Research On Transcutaneous Energy Transmission System For Implanted Devices

The extensive use of implanted devices has led to the development of medical implantable electronic system. Every year about 8,000?15,000 patients who suffer from heart attack have the chance to transplant assist device for circulatory. It is hoped that these devices are powered with an intact skin, therefore, transcutaneous energy transmission system (TETS) is necessary. It delivers electrical energy to load with the help of transcutaneous transformer that has no mechanical contact. Due to the electromagnetic induction, the"wireless power supply"can be realized.The major difference between TETS and tranditional DC-DC converters is the transcutaneous transformer, which has a large air gap. It leads to a large leakage inductance, small magnetizing inductance and low coupling coefficient; simultaneously, as the patient's activities, the air gap as well as the parameter of transformer is in real-time change. In accordance with the two characteristics of TETS, this project is studied from three aspects.In order to minimize the effect of large leakage inductance, frequency-domain analysis of the four basic compensation topology and input-to-output voltage transfer function indicated the existence of load insensitive frequency which is adaptable to the variable parameter characteristics.In this paper, a PWM control strategy using a phase locked loop for transcutaneous power regulation is adopted. This integrated control strategy is capable of locking the switching frequency at just above the load insensitive frequency at full load and low input voltage condition. Using a digital phase locked loop (PLL), zero-voltage switching is achieved with optimized efficiency. A prototype of transcutaneous power regulator rated 24V/12~60W is built and found to perform excellently with high efficiency and tight regulation. The highest efficiency at full load can reach 89%. Experimental results verify the validity of theoretical analysis and parameters design.Aiming to obtain higher k, smaller size and lighter weight for the transcutaneous transformer, techniques for the improvement of core structure and coil arrangement are proposed in this paper. A accurate magnetic reluctance circuit is also proposed. Based on magnetic flux coupling, magnetic reluctances are found for the calculation of k. A novel structure of transcutaneous transformer with k of 0.6 and weight of 60g is achieved. The k calculated is verified with experimental measurement to be very accurate. Compared with our previous transformer having k of 0.53 and weight of 122g, the new transformer offers about 2.5% improvement in the maximum efficiency.