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How to Use Toroidal Transformer to Achieve Impedance Matching

A self-resonant type radio that resonates the transmitter and receiver coils according to the transmission frequency.Because the linear power transmission system is capable of transmitting power with high efficiency, research is currently being actively conducted to apply it to electric vehicles, home appliances, and mobile devices. However, in order to transmit power with high efficiency, impedance matching is essential to properly transmit the energy stored in the resonance coil along with resonance.

In the existing self-resonance wireless power transmission system, impedance matching was mainly performed using a coupling coil. However, if the impedance matching conditions change due to changes in the spacing and arrangement between the transmitting and receiving coils, impedance matching is possible only by physically moving the coupling coil or using multiple coupling coils. Physical movement is difficult to apply to actual systems, and the method of using multiple coupling coils requires designing and using multiple coupling coils in a limited area because the larger the resonance coil, the size of the coupling coil must also be correspondingly large. There is a disadvantage that it is difficult to do.

To solve this problem, this article proposes an impedance matching method using a toroidal transformer for a self-resonant wireless power transmission system.

In many electronic applications such factors as the efficiency of electrical power, sources and the ratings of key components may determine the transformer current. However, no theorem exists for determining the design of the most efficient transformer when current is not a variable. This article provides a criterion for maximum efficiency for a toroidal transformer with a given current, frequency, volt-ampere rating, magnetic flux density, window fill factor, and materials.

A comparative analysis of the coupling capacitance of the designed multiple output power supply and the commercially available single-input, single-output power supply demonstrates that the designed power supply for the MV gate driver has relatively lower coupling capacitance than the commercial power supply. The designed power supply can effectively reject the common mode current. The designed power supply can generate three outputs and has relatively smaller size with the flexibility to increase the number of outputs as required by merely changing some of the 72 components in the design. The isolation for the power supply is realized using the single-turn primary winding for the toroidal core transformer. The designed toroidal transformer can achieve higher insulation voltage up to 20 kV without adding any external dielectric material as the medium (i.e., air insulated design).

The expressions derived are specifically for the toroidal transformer, both because this type has wide applicability and because its description may be reduced to dependence on a single dimension, height H, and two geometric factors, the ratio of inside to outside diameter Y and the ratio of height to build Z. However, appropriately restated, the basic results presented here probably hold for any type of transformer.

A continuum of wire and core sizes and shapes are permitted in the analysis. Two winding schemes are considered, the basic two winding transformer with equal current densities in both windings and the inverter transformer with a center tapped primary designed for twice the current density of the secondary.

A method of using a toroidal transformer connected in parallel to a resonance coil was proposed for impedance matching of a self-resonant wireless power transmission system. Through the proposed method, it was confirmed that by changing the number of turns of the toroidal transformer’s primary coil, the impedance matching conditions according to the change in the distance between the transmitting and receiving coils could be met with almost no power loss due to the transformer. Therefore, it is expected that the impedance matching method using a toroidal transformer can be applied to wireless charging of electric vehicles, etc.

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