Arindam Maitra

Evaluation of the impact of plug-in electric vehicle loading on distribution system operations

Electric transportation has many attractive features in todays energy environment including decreasing greenhouse gas emissions from the transportation sector, reducing dependence on imported petroleum, and potentially providing consumers a lower cost alternative to gasoline. Plug-in hybrid Electric (PHEV) vehicles represent the most promising approach to electrification of a significant portion of the transportation sector. Electric power utilities recognize this possibility and must analyze the associated impacts to electric system operations. This paper provides details of analytical framework developed to evaluate the impact of PHEV loading on distribution system operations as part of a large, multi-utility collaborative study. This paper also summarizes partial results of the impact of PHEVs on one utility distribution feeder.

Multilevel intelligent universal transformer for medium voltage applications

The solid-state transformer allows add-on intelligence to enhance power quality compatibility between source and load. It is desired to demonstrate the benefits gained by the use of such a device. Recent advancement in semiconductor devices and converter topologies facilitated a newly proposed intelligent universal transformer (IUT), which can isolate a disturbance from either source or load. This paper describes the basic circuit and the operating principle for the multilevel converter based IUT and its applications for medium voltages. Various power quality enhancement features are demonstrated with computer simulation for a complete IUT circuit.

Evaluations of plug-in electric vehicle distribution system impacts

With plug-in electric vehicles poised to enter the automotive market this year, a remaining concern for electrical distribution utilities is the potential impact these loads may have on their system and how to account for them in their planning process. In order to address this concern, EPRI has initiated a multi-utility project to quantify the potential impacts across numerous distribution feeders of varying characteristics. As part of this project, an analysis methodology which accounts for PEV spatial and temporal diversities has been developed and used to study these potential impacts. Preliminary findings from some of the initial circuits studied are presented as well as initial insights developed thus far.

Grid impacts of plug-in electric vehicles on Hydro Quebec's distribution system

As the potential economic and environmental benefits of plug-in electric vehicles (PEVs) become apparent and as strong interest develops among automakers, seamless integration of PEVs to the grid will be a critical step to encourage utility support for PEV commercialization. Technological barriers continue to fall, but taking advantage of opportunities to increase revenue and improve power system efficiency using PEVs will require active participation by utilities and OEMs in how the vehicles are introduced to customers. PEVs are transformational in that they introduce electricity as a meaningful automotive fuel to a potentially very large market. This paper will focus on some of the most pressing technical issues associated with the act of plugging these vehicles into the electric grid. This paper presents key impact results using the EPRI study methodology [1] for one representative Hydro-Québec distribution feeders. This study is part of the multiyear collaborative project geared towards evaluating the localized impacts of plug-in electric vehicles on individual utilitys distribution systems.

Load model parameter derivation using an automated algorithm and measured data

This paper summaries some of the key results achieved in the second phase of a multi-year collaborative load modeling research project. After having identified suitable types of load monitoring devices, actual field data for load model development and validation were collected at appropriate locations for several months to more than a year in three different utilities. This data was post-processed using an automated methodology to filter out events suitable for load model parameter estimation. Two load model structures were then used with an automated parameter estimation algorithm to fit model parameters using the field data collected. The models thus developed were then validated using Siemens PTI PSS/ETM dynamic simulation program. This whole process resulted in some key insights and valuable conclusions for future load modeling research efforts.

Performance of a Distribution Intelligent Universal Transformer under Source and Load Disturbances

A bench model of the new generation intelligent universal transformer (IUT) has been recently developed for distribution applications. The distribution IUT employs high-voltage semiconductor device technologies along with multilevel converter circuits for medium-voltage grid connection. This paper briefly describes the basic operation of the IUT and its experimental setup. Performances under source and load disturbances are characterized with extensive tests using a voltage sag generator and various linear and nonlinear loads. Experimental results demonstrate that IUT input and output can avoid direct impact from its opposite side disturbances. The output voltage is well regulated when the voltage sag is applied to the input. The input voltage and current maintains clean sinusoidal and unity power factor when output is nonlinear load. Under load transients, the input and output voltages remain well regulated. These key features prove that the power quality performance of IUT is far superior to that of conventional copper-and-iron based transformers

Hybrid distribution transformer: Concept development and field demonstration

Todays distribution system is expected to supply power to loads for which it was not designed. Moreover, high penetration of distributed generation units is redefining the requirements for the design, control and operation of the electric distribution system. A Hybrid Distribution Transformer is a potential cost-effective alternative solution to various distribution grid control devices. The Hybrid Distribution Transformer is realized by augmenting a regular transformer with a fractionally rated power electronic converter, which provides the transformer with additional control capabilities. The Hybrid Distribution Transformer concept can provide dynamic ac voltage regulation, reactive power compensation and, in future designs, form an interface with energy storage devices. Other potential functionalities that can be realized from the Hybrid Distribution Transformer include voltage phase angle control, harmonic compensation and voltage sag compensation. This paper presents the concept of a Hybrid Distribution Transformer and the status of our efforts towards a 500 kVA, 12.47 kV/480 V field demonstrator.

Results of residential air conditioner testing in WECC

This paper summarizes the key results of testing work performed by three organizations (EPRI, SCE, and BPA) on a total of twenty seven air conditioning units in order to better understand and thus characterize their behavior for power system simulations. The diversity of the tested air conditioner units included sizes (tonnage), compressor technology (reciprocating and scroll), type of refrigerant (R-22 and R-410A), efficiencies (between 10 and 13 SEER), and vintage (new and old). A common test plan was developed by the three organizations. The tests were then performed independently by each of the three organizations. The EPRI work was sponsored by APS and SRP. This effort was part of the current load modeling effort going on in WECC under the load modeling task force. The key findings of this work are presented here together with a description of the testing methodology. All three organizations found very similar results despite testing a variety of different sizes and manufacturer units. The key results presented are associated with the stalling behavior of the units at different outdoor temperatures, the behavior of thermal overload tripping, contactor dropout, and the behavior of the units in response to different emulated types of system events.

Empirical estimation of system parallel resonant frequencies using capacitor switching transient data

Simple yet accurate techniques for estimating system parallel resonant frequencies are presented. The proposed techniques make use of existing power quality data, specifically those of capacitor switching transients, to determine frequency estimates. A detailed representation of the system including the data required to develop device models (transmission lines, transformers, loads, etc.) is not required. The efficacy and pitfalls of the technique was demonstrated using power quality data collected at transmission and distribution systems where resonant frequencies were known so as to identify the best application environment of the technique. Frequency estimation results correspond closely to actual system resonant frequencies.

Understanding photovoltaic hosting capacity of distribution circuits

A widespread integration of residential photovoltaics (PVs) into the distribution system may potentially disrupt the nominal circuit operating conditions and result in power quality issues. The objective of this paper is to investigate the impacts of residential PVs on distribution voltages. A stochastic analysis framework is used to simulate possible PV deployment scenarios. The PV integration limit, termed hosting capacity, is calculated with respect to bus overvoltages, voltage deviations, and voltage unbalance. A thorough interpretation of PV hosting results is presented, and several factors potentially affecting the circuits voltage quality are identified. Additionally, the impacts of increasing the circuits minimum load on the PV hosting capacity are evaluated. Finally, the voltage quality impacts of PV locations are identified, and, based on the results, useful and generic recommendations for PV integration are presented.