Jerry W. Ginn

Development and Testing of an Approach to Anti-Islanding in Utility-Interconnected Photovoltaic Systems

This report documents the development of an inverter control method that detects and avoids islanding in utility-interconnected photovoltaic installations. This method is applicable to single and multiple inverters connected to a single utility distribution line. The anti-islanding approach is described and its performance is demonstrated on both a theoretical basis and with results from tests conducted at Sandia National Laboratories and Ascension Technology, a division of Applied Power Corporation. It has been demonstrated that this approach is effective for single and multiple photovoltaic inverter installations for the special case where the inverter contains a version of anti-islanding software compatible with IEEE Std 929-2000.The report also describes the anti-islanding technique so that it can be incorporated into photovoltaic systems lacking this feature. A test procedure that ascertains whether an anti-islanding capability exists in a PV inverter is also presented. This page intentionally left blank

Array Performance Characterization and Modeling for Real-Time Performance Analysis of Photovoltaic Systems

Improvements in the methods used for photovoltaic (PV) system design, performance rating, and long-term monitoring are needed by the rapidly growing industry, as well as by the U.S. Department of Energy in evaluating progress by solar technology development initiatives. This paper describes an improved model for rating and monitoring PV array performance, discusses initial results from an outdoor laboratory designed to assist industry in optimizing system components and integration, and provides a brief discussion of the system performance metrics currently being used by the PV community

Design considerations for three-phase grid connected photovoltaic inverters

This paper discusses the design considerations for three-phase inverters for grid connected photovoltaic systems. Specific performance considerations are addressed including topology trade-offs, efficiency trade-offs, and maximum power point tracking. Additionally, utility interconnect issues are examined including power quality and anti-islanding. Testing results are provided for the Xantrex PV series of inverter products. These systems operate with a variety of PV panels and are designed to meet the UL-1741 utility interconnection standard. Power levels are from 5 kW to 300 kW, and the output is a nominal 208 VAC. Experimental results showing successful operation are given for the 10 kW system. Testing was performed at the Sandia National Laboratories Photovoltaic Systems Evaluation Lab in Albuquerque, NM.

Simulation and Experimental Study of the Impedance Detection Anti-Islanding Method in the Single-Inverter Case

The impedance detection method of islanding prevention is often touted as one that possesses no nondetection zone in the single-inverter case. However, simulation results and experiments indicate that this is not necessarily true; the effectiveness of impedance detection is highly dependent on the specific implementation of the method. This paper discusses a simulation and experimental study to examine the origins of this nondetection zone, and a simple modification that appears to significantly reduce the size of the nondetection zone

Removing barriers to utility interconnected photovoltaic inverters

The Million Solar Roofs Initiative has motivated a renewed interest in the development of utility interconnected photovoltaic (UIPV) inverters. Government-sponsored programs (PVMaT, PV:BONUS) and competition among utility interconnected inverter manufacturers have stimulated innovations and improved the performance of existing technologies. With resurgence, Sandia National Laboratories (SNL) developed a program to assist industry initiatives overcome barriers to UIPV inverters. In accordance with newly adopted IEEE Std 929-2000, the interconnected PV inverters are to energizing the utility grid when disturbance occurs or the utility experiences an interruption in service. Compliance with IEEE Std 929-2000 is being widely adopted by utilities as a minimum requirement for utility interconnection. This report summarizes work done at the SNL balance-of-systems laboratory to support the development of IEEE Std 929-2000 and to assist manufacturers in meeting its requirements.

Inverter testing at Sandia National Laboratories

Inverters are key building blocks of photovoltaic (PV) systems that produce ac power. The balance of systems (BOS) portion of a PV system can account for up to 50% of the system cost, and its reliable operation is essential for a successful PV system. As part of its BOS program, Sandia National Laboratories (SNL) maintains a laboratory wherein accurate electrical measurements of power systems can be made under a variety of conditions. This paper outlines the work that is done in that laboratory.

Discussion of the Physical Mechanisms Behind the Observed Behavior of Motors in Islanded Loads

As work continues on synchronizing anti-islanding standards worldwide, disagreement remains as to whether it is necessary to include motors in the loads used in the tests. One reason is that there is still a lack of a full physical understanding of the behavior of motor loads in islands. This paper explores the behavior of single-phase induction motors in islands and proposes a theory to explain the available observations. The use of parallel RLC loads to adequately model motors for islanding tests is discussed. Finally, the appropriateness of including a motor acting as a flywheel is questioned

Sandia National Laboratories photovoltaic balance of systems program

The Sandia National Laboratories photovoltaic balance of system (BOS) program is sponsored by the Department of Energy to increase the reliability and lower the cost of BOS components. Efforts for FY1998 are discussed. Principal efforts include a quality program for inverter manufacturers, a grid-tied anti-islanding program, development of a hybrid inverter, hardware benchmarking program, and a battery evaluation program.

Laboratory tests of IEC DER object models for grid applications.

This report describes a Cooperative Research and Development Agreement (CRADA) between Salt River Project Agricultural Improvement and Power District (SRP) and Sandia National Laboratories to jointly develop advanced methods of controlling distributed energy resources (DERs) that may be located within SRP distribution systems. The controls must provide a standardized interface to allow plug-and-play capability and should allow utilities to take advantage of advanced capabilities of DERs to provide a value beyond offsetting load power. To do this, Sandia and SRP field-tested the IEC 61850-7-420 DER object model (OM) in a grid environment, with the goal of validating whether the model is robust enough to be used in common utility applications. The diesel generator OM tested was successfully used to accomplish basic genset control and monitoring. However, as presently constituted it does not enable plug-and-play functionality. Suggestions are made of aspects of the standard that need further development and testing. These problems are far from insurmountable and do not imply anything fundamentally unsound or unworkable in the standard.

Testing and Development of a 30-kVA Hybrid Inverter: Lessons Learned and Reliability Implications

A 30-kVA Trace Technologies hybrid power processor was specified and tested at the Sandia inverter test facility. Trace Technologies involving the control system, in response to suggestions made modifications, primarily by Sandia and Arizona Public Service (APS) personnel. The modifications should make the inverter more universally applicable and less site-specific so that it can be applied in various sites with minimal field interaction required from the design engineer. The project emphasized the importance of battery management, generator selection, and site load management to the performance and reliability of hybrid power systems.