A new control approach for control of torque ripple and electromagnetic noises in induction motor

Induction motors are widely studied about the control of their torque and speed in the academia and industry due to their robust structure, low maintenance needs, high power/weight ratio and their flexibility on working conditions. In the industry, squirrel cage induction motors are preferred over the DC motors, which are expensive and require costly maintenance.In the recent industrial applications, complex control algorithms for the induction motors are required because of their nonlinear structure. Therefore, researchers are focused on methods that provide high performance such as vector control methods of field oriented control (FOC) and direct torque control (DTC).DTC is a control method which is applied with inserting the switching sequence to the inverter without converting the current, using PWM method or the speed sensor. Thus, we developed a new technique using the direct torque control algorithm.In this study, we investigate the minimization and control of torque ripple, harmonics and electromagnetic noises in the induction motors.In order to study torque ripple and harmonic noises, we firstly explore the fundamental theory of the vector control and construct the Matlab/Simulink models of the DTC. We determine the effect of the control algorithms on the level of harmonics and ripple by using the same parameters for all algorithms.The following methods are investigated in order to reduce harmonics and ripple. First of all, the flux regions of the DTC model are altered and the numbers of sectors are increased by increasing the hysteresis controllers of the torque control. Afterwards, a new direct torque control (DTC) algorithm is proposed for squirrel cage induction motors. This algorithm determines two adjacent vectors using the hysteresis blocks of the traditional DTC in order to provide the voltage of the motor. The switching times for the two vectors are regulated by using the flux position and the magnitude of flux error. The selection of the switching time from the suggested table reduces the complexity of the algorithm. The simulation and experimental results of the proposed algorithm suggest lower harmonic current and lower EMI noise level as well as a considerable reduction in torque ripple and an adequate dynamic torque performance in comparison with the traditional DTC.The second model is the design of the active filter. The parallel active filter design consists of switching components and it controls the signal of DC link supply source in the new DTC system. The active filter compares the reference current with the current of the AC voltage source in order to determine signals of the filter. Reference current is estimated from the instantaneous reactive power theory. The parallel active filter is used for providing harmonics in DC voltage of the new DTC motor control system. The simulation results of the active filter design show that the level of harmonic due to the source and torque ripple are significantly reduced and the dynamic torque performance of the system improves. In addition, the EMI noise resulted from AC source is decreased.