More Like this

1. Surface wave propagation control with locally resonant metasurfaces using topology-optimized resonators

   https://doi.org/10.1121/10.0025989  

   Giraldo_Guzman, Daniel; Pillarisetti, Lalith_Sai Srinivas; Frecker, Mary; Lissenden, Cliff J; Shokouhi, Parisa (May 2024, The Journal of the Acoustical Society of America)

   Locally resonant elastodynamic metasurfaces for suppressing surface waves have gained popularity in recent years, especially because of their potential in low-frequency applications such as seismic barriers. Their design strategy typically involves tailoring geometrical features of local resonators to attain a desired frequency bandgap through extensive dispersion analyses. In this paper, a systematic design methodology is presented to conceive these local resonators using topology optimization, where frequency bandgaps develop by matching multiple antiresonances with predefined target frequencies. The design approach modifies an individual resonator's response to unidirectional harmonic excitations in the in-plane and out-of-plane directions, mimicking the elliptical motion of surface waves. Once an arrangement of optimized resonators composes a locally resonant metasurface, frequency bandgaps appear around the designed antiresonance frequencies. Numerical investigations analyze three case studies, showing that longitudinal-like and flexural-like antiresonances lead to nonoverlapping bandgaps unless both antiresonance modes are combined to generate a single and wider bandgap. Experimental data demonstrate good agreement with the numerical results, validating the proposed design methodology as an effective tool to realize locally resonant metasurfaces by matching multiple antiresonances such that bandgaps generated as a result of in-plane and out-of-plane surface wave motion combine into wider bandgaps. 

   more » « less
2. Frequency Regulation using Sparse Learned Controllers in Power Grids with Variable Inertia due to Renewable Energy

   https://doi.org/10.1109/CDC40024.2019.9029534  

   Hidalgo-Gonzalez, Patricia; Henriquez-Auba, Rodrigo; Callaway, Duncan S.; Tomlin, Claire J. (December 2019, 2019 IEEE 58th Conference on Decision and Control (CDC))

   Inertia from rotating masses of generators in power systems influence the instantaneous frequency change when an imbalance between electrical and mechanical power occurs. Renewable energy sources (RES), such as solar and wind power, are connected to the grid via electronic converters. RES connected through converters affect the system's inertia by decreasing it and making it time-varying. This new setting challenges the ability of current control schemes to maintain frequency stability. Proposing adequate controllers for this new paradigm is key for the performance and stability of future power grids. The contribution of this paper is a framework to learn sparse time-invariant frequency controllers in a power system network with a time-varying evolution of rotational inertia. We model power dynamics using a Switched-Affine hybrid system to consider different modes corresponding to different inertia coefficients. We design a controller that uses as features, i.e. input, the systems states. In other words, we design a control proportional to the angles and frequencies. We include virtual inertia in the controllers to ensure stability. One of our findings is that it is possible to restrict communication between the nodes by reducing the number of features in the controller (from 22 to 10 in our case study) without disrupting performance and stability. Furthermore, once communication between nodes has reached a threshold, increasing it beyond this threshold does not improve performance or stability. We find a correlation between optimal feature selection in sparse controllers and the topology of the network. 

   more » « less
3. A Control Scheme Based on Lyapunov Function for Cascaded H-Bridge Multilevel Active Rectifiers

   https://doi.org/10.1109/APEC39645.2020.9124234  

   Jean-Pierre, Garry; Altin, Necmi; Shafei, Ahmad El; Nasiri, Adel (March 2020, 2020 IEEE Applied Power Electronics Conference and Exposition (APEC))

   null (Ed.)

   The cascaded H-bridge multilevel active rectifier is a prominent converter configuration. It presents compelling advantages, including high adjustability for a number of applications, such as in solid-state transformers, traction applications, medium and high power motor drives and battery chargers. However, when the H-bridge is operating under an unbalanced load and asymmetrical voltage conditions, it becomes important to design advanced control strategies to maintain the stability of the system. In this study, a Lyapunov-function based control method is proposed for controlling the single-phase cascaded H-bridge active rectifier to achieve global asymptotic stability. A capacitor voltage feedback is added to the conventional Lyapunov-function based stabilizing control method to minimize the resonance of the LCL filter. Additionally, a Proportional-Resonant (PR) control approach is adopted to obtain the reference current signal. This increases the robustness of the current control scheme. A DC voltage balancing control procedure is also employed to prevent the unbalanced DC voltage conditions among the H-bridges. The DC voltage is controlled via a PI controller. The capability of the control approach is verified with simulation and experimental studies. 

   more » « less
4. Structured Neural-PI Control with End-to-End Stability and Output Tracking Guarantees

   Wenqi Cui, Yan Jiang (December 2023, Advances in Neural Information Processing Systems 36 (NeurIPS 2023))

   A. Oh and T. Neumann and A. Globerson and K. Saenko and M. Hardt and S. Levine (Ed.)

   We study the optimal control of multiple-input and multiple-output dynamical systems via the design of neural network-based controllers with stability and output tracking guarantees. While neural network-based nonlinear controllers have shown superior performance in various applications, their lack of provable guarantees has restricted their adoption in high-stake real-world applications. This paper bridges the gap between neural network-based controllers and the need for stabilization guarantees. Using equilibrium-independent passivity, a property present in a wide range of physical systems, we propose neural Proportional-Integral (PI) controllers that have provable guarantees of stability and zero steady-state output tracking error. The key structure is the strict monotonicity on proportional and integral terms, which is parameterized as gradients of strictly convex neural networks (SCNN). We construct SCNN with tunable softplus-β activations, which yields universal approximation capability and is also useful in incorporating communication constraints. In addition, the SCNNs serve as Lyapunov functions, giving us end-to-end performance guarantees. Experiments on traffic and power networks demonstrate that the proposed approach improves both transient and steady-state performances, while unstructured neural networks lead to unstable behaviors. 

   more » « less
5. A Hybrid PID Design for Asymptotic Stabilization with Intermittent Measurements

   https://doi.org/10.1109/CDC.2018.8619150  

   Lavell, Daniel; Phillips, Sean; Sanfelice, Ricardo G. (December 2018, 2018 IEEE Conference on Decision and Control)

   In this paper, we propose a modeling and design technique for a proportional-integral-derivative (PID) controller in the presence of aperiodic intermittent sensor measurements. Using classical control design methods, PID controllers can be designed when measurements are available periodically, at discrete time instances, or continuously. Unfortunately, such design do not apply when measurements are available intermittently. Using the hybrid inclusions framework, we model the continuous-time plant to control, the mechanism triggering intermittent measurements, and a hybrid PID control law defining a hybrid closed-loop system. We provide sufficient conditions for uniform global asymptotic stability using Lyapunov set stability methods. These sufficient conditions are used for the design of the gains of the hybrid PID controller. Also, we propose relaxed sufficient conditions to provide a computationally tractable design method leveraging a polytopic embedding approach. The results are illustrated via numerical examples. 

   more » « less