Low-THD Three-Leg Inverter with Variable Modulation Index

Simulation of a three-phase inverter using unipolar SPWM in MATLAB with FFT-based THD measurement and waveform analysis.

This model implements a three-phase voltage source inverter controlled using the unipolar sinusoidal PWM (SPWM) technique. Three sinusoidal reference signals displaced by 120 degrees are compared with a high-frequency carrier to generate gate pulses for the inverter switches. The method reduces harmonic content and switching losses compared with conventional bipolar modulation.

The simulation includes PWM generation, inverter power stage, and measurement blocks to observe phase voltages, currents, and waveform quality. The structure is arranged so that reference generation, modulation, and power conversion stages can be studied independently.

Main features

• Three-phase voltage source inverter
• Unipolar sinusoidal PWM generation
• Three-phase reference generation (120° phase shift)
• Measurement of output voltages and currents
• Suitable for studying PWM techniques and inverter operation