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The paper analyses a kind of technology and products of ideal and normal non-contact electromagnetism tap changer, poses the calculating formula of circulating current. It is easy to control with the project of normal tap changer technology, but in this case the transition resistances and reactors need to be used, and the circulating current will appear when the tap position is changed. It will lead to electricity dropping, so the performance is not good. There is the accurate test technology of current zero and voltage zero in the project of tap changer technology based on intelligent module MCT801A, the high power current limiting resistances or reactors will not be used, the current can be continuous without impact, over-electricity or electricity dropping phenomena when the tap position is changed, the waveform of computer simulation and the waveform measured exactly of voltage and current are provided by the paper when the tap position is changed ideally, It will have positive significance on On-Load Tap Changer (OLTC) study of the Smart Grid.

Microgrids are local electricity systems that integrate demand and distributed energy resources. They represent a basic building block for future electricity systems that are more cost-effective than conventional grids. Real-time energy generation scheduling is an important issue in microgrid operations. However, common approaches in conventional grids suffer from various limitations and do not apply to microgrids: (1) stochastic optimization approaches rely on stochastic modeling, which is difficult to obtain in microgrids with significant wind penetration and varying demand responses participation; (2) robust optimization approaches provide no cost-efficiency performance guarantee. In this paper, we present a real-time scheduling solution without stochastic modeling, considering a flexible time-window of prediction and providing performance guarantee with minimal risk. Our solution is an generalization of our previous work from homogeneous local generation to heterogeneous settings. We evaluate the performance of our proposed solution using the operating trace of a pilot microgrid on the Bornholm Island, Denmark. We show that our solution achieves a performance close to perfect dispatch, and is robust to prediction errors.

Microgrids represent an emerging paradigm of future electric power systems that can utilize both distributed and centralized generations. Two recent trends in microgrids are the integration of local renewable energy sources (such as wind farms) and the use of co-generation (i.e., to supply both electricity and heat). However, these trends also bring unprecedented challenges to the design of intelligent control strategies for microgrids. Traditional generation scheduling paradigms rely on perfect prediction of future electricity supply and demand. They are no longer applicable to microgrids with unpredictable renewable energy supply and with co-generation (that needs to consider both electricity and heat demand). In this paper, we study online algorithms for the microgrid generation scheduling problem with intermittent renewable energy sources and co-generation, with the goal of maximizing the cost-savings with local generation. Based on the insights from the structure of the offline optimal solution, we propose a class of competitive online algorithms, called CHASE (Competitive Heuristic Algorithm for Scheduling Energy-generation), that track the offline optimal in an online fashion. Under typical settings, we show that CHASE achieves the best competitive ratio among all deterministic online algorithms, and the ratio is no larger than a small constant 3., 26 pages, 13 figures. It will appear in Proc. of ACM SIGMETRICS, 2013