Author Topic: Mitigation of Harmonics in Distribution System Using D - STATCOM  (Read 4013 times)

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Mitigation of Harmonics in Distribution System Using D - STATCOM
« on: December 13, 2011, 09:09:55 am »
Author : E.Rambabu, E.Praveena, Dr.P.V.Kishore
International Journal of Scientific & Engineering Research Volume 2, Issue 11, November-2011
ISSN 2229-5518
Download Full Paper : PDF

Abstractó This paper deals with the performance, analysis of, operating principles of a new generation of power electronics based equipment called Distribution Static Compensator (D-STATCOM) aimed at enchancing the reliability, and quality of power flow in low voltage distribution network. The model is based on the Voltage Source Converter (VSC) principle. The D-STATCOM injects a current into the system to mitigate the voltage sags.LCL Passive Filter was then added to D-STATCOM to improve harmonic distortion and low power factor.

Index Termsó D-STATCOM, Power Quality, Voltage sag, Voltage source converter, harmonic distortion 

1   INTRODUCTION                                                                      
In the early days of power transmission in the late 19th      century problems like voltage deviation during load changes and power transfer limitation were observed due to reactive power unbalances. Today these Problems have even higher impact on reliable and secure power supply in the world of Globalization and Privatization of electrical systems and energy transfer. The development in fast and reliable  semiconductors devices (GTO and IGBT) allowed new power electronic Configurations to be introduced to the tasks of power Transmission and load flow control. The FACTS       devices offer a fast and reliable control over the transmission parameters, i.e. Voltage, line impedance, and phase angle   between the sending end voltage and receiving end voltage. On the other hand, the custom power is for low voltage   dis-tribution, and improving the poor quality and reliability of supply affecting sensitive loads. Custom power devices are very similar to the FACTS. Most widely known custom power devices are DSTATCOM, UPQC, DVR among them DSTATCOM is very well known and can provide cost effective solution for the compensation of reactive power and unbalance loading in distribution system

The performance of the DSTATCOM depends on the control algorithm i.e. the extraction of the current com-ponents. For this purpose, there are many control schemes, which are reported in the literature, and some of these are instantaneous reactive power (IRP) theory, instantaneous compensation, instantaneous symmetrical components, synchronous reference frame (SRF) theory, computation based on per phase basis, and scheme based on neural network. Among these control schemes, instantaneous reactive power theory and synchronous rotating reference frame are most widely used. This paper focuses on the compensating the voltage sag, swells and momentary interruptions.

In this paper, the configuration and design of the DSTATCOM with LCL Passive Filter are analyzed. It is      connected in shunt or parallel to the 11 kV test distribution system. It also is design to enhance the power quality such as voltage sags, harmonic distortion and low power factor in distribution system.

2.1 Voltage Disturbances
   Voltage sag or dip represent a voltage fall to 0.1 to 0.9 p.u. and existing for less than one minute and voltage swell is the rise in voltage of greater than 1.1 p.u. and exists for less than one minute.
2.2 Voltage Cintrol by Reactive Power Compensation

First, we consider an uncompensated line.The current drawn by a load depends on the load itself and the line vol-tage. The current engenders the voltage drop in the transfor-mer and the line reactance. It results in decrease in transmis-sion voltage VT and distribution voltage VD. Figure 2.1 shows the vector diagram of a single load center connected to un-compensated line. The voltage drop in the line mainly de-pends on the current taken by the load as well as the resis-tance and inductance in the line.

It can also be seen that the angle between the voltage and the current is playing a major role in maintaining the voltage. Let us consider the supply voltage is E. Now due to the voltage drops IR and IX the load voltage is V.

It is possible to bring V=E, just by making the current to lead so that the vector diagram will get modified as shown in figure 2.2.  i.e by the use of shunt compensation (either at the transmission line or at the distribution line) the voltage at the load end can be regulated.

The same principle can be used in case of capacitive load also. If the load is capacitive, a lagging current will help in regulation of voltage.

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