Automatic generation control for DC-link power system

This paper discusses LFC (load frequency control) with HVDC (High Voltage DC transmission system). So far, AGC (Automatic generation control) has been focused on economic dispatch control and load frequency control; especially the latter is mainly on frequency stabilization for ac-link network systems. However, the upcoming power-electronics based HVDC transmission system offers new aspects for the improvement of frequency control. In this paper, 2-area and 3-area network systems are used to discuss how a HVDC interconnected system works to improve frequency fluctuation for random load disturbance. Because DC-interconnection provides an adequate power exchange, reduction of frequency deviations for both systems is achieved if the control gain is tuned properly. However, the effect differs by geometrical differences. In order to discuss the effectiveness of HVDC link for load frequency control, the HVDC-link is designed as a feedback system of system state variables, whose concept has been used for Hokkaido-Honshu link in Japan and also proposed for Minami-Fukumitsus link in Japan. The simulated load fluctuation model is constructed to demonstrate actual load's behavior. In AC-interconnected power systems, the HVDC-link connecting two of the local systems does not provide frequency improvement since power exchange has been already achieved on the links. However, if two isolated power systems are interconnected, the HVDC-link will make the important role to sustain the frequency deviation within regular tolerance even if the capacity is very small compared to those of two systems, these acts as a single system and the disturbance to the smaller system is cancelled as a tiny disturbance of the whole system.