Study of Single Pulse Width Modulated Inverter and Sinusoidal Pulse Width Modulated Inverter using Low Pass Filter and Comparison of the Respective Total Harmonic Distortion of Output Voltages using FFT Technique
Abstract- This paper highlights the problems associated with single pulse width modulation, the most important being high harmonic content in output voltage. A comparative study with Sinusoidal Pulse Width Modulation Technique is done highlighting the reduction in Total Harmonic Distortion of the output voltage waveform.
Keywords- Sinusoidal Pulse Width Modulation(SPWM), Total Harmonic Distortion(THD), Fast Fourier Transform(FFT) Analysis, Carrier Wave Frequency, Modulating Index(MI), Low Pass Filter(LPF).
The DC to AC power converters are known as inverters. In other words, an inverter is a circuit which converts a DC
power into an AC power at desired output voltage and frequency. The conversion is achieved by controlled turn-on
and turn-off devices like BJT’s, MOSFET’s, IGBT’s, etc or by forced commutated thyristors, depending on applications. Some of the important industrial applications of inverters are as follows:
- Variable speed AC motor drives.
- Aircraft power supplies.
- Uninterruptible power supplies (UPS).
- Induction heating.
- Battery vehicle drives.
- Regulated voltage and frequency power supplies, etc.
The output voltage waveform obtained from an inverter contain harmonics which is undesirable. The presence of harmonics reduces the power quality and hampers sophisticated electronic devices.
II. PULSE WIDTH MODULATED INVERTER
For internal control of an inverter, we use Pulse-width modulation technique . It uses a switching scheme within the inverter to modify the shape of the output voltage waveform.
- The advantage of using Pulse-width modulation technique is that the lower order harmonics in the output voltage gets eliminated .
- The filtering requirements are minimized as higher order harmonics can be filtered easily .
- The output voltage can be controlled easily by modifying the width of the pulses. There are various pulse width modulation technique (PWM) among which sinusoidal pulse width modulation (SPWM) is discussed here.
III. SINGLE PULSE WIDTH MODULATION
In Single-pulse width modulation, the gating signals are generated by comparing a rectangular reference signal with a triangular carrier wave thus producing only one pulse per half cycle of the output voltage.