CN115133666A - Bilateral capacitor array WPT system and adaptive critical coupling coefficient adjusting method - Google Patents

Bilateral capacitor array WPT system and adaptive critical coupling coefficient adjusting method Download PDF

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CN115133666A
CN115133666A CN202210696511.6A CN202210696511A CN115133666A CN 115133666 A CN115133666 A CN 115133666A CN 202210696511 A CN202210696511 A CN 202210696511A CN 115133666 A CN115133666 A CN 115133666A
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circuit
current
capacitor array
primary side
coupling coefficient
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张路
胡佳伟
杨奕
谢诗云
易皓鹏
李欢
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Chongqing University of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/005—Mechanical details of housing or structure aiming to accommodate the power transfer means, e.g. mechanical integration of coils, antennas or transducers into emitting or receiving devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
    • H02J50/12—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling of the resonant type
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
    • H02J7/04—Regulation of charging current or voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
    • H02J7/04—Regulation of charging current or voltage
    • H02J7/06—Regulation of charging current or voltage using discharge tubes or semiconductor devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02T90/10—Technologies relating to charging of electric vehicles
    • Y02T90/14—Plug-in electric vehicles

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

The invention provides a double-side capacitor array WPT system and a self-adaptive critical coupling coefficient adjusting method, wherein a primary side circuit is provided with a direct-current power supply, a high-frequency inverter circuit, a primary side adjustable capacitor array and a transmitting coil, and a secondary side circuit is provided with a receiving coil, a secondary side adjustable capacitor array, a rectifying module and a power load; the equivalent capacitor of the primary side adjustable capacitor array and the transmitting coil form a primary side resonant circuit, the equivalent capacitor of the secondary side adjustable capacitor array and the receiving coil form a secondary side resonant circuit, a current detection circuit for detecting primary side resonant current and a driving module for controlling the output voltage and the output current of the high-frequency inverter circuit to keep the same phase according to the primary side resonant current are further arranged in the primary side circuit; the bilateral capacitor array is used for adjusting natural resonant frequency, so that adjustment of a critical coupling coefficient of a system is realized, the transmission distance range is widened, remote constant-power constant-efficiency wireless power transmission is effectively realized, the circuit topology is simple, and the implementation is convenient.

Description

Bilateral capacitor array WPT system and adaptive critical coupling coefficient adjusting method
Technical Field
The invention relates to a wireless power transmission technology, in particular to a bilateral capacitor array WPT system and a self-adaptive critical coupling coefficient adjusting method.
Background
Wireless Power Transfer (WPT) technology realizes non-electrical contact transmission of electrical energy through media such as magnetic fields, electric fields, lasers, microwaves and the like. The technology can effectively solve the problems of limited flexibility and potential safety hazard of equipment caused by the traditional wired power taking mode. At present, the method is applied to the fields of electric automobiles, consumer electronics, household appliances and the like.
At present, a resonant wireless power transmission technology is mostly adopted in the research field of WPT systems, and the technology is mainly realized based on a magnetic resonance principle and an electric field resonance principle. The system can maintain higher transmission efficiency and output power within a certain transmission distance. But the system is sensitive to transmission distance, and the relative position of the coils. Once the coil position is shifted, a large change in transmission efficiency and output power will result. For the above problems, most of the scholars at home and abroad optimize the influence caused by the coil offset by two strategies, namely a frequency control strategy and an impedance matching strategy.
The literature is as follows: zhang wave, sparse and promising, Wu Li Hao, etc. the wireless power transmission technology is urgent to solve the problems and countermeasures [ J ] power system automation 2019,43(18):1-12. the WPT system is theoretically modeled by series-series (SS) and parallel-parallel (PP), and a maximum power frequency tracking method is provided, which determines the optimal working frequency at the moment by applying small disturbance to the frequency and measuring the output frequency change on the basis.
The literature: xueming, Yangqingxin, Chapengcheng, etc. the wireless power transmission technology applies the current research situation and the key problem [ J ] the report of electrotechnics 2021,36(08): 1547-. The working frequency is adjusted in real time by detecting the phase difference between the output voltage of the inverter on the primary side and the current of the transmitting coil, so that the phase difference between the output voltage of the inverter and the current of the transmitting coil is always in a Zero Phase Angle (ZPA) mode.
The literature: liyang, Shishao, Liuxueli, etc. magnetic field coupling type wireless power transmission coupling mechanisms are reviewed in [ J ] electrotechnical Commission.2021, 36(S2):389-403. WPT system based on LCC-S analyzes that the cross coupling between multiple coils of load can shift the operating frequency of the system from the free resonant frequency, thereby causing the transmission efficiency to be greatly reduced. On the basis, a capacitor array is added on the primary side, and a proper compensation capacitor is selected by utilizing a radial basis function neural network, and an experimental result shows that the system can be improved to 78% at the lowest transmission efficiency point of 34%. The above documents optimize the changed power and efficiency, but the transmission efficiency and output power of the system as a whole still have large amplitude changes.
In 2017, Assawaworrit et al firstly applied the space-Time (PT) symmetry theory to the WPT system, and the research utilized an operational amplifier circuit to construct a nonlinear saturated gain-negative resistance and utilized a self-excited oscillation system of the operational amplifier to have a frequency-selective characteristic, namely, the reflection impedance of the secondary side is regarded as a frequency-selective network which is only related to the frequency of the output voltage and is not related to the amplitude phase thereof; more importantly, the amplitude is not influenced by the transmission distance; the system can achieve a constant output power and a constant transmission frequency. However, the output power of the system is low, namely only 19.7mW, because the output voltage amplitude of the operational amplifier is low. But since it can achieve constant output power, constant transmission efficiency, a large number of researchers have been motivated to study PT symmetry in WPT applications. In subsequent research, because the output power of the operational amplifier is low, it is proposed to use the inverter to output the output voltage and current with the same phase, so as to construct the nonlinear gain, and the essence is to construct the forced response system.
The literature: wang Youyan, Zhaiyan, Qiliang, key technical research on magnetic coupling resonant wireless power transmission [ J ]. Shanghai electrical technology [ 2019,12(01):1-6 ] the PT symmetrical theory is applied to a double-coupling (magnetic field coupling and electric field coupling) WPT system, and the system is theoretically deduced by using a coupling-mode theory (CMT), which indicates that the system can realize constant output power and constant transmission efficiency at a longer distance compared with a single-coupling system, but the overall output transmission efficiency is lower.
Disclosure of Invention
Based on the above requirements, the primary objective of the present invention is to provide a bilateral capacitor array WPT system, which only introduces two groups of adjustable capacitor arrays, and reduces the critical coupling coefficient of the system through the adjustable capacitor arrays, thereby implementing remote constant-power and constant-efficiency wireless power transmission.
In order to achieve the purpose, the invention adopts the following specific technical scheme:
the utility model provides a bilateral capacitance array WPT system, includes former limit circuit and vice limit circuit, its key lies in: the primary side circuit is provided with a direct current power supply, a high-frequency inverter circuit, a primary side adjustable capacitor array and a transmitting coil, and the secondary side circuit is provided with a receiving coil, a secondary side adjustable capacitor array, a rectifying module and a power load;
the equivalent capacitor of the primary side adjustable capacitor array and the transmitting coil form a primary side resonant circuit, the equivalent capacitor of the secondary side adjustable capacitor array and the receiving coil form a secondary side resonant circuit, a current detection circuit for detecting primary side resonant current and a driving module for controlling the output voltage and the output current of the high-frequency inverter circuit to keep the same phase according to the primary side resonant current are further arranged in the primary side circuit; the secondary side adjustable capacitor array and the primary side adjustable capacitor array are used for changing corresponding equivalent capacitance values according to the change of the load, so that the system is maintained in an astronomical time symmetry state.
Optionally, the high frequencyThe inverter circuit adopts a switch tube Q 1 And a switch tube Q 2 And a switching tube Q 3 And a switching tube Q 4 The full-bridge inverter circuit is formed.
Optionally, the current detection circuit comprises a current sensor and a zero-crossing comparator.
Optionally, the natural resonant angular frequency of the primary resonant circuit is set to be omega p The natural resonant angular frequency of the secondary resonant tank is omega s When the working angular frequency of the resonant current output by the high-frequency inverter circuit is omega, the system is according to omega p ＝ω s And controlling the working states of the primary side adjustable capacitor array, the secondary side adjustable capacitor array and the high-frequency inverter circuit by the constraint relation not equal to omega, so that the system is maintained in a space-time symmetric state.
Optionally, the primary adjustable capacitor array and the secondary adjustable capacitor array are both formed by connecting multiple paths of capacitor elements in parallel, and each path of capacitor element is connected with a circuit breaker.
Based on the system, the invention also provides a self-adaptive critical coupling coefficient adjusting method of the double-sided capacitor array WPT system, which is characterized by comprising the following steps:
s1: collecting primary side resonance current through the current detection circuit;
s2: judging the deviation value of the current input impedance of the system and the input impedance under the space-symmetric time symmetry state according to the current primary side resonance current;
s3: when the deviation value obtained in the step S2 is greater than the preset threshold, changing a system critical coupling coefficient by adjusting equivalent capacitance values of the primary adjustable capacitor array and the secondary adjustable capacitor array, so that the current system coupling coefficient is greater than or equal to the system critical coupling coefficient;
s4: and adjusting the working angular frequency of the system according to the adjusted natural resonant angular frequencies of the primary side resonant circuit and the secondary side resonant circuit, so that the system is maintained in an astronomical time symmetry state again, and returning to the step S1 for cyclic execution.
Optionally, the current input impedance Z of the system in step S2 1 ' in accordance with
Figure RE-GDA0003823582550000041
Calculation of where V p Is the fundamental wave component i 'of the output voltage of the high-frequency inverter circuit' p Current transmit coil current; input impedance Z under the state of space-time symmetry 1 According to the following
Figure RE-GDA0003823582550000042
Calculation of where L p To transmit the self-inductance value of the coil, R p Is a parasitic resistance value of the transmitting coil, L s For receiving coil self-inductance value, R s For receiving coil parasitic resistance value, R eq For electrical load equivalent resistance, deviation value delta ═ Z 1 -Z' 1 |。
Optionally, in step S3, when the deviation value obtained in step S2 is greater than the preset threshold, the current coupling coefficient of the system is measured by the LCR bridge and is taken as the critical coupling coefficient k of the system a Then according to
Figure RE-GDA0003823582550000043
To determine the equivalent capacitance value C of the secondary side adjustable capacitor array s Wherein L is s For receiving coil self-inductance value, R s For receiving coil parasitic resistance value, R L And finally, adjusting the equivalent capacitance value of the primary side adjustable capacitor array according to the constraint relation that the natural resonance angular frequency of the primary side resonance circuit is equal to the natural resonance angular frequency of the secondary side resonance circuit.
Optionally according to
Figure RE-GDA0003823582550000051
Determining the angular frequency of operation of the system, where ω 0 Is the natural resonant angular frequency of the primary resonant circuit and the secondary resonant circuit, k is the current coupling coefficient of the system,
Figure RE-GDA0003823582550000052
representing the secondary side circuit quality factor.
The invention has the following effects:
according to the self-adaptive critical coupling coefficient adjusting method of the bilateral capacitor array WPT system, the natural resonant frequency is adjusted by the bilateral capacitor array, so that the critical coupling coefficient of the system is adjusted, the transmission distance range is widened, the long-distance constant-power constant-efficiency wireless electric energy transmission is effectively realized, the circuit topology is simple, and the implementation is convenient.
Drawings
In order to more clearly illustrate the detailed description of the invention or the technical solutions in the prior art, the drawings that are needed in the detailed description of the invention or the prior art will be briefly described below.
FIG. 1 is a diagram of a system architecture in an embodiment of the present invention;
FIG. 2 is an equivalent circuit diagram of FIG. 1;
FIG. 3 is a control flow diagram of adaptive critical coupling coefficient adjustment in an embodiment of the present invention;
FIG. 4 is a graph showing the variation of the operating frequency with the change of the coupling coefficient;
FIG. 5 is a waveform diagram of an input signal before adjustment by the adjustable capacitor array;
FIG. 6 is a waveform diagram of an input signal after adjustment by the adjustable capacitor array;
FIG. 7 is a waveform diagram of an output signal of the tunable capacitor array before tuning;
FIG. 8 is a waveform diagram of the output signal after adjustment by the adjustable capacitor array;
FIG. 9 is a diagram of a current comparison relationship between the transmitting coils before and after adjustment by the adjustable capacitor array;
FIG. 10 is a graph of the transmission efficiency and coupling coefficient change before and after tuning of the tunable capacitor array;
fig. 11 is a graph of output power versus coupling coefficient change before and after adjustment of the adjustable capacitor array.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and therefore are only used as examples, and the protection scope of the present invention is not limited thereby.
It is to be noted that, unless otherwise specified, technical or scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art to which the present invention belongs.
As shown in fig. 1, this embodiment provides a two-sided capacitor array WPT system, which includes a primary side circuit and a secondary side circuit, where the primary side circuit is provided with a dc power supply, a high-frequency inverter circuit, a primary side adjustable capacitor array, and a transmitting coil, the secondary side circuit is provided with a receiving coil, a secondary side adjustable capacitor array, a rectification module, and an electric load, an equivalent capacitor of the primary side adjustable capacitor array and the transmitting coil form a primary side resonant circuit, an equivalent capacitor of the secondary side adjustable capacitor array and the receiving coil form a secondary side resonant circuit, and the secondary side adjustable capacitor array and the primary side adjustable capacitor array are configured to change corresponding equivalent capacitance values according to a change of the load, so that the system is maintained in a state of parity time symmetry.
As can be seen from FIG. 1, L p ，L s ，R p ，R s The self-inductance and the parasitic resistance are respectively corresponding to the transmitting coil and the receiving coil; m is the mutual inductance between the transmitting coil and the receiving coil; q 1 ，Q 2 ，Q 3 ，Q 4 4 switch tubes for high-frequency inverter circuit, adopting switch tube Q 1 And a switching tube Q 2 And a switch tube Q 3 And a switching tube Q 4 A full-bridge inverter circuit is formed; u shape d Is the input voltage of the DC power supply; d 1 ，D 2 ，D 3 ，D 4 4 diodes of the rectifying module; r L Is a load resistor; i.e. i p ，i s The resonance currents corresponding to the transmitting coil and the receiving coil are respectively.
In order to realize the realization of the negative resistance in the primary circuit, a current detection circuit for detecting the primary resonant current and a driving module for controlling the output voltage and the output current of the high-frequency inverter circuit to keep the same phase according to the primary resonant current are further arranged in the primary circuit, as can be seen from fig. 2, the current detection circuit comprises a current sensor and a zero-crossing comparator, and the embodiment adopts the high-frequency inverter circuit (4 MOS transistors Q and Q are used for realizing the realization of the negative resistance in the primary circuit) 1 、Q 2 、Q 3 、Q 4 Connected) to a DC power supply U d Inverting to obtain high-frequency voltage, and obtaining output current signal i by current sensor p And then the zero-crossing comparator feeds the zero-crossing signal back to a driving module of the high-frequency inverter to generate a corresponding driving signal. Through the operation, the output voltage and the output current of the full-bridge inverter can be kept in the same phase, so that the full-bridge inverter is equivalent to nonlinear saturation gain, namely negative resistance-R N 。
For simplicity of analysis, the circuit shown in fig. 1 can be simplified into the structure shown in fig. 2, and the natural resonant angular frequency of the primary side resonant tank is set to be ω p The natural resonant angular frequency of the secondary resonant circuit is omega s The working angular frequency of the resonant current output by the high-frequency inverter circuit is omega, and if the system is maintained in an astronomical time symmetry state, the system is according to omega p ＝ω s And controlling a constraint relation not equal to omega, wherein the specific analysis process is as follows:
the circuit shown in fig. 2 can be expressed as follows according to kirchhoff's voltage law:
Figure RE-GDA0003823582550000071
the above equation can be expressed as:
Figure RE-GDA0003823582550000072
where k is the coupling coefficient, ω 0 At natural resonant frequency, the above formula
Figure RE-GDA0003823582550000073
Real number solution, then it needs to satisfy:
Figure RE-GDA0003823582550000074
then there are:
Figure RE-GDA0003823582550000075
separating the real part and the imaginary part in the formula (4) can obtain:
Figure RE-GDA0003823582550000076
if the system is in PT symmetrical state, it is necessary to meet the condition that omega is not equal to omega 0 Therefore, the following are:
Figure RE-GDA0003823582550000081
further, it can be obtained from formula (5):
Figure RE-GDA0003823582550000082
wherein
Figure RE-GDA0003823582550000083
Which is effectively the quality factor of the secondary side.
If ω is made to 1,2 For real numbers, then:
Figure RE-GDA0003823582550000084
in practical conditions, the coil quality factors in the WPT system are high, so that the inequality condition is automatically satisfied by the equation (8).
Will be provided with
Figure RE-GDA0003823582550000085
k a Is called critical coupling coefficient, k is more than or equal to k a The region of (a) is referred to as a strongly coupled region.
Converting formula (2) to:
Figure RE-GDA0003823582550000086
from formula (10):
Figure RE-GDA0003823582550000087
an expression of the output power P and the transmission efficiency η of the WPT system in the PT symmetric state can be obtained from the equation (11):
Figure RE-GDA0003823582550000091
Figure RE-GDA0003823582550000092
in the formula, V P Is the fundamental component of the inverter output voltage.
From the equation (12) and the equation (13), it can be seen that the WPT system in the PT symmetric state has the transmission efficiency only with the self-inductance L of the load resistor, the transmitting coil and the receiving coil s 、L p (ii) a Parasitic resistance R s 、R p Correlated, independent of the coupling coefficient k. And the output power is only equal to the self-inductance L of the load resistor, the transmitting coil and the receiving coil s 、L p (ii) a Parasitic resistance R s 、R p (ii) a And V p Correlated, independent of the coupling coefficient k.
Equation (9) can be expanded as:
Figure RE-GDA0003823582550000093
as can be seen from equation (14), the self-inductance (L) due to the adjustment coil s ) Accordingly, parasitic resistance is affected and there is coupling between the parameters. Therefore, the secondary side compensation capacitor C can be changed s Realizing a critical coupling coefficient k a Considering the PT symmetrical state, when the coil parameters are not changed, oneThe secondary side and the secondary side have the same resonant frequency. Therefore, in order to adjust the critical coupling coefficient by changing the secondary side resonance capacitance, the capacitance C of the primary side and the secondary side p ，C s Must be changed simultaneously and satisfy that the natural resonant frequencies of the primary and secondary sides are equal. In specific implementation, the primary adjustable capacitor array and the secondary adjustable capacitor array are formed by connecting multiple paths of capacitor elements in parallel, each path of capacitor element is connected with a circuit breaker, different equivalent capacitance values are realized through the closed state of the switch, and in order to realize wide-range adjustment of the capacitor arrays, the resistance values of all the adjusting capacitors are different.
The following is to analyze the influence of the equivalent capacitance value of the adjustable capacitor array on the output power and the transmission efficiency, specifically as follows:
changing equivalent capacitance value C of switch adjustable capacitor array p ，C s The essence of (1) is to adjust the natural resonant frequency of the transmitting side and the receiving side, and to make the secondary side impedance equivalent to the primary side according to kirchhoff's voltage law, and to be recorded as Z 21 Then, there are:
Figure RE-GDA0003823582550000101
from the negative resistance-R N Seen from its input impedance Z 1 Comprises the following steps:
Figure RE-GDA0003823582550000102
changing omega to omega 1，2 Substitution of formula (16) gives:
Figure RE-GDA0003823582550000103
therefore, when the WPT system is in PT symmetrical state, the input impedance Z of the WPT system is 1 Angular frequency omega of natural resonance 0 Independently, it has only a self-inductance L corresponding to the transmitting coil and the receiving coil p ,L s And a parasitic resistance R p 、R s And negativeThe load resistance Req is relevant. If the input impedance is not changed, Z 1 The current i in the primary side transmitter coil p And is not changed.
According to equation (11), if the transmitting coil current is constant, the current i in the receiving coil p Without change, the current i in the receiving coil s Also, the output power P and the transmission efficiency η will not change because of the invariance. In summary, the equivalent capacitance value C of the tunable capacitor array is changed p ，C s And adjusting the natural resonant frequency of the transmitting side and the receiving side, adjusting the working frequency of the system accordingly, and not influencing the transmission efficiency eta and the output power P of the system when the system reaches the PT symmetrical state again.
Based on the conclusions from the previous analysis, when k < k a When the system is in the weak coupling area, the system is no longer in the PT symmetrical state. The transmission efficiency η and the output power P of the system are then susceptible to the coupling coefficient k. But may adopt changing the tunable capacitor array C P ，C s To reduce the critical coupling coefficient k a . Then substituting the adjusted volume value into a formula (7) to obtain a corresponding working angular frequency omega' 1，2 And the system is in PT symmetrical state again. Thereby enabling the system to achieve constant output power and constant transmission power over a greater transmission distance. Therefore, in order to detect whether the WPT system is in the strong coupling region, this embodiment further provides an adaptive critical coupling coefficient adjustment method for the double-sided capacitor array WPT system, which only needs to measure the current i in the primary side transmitting coil p According to the formula (17), if the whole WPT system is in PT symmetrical state, i.e. in strong coupling region, the input impedance of the system is Z 1 Using the measured transmit coil current i' p At this time, the input impedance Z 'is calculated' 1 ：
Figure RE-GDA0003823582550000111
Suppose that:
Δ＝|Z 1 -Z' 1 | (19)
when delta is less than or equal to epsilon, the system is considered to be in a PT state, namely in a strong coupling area, and epsilon is the error magnitude. When Δ > ε, then the system is considered to be not in the PT state, i.e., in the weak coupling region, ε is the magnitude of the error.
Therefore, as shown in fig. 3, in this embodiment, the method for adjusting an adaptive critical coupling coefficient of a double-sided capacitor array WPT system specifically includes the following steps:
s1: collecting primary side resonance current through a current detection circuit;
s2: judging the deviation value of the current input impedance of the system and the input impedance under the space-time symmetric state according to the current primary side resonance current;
s3: when the deviation value obtained in the step S2 is greater than the preset threshold, changing a system critical coupling coefficient by adjusting equivalent capacitance values of the primary adjustable capacitor array and the secondary adjustable capacitor array, so that the current system coupling coefficient is greater than or equal to the system critical coupling coefficient;
s4: and adjusting the working angular frequency of the system according to the adjusted natural resonant angular frequencies of the primary side resonant circuit and the secondary side resonant circuit, so that the system is maintained in an astronomical time symmetry state again, and returning to the step S1 for cyclic execution.
Specifically, in step S3, when the deviation value obtained in step S2 is greater than the preset threshold, the current coupling coefficient of the system is measured by the LCR bridge and is taken as the critical coupling coefficient k of the system a Then according to
Figure RE-GDA0003823582550000112
To determine the equivalent capacitance value C of the secondary side adjustable capacitor array S And finally, adjusting the equivalent capacitance value of the primary side adjustable capacitor array according to the constraint relation that the natural resonance angular frequency of the primary side resonance circuit is equal to the natural resonance angular frequency of the secondary side resonance circuit.
When the natural resonant frequency of the primary side and the secondary side is adjusted through the change of the resonant capacitor, the method is as follows:
Figure RE-GDA0003823582550000121
and determining the working angular frequency of the system.
In order to verify the correctness of the system and the method proposed by the present invention, a simulation circuit as shown in fig. 2 is built in Simulink. Specific simulation parameters are shown in table 1, wherein the parasitic resistances of the transmitter coil and the receiver coil are empirical values based on experimental data in the previous period.
TABLE 1 simulation parameters
Figure RE-GDA0003823582550000122
Substituting the simulation parameters in table 1 into equation (7) can obtain the variation graph of the operating frequency with the change of the coupling coefficient as shown in fig. 4. It can be seen from FIG. 4 that at k<At 0.15, the system is in a weak coupling state, and the working frequency f is equal to f 0 At this time, the transmission efficiency and transmission power of the system are no longer stable. When k is more than or equal to 0.15, the system is in a strong coupling state, the working frequency is bifurcated, and the working frequency f is equal to f 1,2 The transmission efficiency and transmission power of the system are kept stable.
In order to verify the conclusion, the input and output waveforms, the output power and the transmission efficiency of the system before and after the adjustment of the adjustable capacitor array are respectively compared in the experiment. C before adjustment p ,C s 77.6nF, corresponding natural resonant frequency f 0 57.1kHZ, critical coupling coefficient k a 0.15. Conditioned C' p ,C' s 77.6nF, corresponding natural resonant frequency f 0 95.4kHZ, critical coupling coefficient k a The simulation results are shown in fig. 5-11, when the value is 0.09.
As can be seen from fig. 5 and 6, after the adjustment of the tunable capacitor array, the adjustment of the natural resonant frequency is achieved, and the inverter output voltage at the input side and the transmitting coil current have no phase angle difference, thereby confirming that, after the adjustment of the natural resonant frequency, the inverter output voltage V at the input side is V when the system is in the PT symmetric state in And a transmitting coil current i s In the ZPA state.
From FIGS. 7, 8 andfig. 9 shows that the natural resonant frequency of the system changes after the adjustable capacitor array is adjusted, but the system reaches the symmetric state of PT again after the working frequency of the system is adjusted according to the frequency obtained by equation (7), and the equivalent load voltage U is equal to the PT symmetric state L And the amplitude of the current of the receiving coil is unchanged, and the amplitude of the current of the receiving coil and the amplitude of the current of the transmitting coil are different only in frequency.
As is apparent from fig. 10 and 11, when k is 0.15, the system has an efficiency trip point and a power trip point unless the natural resonant frequency, i.e., the tunable capacitor array, is adjusted. As can be seen from FIG. 11, the critical coupling coefficient of the system before the tuning of the tunable capacitor array is 0.15, and when the transmission distance of the system is too far, k is<k a At this time, the system is no longer in the PT symmetric state, and the transmission efficiency at this time is drastically reduced. After the adjustable capacitor array is adjusted, the critical coupling coefficient of the system can be reduced to 0.09, so that the transmission efficiency of 87.2% can still be maintained in the range of k being 0.09-0.15. Similarly, k is the distance over which the system is transmitted before the tunable capacitor array is tuned<k a The output power at this time is greatly increased, and this phenomenon occurs due to mode overlapping. Sudden power jump can increase the output current greatly, and in severe cases, the load can be burnt. After the adjustable capacitor array is adjusted, the critical coupling coefficient of the system can be reduced to 0.09, so that the system can still maintain 300W output power in the range of k being 0.09-0.15.
In summary, the bilateral capacitor array WPT system and the adaptive critical coupling coefficient adjusting method fully disclose the change of the natural resonant frequency, do not affect the output power and the transmission efficiency of the WPT system under PT symmetry, and adjust the natural resonant frequency by using the bilateral capacitor array, thereby realizing the adjustment of the critical coupling coefficient, widening the transmission distance range, and having simple circuit topology and convenient implementation.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention, and such changes and modifications are intended to be included within the scope of the appended claims and the description.

Claims (9)

1. The utility model provides a bilateral capacitance array WPT system, includes former limit circuit and vice limit circuit, its characterized in that: the primary side circuit is provided with a direct current power supply, a high-frequency inverter circuit, a primary side adjustable capacitor array and a transmitting coil, and the secondary side circuit is provided with a receiving coil, a secondary side adjustable capacitor array, a rectifying module and a power load;
the equivalent capacitor of the primary side adjustable capacitor array and the transmitting coil form a primary side resonant circuit, the equivalent capacitor of the secondary side adjustable capacitor array and the receiving coil form a secondary side resonant circuit, a current detection circuit for detecting primary side resonant current and a driving module for controlling the output voltage and the output current of the high-frequency inverter circuit to keep the same phase according to the primary side resonant current are further arranged in the primary side circuit; the secondary side adjustable capacitor array and the primary side adjustable capacitor array are used for changing corresponding equivalent capacitance values according to the change of the load, so that the system is maintained in an astronomical time symmetry state.
2. The double-sided capacitive array WPT system according to claim 1, wherein: the high-frequency inverter circuit adopts a switching tube Q 1 And a switching tube Q 2 And a switching tube Q 3 And a switching tube Q 4 The full-bridge inverter circuit is formed.
3. The double-sided capacitive array WPT system according to claim 2, wherein: the current detection circuit comprises a current sensor and a zero-crossing comparator.
4. A bilateral capacitive array WPT system as claimed in any one of claims 1 to 3, wherein: setting the natural resonant angular frequency of the primary resonant tank to omega p The natural resonant angular frequency of the secondary resonant circuit is omega s When the working angular frequency of the resonant current output by the high-frequency inverter circuit is omega, the system is according to omega p ＝ω s And controlling the working states of the primary side adjustable capacitor array, the secondary side adjustable capacitor array and the high-frequency inverter circuit by the constraint relation not equal to omega, so that the system is maintained in a space-time symmetric state.
5. The double-sided capacitive array WPT system according to claim 1, wherein: the primary side adjustable capacitor array and the secondary side adjustable capacitor array are formed by connecting multiple paths of capacitor elements in parallel, and each path of capacitor element is connected with a circuit breaker.
6. An adaptive critical coupling coefficient adjusting method based on the double-sided capacitor array WPT system of any one of claims 1 to 5, characterized by comprising the following steps:
s1: collecting primary side resonance current through the current detection circuit;
s2: judging the deviation value of the current input impedance of the system and the input impedance under the space-symmetric time symmetry state according to the current primary side resonance current;
s3: when the deviation value obtained in the step S2 is greater than the preset threshold, changing a system critical coupling coefficient by adjusting equivalent capacitance values of the primary adjustable capacitor array and the secondary adjustable capacitor array, so that the current system coupling coefficient is greater than or equal to the system critical coupling coefficient;
s4: and adjusting the working angular frequency of the system according to the adjusted natural resonant angular frequencies of the primary side resonant circuit and the secondary side resonant circuit, so that the system is maintained in an astronomical time symmetry state again, and returning to the step S1 for cyclic execution.
7. The adaptive critical coupling coefficient regulation method for the double-sided capacitive array WPT system as claimed in claim 6, wherein the current input impedance Z of the system in step S2 is 1 ' in accordance with
Figure FDA0003702804500000021
Calculation of where V p Is the fundamental wave component i 'of the output voltage of the high-frequency inverter circuit' p Current transmit coil current; input impedance Z under space-time symmetric state 1 According to
Figure FDA0003702804500000022
Calculation of where L p For the self-inductance value of the transmitting coil, R p Is a parasitic resistance value of the transmitting coil, L s For receiving coil self-inductance value, R s For receiving coil parasitic resistance value, R eq For electrical load equivalent resistance, deviation value delta ═ Z 1 -Z 1 '|。
8. The adaptive critical coupling coefficient adjusting method of a double-sided capacitive array WPT system as claimed in claim 6, wherein in step S3, when the deviation obtained in step S2 is greater than a preset threshold, the current coupling coefficient of the system is measured by LCR bridge and taken as the critical coupling coefficient k of the system a Then according to
Figure FDA0003702804500000023
To determine the equivalent capacitance value C of the secondary side adjustable capacitor array s Wherein L is s For receiving coil self-inductance value, R s For receiving coil parasitic resistance value, R L And finally, adjusting the equivalent capacitance value of the primary side adjustable capacitor array according to the constraint relation that the natural resonance angular frequency of the primary side resonance circuit is equal to the natural resonance angular frequency of the secondary side resonance circuit.
9. The bilateral capacitor of claim 8The adaptive critical coupling coefficient adjusting method of the array WPT system is characterized by comprising the following steps of
Figure FDA0003702804500000031
Determining the angular frequency of operation of the system, where ω 0 Is the natural resonance angular frequency of the primary side resonance loop and the secondary side resonance loop, k is the current coupling coefficient of the system,
Figure FDA0003702804500000032
representing the secondary side circuit quality factor.
CN202210696511.6A 2022-06-20 2022-06-20 Bilateral capacitor array WPT system and adaptive critical coupling coefficient adjusting method Pending CN115133666A (en)

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