Inductance-capacitor-inductance (LCL)-filters installed at converter outputs offer higher harmonic attenuation than L-filters, but careful design is required to damp LCL resonance, which can cause poorly damped oscillations and even instability. A new topology is presented for a discrete-time current controller which damps this resonance, combining deadbeat current control with optimal state-feedback pole assignment. By separating the state feedback gains into deadbeat and damping feedback loops, transient overcurrent protection is realizable while preserving the desired pole locations. Moreover, the controller is shown to be robust to parameter uncertainty in the grid inductance. Experimental tests verify that fast well-damped transient response and overcurrent protection is possible at low switching frequencies relative to the resonant frequency. Index Terms-Electromagnetic interference (EMI), inductance-capacitor-inductance (LCL)-filter, voltage source converters (VSCs).
Rotary left ventricular assist devices (LVADs) are commonly operated at a constant speed, attenuating blood flow pulsatility. Speed modulation of rotary LVADs has been demonstrated to improve vascular pulsatility and pump washout. The effect of LVAD speed modulation on intraventricular flow dynamics is not well understood, which may have an influence on thromboembolic events. This study aimed to numerically evaluate intraventricular flow characteristics with a speed modulated LVAD. A severely dilated anatomical left ventricle was supported by a HeartWare HVAD in a three‐dimensional multiscale computational fluid dynamics model. Three LVAD operating scenarios were evaluated: constant speed and sinusoidal co‐ and counter‐pulsation. In all operating scenarios, the mean pump speed was set to restore the cardiac output to 5.0 L/min. Co‐ and counter‐pulsation was speed modulated with an amplitude of 750 rpm. The risk of thrombosis was evaluated based on blood residence time, ventricular washout, kinetic energy densities, and a pulsatility index map. Blood residence time for co‐pulsation was on average 1.8 and 3.7% lower than constant speed and counter‐pulsation mode, respectively. After introducing fresh blood to displace preexisting blood for 10 cardiac cycles, co‐pulsation had 1.5% less old blood in comparison to counter‐pulsation. Apical energy densities were 84 and 27% higher for co‐pulsation in comparison to counter‐pulsation and constant speed mode, respectively. Co‐pulsation had an increased pulsatility index around the left ventricular outflow tract and mid‐ventricle. Improved flow dynamics with co‐pulsation was caused by increased E‐wave velocities which minimized blood stasis. In the studied scenario and from the perspective of intraventricular flow dynamics, co‐pulsation of rotary LVADs could minimize the risk of intraventricular thrombosis.
Controlled and repeatable in vitro evaluation of cardiovascular devices using a mock circulation loop (MCL) is essential prior to in vivo or clinical trials. MCLs often consist of only a systemic circulation with no autoregulatory responses and limited validation. This study aimed to develop, and validate against human data, an advanced MCL with systemic, pulmonary, cerebral, and coronary circulations with autoregulatory responses. The biventricular MCL was constructed with pneumatically controlled hydraulic circulations with Starling responsive ventricles and autoregulatory cerebral and coronary circulations. Hemodynamic repeatability was assessed and complemented by validation using impedance cardiography data from 50 healthy humans. The MCL successfully simulated patient scenarios including rest, exercise, and left heart failure with and without cardiovascular device support. End-systolic pressure-volume relationships for respective healthy and heart failure conditions had slopes of 1.27 and 0.54 mm Hg mL −1 (left ventricle), and 0.18 and 0.10 mm Hg mL −1 (right ventricle), aligning with the literature. Coronary and cerebral autoregulation showed a strong correlation (R 2 : .99) between theoretical and experimentally derived circuit flow. MCL repeatability was demonstrated with correlation coefficients being statistically significant (P < .05) for all simulated conditions while MCL hemodynamics aligned well with human data. This advanced MCL is a valuable tool for inexpensive and controlled evaluation of cardiovascular devices.
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