Jacob Glower

Designing fuzzy controllers from a variable structures standpoint

A procedure is presented for designing fuzzy controllers based upon variable structures techniques. Three such controllers are presented: the fuzzy equivalents of sliding-mode controllers, saturating controllers, and tanh controllers. By using an approach based upon variables structures (VSS) techniques, the stability of each of these controllers is assured. By using a sliding surface, the order of the rule base is reduced to size r/spl times/m, where r is the number of inputs and m is the number of fuzzification levels. This combination makes the proposed design procedure able to generate simple controllers with guaranteed stability properties. To illustrate the proposed design procedure, fuzzy controllers are designed for a ball-and-beam system. It is demonstrated that in spite of this system being a fourth-order unstable system, the proposed design procedure results in simple stable fuzzy controllers.

A Printed Rampart-Line Antenna with a Dielectric Superstrate for UHF RFID Applications

A printed Rampart line antenna with a dielectric superstrate for passive radio frequency identification (RFID) tags is presented. A design process is outlined to determine the number of elements used in the rampart line antenna to achieve the required gain for the desired read range. An inductive loop is then added to the port to match the antenna with the passive tag circuitry. It is shown that a passive tag with a printed Rampart line antenna and a dielectric superstrate can achieve comparable read ranges to commercially available passive RFID tags.

A Compact Meander-Line UHF RFID Tag Antenna Loaded With Elements Found in Right/Left-Handed Coplanar Waveguide Structures

A new planar meander-line antenna for passive UHF radio frequency identification (RFID) tags is presented. Specifically, a meander-line antenna is loaded periodically with coplanar waveguide (CPW) LC elements traditionally found in right/left-handed waveguide structures. It is shown that by using the antenna presented in this letter in a prototype passive UHF RFID tag, effective read ranges up to 4.87 m can be achieved. Many different dielectric substrates and CPW-LC load dimensions are investigated to illustrate how the input impedance, gain, and overall dimensions of the antenna are affected by these structural differences. It is shown that the overall dimension of the meander-line antenna can be reduced by slightly more than 18% with the introduction of the CPW-LC elements to the design. Several of the simulation results are validated by comparison with measurements.

A comparison of slip control, FMA control and vector control in DFIG converter

This paper developed three control schemes to coordinate maximum power extraction and voltage control for doubly fed induction generators wind turbines during wind fluctuation. Via PWM, the rotor-side converter can generate a controllable AC voltage with controllable magnitude and frequency. Based on PWM, control schemes: slip control, flux magnitude and angle (FMA) control and vector control are developed. Wind turbine aerodynamics are modeled in dynamic simulation and to obtain a lookup table for torque/power control. In slip control, the voltage is coordinated with torque via voltage/Hz type control. In FMA control, the inner feedback loops of rotor flux magnitude and angle are developed. Torque control loop is added outside the flux angle control loop while voltage control loop is added outside of the flux magnitude control loop. In vector control, the power control loop and voltage control loop are added as the outside control loops while the current control loops is designated as the inner control loops. The purpose of the voltage control is to keep a constant stator voltage, and the power/torque control is used to get maximum wind power under varying wind speeds. Dynamic performance and robustness of the three control schemes are analyzed via linear system analysis tools (Bode plots). Matlab-based time-domain simulations are performed to verify the analysis results and the proposed control schemes.

Electric analog model of the aortic valve for calculation of continuous beat-to-beat aortic flow using a pressure gradient.

The objective was to develop a technique for calculating continuous, beat-to-beat aortic flow (AoF) using only left ventricular pressure (LVP) and aortic pressure (AoP). An electric analog model of the aortic valve was developed that includes resistance (R), inertance (L), and compliance (C) parameters, and resulting second order differential equations were derived. Aortic flow, AoP, and LVP recorded in eight subjects during a 5 day period and during lower body negative pressure (LBNP) were used to validate the model. Resistance, L, and C were estimated using a least-squares fit to the measured AoF on day 0 and during 0 mm Hg LBNP. For days 1-4, AoF was calculated using measured values of AoP and LVP and the R, L, and C values from day 0. Similarly, for LBNP, AoF was calculated using measured values of AoP and LVP, and the R, L, and C values from 0 mm Hg LBNP. The calculated and measured AoF were compared. Differences in cardiac output between the calculated and measured flows were less than 13.1+/-17% across days and under minor altered physiologic conditions (LBNP). Waveform morphology for the calculated AoF also agreed well with the measured AoF. Spectral analysis showed differences in magnitude and phase between measured and calculated aortic flow for the first five harmonics across days, less than 20+/-6% and 25+/-14 degrees, respectively. Preliminary evaluation indicates that our model works well for calculating flow through a biologic valve using LVP and AoP. We speculate that it may perform better for a mechanical valve, and if so it may be possible to develop an instrumented mechanical valve capable of continuous LVP, AOP, and AoF measurements.

In Vitro Evaluation of Control Strategies for an Artificial Vasculature Device

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. An artificial vasculature device (AVD) that may better facilitate myocardial recovery than VAD by controlling the afterload seen by the ejecting heart is being developed. The AVD concept is to enable any user-defined input impedance (IM) with resistance (R) and compliance (C) components. In this study, a pulse duplicator was used to test the efficacy of the AVD concept for two control strategies in an adult mock circulation: (1) R-C in series and (2) 2-element Windkessel (R-C in parallel) using instantaneous impedance position control (IIPC) to maintain a desired value or profile of R and C. In vitro experiments were performed and the resulting cardiovascular pressures, volumes, flows, and the afterload (R and C) seen by the LV during ejection for simulated cardiac failure were recorded and analyzed. Our results indicate that setting the AVD to lower IM reduced LV volume and pressure, restored LV stroke volume, and increased coronary flow. The IIPC control algorithms are better suited to maintain any instantaneous IM or an IM profile, but are susceptible to measurement noise.

Design of computer simulation experiments for an introductory controls course

In this paper, experiments using computer simulations for an introductory controls course taught at North Dakota State University are described. These experiments serve to motivate the students, to build their intuition as to what the controller should look like, and to illustrate how and why feedback controllers work. Observations gained over the past two years as to what makes such experiments successful are discussed and the intent of homework assignments used throughout the semester are described.

Can a linear electrical analog model of a mechanical valve predict flow by using a pressure gradient

The objective was to determine whether a previously developed technique for biological aortic valves could predict flow through a mechanical valve. An electrical analog model of the aortic valve that includes compliance, resistance, and inertance parameters, and corresponding second order differential equations was used to predict flow given a pressure gradient, as previously reported. Simulated pressures and flow were recorded by using a pulse duplicator system. The heart rate was varied from 60 to 180 bpm, and the stroke volume was varied from 22 to 67 cc. Resistance, inertance, and compliance parameters of the governing differential equation were estimated by using a least-squares fit to the measured flow at 120 bpm and 50 cc stroke volume. By using these parameter estimates, flow was calculated for other heart rates and stroke volumes. To achieve a better flow prediction, a nonlinear filter (third order polynomial range calibration equation) was applied to the output of the linear model (flow). The mean error, full-scale error, and spectral error in magnitude and phase between measured and predicted flow were compared. Error in mean flow ranged from 3% at medium flow rates to 90% at low flow rates. The maximum and minimum full scale errors were 12% and 5%, respectively. Error in the harmonics of measured and calculated flow ranged from 0% to 55%. Larger errors were usually present at the higher harmonics. The agreement between measured and calculated flow was better at normal and high flows but rather poor at low flows. The nonlinear filter (range calibration equation) was unable to account for the discrepancies between the measured and calculated flow over all flow ranges. It seems that this linear model and nonlinear filter have limited application, and an alternate nonlinear approach may produce better results.

Control strategies for afterload reduction with an artificial vasculature device.

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. An artificial vasculature device (AVD) is being developed that may better facilitate myocardial recovery than VAD by controlling the afterload experienced by the native heart and controlling the pulsatile energy entering into the arterial system from the device, potentially reconditioning the arterial system properties. The AVD is a valveless, 80 ml blood chamber with a servo-controlled pusher plate connected to the ascending aorta by a vascular graft. Control algorithms for the AVD were developed to maintain any user-defined systemic input impedance (IM) including resistance, elastance, and inertial components. Computer simulation and mock circulation models of the cardiovascular system were used to test the efficacy of two control strategies for the AVD: 1) average impedance position control (AIPC)—to maintain an average value of resistance during left ventricular (LV) systole and 2) instantaneous impedance force feedback (IIFF) and position control (IIPC)—to maintain a desired value or profile of resistance and compliance. Computer simulations and mock loop tests were performed to predict resulting cardiovascular pressures, volumes, flows, and the resistance and compliance experienced by the native LV during ejection for simulated normal, failing, and recovering LV. These results indicate that the LV volume and pressure decreased, and the LV stroke volume increased with decreasing IM, resulting in an increased ejection fraction. Although the AIPC algorithm is more stable and can tolerate higher levels of sensor errors and noise, the IIFF and IIPC control algorithms are better suited to maintain any instantaneous IM or an IM profile. The developed AVD impedance control algorithms may be implemented with current VADs to promote myocardial recovery and facilitate weaning.

On the effect of mutual coupling on LF and UHF tags implemented in dual frequency RFID applications

The performance of many different dual frequency tag configurations were tested in a commercially available dual frequency RFID system. It has been shown that the interaction between the LF and UHF tags can have a significant impact (i.e., 91.84% reduction in read range) on the performance of each individual tag. But, in all cases it has been shown that by proper placement of the LF and UHF RFID tags the performance of each individual tag in the dual-frequency tag can be preserved. In the Rampart line case to preserve the performance of an individual tag a larger footprint was not needed.