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In response to near- and long-term market and policy shifts, power systems are integrating increasingly-distant renewable energy resources. No analyses quantify the spatial heterogeneity of resource adequacy contributions of renewables at the interconnection-scale in the United States, which would indicate the value to resource adequacy of integrating increasingly-distant renewables. To fill this gap, we develop a Monte Carlo-based probabilistic reliability model to estimate the effective load carrying capability (ELCC) of wind or solar generators. We apply our model to estimate the ELCCs of new solar or wind generators at 1406 locations across the Western Interconnection when contributing to each of five power pools within the Interconnection. Across the five power pools, we find solar ELCCs range from 0% to 44% and wind ELCCs range from 0% to 55% across the Western Interconnection. Solar ELCCs increase from east to west for all but one power pool, incentivizing integration of western renewables into eastern power pools. Deploying storage with wind or solar generators increases their ELCCs, with larger increases occurring at locations with lower renewable-only ELCC values. Thus, resource adequacy gains from deploying storage with renewables can partly substitute for those from integrating increasingly-distant renewables.

This paper proposes a frequency control strategy for voltage source converter based multi-terminal HVDC systems (VSC-MTDC) to facilitate the exchange of primary frequency reserves among asynchronous AC systems, thus providing frequency support from each AC system to the others. The proposed frequency control utilizes a reference signal calculated from global measurements which reflects the overall frequency dynamics of all connected asynchronous AC systems. The proposed control outperforms the traditional frequency droop scheme by reducing impact on the DC voltage profile and improving frequency nadir. The performance of the designed frequency control with different DC voltage droop controls is evaluated. The adaptation of the proposed frequency control for converter outages is analyzed. The robustness of the proposed control to communication latency and the sensitivity of frequency support to power limits are also investigated. The VSC-MTDC model and the proposed control are implemented in the commercial grade software PSS/E and thus is suitable to study large-scale realistic systems and can be incorporated into the power system planning process at utilities and ISOs. The effectiveness of the proposed control is illustrated on a developed AC-MTDC test system and also on a large-scale realistic model combining the North American Western Interconnection (WI) and Eastern Interconnection (EI) with continental HVDC interconnections.

As smart load adoption grows on the electric power system, potential for losing load diversity increases, possibly in ways that impact system stability. Cloud computing resources are able to coordinate large amounts of behind-the-meter loads and resources. Inadvertent or malicious actions could potentially result in gigawatts of load, distributed across large regions, acting nearly simultaneously. We study the resulting impacts of such a perturbation, which were previously recognized, with improved fidelity and granularity using a physically-based power system and demand model. The ResStock tool was used to calculate residential air conditioning load at more than 3,000 locations across the Western Interconnection, corresponding in time to heavy summer and light spring loading. Under an assumption that one cloud platform managed smart thermostats controlling 10%, 15%, or 20% of residential air-conditioning, calculated load steps could be injected into Positive Sequence Load Flow dynamic simulations. These load-driven effects were coupled with two classes of distributed generation ride-through to evaluate the potential for cascading outages. We found frequency deviations in the spring case far exceed the credible contingency event, leading to widespread distributed generation loss, while voltage depressions during the summer loading lead to widespread distributed generation loss and system separation.

Power system is one of the largest man-made systems, which over the years has become the vital infrastructure for modern life. The foundation of today’s power system is three-phase alternating current (AC), which is adopted as the main stream technology for its advantages in voltage transforming, wide-area networking and long-distance power transmitting. The AC power system is a self-sustained oscillatory system operating at nominal frequency, i.e., 50 or 60 Hz. However, the multi-time-scale dynamics in a power system, mechanical, electrical or their coupled are prone to cause the exchange of energy at wide range of frequencies other than the nominal one, which is collectively known as the oscillation issues in a power system. Such oscillations would lead to power quality degradation, equipment failure, or even worse, system instability. Actually, the development history of power system is also a history of continuous “battle” against the oscillation problems. This article reviews the basic concepts and classification of the classical as well as emerging power system oscillations. The mechanism, origin and research advances of various oscillations are re-visited and discussed, from the earlier and long-standing low frequency oscillation (LFO), and then subsynchronous oscillation/resonance (SSO/SSR) associated with turbo-generators and wind turbine generators, to the latest wide-band oscillations involving the sophisticated dynamics of increasing renewables and power electronics in a power system. LFO incident was reported for the first time in 1964 in American Western Interconnection, where the formation of a larger power system by combining two smaller one, i.e., Northwest and Southwest systems, caused power oscillation at about 0.1 Hz. Later studies showed that the multiple machines with mechanical inertial but electrically connected through networks function like a mass-spring system, leading to LFOs at a frequency ranging from 0.01 to 2.5 Hz, depending on the size of the system. Initially, excitation control was improved by adding the function of power system stabilizer (PSS) to mitigate LFO. Later, advanced control, including linear optimal control, nonlinear control and optimal decentralized coordinated control, were developed to solve the problem. Since 2000, the continuous increase of system size and coverage causes very-low-frequency oscillation issues, to address which, several new technologies, for instance, wide-area monitoring and control, flexible AC transmission system (FACTS) control, has been commissioned in China and around the world. SSR/SSO is induced by the interactions between the multi-mass shaft of a turbo-generator and the series-compensated AC or HVDC transmissions. The frequency of power oscillation is subsynchronous, or less than the nominal frequency but generally above the 2.5 Hz. The first SSR incident was captured at Mohave Power generating Station in 1970. In China, however, SSR/SSO has been a severe stability concern since 2000, the time witnessing the widely usage of series compensation and HVDC to transfer electricity from remote coal-fueled power plants. After more than ten years’ continuous research, we have developed effective tools and countermeasures, for instance, multi-dimensional analysis, optimized control and coordinated protection, to solve practical SSR/SSO problems in China and some other countries. The integration of wind power introduces new interactive dynamics that involve wind turbine converters and AC grids. It is called sub-/super-synchronous control interaction (SSCI), which would result in a different type of oscillation from several Hz to double nominal frequency. Such sub/super-synchronous oscillations associated with wind power has entered people’s vision since 2009 and gained widespread attention after the occurrence of several actual incidents in US and China. To address this new issue, we have developed novel frequency-domain modeling and analysis methods to quantify the risk first, and then control strategies on either generator/converters side or grid side to modify the interaction to stabilize SSCI. These methods and strategies have been put into practice, for instance in Guyuan and Hami systems in China, to verify their effectiveness. At this moment, power system is undergoing profound changes, one of which is the rapid growth of renewables and power electronics in all sections, including generation, transmission and consumption of electricity. Such a change is triggering power system oscillations in a very wide band, i.e., from several Hz to several thousand Hz. The underlying reason is the multi-time-scale dynamic interactions among the huge number of converters and the increasingly complicated power grid. This leads to open challenges that are yet to be solved, including the need of: (1) Wide-spectrum models to represent the multi-time-scale dynamics; (2) advanced analysis methods to quantify the stability of wide-band oscillations; and (3) adaptive and coordinated controls to mitigate the oscillation under varying system conditions. In a nutshell, systematic and in-depth researches are required to establish new theories and methodologies for this emerging issue so as to promote the sustainable growth of renewable energy and the low-carbon development of power system.

This paper presents a sufficient and necessary condition for transient stability of multimachine power systems based on the passivity formalism. The condition derived using the extended classical model (ECM) with zero transfer conductance (TC). The ECM of power systems relaxes slightly the assumption of “voltage-behind-transient-reactance” from “constant”, which is used in the conventional classical model to “positive, bounded and independent of machine rotor angles”. The results of time domain simulation of a full model of Western Interconnection used for regular operation planning study are presented for verifying the model assumptions and the storage functions of the system in four different scenarios (well stable, marginally stable, marginally unstable and very unstable), thus illustrating the sufficiency and necessity of stability criterion based on passivity.

As the deployment of wind and solar energy increases in the USA, energy storage (ES) will play an important role in future electric power grids to help manage the variability from high penetration levels of renewable generation, ES can provide promising power/energy demand to coordinate with renewables generation, as a virtual power plant (VPP). There is an industry need for the capability in power system studies to model ternary pumped storage hydropower (T-PSH), a pumped storage technology that offers increased system benefits. This study presents a comprehensive vendor-neutral dynamic model of T-PSH in GE's commercial software positive sequence load flow. A new governor model is developed with detailed gate valve modelling and a shared-penstock function. Specifically, this model is designed to simulate the seamless transition among three operation modes: generation mode, pumping mode, and hydraulic short-circuit mode. The developed T-PSH model has been tested and validated on a 10-bus test system. A comparison study of T-PSH to conventional pumped storage hydropower has also been conducted on the Western interconnection system.

Low-frequency oscillations in power system degrade power quality and may trigger blackouts. This study identifies the source location of these oscillations using measurements from phasor measurement unit (PMU), offline credibility estimation and classification models. The performance of these classification models is ranked for each reported feature to use highly ranked models during the online stage. This proposed framework named as credibility search ensemble learning was tested and validated with promising results using western interconnection power system in North America (WECC-179). The reliability and robustness of the proposed framework were checked against measurement errors in PMUs as well as for practical topology change scenarios. Experimental results and performance comparison with average weight-based approach proved that the proposed approach is capable enough to predict the source location of oscillations with good accuracy. An interfacing tool, for MATLAB-WEKA, was developed and employed in this work for validation and testing of the proposed approach.

Analysis and improvement of power grids resilience and efficiency requires the topologies and geographical coordinates of the real transmission networks. However, due to security reasons, such topologies and particularly the locations of the substations and lines are usually not publicly available. In this work, we thoroughly study the structural properties of the U.S. Western Interconnection grid (WI) and, based on the results, present the network imitating method based on learning (NIMBLE) for generating synthetic spatially embedded networks with similar properties to a given grid. We apply NIMBLE to the WI and show that it can generate networks with similar structural and spatial properties as well the same level of robustness to failures to the WI, without revealing the real locations of the lines and substations. To the best of our knowledge, this is the first attempt to consider the spatial distributions of the buses (nodes) and lines and their importance in generating synthetic grids. Moreover, this is the first time that the power flows and vulnerability against failures are considered in evaluating a synthetic power grid.

This letter derives an analytical formula to estimate the electromechanical oscillation frequencies for multi-machine systems. The proof of the analytical formula is given via matrix determinant simplification and matrix decomposition considering line power losses. A half-size system matrix is obtained, which can speed up the computing of eigenvalues. The accuracy of the derived solution is evaluated by comparing with the PSAT toolbox on the eastern and western interconnection systems, respectively, under different operating conditions. Results highlight the accuracy and acceleration effect of the proposed method.

With an increase in the oscillation events observed in the U.S. Eastern Interconnection (EI), it has become increasingly important to have a good understanding of the EI system oscillatory behavior. However, as compared to the Western Interconnection system (WI), not much work has been done in this regard for the EI system. Therefore, in this paper, a thorough analysis is carried out to identify inter-area modes and their properties for the EI system using a 80000+ bus real EI model. Multi-channel Prony method is used in this paper for estimating system modes and mode-shapes.

The significant offshore wind energy potential of Oregon faces several challenges, including a power grid which was not developed for the purpose of transmitting energy from the ocean. The grid impacts of the energy resource are considered through the lenses of (i) resource complementarity with Variable Renewable Energy resources, (ii) correlations with load profiles from the four balancing authorities with territory in Oregon, and (iii) spatial value to regional and coastal grids as represented through a production cost model of the Western Interconnection. The capacity implications of the interactions between offshore wind and the historical east-to-west power flows of the region are discussed. The existing system is shown to accommodate more than two gigawatts of offshore wind interconnections with minimal curtailment. Through three gigawatts of interconnection, transmission flows indicate a reduction of coastal and statewide energy imports as well as minimal statewide energy exports.

This paper presents a preliminary investigation on controlling the existing high voltage dc (HVDC) links connecting the North American western interconnection (WI) to the other interconnections, to provide damping to inter-area oscillations. The control scheme is meant to damp inter-area modes of oscillation in the WI by using wide area synchrophasor feedback. A custom model is developed in General Electric's PSLF software for the wide area damping control scheme, and simulations are analyzed on a validated full ~22,000 bus WI model. Results indicate that implementing the proposed control technique to the existing HVDC links in the WI can significantly improve the damping of the inter-area modes of the system.

The integration of high shares of variable renewable energy raises challenges for the reliability and cost-effectiveness of power systems. The value of long-duration energy storage, which helps address variability in renewable energy supply across days and seasons, is poised to grow significantly as power systems shift to larger shares of variable generation such as wind and solar. This study explores the system-level services and associated benefits of long-duration energy storage on the 2050 Western Interconnection (WI). The operation of the future WI system with 85% renewable penetration is simulated using a two-stage production cost model. The impact of long duration energy storage on systemwide operations is examined for the 2050 WI system, using a range of round-trip efficiencies corresponding to four different energy storage technologies. The analysis projects the energy storage dispatch profile, system-wide production cost savings (from both diurnal and seasonal operation), and impacts on generation mix, and change in renewable generation curtailment.

This paper presents a trajectory tracking control strategy that modulates the active power injected by geographically distributed inverter-based resources to support transient stability. Each resource is independently controlled, and its response drives the local bus voltage angle toward a trajectory that tracks the angle of the center of inertia. The center-of-inertia angle is estimated in real time from wide-area measurements. The main objectives are to stabilize transient disturbances and increase the amount of power that can be safely transferred over key transmission paths without loss of synchronism. Here we envision the actuators as utility-scale energy storage systems; however, equivalent examples could be developed for partially-curtailed photovoltaic generation and/or Type 4 wind turbine generators. The strategy stems from a time-varying linearization of the equations of motion for a synchronous machine. The control action produces synchronizing torque in a special reference frame that accounts for the motion of the center of inertia. This drives the system states toward the desired trajectory and promotes rotor angle stability. For testing we employ a reduced-order dynamic model of the North American Western Interconnection. The results show that this approach improves system reliability and can increase capacity utilization on stability-limited transmission corridors., 31 pages, 15 figures, 2 tables, IET pre-print

This chapter introduces a framework of PMU Registry, online oscillation monitoring systems and forced oscillation detection and source location tools that Peak RC has implemented for the Reliability Coordinator (RC) function of the Western Interconnection. The framework consists of four main components: (1) Montana Tech’s Modal Analysis Software (MAS) engine; (2) Washington State University’s Oscillation Monitor System (OMS) software; (3) Forced Oscillation Detection and Source Location Algorithms (FODSL); and (4) Peak RC in-house visualization tool and alarming logic built in PI Processbook. The framework was validated and applied for real system oscillation studies. Implementation experience and lessons learned are reviewed in this chapter.

This chapter introduces Peak RC’s experience, in collaboration with vendor and impacted operating entities, on implementation of a Real-Time Voltage Stability Analysis (RT-VSA) tool in the control rooms to calculate the Interconnection Reliability Operating Limits (IROLs) across the Western Interconnection (WI). Major technical challenges and technical resolutions, including modeling aspects, software improvements, validation approaches, and integration efforts, are presented in detail. A number of RT-VSA case studies and some lessons learned are reviewed in the chapter. Key findings and several recommendations for future work are summarized in the end.

Implementation of real-time transient stability application in the control room covering the Western Interconnection is a tremendous task. Some of the prerequisites are real-time steady-state model of interconnection, dynamic models, development of clearly defined user cases, and defining stability criteria together with operation procedures. This chapter addresses these industry needs and provides a framework for the implementation of real-time transient stability application for the Western Interconnection based on Peak Reliability experience and efforts.

The Western Interconnection has experienced several major blackouts over the last 32 years. To train Reliability Coordinators (RC) and system dispatchers of operating entities for restoration skills, a West-wide System Model (WSM)-based Dispatcher Training Simulator (WSM-DTS) is used since the west-wide system restoration drills started in 2011. This chapter reviews the Peak Reliability WSM-DTS tool which utilizes a Cloud connectivity in connection with restoration training drills.

Author(s): Carvallo Bodelon, Juan Pablo; Zhang, Nan; Leibowicz, Benjamin; Carr, Thomas; Galbraith, Maury; Larsen, Peter H | Abstract: LBNL collaborated with the Western Interstate Energy Board and the University of Texas-Austin to investigate the implications of a regional resource adequacy (RA) program on utility integrated resource planning (IRP). This report is focused on an active policy discussion to develop a novel voluntary program to share capacity resources and improve RA in the Western Interconnection. This report identifies two RA components of IRP that will be highly impacted by a regional RA program: resource capacity accreditation and RA targets. There are at least four resources that will require specific attention for their capacity credit calculations: (1) variable renewable resources, (2) demand-side resources, (3) hydroelectric resources, and (4) power purchase agreements. It will also be necessary to decide on a RA target reliability metric (e.g., a planning reserve margin) that is at least the minimum requirement in IRPs to ensure consistency in RA requirement calculations. The report finds that load forecasting and transmission expansion analyses will be moderately impacted, but that most of IRP components will be not significantly impacted. The report includes a review of traditional resource adequacy practices in IRP; a case study of an existing regional RA program that interacts with IRP (Southwest Power Pool) and it presents the Northwest Power Pool (NWPP) regional resource adequacy proposal that is a focus of this research. This paper addresses three research questions: • How would typical IRP processes change if a utility joined a regional RA program? • Which RA elements would remain local (i.e. within IRP) and which would become regional (i.e. within the RA program)? • How much control would utilities and states retain over their utility resource mixes considering the influence of a regional RA program? This paper is primarily written for state policymakers, public utility commission staff, and resource planners from states in the NWPP footprint that are pondering how their IRP guidelines and regulations may need to adjust to operate jointly with a regional RA program. The content of this paper may also help the NWPP RA program developer as it interacts with potential member states and utilities to understand what aspects of energy policy may be influenced by the program. This work was funded by the Energy Resilience Division of the U.S. Department of Energy’s Office of Electricity under Lawrence Berkeley National Laboratory Contract No. DE-AC02-05CH11231.

In the future, with high levels of renewable energy sources penetration, the transmission corridors will have to be flexible to operate under faster transients and variable power flows. Fast power ramping and overloading capabilities of HVDC system can be utilized to ensure transient stability of the interconnected power grid. In this paper, HVDC auxiliary controllers have been studied that can provide the power grid with additional synchronizing torques through fast DC power changes in response to arising system conditions. The effectiveness of the auxiliary controllers in improving transient stability is demonstrated by performing dynamic simulations on the detailed model of the Western Interconnection system (WECC).

Models that characterize life cycle greenhouse gases from electricity generation are limited in their capability to estimate emissions changes at scales that capture the grid-scale benefits of technologies and policies that enhance renewable systems integration. National assumptions about generation mixes are often applied at annual time steps, neglecting spatiotemporal resolutions that provide insights on impacts from time-variable emissions. Our grid-scale model incorporates details of transmission and generation planning that allows a geographically and temporally textured and more realistic assessment of the life cycle greenhouse gas emissions outcomes, using a case study of the Western Interconnection of North America. Results from a co-optimized model of generation, transmission, and operations-the Johns Hopkins Stochastic Multistage Integrated Network Expansion Model-provide a detailed characterization of twenty-one scenarios with different configurations of storage additions, new renewable capacity, and carbon prices. Life cycle results suggest that optimization models that focus on generation alone may underestimate emissions by 18-29% because only emissions from power generation are quantified (i.e., supply chain emissions are omitted) but also that carbon pricing is the predominant driver of reducing emissions in the scenarios we examine. Life cycle assessment of electricity generation should move beyond individual technologies toward capturing the influence of policies at the system level to better understand technology-policy dynamics for the grid.

The prevalence of power electronics in the bulk power system is increasing rapidly in both the generation and consumption of electricity. This work focuses on the effect of changing load composition - specifically the transition from single phase air conditioner motors to power electronics backed air conditioners - on power system stability. Various transmission and generation contingency events for the Western Interconnection were simulated using Positive Sequence Load Flow software and planning models from the Western Electricity Coordinating Council. In general, an increased proportion of power electronic load leads to more instability. For some specific faults resulting in fault-induced delayed voltage recovery, transitioning to higher proportions of power electronic loads helps expedite system recovery. These results demonstrate that load composition should be examined in conjunction with generation composition when evaluating system stability.

For decades, power system stabilizers paired with high initial response automatic voltage regulators have served as an effective means of meeting sometimes conflicting system stability requirements. Driven primarily by increases in power electronically-coupled generation and load, the dynamics of large-scale power systems are rapidly changing. Electric grids are losing inertia and traditional sources of voltage support and oscillation damping. The system load is becoming stiffer with respect to changes in voltage. In parallel, advancements in wide-area measurement technology have made it possible to implement control strategies that act on information transmitted over long distances in nearly real time. In this paper, we present a power system stabilizer architecture that can be viewed as a generalization of the standard $\Delta \omega -$ type stabilizer. The control strategy utilizes a real-time estimate of the center-of-inertia speed derived from wide-area measurements. This approach creates a flexible set of trade-offs between transient and small-signal response, making synchronous generators better able to adapt to changes in system dynamics. The phenomena of interest are examined using a two-area test case and a reduced-order model of the North American Western Interconnection. To validate the key findings under realistic conditions, we employ a state-of-the-art co-simulation platform to combine high-fidelity power system and communication network models. The benefits of the proposed control strategy are retained even under pessimistic assumptions of communication network performance.

This paper describes the design and implementation of a proof-of-concept Pacific dc Intertie (PDCI) wide area damping controller and includes system test results on the North American Western Interconnection (WI). To damp inter-area oscillations, the controller modulates the power transfer of the PDCI, a ±500 kV dc transmission line in the WI. The control system utilizes real-time phasor measurement unit (PMU) feedback to construct a commanded power signal which is added to the scheduled power flow for the PDCI. After years of design, simulations, and development, this controller has been implemented in hardware and successfully tested in both open and closed-loop operation. The most important design specifications were safe, reliable performance, no degradation of any system modes in any circumstances, and improve damping to the controllable modes in the WI. The main finding is that the controller adds significant damping to the modes of the WI and does not adversely affect the system response in any of the test cases. The primary contribution of this paper, to the state of the art research, is the design methods and test results of the first North American real-time control system that uses wide area PMU feedback.

As we move into the future, variable energy resources (VERs), such as wind and solar, will begin to dominate utilities resource portfolios. We see indicative signs of this in the western interconnection with utility Integrated Resource Plans (IRPs) bypassing the natural gas "bridge resource" and identifying copious quantities of wind and solar in their 20-year plans as they work to retire increasing amounts of higher energy-cost fossil-based resources – especially coal. Adequacy assessment of systems with ongoing integration of VER, has added new requirements to enhance the current methodologies and tools for computing the widely-used Loss-of-Load-Expectation (LOLE) index. This paper presents the practical experience in evaluating the adequacy of the Idaho Power Company (IPC) generation system with integrated VER such as wind and solar. In this paper the adequacy assessment includes an analysis of uncertainties associated with load, limited energy sources (hydro), variable wind and solar energy sources, and forced and maintenance outages of generating units. The transmission contingency driven constraints have not been considered. The adequacy indexes, such as LOLE and Expected Unserved Energy (EUE), are calculated by using an analytical convolution approach that considers the realistic time series of available generation produced by VER, such as hydro, wind and solar. This paper explores, compares and presents the reliability results of four top Idaho IRPs portfolios that are selected among the 24 studied portfolios based on the cost and risk. The results suggest that the portfolio that includes a new transmission line, wind, and solar resources has the highest reliability and was one selected by IPC. In addition, the case study results indicate which wind and solar resources by location will provide more value in reducing LOLE index and show the impact of Load Forecast Uncertainty (LFU) on the LOLE and EUE indexes. The capacity contributions of future VER are also evaluated by using the Effective Load Carrying Capability (ELCC) approach across five different meteorological profile years (2015-2019).

During major power system disturbances, when multiple component outages occur in rapid succession, it becomes crucial to quickly identify the transmission interconnections that have limited power transfer capability. Understanding the impact of an outage on these critical interconnections (called saturated cut-sets) is important for enhancing situational awareness and taking correct actions. This paper proposes a new graph theoretic approach for analyzing whether a contingency will create a saturated cut-set in a meshed power network. A novel feature of the proposed algorithm is that it lowers the solution time significantly making the approach viable for real-time operations. It also indicates the minimum amount by which the power transfer through the critical interconnections should be reduced so that post-contingency saturation does not occur. Robustness of the proposed algorithm for enhanced situational awareness is demonstrated using the IEEE-118 bus system as well as a 17,000+ bus model of the Western Interconnection (WI). Comparisons made with different approaches for power system vulnerability assessment prove the utility of the proposed scheme for aiding power system operations during extreme exigencies., Accepted in IEEE Transactions on Power Systems