Abstract:It is very important to control the speed of induction motors in industrial and engineering applications. Efficient control strategies are used for reducing operation cost too.This paper presents a direct flux and torque control of three phase induction motor drive using PI and Fuzzy logic controller. The Direct Flux and Torque Control (DTC) is one of the most excellent direct control strategies of stator flux and torque ripple of Induction Motor Drive(IMD). The conventional method of DTC uses PI controller for speed regulation where speed is reduced under transient and dynamic state. This drawback was eliminated in proposed system by regulating the speed with the help of PI controller and torque controlled by fuzzy logic controller.
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The schematic diagram of conventional DTC of IMD is shown Fig. This schematic diagram consists of a torque and flux hysteresis band comparators (T, Ψ), voltage vector sector selection, stator flux and torque estimators (Ψs, Te), induction motor, speed controller, and voltage source inverter (VSI).
A.PULSE WIDTH MODULATION
It is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches. The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher power supplied to the load is. The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switching have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies. The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications
The schematic diagram of conventional DTC of IMD is shown Fig. This schematic diagram consists of a torque and flux hysteresis band comparators (T, Ψ), voltage vector sector selection, stator flux and torque estimators (Ψs, Te), induction motor, speed controller, and voltage source inverter (VSI).
A.PULSE WIDTH MODULATION
It is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches. The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher power supplied to the load is. The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switching have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies. The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on. The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications