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Falahi M.,Itron Inc. | Chou H.-M.,Texas A&M University | Ehsani M.,Texas A&M University | Xie L.,Texas A&M University | Butler-Purry K.L.,Texas A&M University
IEEE Transactions on Sustainable Energy | Year: 2013

Electric vehicles (EVs) are likely to have a continued presence in the light-vehicle market in the next few decades. As a result, EV charging will put an extra burden on the distribution grid and adjustments need to be made in some cases. On the other hand, EVs have the potential to support the grid as well. This paper presents a single-phase bidirectional charger topology which pairs up a photovoltaic (PV) source with an EV charger resulting in production cost reduction. The presented topology is then used for vehicle-to-grid (V2G) services. The main focus of this paper is on power quality services which only slightly discharge the battery. Among these services, it studies the possibility of local reactive injection of EVs connected to the grid through a single-phase charger to compensate for voltage drops caused by motor startup or inductive loads. It also studies the possibility of active power injection of EVs for short time periods during PV transients in cloudy weather to keep the system stable. It also studies the potential of EVs to help during low voltage ride-through of the PV sources. The studies are performed using Simulink simulations and a real-time implementation in Real Time Digital Simulator (RTDS). The results demonstrate the effectiveness of power quality V2G services with small wear on the EV battery. © 2013 IEEE. Source

Wei M.,Lawrence Berkeley National Laboratory | Nelson J.H.,University of California at Berkeley | Greenblatt J.B.,Lawrence Berkeley National Laboratory | Mileva A.,University of California at Berkeley | And 6 more authors.
Environmental Research Letters | Year: 2013

Meeting a greenhouse gas (GHG) reduction target of 80% below 1990 levels in the year 2050 requires detailed long-term planning due to complexity, inertia, and path dependency in the energy system. A detailed investigation of supply and demand alternatives is conducted to assess requirements for future California energy systems that can meet the 2050 GHG target. Two components are developed here that build novel analytic capacity and extend previous studies: (1) detailed bottom-up projections of energy demand across the building, industry and transportation sectors; and (2) a high-resolution variable renewable resource capacity planning model (SWITCH) that minimizes the cost of electricity while meeting GHG policy goals in the 2050 timeframe. Multiple pathways exist to a low-GHG future, all involving increased efficiency, electrification, and a dramatic shift from fossil fuels to low-GHG energy. The electricity system is found to have a diverse, cost-effective set of options that meet aggressive GHG reduction targets. This conclusion holds even with increased demand from transportation and heating, but the optimal levels of wind and solar deployment depend on the temporal characteristics of the resulting load profile. Long-term policy support is found to be a key missing element for the successful attainment of the 2050 GHG target in California. © 2013 IOP Publishing Ltd. Source

Falahi M.,Itron Inc. | Butler-Purry K.L.,Texas A&M University | Ehsani M.,Texas A&M University
IEEE Transactions on Power Systems | Year: 2013

Voltage and reactive power control is a fundamental issue in all-electric shipboard power systems (SPS). However, coordination between generation and propulsionmanagement to match reactive power is poor in current SPS designs. This paper presents a new model predictive control based dynamic Volt/Var control scheme to control the voltage in the system. This method uses a dynamic model of the sources and loads and finds the optimal reactive control inputs to the system to minimize the voltage deviations in the future. Since this method uses prediction of the reactive demand of pulsed loads, it is able to achieve a smooth voltage profile in the SPS in presence of pulsed power loads. This method is also able to control voltage of the system during propulsion motor startup. The controller is tested in presence of high power pulsed loads in the system. The results demonstrate that the dynamic reactive controller is able to keep the voltage profile of the system smooth and within system limits. © 2013 IEEE. Source

Falahi M.,Itron Inc. | Butler-Purry K.,Texas A&M University | Ehsani M.,Texas A&M University
IEEE Transactions on Power Systems | Year: 2013

Reactive power control is a fundamental issue in microgrids, especially during islanded mode operation with no support from the main grid. Lack of infinite bus, tightly coupled generation and consumption, and existence of nondispatchable intermittent renewable power sources reinforce the need for a new VVC scheme. This paper presents a new model predictive control (MPC)-based dynamic voltage and var control (VVC) scheme, which includes the dynamics of the microgrid in the VVC formulation. The MPC-based controller uses a simplified voltage prediction model to predict the voltage behavior of the system for a time horizon ahead. The advantage of this method is that it can avoid unstable voltage conditions in microgrids by prediction of the instability ahead of time. This method can also avoid voltage drops or swells in any of the phases of the system since the model can predict the voltage of each phase separately. Also, the presented method can be implemented online so it can efficiently use the time-variant reactive capabilities of the distributed generators to compensate for reactive power needs of the system. This controller is tested for different operating conditions of the microgrid and the simulation results confirm that the MPC controller successfully keeps the system stable and achieves a smooth voltage profile. © 2013 IEEE. Source

Ehsani M.,Texas A&M University | Falahi M.,Itron Inc. | Lotfifard S.,University of Central Florida
Energies | Year: 2012

Electric Vehicle (EV) technology is expected to take a major share in the light-vehicle market in the coming decades. Charging of EVs will put an extra burden on the distribution grid and in some cases adjustments will need to be made. On the other hand, EVs have the potential to support the grid under various conditions. This paper studies possible potential and applications of Vehicle to Grid (V2G) services, including active power services, which discharge the EV batteries, and power quality services, which do not engage the battery or require only small amounts of battery charge. The advantages and disadvantages of each service and the likelihood that a given service will be effective and beneficial for the grid in the future are discussed. Further, the infrastructure cost, duration, and value of V2G services are compared qualitatively. ©2012 by the authors. Source

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