Energy transmission system for an artificial heart- leakage inductance compensation

Posted on 5:53 PM by Admin

The artificial heart now in use, like the natural heart it is designed to replace , is a four –chambered device for pumping blood. such electrical circulatory assist devices such as total artificial heart or ventricular assist devices generally use a brushless dc motor as their pump They require 12–35 W to operate and can be powered by a portable battery pack and a dc–dc converter.
It would be desirable to transfer electrical energy to these circulatory assist devices transcutaneously without breaking the skin. This technique would need a power supply which uses a transcutaneous transformer to drive  use,the motor for the circulatory assist devices. The secondary of this transformer would be implanted under the skin, and the primary would be placed on top of the secondary, external to the body. The distance between the transformer windings would be approximately equal to the thickness of the patient’s skin, nominally between 1–2 cm. This spacing cannot be assumed constant; the alignment of the cores and the distance between them would certainly vary during the operation.
A transformer with a large (1–2 cm) air gap between the primary and the secondary has large leakage inductances. In this application, the coupling coefficient k ranges approximately from 0.1 to 0.4. This makes the leakage inductances of the same order of magnitude and usually larger than the magnetizing inductance. Therefore, the transfer gain of voltage is very low, and a significant portion of the primary current will flow through the magnetizing inductance. The large circulating current through the magnetizing inductance results in poor efficiency.
A dc–dc converter employing secondary-side resonance has been reported to alleviate the problems by lowering the impedance of the secondary side using a resonant circuit .Although the circulating current is lowered, the transfer gain of the voltage varies widely as the coupling coefficient varies .So, advantages characteristics are reduced as the coupling coefficient deviates at a designated value.
In this paper, compensation of the leakage inductances on both sides of the transcutaneous transformer is presented. This converter offers significant improvements over the converter presented in the following aspects.

·         High-voltage gain with relative small variation with respect to load change as well as the variation of the coupling coefficient of the transformer—this reduces the operating frequency range and the size of the transcutaneous transformer is minimized.

·         Higher efficiency—minimize circulating current of magnetizing inductance and zero-voltage switching (ZVS) of the primary switches, and zero-current switching (ZCS) of the secondary rectifier diodes improves the efficiency significantly, especially at the secondary side (inside the body).

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