Complete harmonic-domain modeling and performance evaluation of an optimal-PWM-modulated STATCOM in a realistic distribution network

Power systems use STATCOM for compensating purposes that is subjected to the high switching frequencies. Various PWM techniques make selective harmonic elimination possible, which effectively control the harmonic content of voltage source inverters. On the other hand, distribution systems have to supply unbalanced nonlinear loads, transferring oscillations to the DC-side of the converter in a realistic operating condition. Thus, additional uncharacteristic harmonics are modulated through the STATCOM at the point of common coupling (PCC). This requires more attention when switching angles are calculated offline using the optimal-PWM technique. This paper suggests a harmonic-domain model in order to realistically evaluate the injected harmonics at the PCC. This model properly takes into account the DC capacitor effect, effects of other possible varying parameters such as voltage unbalance as well as network harmonics, and effects of operating conditions on the STATCOM harmonic performance. The model is programmed, and can be easily run with other algorithms such as Monte Carlo simulation. Further, a semi-stochastic method is proposed to predict and simulate the three-phase voltage unbalance, leading to an analytical tool for prediction of harmonic performance of STATCOM. The predictive method is developed based on the measured data obtained from a low-voltage distribution network. Finally, the modeled STATCOM is linked with the distribution substation, applying the proposed voltage unbalance modeling to evaluate aggregate harmonics of the load.