Study on harmonic interaction between paralleled STATCOMs with cascaded H-bridge topology in wind farm clusters

To ensure reasonable reactive power distribution and voltage standard, a large number of STATCOMs are integrated to wind farms and afflux stations. However, the issue of device tripping caused by the interaction between STATCOMs is emerging. This paper sets out to bring a clear understanding of the fault mechanism of single STATCOM tripping caused by the harmonic circulation between STATCOMs in a clustered wind-farm afflux station in North-China grid. The equivalent circuit of harmonic circulation between two paralleled STATCOMs based on cascaded H-bridge topology is established first. Thereafter, the intrinsic relationship between high-order harmonic circulation and inter-converter harmonic voltage difference as well as the phase deviation of SPWM carriers are analysed. A generalized model is also built to estimate the higher-order harmonics. The impact of non-characteristic harmonics on DC voltage of each H-bridge cell is investigated by calculating the difference of active power flowing through DC capacitors. It is pointed out that the harmonic circulation is one of the main reasons resulting in the DC overvoltage protection action of STATCOM. Finally, the correctness of theoretical analysis is verified by real-time simulation and hardware experiments.