Received: 15 November 2017 Revised: 31 March 2018 Accepted: 21 May 2018 DOI: 10.1002/oca.2443 RESEARCH ARTICLE Modified whale optimization algorithm for fractional-order multi-input SSSC-based controller design Preeti Ranjan Sahu Prakash Kumar Hota Sidhartha Panda Department of Electrical Engineering, Veer Surendra Sai University of Technology, Burla, India Correspondence Preeti Ranjan Sahu, Department of Electrical Engineering, Veer Surendra Sai University of Technology, Burla-768 018, India. Email: preetiranjan.sahu@gmail.com Summary In this paper, the design of a fractional-order (FO) multi-input–single-output (MISO)–type static synchronous series compensator (SSSC) is proposed with a goal to improve the power system stability using modified whale optimiza- tion algorithm (MWOA). The proposed MWOA achieves an appropriate balance between exploitation and exploration stages of the original whale optimization algorithm. The performance of MWOA is validated by employing the bench- mark test functions and further contrasted with whale optimization algorithm and other heuristic algorithms like gravitational search algorithm, particle swarm optimization, differential evolution, and fast evolutionary programming algorithms to demonstrate its strength. The proposed FO MISO SSSC controller is optimized by the MWOA technique and tested under single-machine infinite bus system and further extended to a multi-machine framework. To demonstrate the superiority of MISO-type SSSC controller, the results obtained from it are compared with particle swarm optimization and differential evolution–based conventional single-input–single-output structured SSSC controllers. The com- parison of results of MWOA with that of other methods validates its superiority in the present context. KEYWORDS fractional-order (FO) controller, modified whale optimization algorithm (MWOA), power system stability, single-machine infinite bus (SMIB), static synchronous series compensator (SSSC) 1 INTRODUCTION In the recent days, the significance of dynamic and transient stability is worth utmost importance to accomplish increased power transfer. FACTS controllers can possibly improve the transient and dynamic stability margin. 1 SSSC is a preeminent FACTS controller that has the capacity to alter its reactance characteristics from capacitive to inductive without changing the amount of line current. Hence, SSSC is very efficient in controlling line power flow. 2 SSSC operation does not get affected due to classical system resonances. In order to improve the power transfer controllability, a SSSC controller is inserted in the transmission line to damp out power oscillations. 3 Nomenclature: FACTS, flexible AC transmission system; FO, fractional-order; SSSC, static synchronous series compensator; GA, genetic algorithm; PSO, particle swarm optimization; DE, Differential evolution; GSA, gravitational search algorithm; FEP, fast evolutionary programming; CMA-ES, evolution strategy with covariance matrix adaptation. Optim Control Appl Meth. 2018;1–16. wileyonlinelibrary.com/journal/oca © 2018 John Wiley & Sons, Ltd. 1