Murali Baggu

Accurate power prediction of spatially distributed PV systems using localized irradiance measurements

In this paper, a method for estimating power injected into an electrical distribution system from spatially distributed residential PV systems using data from ground-based weather stations is described. This method was developed as part of the High Penetration PV Deployment Project at the Arizona Public Service (APS). Verification of this predictive method is also described in this paper. Finally, correlation statistics and power production ramp rates are calculated for irradiance based on measured power within the APS study area using two different sets of weather station measurements. The method has potential applications to real-time or forecasted power estimation on distribution circuits in addition to the development of broader guidelines on the optimal number and location of irradiance sensors for power estimation in distribution circuits with high penetrations of PV.

Microgrid Controllers : Expanding Their Role and Evaluating Their Performance

Microgrids have long been deployed to provide power to customers in remote areas as well as critical industrial and military loads. Today, they are also being proposed as grid-interactive solutions for energy-resilient communities. Such microgrids will spend most of the time operating while synchronized with the surrounding utility grid but will also be capable of separating during contingency periods due to storms or temporary disturbances such as local grid faults. Properly designed and grid-integrated microgrids can provide the flexibility, reliability, and resiliency needs of both the future grid and critical customers. These systems can be an integral part of future power system designs that optimize investments to achieve operational goals, improved reliability, and diversification of energy sources.

Feeder model validation and simulation for high-penetration photovoltaic deployment in the Arizona Public Service system

In an effort to better understand the impacts of high penetrations of photovoltaic (PV) generators on distribution systems, Arizona Public Service and its partners are implementing a multi-year project to develop the tools and knowledge base needed to safely and reliably integrate high penetrations of utility- and residential-scale PV. Building on the APS Community Power Project-Flagstaff Pilot, this project investigates the impact of PV on a representative feeder in northeast Flagstaff. To quantify and catalog the effects of the estimated 1.3 MW of PV that will be installed on the feeder (both smaller units at homes, as well as large, centrally located systems), high-speed weather and electrical data acquisition systems and digital “smart” meters were designed and installed to facilitate monitoring and to build and validate comprehensive, high-resolution models of the distribution system. These models are being developed to analyze the impacts of PV on distribution circuit-protection systems (including coordination and anti-islanding), predict voltage regulation and phase-balance issues, and develop volt/VAr control schemes. This paper expands upon a paper presented at the 2013 IEEE PVSC conference that described updated results from the data acquisition effort, newly developed graphical analysis tools, continued feeder modeling, utility-scale PV integration and performance, and continued model validation. This paper presents results from Phases 3 and 4 of the project. Specifically, the paper discusses feeder model evaluation and extended application for advanced scenario analysis, specifically feeder reconfiguration, smart-grid device interaction study, smart inverter grid, and support functionality.

Look ahead Volt/VAR Control: A comparison of integrated and coordinated methods

In this paper, multiple approaches for solving Volt/VAR Control (VVC) optimization problem are compared. Two different VVC schemes are evaluated in detail for managing Distribution control assets such as Load Tap Changers, capacitor banks and voltage regulators on day ahead basis to achieve multiple objective functions by minimizing switching operations of the assets. The first approach is an integrated optimization based on a dynamic programming algorithm converging to a global optimal solution with the drawback of time of convergence. The second approach is a coordinated optimization algorithm that is computationally efficient at the expense of optimality (an approximate solution to the minimum cost of the objective function). The algorithms are applied on a real world distribution network. Robust Matlab/OpenDSS simulation platform is used to compare the effectiveness of the algorithms.

Modeling and compensation design for a power hardware-in-the-loop simulation of an AC distribution system

Power hardware-in-the-loop (PHIL) simulation, where actual hardware under text is coupled with a real-time digital model in closed loop, is a powerful tool for analyzing new methods of control for emerging distributed power systems. However, without careful design and compensation of the interface between the simulated and actual systems, PHIL simulations may exhibit instability and modeling inaccuracies. This paper addresses issues that arise in the PHIL simulation of a hardware battery inverter interfaced with a simulated distribution feeder. Both the stability and accuracy issues are modeled and characterized, and a methodology for design of PHIL interface compensation to ensure stability and accuracy is presented. The stability and accuracy of the resulting compensated PHIL simulation is then shown by experiment.

Interconnection assessment methodology and cost benefit analysis for high-penetration PV deployment in the Arizona Public Service system

In an effort to better understand the impacts of high penetrations of photovoltaic (PV) generators on distribution systems, Arizona Public Service and its partners completed a multi-year project to develop the tools and knowledge base needed to safely and reliably integrate high penetrations of utility- and residential-scale PV. Building upon the APS Community Power Project-Flagstaff Pilot, this project investigates the impact of PV on a representative feeder in northeast Flagstaff. To quantify and catalog the effects of the estimated 1.3 MW of PV that will be installed on the feeder (both smaller units at homes and large, centrally located systems), high-speed weather and electrical data acquisition systems and digital “smart” meters were designed and installed to facilitate monitoring and to build and validate comprehensive, high-resolution models of the distribution system. These models are being developed to analyze the impacts of PV on distribution circuit protection systems (including coordination and anti-islanding), predict voltage regulation and phase balance issues, and develop volt/VAr control schemes. This paper continues from a paper presented at the 2014 IEEE PVSC conference that described feeder model evaluation and high penetration advanced scenario analysis, specifically feeder reconfiguration. This paper presents results from Phase 5 of the project. Specifically, the paper discusses tool automation; interconnection assessment methodology and cost benefit analysis.

Advanced inverter functions and communication protocols for distribution management

This paper aims at identifying the advanced features required by distribution management systems (DMS) service providers to bring inverter-connected distributed energy resources into use as an intelligent grid resource. This work explores the standard functions needed in the future DMS for enterprise integration of distributed energy resources (DER). The important DMS functionalities such as DER management in aggregate groups, including the discovery of capabilities, status monitoring, and dispatch of real and reactive power are addressed in this paper. It is intended to provide the industry with a point of reference for DER integration with other utility applications and to provide guidance to research and standards development organizations.

Application of autonomous smart inverter Volt-VAR function for voltage reduction energy savings and power quality in electric distribution systems

This paper evaluated the impact of smart inverter Volt-VAR function on voltage reduction energy saving and power quality in electric power distribution systems. A methodology to implement the voltage reduction optimization was developed by controlling the substation LTC and capacitor banks, and having smart inverters participate through their autonomous Volt-VAR control. In addition, a power quality scoring methodology was proposed and utilized to quantify the effect on power distribution system power quality. All of these methodologies were applied to a utility distribution system model to evaluate the voltage reduction energy saving and power quality under various PV penetrations and smart inverter densities.

Improving advanced inverter control convergence in distribution power flow

Simulation of modern distribution system powerflow increasingly requires capturing the impact of advanced PV inverter voltage regulation on powerflow. With Volt/var control, the inverter adjusts its reactive power flow as a function of the point of common coupling (PCC) voltage. Similarly, Volt/watt control curtails active power production as a function of PCC voltage. However, with larger systems and higher penetrations of PV, this active/reactive power flow itself can cause significant changes to the PCC voltage potentially introducing oscillations that slow the convergence of system simulations. Improper treatment of these advanced inverter functions could potentially lead to incorrect results. This paper explores a simple approach to speed such convergence by blending in the previous iterations reactive power estimate to dampen these oscillations. Results with a single large (5MW) PV system and with multiple 500kW advanced inverters show dramatic improvements using this approach.