Simulation of STATCOM for Improving Power Quality Under Induction Motor Loads

Simulation of STATCOM for Improving Power Quality Under Induction Motor Loads
Authors:PALUTLA GOPI SAI SIMHA GUPTA

Abstract: Adjustable speed drives (ASD) employing induction motors are widely used in the industrials and process control in the form of varied applications such as fans, compressors, pumps etc. They are energy efficient and can result in substantial energy saving when properly installed. However, they inject high harmonic content into current drawn from the ac system. This paper deals with the application of a STATCOM for compensation of such loads. The MATLAB/Simulink based models are developed for adjustable speed drive loads. The analysis is carried out with and without STATCOM. The results shown in the paper prove that STATCOM can be used as a good harmonic filter. Cascaded multi-level converter based STATCOM (CMCSTATCOM), with a topology of modular-cascaded structure, has a wide prospect of applications in both transmission and distribution system. Under the background of application of STATCOM in high voltage power grid, there are many advantages of CMC-STATCOM compared with other kinds of STATCOM. On the basis of mathematical model of main topology, the states feedback decoupled reactive power control strategy based on the d-q coordinate system is studied in this paper, together with the application principle of carrier phase shift PWM modulation method in CMC. The balance of DC bus voltage is a key factor to the stable operation of devices In this paper, the hierarchical control method is used to achieve a balance of DC bus voltage, and it involves the DC bus voltage overall control and individual control of each cascade module. 

Keywords: Cascaded H-Bridge, Multilevel Converter, STATCOM, Drives. 

INTRODUCTION 

       Harmonic disturbances and their study has been a topic of research and today we can find a whole array of devices used to mitigate such problems. The ever growing use of power electronic based systems has aggravated the harmonics problem. These devices themselves require clean and good power quality but inject undesirable harmonics into the supply system as well as the neighboring loads. Literature review [1-6] indicate the problems, effects and solutions for harmonics in power systems. Different type of low voltage loads can also introduce harmonics in the power network and adversely effect on the overall performance and operation of the power system. In this paper, use of custom power device for harmonic reduction is studied. There are three kinds of structure of the commonly used multi-level converter, which are flying-capacitor multi-level converter [6], diode-clamp multi-level converter [7], and Hbridge cascade multi-level converter. Cascaded multi-level converter has a lower output of waveform harmonic content, save more switching devices and has a more simple control system than other kinds of multi-level converter. Moreover its H-bridge modules have a compact structure, flexible configuration and reliable performance 

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