Scheduling Optimization And Real-time Control Method For Micro-Grids Interconnection

As the demand for conserving energy and reducing emissions is going up in the world, more and more countries realize the importance and urgency of renewable energy replacing fossil energy. Micorgrid (MG) have been developted greatly because it’s able to a) integrate renewable resources effectively and flexibly, b) work isolated from the main grid, c) storage energy by batteries, d) reduce power loss by distributed generation. With the development of MGs, the interconnection of them under different scenarios has become a natural requirement. Generally, the interconnection requirement exists in two ways. One is for the service restoration in a self-healing distributed network to improve the dynamic performance when islanding occurs and to extend the range of power supply during the system outages. The other is for those on islands or isolated areas to ensure fuller consumption of renewable energy and higher reliability. But the following problems about interconnected microgrids (IMGs) should be taken into account:a) the output of controllable distributed energy resources (CDERs) is supposed to be reset after interconnected, in case the high costly CDER produces a lot of power while the low costly one produces a little, which is definitely not economical, b) synthetical and real-time control of the CDERs in the IMGs is facing new challenges. A method of jointly optimization of generation scheduling and distributed control of CDERs for interconnected operation of autonomous MGs is proposed in this paper.On the aspect of jointly optimization, taking the minimum generation cost as objective, an optimization model is proposed. As the charge and discharge cycle is usually not complete during the operation of batteries, this paper put forward a method of calculating the generation cost of battery energy storage system operating in a short time. And then on the aspect of real-time controlling, a dynamic droop control strategy is designed for the real-time control of CDERs in each MG, so as to keep the power on tie-line to the optimizing result, guaranteeing the autonomy of MGs. Taking the difference between the actual power on tie-line and the planned value as the control error reference, the equal generation costs increment principle is adopted for the CDERs the share the power. Finally, an optimization example based on MATLAB demonstrates the effectiveness on optimizing resource and reducing the cost of operation. The simulation result based on PSCAD/EMTDC confirms the validity of the proposed dynamic control strategy.