MATLAB SIMULINK Based Model of Single-

Machine Infinite-Bus with TCSC for Stability

Studies.

EEE227 AC MACHINES

A project Report

Submitted To:

Prof. Srikanth Gollapudi

Submitted By:

1. Shivangi R Tripathi (13BEE1135)

2. Shreya Sinha (13BEE1136)

INDEX

1. Abstract

2. Introduction

3. Modeling of generator

4. TCSC and its structure

5. Simulink Model

6. Simulation Result

7. Conclusion

Abstract

Our project presents a systematic procedure for modeling and simulation of a single-machine infinite-bus power system installed with a thyristor controlled series compensator (TCSC).We used TCSC so that impact of TCSC on power system stability can be more reasonably evaluated. The model of the example power system is developed using MATLAB/SIMULINK and the system results are being presented to validate the effectiveness of using TCSC on power system stability.

INTRODUCTION

For the small signal stability studies of a single-machine infinite-bus (SMIB) power system, the linear model provides reliable results. It has also been successfully used for designing and tuning the classical power system stabilizers (PSS). Although the model is a linear model, it is quite accurate for studying low frequency oscillations and stability of power systems. These models are the popular tools amongst power engineers for studying the dynamic behavior of synchronous generators, with a view to design control equipment.

Alternator usually has two types of rotors.

1. Salient pole type

2. Smooth cylindrical type

A multi-polar machine with cylindrical rotor has a uniform air gap, because of which its reactance remains the same, irrespective of the spatial position of the rotor.

However, a synchronous machine with salient or projecting poles has non-uniform air gap due to which its reactance varies with the rotor position. Consequently, a cylindrical rotor machine possesses one axis of symmetry (pole axis or direct axis) where as salient pole machine possesses two axes of geometric symmetry.

1. Field pole axis, called direct axis or d-axis and

2. Axis passing through the center of the inter polar space called quadrature axis or q-axis.

Because of difference in reactance between the poles of a Salient Pole type rotor different mmf links to the two axes.

Consecutively,

1. Armature current Ia can be resolved into two components i.e. Id perpendicular to Eo and Iq along Eo.

2. Armature reactance has two components i.e. d-axis armature reactance - Xad associated with Id and q-axis armature reactance - Xaq linked with Iq.

Modeling the Synchronous Generator Infinite-bus Power System.

In our project we have used linear block model to calculate various machine parameters which includes Id, Iq, E'd (d-axis voltage), E'q (q-axis voltage), vt, Efd (excitation system voltage) and Pe.

The electrical power Pe and terminal voltage vt are expressed as-

Pe = E'q iq + E'd id + (x'd - x'q) id iq

vt = sqrt [((-xe id + Eb cosδ)^2)+((xe iq–Eb sinδ)^2)]

For a lossless network, the stator algebraic equations and network equations are represented as-

vq = E'q + x'd id and vd = E'd − x'q iq --(i)

vq = −xe id + Eb cosδ and vd = xe iq − Eb sinδ --(ii)

Solving above equations we get,

Id = (Eb cosδ - E'q)/ (xe+x'd)

Iq = (Eb sinδ + E'd)/ (xe+x'q)

Modeling of TCSC and its structure

Thyristor controlled series compensator is a Flexible AC Transmission System. Reactance-adjusting of TCSC is a complex dynamic process. Effective design and accurate evaluation of the TCSC control strategy depend on the accuracy of modeling of this process.

It has been in use for many years to increase line power transfer as well as to enhance system stability.

The basic module of TCSC is shown below-

It consists of three components: capacitor banks C, bypass inductor L and bidirectional thyristors T1 and T2.

The structure of TCSC-based damping controller is such that we modulate the reactance offered by the TCSC. The input signal of the proposed controllers is the speed deviation (∆ω), and the output signal is the reactance offered by the TCSC (Xtcsc). The structure consists of a gain block with gain KT, a signal washout block and two-stage phase compensation blocks. The signal washout block serves as a high-pass filter, with the time constant TWT, high enough to allow signals associated with oscillations in input signal to pass unchanged.

SIMULINK model for calculation of id, iq , E' d , E' q and Pe

Simulink model of SMIB with TCSC controller

SIMULATION OUTPUT –

Calculation of E’d, E’q, Id, Iq, Vt, E fd and Pe:

Simulation of SMIB with TCSC

CONCLUSION

The MATLAB/SIMULINK model of a single-machine infinite-bus power system with a TCSC controller provides a means for carrying out power system stability analysis and for explaining the generator dynamic behavior as affected by a TCSC. This model is far more realistic compared to the model, since the synchronous generator with field circuit and one equivalent damper on q-axis is considered. Further, for the TCSC controller design problem, a parameter-constrained, time-domain based, objective function, is developed to improve the performance of power system subjected to a disturbance. The simulation results show that, the genetically tuned TCSC controller improves the stability performance of the power system and power system oscillations are effectively damped out. Hence, it is concluded that the proposed model is suitable for carrying out power system stability studies in cases where the dynamic interactions of a synchronous generator and a TCSC are the main concern.