Estimation of AC voltages under unbalanced condition using state observer control

Statcom behaviour under unbalanced power system condition is examined. State observer based control strategy is used to estimate the voltages at the point of common coupling from the measured injected current so that hardware requirement gets reduced and hence cost gets reduced. Feedback linearization control strategy has been used to linearize the system and to decouple the positive and negative sequence component of ac side current to evade the possibility of over current to statcom under unbalanced power system condition. The instantaneous active and reactive power theory is used for calculating the positive sequence component of current in α-β reference frame with the help of desired active and reactive power reference. The sinusoidal pulse width modulation control technique has been implemented for voltage source inverter to produce the gating pulses. Two level statcom is used for realization the above mentioned control scheme.