R. Thirumalaivasan

Bio: R. Thirumalaivasan is an academic researcher from VIT University. The author has contributed to research in topics: Damping torque & AC power. The author has an hindex of 7, co-authored 26 publications receiving 179 citations.

Damping of SSR Using Subsynchronous Current Suppressor With SSSC

Abstract: Hybrid series compensation using static synchronous series compensator (SSSC) and passive series capacitor can improve the stability of the system, increases the power transfer capability and is useful for the fast control of power flow. This paper analyzes the subsynchronous resonance (SSR) characteristics of the hybrid series compensated power system in detail and proposes a simple method for the extraction of subsynchronous components of line current using filter. The extracted subsynchronous frequency component of line current is used to inject a proportional subsynchronous voltage in series with the transmission line which suppresses subsynchronous current in the transmission network. This novel technique is termed as subsynchronous current suppressor. The design of subsynchronous current suppressor is based on damping torque analysis and using genetic algorithm. A novel graphical representation of series resonance condition when SSSC is incorporated in the system is presented. The detailed study of SSR is carried out based on eigenvalue analysis, transient simulation and damping torque analysis. The results of the case study on a system adapted from IEEE First Benchmark Model demonstrates the effectiveness and robust performance of subsynchronous current suppressor in damping of SSR under various system operating conditions.

Stability Analysis on Torsional Interactions of Turbine-Generator Connected With DFIG-WECS Using Admittance Model

Abstract: To evaluate the stability of Subsynchronous Torsional Interactions (SSTI), we propose a simple and effective approach using admittance model. The proposed approach gives the subsynchronous conductance based criterion to find the stability of torsional interactions. The subsynchronous conductance based approach is utilized to evaluate the impact of Doubly-Fed Induction Generator based Wind Energy Conversion System (DFIG-WECS) on the torsional vibrations of nearby turbine-generator. The damping of Induction Generator Effect (IGE) and SSTI is analyzed through admittance model at different wind speed with various compensation level. The results of admittance analysis are validated through eigenvalue analysis and transient simulation. The results show that, the DFIG-WECS reduces the damping of torsional modes in the low frequency region of subsynchronous network mode. The damping of SSTI reduces with increase in wind speed. Hence, the DFIG-WECS significantly destabilizes the low frequency torsional modes at high wind speed with high compensation level. Further, it is found that, the network conductance at all critical torsional modes marginally reduces with Subsynchronous Damping Controller (SSDC) at the inner loop of Grid Side Converter (GSC) controller compared to other locations in DFIG converter controllers.

Design of Robust Current Controller Using GA for Three Level 24-Pulse VSC Based STATCOM

Abstract: A STATic synchronous COMpensator (STATCOM) is a shunt connected voltage source converter (VSC) based FACTS controller using Gate Turn Off (GTO) power semiconductor devices employed for reactive power control. The operation principal is similar to that of a synchronous condenser. A typical application of a STATCOM is voltage regulation at the midpoint of a long transmission line for the enhancement of power transfer capability and/or reactive power control at the load centre. This paper presents the modeling of STATCOM with twenty four pulse three level VSC and Type-1 controller to regulate the reactive current or the bus voltage. The performance is evaluated by transient simulation. It is observed that, the STATCOM shows excellent transient response to step change in the reactive current reference. While the eigenvalue analysis is based on D-Q model, the transient simulation is based on both D-Q and 3 phase models of STATCOM (which considers switching action of VSC).

Overview of emerging subsynchronous oscillations in practical wind power systems

Abstract: Emerging subsynchronous oscillation (SSO) issues in grid-connected wind farms have gained serious attention after several incidents occurred in the US and China. The temporal and spatial variation of wind speed, the diversified converter control structures, and the continuously varying number of in-service wind turbine generators (WTGs) greatly affect the equivalent impedance reflected by the wind farms. Such frequency-dependent equivalent impedance, as indicated by both theoretical analyses and practical experiences, has a huge impact on the mechanism and characteristics of SSO. In this regard, WTGs contribute to a more complicated type of SSO than those in conventional turbo-generators (CTGs). For instance, SSO in practical wind power systems can be triggered without the participation of series compensation in the transmission network. The emerging SSO phenomena observed in practical WTGs are relatively new, and cannot be properly interpreted by existing literature. This work will first review the historical development of SSO definitions and classification by IEEE, followed by discussions on recent incidents in practical wind farms due to the emerging SSO. Subsequently, new terminologies and classification of SSO are proposed with the aim to better understand SSO in large-scale wind integrated power systems. This paper offers a practical insight and a future perspective for the reader to properly deal with SSO associated with wind power systems.

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

Abstract: 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.

Sub-Synchronous Resonance Damping Control for Series-Compensated DFIG-Based Wind Farm With Improved Particle Swarm Optimization Algorithm

Abstract: In this paper, we propose an improved sub-synchronous resonance (SSR) damping controller (SSRDC) and a related control strategy to mitigate the SSR in a capacitive series-compensated double-fed induction generator based wind farms, based on the damping torque analysis. The proposed strategy is utilized for enhancing the system stability. Compared with the traditional damping controller, the proposed SSRDC is simultaneously embedded into the $d$ -axis and $q$ -axis control channels in the inner current loop of the rotor-side converter. On this basis, combined with the eigenvalue analysis and improved particle swarm optimization algorithm, the optimum gain coefficients of the SSRDC can be determined for maximizing the mitigation effect under different operation conditions of the series compensation levels and wind speeds. Moreover, the effect of the weight coefficients in the objective function on the SSR suppression is also investigated. Finally, the time-domain simulations are carried out to demonstrate the effectiveness of the proposed control strategy for mitigating the SSR and suppressing the connected power system oscillations.

Nyquist stability criterion based ssr explanation for type 3 wind generators

Abstract: Summary form only given. Type-3 wind generators in series-compensated networks could lead to subsynchronous resonance (SSR) oscillations- a phenomenon observed recently. In this letter, impedance-based Nyquist stability criterion is applied to explain the phenomenon. The resonance is not due to the shaft's torsional characteristics, but rather due to its slip related impedance, which can give rise to equivalent negative resistance. The explanation corroborates the authors' previous explanation of self-excitation using net negative resistance concept. Nyquist map is also able to demonstrate the impact of wind speed on SSR.