With advances in solid-state power electronic devices and microprocessors, various inverter control techniques employing pulse-width-modulation (PWM) techniques are becoming increasingly popular in AC motor drive applications. These PWM based drives are used to control both the frequency and the magnitude of the voltages applied to motors. Various PWM strategies, control schemes, and realization techniques have been developed in the past two decades . PWM strategy plays an important role in the minimization of harmonics and switching losses in converters, especially in three-phase applications.
Various PWM technique have been developed to reduce the total harmonic distortions of Voltages and Current Waveforms .
Method of increasing the output voltage is the space-vector PWM (SVPWM) technique. With the development of microprocessors, SVPWM has become one of the most important PWM methods for three-phase inverters.
The SVPWM technique utilizes the DC bus voltage more efficiently and generates less harmonic distortion when compared with other techniques.
By using SVPWM PWM with Variable frequency to control speed of three phase induction motor. In recent years, Space vector modulation (SVM) is used for controlling three-phase PWM inverters. This is the one of the best available methods for PWM signals. It is an advanced control mechanism that generates three-phase AC voltages of the desired magnitude and frequency at the output of the inverter.
Increasing voltage without frequency will cause the material in the magnetic circuit to saturate. Excessive current will flow giving rise to high heat.
Dissipation due to I2R losses in the windings and high eddy current losses in the magnetic circuit and ultimately failure of the motor due to overheating.