This paper presents a control philosophy for multiterminal DC grids, which are embedded in the main AC grid. DC transmission lines maintain higher power flow at longer distances compared with AC lines. The voltage losses are also much lower. DC power transmission is good option for Russian north. Arctic seashore regions of Russia don't have well developed electrical infrastructure therefore power line lengths are significant there. Considering above it is possible to use DC grids for supply mining enterprises in Arctic regions (offshore drilling platforms for example). Three different control layers are presented in an hierarchical way: local, primary and secondary. This whole control strategy is verified in a scaled three-nodes DC grid. In one of these nodes, a modular multilevel converter (MMC) is implemented (five sub-modules per arm). A novel model-based optimization method to control AC and circulating currents is discussed. In the remaining nodes, three-level voltage source converters (VSC) are installed. For their local controllers, a new variant for classical PI controllers are used, which allow to adapt the values of the PI parameters with respect to the measured variables. Concerning the primary control, droop control technique has been chosen. Regarding secondary level, a new power flow technique is suggested. Unbalance conditions are also verified in order to show the robustness of the whole control strategy.
The paper considers issues related to the analysis and adjustment of electrical load schedules. The main characteristics of the load graphs are represented in this paper. The research deals with issues of possibility of aligning load graphs by using energy storage devices. The configuration of the storage system has been identified, which allows expanding its functionality. A logical-numerical model of a hybrid energy storage system has been developed. As a result of the simulation, dependencies are obtained that confirm the efficiency of using power storage devices to align the load schedules.
At enterprises, electricity metering devices are used everywhere, which incorporate various formulas for calculating power. The division of power into active, reactive and full is valid only in the case of sinusoidal currents and voltages. In the case of non-sinusoidal waveforms of current and voltage, which are most often found in industrial networks of enterprises, it is necessary to use additional concepts and correct formulas for calculating powers in order to avoid errors. The article compares the methods of calculating the power in the non-sinusoidal mode, which can be used to more correctly record electricity in industrial networks of enterprises.
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