JP7066046B2 - Wireless power transmission - Google Patents

Description

The present invention relates to a wireless power transmission device that transmits power to a power receiving device in a non-contact manner, that is, wirelessly.

In recent years, non-contact power transmission technology for electric vehicles, industrial equipment, portable electronic equipment, etc. has been attracting attention. In particular, this technique is useful in the fields of electric appliances such as electric toothbrushes and electric shavers used around water, cordless telephones, mobile phones, etc., and has been put into practical use in some products.

As a non-contact power transmission device currently in practical use, an electromagnetic induction type wireless power transmission device using electromagnetic induction between a power transmission coil provided in a power transmission device and a power reception coil provided in the power reception device is known. Has been done. In this electromagnetic induction type wireless power transmission device, in order to improve the power transmission efficiency, it is necessary to arrange the coils on the power transmission side and the power reception side close to each other, and there is a problem that the distance at which power can be wirelessly transmitted is short. Have.

Therefore, a technique for wirelessly supplying electric power to a device several meters away has also been developed. It is a magnetic field resonance coupling type wireless power transmission technology that performs power transmission using a magnetic field resonance coupling (magnetic field resonance) between a transmission coil and a power receiving coil.

Magnetic resonance coupling is a non-radiative and coupled power transmission principle, in which the power transmission coil of the power transmission resonance circuit and the power reception coil of the power reception resonance circuit are coupled (resonant) by a magnetic field in a state where the power transmission resonance circuit and the power reception resonance circuit resonate with each other. ), And power transmission is performed. The magnetic field resonance coupling is more efficient than the electromagnetic induction method, and can transmit power with high efficiency even when a large air gap or misalignment occurs. In the magnetic field resonance coupling method, the resonance frequencies of the transmission resonance circuit and the power reception resonance circuit are matched, and the impedance is optimized for operation, so that high-efficiency power transmission is possible even if the coupling coefficient is very small.

The magnetic resonance coupling type wireless power transmission device includes a power transmission device having a power transmission resonance circuit composed of a power transmission coil and a capacitor, and a power reception device having a power reception resonance circuit composed of a power reception coil and a capacitor. Power is transmitted from the power transmitting device to the power receiving device in a non-contact manner by utilizing the fact that the coil and the power receiving coil resonate in a magnetic field. That is, when the transmission resonance circuit and the power reception resonance circuit resonate at the resonance frequency in the magnetic field resonance coupling state, high power transmission efficiency can be obtained.

In Patent Document 1, in a magnetic field resonance coupling type non-contact power transmission device, the resonance frequencies of the transmission resonance circuit and the power reception resonance circuit are matched, and the frequency of the drive voltage of the transmission resonance circuit is also matched with the resonance frequency. , A technique for resonating a power transmitting coil and a power receiving coil in a magnetic field is disclosed.

However, the resonance frequency of the power transmission resonance circuit, the resonance frequency of the power reception resonance circuit, and the drive frequency of the power transmission resonance circuit are all the aging deterioration of the circuit element, the operating environment temperature, the distance between the power transmission coil and the power reception coil, and others. It fluctuates due to various factors such as the surrounding environment. For example, as the distance between the power transmission coil and the power reception coil deviates from the optimum distance, the mutual inductance changes, the coupling coefficient changes, and the resonance frequency also deviates slightly. Further, when a foreign substance such as a metal piece is inserted between the power transmission coil and the power reception coil, the coupling coefficient changes and the resonance frequency changes. Further, the Q value of the resonance circuit also changes due to the fluctuation of the power load of the power receiving device, which contributes to the fluctuation of the resonance frequency.

Patent Document 1 discloses that the output frequency of the drive voltage of the transmission resonance circuit can be freely adjusted, but the output frequency of the drive voltage is adjusted according to the fluctuation of the resonance frequency of the transmission resonance circuit and the power reception resonance circuit. Is not disclosed to automatically follow. Therefore, it is considered that the power transmission resonance circuit operates in a state where the drive voltage frequency is set to a predetermined value, but there is a problem that the power transmission efficiency is lowered if the drive frequency of the power transmission resonance circuit remains a constant value.

Patent Document 2 describes a switching element that outputs a drive voltage of a predetermined frequency to a transmission resonance circuit, a current detection unit that detects a current flowing through the transmission resonance circuit, and a time from when the switching element is turned on to a current zero crossing point. A magnetic resonance coupling type non-contact power transmission device including a timer for measuring the frequency and a frequency setting unit for setting the frequency of the drive voltage of the transmission resonance circuit based on the time measured by the timer is disclosed.

Further, Patent Documents 3 and 4 disclose a technique of detecting a zero cross point of the resonance current of the power transmission resonance circuit, switching the switching element at the timing of the zero cross of the resonance current, and continuing the resonance state.

Japanese Unexamined Patent Publication No. 2010-130878 Japanese Unexamined Patent Publication No. 2012-120253 Japanese Unexamined Patent Publication No. 2019-54629 Japanese Unexamined Patent Publication No. 2018-183056

The techniques disclosed in Patent Documents 2 to 4 are based on the premise that the zero crossing point of the resonance current of the power transmission resonance circuit can be accurately detected, but in reality, the current detection is delayed. Further, after the zero cross point is detected, there is a delay in the switching operation of the switching element by the command from the control unit.

Therefore, in the method of driving the switching element after detecting the zero crossing point of the resonance current, there is a problem that the switching element is driven at a frequency lower than the optimum driving frequency because a delay occurs in principle. When the drive frequency is relatively low, the delay is not a problem, but when the drive frequency is relatively high, the delay of the above-mentioned current detection circuit and drive circuit cannot be ignored, and the frequency deviates from the optimum resonance frequency. As a result of being driven by the frequency, the transmission power is reduced and the transmission efficiency is reduced.

Also, in an electromagnetic induction type wireless power transmission device, it is expected that the transmission power will be increased and the power transmission efficiency will be improved by creating a high resonance state by using the transmission resonance circuit consisting of the transmission coil and the capacitor. However, if the drive frequency deviates from the resonance frequency of the transmission resonance circuit, the transmission power will decrease and the transmission efficiency will decrease.

According to the present invention, even if the operation of each circuit constituting the power transmission device is delayed, the switching circuit is accurately switched and operated at the zero crossing point of the resonance current of the power transmission resonance circuit, so that the frequency is higher than the appropriate frequency. It is an object of the present invention to provide a wireless transmission device capable of supplying a voltage to a transmission resonance circuit.

The wireless power transmission device according to the present invention is a wireless power transmission device that transmits power to a power receiving device by non-contact, and uses a resonance circuit having a transmission coil and a capacitor and power supplied from a power source to generate a high frequency in the resonance circuit. A switching circuit configured to be able to alternately switch between a first switching mode and a second switching mode in order to apply a voltage, a control unit that controls switching of the switching mode of the switching circuit, and the resonance circuit. A current detection unit for detecting the generated resonance current is provided.

Based on the detected value of the resonance current by the current detection unit, the control unit may perform the next zero cross point of the actual current waveform of the resonance current before the actual current waveform of the resonance current reaches the next zero cross point. It may be provided with a current waveform prediction unit for predicting. In the present specification, the zero crossing point of the high-frequency current waveform means a time point at which the high-frequency current becomes zero when the high-frequency current changes from positive to negative or negative to positive, that is, a predetermined time on the time axis.

Further, the control unit may be configured to switch the switching mode of the switching circuit at the predicted next zero crossing point. If it is predicted that the next zero crossing point will be the time T, the control unit may be configured to switch the switching mode of the switching circuit at the time T, but the switching mode may be switched only slightly. In consideration of this delay, the time T is the time when the switching mode of the switching circuit is switched by configuring the control unit so as to output the switching control command of the switching mode of the switching circuit immediately before the time T. It is preferable to match with.

Preferably, the current waveform predictor can be configured to sample the current detected by the current detector at predetermined time intervals that are sufficiently small with respect to the resonant current. According to this, the current waveform of the resonance current can be grasped more accurately. The sampling interval can be preferably 1/16 or less, more preferably 1/32 or less, and further preferably 1/64 or less of one cycle of the resonance current.

In the wireless power transmission device according to the present invention, the current waveform predictor predicts the next zero cross point based on the measurement time from a predetermined time point to the detection of the peak of the detected current waveform based on the detected value of the resonance current. It may be configured as follows. For example, the measurement time is t, the time corresponding to the delay of the peak detection operation of the detected current waveform by the current detection circuit is Δt, and the time when 2 × (t−Δt) has elapsed from a predetermined time point is set as the next zero crossing point. Can be predicted.

The predetermined time point may be the time point when the control unit performs the switching immediately before the switching mode, or the time when the current waveform prediction unit outputs the switching mode switching command most recently. It may be the previous zero cross point predicted for the previous switching mode switching. In any case, appropriate correction processing can be performed in predicting the next zero crossing point.

The current waveform predictor may be configured to detect the peak of the detected current waveform of the resonance current based on the differential value of the detected current waveform, or the absolute value of the detected current may increase. It can also be detected by detecting that the current has turned from a declining state to a decrease. In consideration of the influence of noise and the like, it is also possible to set the peak detection condition that the absolute value of the detected current starts to decrease and then continuously decreases a predetermined number of times. In this case, since the current detection time of a predetermined number of times has elapsed, it is preferable to calculate the measurement time assuming that the time point before the lapse of the current detection time of the predetermined number of times is the peak of the detected current waveform.

Further, the current waveform prediction unit is next to the actual current waveform of the resonance current based on the time when the absolute value of the detection value of the resonance current by the current detection unit transitions from the reference value or more to the reference value or less. It can also be configured to predict the zero crossing point. According to this, it is determined whether or not the transition has occurred from above the reference value to below the reference value in a region where the amount of current fluctuation per unit time is larger than near the peak of the current waveform, preferably immediately before the next zero crossing point of current. be able to.

The reference value may be a constant value regardless of the amplitude of the resonance current. However, even if the amplitude of the resonance current fluctuates due to various factors, the time from the time when the absolute value of the detected value of the resonance current transitions from the reference value or more to less than the reference value to the current zero crossing point is made uniform. Therefore, preferably, the reference value for the previous period can be obtained by calculation based on the peak value immediately before the detected current waveform based on the detected value of the resonance current. For example, the reference value can be obtained by multiplying the absolute value of the peak value immediately before the detected current waveform by a predetermined coefficient greater than 0 and less than 1. The predetermined coefficient can be determined in consideration of the delay in the detection operation of the current detection circuit, the delay in the operation of the control unit and the switching circuit, and the like.

According to the present invention, the zero cross point of the actual resonance current waveform of the resonance circuit is predicted in advance, and the switching mode of the switching circuit is switched at the predicted zero cross point to transmit a high frequency voltage having a more appropriate frequency. It can be applied to a resonance circuit, and the transmission power can be improved or the transmission efficiency can be improved.

It is a schematic block block diagram of the wireless power transmission apparatus which concerns on one Embodiment of this invention. It is a schematic circuit diagram of the wireless power transmission device. It is an overall operation flowchart of the wireless power transmission device. It is a waveform diagram which shows the resonance current waveform and the switching waveform in the conventional power transmission apparatus. It is a waveform diagram which shows the resonance current waveform and the switching waveform in the power transmission apparatus by this invention. It is a graph which measured transmission power and transmission efficiency while changing a switching frequency. It is a flowchart of the current waveform prediction part which concerns on embodiment.

FIG. 1 shows the configuration of a non-contact power transmission device according to an embodiment of the present invention. This device is composed of a power transmission device 10 and a power reception device 20, and transmits electric power from the power transmission device 10 to the power reception device 20 by a magnetic field resonance coupling method in a non-contact manner. Typically, one power transmission device 10 and one power receiving device 20 operate as a pair, but it is also possible to configure the power transmission device 10 to be capable of transmitting power to a plurality of power receiving devices 20. The power transmission device 10 may be configured to transmit electric power to one power receiving device 20, or the plurality of power transmitting devices 10 and the plurality of power receiving devices 20 may be configured to be simultaneously usable.

The power receiving device 20 has a power receiving resonance circuit 21 that receives power transmitted from the power transmission resonance circuit 13 of the power transmission device 10, a rectifier circuit 22 that rectifies the received power and converts it into DC power, and a rectified DC power. It is provided with an output unit 23 that outputs to a built-in or external load. The power receiving device 20 may have the same device configuration as the power transmitting device 10, and the switching circuit 12 is used as a rectifier circuit 22 composed of a diode bridge by turning off all the switching elements Q1 to Q4 of the switching circuit 12 described later. Can be made to work.

The power receiving resonance circuit 21 is configured as an LC resonance circuit in which a power receiving coil and a capacitor are connected in series or in parallel. The configuration is such that the resonance frequency is substantially the same as that of the power transmission resonance circuit 13, and the magnetic field generated from the power transmission resonance circuit 13 is received and converted into AC power. The rectifier circuit 22 rectifies the AC power received by the power receiving resonance circuit 21 and converts it into DC power. The rectifier circuit 22 is configured by a diode bridge or the like. The output unit 23 can be configured to perform smoothing, voltage conversion, or the like as necessary when outputting electric power to the load.

The power transmission device 10 includes a power supply 11, a switching circuit 12 that converts the power supplied from the power supply 11 into high-frequency drive power for non-contact transmission, and a transmission coil L that converts the high-frequency drive power output by the switching circuit 12 into a magnetic field. It is provided with a power transmission resonance circuit 13 having a power transmission resonance circuit 13, a current detection circuit 14 for detecting a resonance current flowing through the power transmission resonance circuit 13, and a control unit 15 for generating and outputting a drive command signal voltage of the switching circuit 12. Further, the control unit 15 performs switching drive control of the current waveform prediction unit 16 that predicts the zero cross point of the resonance current based on the detection value of the resonance current by the current detection circuit 14, and the switching drive 12 at the predicted current zero cross point. It is provided with a drive control unit 17.

The power source 11 is typically a power source that supplies DC power, and can be composed of a converter that converts a commercial AC power source into a DC power source, a storage battery, or the like.

The switching circuit 12 is configured to be able to alternately switch between a first switching mode and a second switching mode in order to apply a high frequency voltage to the power transmission resonance circuit 13 using the electric power supplied from the power supply 11. Typically, the switching circuit 12 is composed of a half-bridge or full-bridge configuration inverter, and has a voltage polarity applied to the transmission coil L in the first switching mode and a voltage applied to the transmission coil L in the second switching mode. The polarity can be configured to be positive or negative inverted.

FIG. 2 shows a simplified circuit configuration example of a power transmission device 10 having a switching circuit 12 composed of a full-bridge inverter, and the switching circuit 12 includes four FETs as switching elements Q1 to Q4. More specifically, the first leg on the left side of the figure and the second leg on the right side of the figure are connected in parallel between the power supply 11 and the ground, and the first switching element is attached to the upper arm (power supply side arm) of the first leg. Q1 is provided, a second switching element Q2 is provided on the lower arm (ground side arm) of the first leg, a third switching element Q3 is provided on the upper arm of the second leg, and the lower arm of the second leg is provided. Is provided with a fourth switching element Q4.

Each of the switching elements Q1 to Q4 operates on / off according to the drive command signal voltage output from the drive control unit 17. In the first switching mode, the first and fourth switching elements Q1 and Q4 are turned on, and the second and third switching elements Q2 and Q3 are turned off, whereby the power supply voltage is operated via the switching element Q1. Is supplied to one terminal of the power transmission resonance circuit 13. In the second switching mode, the second and third switching elements Q2 and Q3 are turned on, and the first and fourth switching elements Q1 and Q4 are turned off, whereby the power supply voltage is operated via the switching element Q3. Is supplied to the other terminal of the transmission resonant circuit.

When switching the switching mode, a dead time is provided for turning off all the switching elements Q1 to Q4 in order to prevent the power supply from being short-circuited to the ground. In each switching mode, a high-frequency drive voltage composed of a square wave is typically output to the resonance circuit 13 by continuing the on or off operation of each switching element, but the switching element to be turned on is controlled by PWM control. By pulse-driving, a high-frequency drive voltage having a waveform close to a sine wave may be output to the resonance circuit 13.

When the switching elements Q1 to Q4 are configured by the N MOSFET, the body diodes included in the N MOSFET are all arranged in the direction in which the current flows only from the ground side to the power supply side. As a result, when all the switching elements Q1 to Q4 are in the off operating state, the switching circuit 12 functions as a full-wave rectifier composed of four diodes and rectifies the high-frequency power on the resonance circuit 13 side. It can be supplied to the power supply 11 side. Therefore, it is also possible to operate the power transmission device 10 as a power receiving device.

The transmission resonance circuit 13 is configured as an LC resonance circuit in which a transmission coil L and a capacitor C are connected in series, and when a high-frequency drive voltage generated by the switching circuit 12 is supplied, a resonance voltage and a resonance current having the same period are transmitted. A high-frequency magnetic field is generated in the coil L. The resonance current generated in the power transmission coil L has substantially the same phase as the high frequency drive voltage, but the resonance voltage has a lead phase of 90 degrees. When the resonance frequency (f = 1 / 2π√LC) of the resonance circuit 13 and the frequency of the high frequency drive voltage (that is, the switching frequency of the switching circuit 12) are the same, the amplitudes of the resonance voltage and the resonance current are maximized.

In the power transmission device 10 of the present embodiment, by switching the switching mode of the switching circuit 12 at the zero crossing point of the resonance current, resonance is performed while applying positive feedback, and the frequency of the high frequency drive voltage becomes the resonance frequency of the resonance circuit 13. It will converge. Since this operating principle is the same as that disclosed in Patent Document 4, detailed description thereof will be omitted.

The current detection circuit 14 is a circuit that detects the resonance current flowing through the resonance circuit 13, and may be an appropriate circuit such as a method using a shunt resistor, a method using a current sensor, or a method using a Hall element. In the illustrated example, the potential difference between both ends of the shunt resistor R connected in series with the power transmission coil L is amplified by the amplifier 14a, and the output voltage is input to the analog signal input terminal of the control unit 15 as the detection value of the resonance current. ..

The control unit 15 predicts the next zero cross point of the actual current waveform of the resonance current before the actual current waveform of the resonance current reaches the next zero cross point based on the detected value of the resonance current by the current detection circuit 14. A waveform prediction unit 16 and a drive control unit 17 that outputs a drive command signal voltage to each of the switching elements Q1 to Q4 so as to switch the switching mode of the switching circuit at the predicted next zero crossing point are provided. In the illustrated embodiment, the drive control unit 17 is driven by the switching control unit 17a that generates and outputs the control signals of the switching elements Q1 to Q4, and the switching control units Q1 to Q4 based on the control signals output by the switching control unit 17a. It is equipped with a gate driver 17b that outputs a command signal voltage. In FIG. 2, the current waveform prediction unit 16 and the switching control unit 17a are shown as a functional block diagram, but these are configured by a single microprocessor, FPGA, or a circuit integrally mounted on a substrate. It may be configured by physically different circuits. Further, the switching control unit 17a and the gate driver 17b may also be configured by a driver LSI having these functions integrally, or may be configured as physically different circuits. Further, the current waveform prediction unit 16, the switching control unit 17a, and the gate driver 17b may be configured by a single driver LSI or the like.

The current waveform prediction unit 16 is a circuit unit that predicts in advance the next zero crossing point of the resonance current waveform as the optimum timing for switching based on the detection value of the resonance current by the current detection circuit 14, and is the core of the present invention. It is the part that makes up. The current waveform prediction unit 16 is preferably configured by a microprocessor having an analog input and a digital output, but can also be configured by an FPGA or an individual electronic circuit.

Further, the current waveform prediction unit 16 may be configured to output a switching mode switching command to the drive control unit 17 at the timing when the predicted current zero cross point is reached, or data on the predicted current zero cross point may be output. It can also be configured to be passed to the drive control unit 17 in advance so that the drive control unit 17 voluntarily switches the switching mode at the current zero crossing point.

The drive control unit 17 generates signals necessary for driving the switching elements Q1 to Q4 of the switching circuit 12. That is, a voltage for driving the gates of the switching elements Q1 to Q4 of the switching circuit 12 is generated, and a dead time is generated so that the through current does not flow in the switching circuit 12. The drive control unit 17 may be configured such that the dead time processing and other correction processing of the switching circuit 12 are performed by the switching control unit 17a or the gate driver 17b.

Next, the operation of the power transmission device 10 according to the embodiment will be described with reference to the overall operation flowchart of FIG.

The power transmission device 10 detects the resonance current of the power transmission resonance circuit 13 and performs a self-excited oscillation operation in which the next switching is performed using the detected resonance current waveform. Oscillation operation does not start. Therefore, after the start, the switching circuit 12 is driven at a predetermined initial frequency to start power transmission (S101). As the initial frequency, the resonance frequency f obtained from the rated inductance of the power transmission coil L and the rated capacity of the capacitor C can be used. It is also possible to store the frequency at the time of the previous power transmission operation and start power transmission using that frequency as the initial frequency. In one example, the resonance frequency of the power transmission resonance circuit 13 may be 70 to 100 kHz.

Next, it waits until the power transmission becomes stable (S102). It may wait until a predetermined time elapses, or it may wait until the resonance voltage and / or the resonance current of the transmission resonance circuit becomes stable.

Next, the initial power transmission operation by driving the switching circuit 12 at a constant initial frequency is switched to the self-excited oscillation operation using the current waveform prediction unit 16 according to the present invention (S103).

After that, the power transmission operation is continued until a predetermined power transmission end condition (for example, when a power transmission end operation is performed or an abnormality is detected) is satisfied (S104).

Here, the power transmission operation according to the present invention and the power transmission operation by the conventional power transmission device not provided with the current waveform prediction unit will be described in comparison with reference to FIGS. 4 and 5. The switching waveform shows the gate signals (drive command signal voltage) of the first and fourth switching elements Q1 and Q4, and the gate signals of the second and third switching elements Q2 and Q3 are of Q1 and Q4. It is not shown because it has the opposite phase of the gate signal.

As shown by the dotted line in FIG. 4, when switching is performed without delay at the current zero crossing point, the switching waveform has no delay, and the resonance current waveform becomes the target current waveform. The target current waveform is in an ideal resonance state in which switching is performed at a frequency that matches the resonance frequency when the frequency characteristics of the transmission resonance circuit 13 fluctuate due to various external factors and magnetic resonance coupling with the power receiving resonance circuit 21. It is a resonance current waveform at the time. By switching the gate signals of Q1 and Q4 from on to off and the gate signals of Q2 and Q3 from off to on at the zero crossing point where the resonance current changes from positive to negative, the operation is performed in the next half cycle. The next half cycle is also operated in the same manner, and the gate signals of Q2 and Q3 are switched from on to off and the gates of Q1 and Q4 are switched from off to on at the zero cross point where the resonance current changes from negative to positive. By repeating this operation, the resonance state continues at an ideal frequency that matches the resonance frequency of the resonator.

However, since the conventional power transmission device performs the next switching immediately after detecting the zero crossing point of the resonance current waveform, as shown by the solid line in FIG. 4, before switching is performed from the current zero crossing point of the actual resonance current waveform. A delay Δt occurs. As a result of switching not being performed even if the current zero crossing point is exceeded due to this delay Δt, the actual resonance current waveform is distorted and its period becomes longer by the amount corresponding to the delay Δt.

The current detection circuit 14 takes a certain amount of time to detect a change in current, and the delay Δt becomes large particularly when a current transformer or a Hall element is used as a current sensor. In the method using a shunt resistor, the delay Δt is relatively small, but when an element such as an operational amplifier 14a is used, a delay always occurs.

Further, since the delay Δt also occurs at the next current zero crossing point, the delay Δt accumulates every half cycle, and the cycle of the actual resonance current waveform is larger than the cycle of the ideal target current waveform. Is also 2Δt longer. When there is a delay Δt in the current detection in this way, switching continues at a frequency lower than the ideal resonance frequency.

Although it has been described that only the current detection is delayed, the delay is further increased because the operation of the drive control unit 17 is actually delayed.

FIG. 6 is a graph in which transmission power and transmission efficiency are measured while changing the switching frequency using a non-contact wireless power transmission device in which the resonance frequency is adjusted to 85 kHz for both the transmission resonance circuit and the power reception resonance circuit. At 85 kHz, both transmission power and transmission efficiency are maximum. When the drive control method of the conventional zero-cross point detection type power transmission device is used as it is, it operates at 84.3 kHz, which is lower than the ideal resonance frequency, which is the maximum power transmission power and power transmission efficiency. It fell below the maximum value. Since the delay time changes depending on the current sensor and drive control circuit used, the frequency of self-excited oscillation changes, but since there is always a delay, it always operates at a frequency lower than the ideal resonance frequency, and the transmitted power Both transmission efficiency will decrease. When the frequency used for non-contact power transmission is relatively low, the delay of the drive control unit 17 is relatively not a problem, but when the frequency is high, the delay of the operation of the drive control circuit 17 also becomes a problem.

On the other hand, the resonance current waveform when the control unit 15 including the current waveform prediction unit 16 according to the present embodiment is used is shown in FIG. 5 in comparison with the resonance current waveform by the conventional current zero cross point detection method. The control unit 15 according to the present embodiment predicts the resonance current waveform based on the detection value of the resonance current by the current detection circuit 14, and considers the delay of the current sensor 14a and the drive control circuit 17, and actually resonates the current waveform. The drive command signal voltage is output to the switching circuit 12 so that switching can be performed accurately at the zero crossing point.

FIG. 7 shows an example of an operation flowchart of the current waveform prediction unit 16, and the operation of the current waveform prediction unit 16 is performed after the start of the self-oscillation operation (S103) shown in FIG.

The current waveform prediction unit 16 starts counting for measuring the time from a predetermined time point, for example, the latest last switching command output time point with respect to the drive control unit 17 (S201). Since the last switching command output does not exist at the time of the first operation, it is possible to measure the time from an appropriate time point such as measuring the time from the start time of the self-excited oscillation operation.

Next, while continuing the count, it waits until the peak of the resonance current waveform is detected (S202). The peak detection method of the resonance current waveform may be appropriate, but for example, the time when it is detected that the absolute value of the detected current has changed from the increasing state to the decreasing state is determined as the peak of the resonance current waveform. can. At this time, when it is assumed that noise is mixed in the current waveform, it can be determined that the peak is detected when the absolute value of the detected current decreases continuously a plurality of times.

Further, the time point at which the differential value of the resonance current waveform satisfies a predetermined condition can be determined as the peak of the resonance current waveform. Since the resonance current waveform is a roughly sine wave, the differentiated waveform is a roughly cosine wave. Therefore, as an example of the predetermined condition, it is the time when the differential value becomes close to 0. Since the fact that the differential value becomes almost 0 coincides with the peak time of the current waveform, it waits until the peak of the current waveform is reached by waiting until the differential value becomes almost 0.

When the peak of the resonance current waveform is detected, the counter for time measurement is read out, and as shown in step (1) in FIG. 5, the time from the latest last switching command output time to the peak of the resonance current waveform is calculated. (S203).

Next, using the time from the time of the previous switching command output to the peak of the resonance current waveform, the zero cross point of the next resonance current waveform is predicted as shown in step (2) in FIG. 5 (S204). For example, when the time from the previous switching command output time to the peak of the resonance current waveform is t, and the current sensor delay and the drive control circuit delay are Δt, the ideal switching waveform has no delay from the previous switching command output time. The period until the next zero crossing point of the resonance current waveform can be calculated by (t−Δt) × 2. Further, the period may be set in consideration of the switching loss of the semiconductor.

When the prediction of the next zero cross point of the resonance current waveform is completed, the drive control unit 17 waits until the predicted current zero cross time (S205), and at the predicted current zero cross time as shown in step (3) in FIG. A switching command signal is output to (S206).

The current waveform prediction unit 16 repeatedly continues the above operations of steps S201 to S206 during the power transmission operation. As a result, switching is continued with a waveform equivalent to the switching waveform without delay, and wireless power transmission is controlled by the resonance frequency of the resonance circuit, so that high power and high efficiency wireless power transmission can be performed.

The current waveform prediction unit 16 can also be configured to predict the next zero crossing point by a method other than the peak detection of the resonance current waveform. For example, if it is detected that the absolute value of the detected value of the resonance current by the current detection circuit 14 has transitioned from a predetermined threshold value A or more to less than the threshold value A, a switching command is immediately output to the drive control unit 17 and the following is performed. It can be configured to predict that switching will occur exactly at the zero crossing point of the current.

The threshold A may be a fixed value set in advance, but resonance is performed so that switching can be performed accurately at the next zero crossing point even when the amplitude of the resonance current waveform fluctuates due to operating conditions or the like. It can be obtained by multiplying the amplitude of the peak immediately before the current waveform by a predetermined coefficient greater than 0 and less than 1. The coefficient is used when the degree of delay in the operation of the current detection circuit 14 and the drive control unit 17 is measured in advance and it is detected that the absolute value of the detected value of the resonance current has transitioned from the threshold value A or more to the threshold value A or less. By outputting the switching command to the drive control unit 17 at the immediate timing, it is possible to set so that the switching is accurately performed at the next current zero crossing point by just canceling the above delay.

The present invention is not limited to the above embodiment, and the design can be changed as appropriate. For example, in the above embodiment, the present invention is applied to a magnetic field resonance coupling type wireless power transmission device, but the present invention can also be applied to an electromagnetic induction type wireless power transmission device having a resonance circuit on the power transmission side. Further, the present invention can be particularly suitably used for an underwater vehicle, for example, a wireless power transmission device such as a submarine or an underwater drone, which tends to change the optimum power transmission frequency due to a position change in seawater.

10 Wireless power transmission device 11 Power supply 12 Switching circuit 13 Power transmission resonance circuit 14 Current detection circuit 15 Control unit 16 Current waveform prediction unit 17 Drive control unit

Claims (6)

A resonant circuit with a power transmission coil and a capacitor,
A switching circuit configured to be able to alternately switch between a first switching mode and a second switching mode in order to apply a high frequency voltage to the resonance circuit using electric power supplied from a power source.
A control unit that controls switching of the switching mode of the switching circuit,
A current detection unit that detects the resonance current generated in the resonance circuit, and
In a wireless power transmission device that transmits power to a power receiving device by non-contact
The control unit determines the next zero cross point of the actual current waveform of the resonance current before the actual current waveform of the resonance current reaches the next zero cross point based on the detected value of the resonance current by the current detection unit. A wireless power transmission device including a current waveform predictor for predicting, and configured to switch the switching mode of the switching circuit at the next zero crossing point predicted. In the wireless power transmission device according to claim 1,
The current waveform predictor is configured to predict the next zero crossing point based on the measurement time from a predetermined time point to the detection of the peak of the detected current waveform based on the detected value of the resonant current. Device. In the wireless power transmission device according to claim 2,
The time point is a time point when the control unit performs switching immediately before the switching mode, that is, a wireless power transmission device. In the wireless power transmission device according to claim 2 or 3.
The current waveform prediction unit is a wireless power transmission device configured to detect the peak of the detected current waveform of the resonance current based on the differential value of the detected current waveform. In the wireless power transmission device according to claim 1,
The current waveform prediction unit is the next zero crossing point of the actual current waveform of the resonance current based on the time when the absolute value of the detection value of the resonance current by the current detection unit transitions from the reference value or more to the reference value or less. A wireless power transmission device that is configured to predict. In the wireless power transmission device according to claim 5,
The reference value is a value obtained by calculation based on the peak value immediately before the detected current waveform based on the detected value of the resonance current, and is a wireless power transmission device.

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