IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 10, Issue 4 Ver. III (July – Aug. 2015), PP 94-97 www.iosrjournals.org DOI: 10.9790/1676-10439497 www.iosrjournals.org 94 | Page Strategies for Eliminating Harmonics in an Inverter AC Power Supply Nweke F. U. Industrial Physics Department, Ebonyi State University, Abakaliki, Nigeria. Abstract: An intensive effort has been made to articulate the strategies of eliminating or reducing harmonics in the output of an inverter circuit. An inverter is a circuit that converts direct current, dc to alternating current, ac which power most of domestic appliances. The output of this conversion is not free from harmonic distortion. Fourier series expression of the modulating output voltage waveform was analyzed. The amplitude of the fundamental frequency is controlled by adjusting  and its harmonic content can be controlled by adjusting the , which makes the cosine(s) term of the output voltage to be zero. The elimination is important as it helps to safe guide our electronics devices from failure or burnout. Key words: Harmonics, Inverter, direct current, non-sinusoidal, power system, distortion I. Introduction Harmonics are produced by rapid rise of current, either in positive or negative direction. This results to non-sinusoidal nature of the waveform of the output of an inerter voltage source. Square waves and pulse wave produce a rapid and abrupt rise in this type of waveform [ 1,2,3,5 ]. Harmonics currents are the results of non-linear loads demanding a current waveform different from the shape of applied voltage wave. The non-linear load devices includes solid state power switching devices such as diodes, thyristors, SCRs or transistors that converts dc power by drawing the current in pulses. These semiconductor devices forms the majority of electronic component used in electronic devices. Harmonics in power circuit are frequencies that are integer multiples of fundamental frequency generated by non-linear electrical and electronic equipments. The fundamental frequency (i.e. 50 or 60 th ) combines with the harmonic sine wave to form repetitive, non-sinusoidal distorted wave shapes [2,3,4]. Nature of Harmonics Generally, in any facilities, the voltage supplied by a power system is not a pure sine wave. Rather, it usually possesses some amount of distortion, which has a fundamental frequency and harmonics at that frequency. Harmonics produced with even number (i.e. 2,4,6,8, etc) are referred to as even harmonics and those derived from odd numbers are referred to as odd harmonics. Also harmonics produced above the original frequency is called upper harmonics and that below the original frequency are called lowe harmonics. Harmonic Current and Voltages Harmonic current are as a result of non-linear loads demanding a current waveform different from the shape of applied voltage wave. Non-linear load devices are those that switch the current ‘on’ and ‘off’. These devices includes solid state power switching devices such as diodes, thyristors, SCRs or transistors that convert direct current, dc power by drawing the current in pulses. Harmonics in power circuit are frequencies that are integer multiplies of a fundamental generated by non-linear electrical and electronics equipments. The fundamental frequency (i.e. 50 or 60 th ) combines with the harmonics sine wave to form repetitive, non- sinusoidal distorted wave shapes. However, contemporary electronic loads have different current and voltage wave shapes. For instance, the voltage may still appear to be sine wave, but the current waveform appears peaked, as if squeezes together. Such kind of load contains what is called switching power supply. Total harmonic distortion (THD) This is the measure of the amount of distortion produced as current flows from the power line. The THD value is the effective value of all harmonic currents added together, compared with the value of the fundamental current. The THD is used to qualify the non-sinusoidal property of a waveform. This can further be expressed as the ratio of the root mean square value of all the fundamental frequency terms to the root mean square value of the fundamental terms [2, 4].