INTRODUCTIONInstalling on-site energy generation offers the potential to reduce energy use and greenhouse gas emissions while increasing local energy security. These energy generation and storage devices, collectively called distributed energy resources (DERs), can be networked into a local electrical system called a microgrid. These microgrids have the ability to operate connected to or independent from the external electrical grid, and are particularly useful when energy security is important, and/or where electrical distribution infrastructure does not

Homogeneous charge compression ignition technology can improve fuel economy by providing increased efficiency at low-load operation. This article examines the implementation of this technology in hybrid propulsion systems. To assess the benefits, a physics-based model for a spark ignition–homogeneous charge compression ignition dual-operation engine is developed, together with system and component models, and is used to optimize a crossover sport utility van with a power-split hybrid powertrain. Comparison of optimal designs for the pure spark ignition and dual homogeneous charge compression ignition cases indicates the reduction in the fuel consumption based on our modeling assumptions to be in the range 2.5–5%, depending on the test cycle. These benefits increase substantially when the acceleration performance requirements increase. An analysis method is presented to show how such engine-level changes affect the entire powertrain characteristics, and mode maps are developed to indicate when the benefits are expected.

Abstract-Increasing energy security and reliability concerns are intensifying the interest in microgrids. In this setting, design optimization is vital to achieve a reliable infrastructure without overbuilding. This paper considers the impact of frequency and voltage regulation on the optimal design of a conceptual, autonomous military microgrid. This microgrid comprises a solar panel and vehicles as power sources, with each vehicle incorporating a battery and generator. The power output and terminal voltage of these inverter-based sources must be regulated. The paper investigates the effects of battery DC voltage variations on a decentralized regulation scheme, and the resulting influence on optimal component sizing. To this end, controllers are first designed based on the typical assumption that the voltage on the DC side of each inverter is constant. The battery internal resistance is then considered and its impact on regulation performance is investigated. The results show that the battery internal resistance can affect the performance of both frequency and voltage regulation, and consequently must be taken into account in component sizing decisions. Thus, the paper identifies an important coupling between regulation and component sizing problems through battery characteristics, and highlights the need for a combined sizing and regulation framework for microgrid design.

Designing vehicles specifically for city use is a topic of increasing interest in the transportation community. Hybrid vehicle design typically seeks to maximize fuel economy subject to acceleration performance and other constraints, based upon the expected driving needs of the average user. Fuel economy predictions are inaccurate when the vehicle's expected and actual uses are different. This paper studies the variation in design and fuel economy for a vehicle with a power-split hybrid electric powertrain optimized on a range of U.S. Environmental Protection Agency drive cycles, from the high-speed US-06 cycle to the low-speed New York City cycle. Results show variation of up to 9.8% in fuel economy and up to 41% in electric motor size. The vehicle designed for the dense urban environment has the largest variation in fuel economy, whereas the other vehicles have more similar performance. These results imply that the urban vehicle is the least robust and offers motivation for developing urban-specific vehicles. This analysis provides only a lower bound on potential performance because it does not consider possible vehicle downsizing or other design changes to meet customer expectations in urban use.

We demonstrate the use of model predictive control (MPC) for a microgrid with plug-in vehicles. A predictive model is developed based on a hub model of the microgrid, and the control is optimized for minimum generator fuel usage. A variety of horizons and levels of prediction error are used in the optimization. A new method to model expected load and error is presented based on radial basis functions. Results show that for a given prediction horizon, as the level of prediction error increases, the amount of fuel used increases. Results also show that in some cases there is little benefit in extending the prediction horizon. While an extended prediction horizon does result in increased use of battery storage, this does not necessarily produce significant decreases in fuel usage. This result is analyzed and explained in terms of battery charging and discharging limitations.