This paper presents a real-time simulation platform for smart grid applications. The developed platform is capable of simulating complex smart grid models with large numbers of high-speed switching devices at real time. Furthermore, an integrated approach is adopted to combine real-time simulations of communication systems and electric power systems together, which provides an effective approach to examine communication and distributed control related issues in smart grids. With the flexibility in representing a wide range of communication network configurations, the developed platform can also be used to evaluate reconfiguration strategies of communication networks in smart grids. A case study is demonstrated based on this platform. Simulation results validate the capability of the platform and also show the importance of the proposed comprehensive approach for the study of smart grids.

The introduction of communication systems to power system controllers have brought in another layer of complexity in their design and operation. In this paper a Plug-in Hybrid Electric Vehicle (PHEV) charging facility is studied. A linearized model of the facility is built including both the dc/dc and dc/ac converters of the Distributed Energy Resources (DER). In addition, a control strategy that includes both local and networked loops is proposed to monitor and control the dc bus voltage of a Local Energy Storage (LES) unit. This dc bus voltage is crucial to the self-sustaining capabilities of the system. Impacts of different communication factors to the system stability are analyzed. Lastly, the small signal model, control strategy, and stability analysis are verified with real time simulations.

This paper provides a full study of a photovoltaic (PV)-aided plug-in hybrid electric vehicle (PHEV) charging facility by investigating the two most challenging technical issues: 1) sizing of the local energy storage (LES) unit and 2) control strategies of the facility. First, the paper proposes a method for determining the optimal size of LES for a charging facility. Second, the paper develops a control strategy for the integration of the PHEV charging stations with the proposed LES and PVs. The proposed LES-sizing method, which is based on optimal control theory, minimizes a cost function based on the average value of kilowatt-hour price, irradiance, and PHEVs' usage patterns. A power-loss/temperature-based battery model and a temperature-based charging strategy previously developed by the authors are utilized to determine the optimal LES size. Afterward, with the optimized facility parameters, a detailed circuit model of the charging facility, including PVs, PHEVs, and LES, is constructed with a real-time simulation system. While an experimental setup for this kind of complex and high-cost system was not readily feasible, real-time simulation was carried out to prove the effectiveness of the proposed control strategy. To validate the effectiveness and accuracy of the real-time simulation, control hardware-in-the-loop (HIL) and power-inverter-based experiments have been carried out at the subsystem level.

This paper introduces a new method to solve the sensorless control problem for a grid-connected Doubly-Fed Induction Machine (DFIM). The proposed method is based on high-frequency signal injection and the fact that the rotor of a DFIM can be seen as the rotating secondary of an induction transformer. The currently used sensorless techniques, besides being parameter sensitive, do not work during fault ride through (FRT) conditions. Nevertheless, the proposed method is parameter independent, and remains fully functional during FRT conditions. Moreover, as opposed to other high frequency injection methods, the proposed method does not require rotor saliency. The mathematical principle of the proposed technique and its implementation are presented. Computer simulations and initial experimental results are also included for verification.

A Gallium Nitride (GaN) based switched-capacitor module integrated inverter (MII) is presented in this paper. This two stage solution first employs a dc/dc quadrupler that utilizes an interleaving charging scheme. This strategy not only reduces the high frequency current ripple subjected to the photovoltaic panel, but also decreases the voltage ripple on the DC link between the two stages. The second stage is a five-level boost inverter that is responsible for both maximum power point tracking (MPPT) and minimizing reactive power flow. Both stages utilize a resonant soft-switching scheme in the capacitor charging current loops to increase the MII's efficiency. Basic theoretical analysis and experimental results for the individual stages are included.

This paper provides insight into two important issues arising in scenarios with high level of penetration of photovoltaic (PVs) based Plug-In Hybrid Vehicles (PHEVs) charging stations. Namely, the paper proposes a method to determine the optimal size of the local energy storage (LES) for a charging facility and also develops the control strategy for the proper integration of these LES and PVs with the PHEV charging stations. The proposed LES sizing method, which is based on optimal control theory, minimizes a cost function based on the average value of kWh price, irradiance and PHEVs usage patterns. A power-loss/temperature model and a temperature based charging strategy, previously developed by the authors, are utilized in determine the optimized LES sizing. Then, with the optimized facility parameters, a detailed circuit model of a charging facility is built. Control strategies of the power electronics networks in this charging facility is proposed and tested with real time simulations.

This paper introduces the latest real time simulation technologies and their applications to the smart grid related studies. A real time simulation platform now built at the Ohio State University is described in detail. With the help of this platform, distributed real time simulation of complex power system integrated with high switching speed power electronics components, renewable energy resources, and communication networks can be fulfilled. Two case studies are performed to illustrate the platform. The first realizes intentional islanding and seamless transition of the smart grid during a power grid failure; the other integrates communication network and power network simulation together to explore communication and distributed control issues in the smart grid.

This paper introduces a platform for real time simulation and its contribution towards smart grid related research, with focus on Plug-in Hybrid Electric Vehicles (PHEV) charging stations. The current system is able to simulate in real time key elements of a smart grid such as: high speed power electronics, distributed energy resources (DER), and communication networks. A description of the platform for real time simulation is presented along with the integration of communication emulation; achieved through OPNET's System in the Loop (SITL) package. In addition, an introduction to Networked Control Systems (NCS) is presented and a case study of PHEV charging stations which displays the latest results accomplished with the current setup.

This paper studies the charging strategies of an Li-ion battery with a focus on the battery's power loss model. It is found that when the temperature is assumed constant, constant current/constant voltage (CC/CV) is near optimal for energy loss minimization. However, when the temperature is considered as a state variable, an optimal profile different from CC/CV is found. This new profile can be used to warm-up batteries during cold days, hence reducing the need for existing battery heating systems. As a result of the elevated battery temperature, significant energy savings can be achieved if the vehicle is used soon after the charging process ends. In this paper, the form of the optimization problem resembles a classic form, with the peculiarity of being highly nonlinear and time varying. The charging strategies resulting from this study will have significant impact on how plug-in hybrid electric vehicles (PHEVs) are charged and utilized.