Modeling of an industrial enterprise power supply system using direct current

Abstract

Modern technological equipment driven by three-phase electric asynchronous motors, with a view to simplifying the kinematic scheme, improving performance characteristics, and extending capabilities, is as a rule equipped with a variable-frequency drive, which permits one to smoothly and in a wide range adjust the rotational speed of the motor shaft and the shaft torque. Widespread frequency control is leading to a significant change in the structural composition of consumers of electrical energy and confronting manufacturers, suppliers, and consumers of electrical energy with new problems. A frequency converter is usually constructed according to a two-stage scheme. The first stage is an ac to dc converter. The direct voltage is then converted into alternating (usually three-phase) current of required frequency and amplitude. A converter of industrial three-phase voltage to direct voltage represents a load of fundamentally different nonlinear nature, and moreover the parameters of these nonlinearities change over time. With wide use of frequency converters for power supply of electric motors of different machines, problems appear that are related to the strong distortion of the frequency composition of the supply voltage. These distortions are much more difficult to compensate for than the usual problems of increasing the power factor. Overloading of generating equipment and power lines with the harmonics of high multiplicity is not less dangerous than overloading with the reactive power, and methods of dealing with these phenomena are much more energy-intense. It is clear that, at this stage of development of the power industry, the structure of intrashop power supply consisting of a centralized powerful converter of industrial three-phase current to the direct current and intrashop power system of direct current and individual converters of direct current into alternating is becoming economically more profitable. In this paper, a part of the dc system of power supply to group consumers of an industrial enterprise is described containing two converting–distributing gears (CDGs) with a capacity of 3 kW each with an intelligent control system. The converting–distributing gear should provide conversion of three-phase alternating current 380/220 V 50 Hz to direct 220/440 V with the capability of parallel operation on dc buses to ten hierarchically arranged devices in the modes of the master, slave, and mode of proportional load distribution. The computer modeling proves the operating capability of the experimental sample of the part of the dc system of power supply.