Series connected converter for control of multi-bus spacecraft power utility

The invention provides a power system using series connected regulators. Power from a source, such as a solar array, is processed through the regulators and provided to corresponding buses used to charge a battery and supply loads. The regulators employ a bypass loop around a DC--DC converter. The bypass loop connects a hot input of the converter to a return output, preferably through an inductor. Part of the current from the source passes through the bypass loop to the power bus. The converter bucks or boosts the voltage from the source to maintain the desired voltage at the bus. Thus, only part of the power is processed through the converter. The converter can also be used without the bypass loop to provide isolation. All of the converters can be substantially identical.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the field of power conversion and 
regulation and specifically to a power converter and system employing the 
converter. 
2. Description of the Related Art 
Spacecraft and other apparatus requiring electrical power are commonly 
provided with direct current power supply systems. A battery, generator, 
solar array, or other power source provides power to one or more buses at 
voltages required by various loads. Typically, power is processed through 
a converter that converts voltage from the source to a desired voltage and 
may also regulate the voltage and isolate the load from the source. For 
example, spacecraft use power from a solar array to charge a battery 
through a regulating converter. Power from the battery is supplied to high 
and low voltage buses through separate converters processing all of the 
power to! the buses. Processing full power generates substantial losses, 
taxing cooling systems and requiring cooling to be sized for relatively 
high peak loads. The converters must be sized to handle the full power of 
the power supply system. 
U.S. Pat. Nos. 3,480,789 to Binckley and U.S. Pat. No. 4,245,286 to 
Paulkovich show voltage regulators. U.S. Pat. No. 4,644,247 to Burmenko 
shows a regulated battery charging circuit. U.S. Pat. Nos. 3,740,636 to 
Hogrefe, U.S. Pat. No. 4,494,063 to Callen, U.S. Pat. No. 4,691,159 to 
Ahrens, U.S. Pat. No. 4,706,010 to Callen show power systems associated 
with solar cells, particularly for spacecraft. 
SUMMARY OF THE INVENTION 
The present invention provides a power supply system including an input 
bus, an output bus, and a return. The system is adapted for having a load 
connected between the output bus and the return. A power converter has a 
hot input connected to the input bus, a hot output connected to the output 
bus, a return input connected to the return, and a return output. A bypass 
loop connects the return output to the input bus. 
An inductor is connected in the bypass loop. A fuse is connected between 
the input bus and the hot input. A power source, such as a solar array, is 
connected to the input bus and the return. The power source can also be a 
battery or another bus. 
The system can also include a second output bus. The system is adapted for 
having a second load connected between the:second output bus and the 
return. A second power converter has a second hot input connected to the 
first output bus, a second hot output connected to the second output bus, 
a second return input connected to the return, and a second return output. 
A second bypass loop connecting the second return output to the first 
output bus. An inductor is connected in the second bypass loop. A first 
fuse is connected between the input bus and the first hot input. A second 
fuse is connected between the first output bus and the second hot input. 
The system also includes a third output bus. A third power converter has a 
third hot input connected to the second output bus, a third return input 
connected to the return, a third hot output connected to the third output 
bus, and a third return output. The system is adapted for having a third 
load connected between the third output bus and the return the third 
return output. The third converter is an isolating converter. 
The invention also provides a regulator that can be used in the power 
supply system according to the invention, for example, The regulator 
includes a converter having a hot input connection; a return input 
connection; a hot output connection; and a return output connection. The 
bypass loop connects the return output to the hot input connection. The 
inductor is connected in the bypass loop between the hot input connection 
and the return output connection. The converter includes a transformer 
with a secondary having a center tap, the return output being connected to 
the center tap. A pair of rectifiers are connected to outputs of the 
transformer. An LC filter is connected at the output of the transformer. A 
first pair of switches is adapted for alternately connecting the hot input 
connection to inputs of the transformer. A second pair of switches is 
adapted for alternately connecting the return input connection to the 
inputs of the transformer. An inverter control is adapted for alternately 
closing one of each pair of switches to alternately connect the hot input 
and return input to opposite inputs of the transformer. A LC filter is 
connected at the input connection. The converter is an isolating 
converter. 
The system and regulator according to the invention permits use of smaller 
converters for a given load. Losses are reduced and remain relatively 
constant for more efficient power conversion and cooling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a direct current; power supply system 10 is adapted 
for use in a spacecraft, such as a satellite, or other apparatus requiring 
DC power. The system 10 includes a battery bus 12, a high voltage bus 14, 
and a low voltage bus 16. "High" and "low" are relative terms for the 
particular application. Power is derived from a solar array 18 or other 
suitable source of direct current. The solar array 18 has a hot output 20 
preferably providing positive direct current at about 130 volts open 
circuit with a short circuit current of about 102.5 amps. In a spacecraft 
application, the solar array voltage will typically fall from 130 volts to 
about 90 volts during loading. Another output of the solar array 18 
defines a return 22, known in some systems as a common or ground. 
A storage battery 24 is connected between the battery bus 12 and the return 
22, preferably through a fuse 26. The battery is of any suitable type. In 
the spacecraft system 10, the battery 24 provides about 90 to 120 volts. 
High voltage loads 28 are connected between the high voltage bus 14 and 
the return 22 through suitable distribution means. The high voltage bus 14 
provides about 120 volts DC to the high voltage loads. Low voltage loads 
30 are connected to the high voltage bus 16, which is adapted to provide 
about 28 volts DC through suitable distribution means. 
A battery charger 32, such as a voltage regulator, is connected to provide 
power to the battery bus 12 at about 90 to 120 volts for charging the 
battery 24. The battery charger 32 includes a first power converter 34a 
having a hot input 36a, a return input 38a, a hot output 40a, and a return 
output 42a. The hot input 36a is connected to the solar array hot output 
20 through a fuse 44a. The return input 38a is connected to the return 22. 
The hot output 40a is connected to the battery bus 12. The return output 
42a is connected to the hot input 36a through the fuse 44a and an inductor 
46a in a bypass loop 47a, that is, the inductor is connected to the solar 
array hot output 20. The power converter 34a is described below with 
reference to FIG. 2. 
A high voltage bus regulator 48 is connected to provide power to a constant 
regulated high voltage bus 14. The high voltage bus regulator 48 includes 
a second power converter 34b having a hot input 36b, a return input 38b, a 
hot output 40b, and a return output 42b. The hot input 36b is connected to 
the battery bus 12 through a fuse 44b. The return input 38b is connected 
to the return 22. The hot output 40b is connected to the high voltage bus 
14, preferably through a fuse 50. The return output 42b is connected to 
the hot input 36b through an inductor 46b in a bypass loop 47b, that is, 
the inductor is connected to the battery bus 12. Thus, the battery charger 
32 and high voltage bus regulator 48 are series connected. The power 
converter 36b is described below with reference to FIG. 2. 
A low voltage bus regulator 52 is Connected to provide power to the low 
voltage bus 16. The low voltage bus regulator 52 includes a third power 
converter 34c having a hot input 36c, a return input 38c, a hot output 
40c, and a return output 42c. The hot input 36c is connected to the high 
voltage bus 14. The return input 38c is connected to the return 22. The 
hot output 40c is connected to the low voltage bus 16. The return output 
42c is connected to the low voltage loads 30 as a low voltage return. The 
power converter 36c is described below with reference to FIG. 2. 
Any suitable DC--DC power converter having desired isolation and voltage 
characteristics is suitable for use as the power converters 34a, 34b, 34c. 
Preferably, all of the power converters 34a, 34b, 34c are substantially 
identical. Thus, the converters are interchangeable providing economies of 
scale and fewer replacement parts. 
FIG. 2 shows an example of a suitable power converter topology that has 
worked effectively in practice. The power converter 84 includes the hot 
input 36, return input 88, hot output 40, and return output 42 previously 
discussed. A transformer 54 has a primary winding 56 with two inputs 58 
and a secondary winding 60 with two outputs 62 and a center tap 64. A 
first pair of switches 66 is connected between respective primary winding 
inputs 58 and the hot input 86. A second pair of switches 68 is connected 
between respective primary winding inputs 58 and the return input 88. The 
switches 66, 68 can be any electrically controllable switch having a 
suitable rating, such as field effect transistors. The switches 66, 68 are 
connected to be operated by an switch control, such as an inverter control 
70. The inverter control is adapted for alternately closing one of each 
pair of switches 66, 68 to alternately connect the hot input 36 and return 
input 38 to opposite inputs 58 of the primary winding. Thus, the inverter 
control 70 and switches 66, 68 invert direct current at the converter 
inputs 36, 38 to provide alternating current to the primary winding 56 
thereby inducing alternating current in the secondary winding 60. 
A pair of rectifiers 72, such as power diodes, are connected between the 
secondary outputs 62 to provide pulsating direct current. An LC filter 
including an inductor 74 and a capacitor 76 is connected to the rectifiers 
to provide relatively smooth direct current at the hot output 40. An LC 
filter 78, 79 is also provided at the inputs 86, 88. The output voltage at 
the hot output 40 depends on the input voltage at the hot input 86, the 
transformer configuration, and the wave form created by the inverter 
control 70 and switches 66, 68. The inverter can be adjusted to provide 
different output voltages. The converter power rating depends on input 
voltage, output voltage, and converter current limit. 
The center tap 64 is connected to the return output 42. The return output 
is so-called because it can be connected as a return for current supplied 
by the hot output 40, as shown for the low voltage bus regulator 52 in 
FIG. 1. However, in the battery charger 32 and high voltage ;bus regulator 
48 of FIG. 1, the return output 42 is connected to the hot input 36 
through the inductor 46 in the bypass loop 47 and, preferably, the fuse 
44. 
In operation, the solar array 18 charges the battery 24 through the battery 
charger 32. The battery 24 supplies power to the loads 28, 30 through the 
high and low voltage bus regulators 48, 52. The battery charger 32 and 
regulators 48, 52 provide desired voltage conversion, regulation, and 
isolation of the buses 12, 14, 16. 
A portion of the power through the battery charger 32 and high voltage 
regulator 48 bypasses the converter 34 through the bypass loop 47. The 
inductor 46 filters alternating current to prevent oscillations when the 
converters 34 are cascaded as shown. 
The inverter control 70 of the battery charger 32 can control the switches 
66, 68 to short the solar array 18, thereby bucking the array voltage to 
maintain a desired voltage at the battery bus 12 The converter 34a of the 
battery charger can also be used to boost the array voltage for charging 
above the open circuit voltage of the array up to the sum of the array 
voltage and converter voltage. When the converter 34a is not operating, 
the array voltage is clamped at the battery voltage and rises with the 
battery voltage to the open circuit voltage of the array 18. The battery 
charger 32 is controlled to provide a constant current to the battery bus 
12. 
The high voltage bus regulator 48 boosts the battery bus voltage, when 
necessary, to maintain 120.+-.3 volts at the high voltage bus 14. As an 
orbit progresses, the power processed by the converter 34a of the battery 
charger 32 increases as the battery is charged and the battery voltage 
increases. Accordingly, the power processed by converter 34b of the high 
voltage regulator 48 decreases as the battery voltage increases. Thus, the 
total losses of the converters 34a, 34b are relatively constant and 
substantially less than the losses for two converters processing full 
power. The constant losses provide constant loading for cooling systems. 
Since only a fraction of the power is processed through the converters, 
smaller converters can be used than would be required for full power 
processing. The fuses 44 are connected to remove the converters 34a, 34b 
from the system 10 if necessary. If the converters 34a, 34b are removed, 
the system 10 remains operational without the regulation provided by the 
converters. 
The low voltage bus regulator 52 is not series connected to provide full 
isolation from the high voltage bus 14. The converter 34c of the low 
voltage regulator 52 processes full power to provide regulated 28 volts at 
the low voltage bus 16. 
The present disclosure describes several embodiments of the invention, 
however, the invention is not limited to these embodiments. Other 
variations are contemplated to be within the spirit and scope of the 
invention and appended claims.