Introduction to Space Systems and Spacecraft Design Space Systems Design

Introduction to Space Systems and Spacecraft DesignSpace Systems Design

Power Systems Design -II


2

Power Systems Design II

Power Systems or EPS


3



4


Look at the parts of the EPS


5


Take Solar Panel


6


5.6.

1350

1350


7


What do we need from the solar panel?

What are the attributes of a solar panel?

1. Total output power of solar panel.2. Voltage of solar panel.3. Maximum packing factor.4. Efficiency of the solar cells.5. Operating temperature of the panels.

Lets go back and look at the solar cell.


8


This dual junction cell

1. Has an efficiency of ~ 22%2. Open circuit voltage ~ 2.2v3. Size – 76 x 37 mm

Lets go back and look at the solar cell.


9



1. Has an efficiency of ~ 22%2. Open circuit voltage ~ 2.2v3. Size – 76 x 37 mm

Solar cell has an I-V curve like this


10





1. Has an efficiency of ~ 22%

2. Open circuit voltage ~ 2.2v

3. Size – 76 x 37 mm

Looked at the solar cell.


11




Need to select a battery to design forsolar panel voltage


12

RechargeablePower Systems Design II


13


Use a lithium ion batteryLi Ion batteries = 3.6 v nominal

Design Criteria for charging Li Ion battery:

1. Need 10-15% more voltage to charge than the nominal voltage.

2. Here we would need solar panel voltage of ~ 4.0 – 4.2v to charge this battery.

Design Criteria solar panel:

1. Number of cells = Max voltage/cell voltage.

2. Take minimum number of whole cells.

# cells = (4.2v/string)/(2.2v/cell) = 1.9 or 2 cell for a string voltage of 4.4v


14



15


Use two lithium ion batteriesLi Ion batteries = 7.2 v nominal

Design Criteria for charging Li Ion battery:

1. Need 10-15% more voltage to charge than the nominal voltage.

2. Here we would need solar panel voltage of ~ 8.0 – 8.3v to charge this battery.Design Criteria solar panel:

1. Number of cells = Max voltage/cell voltage.

2. Take minimum number of whole cells.

# cells = (8.3v/string)/(2.2v/cell) = 3.77 or 4 cell for a string voltage of 8.8v

Lets be conservative and use 5 cells for 11v.


16


Now we have:

Two Li Ion batteries = 7.2 v nominal

5 cells for 11v to charge with.


17




What is packing factor?

Got

Got

Total Panel Area


18


Packing Factor

Packing Factor = Total Cell Area/ Total Panel Area

Total Cell Area


19

Packing Factor

What do you do if given a fixed size panel on which to put solar cells and you have these different size solar cells?

Fixed solar panel size

Cell type 3

Cell type 1 Cell type

2



20

Packing Factor

What do you do if given a fixed size panel on which to put solar cells and you have these different size solar cells?



21


Now we have:5 cells for 11v where the string has all of the cells hooked in series

11v

Total Panel Area

How do you mount these 5 cells on this panel?


22


How do you mount these 5 cells on this panel?

NO!OK!

Visually we can see a very poor packing factor.


23


What if the cells were bigger?

Oh Oh!

Now you have only 4.4v in the string.


24


Can’t do. All cells for a single string must be on same face.

Got a cube? Put other cells on another face?


25


Where are we now in the solar panel design?



Assume we could mount the 5 cells on a panel, what is total power for the cells selected?

Got

Got

Not got, but understand


26


How much power from these cells?5 cells for

11v

11v

One cell area = 76 x 37 mm = 2812 mm^2Total cell area = 8*2812 = 22496 mm^2 = 2.25 x10-2 m^2

We have 1350 watts/m^2 from the sun in space

Direct power = (1350 w/m^2) x (2.25 x10-2 m^2) = 34.4 watts

Converted power = direct power x cell efficiency = 34.4 w x 0.22 eff

= 7.5 watts7.5 wattsFor this dual junction cell

1. Has an efficiency of ~ 22%

2. Open circuit voltage ~ 2.2v

3. Size – 76 x 37 mm


27


Where are we now in the solar panel design?



Now we can assume to start:1. panel is at 90 degrees with sun – max power2. operating temperature 20 degrees.. Centigrade –

22% eff

Got

Got

Not got, but understand

Got

Don’t forget, temperature counts a lot.


28

Start here Tuesday for Idaho



29


Now that we have beat our way through the solar panel design ----- lets go look at the some more parts of the EPS.


30



What is this?


31



Back bias diode

When panel 1 is shaded, the back bias diode keeps the current from flowing backwards through panel 1, when panel 2 is generating a voltage across it.

Panel 1

Panel 2


32



What is this?

R V

Measure current by measuring voltage across a low resistance precision resistor


33

Power Systems Design IIPower Systems or EPS


34

Power Systems Design IIPower Systems or EPS


35



36



37

Power Systems Design IIExpanded subsystem control


38



39


What does a charge regulator do?

1. Controls voltage from PV to battery2. Controls rate of charge3. Prevents overcharging4. Can “boost” or “buck” PV voltage to match

battery needs.


40



41


Consider:

When high current occurs in a subsystem, it could be from latch-up. What to do? Cycle power. Where do you do this – hardware controlled in the EPS.


42


Consider the satellite’s attitude control for solar power generation.


43

Eclipse

Parallel Sun Rays

Sun

Earth

Satellite Orbit



44

Gravity Gradient StabilizedPower Systems Design II


45

Passive Magnetic Stabilized

N

S

SNSN

S N

S NS

N

S

N

S

N

S

N

S

N

S

N

S

N

SN

SN

SN



46

Inertially StabilizedPower Systems Design II


47



48



49

• Power from sun in orbit ~ 1350 watts/meter2

• Power from cells on ground ~ 35% less than in space

• Can get some power form albedo – earth shine ~ 35%

Some Solar Notes



50



51


Need to consider the power requirements of all of the subsystems and when they are used to build a power budget.


52


Questions?

Introduction to Space Systems and Spacecraft Design Space Systems Design

Documents

Transcript of Introduction to Space Systems and Spacecraft Design Space Systems Design