Power processing units (PPUs) are circuit devices that convert an electricity input from a utility line into the appropriate voltage and current to be used for the device in question. They serve the same purpose as linear amplifiers, but they are much more efficient, since the use of linear amplifiers results in much power loss due to the use of a resistor to change the voltage and current. Instead of using a resistor, PPUs use switches to turn a signal on and off quite rapidly in order to change the average current and voltage. In this way, they could be conflated with dc-ac converters, but the frequency at which they switch the signal on and off is a few orders of magnitude higher than that of ac signals. They are used to convert the current and voltage of both dc and ac signals.
In the context of spacecraft, the power processing unit (PPU) is a module containing the electrical subsystem responsible for providing electrical power to other parts of the spacecraft. The PPU needs to be able to cope with varying demands for power output and provide that power in the most efficient manner possible.
There are two main constrains placed on PPU:
- Power generation from for instance a solar array or radioisotope thermoelectric generator where power generation can vary based on external conditions.
- Power utilization which varyies depending of the current internal activities performed by the spacecraft such as burst radio transmission or external demand factors like outside temperature and the need to provide heat to maintain constant internal temperature.
Major considerations in building PPUs are weight, size and efficiency.
Most PPUs process and supply direct current because that is what is generated by a solar array.
The PPU is also responsible for voltage conversion and supplying the required voltage to other subsystems of the spacecraft.
Famous quotes containing the words unit and/or power:
“During the Suffragette revolt of 1913 I ... [urged] that what was needed was not the vote, but a constitutional amendment enacting that all representative bodies shall consist of women and men in equal numbers, whether elected or nominated or coopted or registered or picked up in the street like a coroners jury. In the case of elected bodies the only way of effecting this is by the Coupled Vote. The representative unit must not be a man or a woman but a man and a woman.”
—George Bernard Shaw (18561950)
“[The Republican Party] consists of those who, believing in the doctrine that mankind are capable of governing themselves and hating hereditary power as an insult to the reason and an outrage to the rights of men, are naturally offended at every public measure that does not appeal to the understanding and to the general interest of the community.”
—James Madison (17511836)