pwc-archive/papers-with-abstracts huggingface dataset:
Forward-Backward Extended DMD with an Asymptotic Stability Constraint
Authors: Louis Lortie, Steven Dahdah, James Richard Forbes
Date: 2024-03-15 00:00:00

This paper presents a data-driven method to identify an asymptotically stable Koopman system from noisy data. In particular, the proposed approach combines approximations of the system's forward- and backward-in-time dynamics to reduce bias caused by noisy data while enforcing asymptotic stability. A Koopman model of an inherently asymptotically stable system can be unstable due to noisy data and a poor choice of lifting functions. To prevent identifying an unstable model, the proposed approach imposes an asymptotic stability constraint on the Koopman model. The proposed method is formulated as a semidefinite program and its performance is compared to state-of-the-art methods with a simulated Duffing oscillator dataset and experimental soft robot dataset.
Lyapunov Neural Network with Region of Attraction Search
Authors: Zili Wang, Sean B. Andersson, Roberto Tron
Date: 2024-03-15 00:00:00
Tasks: Deep Reinforcement Learning, valid

Deep learning methods have been widely used in robotic applications, making learning-enabled control design for complex nonlinear systems a promising direction. Although deep reinforcement learning methods have demonstrated impressive empirical performance, they lack the stability guarantees that are important in safety-critical situations. One way to provide these guarantees is to learn Lyapunov certificates alongside control policies. There are three related problems: 1) verify that a given Lyapunov function candidate satisfies the conditions for a given controller on a region, 2) find a valid Lyapunov function and controller on a given region, and 3) find a valid Lyapunov function and a controller such that the region of attraction is as large as possible. Previous work has shown that if the dynamics are piecewise linear, it is possible to solve problems 1) and 2) by solving a Mixed-Integer Linear Program (MILP). In this work, we build upon this method by proposing a Lyapunov neural network that considers monotonicity over half spaces in different directions. We 1) propose a specific choice of Lyapunov function architecture that ensures non-negativity and a unique global minimum by construction, and 2) show that this can be leveraged to find the controller and Lyapunov certificates faster and with a larger valid region by maximizing the size of a square inscribed in a given level set. We apply our method to a 2D inverted pendulum, unicycle path following, a 3-D feedback system, and a 4-D cart pole system, and demonstrate it can shorten the training time by half compared to the baseline, as well as find a larger ROA.
Depreciation Cost is a Poor Proxy for Revenue Lost to Aging in Grid Storage Optimization
Authors: Volkan Kumtepeli, Holger Hesse, Thomas Morstyn, Seyyed Mostafa Nosratabadi, Marko Aunedi, David A. Howey
Date: 2024-03-15 00:00:00

Dispatch of a grid energy storage system for arbitrage is typically formulated into a rolling-horizon optimization problem that includes a battery aging model within the cost function. Quantifying degradation as a depreciation cost in the objective can increase overall profits by extending lifetime. However, depreciation is just a proxy metric for battery aging; it is used because simulating the entire system life is challenging due to computational complexity and the absence of decades of future data. In cases where the depreciation cost does not match the loss of possible future revenue, different optimal usage profiles result and this reduces overall profit significantly compared to the best case (e.g., by 30-50%). Representing battery degradation perfectly within the rolling-horizon optimization does not resolve this - in addition, the economic cost of degradation throughout life should be carefully considered. For energy arbitrage, optimal economic dispatch requires a trade-off between overuse, leading to high return rate but short lifetime, vs. underuse, leading to a long but not profitable life. We reveal the intuition behind selecting representative costs for the objective function, and propose a simple moving average filter method to estimate degradation cost. Results show that this better captures peak revenue, assuming reliable price forecasts are available.
On the Use of Cramer-Rao Lower Bound for Least-Variance Circuit Parameters Identification of Li-ion Cells
Authors: Vladimir Sovljanski, Mario Paolone
Date: 2024-03-15 00:00:00

Electrochemical Impedance Spectroscopy (EIS) and Equivalent Circuit Models (ECMs) are widely used to characterize the impedance and estimate parameters of electrochemical systems such as batteries. We use a generic ECM with ten parameters grouped to model different frequency regions of the Li-ion cell's impedance spectrum. We derive a noise covariance matrix from the measurement model and use it to assign weights for the fitting technique. The paper presents two formulations of the parameters identification problem. Using the properties of the ECM EIS spectra, we propose a method to initialize ECM parameters for the Complex Non-linear Least Squares (CNLS) technique. The paper proposes a novel algorithm for designing the EIS experiments by applying the theory on Cramer-Rao Lower Bound (CRLB) and Fisher Information Matrix (FIM) to the identification problem. We show that contributions to the FIM elements strongly depend on the frequencies at which EIS is performed. Hence, the algorithm aims to adjust frequencies such that the most information about parameters is collected. This is done by minimizing the highest variance of ECM parameters defined by CRLB. Results of a numerical experiment show that the estimator is efficient, and frequency adjustment leads to more accurate ECM parameters' identification.
On well-posedness of the leak localization problem in parallel pipe networks
Authors: Victor Molnö, Henrik Sandberg
Date: 2024-03-15 00:00:00

With the advent of integrated sensor technology (smart flow meters and pressure sensors), various new numerical algorithms for leak localization (a core element of water distribution system operation) have been developed. However, there is a lack of theory regarding the limitations of leak localization. In this work, we contribute to the development of such a theory by introducing an example water network structure with parallel pipes that is tractable for analytical treatment. We define the leak localization problem for this structure and show how many sensors and what conditions are needed for the well-posedness of the problem. We present a formula for the leak position as a function of measurements from these sensors. However, we also highlight the risk of finding false but plausible leak positions in the multiple pipes. We try to answer the questions of how and when the leaking pipe can be isolated. In particular, we show that nonlinearities in the pipes' head loss functions are essential for the well-posedness of the isolation problem. We propose procedures to get around the pitfall of multiple plausible leak positions.
Hierarchical Provision of Distribution Grid Flexibility with Online Feedback Optimization
Authors: Florian Klein-Helmkamp, Irina Zettl, Florian Schmidtke, Lukas Ortmann, Andreas Ulbig
Date: 2024-03-15 00:00:00
Tasks: Computational Efficiency, Point Tracking

Utilizing distribution grid flexibility for ancillary services requires the coordination and dispatch of requested active and reactive power to a large number of distributed energy resources in underlying grid layers. This paper presents an approach to hierarchically dispatch flexibility requests based on Online Feedback Optimization (OFO). We implement a framework of individual controllers coordinating actors, contributing to flexibility provision, to track a requested operating point at the interface between grid layers. The framework is evaluated in terms of performance during coordination and possible interaction between individual controllers, both central and distributed. Results show high reliability and robustness of the OFO controllers as well as an efficient dispatch of active and reactive power. Its computational efficiency and capabilities in set point tracking during online grid operation are making OFO a promising approach to the flexibility dispatch problem.
Compositionally Verifiable Vector Neural Lyapunov Functions for Stability Analysis of Interconnected Nonlinear Systems
Authors: Jun Liu, Yiming Meng, Maxwell Fitzsimmons, Ruikun Zhou
Date: 2024-03-15 00:00:00

While there has been increasing interest in using neural networks to compute Lyapunov functions, verifying that these functions satisfy the Lyapunov conditions and certifying stability regions remain challenging due to the curse of dimensionality. In this paper, we demonstrate that by leveraging the compositional structure of interconnected nonlinear systems, it is possible to verify neural Lyapunov functions for high-dimensional systems beyond the capabilities of current satisfiability modulo theories (SMT) solvers using a monolithic approach. Our numerical examples employ neural Lyapunov functions trained by solving Zubov's partial differential equation (PDE), which characterizes the domain of attraction for individual subsystems. These examples show a performance advantage over sums-of-squares (SOS) polynomial Lyapunov functions derived from semidefinite programming.
Optimal Sequencing and Motion Control in a Roundabout with Safety Guarantees
Authors: Yingqing Chen, Christos G. Cassandras, Kaiyuan Xu
Date: 2024-03-14 00:00:00
Tasks: Model Predictive Control

This paper develops a controller for Connected and Automated Vehicles (CAVs) traversing a single-lane roundabout. The controller simultaneously determines the optimal sequence and associated optimal motion control jointly minimizing travel time and energy consumption while providing speed-dependent safety guarantees, as well as satisfying velocity and acceleration constraints. This is achieved by integrating (a) Model Predictive Control (MPC) to enable receding horizon optimization with (b) Control Lyapunov-Barrier Functions (CLBFs) to guarantee convergence to a safe set in finite time, thus providing an extended stability region compared to the use of classic Control Barrier Functions (CBFs). The proposed MPC-CLBF framework addresses both infeasibility and myopic control issues commonly encountered when controlling CAVs over multiple interconnected control zones in a traffic network, which has been a limitation of prior work on CAVs going through roundabouts, while still providing safety guarantees. Simulations under varying traffic demands demonstrate the controller's effectiveness and stability.
Wildfire Resilient Unit Commitment under Uncertain Demand
Authors: Ryan Greenough, Kohei Murakami, Michael Davidson, Jan Kleissl, Adil Khurram
Date: 2024-03-14 00:00:00

Public safety power shutoffs (PSPS) are a common pre-emptive measure to reduce wildfire risk due to power system equipment. System operators use PSPS to de-energize electric grid elements that are either prone to failure or located in regions at a high risk of experiencing a wildfire. Successful power system operation during PSPS involves coordination across different time scales. Adjustments to generator commitments and transmission line de-energizations occur at day-ahead intervals while adjustments to load servicing occur at hourly intervals. Generator commitments and operational decisions have to be made under uncertainty in electric grid demand and wildfire potential forecasts. This paper presents deterministic and two-stage mean-CVaR stochastic frameworks to show how the likelihood of large wildfires near transmission lines affects generator commitment and transmission line de-energization strategies. The optimal costs of commitment, operation, and lost load on the IEEE 14-bus test system are compared to the costs generated from prior optimal power shut-off (OPS) formulations. The proposed mean-CVaR stochastic program generates less total expected costs evaluated with respect to higher demand scenarios than costs generated by risk-neutral and deterministic methods.
Impact of Objective Function on Spectral Efficiency in Integrated HAPS-Terrestrial Networks
Authors: Afsoon Alidadi Shamsabadi, Animesh Yadav, Halim Yanikomeroglu
Date: 2024-03-14 00:00:00
Tasks: Fairness

Integrating non-terrestrial networks (NTNs), in particular high altitude platform stations (HAPS), with terrestrial networks, referred to as vHetNets, emerges as a promising future wireless network architecture for providing ubiquitous connectivity. In this context, optimizing the performance of vHetNets has become a paramount concern, particularly in harmonized spectrum vHetNets, where HAPS and terrestrial networks share the same frequency band, resulting in severe inter-/intra-tier interference. This paper provides a comparative analysis of different objective functions, specifically focusing on weighted sum rate (WSR), network-wide proportional fairness (NW-PF), and network-wide max-min fairness (NW-MMF), with an aim to design a joint user association scheme and multiple-input multiple-output (MIMO) beamforming weights in a vHetNet, operating in an urban area. The simulation results comprehensively compare the behavior of different objective functions in vHetNets and standalone terrestrial networks. This analysis aims to shed light on the impact of diverse objective functions on the achievable spectral efficiency (SE) of vHetNets.
Learning High-Order Control Barrier Functions for Safety-Critical Control with Gaussian Processes
Authors: Mohammad Aali, Jun Liu
Date: 2024-03-14 00:00:00
Tasks: Gaussian Processes

Control barrier functions (CBFs) have recently introduced a systematic tool to ensure system safety by establishing set invariance. When combined with a nominal control strategy, they form a safety-critical control mechanism. However, the effectiveness of CBFs is closely tied to the system model. In practice, model uncertainty can compromise safety guarantees and may lead to conservative safety constraints, or conversely, allow the system to operate in unsafe regions. In this paper, we use Gaussian processes to mitigate the adverse effects of uncertainty on high-order CBFs (HOCBFs). A properly structured covariance function enables us to convert the chance constraints of HOCBFs into a second-order cone constraint. This results in a convex constrained optimization as a safety filter. We analyze the feasibility of the resulting optimization and provide the necessary and sufficient conditions for feasibility. The effectiveness of the proposed strategy is validated through two numerical results.
Mixed Algorithm of SINDy and HAVOK for Measure-Based Analysis of Power System with Inverter-based Resources
Authors: Reza Saeed Kandezy, John Ning Jiang
Date: 2024-03-14 00:00:00

Artificial intelligence and machine learning is enhancing electric grids by offering data analysis tools that can be used to operate the power grid more reliably. However, the complex nonlinear dynamics, particularly when coupled with multi-scale interactions among Inverter-based renewable energy Resources, calls for effective algorithms for power system application. This paper presents affective novel algorithm to detect various nonlinear dynamics, which is built upon: the Sparse Identification of Nonlinear Dynamics method for nonlinear dynamics detection; and Hankel Alternative View of Koopman method for multi-scale decomposition. We show that, by an appropriate integration of the strengths of the two, the mixed algorithm not only can detect the nonlinearity, but also it distinguishes the nonlinearity caused by coupled Inverter-based resources from the more familiar ones caused synchronous generators. This shows that the proposal algorithm can be a promising application of artificial intelligence and machine learning for data measure-based analysis to support operation of power system with integrated renewables.
Defense via Behavior Attestation against Attacks in Connected and Automated Vehicles based Federated Learning Systems
Authors: Godwin Badu-Marfo, Ranwa Al Mallah, Bilal Farooq
Date: 2024-03-14 00:00:00
Tasks: Federated Learning

The recent application of Federated Learning algorithms in IOT and Wireless vehicular networks have given rise to newer cyber threats in the mobile environment which hitherto were not present in traditional fixed networks. These threats arise due to the intrinsic nature of wireless transmission medium and other inherent characteristics of mobile networks such as high-node mobility and rapidly changing topology. This paper investigates the robustness of Vehicular AttestedFL defense strategies against falsified information attacks by tracking the behavior. We show that the defense strategies are capable of detecting and eliminating malicious nodes in the wireless mobile setting of the future smart road networks.
Reliability and Preventive Maintenance of Ducted Wind Turbines
Authors: Shafat Sharar, Carl D. Hoover
Date: 2024-03-14 00:00:00

This paper presents a reliability life analysis and preventive maintenance schedule for ducted wind turbines. Ducted wind turbines (DWT) are an emerging segment of the renewable energy industry with innovations that promise reliable, efficient, low-cost energy for consumer and small business markets. Many attempts have been made to build viable ducted turbines over the last century, but until recently none have succeeded commercially. Optimal shroud and blade designs are the focus of most engineering research to improve performance and efficiency, however, we hypothesize that an equally important key to the long-term success of small wind innovations is reliability analysis. For consumers and companies who want to efficiently maximize the lifespan of DWTs, this has significant ramifications. Operating beyond service life can result in catastrophic component failure and high replacement costs, making the technology economically infeasible. Our approach is focused on the analysis of 3.5 kW D3 turbines manufactured by Ducted Wind Turbines, Inc. We develop a component-level reliability analysis using ASTM E3159 and a consumer-level preventative maintenance schedule including failure modes and life estimates. Future research can use these findings to guide options for DWT life extension as well as localized maintenance solutions meant to reduce operational costs while preserving energy output.
The Development of Investment Planning Models for the United Kingdoms Wind and Solar Fleets
Authors: Anthony D Stephens, David R Walwyn
Date: 2024-03-14 00:00:00

Previous work has resulted in the development of an energy model able to calculate wind and solar fleet efficiencies. However, for investment planning purposes, it is necessary to calculate from the lowest economically acceptable efficiencies how much wind and solar generation would be economically justified. The paper explains how this objective has been achieved with arrays (investment planning tables) created after carrying out a structured investigation of the behaviour of the electricity system over the whole of its operational range. The tables are then applied to National Grid prediction of the size and composition of the system in the year 2035. A conclusion is reached that wind and solar generation will only be able to supply about 70% of electrical demand, the other 30% being provided by dispatchable sources of generation, which must be sufficiently fast acting to maintain electricity system stability, such as the use of combined cycle gas turbines. This limit on deployment of wind and solar generation restricts their ability to decarbonise the electricity system and is likely to lead in 2035 to a residual of 72 million tonnes per annum of carbon dioxide emissions which wind and solar generations will be unable to address
A Modified da Vinci Surgical Instrument for OCE based Elasticity Estimation with Deep Learning
Authors: Maximilian Neidhardt, Robin Mieling, Sarah Latus, Martin Fischer, Tobias Maurer, Alexander Schlaefer
Date: 2024-03-14 00:00:00

Robot-assisted surgery has advantages compared to conventional laparoscopic procedures, e.g., precise movement of the surgical instruments, improved dexterity, and high-resolution visualization of the surgical field. However, mechanical tissue properties may provide additional information, e.g., on the location of lesions or vessels. While elastographic imaging has been proposed, it is not readily available as an online modality during robot-assisted surgery. We propose modifying a da~Vinci surgical instrument to realize optical coherence elastography (OCE) for quantitative elasticity estimation. The modified da~Vinci instrument is equipped with piezoelectric elements for shear wave excitation and we employ fast optical coherence tomography (OCT) imaging to track propagating wave fields, which are directly related to biomechanical tissue properties. All high-voltage components are mounted at the proximal end outside the patient. We demonstrate that external excitation at the instrument shaft can effectively stimulate shear waves, even when considering damping. Comparing conventional and deep learning-based signal processing, resulting in mean absolute errors of 19.27 kPa and 6.29 kPa, respectively. These results illustrate that precise quantitative elasticity estimates can be obtained. We also demonstrate quantitative elasticity estimation on ex-vivo tissue samples of heart, liver and stomach, and show that the measurements can be used to distinguish soft and stiff tissue types.
Synchronized states of power grids and oscillator networks by convex optimization
Authors: Carsten Hartmann, Philipp C. Böttcher, David Gross, Dirk Witthaut
Date: 2024-03-14 00:00:00

Synchronization is essential for the operation of AC power systems: All generators in the power grid must rotate with fixed relative phases to enable a steady flow of electric power. Understanding the conditions for and the limitations of synchronization is of utmost practical importance. In this article, we propose a novel approach to compute and analyze the stable stationary states of a power grid or an oscillator network in terms of a convex optimization problem. This approach allows to systematically compute \emph{all} stable states where the phase difference across an edge does not exceed $\pi/2$.Furthermore, the optimization formulation allows to rigorously establish certain properties of synchronized states and to bound the error in the widely used linear power flow approximation.