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Abstract
1- Introduction
2- Model predictive control application for power quality disturbances compensating
3- Designing an MPC for optimal compensation of the PCC voltage and load current
4- Investigating the performance of the “Smart Branch” through simulations
5- Conclusion
References
Abstract
A novel “Smart Branch” is introduced in this paper which compensates for various power quality disturbances. This “Smart Branch” includes a series transformer which its impedance is controlled indirectly by voltage injection to its secondary. By using a finite control set-model predictive controller (FCS-MPC), the “Smart Branch” can be controlled adaptive, flexible and straightforward. The “Smart Branch” is installed at the PCC, where the load current and the PCC voltage can be measured locally without using a communication channel. The “Smart Branch” controller tracks pure sinusoidal waveforms as its references. Thus the “Smart Branch” hardly produces harmonics and therefore its output filter can be eliminated. The controller can be used for multi-objective optimization of power quality in power systems and especially in microgrids. A droop based method is developed for adjusting the objectives’ weightings in the cost function of the MPC. In the last part of the paper, by using the extensive simulations and scenarios, the figure of merits of the “Smart Branch” is proved.
Introduction
Development of microgrids has been pursued with various goals such as solving environmental crisis, increasing power system efficiency, improving power quality, managing of power fluctuations, facilitating of electricity networks extension, and effective exploiting of renewable energy resources without violating the operation principles of classical electricity distribution networks. Especially, Fukushima Daiichi nuclear disaster revealed the importance of the safety which can be achieved by developing renewable energy resources and microgrids [1]. Among the different characteristics which are necessary for the proper operation of microgrids, power quality, safety, and energy balance are the most important issues. In this paper, a novel and effective method for improving the power quality in microgrids is presented. Generally, microgrids are more vulnerable to the power quality disturbances due to the following reasons: 1. Lower inertia level due to the intensive use of electronically coupled-distributed energy resources (EC-DERs) 2. Lower short circuit level. 3. Fluctuation of the power generation and consumption. 4. Existing of multiple owners and decision makers. 5. Necessity of operation mode transition from grid-connected to the island and vice-versa, due to the planned operations or faults. Therefore, improving power quality in microgrids faces more challenges than conventional electricity distribution networks [2]. At the moment, two general trends can be observed for power quality improvement in microgrids: 1. Using of the EC-DERs with multiple objectives. The inverters of these EC-DERs are known as multi-functional grid-tied inverters (MFGTI). In this case, by employing a proper control algorithm, the extra capacity of the inverters can be used for power quality conditioning [3]. 2. Developing of cheap and dedicated equipment for power quality improvement. So far, many studies have been conducted on multi-functional gridtied inverters and optimum usage of their extra capacity for power quality compensation [4–8].