Discrete multi-coil compensation method for loosely coupled transformer

Abstract

The invention discloses a discrete multi-coil compensation method for a loosely coupled transformer, and belongs to the technical field of coil compensation. The problem that an existing multi-coil magnetic coupling structure needs concentrated series compensation or decoupling design is solved. Comprising the steps that a primary side coil is arranged to be of a parallel structure of a plurality of primary side independent coils, and each primary side independent coil is connected with a primary side compensation capacitor in series; meanwhile, the secondary side coil is arranged to be of a parallel structure of a plurality of secondary side independent coils, and each secondary side independent coil is connected with a secondary side compensation capacitor in series. According to the invention, the compensation of the loosely coupled transformer coil is realized.

Description

Technical Field

[0001] The invention relates to a discrete multi-coil compensation method for a loosely coupled transformer, belonging to the technical field of coil compensation. Background Art

[0002] In wireless power transmission systems, due to the limitations of coil structure and compensation methods, the currents of each coil are almost strictly equal, which limits the improvement of the transmission efficiency of the loosely coupled transformer (LCT). Discrete compensation multi-coils can be divided into multi-stage relay multi-coil networks, single-stage hybrid compensation multi-coil networks and single-stage multi-transmit / receive multi-coil networks according to different system structures. Among them, multi-stage relay multi-coil compensation networks are widely used in high-distance-to-diameter ratio wireless power transmission systems.

[0003] In the existing centralized series compensation multi-coil, although there can be a coupling relationship between the multiple coils, the compensation method is limited to the series centralized compensation. The traditional centralized series capacitor compensation method has the problem of high coil electric field strength leading to high dielectric loss, reducing the coil quality factor, and limiting the design freedom of the magnetic coupling structure and compensation network. The traditional loosely coupled transformer is based on uniform current distribution, without considering the uneven coupling and loss distribution factors between each turn of the coil, which limits the efficiency improvement potential of the wireless power transmission system, especially for coils with a large number of turns.

[0004] In order to solve the problem that multi-coil magnetic coupling structures require centralized series compensation or decoupling design, new compensation methods are needed to improve the freedom of system design and transmission efficiency. Summary of the invention

[0005] In view of the limitation that the existing multi-coil magnetic coupling structure requires centralized series compensation or decoupling design, the present invention provides a discrete multi-coil compensation method for a loosely coupled transformer.

[0006] A discrete multi-coil compensation method for a loosely coupled transformer of the present invention comprises:

[0007] The primary coil is set to a parallel structure of multiple primary independent coils, and each primary independent coil is connected in series with a primary compensation capacitor;

[0008] At the same time, the secondary coil is set to a parallel structure of multiple secondary independent coils, and each secondary independent coil is connected in series with a secondary compensation capacitor.

[0009] According to the discrete multi-coil compensation method of the loosely coupled transformer of the present invention, the capacitance of the primary compensation capacitor is determined based on the uniform distribution of currents of multiple primary independent coils;

[0010] The capacitance of the secondary compensation capacitor is determined based on the uniform current distribution of multiple independent secondary coils.

[0011] According to the discrete multi-coil compensation method of the loosely coupled transformer of the present invention, the calculation method of the primary compensation capacitor is:

[0012]

[0013] Where C pn is the primary compensation capacitor of the nth primary independent coil, w is the operating frequency, L pn is the inductance of the nth primary independent coil, M pnp(n-1) is the mutual inductance between the nth primary independent coil and the n-1th primary independent coil, M pnsn is the mutual inductance between the nth primary independent coil and the nth secondary independent coil.

[0014] According to the discrete multi-coil compensation method of the loosely coupled transformer of the present invention, the calculation method of the secondary side compensation capacitor is:

[0015]

[0016] Where C sn is the secondary compensation capacitor of the nth secondary independent coil, L sn is the inductance of the nth secondary independent coil, M snpn is the mutual inductance between the nth secondary independent coil and the nth primary independent coil, M sns(n-1) is the mutual inductance between the nth secondary independent coil and the n-1th secondary independent coil.

[0017] According to the discrete multi-coil compensation method of the loosely coupled transformer of the present invention, the primary coil further includes a turn of the primary excitation coil; the secondary coil further includes a turn of the secondary excitation coil.

[0018] According to the discrete multi-coil compensation method of the loosely coupled transformer of the present invention, adjacent primary independent coils of the primary coil are closely adjacent to each other; and adjacent secondary independent coils of the secondary coil are closely adjacent to each other.

[0019] Beneficial effects of the invention: The method of the invention is proposed to address the limitations of multi-coil magnetic coupling structures, such as the need for centralized series compensation or decoupling design, and is intended to achieve reactive compensation of multi-coil coupling, reduce voltage stress between multiple coils, and improve the freedom of system design and transmission efficiency.

[0020] The method of the present invention first separates each section or each turn of the coil to realize the segmented linearization of the coil current and realize a discrete multi-coil structure system; then the compensation network parameters of each section or each turn are designed accordingly. Under this method, the discrete multi-coils are isolated from each other, and the current distribution of the multi-coil system can be designed. At the same time, the voltage stress between each section or each turn of the multi-coil is greatly reduced, and the content of reactive power is reduced. This compensation method greatly improves the design freedom and explores the potential for improving the transmission efficiency of the discrete multi-coil system; in addition, the contactless discrete compensation also greatly reduces the dielectric loss of the coil, which can improve the power density of the loosely coupled transformer and reduce the volume and production cost of the loosely coupled transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a physical effect diagram of the discrete multi-coil compensation method of the loosely coupled transformer of the present invention; p is the compensation capacitor set on the primary excitation coil, C s L is the compensation capacitor set on the secondary excitation coil; p is the inductance of the primary excitation coil, L s is the inductance of the secondary excitation coil;

[0022] Figure 2 This is the physical effect diagram of the traditional coil concentrated compensation method;

[0023] Figure 3 : is a circuit diagram of a discrete multi-coil WPT system based on S / S compensation in an embodiment; U in is the DC input voltage, C in is the DC input side filter capacitor, Q1 to Q4 are the four MOS tubes of the inverter, u in is the AC output voltage of the inverter, i p is the AC output current of the inverter, R Lp is the parasitic resistance of the primary excitation coil; R pLn is the parasitic resistance of the nth primary discrete coil, R sLn is the parasitic resistance of the nth discrete coil on the secondary side, i s is the AC input current of the rectifier, R Ls is the parasitic resistance of the secondary receiving coil, u re is the AC input voltage of the rectifier; D1 to D4 are the four diodes of the rectifier, C F is the filter capacitor on the DC output side, R L is the load resistance on the output side;

[0024] Figure 4 is based on Figure 3 The multi-turn discrete coil model obtained by simulation;

[0025] Figure 5 yes Figure 4 Compensation circuit diagram;

[0026] Figure 6 is the distribution diagram of compensation capacitance values;

[0027] Figure 7 It is the current waveform of all independent coils. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0030] The present invention will be further described below in conjunction with the accompanying drawings, but is not intended to be a limitation of the present invention.

[0031] Combination Figure 1 As shown, the present invention provides a discrete multi-coil compensation method for a loosely coupled transformer, comprising:

[0032] The primary coil is set to a parallel structure of multiple primary independent coils, and each primary independent coil is connected in series with a primary compensation capacitor;

[0033] At the same time, the secondary coil is set to a parallel structure of multiple secondary independent coils, and each secondary independent coil is connected in series with a secondary compensation capacitor.

[0034] Furthermore, the capacitance of the primary compensation capacitor is determined based on the uniform current distribution of the multiple primary independent coils;

[0035] The capacitance of the secondary compensation capacitor is determined based on the uniform current distribution of multiple independent secondary coils.

[0036] In this implementation, the calculation method of the primary compensation capacitor is:

[0037]

[0038] Where C pn is the primary compensation capacitor of the nth primary independent coil, w is the operating frequency, L pn is the inductance of the nth primary independent coil, M pnp(n-1) is the mutual inductance between the nth primary independent coil and the n-1th primary independent coil, M pnsnis the mutual inductance between the nth primary independent coil and the nth secondary independent coil.

[0039] The calculation method of the secondary side compensation capacitor is:

[0040]

[0041] Where C sn is the secondary compensation capacitor of the nth secondary independent coil, L sn is the inductance of the nth secondary independent coil, M snpn is the mutual inductance between the nth secondary independent coil and the nth primary independent coil, M sns(n-1) is the mutual inductance between the nth secondary independent coil and the n-1th secondary independent coil.

[0042] In this implementation manner, the primary coil further includes a turn of the primary excitation coil; and the secondary coil further includes a turn of the secondary excitation coil.

[0043] The adjacent primary independent coils of the primary coil are close to each other; the adjacent secondary independent coils of the secondary coil are close to each other.

[0044] The physical effect diagram of the traditional coil centralized compensation method is as follows: Figure 2 As shown, the original side L p1 ~L pn Connected in series, in a spiral tube structure, the self-inductance is L pp , the secondary side is similar, the self-inductance is L ss The compensation capacitor corresponding to each coil is C p , C pp , C s , C ss .

[0045] Using a fully resonant compensation method, the capacitor completely compensates for the self-inductance of the excitation coil. The numerical calculation expression of the compensation capacitor of the primary and secondary excitation coils is:

[0046]

[0047] At the same time, the compensation capacitor in the traditional method must also satisfy the following relationship:

[0048]

[0049] Example:

[0050] The effects of the present invention are described below with specific examples.

[0051] Taking S / S compensation as an example, the circuit diagram of the discrete multi-coil wireless power transmission system is as follows: Figure 3 shown.

[0052] A multi-turn discrete coil model is built based on Ansys Maxwell electromagnetic simulation software, such as Figure 4 The primary transmitting part is a 6-turn coil, and the secondary receiving part is also a 6-turn coil, numbered 1-12 from left to right. The coils numbered 1 and 12 are the excitation coils at the head and tail positions, and the excitation coils are connected to the inverter and rectifier respectively.

[0053] The inductance matrix of each discrete coil on the primary and secondary sides is obtained through simulation results. The inductance matrix is ​​input into the compensation parameter calculation program to obtain a set of capacitance parameters for discrete coil compensation.

[0054] Compared with the traditional multi-coil compensation method, the traditional coil centralized compensation method has the problem of excessive voltage stress of the parasitic capacitance between coil turns. This is because the two ends of the parasitic capacitance between turns are connected in series by a turn of coil, and the inductance is large. Therefore, the voltage on the inductance is also large, that is, the voltage of the parasitic capacitance between turns is large.

[0055] The novel discrete compensation method proposed in the present invention can greatly reduce the voltage stress of the capacitor, because each turn of the coil is isolated and discrete, and there is no direct electrical connection between the turns, so the voltage stress is low. In addition, through the design method of the compensation capacitor of the present invention, the coil current can still be approximately evenly distributed without changing the original transmission effect. This is also conducive to reducing some energy losses caused by parasitic capacitance during transmission in a high-frequency environment, and plays an important role in improving the efficiency of the wireless power transmission system.

[0056] Through the above analysis, the compensation method proposed by the present invention based on discrete multi-coils is determined. The compensation capacitance value of each discrete coil is obtained through design calculation. Figure 5 As shown. Figure 5 It can be seen that the primary and secondary sides of the coil each have one turn of the excitation coil, the primary and secondary sides of the discrete coil each have 5 turns, and the primary and secondary coils have a total of 12 turns of coils. The coils are closely connected to each other, that is, there is no turn spacing. The diameter of the coil is 200mm, the transmission distance is 300mm, and the wire diameter of the coil is 4mm.

[0057] Based on the Maxwell simulation software, a discrete multi-coil model with 6 turns on the primary and secondary sides is established, in which the small excitation coil is in the first position. Tables 1 and 2 are the inductance matrix parameters obtained through Maxwell simulation. The inductance matrix parameters are input into the discrete multi-coil compensation network calculation program to obtain the compensation capacitance value of the multi-coil, where the frequency is 6.78MHz.

[0058] Table 1 Inductance matrix parameters of the primary coil

[0059]

[0060] Table 2 Inductance matrix parameters of the secondary coil

[0061]

[0062] Figure 6 The figure shows the distribution of compensation capacitance parameters based on 12 discrete coil models. The compensation method corresponding to the first and last excitation coils still uses reactive full compensation, and the compensation capacitance of the 10 turns of the coil in the middle is calculated based on the uniform current distribution. Figure 7 Indicates that currents I1 to I2 flow through coils numbered 1 to 12. 12 The current waveform is given by Figure 7 It can be seen that the current in the primary and secondary relay coils is equal, indicating that the coil current is evenly distributed. In the isolated discrete multi-coil structure, the voltage stress between adjacent coils is obviously smaller because they have no direct electrical connection. The voltage stress of the parasitic capacitance between adjacent coils is reduced, which is conducive to reducing losses.

[0063] In summary, the novel discrete multi-coil compensation method proposed in the present invention obtains the compensation capacitance value based on the uniformly distributed current, without any additional cost. It only needs to divide the coil into a discrete structure for each turn, and connect a compensation capacitor in series respectively. This greatly increases the flexibility of system design, because each compensation capacitor can be designed later. At the same time, it reduces the voltage stress of parasitic capacitance between each turn of the coil due to high-frequency environment, which is conducive to improving the transmission efficiency of the multi-stage coil system, and broadens the research and development field of improving transmission efficiency in the application of high-distance-to-diameter ratio wireless power transmission system. This simulation experiment realizes a wireless power transmission system under discrete multi-stage coils, which has broad application prospects in wireless power transmission. In addition, it also provides new ideas for broadening the research field in the entire power electronics field.

[0064] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A discrete multi-coil compensation method for a loosely coupled transformer, characterized in that include, The primary coil is set to a parallel structure of multiple primary independent coils, and each primary independent coil is connected in series with a primary compensation capacitor; At the same time, the secondary coil is set to a parallel structure of multiple secondary independent coils, and each secondary independent coil is connected in series with a secondary compensation capacitor.

2. The discrete multi-coil compensation method for a loosely coupled transformer according to claim 1, characterized in that: The capacitance of the primary compensation capacitor is determined based on the uniform current distribution of multiple primary independent coils; The capacitance of the secondary compensation capacitor is determined based on the uniform current distribution of multiple independent secondary coils.

3. The discrete multi-coil compensation method for a loosely coupled transformer according to claim 2, characterized in that: The calculation method of the primary compensation capacitor is: Where C pn is the primary compensation capacitor of the nth primary independent coil, w is the operating frequency, L pn is the inductance of the nth primary independent coil, M pnp(n-1) is the mutual inductance between the nth primary independent coil and the n-1th primary independent coil, M pnsn is the mutual inductance between the nth primary independent coil and the nth secondary independent coil.

4. The discrete multi-coil compensation method for a loosely coupled transformer according to claim 3, characterized in that: The calculation method of the secondary side compensation capacitor is: Where C sn is the secondary compensation capacitor of the nth secondary independent coil, L sn is the inductance of the nth secondary independent coil, M snpn is the mutual inductance between the nth secondary independent coil and the nth primary independent coil, M sns(n-1) is the mutual inductance between the nth secondary independent coil and the n-1th secondary independent coil.

5. The discrete multi-coil compensation method for a loosely coupled transformer according to claim 1, characterized in that: The primary coil also includes a turn of the primary excitation coil; the secondary coil also includes a turn of the secondary excitation coil.

6. The discrete multi-coil compensation method for a loosely coupled transformer according to claim 1, characterized in that: The adjacent primary independent coils of the primary coil are close to each other; the adjacent secondary independent coils of the secondary coil are close to each other.

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