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Figure 94.- Functional block diagram of 30 V dc converter.

The main winding of the transformer fed a full-wave rectifier and an LC filter, and the output from the two converters was combined through blocking diodes to provide a single 30 V dc output. The output voltage of the converters was not regulated. Regulation was dependent on the internal impedances of the converter and the regulation of the redundant 55.2 V dc bus. A 5-W resistive load was applied as a minimum load on the 30 V dc output bus. The load was located on the structure in a cable harness. Its purpose was to condition output capacitors in the 30 V dc converters so that the output voltage of the units was at specification for any load additional to the minimum load. The output voltage rose in open-circuit units. Figure 95 shows the variation of the 30 V dc converter output voltage and its efficiency with load.

The next four paragraphs describe PWRS subassemblies whose primary function was not power conditioning but rather housing electronics that perform a variety of functions required for power management and power distribution. They contained failure sensing circuitry and means for activating automatic

Conv output load, W

Figure 95.- Typical 30 V dc converter output voltage and efficiency as function of load.

Conv output load, W

Figure 95.- Typical 30 V dc converter output voltage and efficiency as function of load.

corrective circuitry, contained isolation diodes and fuses, received special status signals, and contained elements that related the PWRS to VO commands, switching, and telemetry.

Most of the contents of the battery electronics subassembly related to battery functions. (See fig. 96.) The one exception was that it contained one of the two redundant 30 V dc bias supplies. The other 30 V dc bias supply was in bay 12 in the power distribution subassembly. The 30 V dc bias supply redundant circuit was one of two in the PWRS, four redundant supplies in all, that converted 55.2 V dc redundant bus power to that at 32.2 V dc ± 6 percent. All the supplies operated continuously and their outputs were connected in parallel. As the command power supply, its regulated output served the CCS as its power source to activate spacecraft relays. The battery chargers also used the 30 V dc bias supply to power relays for the automatic transfer to low rate. The discharge path of each battery was isolated from the unregulated dc bus with quad connected redundant diodes that were located in the battery electronics subassembly. The battery electronics subassembly also contained the following switching functions:

Internal power: A motor-driven switch was used to connect and disconnect the batteries from the spacecraft during ground tests. The switch was activated by ground support equipment through the V S/C umbilical, and the flight command system had no control over its functions. One of the major prelaunch events was to transfer the VO power source from external power to its batteries by means of this switch. This event occurred 7 min before lift-off, and the switch then remained in this position for the balance of the mission.

Figure 96.- Functional block diagram of battery electronics subassembly.

Battery charger select switch: Relays K6 and K7 in the battery electronics subassembly could be commanded to select the charger for each battery, although charger A was expected to charge battery 1 and charger B to charge battery 2 for the entire mission. But in the event of a charger failure, the remaining unit was used to sequentially charge one then the other battery.

Battery select switch: Relays K8 and K9 in the battery electronics subassembly could be commanded to connect either or both batteries to the unregulated dc power bus. This design permitted a discharged battery to be recharged isolated from the V S/C and from the possibility of an unscheduled discharge sequence. The discharge path of both batteries could not be simultaneously disconnected from the unregulated bus. VO telemetry indicated the status of the K8 and K9 relays.

Boost mode switches: The battery electronics subassembly also contained relays that controlled boosting, a PWRS feature that automatically selected a more favorable power subsystem operating point. The K1 relay enabled or inhibited the boost mode upon command and simultaneously enabled or inhibited the CCS share mode correction routine. This relay was enabled during the mission. During the boost sequence, the K2 and K3 nonlatching redundant relays in the subassembly were repetitively actuated by the share mode detector.

Battery test loads: The K4 and K5 relays in the battery electronics subassembly connected 30-il resistive loads to the batteries for special battery operations. The loads could be used to safely investigate the condition of a battery or aid in battery reconditioning. The K4 and K5 relays plus the K8 and K9 relays could be commanded in a manner that connected either load to one battery or both loads in parallel (15 Q) to one battery. The test loads were resistors that wore physically located in a cable trough. VO telemetry indicated the status of the K4 and K5 relays.

Much of the solar-array electronics subassembly was concerned with solararray functions, but it also contained switching controls for the VLC, XTXS, and RES, telemetry sensors, and fuses. (See fig. 97.) This subassembly contained the 40 isolation diodes used in the circuit of each of the 40 sections in the solar array. The purpose of the isolation diodes was to prevent a faulty subpanel section from loading the others. On separate commands, the Kl relay in this subassembly switched raw power to the VL regulator 1, the relay K2 switched raw power to VL regulator 2, the K3 relay switched raw power to the RFS TWTA power converter, and the K4 relay switched raw power to the XTXS. This subassembly contained the circuit that isolated the unregulated power bus return from chassis ground, 3.01 kil in parallel with a 0.01-mF capacitor. The circuit current limited any array or battery short to chassis, and it also shunted to chassis ac noise on the unregulated dc bus. The subassembly provided the tie point for the chassis grounds of this unit, the two battery chargers, the 30 V dc converter, and the bay 10 electronic case chassis.

pant' 1

pant' 1

Figure 97.- Functional block diagram of solar-array electronics subassembly.

Figure 98 is the functional block diagram of the power control subassembly. This subassembly contained the redundant fail sensing circuit that monitored the output of the main power chain. Sensing a failure, this circuit activated redundant relays, also in this subassembly, that connected the system to the standby power chain. The other contents of the power control subassembly are as follows:

Figure 98.- Functional block diagram of power control subassembly.

Booster regulator voltage limiter: This Zener diode circuit limited the booster regulator output voltage at a maximum of 64 V dc ± 1 percent during transient conditions or certain internal failures.

F ilter: This subassembly also contained a physically large inductor that filtered the ripple current present on the unregulated dc bus from the input to the booster regulators.

Switching: The redundant Kl and K3 relays in this subassembly were in the set mode at launch for system operation in the main power chain. If the fail sensing circuit during the mission detected a main power chain failure, the relays were automatically reset to substitute the standby power chain.

Most of the VO power distribution functions were in the power distribution subassembly that contained 21 magnetic latching relays controlled by commands issued to the CCS. The commands caused the CCS to issue signals to the B sink-source power matrix that was designed into the power distribution subassembly. Switchable functions on the 2.4-kHz power bus are as follows:

ACE 1 and 2

ARTCS 1 and 2

DTR A and B

FDS power converter A and B

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