well, AC drives control the speed of either an induction motor or a synchronous motor by adjusting the frequency of the power supplied to the motor.
AC drives are also known as adjustable speed drives (ASD) or adjustable frequency drives (AFD) or variable frequency drives (VFD) or variable speed drives (VSD) or frequency converters (FC).If speed control is required, that controller is called a (variable speed) AC drive. AC drives are used in a wide variety of industrial applications. To give an easy example, AC drives are often used with fans to provide adjustable airflow in large heating and air conditioning systems. The flow of water and chemicals in industrial processes is often controlled by adjusting the speed of pump.
DC motor drives act as an interface between a controller and the motor. The drive must match the control signals (voltage and power levels) and signal type (analog or digital). The drive produces power conversion, amplification, and sequencing of waveform signals. Types of DC motor drives include adjustable or variable speed control, servo control, and integral motion control. Some drives are capable of delivering adjustable or variable speed control. Servomotors are generally small, powerful for their size, and easy to control. Integral motion control includes feedback and a controller. Important specifications to consider when searching for DC motor drives include considering whether or not a brushless DC motor drive or amplifier is needed. Some DC motor drives operate in conjunction with a brushless DC motor. Types of DC brushless motor drives include sine wave, trapezoidal, hall sensor commutation, and no sensor.
Source Site could give you more information :
http://motion-controls. globalspe c.com/LearnMore/Motion_Control s/Con
Answered by
Yash
, an ibibo Master,
at
10:10 AM on July 17, 2008