Priority-driven self-optimizing power control scheme for interlinking converters of hybrid AC/DC microgrid clusters in decentralized manner

Hybrid AC/DC microgrid clusters are key building blocks of smart grid to support sustainable and resilient urban power systems. In microgrid clusters, the subgrid load-priorities and power quality requirements for different areas vary significantly. To realize optimal power exchanges among microgrid clusters, this paper proposes a decentralized self-optimizing power control scheme for interlinking converters (ILC) of hybrid microgrid clusters. A priority-driven optimal power exchange model of ILCs is built considering the priorities and capacities in subgrids. The optimization objective is to minimize the total DC-voltage/AC-frequency state deviations of subgrids. To realize the decentralized power flow control, an optimal-oriented quasi-droop control strategy of ILCs is introduced to not only achieve a flexible self-optimizing power flow management, but also provide an ancillary function of voltage support. Consequently, as each of ILCs only monitors the local AC-side frequency and DC-side voltage signals, the whole optimal power control of the wide-area microgrid clusters is achieved in a decentralized manner without any communication link. Thus, the proposed control algorithm has the features of decreased cost, increased scalability, reduced geographic restrictions and high resilience in terms of communication faults. Finally, the proposed method is validated by case studies with four interconnected microgrids through hardware-in-loop tests

An overview of power quality enhancement techniques applied to distributed generation in electrical distribution networks

It is obvious that power quality is an important characteristic of today's distribution power systems as loads become more sensitive on the other hand nonlinear loads are increasing in the electrical distribution system. Considering the distributed nature of harmonic loads, the need for distributed power quality improvement (PQI) is inevitable. From years ago, researchers have been working on various kinds of filters and devices to enhance the overall power quality of power system, but today the nature of distribution system has been changed and power electronic based DGs play an important role in distribution grids. In this paper, a thorough survey is done on power quality enhancement devices with emphasis on ancillary services of multi-functional DGs. A literature review is also done on microgrids concept, testbeds and related control methods. Although there were some applications of DGs for PQI improvement these applications were not defined multi-functional DGs. Various control methods are studied and categorized regarding different viewpoints in the literature. Finally, a couple of thorough comparisons are done between the available techniques considering the nature, capabilities, advantages and implementation costs

A distributed control architecture for global system economic operation in autonomous hybrid AC/DC microgrids

It is renowned that the entire power system operation cost can be minimized when distributed generators (DGs) have the same incremental costs (ICs). This paper proposes a distributed control architecture for a hybrid ac/dc microgrid (MG) to realize global system economic operation. The architecture consists of two levels. In the first level, the ac frequency-IC (f ac -IC) droop and the dc bus voltage-IC (VdcIC) droop are employed in the ac and dc subgrids, respectively. With the synchronization of f ac and V dc , DG ICs in each subgrid will be equalized. However, the droops will inevitably cause deviations of f ac and V dc . Then a distributed control canonical form (DCCF), which provides a generalized method for f ac and V dc recoveries, is proposed in the second level. The DCCF allows DGs to communicate only with their neighbors, thus alleviating the communication burdens and enhancing the system scalability. Due to the presence of DCCF, f ac and V dc fluctuations, which naturally indicate subgrid loading conditions, are invisible. An original relative loading index (RLI) is proposed to extract the hidden loading condition of each subgrid even thoughfac and V dc are clamped as constants. By using RLI, the power reference of the bidirectional interlinking converter can be easily defined. All DG ICs the hybrid MG converge to the same value in the steady state. The feasibility and effectiveness of the proposed control architecture are verified by simulations and RT-LAB hardware in loop tests.EDB (Economic Devt. Board, S’pore