Microgrids are low-voltage (LV) distribution networks comprising various distributed generators (DGs), storage devices, and controllable loads that can operate either interconnected or isolated from the main distribution grid as a controlled entity. This paper describes the operation of a central controller for microgrids. The controller aims to optimize the operation of the microgrid during interconnected operation, i.e., maximize its value by optimizing the production of the local DGs and power exchanges with the main distribution grid. Two market policies are assumed including demand-side bidding options for controllable loads. The developed optimization algorithms are applied on a typical LV study case network operating under various market policies and assuming realistic spot market prices and DG bids reflecting realistic operational costs. The effects on the microgrid and the distribution network operation are presented and discussed.

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Restructuring of power markets has helped in the penetration of Distributed Generation (DG) in the electricity networks. Microgrids are Low Voltage distribution networks comprising various distributed generators (DG), storage devices and controllable loads that can operate interconnected or isolated from the main distribution grid, as a controlled entity. This paper describes the main functions of the Microgrid Central Controller required for the optimization of Microgrid operation its interconnected operation. This is achieved by maximizing its value, i.e. optimizing production of the local DGs and power exchanges with the main distribution grid.

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a b s t r a c tFaster market integration of new energy technologies can be achieved by use of proper support mechanisms that will create favourable market conditions for such technologies. The best examples of support mechanisms presented in the last two decades have been the various schemes for the promotion of renewable energy sources (RES). In the EU, the most successful supporting schemes are feed-in tariffs which have significantly increased utilisation of renewable energy sources in Germany, Spain, Portugal, Denmark and many other EU countries. Despite the successful feed-in tariffs for RES promotion, in many cases RES penetration is limited by power system requirements linked to the intermittency of RES sources and technical capabilities of grids. These problems can be solved by implementation of energy storage technologies like reversible or pumped hydro, hydrogen, batteries or any other technology that can be used for balancing or dump load. In this paper, feed-in tariffs for various energy storage technologies are discussed along with a proposal for their application in more appropriate regions. After successful application on islands and outermost regions, energy storage tariffs should be also applied in mainland power systems. Increased use of energy storage could optimise existing assets on the market.

Microgrids are Low Voltage distribution networks comprising various distributed generators (DG), storage devices and controllable loads that can operate either interconnected or isolated from the main distribution grid as one controlled entity. The effect of the use of a Microgrid Central Controller (MGCC) to achieve this co-ordinate operation with regards to the potential economic benefits and the power losses avoided in both the local network and the upstream network are presented. Finally, a methodology based on the marginal emissions curve of the upstream network is presented, taking also into account the calculated losses is used for the environmental assessment of the co-ordinate operation of Microgrids. All the above studies have been applied to a typical LV Microgrid interconnected to an actual MV network using actual market prices and DG bids reflecting realistic operational costs.

SUMMARYThis paper aims to present a detailed analysis on the impact that demand side bidding (DSB) has on microgrids operation, taking into account variations in market prices, RES production, and seasonal demand for a typical LV network. Additionally, the economic impact of applying adequacy constraints, i.e. request specific part of the microgrid demand to be supplied by local power production, in case of intentional islanding, is estimated. This is essential to achieve seamless transition from interconnected to autonomous operation of microgrids. Two cases are examined: adequacy constraint applied to the whole microgrid demand and only to the critical loads. Moreover, the magnitude and frequency of interruption of critical and noncritical loads, in case of an upstream network fault is calculated. The potential of DSB to reduce operating costs improving at the same time the quality of service to the loads of higher priority is shown.