M. Janaki

Damping of SSR Using Subsynchronous Current Suppressor With SSSC

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.

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

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).

Damping of subsynchronous resonance by subsynchronous current injector with STATCOM

A long transmission line needs controllable series as well as shunt compensation for power flow control and voltage regulation. This can be achieved by suitable combination of passive elements and active FACTS controllers. In this paper, series passive compensation and shunt active compensation provided by a static synchronous compensator (STATCOM) connected at the electrical center of the transmission line are considered. This paper presents investigation of subsynchronous resonance (SSR) characteristics of the system and proposes a novel method for the extraction of subsynchronous component of line current using filter. The extracted subsynchronous frequency component of line current is injected to the system by the STATCOM which prevents the flow of subsynchronous current through the generator and increases the damping of the system at critical torsional frequencies. This novel technique is termed as Subsynchronous Current Injector (SSCI). The design of SSCI is based on damping torque analysis. The 3-phase model of the STATCOM is based on switching functions. By neglecting harmonics in the switching function, D-Q model is derived which is combined with similar models of the other system components for linear analysis. The results of the linear analysis are validated by carrying out transient simulation based on the detailed nonlinear models.

Investigation of SSR Characteristics of Hybrid Series Compensated Power System with SSSC

The advent of series FACTS controllers, thyristor controlled series capacitor (TCSC) and static synchronous Series Compensator (SSSC) has made it possible not only for the fast control of power flow in a transmission line, but also for the mitigation of subsynchronous resonance (SSR) in the presence of fixed series capacitors. SSSC is an emerging controller and this paper presents SSR characteristics of a series compensated system with SSSC. The study system is adapted from IEEE first benchmark model (FBM). The active series compensation is provided by a three-level twenty four-pulse SSSC. The modeling and control details of a three level voltage source converter-(VSC)-based SSSC are discussed. The SSR characteristics of the combined system with constant reactive voltage control mode in SSSC has been investigated. It is shown that the constant reactive voltage control of SSSC has the effect of reducing the electrical resonance frequency, which detunes the SSR. The analysis of SSR with SSSC is carried out based on frequency domain method, eigenvalue analysis and transient simulation. While the eigenvalue and damping torque analysis are based on linearizing the D-Q model of SSSC, the transient simulation considers both D-Q and detailed three phase nonlinear system model using switching functions.

Design and performance evaluation of subsynchronous current suppressor with SSSC

A long transmission line needs controllable series as well as shunt compensation for power flow control and voltage regulation. This can be achieved by suitable combination of passive elements and active FACTS controllers. In this paper, series passive compensation and series active compensation provided by a static synchronous series compensator (SSSC) are considered. This paper presents investigation of subsynchronous resonance (SSR) characteristics of the hybrid series compensated power system and proposes a novel method for the extraction of subsynchronous component of line current using filter. The extracted subsynchronous frequency component of line current is used to modulate the SSSC injected voltage which suppresses subsynchronous current in the transmission network. This novel technique is termed as Subsynchronous Current Suppressor (SSCS). The design of SSCS is based on damping torque analysis. The results show the effectiveness of SSCS in damping in SSR. The 3-phase model of the SSSC is based on the switching functions. By neglecting harmonics in the switching function, D-Q model is derived which is combined with similar models of the other system components for linear analysis. The results of the linear analysis are validated by carrying out transient simulation based on the detailed nonlinear models.

A review on damping of torsional interactions using VSC based FACTS and subsynchronous damping controller

Abstract Improvement in the power transfer capability and the system stability of long transmission lines by series compensation is a cost-effective solution. However, the Subsynchronous Resonance (SSR) due to series compensation leads to severe risk of Torsional Interactions (TI). This paper presents, a review on damping of torsional interactions using Voltage Source Converter (VSC) based FACTS with various Subsynchronous Damping Controllers (SSDC) proposed in the literature. This review can help researchers to make a comparative study of the impact of FACTS devices and various subsynchronous damping controllers on damping of subsynchronous oscillations.

Design of robust controller for VSC based HVDC using Genetic Algorithm

The Voltage Source Converter based HVDC provides asynchronous interconnection between two AC systems. The use of VSC HVDC enables independent control of real and reactive power. The VSC based HVDC transmission system consists of two converter stations connected by a dc cable/line. This paper presents modelling and the design of controller for VSC HVDC. The various operating cases of VSC HVDC are considered. In each case there are several controllers gains in HVDC link. A systematic approach is used for selecting the controller parameters and Genetic Algorithm (GA) is used for tuning the controller parameters. The various operating cases of VSC HVDC are considered in controller parameters optimization. The GA enables the usage of the same controller gains for all operating cases while maintaining the system stability.

Energy function based Fuzzy Logic Discrete control with STATCOM for stability improvement

Static Synchronous Compensator (STATCOM) is a Shunt active FACTS controller when connected at the mid point of the transmission line, it can improve voltage regulation, power flow and stability of the transmission systems. This paper analyzes the use of STATCOM with discrete control to improve the transient stability of power system. During transient period STATCOM is switched between inductive or capacitive or operating value and the reference value of reactive current is obtained from Fuzzy Logic based Discrete Controller (FLDC). The Fuzzy logic discrete controller is based on energy function. Transient simulation is carried out to analyze the system. The results of the case study system adapted from IEEE First Benchmark Model demonstrate the effectiveness of Fuzzy logic discrete controller in stabilizing the rotor angle oscillation. Linear analysis is performed on D-Q model of the system with STATCOM.

Design of Robust Current Controller for Two-Level 12-Pulse VSC-based STATCOM

The static synchronous compensator (STATCOM) is a shunt connected voltage source converter (VSC) based FACTS controller using GTOs employed for reactive power control. A typical application of a STATCOM is for 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. The PI controller-based reactive current controller can cause oscillatory instability in inductive mode of operation of STATCOM and can be overcome by the nonlinear feedback controller. The transient response of the STATCOM depends on the controller parameters selected. This paper presents a systematic method for controller parameter optimization based on genetic algorithm (GA). The performance of the designed controller is evaluated by transient simulation. It is observed that the STATCOM with optimized controller parameters shows excellent transient response for the step change in the reactive current reference. While the eigenvalue analysis and controller design are 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).