297 Jyoti Lalotra, Abhinav Sharma, Randeep Singh Chib and Parveen Lehana, “Investigation of harmonic distortion for frequently changing input voltage”, Journal of Scientific and Technical Advancements, Volume 1, Issue 3, pp. 297-302, 2015. International Journal of Scientific and Technical Advancements ISSN: 2454-1532 Investigation of Harmonic Distortion for Frequently Changing Input Voltage Jyoti Lalotra 1 , Abhinav Sharma 2 , R. S. Chib 3 , Parveen Lehana 4 1 Department of Electrical Engineering, IECS Polytechnic, J&k, India 2 Arni University, H.P, India 3 SKUAST-J, J&K, India 4 Department of Physics & Electronics, University of Jammu, India Email address: 1 jyotilalotra05@gmail.com, 2 abhinavsangotra@gmail.com, 4 pklehana@gmail.com Abstract—This paper present the concept of improving harmonic distortion in power systems. Investigations were carried out for studying the effect of range dependent voltage switching and random voltage switching (sudden changes) in the input line voltage on the harmonic distortion at the output of the system. The analysis of the results showed that the insulated gate bipolar transistor (IGBT) based power system using the concept of switching resistor is capable of reducing harmonic distortion on the input power lines introduced because of external or internal load conditions. Harmonic distortions in the input and output of the conventional systems are estimated and compared. Reduction in the total harmonic distortion (THD) was also investigated for the proposed IGBT based power system. Keywords—Harmonic; IGBT; total harmonic distortion; dsPICmicrocontroller; signal processing technique; power system. I. INTRODUCTION n the last couple of decades harmonics have become a major power quality problem in electric power systems. It is important to identify the harmonic sources in the system to solve and prevent harmonic related problems [1], [2]. Power systems with low harmonic distortion are the key requirement in the modern electronic power systems. Mostly, the power systems are based on switching of the transformer tapings for changing the output voltage. The switching of tapings also introduces distortion in the output. In this paper novel approach using a switching resistor is proposed for reducing the distortion. Investigations are carried out to analyze the effect of load on the IGBT based power system developed using the concept of switching resistor. The scope of this research paper is to evaluate the harmonic distortion in modern power systems under different load conditions [3-15].It has been observed from the literature review that more sophisticated systems are designed using IGBTs and dsPIC controllers. These systems may introduces or improve the amount of harmonic distortion in the output due to fast switching. The objective is to study the harmonic distortions of such systems as a result of varying the loads connected at the output. The research work is carried out to investigate the effect of varying voltage due to range dependent voltage switching and random voltage switching keeping inductance, capacitance and resistance are constant on the designed power system. Signal processing technique is used to calculation of THD. II. METHODOLOGY The figure 1 shows the block diagram of the system. It consist of six blocks namely variac, multimeter, power system, series combination of RLC load, load voltage level shifting, sound card with PC and signal processing unit. Input supply is given to variac ranging from 0 to 250 volt which is connected to the system for variation of voltage and also connected to the multi-meter for observing the input voltage. The output from the variac is applied to power system circuit. Power system block contains voltage measurement circuits; microcontroller based stabilization and input voltage level shifting. The voltage measurement circuit which consists of current transformer stabilizes the voltage. Fig. 1. Block diagram of the experiment. The microcontroller based stabilizer whose, main function to elevate or drop in the input voltage caused by the fluctuations are stabilized which also consists of microcontroller and driver circuits. The controller used in this circuit is DSPIC controller dsPIC30F2010. All decisions regarding stabilization of the power are taken by the microcontroller. The controller is connected to the stabilization block which contains IGBT (CT60), TL3842P current mode PWM controller, TLP250 gate driving circuit of IGBT and other peripheral devices through an isolator circuit consisting of HEF4050B buffer HEX non inverting buffer isolators and IRFBE30 MOSFET. The output from power system block is applied to load. Load consists of series combination of power resistor, capacitor and inductor. These three combinations are used in the experiment. The input and I