Interconnection Of Microgrids And Its Self-Adaptive Hybrid Storage Technology

In recent years, with the gradual depletion of fossil fuels, as well as the stress of environmental pollution, developing and using new energy sources has become an inevitable trend. As the main access points between power system and distributed renewable energy sources, the conventional distribution network is not designed for integration of renewables. The concept of microgrids, provided a feasible method to integrate large-scale renewables to power system, whose structural design and control algorithm are the key factors of improving the penetration of renewables in grids.The significant differences of distributed renewable energy sources from traditional energy generation are the volatility and randomness of their output. They can be integrated in a small, control-easy micro system by microgrids, and provide power energy to decrease the dependence of microgrids on backbone grids, which can be a prerequisite to the autonomy or island operation. However, the volatility and randomness of renewables cannot be eliminated or relieved, since microgrids just play the role of organizer to renewables. So, a strong and reliable method to restrain the volatility of microgrids is still needed. The works of this paper are divided into two main parts:proposing a new distribution network which can be reorganized by microgrids within, and designing a self-adaptive hybrid storage system for microgrids to restrain their volatility network parameters caused by renewables.The research status regarding microgrids, energy storage systems, active distribution system was reviewed in the paper. Several key factors in control of microgrids were discussed and then the technical issues of interconnection between microgrids were proposed based on their extended related key factors. Then the process of interconnection was simplified by introducing of DC system, and a modular urban distribution network which composed by several hybrid microgrids was proposed. It can implement active control and automatic fault recovery in urban power supply, and make the distribution network more reliable. Simulation experiments showed that the ideas for improving the reliability of urban distribution network has a good effect, and can provide an useful reference and new directions for the relevant projects.Because of the proposed modular microgrids are most relied on autonomy control, the accuracy of its control criteria are greatly influenced by fluctuations in the network, which is likely to result in lower system reliability. To address this issue, a supercapacitor-battery hybrid energy storage system was proposed in the later part of this paper. This system uses a simplified "Explicit Congestion Notification" ideas, with broadcast based on Bernoulli general probability index to achieve low bit rate communications dependent distributed control. And according to the current volatility characteristics in microgrids, the load ratio between super capacitor and battery will be adjusted to provide the battery an ideal work condition, with ensuring stabilized performance in fluctuation restraint. After simulation tested with conventional voltage clamp storage system in two different conditions, the design conditions which can adjust itself in order to play a better performance was proved, and can effectively reduce their battery cycles, with the improvement of system economy. Additionally, the entire system is easy to extended, and if a single storage device was breakdown, the potential damage to the performance of entire system will be decreased to minimum by the distributed control algorithm.