Development of Cascaded PI Tuning of Variable Frequency Drive

Variable Frequency Drive (VFD) is widely used in industries. Here cascaded PI method is used for controlling VFD, in which inner loop is current feedback and outer loop is speed feedback. When multiple sensors(speed, current) are there for measuring conditions in controlled process, a cascaded control scheme is used, and cascaded system also gives faster compensation when disturbance occurs. PI tuning for the first order system is easy as it depends only on time constant of system, and for second order system PI tuning is difficult as it depends on peak time, rise time, peak overshoot, settling time parameters of the system. The estimated PI will not give proper output so for better dynamic performance PI need to be tuned based on the whole mechanical system.