MODULATION INDEX AND SWITCHING FREQUENCY EFFECT ON SYMMETRIC REGULAR SAMPLED SPWM

Abstract

Inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC). The output voltage and frequency of the inverter can be changed. There are different modulation methods used in inverter control. Some of these methods can be applied digitally, some analogously. Classical Sinusoidal Pulse Width Modulation (SPWM) is a method normally performed analogously. Known methods for digitally applying this method are regular sampled sinusoidal PWM methods. In this study, the implementation of symmetric regular sampled sinusoidal PWM method is discussed. Two fundamental factors that are effective in this kind of modulation methods are investigated by harmonic analysis of switching frequency and modulation index, inverter pole voltage and line voltage. From an inverter that supplies a three-phase RL load, the fundamental component and the generated harmonics are investigated using the Symmetric Regular Sampled SPWM method with five different switching frequencies and three different modulation index values. Modulation index is investigated for linear region and over modulation regions. Low, normal and high switching frequency samples are also chosen for switching frequency. The obtained harmonic analysis results are presented in the study.

Keywords

• Modulation index,Switching frequency,Inverter,Symmetrical regular sampled SPWM

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