The paper provides the Currents’ Physical Components (CPC)-based fundamentals for reactive balancing of unbalanced loads supplied by a nonsinusoidal voltage in four-wire systems, meaning with a neutral conductor. The whole compensation of the unbalanced and reactive currents in such conditions requires reactive compensators of high complexity, i.e., built of a high number of reactive devices. This complexity can be reduced on the condition that the objective of a whole compensation is abandoned for a goal of only minimization of the supply current three-phase rms value. The paper presents a method of minimization of this three-phase rms value of the supply current by a compensator composed of branches, that have no more than two reactive devices, meaning an inductor and a capacitor.
Słowa kluczowe: Current decomposition, unbalanced loads, asymmetrical systems, power definitions, power theory.
Artykuł przedstawia podstawy, oparte na teorii Składowych Fizycznych Prądów (Ang. CPC), reaktancyjnego równoważenia odbiorników niezrównoważonych, zasilanych napięciem niesinusoidalnym w układach czteroprzewodowych, to jest z przewodnikiem zerowym. Całkowita kompensacja prądu niezrównoważenia i prądu biernego wymaga w takich warunkach kompensatorów o wysokiej złożoności, to jest o dużej liczbie elementów reaktancyjnych. Złożoność tę można obniżyć przez rezygnację z całkowitej kompensacji na rzecz jedynie minimalizacji trójfazowej wartości skutecznej prądu zasilania. Artykuł przedstawia metodę takiej minimalizacji z pomocą kompensatora zbudowanego z gałęzi mających nie więcej niż dwa elementy reaktancyjne, to jest cewkę indukcyjną i kondensator.
Keywords: Rozkład prądu, odbiorniki niezrównoważone, systemy niesymetryczne, definicje mocy, teoria mocy.
Introduction Distribution systems in manufacturing plants supply not only balanced three-phase loads, but also aggregates of single-phase loads such as lightning, instrumentation and control systems, and electrical transportation. Distribution systems that supply such unbalanced loads are built as three-phase systems with neutral, i.e., as four-wire systems. Such unbalanced loads cause asymmetry of voltages and currents in the distribution system. This asymmetry, along with the reactive power, contributes to an increase in energy loss, to equipment overloading and to the reduction of the supply quality in such a system. Consequently, a reduction of the reactive power and asymmetry in such systems is often needed. Because of the power level, compensation of the reactive and unbalanced currents in large manufacturing plants could be above the capability of switching compensators, known as “active power filters", however. Switching compensators are built of power transistors, used for shaping the compensating currents, and such transistors have relatively low switching power. Only reactive compensators can have a sufficient power for that. Balancing compensators for three-wire systems with sinusoidal voltage were first developed by Steinmetz in 1917  and there is a substantial amount of reported research on such compensators design [3-4, 9]. Although some results on methods of design of compensators for four-wire systems were published [8, 10, 11, 14, 15], the development of such methods is substantially retarded. A controversy [12, 13] on how to describe the power properties of four-wire systems is the main reason for that. In the lack of such description, only optimization methods  could provide parameters of a compensator. Optimi-zation methods might not be appropriate for control of adap-tive reactive compensators, when the speed of control is crucial, however. Formulae that would enable direct calcula-tion [...]
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