Engineering topics

Hoke, Anderson F

Publications and source records attributed to Hoke, Anderson F.

At least 19 records

DOE OSTI2020

Grid-Following Inverters and Synchronous Condensers: A Grid-Forming Pair?: Preprint

As power systems across the globe continue to achieve higher instantaneous penetrations of power electronic converterinterfaced renewable sources, the stability of these power systems is challenged because of the removal of synchronous machines, from which stability is traditionally derived. Although technological solutions to these stability challenges are on the horizon, such as the use of grid-forming inverters, they are not yet widely applied to larger power systems, which presents operational challenges for power systems achieving these high instantaneous penetrations today. An interim solution using existing technologies is to pair synchronous condensers with grid-following inverters, which might prolong the stability of an operating power system while synchronous generators are turned off during periods of high renewable energy availability. This work examines the transient stability of such a solution using PSCAD simulations of a two-bus system coupled to a variedlength transmission line, with a synchronous condenser at one bus and a grid-following inverter with grid-support functionality at the other. The system is exposed to load step, balanced fault, and unbalanced fault perturbations. It was found that this simple system returned to a steady state for transmission line lengths up to 125 km after 10% load steps, or a variety of fault types.

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DOE OSTI2020

Impacts of Voltage-Based Grid Support Functions on Energy Production of PV Customers

This paper presents the impact of inverter grid- support functions (GSFs) on photovoltaic (PV) customer energy production on a real distribution feeder in Oahu, HI. These autonomous GSFs based on local voltage measurements are good alternatives to increase PV hosting capacity. However, these functions can result in PV energy curtailment to the customer, and this study addresses the concerns about the impact of inverter GSFs through detailed quasi-static time series (QSTS) simulations. It proposes four metrics: maximum and average GSF curtailment, average increased generation and average net generation change, to assess the impact of a given control on PV systems located on customer sites. It was found that curtailment of PV production is negligible for customers where peak voltage is within ANSI C84.1 range. A reliable relationship between curtailment and peak customer voltage is demonstrated, suggesting that peak voltage could be used as an indicator of customer curtailment.

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DOE OSTI2020

Photovoltaic Inverter Momentary Cessation: Recovery Process is Key

Momentary cessation refers to an inverter control mode. When the inverter terminal voltage falls below (or exceeds) a certain level, the inverter ceases to output any current, but attempts to maintain (or quickly regain) phase-locked loop synchronization to allow for quick reinjection of current when the voltage recovers to a certain point. This paper presents a photovoltaic (PV) momentary cessation model developed in PSS/E. Simulations are presented for a high voltage transmission line fault contingency in the Hawaiian island of Oahu power system on a validated PSS/E model, modified to include a custom distributed PV inverter model, and different near-future distributed PV penetration levels. Simulations for the island power system include different penetration levels of PV, and different recovery times (ramp rates and delays) after momentary cessation. The results indicate that during low voltage events, such as faults, momentary cessation can produce severe under frequency events, causing significant load shed and shortly thereafter, in some cases, over frequency events that cause generation to trip offline. The problem is exacerbated with higher penetration levels of PV. If momentary cessation is used (as is typically the case for distribution-connected resources), the recovery process after momentary cessation should be carefully considered to minimize impacts to bulk power system stability.

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DOE OSTI2020

Inverter Testing for Verification of Hawaiian Electric Rule 14H

As utilities increasingly require inverters to perform grid-supportive functions, it is challenging to ensure that those functions are properly configured in the field. This paper presents details of inverter testing related to Hawaiian Electric's latest rule 14H interconnection requirements to validate that field installation procedures result in the intended advanced inverter behavior. The latest Volt-VAR, Volt-Watt, and frequency-Watt curves in Hawaiian Electric's Source Requirement Document (SRD) V1.1 for UL 1741 Supplement A were tested for two inverter manufacturers used in the utility territory. Both inverters were found to be largely compliant, though several discrepancies were identified and reported to the manufacturers. The results are presented and discussed here.

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DOE OSTI2019

Impacts of Voltage-Based Grid-Support Functions on Energy Production of PV Customers: Preprint

This paper presents the impact of grid-support utility-interactive inverter functions, such as volt/volt-ampere reactive and volt/watt controls, on quasi-steady-state feeder voltages and on photovoltaic (PV) customer energy production on a real distribution feeder in Oahu, Hawai'i. These autonomous inverter controls provide an effective means to modulate active and reactive power based on local voltage measurements and therefore serve as good candidates for non-wire alternatives to increase PV hosting capacity. However, because the activation of these functions can result in PV energy curtailment, this study addresses the concerns about the impact of these advanced inverter controls on curtailment through detailed quasi-static time series (QSTS) simulations. This study proposes four metrics-maximum and average grid-support function curtailments, average increased generation, and average net generation change-to assess the impact of a given control on PV systems located on customer sites. For representative scenarios modeled in detail, it was found that curtailment of PV production is negligible for customers where peak voltage is within ANSI C84.1 ranges. A reliable relationship between curtailment and peak customer voltage is demonstrated, allowing peak voltage to be used as an indicator of curtailment without the need to measure curtailment directly.

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DOE OSTI2019

Inverter Testing for Verification of Hawaiian Electric Rule 14H: Preprint

As utilities increasingly require inverters perform grid-supportive functions, it is challenging to ensure that those functions are properly configured in the field. This paper details inverter testing carried related to Hawaiian Electric's latest rule 14H interconnection requirements to validate that field installation procedures result in the intended advanced inverter behavior. The latest Volt-VAR, Volt-Watt, and frequency-Watt curves in Hawaiian Electric's Source Requirement Document (SRD) V1.1 for UL 1741 Supplement A were tested for two inverter manufacturers used in the utility territory. Both inverters were found to be largely compliant, though several discrepancies were identified and reported to the manufacturers to be addressed. The results are presented and discussed here.

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DOE OSTI2019

DER Testing and Verification - Overview of IEEE P1547.1

This presentation provides an overview of IEEE 1547.1, which contains the test and verification procedures needed to confirm that distributed energy resources comply with IEEE 1547-2018. IEEE 1547.1 is currently in balloting and is not yet finalized. The presentation focuses on aspects of IEEE 1547.1 likely to be of interest to to PJM and their stakeholders. It also touches on related topics such as tests that confirm DER behavior that are not included in IEEE 1547.1

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DOE OSTI2019

Smart Inverter Utility Experience in Hawaii

This publication on utility experience with advanced inverters is a part of a tutorial at the 2019 IEEE Power and Energy Society General Meeting titled 'Smart Inverters for Distributed Generators - Utility Applications and Experiences'. It describes lessons utilities can take from the experience of Hawaiian Electric with deployment of advanced inverter functionality. Hawaiian Electric is one of the leading U.S. utilities in terms of deployment of distributed solar photovoltaic systems and advanced inverters.

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DOE OSTI2019

Estimating Customer Impact of Volt-Watt Using Only Smart Meter Voltage Data

The autonomous inverter control mode known as volt-watt control can be useful as a backstop against high customer voltages outside of the ranges specified in ANSI C84.1 (i.e. above 1.05-1.06 per unit). Volt-watt control mitigates high voltages by directly reducing the active power output of a distributed energy resource based on local voltage measurements. Therefore volt-watt control also can impact the energy produced by the DER (e.g. PV system), especially for customers with persistently high voltages, and in such cases it is difficult to determine exactly how much the DER has been curtailed because it is not generally known exactly how much energy the PV system could have produced. These slides propose a relatively simple method of estimating the DER's energy curtailment using only data from the utility advanced metering infrastructure (AMI) data). The method proves surprisingly accurate when validated against detailed quasi-static time-series simulations and against limited field data.

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DOE OSTI2019

Dynamic Capabilities of an Energy Storage-Embedded DFIG System

Power electronic-based wind turbine generators (WTGs) are capable of providing inertial response to the grid by releasing kinetic energy from the turbine blade; thus, as conventional power plants are retired, the reduction of online inertia can be compensated by designing frequency controls for the WTGs. Deployment of energy storage technology for renewable generations has been increased to have the renewables centralized with a system operator as an independent power supply by making up for their nature of generation. In addition, the cost of energy storage has dropped over time and global research activities on energy storage have been funded by private industries and governments. This paper investigates the opportunity of deploying an energy storage on a doubly fed induction generator (DFIG)-based WTG to respond to the system frequency, and then explores dynamic capabilities of the energy storage-embedded DFIG to boost its contribution while the frequency response is being provided by the power system's online inertia; thus, enabling an effective delivery of ancillary services to the system. To do this, the dynamic models of DFIG and energy storage are combined and simulated under the different operating conditions of a DFIG, such as subsynchronous, synchronous, and supersynchronous operations, using the PSCAD.

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DOE OSTI2019

Low-Cost Multiparameter Device for Solar Resource Applications

The National Renewable Research Laboratory (NREL) Solar Radiation Research Laboratory (SRRL), in collaboration with Arable Labs Inc., deployed, calibrated, and characterized Arable Lab's Mark low-cost, multiparameter sensor system. Arable Labs was selected by the U.S. Department of Energy for a small business voucher to work with NREL to tap into the knowledge and expertise Arable needs to tailor and evaluate the Mark device for broader solar energy applications. The device is a complete and independent unit. It is a self-powered, off-the-shelf solution for remote solar irradiance and meteorological sensing and data collection. Calibration of devices against the SRRL instruments provides an understanding of the quality of a new instrument compared to peers. The characterization process provides an understanding of the variability compared to high-quality instruments and essentially provides methods to correct the sources of the variabilities.

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DOE OSTI2018

Impact of Frequency-Watt Control on the Dynamics of a High DER Penetration Power System

Inverter-coupled generation is slowly displacing synchronous generators in the power system, resulting in reduced system inertia and primary frequency response, which makes the system susceptible to larger frequency deviations. Such deviations may result in load shedding or tripping of inverters, thus reducing the reliability. Frequency-watt control of inverters is an autonomous approach to support grid frequency at a fast timescale by adjusting the inverter output with changes in frequency. This study investigates the dynamics of a power system with a high penetration of distributed PV generation with frequency-watt droop control enabled. A simple aggregated reduced-order two-source model of the O'ahu Island (Hawaii) power system is developed and validated against a full dynamic model, and the small-signal stability of the reduced model is then examined the under various PV penetrations. The impact of frequency-watt parameters on the system frequency dynamics is investigated by observing trajectories of small- signal eigenvalues. The results of the eigenvalue analysis are validated through time-domain simulation. Considerations for frequency-watt parameter selection are discussed.

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DOE OSTI2018

Validating the Test Procedures Described in UL 1741 SA and IEEE P1547.1

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DOE OSTI2018

PV Inverter Fault Response Including Momentary Cessation, Frequency-Watt, and Virtual Inertia

This paper presents two photovoltaic (PV) inverter control methods and an analysis of the two under a significant three-phase transmission line fault contingencies in the Hawaiian island of Oahu power system. Simulations are presented for the two control methods on the island power system with a high penetration of PV generation, approximately 40% of the total. The two control methods discussed are similar: one is a proportional frequency-watt controller, and the second is a proportional-derivative controller, a frequency-watt controller with virtual inertia. Both methods can be beneficial for fast frequency support. The inverter model also emulates inverter fault response including 'momentary cessation' and recovery during low voltage events. The study presented in this paper utilizes a validated power system model of the Hawaiian island of Oahu, modified to include PV resources with the two custom developed control models. Dynamic simulations with PSS/E are presented during a significant transmission line three-phase fault contingency. Simulations are presented with and without PV reserve margin. In addition, a parameter sensitivity analysis is presented for the control methods. Results indicate both methods can significantly improve system response during fault events. Findings indicate that transmission faults can produce severe frequency events, and that fast recovery from momentary cessation is crucial to mitigate severity.

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DOE OSTI2018

Residential Advanced Photovoltaic Inverter Pilot Study Results for Select Distribution Secondaries in Hawai'i

Penetration levels of residential rooftop solar photovoltaic (PV) generation on the Hawaiian island of O'ahu have increased significantly in recent years, with many circuits now at the limits of their PV hosting capacity. NREL and Hawaiian Electric have used this opportunity to deploy advanced inverters at new customer installations that would not otherwise have been approved, as a pilot study to gain first-hand operational field data and experience on the impact of inverter-based grid support functions. At each customer location, the deployed advanced inverters were remotely controlled and monitored. Additionally, customer AMI (smart meter) and secondary distribution transformer data was also available for the analysis. The analysis focused on quantifying the customer behind-the-meter voltage rise due to PV production, determining the customer voltage rise with advanced inverters in unity power factor as well as advanced grid support function modes, and estimating the curtailment when inverters have Volt-VAR and Volt-Watt enabled. The results show that: 1) Behind-the-meter voltage rise is often not negligible. 2) An inverter's operating point on a Volt-VAR/Volt-Watt curve depends strongly on the design of the secondary system on which it is installed. 3) The mitigation of voltage rise on the secondary system using Volt-VAR may not be effective if only a small proportion of inverters have grid support enabled, or if the reactance/resistance (X/R) ratio of the grid is low. 4) Volt-Watt curtailment can be estimated using co-located irradiance sensors but there may be opportunities to estimate it using inverter internal electrical measurements. 5) Estimated curtailment is very low for the locations analyzed to date.

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DOE OSTI2018

Integrating More Solar with Smart Inverters

This presentation provides a high-level overview of integrating more solar with smart inverters.

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DOE OSTI2018

Integrating More Solar with Smart Inverters: Preprint

In Hawai'i, the relatively high cost of electricity costs coupled with various incentives have made it cost-effective to install solar photovoltaics (PV) on residential homes and larger central-station PV plants. On some of the islands, PV has reached over 50% of the installed generation capacity base. To make sure these inverter-based PV plants can maintain stable and safe operations, new smart inverter functionality is being evaluated and demonstrated at significant scale across the islands This paper describes research conducted to validate high PV penetration scenarios with smart inverters and recent progress on the use of these advanced inverter grid support functions in actual power grids in Hawai'i.

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DOE OSTI2018

Validating the Test Procedures Described in UL 1741 SA and IEEE P1547.1: Preprint

This paper investigates the test procedures specified in UL 1741 SA and the upcoming revision to IEEE P1547.1. A 550 kVA photovoltaic inverter was chosen for the tests. This research reveals some of key the components to consider while doing certification tests for UL 1741 SA and IEEE P1547.1. This paper also identifies some issues requiring consideration for future releases of the standard, i.e. IEEE P1547.1. This paper investigates the test procedures specified in UL 1741 SA and the upcoming revision to IEEE P1547.1. A 550 kVA photovoltaic inverter was chosen for the tests. This research reveals some of key the components to consider while doing certification tests for UL 1741 SA and IEEE P1547.1. This paper also identifies some issues requiring consideration for future releases of the standard, i.e. IEEE P1547.1.

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