a first end and a second end, the first end being electrically connected to a connection point between the first and second switching devices, and the second end being electrically connected to a connection point between the third and fourth switching devices.
The first control circuit sweeps a frequency of the AC power during the transmission of the AC power.
The first control circuit controls to suppress variation of a time delay amount between the first and second arms during sweeping of the frequency.
The power transmission device 1 includes a power transmission unit 101 and a control circuit 102. The power transmission unit 101 includes a high-frequency power supply device 111 that is an AC power supply device, and the power transmission resonator 112. The control circuit 102 includes a frequency control circuit 102A, a voltage control circuit 102B, and a switching signal generation circuit 102C.
The power reception device 2 includes a power reception unit 201 and the battery 301. The power reception unit 201 includes the power reception resonator 211 and a power reception circuit 212. In this example, the battery 301 is a part of the power reception device 2; however, the battery 301 may be defined separately from the power reception device 2.
In
The AC power supply 121 supplies AC power (AC voltage and AC current) of a fixed frequency. Examples of the AC power supply 121 include a commercial power supply. The commercial power supply outputs, for example, the AC voltage of single-phase 100 V or three-phase 200V at frequency of 50 Hz or 60 Hz.
The AC/DC converter 122 is a circuit that is connected to the AC power supply 121 through a wiring (e.g., cable) and converts the voltage of the AC power supplied from the AC power supply 121 into a DC voltage.
The DC/DC converter 123 is a circuit that is connected to the AC/DC converter 122 through a wiring and converts (steps up or steps down) the DC voltage supplied from the AC/DC converter 122 into a different DC voltage. The DC/DC converter 123 includes switching devices such as semiconductor switches, and controls the switching devices to perform voltage conversion. A step-up ratio or a step-down ratio (hereinafter, referred to as step-up/down ratio) can be controlled by controlling an operation frequency of each of the switching devices or a pulse width of switching. The DC/DC converter 123 may be omitted.
The inverter 124 is a circuit (DC/AC converter) that is connected to the DC/DC converter 123 through a wiring, and generates AC power (AC current and AC voltage) based on the DC voltage supplied from the DC/DC converter 123. In this example, the inverter 124 generates high-frequency power as the AC power. The inverter 124 supplies the generated AC power to the power transmission resonator 112.
The power transmission resonator 112 is connected to the inverter 124 through a wiring. The power transmission resonator 112 is a resonance circuit that includes a coil (inductor) and a capacitor (capacitance). The power transmission resonator 112 generates, by the coil, a magnetic field corresponding to the high-frequency power (high-frequency current) received from the inverter 124, and couples the magnetic field to a coil of the power reception resonator 211 of the power reception device 2, thereby performing wireless power transmission.
The configuration of the high-frequency power supply device 111 is not limited to the configuration of
The inverter 124 drives the switching devices in response to respective switching signals provided from the switching signal generation circuit 102C, based on the power supply voltage and the ground voltage that are supplied from the DC power supply 510, thereby generating the AC power (AC voltage or AC current). The switching signals each have a pulse waveform. In the following, the switching signals to be supplied to the respective switching devices 501 to 504 are denoted by switching signals 501 to 504 with use of the reference numerals same as the switching devices.
The switching signal generation circuit 102C is configured of a PLL (Phase Locked Loop) that generates a reference signal (clock), a plurality of variable phase shifters, etc. As a simple configuration example, the reference signal output from the PLL is input to the variable phase shifters corresponding to the respective switching devices. A parameter to shift a phase of the input reference signal by a predetermined shift amount is set to each of the variable phase shifters. An output signal of each of the variable phase shifters is input, as the switching signal, to a gate terminal of the corresponding switching device. The configuration described here is illustrative, and other various configurations such as a configuration using a delay device can be used.
The control circuit 102 controls the switching signal generation circuit 102C so as to complementarily drive the switching devices 501 and 502 and to complementarily drive the switching devices 503 and 504, thereby generating the switching signals 501 to 504. More specifically, the voltage control circuit 102B of the control circuit 102 can adjust phase relationship (time delay amount) of the switching signals 501 and 503, and adjust phase relationship (time delay amount) of the switching signals 502 and 504, thereby adjusting an effective value of the output voltage to the power transmission resonator. Further, the frequency control circuit 102A of the control circuit 102 can adjust a period (number of pulse repetition times per unit time) of each of the switching signals 501 to 504, thereby adjusting the frequency of the output current.
When the switching device 501 and the switching device 504 are ON and the switching device 502 and the switching device 503 are OFF, the current flows from the DC power supply 510 to the ground side of the DC power supply 510 through the switching device 501, the coil 522, and the switching device 504. When the switching device 501 and the switching device 504 are OFF and the switching device 502 and the switching device 503 are ON, the current flows from the DC power supply 510 to the ground side of the DC power supply 510 through the switching device 503, the coil 522, and the switching device 502. The current changed in direction is generated by controlling the ON-OFF switching of each of the switching devices in the above-described manner, which generates the AC power. The AC current is supplied to the power transmission resonator to generate an electromagnetic field. When the electromagnetic field is coupled to the coil of the power reception resonator on the power reception side, the power is transmitted.
The relationship between the switching signals 501 to 504 and the output voltage of the inverter 124 is described with reference to
On lower side in
A waveform W represents the output voltage of the inverter 124. A period Ta of the power transmission frequency is 1/fa [second]. The period of each of the switching signals 501 to 504 is Ta (=1/fa) that is the same as the period of the power transmission frequency. A pulse width of each of the switching signals 501 to 504 is ½ of the period Ta (i.e., 1/(2fa)). The switching signal 503 (or switching signal 504) is delayed by a time Td from the switching signal 501 (or switching signal 502). In other words, the second arm AR2 is delayed by the time Td from the first arm AR1. In other words, the time delay amount between the first arm AR1 and the second arm AR2 (hereinafter, interarm delay amount) is Td. A phase difference corresponding to the time Td is 180 degrees when one period is 360 degrees.
In
As can be seen from the description of
The interarm delay amount in
The power reception circuit 212 is connected to the power reception resonator 211 through a wiring, and converts the AC power received by the power reception resonator 211, into a DC voltage suitable for the battery 301, and outputs the DC voltage.
The rectifier 221 is connected to the power reception resonator 211 through a wiring, and converts the receiving power (AC power) received from the power reception resonator 211, into a DC voltage. In other words, the rectifier 221 is a circuit that converts AC into DC. The rectifier 221 includes, for example, a diode bridge; however, the rectifier may include other configurations.
The DC/DC converter 222 is connected to the rectifier 221 through a wiring, and converts the DC voltage output from the rectifier 221 into a voltage (higher than, equal to, or lower than DC voltage) usable by the battery 301, and outputs the voltage. The DC/DC converter 222 includes switching devices such as semiconductor switches, and controls these switching devices to perform voltage conversion. For example, a step-up ratio or a step-down ratio (hereinafter, referred to as step-up/down ratio) can be controlled by controlling an operation frequency of each of the switching devices or a pulse width of switching.
The battery 301 is a device accumulating power provided from the DC/DC converter 222 of the power reception circuit 212. A resistor (e.g., motor) that consumes the power may be used in place of the battery 301. The resistor and the battery are collectively referred to as a load device.
The control circuit 102 of the power transmission device 1 in
The frequency control circuit 102A sweeps (modulates) the frequency (power transmission frequency) of the output AC power of the high-frequency power supply device 111 within the predetermined frequency range during the power transmission period. More specifically, the frequency control circuit 102A sweeps the frequency from a start frequency to an end frequency. Sweeping of the frequency is also referred to as modulation of the frequency. The frequency is changed by controlling the driving timing of the plurality of switching devices 501 to 504 as described above. For example, to increase the frequency, the frequency of each of the switching signals 501 to 504 is increased. In other words, the number of pulse ON/OFF repetition times per unit time is increased. To decrease the frequency, reversed operation is performed.
The start frequency and the end frequency are optionally defined. For example, the start frequency is the lowest frequency within the frequency range, and the end frequency is the highest frequency within the frequency range. Alternatively, the start frequency may be the highest frequency within the frequency range, and the end frequency may be the lowest frequency within the frequency range. A sweeping speed and a sweeping unit width (change width of frequency per one time) of the frequency can be previously determined.
The voltage control circuit 102B of the control circuit 102 determines a target value of the interarm delay amount, based on the receiving voltage of the power reception circuit 212, namely, the receiving voltage of the power reception unit, and performs control to keep the interarm delay amount at the determined target value during the frequency sweeping. The receiving voltage of the power reception circuit 212 is also the input voltage of the rectifier 221. The interarm delay amount is controlled to the target value to suppress occurrence of a ripple voltage on the power reception side during the frequency sweeping.
The voltage control circuit 102B acquires information on one or both of the voltage and the current (hereinafter, voltage/current) at one or a plurality of predetermined positions in the high-frequency power supply device 111, and uses the acquired information to estimate the input voltage of the rectifier 221. The high-frequency power supply device 111 includes a detection circuit that detects the voltage/current at each of the predetermined positions. The voltage control circuit 102B determines the target value of the interarm delay amount based on the estimated input voltage. Note that, as described in a second embodiment described later, information on the input voltage may be received from the power reception side to specify the input voltage of the rectifier 221.
The relationship between the voltage/current at the one or each of the plurality of predetermined positions in the high-frequency power supply device 111 and the input voltage of the rectifier 221 is grasped from circuit simulation or a shipping test. Data representing the relationship (relationship data) is held as a table, a calculation formula, etc. Further, the input voltage of the rectifier 221 is estimated based on the relationship data and the above-described information on the voltage/current.
The voltage/current for estimation of the input voltage of the rectifier 221 can be detected at any position as long as the position has dependence relationship with the input voltage of the rectifier 221. Examples of the voltage to be detected include the output voltage of the AC/DC converter 122, the input voltage of the DC/DC converter 123, the input voltage of the inverter 124, the output voltage of the inverter 124, and the output voltage of the DC/DC converter 123. In addition, the voltage or the current at a terminal of an optional device inside the AC/DC converter 122, the DC/DC converter 123, or the inverter 124 may be detected.
In the related technology, the phase difference between the switching signals 501 and 503 is set to 180 degrees (see
As a range actually used in the wireless power transmission in the frequency range of 70 kHz to 150 kHz, a range from 82 kHz (or slightly-small frequency) that is the resonance frequency to about 110 kHz is assumed. In this range, the receiving current is varied (increased) along with the increase of the frequency (i.e., ripple occurs). In the present embodiment, the control is performed so as to suppress variation of the receiving current. This is achieved by performing control so as to keep the interarm delay amount at the above-described target value during the frequency sweeping (i.e., by performing control so as to suppress variation of interarm delay amount during frequency sweeping). The graph of the present embodiment in
A plurality of candidates of the interarm delay amount are generated. For example, the plurality of candidates of the interarm delay amount are generated at fixed intervals. Each of the candidates is sequentially selected. The power transmission device is started up, and the frequency is swept from the start frequency to the end frequency while performing control so as to keep the interarm delay amount at the selected candidate value. The frequency at the startup of the power transmission device may be the resonance frequency of the power transmission resonator or the power reception resonator, the start frequency of the sweeping range, or any other frequency. The receiving voltage (input voltage of rectifier), the receiving current, etc. of the power reception circuit 212 are measured during the frequency sweeping. The candidate at which variation of the receiving current is the lowest is specified within the range of the frequency sweeping or a part of the range. The specified candidate is regarded as the target value, and the target value is associated with a pair of the input voltage of the rectifier and the frequency at which the input voltage has been measured, and the target value and the pair are stored in a database (first database). The frequency may be the start frequency of the frequency sweeping, the end frequency, or any other frequency. Further, the frequency may be the resonance frequency or the frequency at the startup of the power transmission device. A plurality of pairs of the input voltage of the rectifier and the frequency may be generated, the target value may be associated with the plurality of pairs, and the target value and the pairs may be stored in the database. For example, the input voltage of the rectifier may be measured at each of the sweep frequencies from the start frequency to the end frequency, and each of the pairs of the frequency and the input voltage may be associated with the above-described specified candidate.
The receiving power on the power reception side is changed due to positional relationship between the coil on the power transmission side and the coil on the power reception side (e.g., intercoil distance) and other factors. Therefore, the relationship between the frequency and the receiving current as illustrated in
The database is stored in, for example, a storage in the control circuit 102 or an external storage accessible from the control circuit 102. The storage may be a volatile memory such as a SRAM and a DRAM, or a nonvolatile memory such as a NAND, an MRAM, and an FRAM. Further, the storage may be a storage device such as a hard disk and an SSD. In this example, the database is constructed by the simulation. Alternatively, the database may be constructed by a test. In addition, in place of the database, a function to calculate the target value from at least the former of the input voltage of the rectifier and the frequency may be generated. In the following description, the example using the database is described; however, the function may be used.
The voltage control circuit 102B specifies, from the above-described database (see
In step S11, when receiving a charge control instruction from an external device, the voltage control circuit 102B of the control circuit 102 performs startup operation, and raises the output voltage of the inverter 124 to the target voltage. Examples of the external device include an input interface (e.g., touch panel) for the user, a controller of the wireless power transmission system, and any other devices. The power transmission frequency at the startup operation is, for example, the resonance frequency of the power transmission resonator or the power reception resonator, a frequency close to the resonance frequency, or any other frequency within the sweeping range.
In step S12, when the output voltage of the inverter 124 reaches the target voltage, power transmission is started at the startup frequency (frequency sweeping is not started at this time), and the voltage control circuit 102B acquires the information on the voltage/current at the one or the plurality of predetermined positions in the high-frequency power supply device 111.
In step S13, the voltage control circuit 102B estimates the input voltage of the rectifier 221 (receiving voltage of power reception circuit 212) from the acquired information on the voltage/current with use of the above-described relationship data. The target value of the interarm delay amount is determined from the above-described database (first database), based on at least the former of the estimated input voltage and the power transmission frequency at which the input voltage has been estimated.
In step S14, the voltage control circuit 102B determines whether the interarm delay amount satisfies a target condition. The interarm delay amount can be specified through, for example, measurement of a signal level of each of the switching signals. In a case where the interarm delay amount is coincident with the target value or is within a predetermined error range of the target value, it is determined that the interarm delay amount satisfies the target condition, and otherwise, it is determined that the interarm delay amount does not satisfy the target condition. The predetermined error range is previously determined in such a manner that the variation of the receiving current is within an allowable range, for example, a range plus/minus a from the target value. The value a may be a predetermined value, or a value obtained by multiplying the target value by a constant coefficient. The predetermined error range may be determined from the result of the above-described simulation.
In a case where the interarm delay amount satisfies the target condition (YES in step S14), it is determined in step S15 whether the frequency sweeping has been started. In step S15 at first time after the processing of the flowchart is started, the frequency sweeping has not been started yet (NO in step S15). Accordingly, the processing proceeds to step S16, and the frequency control circuit 102A starts the frequency sweeping. Thereafter, the processing proceeds to step S17.
In step S17, it is determined whether an end condition of the charging has been satisfied. Examples of the end condition include a case where a predetermined time elapses after the power transmission is started, a case where charging of the battery 301 is completed, and a case where a charging end instruction is received from the user of the battery through the input interface. In a case where the end condition has been satisfied (YES), the processing ends. In a case where the end condition has not been satisfied (NO), the processing returns to step S14.
In a case where it is determined in step S14 that the interarm delay amount does not satisfy the target condition (NO), it is determined in step S18 whether the sweeping for one period has been completed or before start of the sweeping (i.e., whether processing in step S16 has been executed).
Completion of the sweeping for one period indicates completion of the sweeping from the start frequency to the end frequency within the sweeping range. In a case where it is determined that the sweeping for one period has been completed or before start of the sweeping, the processing proceeds to step S19 in order to adjust the interarm delay amount. In contrast, in a case other than the above, namely, in a case where the sweeping for one period has not been completed (i.e., in middle of sweeping) (NO), the processing proceeds to step S17. In other words, after the sweeping is started, the interarm delay amount is not adjusted until the sweeping of the period is completed.
In step S19, it is determined whether the interarm delay amount is smaller than the target value. In a case where the interarm delay amount is smaller than the target value (YES in step S19), the switching signal generation circuit 102C is controlled so as to increase the interarm delay amount (step S20). For example, control is performed so as to increase the interarm delay amount by a difference between the current interarm delay amount and the target value. This makes it possible to bring the interarm delay amount close to the target value or to settle the interarm delay amount within the predetermined error range. As another method, the interarm delay amount may be increased by a predetermined increase degree Δα1.
In contrast, in a case where the interarm delay amount is larger than the target value (NO in step S19), the switching signal generation circuit 102C is controlled so as to decrease the interarm delay amount in step S21. For example, the interarm delay amount is decreased by the difference between the current interarm delay amount and the target value. This brings the interarm delay amount close to the target value or settles the interarm delay amount within the predetermined error range. As another method, the interarm delay amount may be decreased by a predetermined decrease degree Δγ1.
After the interarm delay amount is increased or decreased in step S20 or S21, the processing returns to step S12. In step S12 and in subsequent step S13, for example, the input voltage of the rectifier at the start frequency is estimated, and the target value of the interarm delay amount is determined (target value may be same as or different from previous target value). Thereafter, processing in step S14 is similar to the processing described above.
In the operation of this flowchart, the interarm delay amount is adjusted after the frequency is swept from the start frequency to the end frequency; however, the interarm delay amount may be adjusted in the middle of the sweeping. For example, in a case where it is determined in step S14 that the interarm delay amount does not satisfy the target condition, the interarm delay amount may be adjusted at that time (without waiting completion of current sweeping period).
In the operation of this flowchart, the target value is determined again in steps S12 and S13 after step S20 or S21. In a case where possibility of variation of the target value is low because the position of the power reception device is kept after the charging is started, steps S12 and S13 may be skipped and the processing may proceed to step S14.
As described above, the frequency sweeping is performed while generation of the switching signals is controlled such that the interarm delay amount satisfies the target condition, which makes it possible to suppress variation of the receiving current (occurrence of ripple) on the power reception side while reducing radiation magnetic field intensity. As a result, it is possible to prevent a large load from being applied to the electric circuit on the power reception side, and to suppress reduction of the battery lifetime.
In addition, the power transmission side estimates the input voltage of the rectifier from the voltage/current at the predetermined positions in the high-frequency power supply device. In other words, the relationship between the voltage/current at the predetermined positions and the input voltage of the rectifier is previously acquired, and the voltage on the power reception side is estimated with use of the relationship data. Accordingly, it is unnecessary to feed back the state of the power reception device 2 to the power transmission device 1. This simplifies the configuration.
In the present embodiment, the target value of the interarm delay amount is determined from the input voltage of the rectifier. Alternatively, the target value of the interarm delay amount may be determined from the voltage/current at the other position of the power reception circuit. Also in this case, the voltage/current at the other position of the power reception circuit can be estimated from the voltage/current at the predetermined position in the high-frequency power supply device, and the target value of the interarm delay amount can be determined from the estimated voltage/current.
In the first embodiment, the voltage control circuit 102B on the power transmission side estimates the input voltage of the rectifier 221 on the power reception side (receiving voltage of power reception circuit 212) from the voltage/current at the predetermined position in the high-frequency power supply device 111. In the present embodiment, instead of the estimation of the input voltage of the rectifier 221, the communication circuit 203 on the power reception side transmits information representing the input voltage of the rectifier 221. The communication circuit 103 receives the information from the communication circuit 203, and transfers the received information to the voltage control circuit 102B.
The power reception circuit 212 or the rectifier 221 includes a detection circuit that detects the input voltage of the rectifier (receiving voltage of power reception circuit). The detection circuit notifies the information representing the detected input voltage to the communication circuit 203. The communication circuit 203 transmits the information to the power transmission device 1. The detection circuit may detect the input voltage of the rectifier at a predetermined interval, or may detect the input voltage of the rectifier at timing when a measurement instruction is received from the power transmission device 1. In the latter case, the control circuit 102 transmits the instruction to measure the input voltage of the rectifier, through the communication circuit 103. The communication circuit 203 receives the measurement instruction, and notifies the received measurement instruction to the power reception circuit 212 or the rectifier 221.
According to the present embodiment, since it is sufficient for the control circuit 102 of the power transmission device 1 to acquire the information representing the input voltage of the rectifier 221 from the power reception device 2 (it is unnecessary to estimate input voltage of rectifier), it is possible to simplify the configuration of the power transmission device.
A control circuit 230 is provided in the power reception device 2. In addition, a voltage adjustment circuit 223 is provided in the DC/DC converter 222. The control circuit 230 is connected to the DC/DC converter 222. The control circuit 230 estimates the interarm delay amount of the inverter 124 on the power transmission side, based on the voltage/current at one or a plurality of positions in the power reception circuit (rectifier 221 and DC/DC converter 222). The power reception circuit includes a detection circuit that detects the voltage/current at the one or each of the plurality of positions. The control circuit 230 determines an input/output voltage conversion ratio of the DC/DC converter 222 based on the estimated interarm delay amount. The control circuit 230 outputs an instruction signal to specify the determined conversion ratio, to the voltage adjustment circuit 223 of the DC/DC converter. The voltage adjustment circuit 223 adjusts the input/output voltage conversion ratio based on the instruction signal. The input/output voltage conversion ratio is adjusted, for example, for each period of the frequency sweeping. In this case, the input/output voltage conversion ratio is kept during one period of the frequency sweeping.
When the operation of this flowchart is started, the control circuit 230 specifies the voltage/current at the one or each of the plurality of positions in the power reception circuit in step S31. In this case, for example, the input voltage of the rectifier 221 is specified. Subsequently, the control circuit 230 estimates the interarm delay amount of the inverter 124 on the power transmission side based on the specified input voltage (step S32). It is determined whether the input/output voltage conversion ratio of the DC/DC converter 222 is appropriate, based on the estimated interarm delay amount (step S33). In a case where it is determined that the input/output voltage conversion ratio is appropriate (YES), the processing ends. In a case where it is determined that the input/output voltage conversion ratio is not appropriate (NO), the appropriate input/output voltage conversion ratio is determined, and a signal representing the determined value is output to the voltage adjustment circuit 223 (step S34). The voltage adjustment circuit 223 corrects the input/output voltage conversion ratio to the value represented by the signal.
The processing in step S32 is described in detail. A database (second database) in which the input voltage of the rectifier 221 is associated with the interarm delay amount, and a database (third database) in which the interarm delay amount is associated with the input/output voltage conversion ratio are stored in the storage of the control circuit 230 or in an external storage accessible from the control circuit 230. The storage may be a volatile memory such as an SRAM and a DRAM, or a nonvolatile memory such as a NAND, an MRAM, and an FRAM. In addition, the storage may be a storage device such as a hard disk and an SSD. The second database can be constructed by acquiring the relationship between the input voltage of the rectifier 221 and the interarm delay amount from a simulation or a test. The third database can be basically constructed such that the variation of the receiving current is suppressed, based on the database construction method according to the first embodiment. The frequency at which the input voltage of the rectifier has been detected may be included in the database, as with the first embodiment. The control circuit 230 specifies, in the second database, the interarm delay amount corresponding to the input voltage specified in step S31, and the specified interarm delay amount is regarded as the estimated interarm delay amount of the inverter 124.
In step S33, the input/output voltage conversion ratio corresponding to the interarm delay amount estimated in step S32 is specified in the third database. In a case where the current input/output voltage conversion ratio of the DC/DC converter 122 is coincident with the specified input/output voltage conversion ratio or within the predetermined error range (YES in step S33), it is determined that the current input/output voltage conversion ratio is appropriate. In a case other than the above (NO in step S33), it is determined that the current input/output voltage conversion ratio is not appropriate. The instruction signal is transmitted to the voltage conversion circuit such that the input/output voltage conversion ratio of the DC/DC converter 122 becomes the specified input/output voltage conversion ratio (step S34).
According to the present embodiment, it is possible to further suppress variation of the receiving current by also adjusting the input/output voltage conversion ratio of the DC/DC converter 122.
In the third embodiment, the interarm delay amount is estimated on the power reception side. In the fourth embodiment, information on the interarm delay amount (or target value of interarm delay amount, same hereinafter) is transmitted from the communication circuit 103 of the power transmission device 1 to the communication circuit 203 of the power reception device 2. The communication circuit 203 receives the information on the interarm delay amount from the communication circuit 103. The power transmission device 1 transmits the information on the interarm delay amount, for example, for each period of the frequency sweeping such as at the time when the interarm delay amount is corrected (see steps S20 and S21 in
According to the present embodiment, since it is sufficient for the control circuit 230 of the power reception device 2 to acquire the information representing the interarm delay amount of the inverter 124 on the power transmission side from the power transmission device 1 (it is unnecessary to estimate interarm delay amount of inverter 124 on power transmission side), it is possible to simplify the configuration of the power reception device 2.
As with the third or fourth embodiment, the value of the input/output voltage conversion ratio of the DC/DC converter 123 can be kept during the frequency sweeping also in the above-described first and second embodiments. In a manner similar to the third or fourth embodiment, the input/output voltage conversion ratio can be determined from the measured interarm delay amount (or target value of interarm delay amount), and the value of the input/output voltage conversion ratio can be kept at the determined value. Specific description is omitted because it is obvious from the description in the third and fourth embodiments. It is possible to further suppress the variation of the receiving current by also adjusting the input/output voltage conversion ratio of the DC/DC converter 123.
In the first embodiment, one power transmission resonator and one power reception resonator are provided. In the present embodiment, two power transmission resonators and two power reception resonators are provided. In other words, the wireless power transmission is performed by two systems.
Each of a power transmission resonator 112A and a power transmission resonator 112B is connected to the output terminals (plus terminal and minus terminal) of the inverter 124. Polarities of the connection, however, are inverted from each other. In other words, a plus terminal of the power transmission resonator 112A is connected to the plus terminal of the inverter 124, and a minus terminal of the power transmission resonator 112A is connected to the minus terminal of the inverter 124. In contrast, a plus terminal of the power transmission resonator 112B is connected to the minus terminal of the inverter 124, and a minus terminal of the power transmission resonator 112B is connected to the plus terminal of the inverter 124. As a result, the current output from the inverter 124 is provided to the power transmission resonator 112A and the power transmission resonator 112B, as currents (anti-phase currents) shifted in phase by 180 degrees or substantially 180 degrees from each other. The phases are reversed in the above-described manner, which cancels the magnetic field radiated from the power transmission resonator 112A and the magnetic field radiated from the power transmission resonator 112B from each other in a distant location, to reduce leakage magnetic field. Note that the phase difference to obtain the magnetic field cancelling effect is not necessarily 180 degrees, and for example, a phase difference within a range plus/minus a from 180 degrees may be provided to obtain reduction effect of a desired degree.
The magnetic field generated from the power transmission resonator 112A and the magnetic field generated from the power transmission resonator 112B are respectively coupled by power reception resonators 211A and 211B. The power reception resonator 211A and the power reception resonator 2118 are connected to the input terminals (plus terminal and minus terminal) of the rectifier 221. Polarities of the connection, however, are inverted from each other. In other words, a plus terminal of the power reception resonator 211A is connected to the plus terminal of the rectifier 221, and a minus terminal of the power reception resonator 211A is connected to the minus terminal of the rectifier 221. In contrast, a plus terminal of the power reception resonator 211B is connected to the minus terminal of the rectifier 221, and a minus terminal of the power reception resonator 211B is connected to the plus terminal of the rectifier 221. As a result, the power reception resonator 211A and the power reception resonator 211B output in-phase currents, and total power corresponding to the sum of these currents is supplied to the rectifier 221.
In the present embodiment, the wireless power transmission is performed by two systems; however, the wireless power transmission may be performed by three or more systems. In this case, when the number of systems is denoted by N, it is sufficient to control the phase of the output current of the inverter 124 such that currents shifted in phase by 360 degrees/N or by substantially 360 degrees/N are provided to N power transmission resonators.
In the present embodiment, the output of the inverter 124 is shared by the power transmission resonators 112A and 112B; however, the inverter may be individually connected to each of the power transmission resonators. This makes it possible to control inverter driving for each power transmission resonator.
The configuration other than the above is the same as the configuration according to the first embodiment. The configuration including two or more systems in the present embodiment is similarly applicable to the configuration according to any of the second to fifth embodiments.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
Number | Date | Country | Kind |
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2018-168939 | Sep 2018 | JP | national |