They are connected in series with the DC side of the HVDC converter and act as a low-pass filter, allowing the DC voltage to pass through while reducing the amplitude of high-frequency ripple caused by the switching of the converter.
Converter reactors are designed to have a specific impedance at the switching frequency of the converter, which helps to reduce the ripple in the DC voltage. They are typically made from a coil of wire wrapped around a core made of iron or another magnetic material. This core helps to increase the inductance of the reactor, which is necessary to effectively reduce the ripple in the DC voltage.
Converter reactors play an important role in the HVDC systems, as the ripple reduction can have direct impact on the performance of the converter and the lifespan of the equipment. They also help to improve power quality and system stability, and are critical for the safe and efficient operation of the HVDC system.