Self Tuned NFC and Adaptive Hysteresis Based DTC Scheme for IM Drive

The concept of field oriented control scheme brought the revolutionary change in industrial drives. Due to the high initial and running costs of the DC machines, the trend shifted from DC to AC motor drives to obtain high performance variable speed drives. The major achievement with field oriented control was the decoupled and independent control of stator and rotor quantities like DC machines. It is agreed that the control scheme for ac machines is complicated as compared to DC machines. The inherited problem with the ac machine control is the nonlinear relation between process variables e.g. speed and manipulated variables e.g. current, torque etc. Moreover, magnetic saturation of its rotor core causes developed torque relation of nonlinear nature.;This thesis presents a critical analysis of the working components of DTC scheme. The torque production in induction motor (1M) and the factors which influence the ripple level in the developed torque are also analysed. On the basis of this analysis, it presents a new algorithm for the three level torque and two level flux hysteresis controllers. Then another algorithm is designed to vary the bandwidth of the torque hysteresis controllers online to keep the torque ripples within specified limits. This thesis further presents a simpler algorithm to determine the sector number of the stator flux linkage vector. Finally, a Neuro-Fuzzy Logic Controller (NFC) is proposed to improve the dynamic behaviour of the 1M drive. The use of intelligent controller is very limited in the drive industry due to the relevant computational burden of the micro processor. Therefore, in order to reduce the computational burden, linear linguistic variables with lesser number of membership functions have been selected in this thesis. The effectiveness of the proposed NFC and adaptive hysteresis based DTC scheme of the 1M drive is consolidated through the development of a simulation model using Matlab/Simulink. Then the complete 1M drive, incorporating the proposed NFC based DTC scheme, is successfully implemented in real-time using digital signal processor (DSP) board-DS1104 for a laboratory 1/3 hp motor. The effectiveness of the proposed 1M drive is verified both in simulation and experiment at different dynamic operating conditions. The results show the robustness of the drive and its potentiality to apply for real-time industrial drive applications.;Direct torque control (DTC) scheme is a vector control technique like field oriented control (FOC) scheme but it is faster and simpler. The DTC does not need any coordinate transformation like FOC. The DTC controls motor torque directly, so it is faster. The DTC scheme is used to obtain the high dynamic performance for control of AC machines like FOC. Conventional DTC scheme consists of two hysteresis comparators, a flux and torque estimator and a table used to select optimal inverter voltage vector. Both torque and flux are controlled simultaneously by the selection of appropriate voltage form the inverter. Due to the discrete nature of the control system and limited number of possible voltage vectors from the three phase inverter, this scheme suffers from high torque ripples. The bandwidth of hysteresis and variable slope of the torque make the switching frequency of inverter variable.