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 at the power sending side under DC faults is a crucial problem. To solve this problem, based on rotor motion equations, the effect of unbalanced power on the system frequency under DC faults is analyzed. The characteristics and dynamic development process of frequencies after the injection of disturbances are analyzed. In addition, the actions and coordinated strategies of various frequency control measures are also investigated. Based on the testing projects of an asynchronous interconnection in the China Southern Power Grid (CSG), the frequency features are studied according to the measured PMU data. The outcome shows that the frequency problem of the Yunnan Power Grid after an asynchronous interconnection can be solved and controlled. It also shows that the frequency limit control (FLC) is important for the frequency regulation of large scale HVDC asynchronous interconnected DC power grids. As demonstrated, DC FLC can effectively suppress the deviation of the transient frequency. However, reasonable frequency regulation parameters should be set and other area frequency control measures should be coordinated to maintain the frequency stability of the system.