A series-connected boost regulator (SCBR) is, as its name suggests, an electronic circuit for boosting a power-supply voltage to a higher and regulated value. The distinguishing feature of an SCBR is an interconnection topology in which one utilizes the input/output dc-isolating quality of a dc-to-dc converter. (Other, similar terms that have been used to denote an SCBR include "series-connected converter," "series-connected boost converter," and "series-connected boost unit.")
SCBRs were conceived as building blocks of relatively inexpensive, modular power-management-and-distribution (PMAD) systems for future spacecraft. Potential terrestrial applications for the SCBR concept include output regulators and storage-battery chargers for solar photovoltaic arrays.
The top part of Figure 1 is a simplified schematic diagram of a typical dc-to-dc power converter, showing how dc isolation between the input and output sides is achieved by use of transformer coupling. The bottom part of Figure 1 illustrates the utilization of the same dc-to-dc converter in a basic SCBR, in which one connects the input "hot" terminal to the output return ("cold") terminal; in effect, the input and output are connected in series, so that their voltages add to yield a higher overall output voltage.
An important advantage afforded by an SCBR is the ability to use a dc-to-dc converter to regulate more power than it is rated to handle by itself, at an overall efficiency greater than that of the dc-to-dc converter by itself. Figure 2 illustrates the example of an SCBR that supplies a regulated potential of 28 Vdc to a load of 2.8 Ω (thus supplying a load current of 10 A). In this example, the available power-supply potential is 20 Vdc (unregulated), and one uses a dc-to-dc converter as a boost regulator to increase the load potential to the desired regulated 28 Vdc.
The dc-to-dc converter considered by itself is rated to put out a current of 10 A at a potential of 8 Vdc (thus, an output power of 80 W) while drawing an input current of 4.7 A at the supply potential of 20 Vdc (thus, an input power of 94 W). Under these conditions, its efficiency (output power÷ input power) is about 85 percent.
However, the dc-to-dc converter does not operate by itself. With respect to the load current, it is connected in series with the 20-Vdc power supply. As a consequence, it processes only a fraction of the total regulated power of 280 W delivered to the load; this is the sense in which the dc-to-dc converter can be regarded as regulating more power than it is rated to handle by itself.
The current drawn from the 20-Vdc power supply in this example is 14.7 A, comprising the load current of 10 A and the 4.7-A input current for the dc-to-dc converter. The total power consumed is thus 20×14.7 = 294 W. Then the overall efficiency (regulated output power ÷total power consumed) is about 95 percent, which is greater than the efficiency of the dc-to-dc converter considered by itself.
SCBRs can be built at relatively low cost because dc-to-dc converters are commercially available and relatively inexpensive. A basic SCBR can be used by itself or in combination with other building blocks (including other SCBRs). Other advantages of SCBRs include high power densities, adaptability to positive-ground power systems, and capabilities for high degrees of fault tolerance.
This work was done by Raymond F. Beach and Robert Button of Glenn Research Center and Andy Brush of Sverdrup Technolgy, Inc.
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