Barry Mather

Quasi-static time-series test feeder for PV integration analysis on distribution systems

This paper presents a quasi-static time-series test feeder based on the well-known 34 node test feeder [1]. This test feeder is useful for the evaluation and quantification the distribution system impacts of distributed PV integrations. The load profiles and solar resource profiles used are both publically available. The quasi-static time-series test feeder has been developed using data for the year 2010. The fixed time period between power flow solutions is 1 min making the presented quasi-static time-series test feeder appropriate for use in investigating voltage regulation device operations. A load allocation algorithm is also proposed for assigning spot and distributed loads in the 34 node test feeder to time varying load profiles based on rate class load profiles. A simple model for modeling the real AC power output of a PV system based on discrete global horizontal irradiance (GHI) is also presented. The results of analysis completed using the quasi-static time-series test feeder are shown for various single-site 1MW PV deployment scenarios and voltage regulator compensation settings.

Power hardware-in-the-loop testing of a 500 kW photovoltaic array inverter

The testing of a 500 kW photovoltaic array inverter using power hardware-in-the-loop simulation is described. A real-time simulator is used with a DC amplifier in order to emulate a photovoltaic (PV) array and an AC amplifier to emulate a power grid. The test setup is described in detail and a range of tests that were conducted on the inverter are summarized.

Photovoltaic (PV) Impact Assessment for Very High Penetration Levels

This paper describes a granular approach for investigating the impacts of very high photovoltaic (PV) generation penetration. Studies on two real-world distribution feeders connected to PV plants are presented. The studies include both steady-state and time-series power flow analyses, which include the effects of solar variability. The goal of the study is to predict the effects of increasing levels of PV generation as it reaches very high penetration levels. The loss and return of generation with and without regulation is simulated to capture short-term problems such as voltage fluctuations. Impact results from the analyses are described along with potential mitigations.

Integrating high penetrations of PV into Southern California: Year 2 project update

Southern California Edison (SCE) is well into a five-year project to install a total of 500 MW of distributed photovoltaic (PV) energy within its utility service territory. Typical installations to date are 1–3 MW peak rooftop PV systems that interconnect to medium-voltage urban distribution circuits or larger (5 MW peak ) ground-mounted systems that connect to medium-voltage rural distribution circuits. Some of the PV system interconnections have resulted in distribution circuits that have a significant amount of PV generation compared to customer load, resulting in high-penetration PV integration scenarios. The National Renewable Energy Laboratory (NREL) and SCE have assembled a team of distribution modeling, resource assessment, and PV inverter technology experts in order to investigate a few of the high-penetration PV distribution circuits. Currently, the distribution circuits being studied include an urban circuit with a PV penetration of approximately 46% and a rural circuit with a PV penetration of approximately 60%. In both cases, power flow on the circuit reverses direction, compared to traditional circuit operation, during periods of high PV power production and low circuit loading. Research efforts during year two of the five-year project were focused on modeling the distribution system level impacts of high-penetration PV integrations, the development and installation of distribution circuit data acquisition equipment appropriate for quantifying the impacts of high-penetration PV integrations, and investigating high-penetration PV impact mitigation strategies. This paper outlines these research efforts and discusses the following activities in more detail: the development of a quasi-static time-series test feeder for evaluating high-penetration PV integration modeling tools; the advanced inverter functions being investigated for deployment in the projects field demonstration and a power hardware-in-loop test of a 500-kW PV inverter implementing a limited set of advanced inverter functions.

Implementation and validation of advanced unintentional islanding testing using power hardware-in-the-loop (PHIL) simulation

Unprecedented investment in new renewable power (especially solar photovoltaic) capacity is occurring. As this new generation capacity is interconnected with the electric power system (EPS), it is critical that their grid interconnection systems have proper controls in place so that they react appropriately in case of an unintentional islanding event. Advanced controls and methods for unintentional islanding protection that go beyond existing standards, such as UL 1741 and IEEE Std 1547, are often required as more complex high penetration photovoltaic installations occur. This paper describes the implementation, experimental results, and validation of a power hardware-in-the-loop (PHIL)-based platform that allows for the rapid evaluation of advanced anti-islanding and other controls in complex scenarios. The PHIL-based approach presented allows for accurate, real-time simulation of complex scenarios by connecting a device under test to a software-based model of a local EPS. This approach was validated by conducting an unintentional islanding test of a photovoltaic inverter, as described in IEEE 1547.1, using both PHIL and discrete hardware-based test configurations. The comparison of the results of these two experiments demonstrates that this novel PHIL-based test platform accurately emulates traditional unintentional islanding tests. The advantage of PHIL-based testing over discrete hardware-only testing is demonstrated by completing an IEEE 1547.1 unintentional islanding test using a very precisely tuned resonant circuit that is difficult to realize with discrete hardware using PHIL.

Updating technical screens for PV interconnection

Solar photovoltaics (PV) is the dominant type of distributed generation (DG) technology interconnected to electric distribution systems in the United States, and deployment of PV systems continues to increase rapidly. Considering the rapid growth and widespread deployment of PV systems in United States electric distribution grids, it is important that interconnection procedures be as streamlined as possible to avoid unnecessary interconnection studies, costs, and delays. Because many PV interconnection applications involve high penetration scenarios, the process needs to allow for a sufficiently rigorous technical evaluation to identify and address possible system impacts. Existing interconnection procedures are designed to balance the need for efficiency and technical rigor for all DG. However, there is an implicit expectation that those procedures will be updated over time in order to remain relevant with respect to evolving standards, technology, and practical experience. Modifications to interconnection screens and procedures must focus on maintaining or improving safety and reliability, as well as accurately allocating costs and improving expediency of the interconnection process. This paper evaluates the origins and usefulness of the capacity penetration screen, offers potential short-term solutions which could effectively allow fast-track interconnection to many PV system applications, and considers longer-term solutions for increasing PV deployment levels in a safe and reliable manner while reducing or eliminating the emphasis on the penetration screen.

On Distributed PV Hosting Capacity Estimation, Sensitivity Study, and Improvement

This paper first studies the estimated distributed photovoltaic (PV) hosting capacities of 17 utility distribution feeders using the Monte Carlo simulation based stochastic analysis, and then analyzes the sensitivity of PV hosting capacity to both feeder and PV system characteristics. Furthermore, an active distribution network management approach is proposed to maximize PV hosting capacity by optimally switching capacitors, adjusting voltage regulator taps, managing controllable branch switches, and controlling smart PV inverters. The approach is formulated as a mixed-integer nonlinear optimization problem and a genetic algorithm is developed to obtain the solution. Multiple simulation cases are studied and the effectiveness of the proposed approach on increasing PV hosting capacity is demonstrated.

Technologies to increase PV hosting capacity in distribution feeders

This paper studies the distributed photovoltaic (PV) hosting capacity in distribution feeders by using the stochastic analysis approach. Multiple scenario simulations are conducted to analyze several factors that affect PV hosting capacity, including the existence of voltage regulator, PV location, the power factor of PV inverter and Volt/VAR control. Based on the conclusions obtained from simulation results, three approaches are then proposed to increase distributed PV hosting capacity, which can be formulated as the optimization problem to obtain the optimal solution. All technologies investigated in this paper utilize only existing assets in the feeder and therefore are implementable for a low cost. Additionally, the tool developed for these studies is described.

Methods to determine recommended feeder-wide advanced inverter settings for improving distribution system performance

This paper describes methods that a distribution engineer could use to determine advanced inverter settings to improve distribution system performance. These settings are for fixed power factor, volt-var, and volt-watt functionality. Depending on the level of detail that is desired, different methods are proposed to determine single settings applicable for all advanced inverters on a feeder or unique settings for each individual inverter. Seven distinctly different utility distribution feeders are analyzed to simulate the potential benefit in terms of hosting capacity, system losses, and reactive power attained with each method to determine the advanced inverter settings.

Alternatives to the 15% Rule

The third solicitation of the California Solar Initiative (CSI) Research, Development, Demonstration and Deployment (RD&D) Program established by the California Public Utility Commission (CPUC) is supporting the Electric Power Research Institute (EPRI), National Renewable Energy Laboratory (NREL), and Sandia National Laboratories (SNL) with collaboration from Pacific Gas and Electric (PG&E), Southern California Edison (SCE), and San