Architecture Trades

A primary criterion of choosing between alternative architectures is the overall mass, efficiency and cost of the system. Table 4.2 summarizes the trades between various architectures with their best applications. The final selection of the architecture depends on the mission specific details. However, past experience indicates that peak power tracking architecture

Table 4.2 Pros and cons of various architectures and their best applications

System

Sun regulated

Fully regulated

Peak power tracking

Pros

High power transfer

Well regulated

No need for shunt

efficiency from solar

input voltage to

regulator and battery

array and battery to

all loads.

charge regulator.a

load.

Simpler, lighter

Makes the maximum use

Fewer power system

and more

of the incident solar

components.

efficiency load

energy.

converters.

Cons

More complex load

Needs more

Lower efficiency than DET

converters.

power

at EOL in many cases.

converters.

Battery latch-up

More heat dissipation

concern.

Series power loss

inside the spacecraft body.

between battery

Larger solar array.

and load.

Best

Small load variations.

Loads requiring

Large variation in solar

application in

close regulation.

array input energy

missions with

Small variations in

(illumination) throughout

these features

illumination for most

Large solar array

the mission.

of the sun period.

output voltage

variations.

aTrue for a single battery bus with the battery connected directly to the bus. For a multiple battery system, or a fully regulated bus, each battery must have its own charger for effective battery charge management.

is generally advantageous for small satellites in low or irregular orbits having a power requirement of less than 500 W. Between 1000 and 3000 W, the sun-regulated direct energy transfer architecture would most probably be advantageous. For power levels exceeding 5000 W, the regulated direct energy transfer architecture is generally found advantageous. Although the regulated bus requires additional equipment, the added mass is compensated by the elimination of converters and regulators in the loads. Moreover, decoupling the battery design from the solar array voltage, and operating the system at a constant voltage optimizes the operating point of the solar array. The battery voltage is then chosen to optimize the number of battery cells in the most economical capacity.

The PPT architecture is more suitable for LEO satellites having relatively short periods of sunlight. It is also attractive for missions with large variations in solar flux, solar array temperature, and sun angle in satellites with no sun tracking gimbals. It makes the best use of the solar array all the time in such missions.

In addition to the DET and PPT architectures described above, some spacecraft use hybrid architecture, such as two power busses, one regulated and the other sun-regulated. Charging the battery from a dedicated solar array section rather than from the main bus is another possibility.

The architectures of some of the spacecraft busses flying at present are described in the next sections.

Solar Panel Basics

Solar Panel Basics

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