This paper presents a new concept for controlling static VAr compensators (SVC) in power systems. It allows thyristor controlled VAr compensators to effectively damp subsynchronous resonance (SSR) oscillations besides controlling the system voltage. Eigenvalue analysis and digital time simulations for the IEEE SSR benchmark system are utilized to investigate the role of the main voltage regulator of the SVC in stabilizing the system and alleviating the SSR modal interactions that may be introduced by the auxiliary speed signal alone. Stability zones are identified to optimize the compensator parameters for economical application.

Application of a Thyristor Controlled Var Compensator for Damping Subsynchronous Oscillations in Power Systems

This paper presents the results of a study on the application of the recently developed FACTS device, the static compensator (STATCOM), for the damping of torsional oscillations that occur in a series compensated AC system. The IEEE first benchmark system is considered for this study. In order to suppress unstable torsional mode oscillations, a STATCOM with a PI controller to regulate the bus voltage, and with an auxiliary signal derived from the generator speed deviations is employed at the generator terminal. The eigenvalue analysis technique is used for small signal analysis and optimization of the control system parameters is done through step response studies. In addition, dynamic performance of the nonlinear system with optimized STATCOM controller is evaluated under a three-phase fault. Results from the analytical and digital simulation studies reveal the technical feasibility of using STATCOM for damping of turbine-generator torsional oscillations in series compensated AC systems.

Application of STATCOM for damping torsional oscillations in series compensated AC systems

The paper presents the potential use of supplemental control of doubly-fed induction generator (DFIG)-based wind farms for damping subsynchronous resonance (SSR) oscillations in nearby turbine-generators connected to series capacitive compensated transmission systems. SSR mitigation is achieved by introducing a supplemental signal into the control loops of the DFIG voltage-sourced converter-based back-to-back. The validity and effectiveness of the proposed supplemental control are demonstrated on a modified version of the IEEE second benchmark model for computer simulation of subsynchronous resonance by means of time domain simulation analysis using the EMTP-RV program.

Utilizing DFIG-Based Wind Farms for Damping Subsynchronous Resonance in Nearby Turbine-Generators

This paper presents a novel control of a large-scale PV solar farm as STATCOM, termed PV-STATCOM, for alleviation of subsynchronous resonance (SSR) in a steam turbine driven synchronous generator connected to a series compensated transmission line. During nighttime, the PV solar farm can operate as a STATCOM with its entire inverter capacity for SSR mitigation. During daytime, if a system fault triggers SSR, the solar farm autonomously discontinues its normal active power generation and releases its entire inverter capacity to operate as PV-STATCOM for SSR prevention. Once the subsynchronous resonances are damped, the solar farm returns to its normal real power production. Electromagnetic transients studies using EMTDC/PSCAD are performed to demonstrate that a solar farm connected at the terminals of synchronous generator in the IEEE First SSR Benchmark system can damp all the four torsional modes at all the four critical levels of series compensation, and return to normal PV power production in less than half a minute. This proposed PV-STATCOM technology can either obviate or reduce the need of an expensive flexible ac transmission system device to accomplish the same objective. Furthermore, this technology is more than an order of magnitude cheaper than a conventional static var compensators or STATCOM of similar size.

SSR Mitigation With a New Control of PV Solar Farm as STATCOM (PV-STATCOM)

The results of a comparative study on the application of two countermeasures, i.e. the excitation controller and the static VAr compensator (SVC), for damping of subsynchronous resonance (SSR) are presented. To stabilize all the SSR modes, a unified approach based on modal control theory is proposed for the design of the excitation controller and the SVC, which are essentially dynamic output feedback compensators. The two damping schemes differ in the way they modulate the reactive power flow in the system to damp out the subsynchronous oscillations. To demonstrate the effectiveness of the proposed damping schemes under disturbance conditions, time-domain simulations based on a nonlinear system model are also performed. The relative merits of the two countermeasures are compared with respect to their validities under various loading conditions and different degrees of series compensations and their capabilities to expand the stable region on the real-capacitive reactance plane. >

Wasynczuk

Papers

Damping Subsynchronous Resonance Using Reactive Power Control