Abstract
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.
Highlights
H IGH power ac-to-dc conversion is essential for emerging applications, such as wind-energy production [2]–[5], and electric-ship power grids [6], [7]
The ripple factor, defined as the ratio between the rms value of the ac component and the dc component of the dc-bus voltage, is 1.2%, the power factor at the ac port connected to the passive rectifier is 0.8
Without compromising the dc-bus voltage quality, the filter capacitor could be eliminated by introducing appropriate phase shifts between different ac ports connected to the passive rectifiers [19]
Summary
H IGH power ac-to-dc conversion is essential for emerging applications, such as wind-energy production [2]–[5], and electric-ship power grids [6], [7]. The ripple factor, defined as the ratio between the rms value of the ac component and the dc component of the dc-bus voltage, is 1.2%, the power factor at the ac port connected to the passive rectifier is 0.8 This low power factor leads to generator overdesign to accommodate an increased requirement in rms current. Without compromising the dc-bus voltage quality, the filter capacitor could be eliminated by introducing appropriate phase shifts between different ac ports connected to the passive rectifiers [19] This approach requires either a speciallydesigned generator winding layout [7], [20] or by using multiple machines [21].
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