Design of a transcutaneous power regulator for artificial hearts

Abstract

A high-efficiency transcutaneous power regulator for artificial hearts with pulse-width-modulation phase-locked-loop (PWM-PLL) control has been built with a digital signal processor (DSP) as the primary side controller, and a new method of sensing the output voltage inside the human body utilizing the same power transcutaneous transformer as the medium for signal transmission is introduced. The feedback signal is modulated in the secondary in a frequency band above the PWM-PLL cut-off frequency and below the converter switching frequency. In this way, the feedback signal can be demodulated from the primary current that can be measured. A SPICE macromodel for the double-tuned resonant converter is developed to help design the control loop and the selection of modulation-demodulation frequency bands. A hardware prototype using a single-chip DSP together with analog filters was built and the control software was implemented in DSP program codes. A phase-locked-loop (PLL) switching frequency locking function is constructed by using an on-chip analog comparator. It saves extra hardware for the PLL control. Using a DSP controller, closed-loop stability control can be implemented as software codes and digital control algorithms are used in the system design. The steady-state voltage loop control algorithm uses a modified PI controller with input voltage feed-forward. Another software module is added to shorten the time of output voltage transient in the event of an output load change. This algorithm is based on the response characteristics of the primary side inductor current and output loading estimation. The power efficiency of the regulator system is optimized by setting the switching frequency close to the resonant point. The resulting efficiency is between 87% and 94% for the output load power from 12W to 60W. For a more restricted output power range commonly used by artificial heart systems (15W 35W), the power efficiency is over 90% for all loads.