Active Voltage-Ripple Compensation in an Integrated Generator-Rectifier System

An integrated generator-rectifier system can produce high conversion efficiency and reduce the size of the active rectifier in high-power ac-to-dc conversion. A major disadvantage of this system is the use of bulky filter capacitors with passive rectifiers to obtain a low voltage-ripple dc bus. These filters are the main contributor to the overall system size, weight, cost, and failure, as well as to the low power factor at the ac ports powering the passive rectifiers. This article presents an alternative approach: integrating the function of the filter elements into the active rectifier. A voltage opposite the passive-rectifier ripple component is synthesized at the active-rectifier dc-side by modulating the ac-side current. Compensation occurs due to the series connection of the rectifier dc outputs. In addition, an overall control architecture is proposed to use the active rectifier both as a filter element and a dc-bus voltage regulator. Simulation on a 3-MW, 4.9-kV dc system shows the total dc-bus-voltage ripple factor is reduced by 57%, while the power factor at the passive-rectifier ac sides is 0.95. The proposed control architecture achieves regulation of the dc-bus voltage at variable dc-bus current and variable generator speed conditions. Experimental results corroborate the findings.