Abstract:
In industries, conventional drives such as Voltage source inverter (VSI) and Current source inverter (CSI) drives are used for control of small to medium induction motor drives. CSI drive is simple in structure it has many inherent weaknesses in high power applications problems related with output capacitors like resonance phenomena and inherent instability in high frequency region. Similarly VSI drive has very efficient control techniques, for high power induction motor; they face problems like constraints of device ratings.
Recent researches in the field of large induction motor drives are going on in multilevel converter system drives and hybrid converter system drives. Multilevel inverter system overcomes weaknesses of VSI by using different series combinations of devices with latest PWM techniques. Hybrid converter system drive uses VSI parallel to CSI. This strategy allows the operation of the CSI with a safe commutation angle provided by the VSI, regardless of the load speed and torque. By eliminating the requirement of the output capacitors for the conventional CSI-based induction motor drive, this system is quite free from all problems caused by the conventional CSI drives, such as resonance problem and inherent instability. In addition, sinusoidal motor currents and voltages as well as faster response are obtained with this system. It thus removes all difficulties raised by use of output capacitor in high power applications.
