Response characteristics of HVDC system according to frequency sensing methods

This paper deals with the frequency sensing methods at HVDC system. The objects of frequency information in HVDC system are to fire a valve and to control a frequency of AC network. Conventionally, there are two methods to measure a frequency of AC network. The first method is to draw out from the synchronous machine and the second method is from AC network. Two methods have advantages and disadvantage each other. For the extreme case of a receiving system of zero inertia (no generation), synchronous machine is essential. In this situation, the frequency information received from the synchronous machine shaft. However, the speed of synchronous machine is oscillated when a disturbance in AC network occurs, and HVDC may be oscillated due to an oscillation speed. To solve this drawback, in this paper, new frequency sensing method is proposed. A proposed method that is used a modified curve-fitting algorithm, has a robust characteristics against a harmonics and unbalanced faults. Consequently, A proposed method is verified by PSCAD/EMTDC program and experimental test.