Frequency Control at the Power Sending Side for HVDC Asynchronous Interconnections Between Yunnan Power Grid and the Rest of CSG

For a large-scale high voltage direct current (HVDC)asynchronous interconnected power grid, the frequency issue atthe power sending side under DC faults is a crucial problem.To solve this problem, based on rotor motion equations, theeffect of unbalanced power on the system frequency under DCfaults is analyzed. The characteristics and dynamic developmentprocess of frequencies after the injection of disturbances areanalyzed. In addition, the actions and coordinated strategies ofvarious frequency control measures are also investigated. Basedon the testing projects of an asynchronous interconnection in theChina Southern Power Grid (CSG), the frequency features arestudied according to the measured PMU data. The outcome showsthat the frequency problem of the Yunnan Power Grid after anasynchronous interconnection can be solved and controlled. Italso shows that the frequency limit control (FLC) is importantfor the frequency regulation of large scale HVDC asynchronousinterconnected DC power grids. As demonstrated, DC FLC caneffectively suppress the deviation of the transient frequency.However, reasonable frequency regulation parameters shouldbe set and other area frequency control measures should becoordinated to maintain the frequency stability of the system.