Secondary frequency control strategy considering DoS attacks for MTDC system

The utilization of communication networks brings benefits to frequency support strategies for multi-terminal high voltage direct current (MTDC) systems, yet leads to the systems facing cyber security risks. In particular, the denial of service (DoS) attacks will cause loss of measured signals and make the MTDC system unstable. This paper is concerned with the secondary frequency control problem defending DoS attacks in MTDC systems. Focusing on energy-limited and periodic DoS attacks, a Bernoulli process model is firstly adopted, and the control objective considering DoS attacks is built. Thereafter a switching scheme of the attacked station from droop control to secondary frequency regulation is devised for frequency support of MTDC systems. Two strategies respectively using the reference value and the data of the previous time interval are then proposed to compensate for the lost data due to DoS attacks. Four scenarios are simulated on a four-terminal MTDC system to verify the effectiveness of the two proposed solutions. The results show that, if the system is in equilibrium states during DoS attacks, both of the two proposed strategies are effective. Whereas the solution using the data of the previous time interval has better performances in the subsequent regulation process after load disturbance. • A switching control mechanism is devised for restoring the frequency of MTDC systems. • DoS attack will seriously affect the control process of MTDC systems. • Strategy(1) can be utilized when the system is in operating phase of steady state. • Strategy(2) has a better performance in the operating state when the system changes.