Electromagnetic Compatible Current Sources With Relay Control

Abstract

The development of industry leads to an increase in nonlinear loads, which are generators of higher harmonics in the network. The quality indicators of voltage and current consumed from the network are established by international standards for the quality of electricity. The simplest method of filtering harmonics is passive filters, lack of low quality harmonic compensation. The use of active filters improves the quality of the current. But active filters have a complex control system. The use of active rectifiers as part of semiconductor power supplies solves the problem of generating higher harmonics in the network and provides a power factor equal to 1.
 Six variants of three-phase and single-phase power supplies have been developed. They operate as a current source. All circuits consist of two parts: an active rectifier and a DC-DC converter. The scope of use of such sources is different: a direct current electric drive, an electric power system of wind turbines, an electric system of aircraft. The control system of the relay converters provides the formation of current and the maximum speed in the processing of disturbances. 
 Oscillograms of the current sources are obtained by digital modeling. They confirm the efficiency of the proposed sources, the electromagnetic compatibility of the power sources with the mains and the value of the power factor close to unity. Current sources are invarant to the action of disturbances: changes in load resistance, mains voltage. The study of electromagnetic processes made it possible to obtain analytical expressions for the maximum and minimum frequency of the relay mode, the capacitance of the capacitors and the operating conditions of the sources. 
 The developed program allows you to get the parameters for choosing the power elements of the circuit: inductance, capacitance, switching frequency of transistors. 
 The quality of the consumed current is analyzed by calculating the total harmonic distortion (THD). For all considered sources, the THD value is less than 5%, which meets the quality standards for the consumed current.