Search

The automatic generation control (AGC) system is temporally situated between economic dispatch and synchronous generator dynamics, and its primary role is to regulate frequency within and tie-line flows between control areas. Given appropriate choice of participation factors (feed-forward controller gains that govern the disaggregation of the area-level power requirement to individual generators), the AGC can be engineered to nudge system dynamics toward a steady-state operating point corresponding to economic optimality. This paper establishes necessary and sufficient conditions under which a widely accepted choice of participation factors guarantees the alignment of steady-state synchronous generator outputs with a global minimum of a prototypical economic dispatch problem. In so doing, it resolves several ambiguities and formalizes technical assumptions governing the role of the standard AGC architecture in the context of economic dispatch and steady-state operation. Numerical case studies tailored to a modified version of the New England 39-bus 10-machine test system validate the theoretical results. [ABSTRACT FROM AUTHOR]

This paper presents a measurement-based method to determine distributed energy resource (DER) active- and reactive-power setpoints that minimize bus voltage deviations from prescribed reference values, bus active- and reactive-power deviations from desired setpoints, as well as cost of DER outputs. Central to the proposed method is the estimation of a linear sensitivity model from synchronized voltage and power-injection data collected from distribution-level phasor measurement units installed at only a subset of buses in the distribution system. As new measurements become available, the linear sensitivity model is updated via the recursive weighted partial least-squares estimation method. The estimated sensitivity model is then embedded as an equality constraint in a convex quadratic optimization problem, which can be solved via, e.g., the alternating direction method of multipliers. Numerical simulations involving the IEEE 33-bus distribution test system illustrate key benefits of the proposed method, including (i) eliminating the need for an accurate offline system model, (ii) adapting to online network-topology and operating-point changes, and (iii) being robust against delays potentially attributed to communication, computation, and actuation. Additional numerical simulations involving larger test systems demonstrate computational scalability. [ABSTRACT FROM AUTHOR]

Power flow formulated with a distributed slack bus involves modeling the active-power output of each generator with three elements: a nominal injection modulated by a fraction of the net-load imbalance allocated via a participation factor. This setup acknowledges generator dynamics and system operations, but it has long been plagued by ambiguous and inconsistent interpretations of its constituent elemental quantities. In this paper, we establish that, with the: i) nominal active-power injections set to be the economic dispatch setpoints, ii) participation factors fixed to be the ones used in automatic generation control, and iii) net-load imbalance considered to be the total load and loss unaccounted in economic dispatch, the power flow solution best matches results from a simulation unto steady state of the system differential algebraic equation (DAE) model. Numerical case studies tailored to the New England test system validate the analysis by demonstrating that solutions obtained from a distributed slack formulation offer lower errors (with respect to DAE-model simulations) compared to the exhaustive set of all single slack bus choices. [ABSTRACT FROM AUTHOR]

This letter presents an analytical closed-form expression that quantifies the contributions of nodal active- and reactive-power injections to total loss in a power system operating at sinusoidal steady state. We term this as the loss divider, since it is derived by leveraging the ubiquitous current divider law. The proposed loss divider innately embeds the dependence of system loss on both the network topology and the operating point, i.e., voltage profile. The derivation does not rely on any simplifying assumptions, and so the resulting expression delineates the exact quadratic relationship between the system loss and nodal active- and reactive-power injections. [ABSTRACT FROM AUTHOR]

This paper proposes to incorporate goodness-of-fit (GoF) metrics as outputs—in addition to the synchronized phasor (or synchrophasor)—from a phasor measurement unit (PMU) to assess the performance quality of synchrophasor-based real-time applications, with specific focus on the accuracy of fault location along a transmission line. Typically, a PMU outputs quantities that describe the phasor-of-best-fit of a time-domain voltage or current signal. While a phasor accurately represents the actual measured signal in sinusoidal steady state, this may not be the case during electrical transients that occur immediately after sudden events, such as a fault. Unaware of this, the real-time application may not locate the fault accurately. By quantifying the accuracy of the phasor as compared with the actual time-domain signal to which the phasor is fit, GoF metrics help to assess the credibility of fault-location results. This hypothesis is verified via extensive case studies, and GoF-based criteria for sufficiently accurate fault-location results are uncovered. [ABSTRACT FROM PUBLISHER]

This paper proposes a method to directly compute controller parameter values in a synchronverter augmented with a so-called damping correction loop, and in so doing, achieve desired transient and steady-state response. The proposed approach is grounded in a reduced third-order system model that captures pertinent dynamic characteristics of the synchronverter active-power loop (APL), particularly those of the dominant mode. This reduced-order model helps to identify and explain a shortcoming in a previous parameter tuning method. Central to the proposed parameter computation method is to express APL parameters of the original system as closed-form functions of the poles of the reduced-order system. Since the reduced-order model retains dominant-mode dynamic behaviors of the original system, APL parameters can be directly computed according to specified APL dominant mode. Time-domain simulations are provided to validate the accuracy of the reduced-order model and the proposed direct-computation parameter tuning method. [ABSTRACT FROM AUTHOR]

This paper proposes to augment the conventional synchronverter control scheme with an auxiliary loop to freely adjust the dynamic response speed. This loop is dubbed as a damping correction loop since its form and function are reminiscent of the damping component in the classical synchronous generator model. Central to the proposed auxiliary loop is the creation of an additional tuneable parameter that allows for unrestricted adjustment of the system damping ratio without affecting the steady-state frequency droop characteristic, which is an improvement over the conventional synchronverter design. In the proposed method, relevant parameters are analytically tuned and active- and reactive-power coupling effects are reduced when operating with increased response speed. The dynamic response and robustness of the approach are verified via extensive small-signal analysis. Furthermore, time-domain simulations highlight the advantages of the proposed method over existing ones. [ABSTRACT FROM PUBLISHER]

This paper presents analytical closed-form expressions that uncover the contributions of nodal active- and reactive-power injections to the active- and reactive-power flows on transmission lines in an AC electrical network. Paying due homage to current- and voltage-divider laws that are similar in spirit, we baptize these as the power divider laws. Derived from a circuit-theoretic examination of AC power-flow expressions, the constitution of the power divider laws reflects the topology and voltage profile of the network. We demonstrate the utility of the power divider laws to the analysis of power networks by highlighting applications to transmission-network allocation, transmission-loss allocation, and identifying feasible injections while respecting line active-power flow set points. [ABSTRACT FROM PUBLISHER]

A method is proposed to detect and identify power system transmission line outages in near real-time. The method exploits the statistical properties of the small random fluctuations in electricity generation and demand that a power system is subject to as time evolves. To detect and identify transmission line outages, a linearized incremental small-signal power system model is used in conjunction with high-speed synchronized voltage phase angle measurements obtained from phasor measurement units. By monitoring the statistical properties of voltage phase angle time-series, line outages are detected and identified using techniques borrowed from the theory of quickest change detection. As illustrated through case studies, the proposed method is effective in detecting and identifying single- and double-line outages in an accurate and timely fashion. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method to compute linear sensitivity distribution factors (DFs) in near real time without relying on a power flow model of the system. Specifically, we compute the injection shift factors (ISFs) of a particular line of interest with respect to active power injections at all buses (all other DFs can be determined from ISFs). The proposed ISF estimation method relies on the solution of an underdetermined system of linear equations that arise from high-frequency synchronized measurements obtained from phasor measurement units. We exploit a sparse representation (i.e., one in which many elements are zero) of the vector of desired ISFs via rearrangement by electrical distance and an appropriately chosen linear transformation, and cast the estimation problem into a sparse vector recovery problem. As we illustrate through case studies, the proposed approach provides accurate DF estimates with fewer sets of synchronized measurements than earlier approaches that rely on the solution of an overdetermined system of equations via the least-squares errors estimation method. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a method to compute linear sensitivity distribution factors (DFs) in near real-time. The method does not rely on the system power flow model. Instead, it uses only high-frequency synchronized data collected from phasor measurement units to estimate the injection shift factors through linear least-squares estimation, after which other DFs can be easily computed. Such a measurement-based approach is desirable since it is adaptive to changes in system operating point and topology. We further improve the adaptability of the proposed approach to such changes by using weighted and recursive least-squares estimation. Through numerical examples, we illustrate the advantages of our proposed DF estimation approach over the conventional model-based one in the context of contingency analysis and generation re-dispatch. [ABSTRACT FROM PUBLISHER]

This paper proposes a set-theoretic method to capture the effect of parametric uncertainty in reliability and performability indices obtained from Markov reliability and reward models. We assume that model parameters, i.e., component failure and repair rates, are not perfectly known, except for upper and lower bounds obtained from engineering judgment or field data. Thus, the values that these parameters can take are constrained to lie within a set. In our method, we first construct a minimum volume ellipsoid that upper bounds this set, and hence contains all possible values that the parameters can take. This ellipsoid is then propagated via set operations through a second-order Taylor series expansion of the Markov chain stationary distribution, resulting in a set that provides approximate bounds on reliability and performability indices of interest. Case studies pertaining to a two-component shared load system with common-cause failures, and preventative maintenance of an electric-power distribution transformer, are presented. [ABSTRACT FROM PUBLISHER]

This paper proposes a set-theoretic method to assess the effect of variability associated with renewable-based electricity generation on power system dynamics, with a focus on time-scales involving electromechanical phenomena. Performance requirements define a set within which the values of certain system variables, e.g., synchronous generator speeds, system frequency, or bus voltages, must remain at all times. To address this problem, reachability analysis techniques are used; for a given timeframe, if the reach set, i.e., the set that contains all possible system trajectories, is within the set defined by performance requirements, then it may be concluded that variability arising from in renewable-based electricity generation does not have a significant impact on system dynamics. The proposed method is illustrated through several case studies, including the 39-bus New England system model. [ABSTRACT FROM PUBLISHER]

We propose an analytically tractable Bayesian method to infer parameters in power system dynamic models from noisy measurements of bus-voltage magnitudes and frequencies as well as active- and reactive-power injections. The proposed method is computationally appealing as it bypasses the large number of system model simulations typically required in sampling-based Bayesian inference. Instead, it relies on analytical linearization of the nonlinear system differential-algebraic-equation model enabled by trajectory sensitivities. Central to the proposed method is the construction of a linearized model with the maximum probability of being (closest to) the actual nonlinear model that gave rise to the measurement data. The linear model together with Gaussian prior leads to a conjugate family where the parameter posterior, model evidence, and their gradients can be computed in closed form, markedly improving scalability for large-scale power systems. We illustrate the effectiveness and key features of the proposed method with numerical case studies for a three-bus system. Algorithmic scalability is then demonstrated via case studies involving the New England 39-bus test system. [ABSTRACT FROM AUTHOR]

This paper proposes a self-synchronizing synchronverter controller design that leverages the addition of a virtual resistance (along with a suitable coordinate transformation) to compute feedback signals during self synchronization prior to grid connection. With respect to analysis, we exploit separation-of-time-scales arguments and develop appropriate reduced-order models, which are well-suited for studying phase-angle and voltage-magnitude self-synchronization dynamics independently. Our work provides analytical justification for the effects of pertinent controller parameters and system initial conditions on self-synchronization dynamics observed empirically in time-domain simulations. As such, it offers practical guidance on favourable parameter-value settings to achieve fast self synchronization, and it yields accurate estimates for self-synchronization times with well-tuned parameters. Through numerical simulations and experiments, we illustrate the efficacy of the proposed controller design and verify the validity of subsequent analyses. [ABSTRACT FROM AUTHOR]

This paper proposes an approach to obtain dynamic versions of static distribution factors, such as power-transfer, line-outage, and outage-transfer distribution factors. With the proposed dynamic distribution factors (DDFs), one can predict line flows over the post-contingency transient period with the same computational effort as obtaining static distribution factors. Our development centers on deriving closed-form expressions that approximate generator outputs through the post-contingency transient period with a reduced-order aggregate dynamical model to recover dynamic generator participation factors. The full suite of DDFs can then be derived by combining these dynamic generator participation factors with injection shift factors, i.e., static linear sensitivities of line active-power flows with respect to nodal active-power injections, computed at the pre-disturbance steady-state operating point. We illustrate the accuracy and computational benefits of the proposed DDFs via numerical case studies involving the New England test system. [ABSTRACT FROM AUTHOR]

This paper proposes an optimal strategy for regulating active-power flows in electric power systems based on sparsity-promoting linear–quadratic–Gaussian (LQG) control. The proposed method relies on the mapping of nodal active- and reactive-power injections to line flows, which are obtained via a measurement-based approach. Building on this, we outline a combined sparsity-promoting linear–quadratic regulator and Kalman-filter design. The optimal controller sparsity is identified using the alternating direction method of multipliers, which strikes a balance between feedback controller sparsity and the closed-loop dynamic performance. With this, we optimally dispatch generators and controllable loads to achieve desired line flows while ensuring zero steady-state frequency offset. We demonstrate the utility of the proposed LQG controller via a representative congestion-management application deployed on the New England 10-machine 39-bus test system. [ABSTRACT FROM AUTHOR]

Underwater radiated noise (URN) emanating from ships can adversely impact the life functions of certain marine mammals that rely on sound to navigate, communicate, and locate prey. This paper formulates an optimal voyage scheduling problem to mitigate the impact of URN on sensitive marine species by choosing amongst different possible paths and specifying the cruising speed along the selected path. We focus on all-electric ships (AESs) owing to their greater flexibility for speed regulation by coordinating an integrated power system. The proposed optimization model schedules generators and energy storage devices toward minimizing the operation cost while satisfying constraints pertinent to URN levels and atmospheric greenhouse gas (GHG) emissions, the electric power network and operational limits, and expected voyage timelines, culminating in a mixed-integer nonlinear programming problem. To promote computational tractability, we approximate the nonlinear relationships for URN, propulsion load, and fuel consumption with piecewise linear functions. This leads to a mixed-integer second-order cone programming problem, which enables convergence to the global optimum and computationally efficient solutions. We illustrate the effectiveness of the proposed model in curbing URN levels and GHG emissions with numerical case studies involving an 18-node ship test system. • Mitigating the impact of URN on sensitive marine species via efficient voyage plan. • Enabling selection between alternative paths connecting consecutive destinations. • Linearizing the nonlinear relationships for URN, propulsion load and fuel consumption. • Formulating a computationally efficient mixed-integer SOCP problem. • Illustrating the effectiveness of the proposed model with numerical case studies. [ABSTRACT FROM AUTHOR]

This paper presents a frequency dynamics-aware marginal pricing method for real-time electricity markets. The proposed method captures the impact of system frequency dynamics on the marginal price of electricity in the presence of aggressive net-load variations made more likely by greater renewable integration. We formulate a dynamics-aware economic dispatch (ED) by augmenting the traditional single-snapshot ED with constraints pertaining to system frequency dynamics, and frequency deviations from the synchronous speed are penalized in the modified objective function. The resulting ED embeds two distinct time steps to optimize over fast system dynamics and slower decisions on generator set-points. We prove that the dynamics-aware marginal price is the (suitably scaled) Lagrange multiplier of the power balance constraint and that it converges in steady state to the marginal price obtained from traditional ED solved with comparable system load. Numerical case studies involving the Western System Coordinating Council test system validate our findings and confirm added revenue opportunities for generators contributing to frequency regulation. [ABSTRACT FROM AUTHOR]

This paper develops an approach to enable the optimal participation of distributed energy resources (DERs) in inertial- and primary-frequency response alongside conventional synchronous generators. Leveraging a reduced-order model description of frequency dynamics, DERs’ synthetic inertias and droop coefficients are designed to meet time-domain performance objectives of frequency overshoot and steady-state regulation. Furthermore, an optimization-based method centered around classical economic dispatch is developed to ensure that DERs share the power injections for inertial- and primary-frequency response in proportion to their power ratings. Simulations for a modified New England test-case system composed of ten synchronous generators and six instances of the IEEE 37-node test feeder with frequency-responsive DERs validate the design strategy. [ABSTRACT FROM AUTHOR]

This paper outlines a procedure to design power–frequency droop slopes for distributed energy resources (DERs) installed in distribution networks to optimally participate in primary frequency response. In particular, the droop slopes are engineered such that DERs respond in proportion to their power ratings and they are not unfairly penalized in power provisioning based on their location in the distribution network. The main contribution of our approach is that a guaranteed level of frequency regulation can be obtained at the feeder head, while ensuring that the outputs of individual DERs conform to some well-defined notion of fairness. The approach we adopt leverages an optimization-based perspective and suitable linearizations of the power-flow equations to embed notions of fairness and information regarding the physics of the power flows within the distribution network into the droop slopes. Time-domain simulations from a differential algebraic equation model of the 39-bus New England test-case system augmented with three instances of the IEEE 37-node distribution network with frequency-sensitive DERs are provided to validate our approach. [ABSTRACT FROM PUBLISHER]

This paper develops a real-time algorithmic framework for aggregations of distributed energy resources (DERs) in distribution networks to provide regulation services in response to transmission-level requests. Leveraging online primal-dual-type methods for time-varying optimization problems and suitable linearizations of the nonlinear AC power-flow equations, this work establishes a system-theoretic foundation to realize the vision of distribution-level virtual power plants. The optimization framework controls the output powers of dispatchable DERs such that, in aggregate, they respond to automatic generation control and/or regulation-services commands. This is achieved while concurrently regulating voltages within the feeder and maximizing customers’ and utility's performance objectives. Convergence and tracking capabilities are analytically established under suitable modeling assumptions. Simulations are provided to validate the proposed approach. [ABSTRACT FROM AUTHOR]