Yaskawa Whitepaper: The I’s and O’s of VFDs

Since the late 1960s, the AC drive has developed at a tremendous rate. Major advances have been made thanks to developments within the fields of microprocessor and semiconductor technology and the associated price reduction. However, the basic principles of the AC drive remain the same.

A general overview of the standard current control principles for Danfoss AC drives is illustrated in Fig. 3.26 Basic principles of current standard AC drive from Danfoss. The PWM switching patterns are calculated for the inverter using the selected control algorithm.

An electric motor is an electromechanical device that converts electrical energy into mechanical energy. The reverse process of producing electrical energy from mechanical energy is performed by a generator.

Variable speed drives, due to their operating principle, produce a series of unwanted secondary effects, such as: motor winding isolation stress, bearing stress, acoustic switching noise in the motor and electromagnetic interference. In most applications these effects are at an acceptable level – but in some cases these effects need to be mitigated.