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This paper presents results from comparison of an industry-accepted model of the western United States with two different synthetic network models of the same geographic area. The synthetic models were independently produced by different construction algorithms but based on public information concerning the location and size of generation and demand. New realism measures examined include Fiedler Vector Partitioning (FVP), the Spectrum of the Normalized Laplacian (SNL), Topological and Impedance Element Ranking (TIER) and Singular Value decomposition of the power flow Jacobian (SVJ). The synthetic models differ greatly in size and granularity, but each has similarities to the industry-accepted model. However, the industry-accepted model exhibits behaviour not replicated in either of the synthetic models. The suitability of each analysis to assess the realism of a network model is discussed.

Harmonics in synchrophasor measurements of forced-oscillation events in the power grid are used to support localization of oscillation sources. A network-theoretic argument is presented which shows that harmonics at sufficiently high frequencies degrade quickly with spatial distance from the oscillation source, as compared to content at the fundamental frequency. Then, harmonics in synchrophasor measurements are analyzed for three historical forced-oscillation events with known oscillation sources. These data analyses confirm that harmonics are measurable in forced-oscillation responses, and further that they generally show faster spatial degradation as compared to the fundamental-frequency content. Based on these observations, we suggest techniques for localizing forced-oscillation sources based on ratios between signal content at the harmonics and the fundamental frequency.

The number and nature of real-valued solutions to the nonlinear power flow equations are not completely understood and there are no proven simple methods for computing all solutions. It has been noted that in practice the equations tend to admit many fewer real-valued solutions than what might be estimated using traditional bounds. In this paper we examine a means to calculate the distribution of number of solutions as a function of multiple parameters. This method relies on a reduction technique that resolves to an equation in one variable for which the calculation of real-valued solutions is straightforward. Importantly we examine the fundamental question of whether a real-valued solution in one variable necessarily implies all variables will be simultaneously realvalued. We present topologies for which this favorable property is retained and topologies for which it fails.

We consider a robust filtering problem where the robust filter is designed according to the least favorable model belonging to a ball about the nominal model. In this approach, the ball radius specifies the modeling error tolerance and the least favorable model is computed by performing a Riccati-like backward recursion. We show that this recursion converges provided that the tolerance is sufficiently small.

Analyses of power engineering networks rely on an understanding of the power flow equations, a system of quadratic equations relating power injections and voltages at each node. Finding the number of nontrivial, real solutions to these equations is an active area of study. In this paper we propose that in general for a fixed topology, a single, univariate polynomial whose coefficients are polynomials in the network susceptances suffices for determining the number of nontrivial, real solutions to the power flow equations. We then exploit this polynomial to gain geometric insight to the solution regions for a fixed network where a solution region is the region in the space of susceptances wherein the number of real solutions to the system is some fixed constant. This type of analysis allows easier insight to robustness analysis for varying susceptances. We observe that some solution regions resemble thickened hyperplanes and therefore appear as stripes in our figures.

A global measure of the persistence of oscillations in the bulk power grid using PMU has been developed. In this paper the contributions of different spectral bands to the persistence metric are defined and characterized, as a means to learn about the sources and patterns of oscillatory swing dynamics. These persistence-contribution metrics are computed for archived PMU data from the Western Interconnect: it is found that peaks in persistence arise from different spectral bands during the analysis period. The use of the persistence metric in a real-time monitoring system is presented.

Operation and planning of electric grids involve the analysis of certain power flow equations, which exhibit multiple solutions. One solution generally corresponds to a preferred operating condition, while other less desirable solutions are often useful for assessing dynamic angular stability and static voltage stability margins. The number and nature of solutions to these network equations has been studied for decades, yet without revealing a complete understanding. In light of observations that the number of solutions encountered in practice is smaller than the number predicted by the usual mathematical bounds, the most recent theoretical papers on this topic have sought to produce more accurate bounds on the number of solutions, accounting for network structure. In this paper we further refine the analysis to describe distributions of solutions. We present algebraic results for a certain small system and empirical results for others.

The Wireless Automated Urine Analyzer (WAUA) is an alternative to the current convention on medical diagnosis from urinalysis. The WAUA is automated, cost-efficient, and can possibly provide additional coverage to healthcare, especially in rural areas. If implemented, this can conduct urinalysis on hard-to-reach areas where implementing standard routine urinalysis is economically challenging. It's capable of macroscopic and chemical urinalysis, which is advantageous to diagnostic clinic facilities that are short-staffed as with the case of rural areas. Through Global System for Mobile (GSM) Communication service, results of initial diagnosis can be transmitted to a designated computer receiver. The parallel testing of the WAUA with the standard routine urinalysis of a laboratory yielded an average percentage difference of 96%, prototype weight of 92% lighter, 89% smaller, and 89% cheaper than the average weight of commercially available urinalysis machine that does chemical urinalysis.

Wide-area monitoring using phasor measurement units (PMUs) offers the possibility of detecting conditions during which the power system may be vulnerable to destabilizing events. Such events are often characterized by undamped oscillations and are preceded by conditions of very low damping. Current techniques for estimating damping from low SNR ambient data are less accurate than desired, although fairly accurate for estimating frequencies of oscillation. We introduce a robust persistence measure that can be used in lieu of damping estimates to assess conditions for vulnerability to dynamic instability. The measure relies on the calculation of the energies of normalized sample autocorrelations of select signals. In this paper we focus on the technical details associated with spectral smoothing and temporal isolation in the calculation of the normalized autocorrelations, to permit effective calibration of the metric for both stable and unstable systems. An example is provided using measurements from the field.

To aid in the real-time monitoring of system stability, it is useful to assess the relative damping of an underlying impulse response from noisy, ambient data. This is typically done using modal decomposition, procedures that accurately and consistently estimate natural frequencies of oscillation but struggle with estimates of damping. Here we introduce a measure of “persistence” as a robust measure of the duration of an impulse response. The longer a natural response persists the less damping it is perceived to have. The proposed measure scales linearly with the duration of an impulse response. It is easy to calculate as the energy in a normalized autocorrelation signal, and it serves as a measure of (inverse) damping.

Estimation of power-system damping from synchrophasor frequency measurements is studied. Specifically, a procedure for determining the damping of a dominant mode from the turns ratio of the sample autocorrelation function is outlined. The main contribution of the work is to then develop performance bounds on the damping estimates, and demonstrate approximation of these bounds entirely from the measurement data. The technique has been applied to archived historical data from the Western Electricity Coordinating Council (WECC), and a real-time implementation has also been developed.

3GPP has recently accelerated the standardization process for Device-to-Device communications. Sidelink, which refers to the radio link between two user equipments (UEs), is a major update in 3GPP Release 12. In this paper, we will first introduce sidelink related structures and procedures in Release 12. Based on basic LTE signaling schemes, we propose methods of using demodulation reference signal (DMRS), which is used as reference signal in both uplink and sidelink, for advance D2D neighbor discovery and resource scheduling of D2D transmissions. Our study shows that reference signal of normal LTE channels can be well exploited to facilitate the newly proposed sidelink communications.

Reliable power system operation requires maintaining sufficient voltage stability margins. Traditional techniques based on continuation and optimization calculate lower bounds for these margins and generally require appropriate initialization. Building on a previous semidefinite programming (SDP) formulation, this paper proposes a new second-order cone programming (SOCP) formulation which directly yields upper bounds for the voltage stability margin without needing to specify an initialization. Augmentation with integer-constrained variables enables consideration of reactive-power-limited generators. Further, leveraging the ability to globally solve these problems, this paper describes a sufficient condition for insolvability of the power flow equations. Trade-offs between tightness and computational speed of the SDP and SOCP relaxations are studied using large test cases representing portions of European power systems.

In this paper we examine different scalar vulnerability metrics that account for system topology and power injection profile. We pose calculable metrics related to the ratio of power disrupted along a cutset to the number of lines on a cutset. It is intended that the metrics can be used to assess the system's susceptibility to large disturbances.

Large-scale electric power system analysis depends upon representation of vast numbers of components whose individual models must be populated with parameters. The challenge of populating such component models is particularly apparent in optimal power flow applications, in which incorrect parameters and/or constraint limits can yield overall system representations with either unrealistically large feasible regions or an empty feasible set. Unfortunately, many data sets, particularly those of publicly available test cases, were originally developed to illustrate simpler “power flow only” applications, and may contain unrealistic values or wholly omit important constraint limits. This paper describes engineering-based approaches to obtain credible estimates for parameters and limits associated with line-flow constraints and generator capability curves, as may be employed in a number of steady state analyses such as the optimal power flow. These can substitute for missing or unrealistic data in test systems for which more fully detailed, “real-world” component specifications and limits are not available, and thereby make such test systems more valuable as research tools.

In this paper we revisit and revise the method of Ma and Thorp [1] for computing all the real-valued solutions to the power flow equations. In a prior work we presented a counterexample to their algorithm [2]. Here we review the general topologically-inspired approach they proposed to trace between solutions assuming one solution is known. We offer a revision to the method by transforming the equations in such a way that all traces are bounded and all traces emanating from a known solution are explored. Results show that the revised method finds all real-valued solutions for power system problems reported in the literature for which all solutions are provably known, including the counterexample in [2].

This paper introduces locational prices associated with power injection variability. The sensitivity of uncertainty in injected power on system cost is calculated using a probabilistic DC optimal power flow (DC-OPF). This sensitivity may be used as a price for regulation to equitably allocate costs associated with tracking power injections. In this context the price also provides a locational value to energy storage and hence can be used as a tool to investigate best locations for energy storage. As a case study, a 24-bus test system with uncertain variable wind power and uncertain variable loads is analyzed.

National Instruments' (NI) Lab VIEW-based breathing trainer with biofeedback and plethysmography is a pc-guided trainer that aims to provide support in recovering proper breathing for patients who have undergone surgical operations (cardiac, respiratory, and anything of the likes), patients with damage in the ribcage, and those having Chronic Obstructive Pulmonary Disease (COPD). It is a combined technology of plethysmography, incentive spirometer, and LabVIEW application. Through the integration of these technologies, the trainer monitors pulse rate of the patient as he/she undergoes training from the incentive spirometer and displays the result on the LabVIEW-based pc application. It also allows the patients to be guided throughout their training sessions by providing feedback and further instructions. The combination of measurement of health parameters and the biofeedback of the system is the key for the system being a breathing trainer. The monitoring of lung capacity and pulse rate exhibit the status of the oxygen intake and distribution of the user; furthermore the biofeedback teaches the user how to improve such measurable health parameters.

This paper introduces a method to construct a linear transformation on extended coordinates between two AC optimal power flow (OPF) problems. Furthermore, the paper also presents the optimality preserving conditions to map any local extremum of one problem to any local extremum of the other.

A reduced-order model is used to derive a candidate energy function for a system that includes an infinite bus connected with a single frequency-droop-controlled inverter (a ‘MicroSource’) whose frequency command is actuated according to its low-pass-filtered active power measurement. The analysis of the large-signal stability of such a system is important in understanding the duration that a frequency-droop-controlled inverter can withstand a particular grid transient before islanding or tripping offline becomes mandatory. It is shown that a large-signal instability for this system can occur under abnormal grid conditions. Additionally, for poor selections of droop gain and low-pass cutoff frequency, these control parameters can potentially have a significant effect on the ability of the system to maintain synchronism after a fault on the main grid is cleared. The proposed energy function is shown through simulation to provide insight on the impact of the frequency droop gain and filter time constant on this instability during and after faulted conditions, particularly for high levels of droop gain and/or measurement filter time constant.

Recently, a semi definite programming relaxation of the power flow equations has been applied to the optimal power flow problem. When this relaxation is "tight" (i.e., the solution has zero duality gap), a globally optimal solution is obtained. Existing literature investigates sufficient conditions whose satisfaction guarantees zero duality gap solutions. However, there is limited study of non-zero duality gap solutions. By illustrating the feasible spaces for optimal power flow problems and their semi definite relaxations, this paper investigates examples of non-zero duality gap solutions. Results for large system models suggest that non-convexities associated with small subsections of the network are responsible for non-zero duality gap solutions.

In this paper we present a method to transform optimal power flow models to enable the sharing of equivalent data sets while preserving privacy of an original data set. Importantly, the generated models preserve a power system structure with certain characteristics chosen by the developer. The needed transformations are presented on the DC Optimal Power Flow (OPF) model.

Common power system disturbances are characterized by oscillations that either damp out, sustain or grow. This oscillatory response can be measured and analyzed to extract modal information of the system. A previous paper by the authors examined the modal content of data with an approach motivated by the theory of normal form analysis. This paper reports on significant advancements made since that time. The primary advancement has been the inclusion of a variable projection nonlinear optimization technique. A user-friendly tool has recently been developed and tested by power industry members for analysis of real power system data. This paper details practical issues associated with this modal analysis tool, including solve-time speeds, initial condition estimation, model order selection and data-detrending.

Power plants contribute substantially to fine particulate pollution which results in hazardous environmental effects. Air quality can be improved by relocation of real power output between power plants. However, this relocation should include spatial, temporal and chemical effects that contribute towards formation of particulate matter. This paper presents a novel air quality constrained optimal power flow which implicitly includes locational, temporal and chemical aspects. A quadratic response surface of an air quality model is included as an environmental constraint in a DC optimal power flow (OPF). Simulation results on an equivalent model of North Eastern Power Coordinating Council (NPCC) demonstrates the successful implementation of the model to reduce particulate matter at an arbitrary location and time period (NY state) on 14th July 2005.

For the non-linear power flow problem with PQ and reactive power limited slack and PV buses, we present two sufficient conditions under which the specified set of nonlinear algebraic equations has no solution. The first condition uses a semidefinite programming relaxation of the power flow equations along with binary variables to model the generators' reactive power capabilities. As a byproduct, this condition yields a voltage stability margin to the power flow solvability boundary. The second condition formulates the power flow equations, including generator reactive power limits, as a system of polynomials and uses real algebraic geometry and sum of squares programming to create infeasibility certificates which prove power flow insolvability.

In the field of power system engineering, the optimal power flow problem is essential in planning and operations. With increasing system size and complexity, the computational requirements needed to solve practical optimal power flow problems continues to grow. Increasing computational requirements make the possibility of performing these computations remotely with cloud computing appealing. However, power system structure and component values are often confidential; therefore, the problem cannot be shared. To address this issue of confidential information in cloud computing, some techniques for masking optimization problems have been developed. The work of this paper builds upon these techniques for optimization problems but is specifically developed for addressing the DC and AC optimal power flow problems. We study the application of masking a sample OPF using the IEEE 14-bus network.