System-Wide Dynamic Model Validation: Northwest's MOD-033 Principles, Methodology and Experience

Numerous methods have been developed to support the assessment of environmental flow requirements for rivers. Most methods are based around models of hydrologic time series rather than models of the ecological endpoints of interest. Important limitations that arise from this include (1) an inability to represent the state dependency of response to future conditions (i.e. the effects of current ecosystem condition on future condition), (2) the inability to predict ecological states through time under alternative flow regimes and (3) limited sensitivity to compare the differences between flow regimes with similar return intervals of ecologically important events, but different sequencing of those events. Here we outline a simple state‐and‐transition modelling approach to assess differences in ecological responses to alternative sequences of floodplain inundation events in a lowland river system. Our approach explicitly incorporates the state dependency of biotic response to flooding, thereby representing the influences of both antecedent conditions and current condition (in this case population state; good > medium > poor > critical). Our approach thus captures the influence of the entire historical sequence of flow events via a first‐order Markov chain process. We use prior data and expert opinion to determine state transitions for a broad suite of ecological indicators. Despite being implemented with deterministic transitions, and drawing heavily on expert opinion, this approach greatly improves on existing methods used in environmental flows planning, particularly when comparing scenarios with the different sequencing of ecologically relevant flow events. The outputs from these models are testable, and the approach is readily extensible to incorporate probabilistic state transitions and uncertainty, mechanistic links (via increased model complexity) and quantitative measures of population state (e.g. measures of abundance or tree condition). Most importantly, the adoption of such a framework represents a fundamental shift to modelling ecological endpoints rather than relying on just quantifying hydrologic surrogates to compare environmental flow scenarios.

Power system blackouts have become a serious problem for electric utilities especially in recent years. Different forms of system instability have emerged in recent blackouts, such as voltage instability and frequency instability. To counteract each form of system instability, special algorithms have been designed in the protection system, e.g. Under Frequency Load Shedding (UFLS) and Under Voltage Load Shedding (UVLS) schemes. One of the major weaknesses of these algorithms is that combination of different forms of instability is not considered in their design, while any one form of instability may not occur in its pure form. This is particularly true in highly stressed systems and for cascading events. This paper presents an adaptive algorithm to combine UVLS and UFLS schemes. The purpose of this method is to enhance the flexibility of under frequency relays and increase the security of power system during large disturbances by improving system voltage stability margins. In the proposed algorithm, loads with greater voltage decay are shed sooner. In this way, locations of load shedding become dependent to the location of disturbance and voltage stability margins of the system are enhanced. Indeed, load shedding is performed faster for severe events accompanying large voltage or frequency declines. Using this load shedding method, faster reactions could be obtained for major system failures. This way, system blackouts could be better controlled. Performance of the proposed method is compared with the conventional UFLS method. In this paper, dynamic model of the Khorasan HV network of Iran national grid is used for simulation. This network includes 75 high voltage 400 kV and 132 kV buses with about 2700 MW of generation. Performance of the schemes has been evaluated using dynamic simulations as well as the P-V curves, and reactive power margins for a number of events. Simulation results show that conventional UFLS algorithm will not necessarily result in acceptable voltage stability margins for the system following a disturbance. Meanwhile, the proposed algorithm improves voltage stability margins. The proposed algorithm is suitable for saving system stability after occurrence of major system disturbances.

This paper presents the design of a wide area monitor (WAM) using remote area signals, such as speed deviations of generators in a power network, for identifying online the dynamics of a static var compensator (SVC). The design of the WAM is studied on the 12 bus FACTS benchmark system recently introduced. A predict-correct method is used to enhance the performance of the WAM during online operation. Simulation results are presented to show that WAM can correctly identify the dynamics of SVC in a power system for small and large disturbances. Such WAMs can be applied in the design of adaptive SVC controllers for damping interarea oscillations in power networks.

ABSTRACT: The model bankfull discharge recurrence interval (annual series) (Ta) in streams has been approximated at a 1.5‐year flow event. This study tests the linkage between regional factors (climate, physiography, and ecoregion) and the frequency of bank‐full discharge events in the Pacific Northwest (PNW). Patterns of Ta were found to be significant when stratified by EPA Ecoregion. The mean value for Ta in the PNW is 1.4 years; however, when the data is stratified by ecoregion, the humid areas of western Oregon and Washington have a mean value of 1.2 years, while the dryer areas of Idaho and eastern Oregon and Washington have a mean value of 1.4 to 1.5 years. Among the four factors evaluated, vegetation association and average annual precipitation are the primary factors related to channel form and Ta. Based on the results of the Ta analyses, regional hydraulic geometry relationships of streams were developed for the PNW, which relate variables, such as bank‐full cross‐sectional area, width, depth, and velocity, to bankfull discharge and drainage area. The verification of Ta values, combined with the development of regional hydraulic geometry relationships, provides geographically relevant information that will result in more accurate estimates of hydraulic geometry variables in the PNW.

Frequency containment reserves (FCR) or formerly called primary reserves are a major component for the stability of the continental Europe power grid. Up to now, mainly gas power plants are providing FCR and their ongoing decreasing profitability in Europe has a non-negligible impact on the FCR provision cost. In this paper, the concept of FCR with large deadband is introduced and discussed. We show that frequency dynamics after a large disturbance and frequency distribution can be maintained at a satisfactory level. The introduction of FCR with large deadband could lower their procurement cost without impacting significantly the frequency quality and enable new participants, e.g. Demand-Side Management or renewable curtailment, to enter the reserve markets.

The ADREA-I code is a three-dimensional transient analytical tool that can provide atmospheric boundary layer and dispersion analysis at the mesoscale and microscale levels, under any atmospheric stability conditions and with any ground complexity, and it is particularly suitable for large topographical disturbances and consequently large atmospheric altitudes. The code, in response to the need to treat large topographical disturbances with the highest spatial and temporal numerical resolution possible, introduces new features in the description of anomalous topography, turbulent diffusion coefficients, and numerical approach. This paper reports on applications carried out within the framework of validation and demonstration studies of ADREA-I which give reasonable results.

The present work is based on developing a control strategy to mitigate the impact of reduced inertia due to significant DFIG penetration in a large power system. The paper aims to design a supplementary control for the DFIG power converters such that the effective inertia contributed by these wind generators to the system is increased. The paper also proposes the idea of adjusting pitch compensation and maximum active power order to the converter in order to improve inertial response during the transient with response to drop in grid frequency. Results obtained on a large realistic power system indicate that the frequency nadir following a large power impact in the form of generators dropping out is effectively improved with the proposed control strategy. The proposed control is also validated against the sudden wind speed change in the form of wind gust downs and wind ramp downs occurring in conjunction with the generators dropping out. A beneficial impact in terms of damping power system oscillations is also observed, which is validated by eigenvalue analysis. The affected mode is then excited with a large disturbance in time domain. The damping improvement observed in time domain and subsequent Prony analysis support the result obtained from eigenvalue analysis.

Given the continued growth in online learning as well as reports of high attrition rates in it, understanding student readiness for online learning is necessary. Over the years several surveys have been developed to assess student readiness as a predictor of success in online programs; however, a review of the literature yielded limited results of their translation and criterion‐referenced validity. The researchers of this article sought to develop a more rigorous survey instrument for students to self‐assess readiness for online learning. The authors report on findings from a three‐phase study during which the instrument was developed, evaluated, and validated. Through the process of validation, the researchers systematically engaged in an iterative process to refine the instrument, which resulted in not only a more rigorous instrument but one that more clearly defines ready and situates it within the literature on learner characteristics, digital divide, and information and communications technology (ICT) engagement.

Conservation voltage reduction (CVR) will reduce demand on an electric system. More controversial is the idea that CVR can reduce energy usage on a system. Although CVR has its proponents, it is difficult to implement over a wide area without the danger of exposing some customers to unacceptable under voltage conditions. Another issue is that CVR does not cause reduced energy usage for all loads, in fact some loads may increase energy usage when voltage is reduced. Bonneville Power Administration (BPA) has agreed to reimburse several of it's customers who are public utility districts or electric cooperatives for either the cost of installing CVR systems or the energy saved with a CVR system. This manuscript discusses systems installed by two electric utilities in the Pacific Northwest that are being used to implement CVR using new communication and control technologies to prevent under voltage conditions and assure actual reduced energy usage.

This article proposes a fractional- N digital phase-locked loop (DPLL) that achieves a 265- $\mu \text{W}$ ultra-low-power operation. The proposed switching feedback can seamlessly change the DPLL from sampling operation to sub-sampling operation without disturbing the phase-locked state of the DPLL to reduce the number of building blocks that works at the oscillator frequency, leading to significant power reduction. With the reduced number of high-frequency circuits, scaling the reference frequency is fully used to reduce the power consumption of the DPLL. Together with an out-of-dead-zone detector and a duty-cycled frequency-locked loop running in the background, the switching feedback achieves robust frequency and phase acquisition at start-up and helps the sub-sampling PLL recover when large phase and frequency disturbances occur. A transformer-based stacked- $g_{m}$ oscillator is proposed to minimize the power consumption while providing the sufficient swing to drive the subsequent stages. A truncated constant-slope digital-to-time converter is proposed to improve the power efficiency while retaining good linearity. The proposed fractional- ${N}$ DPLL consumes only 265 $\mu \text{W}$ while achieving an integrated jitter of 2.8 ps and a worst case fractional spur of −52 dBc, which corresponds to a figure of merit (FOM) of −237 dB.

Multivariate optimization and validation studies in on-line pre-concentration system for lead determination in drinking water and saline waste from oil refinery

Under large signal conditions, active circuits containing operational amplifiers as elements can exhibit discontinuous response in the frequency domain. A computational procedure is described in this paper for the prediction of large signal frequency response characteristics of active circuits based upon an operational amplifier macromodel containing nonlinear circuit components to represent slew-rate limiting. The interconnection circuitry, exclusive of the operational amplifiers, is mathematically represented in the hybrid matrix form and a mininal set of nonlinear equations for the active circuit is given. A Newton-Raphson iteration, based on a describing function representation for the nonlinear circuit components, is used to numerically solve the circuit equations. Two active circuit configurations that have been observed to exhibit discontinuous large signal frequency response characteristics are described. Data obtained by application of the algorithm to these two circuits is given. Correlation between experimental data and computational results has been excellent.

Linearity characteristics of capacitive tuners under large radio frequency (RF) power have become an important issue for today’s cellphone industry. The use of these devices as antenna tuners has become critically important due to the RF spectrum opening in the low-frequency range. Capacitive tuners connected directly to the antenna to change the RF voltage/current pattern and tune lower frequencies are subjected to suffer large voltage swings, especially in the isolation state or minimum capacitance. In this article, we analyze the effects of the large RF power or equivalent rms voltage to capacitive micro-electromechanical systems (MEMS) switches. The theoretical analysis combined with Coventor MEMS+ simulations will allow us to study the capacitance change and MEMS mechanical frequency response. This article evaluates two types of measurement setups to investigate the RF power effects on nominal capacitance and mechanical frequency response. Measurements up to 6 W were completed with two capacitive MEMS tuner products, confirming the modeling predictions and demonstrating the robustness of this technology under large RF power or voltage swings.

Flash flood prediction using an uncalibrated hydrological model and radar rainfall data in a Mediterranean watershed under changing hydrological conditions

Large increase in wind and photovoltaics will lead to lower and more volatile grid inertia but also to the lack of primary frequency control, i.e. frequency containment reserve (FCR) providers in the Continental Europe Grid. This will therefore impact negatively the frequency dynamics. One potential solution for ensuring the frequency to stay in reasonable bounds is to take the dynamics of potential providers into consideration. From this observation, we develop a novel methodology for having a linear programming problem to select the most suited FCR providers. It is based on the minimization of the overall cost while respecting static and dynamic constraints which are respectively ensuring a sufficient amount of FCR and avoiding too large frequency deviations after a large disturbance. The methodology has been tested on a case with 200 potential FCR providers in function of various grid inertia and load damping factors.