Dynamic Braking Optimization for Reducing Demagnetization Phenomenon during Fast Stopping in AFPM Motor

Abstract

A type of electrical machine geometry is the axial flux permanent magnet (AFPM) machine which has a significant role in industrial applications because of high torque/power density. In these motors, it takes about 10 second to normally stop when working at full load condition and rated speed. In emergency situations, some can perform a crash stop maneuver, which can cut the time down to 0.3 second. For AFPM motor, dynamic braking is easily achieved by cut off motor from main supply and shorting the motor terminals, thus bringing the motor to a fast abrupt stop. But as three phase armature winding are short circuited, a high instantaneous current flow through the stator winding. These peak values of current generate a high armature reaction field that extremely demagnetizes PMs. To solve this problem, the armature terminals are short circuited by means of a current limiting resistor. Then the ohmic value of this optimum resistor is calculated to reduce the three phase short circuit demagnetization and the motor stops in less than 0.52 second.