Dinamičko upravljanje distribucijskim elektroenergetskim sustavima

This paper considers the problem of optimal dynamic management of electrical power distribution networks with distributed generation and storage. Initially, analysis is performed of the Optimal Power Flow (OPF) problem -- a paramount optimization problem that needs to be solved to ensure optimal steady-state power network operation. In the rest of the paper we present a hierarchical control structure for solving the considered optimal control problem in a dynamical framework. At the upper level a dynamic OPF solver computes the optimal power references for distributed generators and storages at slow rate. These references are then transmitted to the intermediate level, where a faster Model Predictive Control algorithm computes small deviations from power references given by the OPF solver to take into account the variability of load profiles that was neglected at the upper layer. Finally, the power references are forwarded to the primary level where local controllers track these power reference values. A realistic simulation case study of a Croatian power distribution grid is used for testing purposes and to demonstrate the applicability and usefulness of the proposed control strategy.U ovom članku razmatramo problem optimalnog dinamičkog upravljanja elektroenergetskim distribucijskim sustavom sa distribuiranom proizvodnjom i pohranom energije. Analizirali smo problem optimalnih tokova snage (OPF), koji je od najveće važnosti za razmatrani upravljački problem. U nastavku članka smo opisali hijerarhijsku upravljačku strukturu za rješavanje razmatranog problema optimalnog upravljanja. Na najvišoj razini (dinamički) OPF algoritam izračunava optimalne reference snage za distribuirane izvore i spremnike energije na sporoj vremenskoj skali. Te se reference zatim šalju srednjoj razini, gdje brži algoritam, temeljen na modelskom prediktivnom upravljanju, izračunava male devijacije od referenci koje je dobio od nadređene razine, kako bi uzeo u obzir brže varijacije profila potrošnje koje su zanemarene u nadređenoj razini. Konačno, reference se prosljeđuju najnižoj razini gdje se nalaze lokalni regulatori koji su zaduženi za njihovo praćenje. Realističan simulacijski ispitni primjer hrvatske elektroenergetske distribucijske mreže korišten je za ispitivanje i demonstraciju primjenjivosti i korisnosti predložene upravljačke strategije

A Comprehensive Analysis of the Voltage Unbalance Factor in PV and EV Rich Non-Synthetic Low Voltage Distribution Networks

With the development of technology and the decrease in prices, power systems are facing a strong growth in the number of end-users with photovoltaics (PVs), battery storages and electric vehicles (EVs). A penetration of low carbon (LC) technologies has an impact not only on the financial aspect, but also on parameters of the power quality (PQ) in the power system. Since most of end-users with renewable energy sources (RES) are connected to a low-voltage (LV) distribution network, there is a high number of single-phase loads and distributed generators (DG) that can cause unwanted effects in LV networks. According to standards, electric energy must be of a certain quality in order to avoid harmful effects on the power system, being both the network or the end-users equipment. One of the PQ parameters is the voltage unbalance. Voltage unbalance occurs in networks with the high share of single-phase loads and generators. Since most loads in households are connected to the only one phase, the voltage unbalance is constantly present in the network, even without LC technologies. Single-phase connected PVs, residential battery storages and EV charging stations can increase voltage unbalance in the system. This paper systematically analyzes a real-world LV network and different stages and shares of connected PVs, residential battery storages and EVs to different phases. The value of the voltage unbalance factor (VUF) is observed for one week in January and August in 10-min intervals. It is shown that connected systems can significantly increase the VUF and potentially cause negative impact on the equipment and the power system as a whole. In turn we analyze a three-phase connection of these new LC technologies and demonstrate how in all analyzed cases PQ values remain within boundaries defined by the EN 50160 and the IEC 61000-3-13