Fazlli Patkar

Comparative study of fuzzy logic speed controller in vector controlled PMSM drive: Minimum number of fuzzy rule-base

This paper presents a comparative study on fuzzy rule-base of fuzzy logic speed control with vector-controlled Permanent Magnet Synchronous Motor (PMSM) drive. Fuzzy rule-base design is viewed as control strategy. All fuzzy rules contribute to some degree in obtaining the desired performance. However, some rules fired weakly do not contribute significantly to the final result and can be eliminated. ‘Standard design’ of fuzzy rule-base of fuzzy logic controller is identified from numerous publications which is 49 rules is used in order to obtain great speed tracking response. It is possible to minimize the complexity of controllers design by reducing number of rule-base from standard 49 rules to 9 rules. Simulation results that verify appropriateness of the approach are included. A comparison of speed response between both designs is studied. Sensitivity of the designs to load disturbance and changes in command settings is studied and also being compared to demonstrate the effectiveness of the reduced rule-base.

A dual mode DTC of open-end winding induction motor drive with reduced torque ripple

In this paper, a new control strategy for Direct Torque Control (DTC) of dual two-level VSI fed 3-phase induction motor drive in an open end winding configuration is presented. The drive can be operated in dual mode; open-end winding or conventional single-sided supply configuration; based on the condition of the motor speed. A block of Optimum Status Detection & Mode Selector (OSD & MS) is introduced to the original structure of the DTC in order to analyze the motor speed condition and also to monitor the torque operating condition. Based on the information from the block, a new lookup table is devised for selecting of the most optimum voltage vectors. Since the open-end winding providing greater numbers of voltage vector, its have the capability to minimize torque ripple. A simulation has been conducted using MATLAB/Simulink in order to achieve the results.

Reduced torque ripple and switching frequency using optimal DTC switching strategy for open-end winding of induction machines

This paper presents an optimal switching strategy to minimize torque ripple and switching frequency for Direct Torque Control of induction machines. In this proposed method, two inverters are connected to the terminals of open-end windings of an induction machine. By doing so, number of voltage vectors is greater same as available in three-level multilevel inverters. The most optimal voltage vectors will be used to improve DTC performances, i.e. reduced torque ripple and switching frequency. The identification of the vectors are based on operating conditions, specifically by examining the behaviors of torque error and switching frequency of error status produced from the hysteresis controllers. It can be shown that, the proposed optimal switching vectors according to the operating conditions can reduce the rate of change of torque and hence minimize torque ripple and switching frequency. The improvements offered in the proposed method were verified through experimental results.

Performance of an asymmetrical six-phase induction machine in single-and two-neutral point configurations

An asymmetrical six-phase induction motor drive can be realised with either one or with two isolated neutral points. Each of the two possibilities has its own merits and shortcomings, which are reviewed in the paper. Further, the performance of these configurations is compared, using waveforms and spectra of the phase voltage and current, obtained by simulations and experimentally. Total harmonic distortion (THD) of the phase voltage and current is also calculated as a function of the modulation index and is used as a figure of merit. It is concluded that the drive with two isolated neutral points offers better phase voltage and current THDs, but is inferior from the point of view of post-fault control.

Constant switching frequency torque controller for DTC of induction motor drives with three-level NPC inverter

This paper presents Direct Torque Control (DTC) of induction motor drives using three-level Neutral Point Clamped (NPC) inverter. The usage of hysteresis controller that utilized in conventional DTC lead to varying switching operation, therefore a Constant Switching Frequency (CSF) torque controller is proposed to replace the torque hysteresis controller. The proposed CSF controller consists of Proportional-Integrator (PI) controller and triangular carrier waveforms are compared with the output of PI controller to produce a torque error status to implement DTC control. The proposed controller is able to improve the DTC drives performance in terms of torque ripple reduction and constant switching frequency operation. The improvement of proposed method is verified using experimental works.

Minimization of torque ripple and switching frequency utilizing optimal DTC switching strategy for dual-inverter supplied drive

This paper presents an optimal switching strategy employed in direct torque control (DTC) of induction machine utilizing dual-inverter supplied drive. In the proposed switching strategy, the utilization of appropriate amplitude of voltage vectors based on machine operating condition can reduce the rate change of torque slope while improving the performance of DTC drive in term of torque ripple reduction and also minimization of switching frequency variation. This is achieved by modifying the torque error status according to the capability of torque regulation which is done by evaluating the switching frequencies of torque and stator flux error status from the hysteresis comparators. By doing that the suitable amplitude of voltage vectors is able to be applied based on machine operation. All the improvements offered in the proposed strategy are verified through simulation results.

Direct Torque Control of induction machine using 3-level neutral point clamped inverter

This paper presents a Direct Torque Control (DTC) of induction motor drives utilizing 3-level neutral-point clamped (NPC) multilevel inverter. This research aims to provide a simple strategy to address capacitor voltage balancing problem of NPC inverter as well as produce better performance for DTC of induction motor in term of reducing torque ripple and high switching frequency. The proposed method uses 2-level hysteresis comparator to restrict the error of upper and lower capacitor voltages and then generate a signal which determine either to increase or decrease the particular capacitor voltage. Using that information, the appropriate selection of small voltage vectors is tabulated in look-up table (LUT) to stabilize the mismatched of capacitor voltage. Simulation results are presented to show the effectiveness of the proposed capacitor voltage balancing strategy.