Engineering Research Paper

       NATIONAL INSTITUTE OF INDUSTRIAL ENGINEERING

                                         PGDIE-42

       INDUSTRIAL ENGINEERING CONCEPTS ASSIGNMENT

                                                        

                                                                       

Title: COMBINED SYSTEM OF STATIC VAR COMPENSATOR AND ACTIVE POWER FILTER FOR HARMONIC SUPPRESSION AND POWER FACTOR IMPROVEMENT

Authors: T.MAHALEKSHMI* S. CHITRA**

*Assist Professor, Dept. of Electrical and Electronics Engineering,

Mepco Schlenk Engineering College, Sivakasi-626005, TamilNadu, India.

**Assist Professor, Dept. of Electrical and Electronics Engineering,

                                       Government College of Technology, Coimbatore, TamilNadu, India

                                                                                                                            

                                           Submitted to                                                                       Submitted by

                                               Narayana Rao K.V.S.S.                                        Rahul Awadhiya, 71

                        Professor, NITIE, Mumbai 

        Introduction

Power quality problems are common in most of the commercial, industrial and utility networks. Harmonics and reactive power are two of the serious problems associated with the grid. They are caused by non-linear loads, including saturated transformers, arc furnaces, and semiconductor switches. The presence of harmonics and reactive power in the grid is harmful, because it will cause additional power losses and malfunctions of the grid component.

The Shunt active power filter compensates current harmonics by injecting equal-but-opposite harmonic compensating current. In this case the shunt active power filter operates as a current source injecting the harmonic components generated by the load but phase shifted by 1800. This principle is applicable to any type of load considered as a harmonic source. Moreover, with an appropriate control scheme, the load power factor can be compensating by active power filter.

To prevent the inflow of harmonic and reactive currents and to improve the operating ability of the transmission systems, a kind of Flexible AC Transmission System (FACTS) has been proposed. The Static VAR compensator (SVC) is an important component of FACTS. It usually installs in power transmission systems and serves in various ways to improve the system performance. By the rapid control of their reactive power output, the SVCs regulate system voltages, improve transient stability, correct power factor, reduce temporary over voltages, and damp synchronous resonances. Usually, an SVC is composed of a Thyristor-Controlled Reactor (TCR) and Fixed Capacitors (FCs). The FCs is often tuned in series with inductors to act as Passive Power Filters (PPFs) in the characteristic harmonic frequencies of the TCR.

 

                       

            Methods for Compensating VAR

Control method of SVC

The SVC mainly regulates system voltages and correct power factor. A non-linear PI controller is proposed to improve the dynamic response, decrease the overshoot of transient response and decrease the steady-state error of SVC. The Kp and KI values of the non-linear PI controller is optimized using the Simplex algorithm.

              

Result

The parameters for the simulation circuit are shown in Table 1.

       

Simulation results without compensating device

The current and voltage waveforms (before compensation) are shown in Figures. Due to non-linear load the supply and load currents contain harmonics so it becomes non-sinusoidal. The supply and load voltages are sinusoidal. The Total Harmonic Distortion of the supply current is 27.84%. The Total Harmonic Distortion analysis is shown in Figure.

      

         

      

Simulation results (after compensation)

The compensating current generatedby the Shunt Active Power Filter is shown in Figure. The compensating current Suppress the harmonic current drawn from the supply side and make current sinusoidal. 

         

     

After compensation the supply current become sinusoidal which can be shown in Figure. The supply and load voltages after compensation is shown in  Figures. After compensation the supply volage and load voltage are sinusoidal without any distortion.

        

         

The simulated values of the three phase systemwith and without any compensating devices are shown in Table 2.

 

    

    

After compensation the Total Harmonic Distortion of the Supply current can be reduced to 1.48% from 27.84%. The power factor of the system without any compensating devices is 0.7961. SVC is the effective compensating devices. After implementation of the combined system the power factor can be improved to 0.9393.

Conclusion

In this research  work, the combined system of a classical SVC and an APF has been tested and analyzed. The system have eliminated the harmonics generated by non-linear loads and there by improved the power factor in power system. The TCR in the SVC is star connected; hence the third order harmonics can be eliminated. Moreover the active power filter

topology has been adopted to suppress the harmonics generated by TCR and reduce the resonance between the grid and PPF. Separate control circuits for SVC and APF has been implemented in this work. The performance of the active power filter can be improved

by using the combined system. Also the harmonics can be reduced below 5% as per the IEEE standard.

Reference

 http://www.jee.ro/covers/editions.php?act=art&art=WY1272442948W4bd7f044ecfcb