A Wireless Power Transmission System and Design Method Resistant to Position Offset

Abstract

The present invention discloses a wireless power transmission system resistant to position offset and a design method thereof. The wireless power transmission system includes a signal generator, a power amplifier, a voltage-controlled variable capacitor, a resonant capacitor, a compensation capacitor, a current-controlled variable inductor, a transmitting coil, a receiving coil, and a load. The present invention also specifically discloses a design method for the wireless power transmission system resistant to position offset. By using the voltage-controlled variable capacitor and the current-controlled variable inductor, without using a feedback network and active devices, the frequency characteristics of the system are changed, and a high transmission efficiency is maintained when the relative positions of the transmitting coil and the receiving coil change. It has high safety and broad market prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless power transmission, and relates to a wireless power transmission system resistant to position offset and a design method thereof. Background Art

[0002] Like wireless communication technology, getting rid of the bondage of physical media and realizing wireless power transmission has been a beautiful pursuit of mankind for many years. Wireless power transmission technology, also known as non-contact power transmission technology, refers to a way of energy transmission in which electrical energy is transmitted from a power source to a load without direct electrical contact. Wireless power transmission technology can be divided into electric field coupling type, microwave radiation type, magnetic coupling resonance type, etc. In the electric field coupling type of wireless power transmission technology, metal plates on the power source side and the load side form a capacitor, and the electric field of the capacitor is used for power transmission, but it can only be applied to low-power occasions. The microwave radiation type of wireless power transmission technology uses far-field for transmission, and its transmission distance is much larger than the geometric size of the transmission device, but its directivity is poor, and the transmission power is generally relatively small. The magnetic coupling resonance type of wireless power transmission technology transmits energy through near-field magnetic coupling between two inductance coils resonating at the same frequency. Compared with the electric field coupling type of wireless power transmission, the transmission distance has been greatly extended; compared with the electric field coupling type and the microwave radiation type of wireless power transmission technology, it has less impact on the electromagnetic environment and has a larger transmission power, so it has received more and more extensive attention and research.

[0003] Although the magnetic coupling resonance type of wireless power transmission technology has increased the transmission distance, especially the axial distance, and its practicability has been greatly improved. However, this technology requires the relative positions of the transmitting coil and the receiving coil to be fixed. Once the relative positions of the coils change, the coupling factor between the transmitting coil and the receiving coil will change violently, the power transmission efficiency will drop rapidly, and the transmission performance will deteriorate extremely. In order to enable the wireless power transmission system to automatically compensate for the influence caused by the change in the relative positions of the transmitting coil and the receiving coil, frequency tracking control or impedance adjustment devices can be adopted. Frequency tracking control is to make the power supply frequency automatically adjusted to maintain the resonant state of the system; the impedance adjustment device is to add adjustable elements to dynamically adjust the input impedance of the system to make the input impedance maintain a pure resistance state. However, the existing methods all require active devices and feedback networks, which greatly increase the complexity and failure rate of the system, and the cost will also increase significantly. Summary of the Invention

[0004] The object of the present invention is to provide a wireless power transmission system resistant to position offset and a design method thereof for the problem that when the relative positions of the transmitting coil and the receiving coil change, the system performance drops significantly due to the change in the coupling factor.

[0005] The present invention is realized through the following technical solutions:

[0006] A wireless power transmission system resistant to position offset, characterized in that it comprises a signal generator, a power amplifier, a voltage-controlled variable capacitor, a resonant capacitor, a compensation capacitor, a current-controlled variable inductor, a transmitting coil, a receiving coil and a load;

[0007] The output end of the signal generator is connected to the input end of the power amplifier. The voltage-controlled variable capacitor and the transmitting coil are connected in series to form a transmitting circuit, and both ends of the transmitting circuit are connected to the output end of the power amplifier;

[0008] The receiving coil, the resonant capacitor, the compensation capacitor and the current-controlled variable inductor are connected in parallel to form a receiving circuit, and both ends of the receiving circuit are connected to both ends of the load;

[0009] The transmitting coil converts electrical energy into magnetic field energy and emits it to the receiving coil. The receiving coil is used to receive the magnetic field energy emitted by the transmitting coil and convert it into electrical energy. The voltage-controlled variable capacitor and the current-controlled variable inductor are used to change the frequency characteristics of the wireless power transmission system, so that the system can still maintain a high transmission efficiency when the relative position of the transmitting coil and the receiving coil changes.

[0010] A design method for a wireless power transmission system resistant to position offset, design given values: the output voltage u of the power amplifier s and the amplitude U of the output voltage of the power amplifier s , the Coulomb-voltage characteristic coefficients a1 and a3 of the voltage-controlled variable capacitor, the self-inductance L1 of the transmitting coil, the self-inductance L2 of the receiving coil, the mutual inductance M between the transmitting coil and the receiving coil, the capacitance value C of the resonant capacitor p1 , the capacitance value C of the compensation capacitor p2 , the Weber-ampere characteristic coefficients b1 and b3 of the current-controlled variable inductor, the resistance value R of the load resistor L .

[0011] The angular frequency ω of the output voltage waveform of the signal generator and the capacitance value C of the compensation capacitor p2 The design method is as follows:

[0012] (1) The design process of the angular frequency ω of the output voltage waveform of the signal generator:

[0013] Step 1: Establish the KVL equation set of the system, that is:

[0014]

[0015] In the formula, u s represents the output voltage of the power amplifier, that is, u s =U s cos(ωt), ω is the angular frequency of the output voltage waveform of the signal generator, ω = 2πf, U srepresents the amplitude of the output voltage of the power amplifier; R s represents the internal resistance of the power amplifier; i1 and i2 are the currents of the transmitting coil and the receiving coil respectively; L1 and L2 are the self-inductances of the transmitting coil and the receiving coil respectively; u cs represents the voltage across the voltage-controlled variable capacitor; M represents the mutual inductance between the transmitting coil and the receiving coil; R L represents the resistance value of the load resistor; u RL represents the voltage across the load; C p1 , C p2 represent the capacitance values of the resonant capacitor and the compensation capacitor respectively; i LP represents the current flowing through the current-controlled variable inductor;

[0016] Step 2: Combine the equations in Step 1, equivalent the receiving circuit to the transmitting circuit, and obtain the time-domain equation of the decoupled transmitting circuit:

[0017]

[0018] In the formula, Z2 represents the total impedance of the receiving circuit, Z ref represents the reflected impedance; the Coulomb-volt characteristic curve of the voltage-controlled variable capacitor can be expressed as u cs (q) = a1q + a3q 3 , where a1 and a3 are constant coefficients, which can be determined by the parameters of the voltage-controlled variable capacitor, u cs is the voltage across the voltage-controlled variable capacitor, q is the electric charge stored in the voltage-controlled variable capacitor, and can be expressed as q = Acos(ωt - θ), where A represents the amplitude of the electric charge stored in the voltage-controlled variable capacitor, and θ is the phase difference between the electric charge stored in the voltage-controlled variable capacitor and the output voltage of the power amplifier;

[0019] Step 3: Substitute q = Acos(ωt - θ) into the equation in Step 2, and use the trigonometric formula cos 3 a = (3cosa + cos3a) / 4, and ignore the high-order harmonics, to obtain:

[0020]

[0021] Among them:

[0022]

[0023] In the formula, ω0 is the natural resonance frequency of the transmitting circuit; γ is the damping coefficient; ε is the coefficient of the cubic term of the restoring force; F is the external excitation parameter;

[0024] Step 4: Respectively make the coefficients before cos(ωt) and sin(ωt) in Step 3 equal, and use the trigonometric formula sin2 a + cos 2 When \(a = 1\), eliminating the phase angle \(\theta\) gives an equation about \(A\) and \(\omega\), that is, the amplitude - frequency response equation:

[0025]

[0026] Step 5: Linearize the equation in Step 2 and use the Routh - Hurwitz criterion to find the condition for the system to be stable, that is:

[0027]

[0028] In the formula, the value of \(L1\) is determined by the wound coil. Adjust the value of \(\omega\) to make \(\omega\) as large as possible when the transmitting circuit satisfies the inequality condition in Step 5.

[0029] (2) The capacitance value \(C\) of the compensating capacitor p2 Design process:

[0030] Step 1: Equivalent the transmitting circuit to the receiving circuit again. Since the value of \(C\) p1 satisfies the resonance condition with \(L2\), that is \(L2C\) p1 \(\omega\) 2 \(= 1\), the branch where \(C\) p1 and \(L2\) are located can be eliminated. The receiving circuit can be equivalent to a circuit composed of a current source in parallel with \(C\) p2 , \(L\) p and \(R\) L . The time - domain equation is:

[0031]

[0032] In the formula, \(I\) p is the amplitude of the current emitted by the equivalent current source, that is \(I\) p \(=\omega AM / L2\), and \(A\) can be obtained from the amplitude - frequency response equation in Step 4. The Weber - Ampere characteristic curve of the current - controlled variable inductor can be expressed as \(i\) LP \((\psi)=b1\psi + b3\psi\) 3 , where \(b1\) and \(b3\) are constant coefficients determined by the parameters of the current - controlled variable inductor, \(i\) p is the current flowing through the current - controlled variable inductor, and \(\psi\) is the magnetic flux stored in the current - controlled variable inductor, which can be expressed as where \(B\) represents the amplitude of the magnetic flux stored in the current - controlled variable inductor, is the phase difference between the magnetic flux stored in the current - controlled variable inductor and the equivalent current source;

[0033] Step 2: Use the same method as Step 3 in (1) to obtain an equation about \(B\) and \(\omega\), that is, the amplitude - frequency characteristic equation of the receiving circuit, that is:

[0034]

[0035] Among them

[0036]

[0037] In the formula, ω1 represents the natural resonance frequency of the receiving circuit; ξ is the damping coefficient, δ is the cubic term coefficient of the restoring force; K is the external excitation parameter after the transmitting circuit is equivalent to the receiving circuit;

[0038] Step 3: Linearize the equation in Step 1, and use the Routh-Hurwitz criterion to find the condition for the system to be stable, that is:

[0039]

[0040] Adjust C p2 value to make the inequality in Step 3 hold while making C p2 as large as possible to obtain the capacitance value of the compensation capacitor, thereby completing the design of the wireless power transmission system against position offset. The wireless power transmission system against position offset can maintain a high transmission efficiency when the relative positions of the transmitting coil and the receiving coil change.

[0041] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention uses a voltage-controlled variable capacitor and a current-controlled variable inductor to change the frequency characteristics of the wireless power transmission system without using a feedback network and active devices, and maintains a high transmission efficiency when the relative positions of the transmitting coil and the receiving coil change, with high safety and broad market prospects. In addition, the structure used in the present invention is simple and reliable, and does not require any active devices or feedback circuits. Description of the Drawings

[0042] Figure 1 is the structural diagram of the wireless power transmission system of the present invention;

[0043] Figure 2 is the schematic diagram of the coil positions of the transmitting coil and the receiving coil of the present invention;

[0044] Figure 3 is the circuit schematic diagram of the present invention;

[0045] Figure 4 is the data analysis diagram of the power transmission efficiency when the axial distance between the transmitting coil and the receiving coil changes in the embodiment of the present invention.

[0046] Figure 5 is the data analysis diagram of the power transmission efficiency when the radial positions of the transmitting coil and the receiving coil are offset in the embodiment of the present invention. Specific Embodiments

[0047] In order to make the content and advantages of the technical solution of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0048] like Figure 1 As shown, the signal generator provides high-frequency sinusoidal alternating current for the entire system; the power amplifier amplifies the sinusoidal signal output by the signal generator and converts it into alternating current that meets the system requirements; the transmitting circuit is used to provide resonance compensation for the transmitting coil; the transmitting coil is used to convert the high-frequency sinusoidal alternating current into magnetic field energy and transmit it to the receiving coil; the receiving circuit is used to provide resonance compensation for the receiving coil.

[0049] The radial offset and axial distance position of the transmitting coil and the receiving coil are shown in the figure below: Figure 2 As shown in the figure, the geometric center of the transmitting coil is defined as the coordinate origin; the x-axis is the radial transmission distance; and the y-axis is the axial offset.

[0050] like Figure 3 As shown, u s Represents the output voltage of the power amplifier, that is, u s =U s cos(ωt), ω is the angular frequency of the output voltage waveform of the signal generator, ω=2πf, U s Represents the amplitude of the power amplifier output voltage; R s represents the internal resistance of the power amplifier; L1 and L2 are the self-inductance of the transmitting coil and the receiving coil respectively; u cs represents the voltage across the voltage-controlled variable capacitor; M represents the mutual inductance of the transmitting coil and the receiving coil; R L Indicates the resistance value of the load resistor; C p1 ,C p2 Respectively represent the capacitance of the resonant capacitor and the compensation capacitor; i LP represents the current flowing through the current-controlled variable inductor. For a current-controlled variable inductor wireless power transfer system including a non-ferrous voltage-controlled variable capacitor and, its KVL equations are:

[0051]

[0052] Where i1 and i2 are the currents of the transmitting coil and the receiving coil respectively; u RL Represents the voltage across the load. By combining the above equations, the receiving circuit is equivalent to the transmitting circuit, and the time domain equation of the decoupled transmitting circuit is obtained:

[0053]

[0054] Where Z2 represents the total impedance of the receiving circuit, Z ref represents the reflected impedance; the Coulomb-Volt characteristic curve of the voltage-controlled variable capacitor can be expressed as ucs i(q) = a1q + a3q 3 , where a1 and a3 are constant coefficients, which can be determined by the parameters of the voltage-controlled variable capacitor, and u cs is the voltage across the voltage-controlled variable capacitor, and q is the electric charge stored in the voltage-controlled variable capacitor, which can be expressed as q = Acos(ωt - θ). Here, A represents the amplitude of the electric charge stored in the voltage-controlled variable capacitor, and θ is the phase difference between the electric charge stored in the voltage-controlled variable capacitor and the output voltage of the power amplifier. The amplitude-frequency characteristic of the transmitting circuit can be expressed as:

[0055]

[0056] where

[0057]

[0058] Linearize the KVL equation of the transmitting circuit and use the Routh-Hurwitz criterion to find the condition for the system to be stable, that is:

[0059]

[0060] In the formula, the value of L1 is determined by winding the coil. Adjust the value of ω to make ω as large as possible under the condition that the above inequality holds, so as to complete the design of the transmitting circuit.

[0061] Then, equivalent the transmitting circuit to the receiving circuit. And because the value of C p1 satisfies the resonance condition with L2, that is, L2C p1 ω 2 = 1, the branch where C p1 and L2 are located can be eliminated. The receiving circuit can be equivalent to a circuit composed of a current source in parallel with C p2 , L p and R L . Its time-domain equation is:

[0062]

[0063] In the formula, I p is the amplitude of the current emitted by the equivalent current source, that is, I p = ωAM / L2, and A can be obtained from the amplitude-frequency response equation of the transmitting circuit. The Weber-Ampere characteristic curve of the current-controlled variable inductor can be expressed as i LP (ψ) = b1ψ + b3ψ 3 , where b1 and b3 are constant coefficients, which can be determined by the parameters of the current-controlled variable inductor, and i p is the current flowing through the current-controlled variable inductor, and ψ is the magnetic flux stored in the current-controlled variable inductor, which can be expressed as Among them, B represents the amplitude of the magnetic flux stored in the current-controlled variable inductor, is the phase difference between the magnetic flux stored in the current-controlled variable inductor and the equivalent current source. The amplitude-frequency characteristic equation of the receiving circuit can be expressed as:

[0064]

[0065] where

[0066]

[0067] Linearize the KVL equation of the receiving circuit, and use the Routh-Hurwitz criterion to obtain the conditions for the system to be stable, that is:

[0068]

[0069] Adjust the value of C p2 to make the above inequality hold and at the same time make C p2 as large as possible to obtain the capacitance value of the compensation capacitor, thereby completing the design of the wireless power transmission system against position offset. The wireless power transmission system against position offset can maintain a high transmission efficiency when the relative positions of the transmitting coil and the receiving coil change.

[0070] Based on the system platform built hereby, relevant experimental data are obtained. The data analysis when the axial distance between the transmitting coil and the receiving coil changes is as Figure 4 shown, and the data analysis when the transmitting coil and the receiving coil are radially offset is as Figure 5 shown. It can be seen that compared with the existing system, the present invention greatly improves the transmission efficiency when the relative positions of the transmitting coil and the receiving coil change.

[0071] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A wireless power transmission system resistant to position offset, characterized in that It includes a signal generator, a power amplifier, a voltage-controlled variable capacitor, a resonant capacitor, a compensation capacitor, a current-controlled variable inductor, a transmitting coil, a receiving coil and a load. The signal generator is connected to the input end of the power amplifier. The voltage-controlled variable capacitor and the transmitting coil are connected in series to form a transmitting circuit, and both ends of the transmitting circuit are connected to the output end of the power amplifier. The receiving coil, the resonant capacitor, the compensation capacitor and the current-controlled variable inductor are connected in parallel to form a receiving circuit, and both ends of the receiving circuit are connected to both ends of the load. The transmitting coil converts electrical energy into magnetic field energy and emits it to the receiving coil. The receiving coil is used to receive the magnetic field energy emitted by the transmitting coil and convert it into electrical energy. The voltage-controlled variable capacitor and the current-controlled variable inductor are used to change the frequency characteristics of the wireless power transmission system to compensate for the influence caused by the decrease in the coupling factor when the relative position of the transmitting coil and the receiving coil changes; The specific design process of the wireless power transmission system resistant to position offset is as follows: Step 1: Establish the KVL equation set of the system, that is: where, u s represents the output voltage of the power amplifier, i.e., u s = U s cos(ωt), where ω is the angular frequency of the output voltage waveform of the signal generator, ω = 2πf, and U s represents the amplitude of the output voltage of the power amplifier; R s represents the internal resistance of the power amplifier; i1 and i2 are the currents of the transmitting coil and the receiving coil respectively; L1 and L2 are the self-inductances of the transmitting coil and the receiving coil respectively; u cs represents the voltage across the voltage-controlled variable capacitor; M represents the mutual inductance between the transmitting coil and the receiving coil; R L represents the resistance value of the load resistor; u RL represents the voltage across the load; C p1 , C p2 represent the capacitance values of the resonant capacitor and the compensation capacitor respectively; i LP represents the current flowing through the current-controlled variable inductor; Step 2: Combine the equations in Step 1, and equivalent the receiving circuit to the transmitting circuit to obtain the time-domain equation of the decoupled transmitting circuit: where Z2 represents the total impedance of the receiving circuit, and Z ref represents the reflected impedance; the Coulomb-Volt characteristic curve of the voltage-controlled variable capacitor can be expressed as u cs (q) = a1q + a3q 3 , where a1 and a3 are constant coefficients that can be determined by the parameters of the voltage-controlled variable capacitor, and u cs is the voltage across the voltage-controlled variable capacitor, and q is the electric charge stored in the voltage-controlled variable capacitor, which is expressed as q = Acos(ωt - θ), where A is the amplitude of the electric charge stored in the voltage-controlled variable capacitor, and θ is the phase difference between the electric charge stored in the voltage-controlled variable capacitor and the output voltage of the power amplifier; Step 3: Substitute \(q = A\cos(\omega t - \theta)\) into the equation of Step 2, and use the trigonometric formula \(\cos\) 3 \(a=(3\cos a+\cos3a) / 4\), and neglect the higher harmonics, to obtain: Where: In the formula, ω0 is the natural resonance frequency of the transmitting circuit; γ is the damping coefficient; ε is the cubic term coefficient of the restoring force; F is the external excitation parameter; Step 4: Respectively make the coefficients before cos(ωt) and sin(ωt) in Step 3 equal, and use the trigonometric formula sin 2 a + cos 2 a = 1 to eliminate the phase angle θ to obtain an equation about A and ω, that is, the amplitude-frequency characteristic equation: Step 5: Linearize the equation in Step 2, and use the Routh-Hurwitz criterion to find the condition for the system to be stable, that is: In the formula, the value of L1 is determined by winding the coil. Adjust the value of ω to make ω as large as possible under the condition that the inequality in Step 5 holds, so as to complete the design of the transmitting circuit; Step 6: Then, the transmitting circuit is equivalent to the receiving circuit. Since the value of C p1 satisfies the resonance condition with L2, that is, L2C p1 ω 2 = 1, the branch where C p1 and L2 are located can be eliminated. The receiving circuit is equivalent to a current source and C p2 , L p and R L in parallel. Its time-domain equation is as follows: Wherein, I p is the amplitude of the current emitted by the equivalent current source, that is, I p = ωAM / L2, A is obtained from the amplitude-frequency response equation in Step 4, and the Weber-Ampere characteristic curve of the current-controlled variable inductor can be expressed as i LP (ψ) = b1ψ + b3ψ 3 , b1 and b3 are constant coefficients determined by the parameters of the current-controlled variable inductor, and i p is the current flowing through the current-controlled variable inductor, ψ is the magnetic flux stored in the current-controlled variable inductor, and is expressed as wherein, B is the amplitude of the magnetic flux stored in the current-controlled variable inductor, is the phase difference between the magnetic flux stored in the current-controlled variable inductor and the equivalent current source; Step 7: Use the same method as in Step 3 to obtain the equation about B and ω, that is, the amplitude-frequency characteristic equation of the receiving circuit, that is: Where In the formula, ω1 is the natural resonance frequency of the receiving circuit; ξ is the damping coefficient, δ is the cubic term coefficient of the restoring force; K is the external excitation parameter after the transmitting circuit is equivalent to the receiving circuit; Step 8: Linearize the equation in Step 6, and use the Routh-Hurwitz criterion to find the condition for the system to be stable, that is: Adjust C p2 so that the inequality in step 8 holds while making C p2 as large as possible, obtain the capacitance value of the compensation capacitor, and thus complete the design of the wireless power transmission system against position offset.

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