Decomposition of Apparent Power in Electrical Networks under Non-Sinusoidal Conditions

Abstract

The work concerns the study of energy distortions introduced by semiconductor converters into the operation of power supply systems, which manifests itself in the deterioration of voltage quality in electrical networks and the reduction of their energy efficiency. The cause of such phenomena is the circulation of non-active components of apparent power in electric power transmission and distribution systems, the accounting and compensation of which are important tasks for the intelligent operation of electrical networks. This problem is especially relevant due to the increasing use of power flow control devices based on controllable semiconductor valves in transmission and distribution systems, which leads to disturbances of the electromagnetic balance of electrical installations. For making decisions, aimed at improving the energy efficiency of power supply systems with power electronic converters, it is important to identify and determine the components of the total electric power and to interpret the role and influence of semiconductor valve elements on the energy exchange processes in electrical systems. The aim of the work is the decomposition of apparent power into components under nonsinusoidal conditions. The study examines the components of power in the electric circuit with AC voltage source supplying a resistive load across a fully controlled bidirectional thyristor. The decomposition of power is based on the approach of IEEE Std. 1459…2010, according to which the Poynting vector flux is represented by a spectrum of orthogonal components of instantaneous power. Answers were obtained to a number of questions regarding the participation of semiconductor elements of power converters both in the overall power balance and in the local balances of its components. It is shown that the source of distortion power is the nonlinear characteristics and phase control of the thyristor’s conducting state. The thyristor acts as a source of displacement reactive power as well as active power of non-fundamental frequency harmonics. A numerical example, visualization, and analysis of the calculated power balance results are presented.