Braking of induction motor with the technique of discrete frequency control

Braking of induction motor has been the subject of many researches in order to improve its performances. Many braking induction motor´s strategies have been developed. Conventional braking modes are electromechanical such as braking with servo motor and counter current braking; then electrical one as direct current braking (DC). These two techniques have major drawbacks which limit their use. The first one is characterized by high braking current which reaches 7 pu and for the second one, brake torque is important only low speeds. In this paper a new electrical braking mode based on discrete variable frequency control (DFC) is suggested. Its is leading to significant reduction of braking current and improve the braking torque. The proposed strategy has been verified experimentally on a laboratory machine using induction motor feed by three phase inverter, AC thyristors monitored by a microcontroller PIC 16F867.