A Coordinated hydro turbine governor with fractional STATCOM for critical power oscillation damping

Hydro turbine governors can be of prime resources for multi-functional contribution to a future power network. But for critical oscillatory conditions brought by uncertain renewable integration, these governors can be coordinated with STATCOM control action for optimal damping torque contribution. Here, a new damping action is proposed, where the governor is provided with additional phase compensation and coordinated with STATCOM based PI with fractional compensator with time delay to impart a mechanical-electrical damping torque for critical oscillations in power system. Uncertain discrete variations in solar and wind penetrations are executed in this work for two area four machine system to observe oscillations and proposed controller being implemented to impart adequate damping torque. Also, the parameters of proposed controller are tuned by a new DE with time varying accelerated PSO algorithm. The damping action has been compared with compensated governor and STATCOM controller and found to be much suitable even for critical oscillatory response.

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.

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A PI with fractional lead-lag action for STATCOM based controller is proposed.

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A coordination of both governors with STATCOM has been implemented for small signal stability enhancement

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A hybrid DE with time varying accelerated PSO (DETVAPSO) is proposed for controller tuning.