Author: M Di Guardo V Marino

Author: M. Di Guardo, V. Marino AN1291 APPLICATION NOTE? SLIP CONTROL OF AN ASYNCHRONOUS THREE-PHASE MOTOR WITH ST52X420 1/33July 2000 1. INTRODUCTION Induction motors with squirrel-cage rotors are the workhorse of industry because of their low cost and rug- ged construction. The aim of this Application Note is to show how to perform the slip control of an AC three- phase induction motor with ST52x420, in order to obtain minimum input power and maximum efficiency operations. This type of control can be achieved by adjusting the amplitude of the applied stator voltage versus torque requirement. Efficiency improvement by voltage control is obtained by reducing the applied voltage when- ever the torque requirement of the load can be met with less flux. The reduced motor flux results in a reduction of core and stator copper losses since the magnetization component of the stator current is reduced as well. However, it is to note that the minimization of the air gap flux requires a larger slip to produce the torque required if compared with operations at full rated flux. This application note shows the implementation of the slip control of an aynchronous motor in order to have energy saving of the global power system, representing a convenient solution to reduce the rotor and stator copper losses. 1.1 Torque Characteristics of Asynchronous Three-Phase Motors Typical torque and current characteristics are represented in figure 1 where the torque Tem is plotted as function of rotor speed and fsl (slip frequency is the difference between stator frequency f and rotor fre- quency).phase motor flux slip frequency constant speed control stator voltage rotor speed torque stator frequency fuzzy logic