Monitoring, Control and Protection
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ItemExperimental Investigation of a Capacity-Based Demand Response Mechanism for District-Scale Applications( 2019-01-08)District heating and cooling systems incorporating heat recovery and large-scale thermal storage dramatically reduce energy waste and greenhouse gas emissions. Electrifying district energy systems also has the effect of introducing city-scale controllable loads at the level of the electrical substation. Here we explore the opportunity for these systems to provide energy services to the grid through capacity-based demand response mechanisms. We present both a planning approach to estimate available demand-side capacity and a control framework to guide real-time scheduling when the program is active. These tools are used to assess the technical feasibility and the economic viability of participating in capacity-based demand response in the context of a real-world, megawatt-scale pilot during the summer of 2018 on the Stanford University campus.
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ItemExtremum Seeking Control of Distributed Energy Resources with Decaying Dither and Equilibrium-based Switching( 2019-01-08)Optimal control of Distributed Energy Resources (DER) may be a critical component for proper operation of the electric distribution grid in the near future. However, many optimization-based approaches for managing DER require knowledge of the underlying distribution system topology, network impedances, and access to feeder-wide real time load information. In order to ameliorate these requirements, we propose a 2-dimensional Extremum Seeking (2D-ES) control scheme to manage DER active and reactive power contributions. We augment the 2D-ES scheme with an exponentially decaying probing (dither) signal that activates based on an equilibrium-based switching criteria. Our simulation results show that the approach can enable substation real and reactive power target tracking with dither signals that exponentially decay once the individual ES controllers have each reached their optimum values.
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ItemScalable Computation of 2D-Minkowski Sum of Arbitrary Non-Convex Domains: Modeling Flexibility in Energy Resources( 2019-01-08)The flexibility of active ($p$) and reactive power ($q$) consumption in distributed energy resources (DERs) can be represented as a (potentially non-convex) set of points in the $p$-$q$ plane. Modeling of the aggregated flexibility in a heterogeneous ensemble of DERs as a Minkowski sum (M-sum) is computationally intractable even for moderately sized populations. In this article, we propose a scalable method of computing the M-sum of the flexibility domains of a heterogeneous ensemble of DERs, which are allowed to be non-convex, non-compact. In particular, the proposed algorithm computes a guaranteed superset of the true M-sum, with desired accuracy. The worst-case complexity of the algorithm is computed. Special cases are considered, and it is shown that under certain scenarios, it is possible to achieve a complexity that is linear with the size of the ensemble. Numerical examples are provided by computing the aggregated flexibility of different mix of DERs under varying scenarios.
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ItemHeterogeneous Electric Vehicle Charging Coordination: A Variable Charging Speed Approach( 2019-01-08)We present a coordination mechanism that reduces peak demand coming from EV charging, supports grid stability and environmental sustainability. The proposed mechanism accounts for individual commuting preferences, as well as desired states of charge by certain deadlines, which can serve as a proxy for range anxiety. It can shape EV charging toward a desired profile, without violating individual preferences. Our mechanism mitigates herding, which is typical in populations where all agents receive the same price signals and make similar charging decisions. Furthermore, it assumes no prior knowledge about EV customers and therefore learns preferences and reactions to prices dynamically. We show through simulations that our mechanism induces a less volatile demand and lower peaks compared to currently used benchmarks.
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ItemIterative Matrix Pencil Method for Power System Modal Analysis( 2019-01-08)This paper introduces a modal analysis approach termed as the Iterative Matrix Pencil method. It uses the Matrix Pencil Method as the primary tool for mode identification, and adds to it by utilizing the concept of a cost function in order to reduce the number of signals needed to identify the modes for a large system. The method is tested for a variety of large synthetic power grids in this paper, with the cost function being reported to measure accuracy. A sensitivity analysis is also considered, showing how this new method behaves when adjusting the two primary user-based inputs; the number of iterations, and the SVD threshold.
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ItemA Stochastic Program for Black Start Allocation( 2019-01-08)The fast and secure restoration of the power system after an extended blackout highly depends on the location of Black Start (BS) resources. In contrast to most generators, BS units have the ability to start without being connected to an already energized power grid. Selecting a unit to provide BS services is associated with costly technical upgrades, continuous testing, and compensation for the services, and once a unit is selected as BS it is expected to provide that service for several years. For these reasons, the selection process to allocate new BS units is very important and currently handled by experts in the field. Building on the existing literature for power system restoration and black start allocation, we formulate an optimization problem aimed at allocating BS units optimally in the power grid. While restoration plans are usually examined under the assumption of a total blackout, in reality most blackouts are partial, leaving parts of the grid energized and certain elements damaged. In order to account for these cases during the selection process, we formulate a two-stage stochastic program that optimizes the allocation of BS resources over a number of outage scenarios. We use a scenario decomposition algorithm to solve the resulting optimization problem to near-optimality in a high performance computing environment. We conduct numerical experiments using the proposed model and decomposition method on the IEEE-39.
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ItemEffects of Wind Turbine Generators on Inter-Area Oscillations and Damping Control Design( 2019-01-08)This paper analyzes the effect of wind turbine integration (WT) on the inter-area oscillation mode of a test two-area power system. The paper uses a root-locus based design method to propose a pair of controllers to provide damping to the inter-area mode of the system. The controllers are selected from the best combination of feedback signal and WT control action. One of the controllers uses the active power control part of the WT while the other uses the reactive power part. The paper analyzes the impact that increases on the transmission line connecting the WT to the system have on the controllers’ performance. Time domain simulations are provided to evaluate the effectiveness of the controllers under different conditions.
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ItemVisual Validation of Estimated Parametric Models of Power Systems Under Ambient Conditions( 2019-01-08)With the advent of synchrophasors, a number of measurement–based algorithms have been developed to estimate system modes using ambient data. The accuracy of these mode estimates depends on a number of factors, such as selection of the system order and data channels. To validate these mode estimates, two methods are proposed in this paper based on how well they agree with the observed data using the estimated parametric system model and observed data. In the proposed methods, the contribution of each mode estimate is analyzed to obtain a combination of system mode estimates to represent the model. The methodology of the proposed methods are illustrated using least–squares ARMA (LS–ARMA) method, which gives a parametric system model estimates. Results obtained by implementing the proposed methods on measured and simulated data validate the effectiveness of the proposed methods.
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