Unbalanced STATCOM analysis in the harmonic domain

System imbalance plays an important role in the harmonic performance of switching devices, and it is important to account for these sequence transfers in computational models. This work considers these sequence transfers and then outlines a nonlinear harmonic domain approach to unbalanced PWM STATCOM modelling. The proposed model is validated against time domain simulation and used to consider a STATCOM under unbalanced conditions. This investigation concludes that the impact of system imbalance on STATCOM performance is two-fold. The imbalance generates noncharacteristic harmonics, which in turn propagate through the control system causing a secondary effect on characteristic harmonic generation. The magnitude of this secondary effect is dependent on the control system, highlighting the necessity of including an accurate control scheme representation. In addition this unbalanced propagation through the controller decreases system linearity, making it necessary to recalculate the Jacobian at each iteration.