Explain sinusoidal PWM (SPWM) for voltage source inverters.

SPWM generates quasi-sinusoidal output by comparing a sinusoidal reference with a triangular carrier. When reference exceeds carrier, upper switch is ON; otherwise lower switch is ON. Modulation index ma = Vref_peak/Vcarrier_peak controls fundamental output magnitude: Vout1 = ma*Vdc/2 (for single-phase H-bridge). Frequency ratio mf = fcarrier/fref affects harmonic spectrum; odd mf places harmonics at integer multiples of carrier frequency. Three-phase SPWM uses three references 120 degrees apart. Space vector modulation offers better DC bus utilization.