STUDY OF PHYSICAL PROCESSES IN THE DIRECT CURRENT LINK OF THE LOADING-BACK SCHEME OF ASYNCHRONOUS MACHINES

Abstract

The article notes the tendency of introducing asynchronous engines, entailing the necessity to introduce the equipment which is intended to carry out maintenance, repair and acceptance check-outs. The general part of test circuits for asynchronous motors by the loading-back method with two controlled inverters is emphasized. The mathematical model of similar schemes’ functioning is shown. The article gives the results obtained by mathematic simulation of physical processes in the direct current link in the loading-back scheme for asynchronous machines Significant ripple voltage of constant voltage and DC in these circuits is noted. The issue of measuring power in the DC link passing through one inverter to the test engine and through another inverter from the load generator is considered. The authors carried out calculation of the capacities mentioned in the steady state modes for asynchronous machines with nominal power of 0.37 kW, 5.5 kW and 250 kW at different values of capacitor capacitance included in the DC link. Basing on the results of calculations, the authors found the dependence between the relative value of the procedural error in determining power in the DC link by the product of the current values of pulsed voltages and current. The current value from the product of instantaneous values of voltage and current at some time interval was taken as the true value of power. It is shown that at the capacitor capacity above some critical value this procedural error does not exceed 0.9% at the nominal power of the test engines 0.37 kW; 0.3% – at the power of 5.5 kW; 0.2% – at the power of 250 kW. This error increases dramatically when capacitor capacitance decreases. It is shown that the value of the capacitance corresponding to the inflection of the considered dependence approximately corresponds to the value necessary for limiting ripple voltage in the DC link of up to 600 V.