A novel control method to minimize distortion in AC inverters

In pulse-width-modulation (PWM) AC inverters, the duty-cycle modulator transfer function must be highly linear to achieve low distortion. Current-mode (CM) control, inherently nonlinear, is needed to actively "damp" otherwise high-Q LC noise-reduction filters. A novel CM control approach is proposed which tailors external ramp characteristics to achieve "perfect" transfer function linearity-regardless of duty cycle-and guarantee subharmonic stability. Supporting mathematical analysis and prototype measurements are included. The method, when applied to DC/DC power converters, provides fixed gain bandwidth in the continuous conduction mode over a broad line and load range.