CN103887896A - Method for designing wireless charging coil allowing charging device to be placed freely - Google Patents

Abstract

The invention discloses a method for designing a wireless charging coil allowing a charging device to be placed freely. The wireless charging coil allowing the charging device to be placed freely is composed of N round single-circle coils which are connected in parallel, two capacitors are connected to each coil in series, and the current ratio between the round single-circle coils is the capacitance ratio between the capacitors connected to the round single-circle coils in series; even magnetic fields can be generated on the surface of a sending coil by reasonably setting the capacitance ratio. According to the method for designing the wireless charging coil allowing the charging device to be placed freely, due to the fact that the parallel connection form is adopted, even magnetic fields can be generated, and requirements for even magnetic fields at different heights of the sending coil can be met by conveniently adjusting the capacitors connected to the coils in series.

Description

Design method of a wireless charging coil for charging equipment that can be placed arbitrarily

technical field

The invention belongs to the field of wireless charging, and in particular relates to the design of a wireless charging coil, which enables charging equipment to be placed freely within a certain range. the

Background technique

Wireless charging technology has broad application prospects in consumer electronics, medical electronics, and industrial electronics. Electromagnetic induction coupling is the most widely used technology in short-range wireless charging, which transmits electric energy through electromagnetic induction between two coupling coils, the sending coil and the receiving coil. the

The efficiency of electromagnetic induction coupling power transfer is closely related to the coupling coefficient between the two coupling coils. Generally, the larger the coupling coefficient, the higher the power transfer efficiency. The coupling coefficient is determined by the shape, size and relative position of the coil. In many applications, such as mobile phone wireless chargers, the shape and size of the coil are fixed, but the position between the sending coil and the receiving coil is variable. Due to the uncertainty of the coupling coefficient caused by the uncertainty of the relative position, the charging system will not be able to achieve optimal efficiency and transmission efficiency, and may even damage the system due to fluctuations in the receiving voltage. Although under a certain fixed coupling coefficient, the transmission efficiency can be maximized through a reasonable compensation circuit design and the circuit works in a resonant state, but the uncertainty of the coupling coefficient will make the compensation circuit invalid, unless the compensation circuit can be based on the coupling coefficient To adjust the changes, this greatly increases the difficulty of circuit design, and even becomes impossible to realize. the

If the sending coil can generate a uniform magnetic field in the working area of the receiving coil, the coupling coefficient between the receiving coil and the sending coil in this area will also be fixed, and the above problems can be solved. the

Contents of the invention

In order to solve the problem that in the electromagnetic induction coupling wireless charging equipment, due to the uncertain relative position between the transmitting coil and the receiving coil, the transmission efficiency of the system cannot be optimized or even the system cannot work normally, the present invention designs a transmitter that can generate a uniform magnetic field coil. the

The technical solution adopted in the present invention is: the sending coil can be realized by using a printed circuit board or a wound coil, and is composed of N single-turn circular coils connected in parallel. The radius r _n of each circular coil is nR/N, where R is the radius of the outermost coil, n=1, 2...N. Two capacitors are connected in series on each coil, and the selection of the value of the capacitor requires that the following conditions be met: at the operating frequency of the coil, the impedance of the capacitor is much greater than the impedance of the coil. At this time, the current on each coil is mainly determined by the capacitance. Since the N coils are connected in parallel, the voltages at both ends of the coils are equal, so the current ratio between the coils is the ratio of the capacitance values of the coils connected in series. In order to meet the requirement that the surface of the sending coil can generate a uniform magnetic field, the ratio between the coils is obtained as follows.

Due to the symmetry of the circular coil, the magnetic field is equal on the circle at the same distance from the center of the circle, so it is only necessary to select points at different radii for analysis. At the height h from the surface of the sending coil, select N points (i=1, 2...N) whose radii p _i are respectively (i-0.5)R/N, then the current in the nth coil in the sending coil is When the unit current is large, the magnitude of the magnetic field perpendicular to the sending coil plane generated by the i-th point above can be expressed by a _ni , and the expression of a _ni is 0.5×10 ^-7 (m/r _n /p _i ) ^0.5 /p _i {p _i K－[r _n m-(2-m)p _i ]E/(2-2m)}, where K and E are the complete elliptic integrals of the first kind and the second kind respectively with m as the modulus, The expression of m is 4r _n p _i /[(r _n +p _i ) ² +h ² ]. Then the relationship between the magnetic field perpendicular to the sending coil plane of the selected N points and the currents of the N coils can be obtained, which can be expressed as [B]=[A][J] in a matrix. When the magnetic field of the selected N points perpendicular to the plane of the sending coil is a uniform magnetic field, that is, when the elements in [B] are all equal, the current matrix [J] of N coils can be obtained, [J]=[A]- ¹ [B], where [A] ^-1 is the inverse of [A].

The present invention has the following advantages:

(1) The coil can generate a uniform magnetic field on the surface of the transmitting coil, and the receiving coil can be placed arbitrarily within the size range of the transmitting coil, and the coupling coefficient between the two remains stable, which is beneficial to the overall design of the system. the

(2) The coil design method for generating a uniform magnetic field is simple. In the traditional sending coil, the coils are connected in series, so the current flowing through each coil is equal, and the radius of each coil needs to be designed to generate a uniform magnetic field. There are two disadvantages: on the one hand, the method of determining the radius of each coil is complicated, The uniformity of the obtained magnetic field is poor, especially at the edge of the sending coil, in order to prevent the magnetic field from dropping rapidly, it is necessary to place multiple or multi-layer coils at the edge; on the other hand, if the designed sending coil is designed and fixed with a printed circuit board, etc. After that, fine-tuning cannot be performed. For example, when the distance between the receiving coil and the sending coil changes, the radius of each coil in the sending coil cannot be adjusted to generate a more uniform magnetic field at the height of the receiving coil. The parallel connection form adopted by the present invention can not only generate a more uniform magnetic field, but also meet the requirement of a uniform magnetic field at different heights from the sending coil by adjusting the capacitance connected in series on the coil more conveniently. the

Description of drawings

FIG. 1 is a schematic diagram of the design of the sending coil according to the present invention, which includes a plurality of coils whose radii increase linearly and are connected in parallel, and each coil has two capacitors connected in series. the

Fig. 2 is an amplitude diagram of the magnetic field strength generated when a voltage with a frequency of 100kHz and an amplitude of 10V is applied to the coil. the

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments. the

Embodiment 1: As shown in Figure 1, a transmitting coil for a mobile phone charging platform is composed of 10 parallel small coils, and the radii of each coil are 0.01m, 0.02m, 0.03m, 0.04m from the inside to the outside. m, 0.05m, 0.06m, 0.07m, 0.08m, 0.09m, 0.1m, the line width of each coil is 2mm. In order to generate a uniform magnetic field at a height of 5mm from the coil, the capacitances (C _a , C _b ) on each coil are (1nF, 18nF), (2.2nF, 15nF), (3.3nF, 27nF) from inside to outside , (4.7nF, 33nF), (5.6nF, 100nF), (10nF, 22nF), (10nF, 82nF), (18nF, 33nF), (15nF, 470nF), (56nF, 0nF), here on the outermost coil Only one capacitor is needed, just short the capacitor with a capacitance value of 0. When a voltage with a frequency of 100kHz and an amplitude of 10V is applied to the coil, the magnitude of the generated magnetic field strength is shown in Figure 2. As can be seen from accompanying drawing 2, in coil radius 0.0968m (accounting for 96.8% of transmitting coil area), the maximum value and minimum value of magnetic field intensity are respectively 0.5292A/m and 0.4509A/m, and the average value is 0.4886A/m, The rate of change was 16%. When the receiving coil is placed on the surface of the sending coil, since the receiving coil covers a larger area, the uniformity of the total magnetic field strength (ie magnetic flux density) covered by the receiving coil at different positions will be greatly improved.

Claims (1)

1. A wireless charging coil design method in which charging equipment can be placed arbitrarily, it is characterized in that: the sending coil is realized by a printed circuit board or a wound coil, and is composed of N single-turn circular coils connected in parallel; each circular coil The radius r _n is nR / N , where R is the radius of the outermost coil, n =1,2…N; two capacitors are connected in series on each coil, and the selection of the capacitor value requires the following conditions: at the operating frequency of the coil , the capacitive impedance is much greater than the impedance of the coil; at this time, the current on each coil is mainly determined by the capacitance. Since the N coils are connected in parallel, the voltages at both ends of the coil are equal, so the current ratio between the coils is the current ratio of each coil. The ratio of the capacitance value in series; in order to satisfy the requirement that the surface of the sending coil can generate a uniform magnetic field, the current ratio between the coils is obtained by the following method: At the height h from the surface of the sending coil, select N points whose radii p _i are respectively ( i -0.5) R / N ; i =1, 2...N, then the current in the nth coil in the sending coil is When the unit current is large, the magnetic field perpendicular to the sending coil plane generated by the i- th point above is represented by a _ni , and the expression of a _ni is 0.5×10 ^?7 ( m / r _n / p _i ) ^0.5 / p _i { p _i K ?[ r _n m ?(2? m ) p _i ] E /(2?2 m )}, where K and E are the complete elliptic integrals of the first kind and the second kind respectively with the modulus of m , The expression of m is 4 r _n p _i /[( r _n + p _i ) ² + h ² ]; then the relationship between the magnetic field perpendicular to the sending coil plane of the selected N points and the currents of the N coils can be Obtained, the matrix can be expressed as [ B ]=[ A ][ J ]; when the magnetic field of the selected N points perpendicular to the plane of the sending coil is a uniform magnetic field, that is, when the elements in [ B ] are all equal, N can be obtained The current matrix [ J ] of coils, [ J ]=[ A ] ⁻¹ [ B ], where [ A ] ⁻¹ is the inverse of [ A ].