Investigation of induction motor performance under high negative slip condition for braking

Investigation on the performance of an induction motor operating with a large negative slip is carried out. It is shown that an operating point in the negative slip region exists at which point all the regenerated energy is consumed as copper loss and core loss in the rotor and stator. This operating point has been experimentally determined for the test motor and load combination and is shown to occur at a slip of about -0.47. The operating point at which no power is returned to the source can be used in voltage source inverter driven induction motors for braking applications to bring large inertia loads to a quick stop without the need for braking resistor units. The stopping times achievable depend on the inverter rating, motor rating, and the inertia of the load. Control of current through the motor during the process of negative slip operation is achieved by modifying the simple V/F pattern. Operating temperature of the motor is seen to play an important role in establishing the point at which no power is returned to the source. Experimental results showing the static performance, temperature effect, and application of proposed method to stopping a large inertia load are presented.