I. Introduction
Small signal stability (SSS) assessment is going to be an all-time issue for a modern power system due to continuous intermittent penetrations of renewable sources. The hydro plants associated with turbine governor system are important sources for future power generations but their governors have been employed for frequency regulations and generally by passed to counteract low frequency oscillation as reported in [1]. This under usage of governor can be compensated by modifying its controllability. With varying penetration levels of renewables, the critical oscillatory response of power system has been more aggravated and for this an adequate damping torque needs to be employed. As per researches, system oscillations are more excited by renewables integration like solar and wind sources [2]–[4]. FACTS controllers can efficiently provide damping torque as reported in [5]–[6] but, their usage can be limited subject to costly control action strategies. Hydro plants are already being installed with their governors. So, if they are properly coordinated with electrical damping torque contribution by FACTS devices, then two important aspects can be addressed. One is prevention of under usage of governor and second is reducing economic stress on controller actions provided by FACTS controller. Because one FACTS can be coordinated with multiple hydro governors. STATCOM control action has been implemented in [7] and governor control action in [8], [9] for small signal stability enhancement. But, in this work a STATCOM has been coordinated with hydro governor to impart a combined mechanical and electrical damping torque for critical oscillations and compared with STATCOM and governor actions. The STATCOM action is based on PI with fractional lead-lag action so as to meet steady state error along with imparting better closed loop response by fractional parameter. The phase lag imparted by hydro governor has been put into compensation by a lead structure because reducing error in steady state is of prime concern in this context. To tune gains of proposed controller a hybrid DE[10] with time varying accelerated PSO [11] has been employed. The prime new contributions of this work for improving SSS are:
A modified turbine governor action is proposed.
A PI with fractional lead-lag action for STATCOM based controller is proposed.
A coordination of both governors with STATCOM has been implemented for small signal stability enhancement
A hybrid DE with time varying accelerated PSO (DETVAPSO) is proposed for controller tuning.