Disturbance-observer based control of voltage-source-converter under unbalanced voltage conditions

A grid voltage dynamic model is represented in symmetrical positive and negative sequence reference frames. A proportional controller structure with a first order low pass filter disturbance observer (DOB) is designed for power control in unbalanced voltage conditions. This controller is capable of meeting the positive sequence power requirements, and it also eliminates negative sequence power components which cause double frequency oscillations on power. The symmetrical components are calculated by using the second order generalized integrator (SOGI) based observer, which accurately estimates the symmetrical components.