Frequency control of MMC-HVDC based on active and reactive power decoupling

High voltage DC systems based on modular multi-level converters have been received increased attention due to the high power quality they provide. When the rated power of the HVDC station is similar to the generating units, the converter station can have an important role in the frequency regulation. The method proposed in this paper uses the relation between the active and reactive power to estimate the load changes adding a feed-forward compensation term for the active power reference thus reducing the dynamical frequency deviation. This method in combination with a frequency PI controller, delivers active power to compensate load changes and keeps the frequency at its reference with a very small deviation.