A SENSORLESS CONTROL METHOD OF THYRISTOR STATICAL FREQUENCY CONVERTER FOR STARTING SYNCHRONOUS MACHINE

Abstract

Relevance of study. Starting of the medium voltage synchronous machine at standstill is one of the main problems in the operation of unregulated synchronous electric drives. The optimal solution is starting the excited synchronous machine fed by the thyristor statical frequency converter. A sensorless control of the statical frequency converter for thyristor switching of load-commutated inverter to functions of synchronous machine angular rotor position in the area of zero and low speed, has not yet received a clear solution. The purpose of this study is the design of the sensorless control method for the thyristor statical frequency converter at the synchronous machine startup under conditions of angular acceleration uncertainty. Materials and methods. Methods of theory of electrical machines and computer mathematical simulation are used in the study. Results of the study. The regularity between the angular rotor position and the non-conductive phase stator voltage of the synchronous machine is determined. The rotor rotation angle of the synchronous machine is defined as the ratio of the conductive state duration of the thyristor arm pair of the load-commutated inverter to the period determined from the non-conductive phase stator voltage of the synchronous machine. The sensorless control method is based on simultaneous operation of scalar control, indirect angular rotor position determination and cross-control channels. The proposed sensorless control method is tested by computer mathematical simulation of the system «thyristor statical frequency converter –synchronous machine». Findings. The application of the considered control method was found for commercially available medium voltage thyristor frequency converters of EKRA Ltd. The considered method can be used for the sensorless control of frequency converter by different topology.