Samer Saleh Hakami, "Torque Ripple Reduction and Flux-droop Minimization of DTC with Improved Interleaving CSFTC of IM fed by Threelevel NPC Inverter," 아주대학교 공학석사 학위 논문, 2020. > Paper

Among advanced AC motor control techniques is direct torque control (DTC), which is known for its fast decoupled control of both

torque and flux. This great feature owning to its basic control structure that needs only three main components; torque and flux

hysteresis, switching table and torque and flux calculation block. Therefore, unlike field oriented control (FOC), it does not require

any modulation function or reference frame transformation. However, when the DTC technique is used to drive an induction motor

(IM), there is a number of drawbacks including large torque and flux ripples, variable switching frequency for the inverter, and drop

of the stator flux especially when the IM operates in the low-speed region. These problems are associated with the usage of the

torque hysteresis controller (THC). To reduce the torque and flux ripples, the basic two-level inverter needs to be replaced by high

level inverter and among these multilevel inverter is the well know threelevel neutral-point clamped (NPC) inverter. In the case of

having low and variable switching frequency for the inverter will create high torque and flux ripples. In addition, the issue related

with unregulated stator flux coming about because of running the IM in the lowspeed region creates high stator current distortion

that thus debases the heartiness of the traditional DTC. To consider a solution for these issues, interleaving constant switching

frequency torque controller based DTC (CSFTC-DTC) was executed. The interleaving CSFTC-DTC was intended to build the duration

of the applied dynamic voltage vector and shorten the length of the applied zero vectors to improve the operation of the IM drives

particularly in the low-speed region. Despite the fact that the conventional interleaving CSFTC-DTC takes care of the issue of the

unregulated stator flux decreases the total harmonics distortion (THD) of the stator current, it delivers enormous torque and flux

ripples—the primary drawback of traditional DTC. In this thesis, modified 5-level interleaving CSFTC-DTC is proposed to shorten the

duration of the applied vectors of the three-level NPC inverter to restrain the impact of the enormous duration of the applied             vectors on stator flux and torque ripples. The simulation and implementation results introduced approve the adequacy of the               proposed method over the conventional interleaving CSFTC-DTC.