Robust decentralised frequency stabilisers design of static synchronous series compensators by taking system uncertainties into consideration

This paper presents a new robust decentralised frequency stabilisers design of Static Synchronous Series Compensators (SSSCs) by taking system uncertainties into consideration. As an interconnected power system is subjected to load disturbances with changing frequency in the vicinity of the inter-area oscillation mode, system frequency may be severely disturbed and oscillate. To compensate for such load disturbances and stabilise frequency oscillations, the dynamic power flow control by an SSSC installed in series with a tie line between interconnected systems can be applied. The proposed decentralised design translates SSSCs installed in interconnected power systems into a Multi-Input Multi-Output (MIMO) system. The overlapping decompositions is used to extract the decoupled Single-Input Single-Output (SISO) subsystem embedded with the inter-area mode of interest from an MIMO system. As a result, each frequency stabiliser of SSSC can be independently designed to enhance the damping of the inter-area mode in the decoupled subsystem. In addition, by incorporating the multiplicative uncertainty model in the decoupled subsystem, the robust stability margin of system against uncertainties such as various load changes, system parameters variations etc., can be guaranteed in terms of the multiplicative stability margin (MSM). In this study, the configuration of frequency stabiliser is practically based on a second-order lead/lag compensator. Without trial and error, the control parameters of the frequency stabiliser are automatically optimised by a micro genetic algorithm, so that the desired damping ratio of the inter-area mode and the best MSM are acquired. Simulation study shows the high robustness of the decentralised frequency stabilisers against various load disturbances and system parameter variations in the three-area loop interconnected power system.