Direct Torque Control forStacked MultiCell (SMC)VSIfedinduction machine

This paperdeals with thecontrol ofSMCconverters for aninduction machine drive. Different degrees of freedom offered bythis topology areaddressed andusedtodevelop strategies aiming tocontrol electromnagnetic variables ofthemachine, tobalance three phase inverter switchings andinverter flying capacitor voltages. Allofthese techniques aredesigned tobeusedwith anSMC converter with any numberoflevels. Forthecontrol oftheelectromagnetic state ofthemachine, a"dittcontrol" basedstrategy isused.This technique iswell-known forboth torque andflux reduced ripple andhigh dynaimcs. These performances obviou slyincrease with the numberoflev elsoftheinv etrter. Another degree offreedom oftheSMC inverterisusedtocontrol theswitching frequency. Two techniques arepresented: Thefirst aims toregulate theswitching frequency andthesecond proposesto minimize theglobal number ofswitchings ofthe converter, Finally,the flyingcapacitorvoltagesare balanced using a third degree of freedom of the SMC conveirer. Itisshownthat thealgorithm regulates thecell voltages, whichiinplies averygoodcontrol ofthe capacitor voltages. Simulation results areshownfor7-, 9-and11- level SMCinverter.