This paper studies the differences in a synthetic inertia controller of using two different feedback measurements: (i) an estimate of the rate of change of frequency from local voltage measurements, and (ii) a remote machine acceleration from a generator nearby to the actuator. The device that provides the synthetic inertia action is a converter interfaced generator (CIG). The paper carries out analysis in the frequency domain, using Bode plots, to show that synthetic inertia control using frequency estimates is more prone to instabilities than for the case where a machine speed is used. The paper then proposes a controller (or a filter) to mitigate these effects. In addition, the paper shows the effects that a delay of the machine speed signal of the nearby generator has on the synthetic inertia control of the system and how a controller is also needed in this case. Finally, the paper shows the difference in performance of a synthetic inertia controller when using these different measurement signals with simulations in time domain a electromagnetic transient program platform.
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.
A significant amount of converter-based generation, such as wind and photovoltaic, is being integrated into thebulk electric power grid to fulfill the future electric demand. Such converter-based distributed energy resources (DERs) will be providing multiple grid support functions (GSFs) to supportvoltage and frequency control of the power system. In thispaper, we present the development of a MA /Simulink-based simulation model to study power system dynamics whenDERs are equipped with GSFs. The simulation model of aninverter with GSFs is validated through comparisons against thecharacteristic curves for each function of the IEEE 1547-2018standard. The normalized root-mean-square-error (NRMSE) wascalculated to be less than 2%. The developed model is then used ina sample power systems dynamics study under various operatingconditions. Results show the exnected resnonse of inverfers withGSFs, properly supporting the grid voltage and frequency andmaintaining the value within an acceptable range.
This paper presents a new method for detecting power quality disturbances, such as faults. The method is based on the dynamic mode decomposition (DMD)-a data-driven method to estimate linear dynamics whose eigenvalues and eigenvectors approximate those of the Koopman operator. The proposed method uses the real part of the main eigenvalue estimated by the DMD as the key indicator that a power quality event has occurred. The paper shows how the proposed method can be used to detect events using current and voltage signals to distinguish different faults. Because the proposed method is window-based, the effect that the window size has on the performance of the approach is analyzed. In addition, a study on the effect that noise has on the proposed approach is presented.
As a result of the increase in penetration of inverter-based generation such as wind and solar, the dynamics of the grid are being modified. These modifications may threaten the stability of the power system since the dynamics of these devices are completely different from those of rotating generators. Protection schemes need to evolve with the changes in the grid to successfully deliver their objectives of maintaining safe and reliable grid operations. This paper explores the theory of traveling waves and how they can be used to enable fast protection mechanisms. It surveys a list of signal processing methods to extract information on power system signals following a disturbance. The paper also presents a literature review of traveling wave-based protection methods at the transmission and distribution levels of the grid and for AC and DC configurations. The paper then discusses simulations tools to help design and implement protection schemes. A discussion of the anticipated evolution of protection mechanisms with the challenges facing the grid is also presented.
As renewable energy sources are becoming more dominant in electric grids, particularly in micro grids, new approaches for designing, operating, and controlling these systems are required. The integration of renewable energy devices such as photovoltaics and wind turbines require system design considerations to mitigate potential power quality issues caused by highly variable generation. Power system simulations play an important role in understanding stability and performance of electrical power systems. This paper discusses the modeling of the Global Laboratory for Energy Asset Management and Manufacturing (GLEAMM) micro grid integrated with the Sandia National Laboratories Scaled Wind Farm Technology (SWiFT) test site, providing a dynamic simulation model for power flow and transient stability analysis. A description of the system as well as the dynamic models is presented.
Power system operations are fundamentally changed by the growing installation of wind generation systems. The undispatchable nature of wind turbine generators (WTGs) causes the operating conditions of power systems to be more volatile. At the same time, the converter-based interface of WTGs are capable, and are increasingly expected to, provide voltage and frequency regulation capabilities. Monitoring of power systems becomes critical under these anticipated conditions and high resolution data, such as synchrophasors, are crucial for this task. This paper presents an approximate low-order model of WTGs that can be readily estimated from available synchrophasor measurements. The identification of the parameters of the model can be used to approximate the control performance of WTGs and their contributions to frequency and voltage regulation.
The state of California is leading the nation with respect to solar energy and storage. The California Energy Commission has mandated that starting in 2020 all new homes must be solar powered. In 2010 the California state legislature adopted an energy storage mandate AB 2514. This required California's three largest utilities to contract for an additiona11.3 GW of energy storage by 2020, coming online by 2024. Therefore, there is keen interest in the potential advantages of deploying solar combined with energy storage. This paper formulates the optimization problem to identify the maximum potential revenue from pairing storage with solar and participating in the California Independent System Operator (CAISO) day ahead market for energy. Using the optimization formulation, five years of historical market data (2014-2018) for 2, 172 price nodes were analyzed to identify trends and opportunities for the deployment of solar plus storage.
This paper presents model formulations for generators that have the ability to use multiple fuels and to switch between them if necessary. These models are used to generate different scenarios of fuel switching penetration from a test power system. With these scenarios, for a severe disruption in the fuel supply to multiple generators, the paper analyzes the effect that fuel switching has on the resilience of the power system. Load not served is used as the proxy metric to evaluate power system resilience. The paper shows that the presence of generators with fuel switching capabilities considerably reduces the amount and duration of the load shed by the system facing the fuel disruption.
Transient stability is highly correlated to the inertia connected to the synchronous grid. Most of the modern control schemes for maintaining transient stability involve generator tripping schemes. However, these type of schemes may become difficult to implement because of the inertia reduction associated with the increase in inverter-based and distributed generation. This paper presents the effect of using machine acceleration feedback in a real-power injection control scheme to improve transient stability without generator tripping. This scheme is based on the equal area criterion and tested on a one machine infinite bus and a two machine system. Its applicability in a multimachine power system is demonstrated on a reduced-order western North American power system. Simulation results indicate that the proposed control strategy provides a simple and effective method for improving transient stability.
Fast-frequency control strategies have been proposed in the literature to maintain inertial response of electric generation and help with the frequency regulation of the system. However, it is challenging to deploy such strategies when the inertia constant of the system is unknown and time-varying. In this paper, we present a data-driven system identification approach for an energy storage system (ESS) operator to identify the inertial response of the system (and consequently the inertia constant). The method is first tested and validated with a simulated genset model using small changes in the system load as the excitation signal and measuring the corresponding change in frequency. The validated method is then used to experimentally identify the inertia constant of a genset. The inertia constant of the simulated genset model was estimated with an error of less than 5% which provides a reasonable estimate for the ESS operator to properly tune the parameters of a fast-frequency controller.
Forced oscillations in power systems are of particular interest when they interact and reinforce inter-area oscillations. This paper determines how a previously proposed inter-area damping controller mitigates forced oscillations. The damping controller modulates active power on the Pacific DC Intertie (PDCI) based on phasor measurement units (PMU) frequency measurements. The primary goal of the controller is to improve the small signal stability of the north south B mode in the North American Western Interconnection (WI). The paper presents small signal stability analysis in a reduced order system, time-domain simulations of a detailed representation of the WI and actual system test results to demonstrate that the PDCI damping controller provides effective damping to forced oscillations in the frequency range below 1 Hz.
With increasing availability of synchrophasor technology, enabled by phasor measurement units (PMUs), applications based on this technology are being implemented as a practical approach for power systems monitoring and control. While synchrophasor data provides significant advantages over SCADA data it has limitations, especially in the area of model validation and estimation. With the increasing complexity of the power system, the need for equipment monitoring and performance evaluation becomes more relevant, traditionally model validation and estimation process can be used to look at control equipment performance. However, due to the challenges associated with these processes there are limitations on the performance evaluation. This work introduces am improved signal-processing based algorithm to monitor control system performance during disturbance events in the power system and during ambient conditions, or normal power system operation, additionally the algorithm is demonstrated on data obtained from the interconnection point of a STATCOM device and a synchronous generator during ambient and disturbance operation.
This paper analyzes how two Kalman Filter (KF) based frequency estimation algorithms react to phase steps. It is demonstrated that phase steps are interpreted as sharp changes in frequency. The paper studies whether the location of the phase step, within the sinusoidal waveform, has any effect on the frequency estimate. Because phase steps are not the product of a permanent change in the underlying frequency, the paper proposes an algorithm to correct frequency estimates deemed erroneous. The algorithm makes use of the residual of the KF to determine when an estimate is incorrect and to trigger a corrective action in which the frequency estimate is replaced by an average of the previous values that were considered accurate. Using synthesized and simulated data with distortions the paper shows the effectiveness of the correction algorithm in fixing frequency estimates.
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.
This paper explores the revenue potential for electric storage resources (ESRs), also referred to as electrical energy storage, in the Southwest Power Pool Integrated Marketplace. In particular, opportunities in the day-ahead market with the energy and frequency regulation products are considered. The revenue maximization problem is formulated as a linear program model, where an ESR seeks to maximize its revenue through the available revenue streams. The ESR has perfect foresight of historical prices and determines the optimal policy accordingly. A case study using FY2018 data shows that frequency regulation services are the most lucrative for revenue potential. This paper also explores different methods of using area control error data to infer the regulation control signal and the consequent effect on the optimization. Finally, the paper conducts a sensitivity analysis of ESR payback period to energy capacity and power rating.
With increasing availability of synchrophasor technology, enabled by phasor measurement units (PMUs), applications based on this technology are being implemented as a practical approach for power systems monitoring and control. While synchrophasor data provides significant advantages over SCADA data it has limitations especially in the area of model validation and estimation. With the increasing complexity of the power system, the need for equipment monitoring and performance evaluation becomes more relevant. Traditionally model validation and estimation process can be used to look at control equipment performance. However, due to the challenges associated with these processes there are limitations on the performance evaluation. This work expands a previously introduced algorithm to monitor control system performance to allow the algorithm to work under power system ambient and disturbance conditions. Additionally the algorithm is demonstrated on data obtained from the interconnection point of a STATCOM device during ambient and disturbance operation.