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 converters, provides fixed gain bandwidth in the continuous conduction mode over a broad line and load range. Index Terms - Harmonic distortion, inverters, modeling, MOSFET amplifiers, power control, power conversion harmonics, pulse-width-modulated inverters.