Serdar YILMAZ, Onur TOKER, Nurullah ARSLAN, Herman SEDEF

Optimal in vitro realization of pulsatile coronary artery flow waveforms using closed-loop feedback algorithms with multiple flow control devices

In this paper, we study optimal in vitro realization of pulsatile coronary artery flows using newly proposed closed-loop feedback algorithms with a clearly defined mathematical performance objective, and we compare several flow control device technologies in terms of their ability to generate pulsatile flow signals as accurately as possible. In the literature, there are several published results for in vitro pulsatile flow realization systems. However, most of the proposed systems operate in an open-loop setting and use a single flow control device, and their performance is assessed mostly by graphical means without a clearly defined mathematical performance objective. Furthermore, some authors take the average of the generated pulsatile flow and compare it with the desired flow signal for performance analysis. What makes this work different from other published results in this area are: 1) the use of closed-loop feedback control rather than an open-loop approach; 2) the use of a clearly defined mathematical performance objective rather than a visual comparison of the generated and desired flow graphs; 3) newly proposed control algorithms with demonstrated performance improvements as compared to the published ones; 4) the use of multiple flow control devices, their performance comparisons, and optimal technology selection; and 5) not taking the average of the generated flow signal over several cycles for performance assessment, but instead using the nonaveraged actual flow signal and comparing it with the desired one. In pulsatile flow realization, what is important is the L1 distance between the desired and delayed versions of the generated flows in the steady state regime, and the defined mathematical performance objective is completely based on this point. Furthermore, there are 3 different flow control devices that are comparatively analyzed: the pneumatic valve, the servo valve, and an AC inverter driving a centrifugal pump. Finally, there are several new closed-loop control algorithms proposed in this paper: P-S , P-S predictive, P-S look ahead, and model-based nonlinear feed-forward, feed-forward predictive, and feed-forward look-ahead control. Each algorithm's performance is compared with that of PID performance as a benchmark test to demonstrate performance improvements. By proper selection of the flow control device, and optimal selection of the control algorithm and its parameters, we were able to achieve up to 75% reduction in error.

Anahtar Kelimeler:

Pulsatile waveforms, coronary artery, feedback control, in vitro realization

Optimal in vitro realization of pulsatile coronary artery flow waveforms using closed-loop feedback algorithms with multiple flow control devices

Keywords:

Pulsatile waveforms, coronary artery, feedback control, in vitro realization,

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P- Σ look-ahead control with the solenoid valve Similar to the performance improvements observed for the centrifugal pump, the look-ahead technique also resulted in an improvement. Compared to the P- Σ controller, the look-ahead technique resulted in 20% per- formance improvement, which is comparable to the performance improvement observed with causal prediction. The search results for a suitable prediction coeﬃcient and a delay value in the Kpp– d plane are summarized in Table 9. Table 9. P- Σ look-ahead controller performance with solenoid valve. Delay d 01 03 2767
Table 10. Type-1 feed-forward controller performance with the centrifugal pump. Kp 01 75 9580
Table 11. Type-2 feed-forward controller performance with the centrifugal pump. p 5 75 8726 4.2.
Feed-forward control with solenoid valve For the solenoid valve, we conducted a similar one-dimensional search in the Kpspace, and the results are summarized in Tables 12 and 13 for type-1 and type-2 feed-forward controllers, respectively. Compared to the best possible performance index of 5.5378 among the PID, P- Σ , P- Σ predictive, and P- Σ look-ahead controllers with a solenoid valve, a small performance improvement of about 3% was achieved.
Table 12. Type-1 feed-forward controller performance with the solenoid valve. Kp 1 75 8689
Table 13. Type-2 feed-forward controller performance with the solenoid valve. 5 75 4590 5.
Table 15. Feed-forward predictive controller performance with the solenoid valve. Delay d 75 6 5466
Figure 23. Best performance for the solenoid valve is obtained with the feed-forward predictive control when the reference signal is the coronary artery blood ﬂow signal. The performance is computed as J = 5.2319.
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