JP2016066960A - Wireless power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wireless power transmission system capable of efficiently transmitting power wirelessly.SOLUTION: A wireless power transmission system 32 for wirelessly transmitting power for actuating each of a plurality of wireless sensor modules 90, ..., 96 to the wireless sensor modules includes: a plurality of wireless transmission antennas 62, ..., 68; and an oscillation signal supply unit for supplying an oscillation signal to each of the wireless transmission antennas so that oscillation signals' phase difference varies as a function of time. The oscillation signal supply unit includes: an oscillator 60 for outputting an oscillation signal having a designated frequency; phase shifters 70, ..., 74, that are connected between an output end of the oscillator 60 and input ends of a plurality of antennas 64, ..., 68, respectively, and make a phase of an oscillation signal output by the oscillator 60 shift by designated phase; and an access point 44 for instructing each phase shifter to change the phase shifter's phase so that phase difference between arbitrary two phase shifters' outputs varies as a function of time.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wireless power transmission system that wirelessly transmits power to other devices, and more particularly to a wireless power transmission system that stably transmits power to a plurality of devices in an environment where multipath interference occurs.

  Many sensor modules are used in modern automobiles, airplanes, and the like. For example, in the case of an automobile, the detection outputs of these sensor modules are transmitted to the vehicle control unit and used for controlling the engine, each actuator, and the like by the vehicle control unit. Wiring for power supply and information communication is required between the sensor module and the vehicle control unit. These wirings are bundled into a bundle of several wirings and attached to the vehicle as a part called a wire harness.

  However, since the number of sensor modules and electronic control parts for vehicle control is large, the wiring is also large. As a result, the weight of the whole wire harness attached to one automobile is increased, and the weight of the vehicle itself is also increased. When the vehicle becomes heavier, the fuel required for acceleration of the vehicle increases. As a result, the fuel efficiency of the automobile is deteriorated, and not only the economic burden on the driver is increased, but also the emission amount of carbon dioxide gas is increased. By reducing the weight of the vehicle, an improvement in fuel consumption can be expected. The number of automobiles sold in 2013 has reached a huge number of over 87 million vehicles worldwide (according to the Japan Automobile Manufacturers Association website). By promoting the weight reduction of individual automobiles, the global carbon dioxide It can make a significant contribution to reducing gas emissions.

  As a means for reducing the weight of the vehicle, it is conceivable to wirelessly communicate with the sensor modules in each part of the vehicle. There is a tendency that more sensors are attached in the vehicle not only for vehicle running control but also for improving the safety of the vehicle and for taking safety measures against pedestrians. Therefore, by wirelessly communicating with the sensor module, the number of wires can be effectively reduced and the vehicle can be expected to be lighter.

  One of the major issues in making the wiring to the sensor module wireless is how to secure the power supply of the sensor module. If the wiring is left only for power supply, the effect of wire reduction is halved. For this problem, it is considered that wireless power transmission (hereinafter referred to as “wireless power transmission”) technology, which has been attracting attention recently, can be used.

  There are three types of wireless power transmission suitable for short distance, medium distance, and long distance transmission. An electromagnetic induction method is used for short-distance transmission, an electromagnetic resonance method is used for medium-distance transmission, and a radio wave emission method is used for long-distance transmission. The previous two methods use coils for power transmission. In these methods, it is necessary to increase the size of the coil as the power transmission distance increases. Since there are a large number of metal units and the like in the engine room and living space of an automobile, the sensor module must also be small. Therefore, it is at least not appropriate to use these schemes. In transmitting wireless power to a sensor module in a vehicle, it is appropriate to adopt a radio wave radiation method.

  There is a peculiar problem when the radio wave radiation method is used to supply power to the sensor module in the automobile. That is, since there are many radio wave reflectors in the vehicle, there are many transmission paths from the power transmitter to the sensor module, and unpredictable interference between radio waves occurs. Further, in the radio wave radiation method, since the wavelength of the used radio wave is short, there is a problem that the power that can be received by the sensor module varies greatly due to a slight difference in the position of the sensor module. Due to these factors, for example, even if sufficient power can be transmitted to one sensor module, an event that the power transmitted to another nearby sensor module is extremely small is likely to occur with a high probability. .

  In wireless communication as well as in-vehicle power transmission, similar problems occur in many environments. Therefore, in general wireless communication, a coping method for performing stable communication is considered.

  Patent Document 1 discloses a technique for wirelessly using a cable used for information transmission between substrates in a housing of a personal computer (hereinafter referred to as “PC”). As in the automobile, radio waves are reflected by components such as the PC casing and the substrate, and therefore there are many radio wave transmission paths in the PC casing. For this reason, the electric field intensity of the radio wave for power transmission varies greatly depending on the position in the housing. In other words, depending on the position of the antenna (board position) used when the cable is wireless, communication may not be possible. Therefore, Patent Document 1 teaches a mechanism for adjusting the antenna position so that the electric field strength at the antenna position is increased by mechanically moving the substrate including the antenna.

JP2009-206878

  The technique described in Patent Document 1 can also be applied to wireless power transmission in a vehicle. However, vibrations are generally intense in the vehicle, and the temperature conditions are particularly severe in the engine room. It is difficult to arrange a large number of sensor modules having mechanical drive units in such a vehicle. Since mechanical driving generally consumes a large amount of electric power, it is not practical to provide a mechanical driving unit on the sensor module side.

  In general, in the case of communication for transmitting information, the permissible range of necessary received power is wide, and even if the received power is relatively weak, communication can be established as long as the power exceeds the sensitivity of the receiver. For this reason, it suffices if there is power exceeding the sensitivity of the receiver. On the other hand, in power transmission, extremely large power is required as compared with power necessary for information transmission. For example, wireless power transmission requires power that is 1,000 times greater than wireless information communication. In wireless power transmission, in order to supply sufficient power to all sensor modules, it is not permitted from the viewpoint of labor saving to increase transmission power without limitation. Accordingly, the target wireless transmission scheme is required to have high power transmission efficiency so that a sufficiently large amount of power can be transmitted with relatively low power. In this case, a further consideration is to make the power received by each sensor module as small as possible. In the case of wireless information communication, even if the reception power varies among the receivers, the required power is small as described above, so that there is no significant trouble in information communication. However, in the case of wireless power transmission, when power is wirelessly transmitted with a constant transmission power, the magnitude of the transmission power must be determined based on the sensor module with the lowest reception power. This is because necessary information cannot be obtained unless power is sufficiently supplied to all the sensor modules. If the variation in the power received by each sensor module is large, the power supply to the sensor modules other than the sensor module having the lowest received power will be excessively large, and the power will be wasted.

  Therefore, an object of the present invention is to provide a wireless power transmission system capable of wirelessly transmitting power with high efficiency.

  An additional object of the present invention is to provide a wireless power transmission system capable of wirelessly transmitting a sufficiently large amount of power to a power receiving apparatus with high efficiency.

  The wireless power transmission system according to the first aspect of the present invention wirelessly transmits power for operating each wireless sensor module to a plurality of wireless sensor modules. In this wireless power transmission system, a plurality of wireless transmission antennas and a phase difference of an oscillation signal supplied between any two of the plurality of wireless transmission antennas change as a function of time. And an oscillation signal supply means for supplying an oscillation signal.

  Preferably, the oscillation signal supply means is connected between an oscillation circuit that outputs an oscillation signal of a designated frequency, and an output end of the oscillation circuit and an input end of a plurality of antennas, and oscillates only in a designated phase. For each of the phase shifters, the phase shifter that shifts the phase of the oscillation signal output by the circuit and the phase difference between any two outputs of the phase shifter changes as a function of time, Phase shifter control means for designating a phase change by the phase shifter.

  More preferably, the wireless power transmission system further determines the frequency of the oscillation signal by the oscillation circuit so that the minimum value of the average received power in each fixed period of each of the plurality of wireless sensor modules is maximized. Oscillation frequency determining means for instructing

  The oscillation frequency determining means includes a frequency indicating means for instructing the oscillation frequency to the oscillation circuit so as to change the frequency of the oscillation signal of the oscillation circuit over a certain range, and a change in the oscillation frequency of the oscillation circuit by the frequency indicating means. While being instructed, a signal receiving means for periodically receiving a received power signal indicating an average received power in a predetermined period immediately before the wireless sensor module from each of the plurality of wireless sensor modules, and the signal receiving means periodically The minimum value specifying means for specifying the minimum value in each cycle of the average received power represented by the received power signal that is received automatically, and the minimum value specified by the minimum value specifying means in a certain period longer than a certain period is the maximum Frequency specifying means for specifying the oscillation frequency of the oscillation circuit at the time, and the oscillation frequency of the oscillation circuit with respect to the oscillation circuit It may include a frequency fixing unit for instructing to secure the frequency specified by the frequency specifying means.

  Preferably, the phase shifter control means provides for each of the phase shifters such that the phase difference between any two outputs of the phase shifter varies as a function of time with a period of time. Periodic phase shifter control means for specifying a phase change by the phase shifter is included. The signal receiving means periodically transmits a signal representing a time constant determined by an average received power in a predetermined period immediately before the wireless sensor module and a filter and a load of a rectifier circuit in the wireless sensor module from each of the plurality of wireless sensor modules. Means for receiving automatically. The wireless power transmission system further includes a time constant specifying means for specifying the time constant received by the means for receiving simultaneously with the oscillation frequency specified by the frequency specifying means, and a change in phase shift of the phase shifter by the phase shifter control means. Phase shift change period determining means may be further included for determining the period based on the time constant specified by the time constant specifying means so that the minimum value in each period specified by the minimum value specifying means is maximized.

  More preferably, the oscillation signal supply means is provided corresponding to the plurality of radio transmission antennas, and outputs an oscillation signal having a designated frequency and supplies the oscillation signal to a corresponding radio transmission antenna among the plurality of radio transmission antennas. A plurality of oscillation circuits and frequency control means for designating the frequencies of the oscillation signals to the plurality of oscillation circuits so that the oscillation signals output from the plurality of oscillation circuits have different frequencies from each other.

  More preferably, the wireless power transmission system further sets each of the frequencies of the oscillation signals by the plurality of oscillation circuits so that the minimum value of the average received power of each of the plurality of wireless sensor modules in a certain period is maximized. Oscillation frequency determination means for determining and instructing each of the plurality of oscillation circuits is included.

  The oscillation frequency determining means is an oscillation circuit control means for changing the frequency of the oscillation signal from the plurality of oscillation circuits according to a combination of a plurality of different frequencies, and a signal indicating the average received power from each of the plurality of wireless sensor modules. Each time the combination of the frequencies of the oscillation signals from the plurality of oscillation circuits is changed by the reception means for receiving and the oscillation circuit control means, the average reception power of the average reception power is received for each of the combinations of the plurality of frequencies. The first minimum value specifying means for specifying the minimum value, and the combination in which the maximum value is obtained among the minimum values of the average received power specified by the first minimum value specifying means for the combination of a plurality of frequencies. The frequency determination means for determining the frequency of the oscillation signal by a plurality of oscillation circuits according to the combination determined by the frequency determination means And a frequency fixing unit for fixing the wave number may be.

  Each time the combination of the frequencies of the oscillation signals from the plurality of oscillation circuits is changed by the oscillation circuit control unit, the reception unit receives the average received power of the wireless sensor module and the wireless sensor module from each of the plurality of wireless sensor modules. And means for receiving a signal indicating a filter and a time constant determined by a load of the rectifier circuit. The oscillation circuit control means includes means for changing the frequencies of the oscillation signals from the plurality of oscillation circuits according to a plurality of combinations of a plurality of frequencies different from each other by a certain difference. The wireless power transmission system further includes the average received power specified by the first minimum value specifying means when the combination of the frequencies determined by the frequency determining means is obtained among the time constants received by the receiving means. The difference for each frequency in the combination of the frequency determined by the frequency determining means, the time constant specifying means for specifying the time constant received simultaneously with the minimum value, and the reciprocal of three times the time constant specified by the time constant specifying means And a frequency redefining means for redefining the combination of the frequencies.

  Preferably, the wireless power transmission system further includes a difference control unit that changes the frequency of the oscillation signal by changing the difference in a plurality of ways within a certain range, and an average reception each time the difference is changed by the difference control unit. A second minimum value specifying means for specifying the minimum value of the average received power received by the power, and a difference such that the minimum value specified by the second minimum value specifying means is maximized while changing the difference in a plurality of ways. And means for further redefining the combination of frequencies redefined by the means for redefining using the difference determined by the means for determining the difference.

  A computer program according to the second aspect of the present invention causes a computer to function as any of the above-described phase shifter control means.

  A computer program according to the third aspect of the present invention causes a computer to function as any of the frequency control means described above.

It is the figure which showed in block diagram the part relevant to this invention of the motor vehicle which employ | adopted the wireless power transmission system which concerns on the 1st Embodiment of this invention. It is a block diagram of the access point of the wireless power transmission system which concerns on 1st Embodiment. It is a block diagram of an example of the sensor module which receives electric power wirelessly from the wireless power transmission system concerning a 1st embodiment. It is a block diagram of an example of the sensor element which makes a part of sensor module. 6 is a flowchart of a program for performing an initial setting for determining a frequency of an oscillator of a wireless power transmission device and a maximum phase shift change period of radio waves for wireless transmission in the first embodiment. 4 is a flowchart of a program for controlling the wireless power device during normal operation after the initial setting is completed in the first embodiment. In 1st Embodiment, it is a figure which shows an example of the waveform of the electromagnetic wave which a sensor module receives. It is the figure which showed in block diagram the part relevant to this invention among the motor vehicles which employ | adopted the wireless power transmission system which concerns on 2nd Embodiment. It is a block diagram of the access point in the wireless power transmission system which concerns on 2nd Embodiment. It is a flowchart of the program which performs the initial process which determines the frequency of each oscillator in the wireless power transmission system which concerns on 2nd Embodiment. It is a figure which shows an example of the waveform of the electromagnetic wave which a sensor module receives in the wireless power transmission system which concerns on 2nd Embodiment.

  In the following description and drawings, the same parts are denoted by the same reference numerals. Therefore, detailed description thereof will not be repeated.

[First Embodiment]
Referring to FIG. 1, a wireless power transmission system 32 according to a first embodiment of the present invention is arranged in a vehicle body of an automobile 30.

  The wireless power transmission system 32 includes a sensor module group 42 including a plurality of sensor modules 90, 92,... 96 arranged at various positions of the automobile 30, and sensor modules 90, 92,. , 96 for controlling the wireless power transmission from the power transmission device 40 for wirelessly transmitting power to each of the power transmission devices 40 and sensors from the sensor modules 90, 92,. An access point 44 for receiving the output wirelessly and generating a signal for controlling each part of the automobile 30, and an engine for controlling each part including the engine of the automobile 30 in response to the control signal from the access point 44 Vehicle control unit 46.

  The power transmission device 40 is connected between the oscillator 60, the (m + 1) antennas 62, 64, 66,..., 68, and the output terminal of the oscillator 60 and the input terminals of the antennas 64, 66,. A first phase shifter 70, a second phase shifter 72,..., Which are supplied to the antennas 64, 66,... 68 by changing the phase of the oscillation signal output from the oscillator 60 by a specified phase amount. M-th phase shifter 74. Here, “m” is the number of phase shifters, but in this embodiment, the transmission phases of the antennas 62, 64, 66,. Is a number m obtained by subtracting 1 from the number of antennas m + 1. The antennas 62, 64, 66,..., 68 are distributed at various positions in the vehicle 30. The access point 44 communicates with each sensor module of the sensor module group 42 and has functions of controlling the phase shift of the phase shifter and the oscillation frequency of the oscillator in addition to using the sensor data for automobile engine / vehicle control.

  The access point 44 receives communication from each sensor module and converts it into an electrical signal, and controls the engine and vehicle according to the information received from each sensor module via the antenna 124 and the wireless circuit 122. The process of controlling the unit 46 and the process of determining the oscillation frequency of the oscillator 60 and the phase shift amount of the first phase shifter 70, the second phase shifter 72,. The CPU 126 that executes a program for executing the program, the ROM (read only memory) 128 that stores the program executed by the CPU 126, constants, and the like, and the area in which the program read from the ROM 128 by the CPU 126 is loaded. RAM 130 to be used.

  In the present embodiment, the plurality of sensor modules 90, 92, ..., 96 all have the same configuration. Referring to FIG. 3, for example, sensor module 90 receives antenna 150 that receives radio waves from the power transmission device, rectifier circuit 154 that converts high-frequency power received by antenna 150 into DC power, and outputs from rectifier circuit 154. A power storage element 156 that stores DC power and a DC-DC converter 158 that controls the voltage of the power stored in the power storage element 156 and outputs it. The sensor module 90 further detects the predetermined information and outputs a data signal, the wireless circuit 162 and the antenna 152 for transmitting data to the access point 44, and the electric power stored in the storage element 156. A CPU 164 that performs processing for wirelessly transmitting data received from the sensor element 160 to the access point 44 via the wireless circuit 162 and the antenna 152; a ROM 166 that stores a program executed by the CPU 164 for wireless transmission; The CPU 164 includes a storage area for loading a program read from the ROM 166 and a RAM 168 for providing a work area when the program is executed. The CPU 164 can monitor the power storage amount of the power storage element 156 and the power (received DC power) supplied to the power storage element 156 through the power storage element 156. The monitored power storage amount is transmitted from the CPU 164 to the access point 44 via the wireless circuit 162 and the antenna 152, and used to control transmission power (output power of the oscillator 60) in a steady operation state as will be described later. A program for performing this control will be described later with reference to FIG.

  Referring to FIG. 4, rectifier circuit 154 includes, for example, rectifier diode 192 and capacitor 200 connected in parallel between two input terminals 190 that receive an antenna output. The power storage element 156 is also connected in parallel with these and serves as a load for the smoothing filter. Two output terminals 194 connected to the storage element 156 are connected to the DC-DC conversion unit 158 and supply electric power for the operation of the sensor element 160. As will be described later, in this embodiment, the time constant τ of the rectifier circuit configured by the rectifier circuit 154 and the storage element 156 is used in order to increase the transmission efficiency of wireless power.

  In the sensor module 90 shown in FIG. 3, the average value of the DC power accumulated in the power storage element 156 (that is, the average received DC power of the sensor module 90. Hereinafter, the average received DC power is simply referred to as the average received power). And the time constant τ of the rectifier circuit described above are transmitted to the access point 44.

  In the present embodiment, the CPU 126 of the access point 44 performs initial setting of the first phase shifter 70, the second phase shifter 72,..., The m-th phase shifter 74 as follows: Control transmission power in steady state. A control structure of a program executed by the CPU 126 for initial setting is shown in a flowchart form in FIG. This process increases the efficiency of the wireless power transmission, and the frequency of the oscillator 60 and the first phase shift so that the minimum received power of the received power of the plurality of sensor modules 90, 92,. , And the phase shift change period of the m-th phase shifter 74.

In the present embodiment, the access point 44 uses the phase shift change period of the first phase shifter 70 as T, and the phase shift φ of the oscillation signal output from the first phase shifter 70 becomes φ = Change according to (360 × t / T mod 360) degrees. The phase shift of the second phase shifter 72 changes in the same manner as the first phase shifter 70, but the phase shift change period is set to T / 2. For the third phase shifter and the fourth phase shifter (both not shown), the phase shift change periods are set to T / 2 ² and T / 2 ³ , respectively. That is, generally, for the k-th phase shifter, the phase shift change period is set to T / 2 ^k−1 .

Referring to FIG. 5, step the program, to set the initial value T ₀ the phase change period T which is the maximum value of the above phase change _period, the oscillation frequency f of the oscillator 60 to an initial value f ₀ 220, step 221 for starting wireless power transmission by the power transmission device 40 shown in FIG. 1 at the set phase shift change period and oscillation frequency, and following step 221, the DC power received by each sensor module from each sensor module Receiving 222 a signal indicating the average received power indicating the average value and the time constant τ of the rectifier circuit of each sensor module.

Here, the initial value _{T 0} of the phase change period is, for example, about 100 ms. The initial value f ₀ of the oscillation frequency is set to the lowest frequency of the system design bandwidth.

The program shown in FIG. 5 further includes the lowest value (minimum average received power) of the average received power received from each sensor module in step 222, and the time constant τ simultaneously received from the sensor module that transmitted the value. Step 224 for correlating the oscillation frequency f of the oscillator 60 when they are received with each other and storing them in the RAM 130, Step 226 for adding the increment df of the oscillation frequency to the oscillation frequency f of the oscillation circuit, and after the addition by Step 226 And step 228, in which it is determined whether or not the frequency f is equal to or lower than a predetermined maximum value f _{max and the} control is returned to step 221 according to whether the result is affirmative or the control is advanced to the next step. The maximum value f _max is a frequency range corresponding to the rectifier circuit 154 and is the highest frequency of the system design bandwidth. Here, the increment df of the oscillation frequency is set to about several MHz, for example.

The program further determines the maximum value of the minimum average received power stored in step 224 during the repetition when the determination result in step 228 is negative, that is, when the frequency f exceeds the maximum value f _max. Step 229 for specifying the oscillation frequency f _d and the time constant τ _d at that time, the oscillation frequency (transmission frequency) f of the oscillator 60 is set to the oscillation frequency f _d , and the phase shift change period T is set to τ _d × 3 Performing step 230, starting step 231 for starting wireless power transmission using the set oscillation frequency and phase shift period, step 232 receiving a signal indicating average received power from each sensor module over a certain period, The minimum value of the average received power of each sensor module received in step 232 is stored in the RAM 130 together with the phase shift change period T at that time. Step 236, step 236 for subtracting a predetermined difference dt from the phase shift change period T, and control flow to step 231 or the subsequent step depending on whether the phase shift change period T after subtraction in step 236 is positive or not. Step 238 for determining the maximum value T among the lowest average received power values stored in step 234 when it is determined in step 238 that the phase shift change period T is not positive. And the step 240 of setting the phase shift change period of one phase shifter 70 to this value T and terminating the execution of this program. The difference dt in step 236 is a decrement time, and is set to about τ / 10, for example.

  When the initial setting is completed in this way, the system is in a steady operation state. FIG. 6 is a flowchart showing a control structure of a program for controlling the transmission power while maintaining the reception power in each sensor module, which is executed by the CPU 126 in the steady operation state.

  Referring to FIG. 6, this program is repeated with time Tp as a cycle, receives the amount of power stored in power storage element 156 in the current cycle from each sensor module, and stores the RAM 130 for each sensor module together with the amount of power received one cycle ago. Step 260, and after step 260, it is determined whether or not there is a sensor module in which the storage amount is reduced compared to one cycle before, and the control flow is branched based on the determination result, When the determination at step 262 is affirmative, step 268 for increasing the transmission power from each antenna by a predetermined difference ΔP, and when the determination at step 262 is negative, the charged amounts of all sensor modules are Step 264 for determining whether or not the flow has increased and branching the flow of control according to the result, and step 264 If the determination is affirmative, step 270 for reducing the transmission power from each antenna by ΔP, and after completion of steps 264, 268, and 270, wait until time Tp has elapsed after the start of processing from step 260. , When the time Tp has elapsed, control is returned to step 260 to start the next iteration.

  That is, the time Tp is a cycle in which the amount of power stored in the power storage element 156 is monitored and transmitted to the access point 44. The time Tp is set to about 30 seconds, for example.

[Operation]
Each phase shifter is controlled as follows by the program whose control structure is shown in FIG. In the present embodiment, the phase shift φ of the first phase shifter 70 changes so as to satisfy φ = (360 × t / T mod 360) with time t as described above. The same applies to the second phase shifter 72, but the change period is T / 2. Similarly, the phase shift change period after the third phase shifter is T / 4, T / 8,.

When there is some trigger for the initial setting, the CPU 126 of the access point 44 shown in FIG. 2 loads the program shown in FIG. 5 from the ROM 128 to the RAM 130 and starts its execution. In step 220, initial values of the phase shift period T and the oscillation frequency f of the oscillator 60 are set to T ₀ and f ₀ , respectively. Subsequently, steps 221, 224, and 226 are changed at a constant period until the value of the frequency f becomes larger than f _max , that is, until the determination result of step 228 becomes negative, power transmission is performed from the power transmission device 40. Each sensor module monitors a value (average received power) obtained by averaging the power supplied to the power storage element at a constant period, and transmits the information to the access point 44 via the CPU 164 (see FIG. 3). The access point 44 stores the lowest value in one cycle among the average received power of all the sensor modules in the RAM 130 together with the oscillation frequency of the oscillator 60 at that time. The access point repeats such processing at regular intervals. If the determination result in step 228 is negative, the lowest value of the average received power of each sensor module stored for each repetition in step 224 during the repetition is the maximum value throughout the entire repetition, and the value In step 230, the time constant τ of the sensor module that has transmitted the signal and the oscillation frequency f at that time are specified. In step 230, the oscillation frequency of the oscillator 60 is further set to the oscillation frequency f thus specified, and the phase shift period T is set to three times the time constant τ thus specified. In step 231, power is transmitted from each antenna according to the setting. Thereafter, the processing in steps 231, 232, 234 and 236 is repeated until the determination in step 238 is negative. That is, the process is repeated until the phase shift change period T becomes negative. When the phase shift change period T becomes negative, during the above-described repetition, the lowest value of the average received power from each sensor module stored in step 234 is specified as the maximum value throughout the repetition. The phase shift change period is set to the current period.

  The oscillation phase of the first phase shifter 70, the second phase shifter 72,..., And the m-th phase shifter 74 is increased to the frequency at which the oscillation frequency of the oscillator 60 is determined as described above. It is determined on the basis of the phase shift change period determined as described above. Thereafter, the oscillator 60, the first phase shifter 70, the second phase shifter 72,..., And the m-th phase shifter 74 operate according to these parameter values, so that the antennas 62, 64, 66,. The phase difference between any two of the radio waves for power transmission transmitted from 68 changes momentarily. That is, the phase difference between the radio waves oscillated by any two antennas 62, 64, 66,..., 68 changes as a function of time.

  Inside the automobile 30, the electrolytic intensity distribution at the position where each sensor module is arranged changes over time due to multipath interference and a change in the phase difference of radio waves from each antenna. Therefore, the power received at each sensor module varies as a function of time as shown in FIG. FIG. 7 shows that the number of antennas of the power transmission device 40 is 3, the received power from each antenna is equal, the phase shift change period of the first phase shifter 70 is T, and the phase shift change period of the second phase shifter 72. Shows the waveform of the received radio wave of the sensor module when T / 2 and the phase shift change period of the third phase shifter (not shown) is T / 4.

  If the phase difference of the radio wave from each antenna is fixed to a certain value, the power received by a certain sensor module may be extremely low due to interference, and the value may be insufficient for operation. If it is fixed to another value, the received power of another sensor module may be extremely low. By changing the phase difference of radio waves from each antenna as a function of time as in the above embodiment, the power received by each sensor module also changes with time. As a result, in terms of the time average received power, the average received power of any sensor module is leveled, and it can be expected that there will be no sensor module receiving only extremely low power. Since the direct current rectified by the rectifier circuit of the sensor is used after being stored in the storage element, the temporal variation of the received power is absorbed. The instantaneous received power is not important, and the average received power is important.

  Further, in the above-described embodiment, the oscillation frequency of the oscillator 60 and the phase shift change periods of the first phase shifter 70, the second phase shifter 72,. The value is set such that the minimum value for each period of the average received power of the sensor module is maximized, and the power transmission using the phase shift as described above is executed. Therefore, electric power can be transmitted more efficiently than when the phase difference of the transmission radio wave is merely changed with time using a phase shifter.

  Normally, by executing a program having a control structure shown in FIG. 6, if there is a sensor module with a reduced storage amount, the transmission power is increased by ΔP, and there is no sensor module with a reduced storage amount. If the amount of power storage is increased in all sensor modules, the transmission power is reduced by ΔP. Therefore, it is possible to reduce transmission power while keeping the amount of power stored in each sensor module within an appropriate range. Here, ΔP is an increment or decrement of the transmission power, and is set to about 0.5 dB, for example. Of course, this value depends on the design.

  Further, in the above-described embodiment, the processing of steps 230 to 238 in FIG. 5 is executed with the period Tp using the phase shift change period T of the phase shifter and the time constant τ determined by the filter and load of the rectifier circuit. A phase shift change period T when the value of the minimum received power in each period is maximized throughout the above repetition is found, and steady operation is performed in the phase shift change period T. If the high-frequency received power before rectification fluctuates over time, that is, if there is a difference between the peak instantaneous power and the average power, the fluctuation of the time varies with the same average power due to the non-linearity of the diode in the rectifier circuit. It is known that the rectification efficiency is higher than the rectification of a non-signal (a signal having no difference between the peak instantaneous power and the average power) (for example, refer to the reference cited at the end). However, a relationship such as “phase shift fluctuation period T = time constant τ / 10−τ × 3 obtained above” is necessary between the phase shift fluctuation period T and the time constant τ. Therefore, in the above embodiment, the optimum value of the phase shift change period is determined after the initial value of the phase shift change period is set to the time constant τ × 3 in step 230.

  As described above, according to the present embodiment, the phase shifter is provided between the antenna and the oscillator. Using this phase shifter, each phase shifter is controlled such that the phase difference between the electric power transmission radio waves oscillated from the antenna changes with time between any two radio waves. By transmitting power using radio waves whose phase difference changes with time in this way, even if there is multipath interference, the power received by each sensor module always changes with time. In addition, the wireless power received by each sensor module is leveled, and there is no sensor module whose received power is extremely deteriorated. Further, the oscillation frequency of the oscillator 60 and the phase shift change period of each phase shifter are values that maximize the minimum received power at each sensor module when power is transmitted at a constant period while changing the oscillation frequency. Is determined. Therefore, wireless power can be transmitted efficiently.

The method for determining the phase shift change period is not limited to the above. In the case of a digital phase shifter in which the phase shifter can change the phase shift between 0 ° and 360 ° in steps of Δφ = 360 ° / 2 ^M every discrete step, the phase shift change may be determined as follows. . In this case, the phase shift of each phase shifter can take a value of φ = i × Δφ (i = 0, 1,..., 2 ^M −1). The phase shift of the first phase shifter is changed in order from i = 0 to 2 ^M −1, and each step is held for a time T / 2 ^M. That is, the phase shift change period of the first phase shifter is T, and this is repeated as one period. Similarly, the phase shift of the first phase shifter 2 is sequentially changed from i = 0 to 2 ^M −1, but the phase shift change period is made to coincide with time T / 2 ^M. As a result, the second phase shifter repeatedly changes from 0 to 2 ^M −1 at each phase shift step of the first phase shifter. Similarly, the third phase shifter causes the phase shift change to make one round at each phase shift step of the second phase shifter. That is, the holding time of each step is changed so that the first phase shifter is T / 2 ^M , the second phase shifter is T / 2 ^2M , the third phase shifter is T / 2 ^4M . Repeat the phase shift control at intervals. Control of the digital phase shifter repeats the phase shift change cycle with a cycle in which the first phase shifter is T, the second phase shifter is T / 2, the third phase shifter is T / 3, and so on. You may control as follows. In addition to this, it goes without saying that there are various ways of determining the phase shift change period.

  It is desirable from the viewpoint of power transmission efficiency that the phase shift change period T is determined so as to be in the range of τ / 10 <T <3τ with respect to the time constant τ.

[Second Embodiment]
FIG. 8 is a block diagram of a portion related to the present invention of an automobile employing a wireless power system according to the second embodiment of the present invention. Referring to FIG. 8, this automobile 300 controls wireless power transmission system 302 according to the second embodiment and each part such as an engine of automobile 300 based on a sensor output given from wireless power transmission system 302. An engine / vehicle control unit 46.

  As in FIG. 1, the wireless power transmission system 302 includes a sensor module group 42 including a plurality of sensor modules, a power transmission device 310 that wirelessly transmits power to the sensor module group 42, and controls the power transmission device 310 to provide power. By changing the oscillation frequency of the radio wave for transmission, an access point 312 that performs power transmission so that the sensor modules of the sensor module group 42 are efficiently generated so that sensor modules whose reception power is extremely low are not generated. Including. The access point 312 has a function of receiving a sensor output signal from each sensor module of the sensor module group 42 and supplying the information to the engine / vehicle control unit 46. As in the first embodiment, the engine / vehicle control unit 46 uses this information to control the engine and other parts of the automobile 300.

  The plurality of sensor modules in the sensor module group 42 are installed at various positions in the automobile 300 as in the first embodiment.

  The power transmission device 310 receives a control signal from the access point 312 and a plurality of antennas 62, 64, 66,..., 68 for supplying power to the sensor module, and the antennas 62, 64, 66,. And a plurality of oscillators 320 to 326 arranged to supply oscillation signals to 68 input terminals. In the present embodiment, the power transmission device 310 includes m antennas 62, 64, 66,..., 68, and the plurality of oscillators 320 to 326 similarly include m oscillators. The antennas are distributed at various positions in the vehicle as much as possible.

  Each of the oscillators 320 to 326 is controlled such that any two oscillators oscillate oscillation signals having different frequencies. When these oscillators oscillate at different frequencies, the relative phase (phase difference) of radio waves transmitted from the antennas always changes. Therefore, the multipath interference situation always changes and does not remain in a specific multipath interference situation. As a result, unlike the first embodiment, there is no need to provide a phase shifter. That is, in the case of this embodiment, the power received by each sensor module naturally changes with time, and as in the case of the first embodiment, the reception power that is time-averaged is extremely low. The sensor module can be expected to disappear.

  Referring to FIG. 9, access point 312 includes antenna 124, radio circuit 122 and RAM 130, CPU 360, and ROM 362. As hardware, the CPU 360 and the ROM 362 are the same as the CPU 126 and the ROM 128 shown in FIG. In order to clearly indicate that the program stored in the ROM 362 is different from the program stored in the ROM 128, and therefore the programs executed by the CPU 126 and the CPU 360 are different, the reference numerals of the CPU and the ROM in FIGS. It is shown instead.

  An oscillator which is stored in the ROM 362 and executed by the CPU 360 so as to stably increase the minimum value of the average received power of the plurality of sensor modules 90, 92,..., 96 and to reduce variations in the average received power. The control structure of the program that executes the initial settings 320 to 326 will be described below.

Referring to FIG. 10, this program sets the oscillation frequency f _k (k = 1 to m) of each of the first oscillator 320 to the m-th oscillator 326 to f _k = f ₀ + kΔf ₀ (k = 1 to m). Step 380 is set. Here, f ₀ is the fundamental frequency of oscillation. Δf ₀ is an initial value of the basis of the frequency difference between the oscillators, and is set to 0.001 Hz, for example. That is, when any two oscillators are used, any oscillation frequency difference is an integral multiple of this base value Δf _{0 in} the initial state.

The program further includes a step 382 of transmitting power for a certain period at the oscillation frequency set to each of the first oscillator 320 to the m-th oscillator 326, and after step 382, the average reception for each certain period from each sensor module. Step 384 for receiving a signal indicating the magnitude of power and the time constant of the rectifier circuit; Step 386 for storing the minimum value of the average received power of each sensor module received in Step 384 together with the time constant at that time; and step 388 of adding the difference df the frequency _{f 0,} the value obtained by further adding Emuderutaf ₀ to the fundamental frequency _{f 0} that is incremented by the difference df is determined whether a predetermined maximum value _{f max} or less at step 388, Step 390 which returns control to Step 382 when the determination is affirmative.

This program is further executed when the determination in step 390 is negative, that is, when f ₀ + mΔf ₀ exceeds the maximum value f _max, and in the iterative process of steps 382 to 390, the lowest value stored in step 386 is executed. Step 392 for specifying the maximum average received power to be f ₀ and specifying the time constant τ received at that time, and the oscillation frequency f _k of the oscillators 320 to 326 are specified in step 392. And step 394 for redefining to f ₀ + kΔf (k = 1 to m) using the frequency f ₀ and the time constant τ. Here, Δf is a value defined as the reciprocal of 3 times τ specified in step 392. That is, Δf = 1 / (3τ).

  The program further includes step 396 for wirelessly transmitting power at an oscillation frequency according to a set value, and an average received power at each sensor module with respect to the power transmitted from each sensor module within a predetermined time with a set value. Step 398 for receiving the indicated value, Step 400 for storing the lowest value (minimum average received power) among the values for the average received power received at Step 398, together with the value of Δf at that time, And a step 402 of adding the difference dt ′. The difference dt ′ is a predetermined relatively small value.

The program further determines whether the control returns to step 398 when the condition that Δf is 10 / τ or less and f ₀ + mΔf is f _max or less is satisfied. Is negative, the lowest average received power stored in step 400 during the repetition of steps 398 to 404 is specified, and Δf at that time is stored in the RAM 130 as Δf _opt. Step 408 of re-defining the oscillation frequency f _k = f ₀ + Δf _opt (k = 1, 2,..., M) of the _k -th oscillator and ending the initialization process.

The wireless power transmission system 302 according to the present embodiment operates as follows. In the initialization process, the access point 312 determines the oscillation frequency of the oscillators 320 to 326 and the difference in oscillation frequency between adjacent oscillators (oscillators with adjacent oscillation frequencies). At this time, each sensor module monitors the average received power supplied to the storage element and transmits the information to the access point 312 via the CPU 360. The access point 312 receives this (step 384) and stores the lowest value of the average received power of all the sensor modules together with the current frequency setting and the time constant τ at that time (step 386). Then, the access point 312 changes the frequency of each of the oscillators 320 to 326 and again stores the minimum value of the average received power of each sensor module together with the current frequency and the time constant τ received simultaneously. This is repeated while changing the combination of the frequencies of the oscillators within the range of the corresponding frequency of the rectifier circuit of the sensor module (f ₀ + mΔf ₀ ≦ f _max ). If the decision result in the step 390 is NO, the combination of frequencies having the largest minimum received DC power among the lowest received DC power stored in the step 386 is specified, and the respective oscillators 320 to 326 are set to those frequencies.

Further, the base value Δf _opt of the difference between the oscillation frequencies of the oscillators used together with the frequency f ₀ is specified by the iterative process of steps 392 to 404 in FIG. 10 (step 406). Using the frequency f ₀ thus identified and the base value Δf _{opt of the} difference, thereafter, the transmission power is set so that the minimum value of the received power that each sensor module receives at a fixed period becomes the power more than the required power. Operation is performed by adjusting (Fig. 6). As a result, it is possible to perform efficient wireless power transmission in which the minimum value of the received power is equal to or higher than the required power and the power is not consumed unnecessarily while maintaining the charged amount of each sensor module within a predetermined range.

  FIG. 11 shows an example of a power waveform received by one of the sensor modules in the wireless power transmission system according to the above embodiment. In this example, the number of antennas on the transmitting side is 3, reception power from each antenna is equal, the frequency of the first oscillator 320 is f, the frequency of the second oscillator 322 is f + Δf, and a third oscillator (not shown). ) Is when f + 2Δf.

  In the above embodiment, each frequency is determined so as to have a difference of an integral multiple of a specific frequency Δf. The frequency difference Δf so that the reciprocal 1 / Δf of this value and the time constant τ determined by the filter and load of the rectifier circuit substantially coincide with each other, and the lowest received power of each sensor module becomes higher. Is optimized. Thereby, high rectification efficiency is obtained in each sensor module, and as a result, efficient power transmission is possible. In this way, by determining the base value of the frequency difference, the temporal variation period of the received power can be determined. As a result, also in the second embodiment, the rectification efficiency of the rectifier circuit can be increased as in the first embodiment.

In the embodiment described above, the oscillation frequency f ₀ or the difference Δf of the oscillation frequency is increased by a certain number for each repetition step in the repetition processing as the initialization processing (steps 226 in FIG. 5 and steps in FIG. 10). 402), the phase shift change period T is subtracted by a certain number for each repetitive step (step 236 in FIG. 5). However, the present invention is not limited to such an embodiment. The frequency increase / decrease in each step may be changed in any way as long as the values are different from each other. However, in order to obtain the initial value within a certain time, it is reasonable to define as in the present embodiment.

  Furthermore, in the second embodiment, the difference in oscillation frequency is constant between adjacent oscillation frequencies. However, the present invention is not limited to such an embodiment, and various differences may be used simultaneously. However, in this case as well, it is reasonable to specify the difference by gradually increasing or decreasing the difference as in the second embodiment.

  Furthermore, in the first and second embodiments, the difference between the oscillation frequency, the phase shift period, or the oscillation frequency that minimizes the power consumption is obtained as the initial process. However, the basic idea of the present invention is to change the multipath interference situation over time by changing the phase difference of radio waves from a plurality of antennas used for power transmission over time. The average power received by the sensor module over a certain period of time is that the effect of multipath interference is leveled in time. Therefore, as described in the first and second embodiments, it is not necessary to optimize the oscillator frequency, the phase shift period, the difference between the oscillation frequencies, and the like.

  In the above embodiment, after the initial value is determined, the minimum necessary power is transmitted while maintaining the minimum value of the transmission power by operating a program whose control structure is shown in FIG. ing. However, the present invention is not limited to such an embodiment. For example, by starting an initialization program whose control structure is shown in FIG. 5 or FIG. 10 at certain time intervals or at the start of the engine in the case of an automobile, the wireless power transmission system operates at any time according to the environment. It can also be made.

  Further, the above embodiment has described the case where wireless power transmission is used to supply power to the sensor module within the body of the automobile. However, the present invention is not limited to such an embodiment. A device in which a plurality of sensor modules are arranged in a metal casing having a certain size, and it is necessary to supply power to the sensor module in a device in which multipath interference of radio waves occurs. The present invention can be applied to any type. In particular, it is effective when applied to an apparatus in which the weight of the casing becomes a problem, for example, an aircraft, a railway vehicle, or the like.

  The embodiment disclosed herein is merely an example, and the present invention is not limited to the above-described embodiment. The scope of the present invention is indicated by each claim of the claims after taking into account the description of the detailed description of the invention, and all modifications within the meaning and scope equivalent to the wording described therein are included. Including.

  Reference: M. S. Trotter, J. D. Griffin, and G. D. Durgin, “Power-optimized waveforms for improving the range and reliability of RFID Systems,” in Proc. IEEE Int. Conf. RFID, 2009, pp. 80-87.

30, 300 Car 32, 302 Wireless power transmission system 40, 310 Power transmission device 42 Sensor module group 44, 312 Access point 46 Engine / vehicle control unit 60, 320, 322, 324, 326 Oscillator 62, 64, 66, 68, 124, 150, 152 Antenna 70, 72, 74 Phase shifter 90, 92, 96 Sensor module 122, 162 Radio circuit 126, 164, 360 CPU
128, 166, 362 ROM
130, 168 RAM
154 Rectifier circuit 156 Power storage element 158 DC-DC converter 160 Sensor element

Claims (12)

A wireless power transmission system that wirelessly transmits power for operating each wireless sensor module to a plurality of wireless sensor modules,
Multiple wireless transmit antennas;
Oscillation signal supply means for supplying an oscillation signal to each of the plurality of radio transmission antennas so that a phase difference between oscillation signals supplied between any two of the plurality of radio transmission antennas changes as a function of time; Including a wireless power transmission system. The oscillation signal supply means includes
An oscillation circuit that outputs an oscillation signal of a specified frequency;
A phase shifter that is connected between the output terminal of the oscillation circuit and the input terminals of the plurality of antennas and moves the phase of the oscillation signal output from the oscillation circuit by a specified phase;
A phase shifter that specifies, for each of the phase shifters, a phase change by the phase shifter such that the phase difference between any two outputs of the phase shifter varies as a function of time. The wireless power transmission system according to claim 1, comprising control means.   The wireless power transmission system further determines a frequency of an oscillation signal by the oscillation circuit so that a minimum value of average received power in each fixed period of each of the plurality of wireless sensor modules is maximized. The wireless power transmission system according to claim 2, further comprising an oscillation frequency determination unit that instructs The oscillation frequency determining means includes
A frequency indicating means for instructing the oscillation frequency to the oscillation circuit so as to change the frequency of the oscillation signal of the oscillation circuit at a constant cycle over a certain range;
While the change of the oscillation frequency of the oscillation circuit is instructed by the frequency instruction means, a reception power signal indicating an average reception power in a predetermined period immediately before the wireless sensor module is received from each of the plurality of wireless sensor modules. Signal receiving means for periodically receiving;
Minimum value specifying means for specifying a minimum value in each cycle of average received power represented by the received power signal periodically received by the signal receiving means;
Frequency specifying means for specifying an oscillation frequency of the oscillation circuit when the minimum value specified by the minimum value specifying means becomes maximum in a fixed period longer than the cycle;
The wireless power transmission system according to claim 2, further comprising: a frequency fixing unit that instructs the oscillation circuit to fix an oscillation frequency of the oscillation circuit to a frequency specified by the frequency specifying unit. The phase shifter control means, for each of the phase shifters, such that the phase difference between any two outputs of the phase shifter varies as a function of time with a period of time. Including a periodic phase shifter control means for specifying a phase change by the phase shifter;
The signal receiving means is a signal representing, from each of the plurality of wireless sensor modules, an average received power in a predetermined period immediately before the wireless sensor module and a time constant determined by a filter and a load of a rectifier circuit in the wireless sensor module. Means for periodically receiving
The wireless power transmission system further includes:
Time constant specifying means for specifying the time constant received by the means for receiving simultaneously with the oscillation frequency specified by the frequency specifying means;
The minimum value in each period specified by the minimum value specifying means based on the time constant specified by the time constant specifying means, the period of the phase shift change of the phase shifter by the phase shifter control means The wireless power transmission system according to claim 4, further comprising phase shift change period determining means for determining so as to be maximum. The oscillation signal supply means includes
A plurality of oscillation circuits which are provided corresponding to the plurality of radio transmission antennas and output oscillation signals of specified frequencies, respectively, and supply the corresponding radio transmission antennas among the plurality of radio transmission antennas;
2. The radio according to claim 1, further comprising: frequency control means for designating frequencies of the oscillation signals to the plurality of oscillation circuits so that the oscillation signals output from the plurality of oscillation circuits have different frequencies. Power transmission system.   The wireless power transmission system further determines each of the frequencies of the oscillation signals by the plurality of oscillation circuits so that the minimum value of the average received power of each of the plurality of wireless sensor modules in a certain period is maximized. The wireless power transmission system according to claim 6, further comprising an oscillation frequency determination unit that instructs each of the plurality of oscillation circuits. The oscillation frequency determining means includes
An oscillation circuit control means for changing the frequency of the oscillation signal by the plurality of oscillation circuits according to a combination of a plurality of different frequencies;
Receiving means for receiving a signal indicating average received power from each of the plurality of wireless sensor modules;
Each time the combination of the frequencies of the oscillation signals from the plurality of oscillation circuits is changed by the oscillation circuit control means, the minimum value of the average reception power received by the average reception power for each of the plurality of frequency combinations. First minimum value specifying means for specifying
Frequency determining means for determining a combination in which a maximum value is obtained among the minimum values of the average received power specified by the first minimum value specifying means for the combination of the plurality of frequencies;
The wireless power transmission system according to claim 7, further comprising: a frequency fixing unit that fixes a frequency of an oscillation signal from the plurality of oscillation circuits according to the combination determined by the frequency determination unit. Each time the reception means changes the frequency combination of the oscillation signals from the plurality of oscillation circuits by the oscillation circuit control means, from each of the plurality of wireless sensor modules, the average received power of the wireless sensor module, Means for receiving a signal indicating a time constant determined by a filter and a load of the rectifier circuit of the wireless sensor module;
The oscillation circuit control means includes means for changing the frequency of the oscillation signal by the plurality of oscillation circuits according to a plurality of combinations of a plurality of frequencies different from each other by a certain difference,
The wireless power transmission system further includes:
Of the time constants received by the means for receiving, the minimum value of the average received power specified by the first minimum value specifying means when a combination of frequencies determined by the frequency determining means is obtained. A time constant specifying means for specifying the time constant received at the same time;
Frequency redefinition means for redefining the combination of frequencies as a difference for each frequency in the combination of frequencies determined by the frequency determination means with a reciprocal of three times the time constant specified by the time constant specifying means The wireless power transmission system according to claim 8. Further, a difference control means for changing the frequency of the oscillation signal by changing the difference in a plurality of ways within a certain range;
A second minimum value specifying means for specifying a minimum value of the average received power received by the average received power every time the difference is changed by the difference control means;
Means for determining a difference such that the minimum value specified by the second minimum value specifying means is maximized while changing the difference in the plurality of ways;
Means for further redefining a combination of frequencies redefined by the redefining means using the difference determined by the means for determining the difference. . A computer program for causing a computer to function as the phase shifter control means according to any one of claims 2 to 5. A computer program for causing a computer to function as the frequency control means according to any one of claims 6 to 10.

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