5.1 A New Class of AC/DC Converter The development of this new class AC/DC converter topology [13] arose because of the stringent set of requirements that prevail for advanced space power systems such as Space Station. These converter topologies convert high frequency AC voltage to controlled output DC voltage while drawing close to sinusoidal input current with a near unity power factor. These topologies utilize only one conversion stage which results in maximum efficiency, low weight and volume. Also the operating frequency of the converter is constant and synchronized with the input frequency. Together with the distortion-less input current and constant frequency, the EMI/EMC requirements are minimized. Amongst various topologies, two types of AC/DC converter have been studied. The feature of both types of converter are given as follows: 5.1.1 Type-1 Converter. A block diagram of Type-1 converter is shown in Fig. 25(a). The performance of this converter has been evaluated in [14]. Figs. 25(b) and (c) show the input and output current and voltage waveforms under turn-on transients and steady-state conditions. The following are the main features and limitations of the Type-1 converter: Main Features (1) High efficiency (96%). (2) Close to unity power factor (0.98). (3) Low total harmonic distortion of input current (2%). (4) Low mass density (3.5 kg/kW). (5) Low input surge current (150% for 4 cycles). Limitations (1) Limited output voltage variation (about 40%). (2) No natural short circuit protection. 5.1.2 Type-2 Converter. A block diagram of Type-2 converter is shown in Fig. 26(a). Various variables of the converter for turn-on transient and steady-state conditions are shown in Fig. 26(b) and (c). The main features and limitations of the converter are given below: Main Features (1) High efficiency (94%). (2) Close to unity power factor (0.98). (3) Low total harmonic distortion of input current (5%). (4) Low mass density (4.0 kg/kW). (5) Slow build-up of input current (no surge current). (6) Inherent short circuit protection. Limitations (1) Input power factor decreases as output voltage is lowered at the constant output current. 6 Conclusions In this paper DC/AC, DC/DC and AC/DC power conversion techniques have been investigated for an advanced high power space application. Resonant mode inverter/ converter topologies have been comprehensively analyzed for these power conversions as they have high efficiency, low mass, low EMI and high reliability. For each class of converter topology, the following conclusions are drawn.
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