Variable Speed Drive (VSD) Features Explained
Modern variable speed drives (VSDs) are equipped with a multitude of features to provide programming flexibility, enhance efficiency and increase the accuracy of control. Let’s dissect some of these features, typified in this case by the A1000 series of industrial AC drives from Yaskawa (www.yaskawa.com).
Control methods: the A1000 provides up to seven different control methods to suit specific motors and applications. Methods range from basic scalar (volts/hertz, or V/f) control, which adjusts frequency and voltage output in direct proportion based on command reference, through open-loop vector control, to closed loop vector control. Vector control essentially “splits” the stator current into separate torque and field components, analogous to the separate armature and field components of a DC motor, and controls VSD output by regulating voltage magnitude, angle of displacement, and frequency. In open loop systems, modeling is used to calculate vectors and adjust output based on measured output current, while in closed loop configuration, sensors such as encoders or tachometers directly measure rotor position and speed and are able to control output even more tightly. In the A1000, V/f control can provide a typical speed control range of 40:1, while open-loop vector can achieve 200:1 […]