Alternative vehicles, such as plug-in hybrid electric vehicles, are becoming more popular. The batteries of these plug-in hybrid electric vehicles are to be charged at home from a standard outlet or on a corporate car park. These extra electrical loads have an impact on the distribution grid which is analyzed in terms of power losses and voltage deviations. Without coordination of the charging, the vehicles are charged instantaneously when they are plugged in or after a fixed start delay. This uncoordinated power consumption on a local scale can lead to grid problems. Therefore, coordinated charging is proposed to minimize the power losses and to maximize the main grid load factor. The optimal charging profile of the plug-in hybrid electric vehicles is computed by minimizing the power losses. As the exact forecasting of household loads is not possible, stochastic programming is introduced. Two main techniques are analyzed: quadratic and dynamic programming.

This paper starts from the observation that there is a renewed interest in small-scale electricity generation. The authors start with a survey of existing small-scale generation technologies and then move on with a discussion of the major benefits and issues of small-scale electricity generation. Different technologies are evaluated in terms of their possible contribution to the listed benefits and issues. Small-scale generation is also commonly called distributed generation, embedded generation or decentralised generation. In a final section, an attempt is made to define the latter concepts more precisely. It appears that there is no consensus on a precise definition as the concept encompasses many technologies and applications.

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In electricity grids the frequency of the voltage is stabilized by a combination of the rotational inertia (rotating mass) of synchronous power generators in the grid and a control algorithm acting on the rotational speed of a number of major synchronous power generators. When in future small nonsynchronous generation units replace a significant part of the synchronous power generation capacity, the total rotational inertia of the synchronous generators is decreased significantly. This causes large frequency variations that can end up in an unstable grid. A way to stabilize the grid frequency is to add virtual rotational inertia to the distributed generators. A virtual inertia can be attained for any generator by adding a short-term energy storage to it, combined with a suitable control mechanism for its power electronics converter. In this way a generator can behave like a "Virtual Synchronous Generator" (VSG) during short time intervals, and contribute to stabilization of the grid frequency.

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