Enrique Mallada

@inproceedings{hcm2017cdc,
  abstract = {The security-constrained economic dispatch (SCED) problem tries to maintain the reliability of a power network by ensuring that a single failure does not lead to a global outage. The previous research has mainly investigated SCED by formulating the problem in different modalities, e.g. preventive or corrective, and devising efficient solutions for SCED. In this paper, we tackle a novel and important direction, and analyze the economic cost of incorporating security constraints in economic dispatch. Inspired by existing inefficiency metrics in game theory and computer science, we introduce notion of price of security as a metric that formally characterizes the economic inefficiency of security-constrained economic dispatch as compared to the original problem without security constraints. Then, we focus on the preventive approach in a simple topology comprising two buses and two lines, and investigate the impact of generation availability and demand distribution on the price of security. Moreover, we explicitly derive the worst-case input instance that leads to the maximum price of security. By extensive experimental study on two test-cases, we verify the analytical results and provide insights for characterizing the price of security in general networks.},
  author = {Hajiesmaili, Mohammad H. and Cai, Desmond and Mallada, Enrique},
  booktitle = {56th IEEE Conference on Decision and Control (CDC)},
  doi = {10.1109/CDC.2017.8263947},
  grants = {1544771, 1711188, 1736448},
  keywords = {Power Networks},
  month = {12},
  pages = {2035-2040},
  title = {Understanding the Inefficiency of Security-Constrained Economic Dispatch},
  url = {https://mallada.ece.jhu.edu/pubs/2017-CDC-HCM.pdf},
  year = {2017}
}

@inproceedings{jpm2017cdc,
  abstract = {Implementing frequency response using grid-connected inverters is one of the popular proposed alternatives to mitigate the dynamic degradation experienced in low inertia power systems. However, such solution faces several challenges as inverters do not intrinsically possess the natural response to power fluctuations that synchronous generators have. Thus, to synthetically generate this response, inverters need to take frequency measurements, which are usually noisy, and subsequently make changes in the output power, which are therefore delayed. This paper explores the system-wide performance tradeoffs that arise when measurement noise, delayed actions, and power disturbances are considered in the design of dynamic controllers for grid-connected inverters. 
Using a recently proposed dynamic droop (iDroop) control for grid-connected inverters that is inspired by classical first order lead-lag compensation, we show that the sets of parameters that result in highest noise attenuation, power disturbance mitigation, and delay robustness do not necessarily have a common intersection. In particular, lead compensation is desired in systems where power disturbances are the predominant source of degradation, while lag compensation is a better alternative when the system is dominated by delays or frequency noise. Our analysis further shows that iDroop can outperform the standard droop alternative in both joint noise and disturbance mitigation, and delay robustness.},
  author = {Jiang, Yan and Pates, Richard and Mallada, Enrique},
  booktitle = {56th IEEE Conference on Decision and Control (CDC)},
  doi = {10.1109/CDC.2017.8264414},
  grants = {1544771, 1711188, W911NF-17-1-0092},
  keywords = {Power Networks},
  month = {12},
  pages = {5098-5105},
  title = {Performance tradeoffs of dynamically controlled grid-connected inverters in low inertia power systems},
  url = {https://mallada.ece.jhu.edu/pubs/2017-CDC-JPM.pdf},
  year = {2017}
}

@inproceedings{omg2017cdc,
  abstract = {In this paper we investigate the performance of linear networked dynamical systems over strongly connected digraphs. We consider first and second order systems subject to distributed disturbance inputs, and define an appropriate system output so that the performance measure is quantified through the input-output $\mathcal H_2$ norm of the system. We first develop a generalized framework for the computation of the $\mathcal H_2$ norm. We apply this framework to systems whose underlying network graphs result in normal weighted graph Laplacian matrices. We consider two performance metrics and find closed form solutions for the first and bounds for the other; which both depend on the eigenvalues of these graph Laplacians.
Numerical examples indicate that: (i) the tightness of the bounds are highly dependent on the graph structure, (ii) the $\mathcal H_2$ norm of a symmetric system is less than or equal to that of the corresponding perturbed non-symmetric system for either line or complete graphs when the network size is sufficiently large.},
  author = {Oral, H. Giray and Mallada, Enrique and Gayme, Dennice},
  bdsk-url-3 = {https://doi.org/10.1109/CDC.2017.8263893},
  booktitle = {56th IEEE Conference on Decision and Control (CDC)},
  doi = {10.1109/CDC.2017.8263893},
  grants = {1544771, W911NF-17-1-0092},
  keywords = {Power Networks},
  month = {12},
  pages = {1688-1694},
  title = {Performance of first and second order linear networked systems over digraphs},
  url = {https://mallada.ece.jhu.edu/pubs/2017-CDC-OMG.pdf},
  year = {2017}
}

@article{dms2017ieee-csl,
  abstract = {The AC power flow equations describe the steady-state behavior of the power grid. While many algorithms have been developed to compute solutions to the power flow equations, few theoretical results are available characterizing when such solutions exist, or when these algorithms can be guaranteed to converge. In this paper, we derive necessary and sufficient conditions for the existence and uniqueness of a power flow solution in balanced radial distribution networks with homogeneous (uniform R/X ratio) transmission lines. We study three distinct solution methods: fixed point iterations, convex relaxations, and energy functions - we show that the three algorithms successfully find a solution if and only if a solution exists. Moreover, all three algorithms always find the unique high-voltage solution to the power flow equations, the existence of which we formally establish. At this solution, we prove that (i) voltage magnitudes are increasing functions of the reactive power injections, (ii) the solution is a continuous function of the injections, and (iii) the solution is the last one to vanish as the system is loaded past the feasibility boundary.},
  author = {Dvijotham, Krishnamurthy and Mallada, Enrique and Simpson-Porco, John W.},
  doi = {10.1109/LCSYS.2017.2717578},
  grants = {1544771},
  journal = {IEEE Control Systems Letters},
  keywords = {Power Networks; Power Flow Solutions},
  month = {10},
  number = {2},
  pages = {322-327},
  title = {High-Voltage Solution in Radial Power Networks: Existence, Properties, and Equivalent Algorithms},
  url = {https://mallada.ece.jhu.edu/pubs/2017-IEEE-CSL-DMS.pdf},
  volume = {1},
  year = {2017}
}

@article{mzl2017tac,
  abstract = {Frequency control rebalances supply and demand while maintaining the network state within operational margins. It is implemented using fast ramping reserves that are expensive and wasteful, and which are expected to grow with the increasing penetration of renewables. The most promising solution to this problem is the use of demand response, i.e. load participation in frequency control. Yet it is still unclear how to efficiently integrate load participation without introducing instabilities and violating operational constraints.
In this paper we present a comprehensive load-side frequency control mechanism that can maintain the grid within operational constraints. Our controllers can rebalance supply and demand after disturbances, restore the frequency to its nominal value and preserve inter-area power flows. Furthermore, our controllers are distributed (unlike generation-side), can allocate load updates optimally, and can maintain line flows within thermal limits. We prove that such a distributed load-side control is globally asymptotically stable and robust to unknown load parameters. Simulations are used to illustrate the properties of our solution.},
  author = {Mallada, Enrique and Zhao, Changhong and Low, Steven H},
  doi = {10.1109/TAC.2017.2713529},
  grants = {1544771},
  journal = {IEEE Transactions on Automatic Control},
  keywords = {Power Networks},
  month = {12},
  number = {12},
  pages = {6294-6309},
  title = {Optimal load-side control for frequency regulation in smart grids},
  url = {https://mallada.ece.jhu.edu/pubs/2017-TAC-MZL.pdf},
  volume = {62},
  year = {2017}
}

@inproceedings{pm2017ifac-wc,
  abstract = {This paper develops a novel framework for power system stability analysis, that allows for the decentralised design of inverter based controllers. The method requires that each individual inverter satisfies a standard H1 design requirement. Critically each requirement depends only on the dynamics of the components and inverters at each individual bus, and the aggregate susceptance of the transmission lines connected to it. The method is both robust to network and delay uncertainties, as well as heterogeneous network components, and when no network information is available it reduces to the standard decentralised passivity sufficient condition for stability. We illustrate the novelty and strength of our approach by studying the design of inverter-based control laws in the presence of delays.},
  author = {Pates, Richard and Mallada, Enrique},
  bdsk-url-3 = {https://doi.org/10.1016/j.ifacol.2017.08.1097},
  booktitle = {IFAC World Congress},
  doi = {https://doi.org/10.1016/j.ifacol.2017.08.1097},
  grants = {1544771},
  keywords = {Power Networks},
  month = {7},
  number = {1},
  pages = {5548 - 5553},
  title = {Decentralised Robust Inverter-based Control in Power Systems},
  url = {https://mallada.ece.jhu.edu/pubs/2017-IFAC-WC-PM.pdf},
  volume = {50},
  year = {2017}
}

@article{cmw2017tps,
  abstract = {Economic dispatch and frequency regulation are typically viewed as fundamentally different problems in power systems and, hence, are typically studied separately. In this paper, we frame and study a joint problem that co-optimizes both slow timescale economic dispatch resources and fast timescale frequency regulation resources. We show how the joint problem can be decomposed without loss of optimality into slow and fast timescale sub-problems that have appealing interpretations as the economic dispatch and frequency regulation problems respectively. We solve the fast timescale sub-problem using a distributed frequency control algorithm that preserves the stability of the network during transients. We solve the slow timescale sub-problem using an efficient market mechanism that coordinates with the fast timescale sub-problem. We investigate the performance of the decomposition on the IEEE
24-bus reliability test system.},
  author = {Cai, Desmond and Mallada, Enrique and Wierman, Adam},
  doi = {10.1109/TPWRS.2017.2682235},
  grants = {1544771},
  journal = {IEEE Transactions on Power Systems},
  keywords = {Power Networks; Markets},
  month = {11},
  number = {6},
  pages = {4370-4385},
  title = {Distributed optimization decomposition for joint economic dispatch and frequency regulation},
  url = {https://mallada.ece.jhu.edu/pubs/2017-TPS-CMW.pdf},
  volume = {32},
  year = {2017}
}

@inproceedings{cmlc2016allerton,
  abstract = {This paper studies the projected saddle-point dynamics for a twice differentiable convex-concave function, which we term saddle function. The dynamics consists of gradient
descent of the saddle function in variables corresponding to convexity and (projected) gradient ascent in variables corresponding to concavity. We provide a novel characterization of the omega-limit set of the trajectories of these dynamics in terms of the diagonal Hessian blocks of the saddle function. Using this characterization, we establish global asymptotic convergence of the dynamics under local strong convexityconcavity of the saddle function. If this property is global, and for the case when the saddle function takes the form of the Lagrangian of an equality constrained optimization problem, we establish the input-to-state stability of the saddlepoint dynamics by providing an ISS Lyapunov function. Various examples illustrate our results.},
  author = {Ashish Cherukuri and Mallada, Enrique and Steven H. Low and Jorge Cortes},
  booktitle = {54th Allerton Conference on Communication, Control, and Computing},
  doi = {10.1109/ALLERTON.2016.7852273},
  grants = {1544771},
  keywords = {Saddle-Point Dynamics; Caratheodory solutions},
  month = {09},
  pages = {504-510},
  title = {The role of strong convexity-concavity in the convergence and robustness of the saddle-point dynamics},
  url = {https://mallada.ece.jhu.edu/pubs/2016-Allerton-CMLC.pdf},
  year = {2016}
}