A novel control method to minimize distortion in AC inverters

In 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 current-mode control approach is proposed which tailors external ramp characteristics to achieve “perfect” transfer function linearity regardless of duty cycle, and guarantee sub-harmonic stability. Supporting mathematical analysis and prototype measurements are included. The method when applied to DC/DC converters provides fixed gain-bandwidth in continuous conduction mode over a broad line and load range