INTERNATIONAL JOURNAL of RENEWABLE ENERGY RESEARCH N. Nahak et al., Vol.10, No.4, December, 2020 Assessment and Damping of Low Frequency Oscillations in Hybrid Power System due to Random Renewable Penetrations by Optimal FACTS Controllers Narayan Nahak* ‡ , Sankalpa Bohidar**, Ranjan Kumar Mallick*** *Department of Electrical Engineering, ITER, Siksha ‘O’ Anusandhan Deemed to be University, India **Department of Electrical Engineering, ITER, Siksha ‘O’ Anusandhan Deemed to be University, India ***Department of Electrical and Electronics Engineering, ITER, Siksha ‘O’ Anusandhan Deemed to be University, India (narayannahak@soa.ac.in, sankalpabohidar@soa.ac.in, rkm.iter@gmail.com) ‡ Corresponding Author; Narayan Nahak, Bhubaneswar, India, narayannahak@soa.ac.in Received: 13.03.2020 Accepted:21.04.2020 Abstract- This paper presents a detail investigation on low frequency oscillations of a variable solar and wind penetrated power system. An optimized UPFC controller is proposed for damping low frequency oscillations to enhance small signal stability of such a power system. The modulation index of series converter and phase angle of shunt converters are controlled simultaneously in proposed UPFC controller there by incorporating the advantage of SSSC and STATCOM. The squirrel search algorithm (SSA) is proposed for tuning controller gains. The proposed UPFC controller has been compared with SSSC and STATCOM controllers to damp oscillations. Random variation of SPV, wind energy and their integration with varying synchronous generations has been considered in this work. It has been observed that increasing solar, variable wind and their interaction with variable synchronous power generation put more detrimental effect on low frequency power system oscillations. The detail time domain simulation and system eigen values predicted that proposed controller is able to damp these oscillations much efficiently for enhancing stability of such a critical power system. Keywords Low frequency oscillations, solar photo voltaic, wind power source, UPFC, SSSC, STATCOM. Nomenclature/Abbreviations Cdc Capacitance of dc link Xd d-axis steady state synchronous reactance for generator Vb Voltage of infinite bus D Coefficient of damping XE Reactance for excitation transformer(ET) Vdc Voltage at the dc link H Inertia constant (MJ/MVA) Xd ’ d-axis transient synchronous reactance for generator Vt Generator terminal voltage Ka, Ta AVR gain and time constant Xq q-axis (quadrature axis) steady state synchronous reactance for generator XB Reactance for the boosting transformer(BT) Pe = Pg Synchronous output power for generator Xe Total equivalent reactance for the system XBV Reactance for the transmission line Pi Mechanical input power for generator XtE Transformer reactance TWG, TV Time constants of wind and solar PV system Td0 Open circuit time constant of generator for d-axis(direct axis) KWG, KV Gains of wind and solar PV system ΦV Solar irradiation(Kw/m 2 ) VW Wind speed (m/s) PW Wind turbine output power PWG Wind energy generated power FACTS Flexible ac transmission system SSSC Static synchronous series compensator STATCOM Static synchronous compensator