Robust Frequency Stabilisation By Coordinated Superconducting Magnetic Energy Storage With Static Synchronous Series Compensator

As large load disturbances with changing frequency in the vicinity of the inter-area oscillations mode occur in an interconnected power system, a system frequency may be heavily perturbed and oscillatory. To stabilise frequency oscillations, the active power controlled by a superconducting magnetic energy storage (SMES) unit placed in a power system, can be utilised. However, it may not be feasible to locate a SMES unit in every area of a multi-area interconnected power system due to the economic reason. Therefore, it should be advantageous if a SMES unit located in an area is available for frequency stabilisation of other interconnected areas. To implement this concept, a static synchronous series compensator (SSSC), can be applied to coordinate with a SMES unit to stabilise frequency oscillations. On the other hand, variations of system parameters, several load changes etc., cause system uncertainties. To enhance the robustness of frequency stabilisers against uncertainties, this paper focuses on a robust frequency stabilisation by SMES in co-ordination with SSSC. To take system uncertainties into account, the multiplicative uncertainty is included in system modeling. As a result, the system robust stability can be easily guaranteed in terms of the multiplicative stability margin (MSM). The structure of frequency stabiliser equipped with SMES and SSSC is a second-order lead/lag compensator. Based on the proposed optimisation technique, control parameters of frequency stabilisers can be automatically tuned by a tabu search. Consequently, the desired damping ratio of the target inter-area mode and the best MSM are achieved. Simulation studies in a two-area interconnected power system confirm the high robustness of the coordinated SMES with SSSC against several uncertainties.