Sensorless control induction motor drive

Medium voltage IGBTs are fast switching devices that require low gate drive power. They inherently generate high voltage and current gradients during switching transitions. These are generally limited by retarding the changes of the gate charge. Additional gate resistors are usually installed for this purpose. The drawback is high switching losses. A novel method is described in this paper that aims at controlling the voltage and current gradients during switching transitions. The gate charge of the input MOS device is controlled by injected gate currents. These follow particular command functions that are predefined and stored in a memory. The method requires reacting within microseconds which traditional closed loop control cannot do. Specific time events are therefore defined to trigger the respective command function. These functions depend on the instantaneous values of the collector current or the collector-emitter voltage, variables that are identified without delay, knowing their predefined gradients and counting the time from the respective event to reach their final values. Experimental results show the performance of event driven control. Low current and voltage gradients are enforced while the switching losses are reduced.