Pulse-width modulation (PWM) is the foundation of control in power electronics. Its design affects almost all aspects of converter operation, from steady-state and dynamic control performance to electromagnetic interference (EMI) and thermal design. The basic principle of commonly used PWM methods has been well established and easy to understand. Yet achieving optimal performance in terms of control, power quality and EMI requires in-depth understanding of the modulation process as well as its spectral and dynamic characteristics, which are mathematically much more involved due to the highly nonlinear nature of the PWM process.