Farid Katiraei

Planned islanding on rural feeders — utility perspective

Planned islanding application, also known as intentional islanding, is an early utility adaptation of the Microgrid concept that is being promoted by major utilities around the world. The main objective of planned islanding projects in Canada is to enhance customer-based power supply reliability on rural feeders by utilizing an appropriately located independent power producer (IPP). This paper considers the process of planned islanding and the necessary steps that need to be taken in order to lead to successful projects. Some of the current experience from Canadian utilities in this area are investigated and the additional requirements, in terms of equipment and system studies, which are needed in order to plan for the operation of a planned island project are discussed. A case of planned islanding on rural feeders with multiple distributed generation units is also investigated, which represents the target of future projects in this area.

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.

Fault contribution of grid-connected inverters

The distribution grid is mainly built on a radial configuration where power is coming from one transformer substation to supply clients. Up to recently, in the rare cases where distributed generation existed, it was almost exclusively constituted of rotating machines, which have quite a different behaviour under fault than inverter-based sources. Consequently, current connection impact assessments rules were built on years of rotating machines experience and often misrepresent inverter-based sources. This paper presents an overview of the issue of short-circuit contribution with respect to distributed generation and highlights the distinctions between rotating and inverter-based sources in this regard. A typical inverter and synchronous machine short-circuit current model is presented as well as simulation results for a 7.5MW implementation on a typical Canadian network.

Dynamic analysis and field verification of an innovative anti-islanding protection scheme based on directional reactive power detection

Based on current utility practice, anti-islanding protection is one of the main protection requirements for interconnection of a distribution generation (DG) to the medium and low voltage grids. For connecting a small synchronous generator to the utility grid, DG interconnection guidelines require the use of a transfer-trip scheme when the minimum load of a connecting feeder is less than twice the rated capacity of the total DG units. Some standards (e.g. IEEE Std. 1547) suggest a more aggressive generation to load ratio of one-third. Implementation of a fast communication based transfer-trip scheme with a detection time of less than a second is very expensive and not economically feasible for small DG projects. The fast islanding detection is mainly required to comply with the feeder protection coordination, especially the first reclosing time of the feeder automatic reclosure (in this case 1.5 seconds). This paper presents the computer modelling, simulation, and field verification of a proposed passive, local anti-islanding protection scheme based on directional reactive power measurement. The protection scheme was tested on a farm-based biogas DG to demonstrate compliance with the utility requirements. The detailed simulation studies and field tests consistently yielded detection times of less than 0.25 seconds. Based on these results the solution and the DG interconnection were approved by the utility. The proposed protection scheme can effectively be utilized for anti-islanding protection of synchronous generator based DG units on feeders with inductive load.

Southern California Edison High Penetration Photovoltaic Project - Year 1

This report discusses research efforts from the first year of a project analyzing the impacts of high penetration levels of photovoltaic (PV) resources interconnected onto Southern California Edisons (SCEs) distribution system. SCE will be interconnecting a total of 500 MW of commercial scale PV within their service territory by 2015. This Year 1 report describes the need for investigating high-penetration PV scenarios on the SCE distribution system; discusses the necessary PV system modeling and distribution system simulation advances; describes the available distribution circuit data for the two distribution circuits identified in the study; and discusses the additional inverter functionality that could be implemented in order to specifically mitigate some of the undesirable distribution system impacts caused by high-penetration PV installations.

Analysis of interconnection of photovoltaic distributed generation

Rapid growth of grid-connected photovoltaic distributed generation (PV-DG) provides many benefits such as clean energy, reduced emissions and creation of new green jobs. However, given its intermittent nature, large scale penetration of PV-DG may challenge the quality and reliability of the grid. This paper evaluates the impact of PV-DG on distribution system voltages. The paper describes the models used for the study, discusses the impacts of PV-DG, and presents the results of detailed simulations. The results show that PV-DG can cause both steady-state and transient overvoltages along the feeder, and may create additional tap operations of line voltage regulators. Finally, the paper proposes a mitigation strategy to eliminate overvoltages, reduce additional tap operations, and validates the proposed method with simulation results.

Modeling and analysis of synchronous generator based distributed energy resources for dynamic impact studies

Although power electronic based generation sources such as solar photovoltaic plants and wind farms are gaining enormous popularity, conventional distributed energy resources (DERs) are commonly used and integrated onto distribution systems. The main reasons are the improving the economy of generation, controllability and maturity of the technology that simplifies operation and maintenance of the plant. Contrary to common belief, recent technological enhancements have brought about many engine driven generation types which are classified as clean (green) sources. This paper deals with the topic of modeling and benchmarking conventional synchronous generator based DERs for application in distribution systems. The DER model incorporates some new aspects of generation controls such as voltage regulation and reactive power compensation that are being asked for by some utilities to help accommodate integration onto existing distribution feeders while minimizing adverse effects. The introduced DER model is applied to and studied on a benchmark distribution network to demonstrate typical applications and impact investigations.

Power hardware-in-loop testing of advanced inverter functionalities

This paper describes an advanced testing approach and a laboratory testbed developed specifically for evaluating controls, communications and protection functionalities of individual inverters and/or multiple inverters operating in parallel on distribution systems. The testbed utilizes power hardware-in-loop for interfacing commercial power electronic based devices to real-time simulator systems representing a simulated model of a target medium voltage distribution circuit. The testing approach is described and compared with conventional testing methods. A number of the laboratory test results are presented, demonstrating the capability of the testing approach in characterizing inverter operation and performance.

Control and monitoring requirements for distribution systems with high penetration of renewable energy sources

Proliferation of renewable and alternative energy resources as part of distribution systems is changing the paradigm of design and operation. This paper describes some of the expected issues due to integrating renewable energy resources at distribution levels and investigates the needs for deployment and/or enhancement of additional/existing measurement devices and controls on distribution grids. The aim is to determine the requirement for installation of accurate meters, how the data will be used, and what analytical applications are needed to detect and mitigate a power quality issues before it becomes widespread and causes cascading failure.

Hardware and software model evaluation of a dynamic load balancer for mitigation of current unbalance in distribution circuits

Current unbalance conditions are a concern to utilities and can negatively affect power quality and safe and reliable system operation if left untreated. Conventional solutions involve physical re-configuration and are typically challenging and less effective as these changes are temporary and will change as circuit and customer load habits evolve. As alternative, power electronic-based devices are promising solutions to mitigating current unbalance. This paper introduces the control theory behind one such power electronics-based Dynamic Load Balancer (DLB) and details the development of a transient software-based simulation model to allow for mitigation planning and performance evaluation in distribution circuits. The physical and software model for DLB were tested under a range of system conditions as verification of model accuracy and also evaluation of the device capabilities and performance.