Optimization of the Low-Frequency Mode for Modular Multilevel Converters Based On Frequency Domain Analysis

2019 ◽  
Author(s):  
Rebecca Dierks ◽  
Jakub Kucka ◽  
Axel Mertens
Keyword(s):  
Frequency Domain ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Frequency Mode ◽  
Multilevel Converters ◽  
Modular Multilevel Converters ◽  
Low Frequency Mode

scholarly journals Impact of mild orthostatic stress on aortic-cerebral hemodynamic transmission: insight from the frequency domain

2017 ◽  
Vol 312 (5) ◽  
pp. H1076-H1084 ◽  
Author(s):  
Jun Sugawara ◽  
Tsubasa Tomoto ◽  
Tomoko Imai ◽  
Seiji Maeda ◽  
Shigehiko Ogoh
Keyword(s):  
Transfer Function ◽  
Frequency Domain ◽  
Systemic Vascular Resistance ◽  
Vascular Resistance ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Slow Oscillations ◽  
Transfer Function Gain ◽  
The Brain

High cerebral pressure and flow fluctuations could be a risk for future cerebrovascular disease. This study aims to determine whether acute systemic vasoconstriction affects the dynamic pulsatile hemodynamic transmission from the aorta to the brain. We applied a stepwise lower body negative pressure (LBNP) (−10, −20, and −30 mmHg) in 15 young men to induce systemic vasoconstriction. To elucidate the dynamic relationship between the changes in aortic pressure (AoP; estimated from the radial arterial pressure waveforms) and the cerebral blood flow velocity (CBFV) at the middle cerebral artery (via a transcranial Doppler), frequency-domain analysis characterized the beat-to-beat slow oscillation (0.02–0.30 Hz) and the intra-beat rapid change (0.78–9.69 Hz). The systemic vascular resistance gradually and significantly increased throughout the LBNP protocol. In the low-frequency range (LF: 0.07–0.20 Hz) of a slow oscillation, the normalized transfer function gain of the steady-state component (between mean AoP and mean CBFV) remained unchanged, whereas that of the pulsatile component (between pulsatile AoP and pulsatile CBFV) was significantly augmented during −20 and −30 mmHg of LBNP (+28.8% and +32.4% vs. baseline). Furthermore, the relative change in the normalized transfer function gain of the pulsatile component at the LF range correlated with the corresponding change in systemic vascular resistance ( r = 0.41, P = 0.005). Regarding the intra-beat analysis, the normalized transfer function gain from AoP to CBFV was not significantly affected by the LBNP stimulation ( P = 0.77). Our findings suggest that systemic vasoconstriction deteriorates the dampening effect on the pulsatile hemodynamics toward the brain, particularly in slow oscillations (e.g., 0.07–0.20 Hz). NEW & NOTEWORTHY We characterized the pulsatile hemodynamic transmission from the heart to the brain by frequency-domain analysis. The low-frequency transmission was augmented with a mild LBNP stimulation partly due to the elevated systemic vascular resistance. A systemic vasoconstriction deteriorates the dampening effect on slow oscillations of pulsatile hemodynamics toward the brain.

scholarly journals Frequency Domain Analysis of Cerebral Blood Flow Velocity and its Correlation with Arterial Blood Pressure

1998 ◽  
Vol 18 (3) ◽  
pp. 311-318 ◽  
Author(s):  
Terry Bo-Jau Kuo ◽  
Chang-Ming Chern ◽  
Wen-Yung Sheng ◽  
Wen-Jang Wong ◽  
Han-Hwa Hu
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Transfer Function ◽  
Flow Velocity ◽  
Frequency Domain ◽  
Blood Flow Velocity ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Arterial Blood

We applied frequency domain analysis to detect and quantify spontaneous fluctuations in the blood flow velocity of the middle cerebral artery (MCAFV). Instantaneous MCAFV of normal volunteers was detected using transcranial Doppler sonography. Spectral and transfer function analyses of MCAFV and arterial blood pressure (ABP) were performed by fast Fourier transform. We found the fluctuations in MCAFV, like ABP, could be diffracted into three components at specific frequency ranges, designated as high-frequency (HF, 0.15 to 0.4 Hz), low-frequency (LF, 0.04 to 0.15 Hz), and very low-frequency (VLF, 0.016 to 0.04 Hz) components. The HF and LF components of MCAFV exhibited high coherence with those of ABP, indicating great similarity of MCAFV and ABP fluctuations within the two frequency ranges. However, it was not the case for the VLF component. Transfer function analysis revealed that the ABP-MCAFV phase angle was frequency-dependent in the LF range ( r = −0.79, P < 0.001) but not in the HF range. The time delay between LF fluctuations of ABP and those of MCAFV was evaluated as 2.1 seconds. We conclude that in addition to traditional B-wave equivalents, there are at least two different mechanisms for MCAFV fluctuations: the HF and LF fluctuations of MCAFV are basically secondary to those of ABP, and cerebral autoregulation may operate efficiently in LF rather than HF range. Frequency domain analysis offers an opportunity to explore the nature and underlying mechanism of dynamic regulation in cerebral circulation.

Frequency-Domain Calculations of Moored Vessel Motion Including Low Frequency Effect

2008 ◽  
Author(s):  
C. Le Cunff ◽  
Sam Ryu ◽  
Jean-Michel Heurtier ◽  
Arun S. Duggal
Keyword(s):  
Frequency Domain ◽  
Drag Force ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Second Order ◽  
Wave Frequency ◽  
Diffraction Radiation ◽  
Floating Structure ◽  
Low Frequency Motion

Frequency-domain analysis can be used to evaluate the motions of the FPSO with its mooring and riser. The main assumption of the frequency-domain analysis is that the coupling is essentially linear. Calculations are performed taking into account first order wave loads on the floating structure. Added mass and radiation damping terms are frequency dependent, and can be easily considered in this formulation. The major non-linearity comes from the drag force both on lines and the floating structure. Linearization of the non-linear drag force acting on the lines is applied. The calculations can be extended to derive the low frequency motion of the floating structure. Second order low frequency quadratic transfer function is computed with a diffraction/radiation method. Given a wave spectrum, the second order force spectrum can then be derived. At the same time frequency-domain analysis is used to derive the low frequency motion and wave frequency motion of the floating system. As an example case, an FPSO is employed. Comparison is performed with time domain simulation to show the robustness of the frequency-domain analysis. Some calculations are also performed with either low frequency terms only or wave frequency terms only in order to check the effect of modeling low and wave frequency terms, separately. In the case study it is found that the low frequency motion is reduced by the wave frequency motion while the wave frequency motion is not affected by the low frequency motion.

Extreme Response Analysis of Floating Structures Using Coupled Frequency Domain Analysis

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Ying Min Low ◽  
Andrew J. Grime
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Coupled Analysis ◽  
Statistical Techniques ◽  
Frequency Domain Methods ◽  
Extreme Response ◽  
The Mean

In the dynamic analysis of a floating structure, coupled analysis refers to a procedure in which the vessel, moorings, and risers are modeled as a whole system, thus allowing for interactions between various system components. Because coupled analysis in the time domain is impractical owing to prohibitive computational costs, a highly efficient frequency domain approach was developed in a previous work, wherein the drag forces are linearized. The study showed that provided the geometric nonlinearity of the moorings/risers is insignificant, which often holds for ultradeepwater systems, the mean-squared responses yielded by the time and frequency domain methods are in close agreement. Practical design is concerned with the extreme response, for which the mean upcrossing rate is a key parameter. Crossing rate analysis based on statistical techniques is complicated as the total response occurs at two timescales, with the low frequency contribution being notably non-Gaussian. Many studies have been devoted to this problem, mainly relying on a technique originating from Kac and Siegert; however, these studies have mostly been confined to a single-degree-of-freedom system. The aim of this work is to apply statistical techniques in conjunction with frequency domain analysis to predict the extreme responses of the coupled system, in particular the modes with a prominent low frequency component. It is found that the crossing rates for surge, sway and yaw thus obtained agree well with those extracted from time domain simulation, whereas the result for roll is less favorable, and the reasons are discussed.

Extreme Response Analysis of Floating Structures Using Coupled Frequency Domain Analysis

2010 ◽  
Author(s):  
Ying Min Low ◽  
Andrew J. Grime
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Coupled Analysis ◽  
Statistical Techniques ◽  
Frequency Domain Methods ◽  
Extreme Response ◽  
The Mean

In the dynamic analysis of a floating structure, coupled analysis refers to a procedure in which the vessel, moorings and risers are modeled as a whole system, thus allowing for the interactions between the various system components. Because coupled analysis in the time domain is impractical owing to prohibitive computational costs, a highly efficient frequency domain approach was developed in a previous work, wherein the drag forces are linearized. The study showed that provided the geometric nonlinearity of the moorings/risers is insignificant, which often holds for ultra-deepwater systems, the mean-squared responses yielded by the time and frequency domain methods are in close agreement. Practical design is concerned with the extreme response, for which the mean upcrossing rate is a key parameter. Crossing rate analysis based on statistical techniques is complicated as the total response occurs at two timescales, with the low frequency contribution being notably non-Gaussian. Many studies have been devoted to this problem, mainly relying on a technique originating from Kac and Siegert; however, these studies have mostly been confined to a single-degree-of-freedom system. The aim of this work is to apply statistical techniques in conjunction with frequency domain analysis to predict the extreme responses of the coupled system, in particular the modes with a prominent low frequency component. It is found that the crossing rates for surge, sway and yaw thus obtained agree well with those extracted from time domain simulation, whereas the result for roll is less favorable, and the reasons are discussed.

Significant and Morbid Changes in Heart Rate Variability Precedes and Complicates Symptomatic Hypotension in Peripheral Blood Stem Cell Apheresis.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 4996-4996
Author(s):  
Hirohisa Nakamae ◽  
Yoshiki Terada ◽  
Mika Akahori ◽  
Takahiko Nakane ◽  
Kiyoyuki Hagihara ◽  
...  
Keyword(s):  
Stem Cell ◽  
Frequency Domain ◽  
Time Domain ◽  
Peripheral Blood Stem Cell ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Hrv Analysis ◽  
Low Frequency Power ◽  
Frequency Power

Abstract Peripheral blood stem cell harvest (PBSCH) has been widely performed for rescue following high-dose chemotherapy or as an alternative to BMT for allogeneic stem cell transplantation. However, severe complications, which caused sudden death, were reported in PBSCH from healthy donors. Recent cumulative evidence shows that decrease in cardiovascular signal variability of the R-R period (heart rate variability, HRV) is strongly associated with sudden death and/or cardiac event after a myocardial infarction. Furthermore, usefulness of HRV as a clinical tool has been explored in numerous conditions such as hypertrophic cardiomyopathy, obstructive sleep apnea, diabetic neuropathy, and various neurological alterations. Two types, time domain and frequency domain, are included in HRV analysis. In this study, we investigated HRV during and after apheresis for PBSCH in 23 cases [8 autologous transplant patients, 15 allogeneic transplant donors; 8 men, 15 women; median age 47 years (27–55)]. Date from 24-hour ambulatory ECG recordings were analyzed with R-R data analysis software (MemCalc/CHIRAM version 1, Suwatrust, Tokyo, Japan). Acknowledged simple markers in time domain analysis are the standard deviation of all normal beats (SDNN) and the square root of the mean of the sum of squared differences between adjacent normal-to-normal intervals (r-MSSD). On the other hand, markers in frequency domain analysis include LH, low frequency power (0.04–0.15Hz); HF, high frequency power (0.15–0.4 Hz); LH/HF ratio; VLF, very low frequency power (0.003–0.04 Hz); and ULF, ultra low frequency power (<0.0033 Hz). These power spectrum analyses of HRV are used to investigate sympathovagal balance, autonomic cardiovascular control and/or target function impairment. Among frequency domain analysis markers, VLF or ULF reportedly have particular prognostic value in all causes of mortality after myocardial infarction. In our study, SDNN, r-MSSD, HF, VLF, and ULF significantly and markedly decreased to morbid levels during apheresis (all P<0.001). Of 23 harvest cases, symptomatic hypotension occurred during apheresis in 2 cases and after apheresis in one case. Notably, in these 3 cases, SDNN and VLF had already begun to decrease about 5–10 minutes before significant symptomatic hypotension occurred (P=0.03, P=0.04, respectively). Our results suggested that morbidly decreased HRV indicates serious cardiovascular load and suppression of the parasympathetic nervous system in apheresis for PBCSH. HRV analysis might be a useful tool to prevent donors from severe autonomic cardiovascular complications in PBCSH.

Sign in / Sign up

Export Citation Format

Share Document