More Like this

1. Hybrid Unscented Kalman Filter: Application to the Simplest Walker

   https://doi.org/10.1016/j.ifacol.2023.11.010  

   Bittler, James; Bhounsule, Pranav A (January 2023, IFAC-PapersOnLine)

   State estimation of hybrid dynamic systems, such as legged robots, is challenging because of the presence of non-smooth dynamics. This paper applies the Unscented Kalman Filter (UKF) state estimator and two novel hybrid extensions (HUKF) to a hybrid system, the simplest walking model. These estimators are identical far from the switching boundary, which partitions dynamic domains, but apply different time update algorithms at the switching boundary. (1) UKF permits sigma points to propagate through the system’s hybrid dynamics. (2) HUKF-SPG (Sigma Point Generation) generates new sigma points when the weighted mean of the initial sigma points is on the switching boundary. (3) HUKF-SPT (Sigma Point Transformation) transforms the sigma points forward and backward in time through the system’s hybrid dynamics only when the weighted mean of the initial sigma points is on the switching boundary. Results here shows that HUKF-SPG and HUKF-SPT have a lower absolute error but modestly more computations compared to UKF. A caveat of HUKF-SPT is it can only apply to conservative systems. HUKF-SPG is more general and could be applied to any hybrid system. 

   more » « less
2. Parametric Dependence of Large Disturbance Response for Vector Fields with Event-Selected Discontinuities

   https://doi.org/10.23919/ECC.2019.8796029  

   Fisher, Michael W.; Hiskens, Ian A. (June 2019, 2019 18th European Control Conference)

   The ability of a nonlinear system to recover from a large disturbance to a desired stable equilibrium point depends on system parameter values, which are often uncertain and time varying. A particular disturbance acting for a finite time can be modeled as an implicit map that takes a parameter value to its corresponding post disturbance initial condition in state space. The system recovers when the post-disturbance initial condition lies inside the region of attraction of the stable equilibrium point. Critical parameter values are defined to be parameter values whose corresponding post-disturbance initial condition lies on the boundary of the region of attraction. Computing such values is important in numerous applications because they represent the boundary between desirable and undesirable system behavior. Many realistic system models involve controller clipping limits and other forms of switching. Furthermore, these hybrid dynamics are closely linked to the ability of a system to recover from disturbances. The paper develops theory which underpins a novel algorithm for numerically computing critical parameter values for nonlinear systems with clipping limits and switching. For an almost generic class of vector fields with event-selected discontinuities, it is shown that the boundary of the region of attraction is equal to a union of the stable manifolds of the equilibria and periodic orbits it contains, and that this decomposition persists and the boundary varies continuously under small changes in parameter. 

   more » « less
3. Design and Implementation of a LLC Resonant Solid State Transformer

   https://doi.org/10.1109/TIA.2020.2982847  

   Rashidi, Mohammad; Altin, Necmi; Ozdemir, Saban; Bani-Ahmed, Abedalsalam; Sabbah, Mohammad; Balali, Farhad; Nasiri, Adel (March 2020, IEEE Transactions on Industry Applications)

   null (Ed.)

   In this study, analysis and control of a highly efficient, high-power full-bridge unidirectional resonant LLC solid-state transformer (SST) are discussed. A combination of pulse frequency modulation and phase-shift modulation is utilized to control this resonant converter for a wide load range. The converter is designed to maintain soft switching by using a resonant circuit to minimize the switching loss of the high-frequency converter. Zero-voltage-switching (ZVS) is achieved for the H-bridge converter. The ZVS boundary for the proposed combined control method is also analyzed in detail. The experimental setup for the suggested configuration was implemented, and the performance of the proposed control scheme and resonant LLC SST have been verified with test results. The proposed combined control scheme improves control performance. The obtained results show that, the proposed system can regulate output voltage and maintain soft switching in a wide range of load. Thus, the efficiency of the system is improved and an efficiency of 97.18% is achieved. 

   more » « less
4. Voltage controlled Néel vector rotation in zero magnetic field

   https://doi.org/10.1038/s41467-021-21872-3  

   Mahmood, Ather; Echtenkamp, Will; Street, Mike; Wang, Jun-Lei; Cao, Shi; Komesu, Takashi; Dowben, Peter A.; Buragohain, Pratyush; Lu, Haidong; Gruverman, Alexei; et al (December 2021, Nature Communications)

   null (Ed.)

   Abstract Multi-functional thin films of boron (B) doped Cr 2 O 3 exhibit voltage-controlled and nonvolatile Néel vector reorientation in the absence of an applied magnetic field, H . Toggling of antiferromagnetic states is demonstrated in prototype device structures at CMOS compatible temperatures between 300 and 400 K. The boundary magnetization associated with the Néel vector orientation serves as state variable which is read via magnetoresistive detection in a Pt Hall bar adjacent to the B:Cr 2 O 3 film. Switching of the Hall voltage between zero and non-zero values implies Néel vector rotation by 90 degrees. Combined magnetometry, spin resolved inverse photoemission, electric transport and scanning probe microscopy measurements reveal B-dependent T N and resistivity enhancement, spin-canting, anisotropy reduction, dynamic polarization hysteresis and gate voltage dependent orientation of boundary magnetization. The combined effect enables H  = 0, voltage controlled, nonvolatile Néel vector rotation at high-temperature. Theoretical modeling estimates switching speeds of about 100 ps making B:Cr 2 O 3 a promising multifunctional single-phase material for energy efficient nonvolatile CMOS compatible memory applications. 

   more » « less
5. Data-Driven Decomposition Control to Output Tracking With Nonperiodic Tracking–Transition Switching Under Input Constraint

   https://doi.org/10.1115/1.4053763  

   Liu, Jiangbo; Zou, Qingze (June 2022, Journal of Dynamic Systems, Measurement, and Control)

   Abstract This paper is concerned with solving, from the learning-based decomposition control viewpoint, the problem of output tracking with nonperiodic tracking–transition switching. Such a nontraditional tracking problem occurs in applications where sessions for tracking a given desired trajectory are alternated with those for transiting the output with given boundary conditions. It is challenging to achieve precision tracking while maintaining smooth tracking–transition switching, as postswitching oscillations can be induced due to the mismatch of the boundary states at the switching instants, and the tracking performance can be limited by the nonminimum-phase (NMP) zeros of the system and effected by factors such as input constraints and external disturbances. Although recently an approach by combining the system-inversion with optimization techniques has been proposed to tackle these challenges, modeling of the system dynamics and complicated online computation are needed, and the controller obtained can be sensitive to model uncertainties. In this work, a learning-based decomposition control technique is developed to overcome these limitations. A dictionary of input–output bases is constructed offline a priori via data-driven iterative learning first. The input–output bases are used online to decompose the desired output in the tracking sessions and design an optimal desired transition trajectory with minimal transition time under input-amplitude constraint. Finally, the control input is synthesized based on the superpositioning principle and further optimized online to account for system variations and external disturbance. The proposed approach is illustrated through a nanopositioning control experiment on a piezoelectric actuator. 

   more » « less