Analysis, design and control of a transcutaneous power regulator for artificial heart

Based on commonly used parameters for a generic transcutaneous transformer model, a remote power supply using resonant topology for artificial heart is analyzed and designed for easy controllability and high efficiency. Primary and secondary windings of the transcutaneous transformer are positioned outside and inside human body respectively for energy transfer. The two large leakage inductances and the mutual inductance of the transformer are varying parameters of the coupling-coefficient which varies with transformer alignment and gap due to external positioning. Varying resonant-frequency resonant-tank circuits are formed using the transformer inductors and external capacitors to obtain a load insensitive frequency for the voltage transfer function at given range of coupling coefficients and loads. Previous researches usually use frequency modulation which may require a wide control frequency range well above the load insensitive frequency. In this paper, fundamental frequency study of the input-to-output voltage transfer function is carried out. Using the proposed control method, the switching frequency can be locked at just above the load insensitive frequency at heavy load for best efficiency. Specifically, above resonant operation in driving the resonant circuits when varying the coupling-coefficient is maintained using a digital-phase-lock-loop (PLL) technique to achieve zero-voltage switching of a full-bridge switches configuration which is also programmed to provide pulse-width-modulation (PWM) in controlling the output voltage. A prototype transcutaneous power regulator is built and found to have good efficiency and regulation in responding to changing alignment or gap of the transcutaneous transformer, load and input voltage dynamically.