How is small-signal modeling used for converter control design?

Small-signal modeling linearizes converter dynamics around an operating point for control design. State-space averaging: average switch states over one period, then linearize. Key transfer functions: control-to-output (duty cycle to output voltage), line-to-output (input voltage disturbance), and output impedance. PWM transfer function adds sampled-data effects at high frequency. Model verification compares predicted and measured frequency responses. Control design uses classical techniques (compensator pole/zero placement for desired crossover and margins) or modern methods (H-infinity for robustness). Model accuracy degrades near half switching frequency.