Narrow Band Disturbance Attenuation Method for AC Drives: A Complex Pole-Zero Placement Approach
The unwanted periodic external excitations on AC drives, such as fluctuation in the DC bus voltage or dead time in the gate drive signals, often act as narrow band disturbances in rela-tively low frequency region. The consequent influences cannot be filtered out by the commonly used low pass filter in hard-ware configuration, thus special attention has to be paid to this kind of disturbances. A robust discrete-time controller using complex pole-zero placement with the assistance of sensitivity function shaping is proposed, which, specifically, utilizes a sec-ond-order notch filter. Comparatively speaking, the widely used proportional-integral controller only employs first- order polynomials in its expression, while the complex pole-zero placement method has no restriction on the degrees of the pol-ynomials, thus provides more freedom in design to meet extra requirements. Moreover, the presence of the notch filter can attenuate disturbances in specific frequency region as well as maintain the robust characteristic. The effectiveness and feasi- bility of the architecture is verified by a design example.