| Heart transplantation is considered as the most effective therapy for end-stage heart failure patient. Lacking of heart donation, implanting artificial heart is regarded as a replacement. As the artificial heart is a blood pump in fact, it is driven by electrical energy, which should be transmitted passing through the skin from a power source outside the human body. Traditionally, energy is transmitted with a wire penetrating the skin, which increases the risk of infection and affects patients’ life. By contrast, transcutaneous energy transmission (TET) can transmit power for the implanted artificial heart wirelessly. As no wires penetrating the user’s skin, this technology can obviously prevent device-related infections and greatly improve the quality of patients’ life. However, in actual applications, the power requirement variation for different body movements such like rest and exercise and coil-couple malposition accompanying the skin peristaltic generated by breathing and various trunk actions etc. The variation of transmission impedance, including load resistance and malposition of the couple-coil change, will affect the performance of TET system. Therefore, the research content of this paper mainly centre on impedance adaptability of the TET for artificial heart.First, mathematical model of the energy transmission system was built based on study of the energy transmission mechanism. According to the changing transmission impedance, a resonance matching and impedance compressing functions coupled network based on parallel-series capacitors is proposed in the design, to enhance the energy transmission efficiency and capacity of the coil-couple through resonating, and meanwhile compress the changing range of the transmission impedance to meet the load requirements of the class-E power amplifier and thus keep the high efficiency of TET system. The coupling performance commonly affected by the malposition between the coils in practice, accompanying the skin peristaltic generated by breathing and various trunk actions of human body. However, it is difficult for users to know the actual position of the implanted receiver coil (RC) and know how to realign the transmitter coil (TC) outside the body. A sensing board with coil array is developed to fit with the TC to detect the coil couple malposition by measuring and processing the induced voltage signal on SCs, which has realized position detection without any magnetic sensor incorporated inside implanted device. Then the detecting method was validated by experiments simulating malposition both in distance and concentricity on an actual coil-couple, which can provide accurate parameterized guide for the users to adjust the installation of the TC for good energy transmission performance. The load voltage provided from the TET to the implanted device should be kept stable to ensure the device working well, which however is easily affected by the required power variation for different body movements and coil-couple malposition accompanying skin peristalsis. A novel primary side control method of the load voltage for TET is proposed, which does not require any additional implanted components. Sensing coils were used to measure the malposition between TC and RC, and the magnitude of the TC current outside the human body, which were used to estimate the load voltage inside the body through calculation. A PI control system was developed to regulate the input power of TET for the load voltage stability. Then the proposed method is experimentally validated on an actual TET for artificial heart by varying its load in a wide range under serious coil-couple malposition.The main contents of this dissertation are as follows:1. Research on adaptive method for Class-E power amplifier (E-PA) according to changing transmission impedance. A resonance matching and impedance compressing functions coupled network (RM-IC-coupled network) based on parallel-series capacitors is studied. In this network, the series capacitor works together with the coil in resonating mode to enhance the energy transmitting efficiency and capacity of the coil-couple; meanwhile, it plays a role in compressing the changing range of the transmission impedance, together with the parallel capacitor to meet the load requirements of the E-PA. Based on the illustration of the proposed TET system, an analytical model of the network is given to analyze the RM-IC-coupled effects and provide bases for following parameter determinations; then, according algorithms are provided to determine the optimal parameters required in the TET system for good performance both in resonance matching and impedance compressing. An actual TETS is designed and tested by a series of experiments to validate the methodology. Transmission efficiency is tested for different transmitted powers (12 to 60 W) and different coil-couple malposition conditions (3 to 15 mm in distance,0 to 20 mm in concentricity.2. Research on detecting malposition of coil-couple for transcutaneous energy transmission. A detecting method of the coil coupling malposition based on detecting magnetic field produced by implanted RC is studied. A sensing board which is a printed circuit board in actual and having coil array on it is fit on the TC to sample the voltage induced by TC and RC. The sensing system and the sampled data processing algorithm separating the SC signal induced by TC and RC currents respectively are introduced. Then, an analytical model formulating the induction effect between the RC and SCs is given. Two inverse computation algorithms of the malposition based on the processed sensing data and the induction effect model are presented at last, including one based on fast table looking up method and the other based on more accurate iterative optimization computation. With this malposition detecting system, the users of the TETSs can know the actual malposition of the coils in real time, and provide parameterized guide for the users to adjust the installation of the transmitter coil for good wireless power transmission performance. The proposed method is validated by experiments simulating malposition both in distance (3mm to 15mm) and concentricity (Omm to 20mm) on an actual coil-couple developed in our lab.3. Research on stability control of the output voltage for transcutaneous energy transmission under changing transmission impedance. A novel primary side control method of the load voltage for TET is studied, which requires no additional components implanted into the body. In the method, sensing coils (SCs) fit on TC outside the human body are used to measure the coil-coupling malposition based on the induced signals on the SCs by the RC current, and meanwhile determine the magnitude of the TC current through measuring the voltage induced by it on one SC. Then, the load voltage can be estimated by calculation from the measured malposition and TC current results. Using the estimated voltage as feedback, a PI control system is developed to regulate the input power for the load voltage stability. The proposed method is validated by experiments carried on an actual TET for artificial heart by varying its load in a wide range under different coil-couple malposition. |
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