A Dynamic Reconfiguration Technique for PV and Capacitor ......to Improve the Efficiency in Energy...
21
A Dynamic Reconfiguration Technique for PV and Capacitor Arrays to Improve the Efficiency in Energy Harvesting Embedded Systems Kyungsoo LEE and Tohru ISHIHARA [email protected]
Transcript of A Dynamic Reconfiguration Technique for PV and Capacitor ......to Improve the Efficiency in Energy...
A Dynamic Reconfiguration Technique for PV and Capacitor Arraysto Improve the Efficiency
in Energy Harvesting Embedded Systems
Kyungsoo LEE and Tohru ISHIHARA
Target System for Today’s Talk
Not a power grid system
2
Target System for Today’s Talk
But, a portable embedded system
3
Energy Harvesting System Tradeoffs
Advantages Mobile: no power wires Easier installation Lower maintenance fee Higher uptime Environmentally friendly
4
Disadvantages Dependent on availability by
harvestable energy source Strict power budget Upfront cost may be higher Less mature technology High cost of recycling
Energy efficiency
Heliomote Sojourner
Energy Efficiency
Efficiency Generating efficiency
Harvesting device efficiency
Consuming efficiency Consumer device efficiency
Transferring efficiency DC-DC converter efficiency Charger efficiency• Harvested energy is not constant• Power is not available on-demand• High peak power is not available
5
Energy Generator
Transfer/Storing Consumer
Contents
Background Motivation
Motivational example Proposed Method Experimental Results Conclusion
6
DC-DC Converter
Always needed in the embedded system Regulate the DC voltage Change the DC voltage
Converting efficiency
7
Pow
er lo
ss (m
W)
Voltage di↵erence (Vin
� Vout
)
0
25
50
75
100
-1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 2.5
Effic
ienc
y (%
)
100
75
50
25
0
Power loss at 10 mA outputPower loss at 100 mA outputEfficiency at 10 mA outputEfficiency at 100 mA output
Actual Buck-boost DC-DC converter form TI (TPS63030)
Reconfigurable Array
Braunstein, A. (1981). On the dynamic optimal coupling of a solar cell array to a load and storage batteries. Power Apparatus and Systems, IEEE Transactions on. Minimize a power loss in a DC-DC converter
By changing the voltage of a solar cell array
8
An example for a configurable array 3 configurations with 4 photovoltaic (PV) cells Each cell has 0.5V, 80mA output Should be balanced because the size of each cell is same in this example
(4,1): 0.5V, 320mA output (2,2): 1V, 160mA output (1,4): 2V, 80mA output
Reduce the difference between
the input and output voltage
in a DC-DC converter
Motivational Example
Target system
A uses a 1.8V with 100mA, and B uses a 5.0V with 1mA 5.0V generator voltage: 2.0V generator voltage:
A and B consume 10mA and 80mA, respectively 5.0V generator voltage: 2.0V generator voltage:
10
DC-DC converter
DC-DC converter
A B
Energygenerator
the total power loss in two DC-DC converters is 40.5mWthe total power loss is reduced to 22.4mW
the total power loss is 51.4mWthe total power loss is 185.1mW
Proposed System Architecture
11
Configurable array
for PV cells
Energy storage
Configurable array
for supercapacitors
DC-DC converter
DC-DC converter
A B
Energygenerator
PV(m,n)
DC-DC
DC-DC
DC-DC
PV(m,n)
DC-DC
DC-DC
DC-DC
Supercapacitor
Charger
Proposed System Architecture
System block diagram
12
Power OR’ing by Linear Technology’s ideal diode
DC-DC
DC-DC
DC-DC
DC-DC
Charger
L1
L2
Li
(mpv, npv)PV
Cap(mc, nc)
SW1
SW2
SW3
Vjunc
Three Different Mode by the Sunlight Strength
Good harvest mode Hybrid mode Bad harvest mode
13
DC-DC
DC-DC
DC-DC
DC-DC
Charger
L1
L2
Li
(mpv, npv)PV
Cap(mc, nc)
SW1
SW2
SW3
Vjunc
Good Harvest Mode
Enough sunlight to operate the loads
14
DC-DC
DC-DC
DC-DC
DC-DC
Charger
L1
L2
Li
(mpv, npv)PV
Cap(mc, nc)
SW1
SW2
SW3
Vjunc = VMPP
Control the charging current
to keep MPP
Maximum Power Point (MPP)
VI curve for PV cells
15
0 2 4 6 8Output voltage (V)
Out
put c
urre
nt (m
A)
IV curve
PV curve
Out
put p
ower
(mW
)400
0
100
200
300
500
80
0
20
40
60
100 MPP (5.08V, 81.8mA)
Good Harvest Mode
Enough sunlight to operate the loads
16
DC-DC
DC-DC
DC-DC
DC-DC
Charger
L1
L2
Li
(mpv, npv)PV
Cap(mc, nc)
SW1
SW2
SW3
Vjunc = VMPP
Control the charging current
to keep MPP
Control the configuration
to minimize the total loss
Control the configuration
to minimize the total loss
Hybrid Mode
Not enough sunlight to operate the loads
17
DC-DC
DC-DC
DC-DC
DC-DC
Charger
L1
L2
Li
(mpv, npv)PV
Cap(mc, nc)
SW1
SW2
SW3
Vjunc = VMPP
Control the output voltage
to keep MPP
Control the configuration
to minimize the total loss
Control the configuration
to minimize the total loss
Bad Harvest Mode
The power loss in the Conv_cap is more than the amount of generated power from the PV array
18
DC-DC
DC-DC
DC-DC
DC-DC
Charger
L1
L2
Li
(mpv, npv)PV
Cap(mc, nc)
SW1
SW2
SW3
Vjunc = VCap
Control the configuration
to minimize the total loss
Control the configuration
to minimize the total loss
Control the charging current
to keep MPP
Selected Cases for the Experiment
Power consumption Processor: 1.2V with 100mA Memory: 3.3V with 30mA RF amplifier for WCDMA: 5V with 100mA
Table of selected cases
19
One Case Result
Power loss in each converter by the configuration Processor, memory and amplifier consume 100, 30, 1mA Sun strength is 100%, and SoC of supercapacitor is 20%
20
Pow
er lo
ss (m
W)
(1,6
,1,1
2)
0
30
60
90
Configuration (mc, nc,mpv, npv)
(2,3
,1,1
2)(3
,2,1
,12)
(6,1
,1,1
2)(1
,6,2
,6)
(2,3
,2,6
)(3
,2,2
,6)
(6,1
,2,6
)(1
,6,3
,4)
(2,3
,3,4
)(3
,2,3
,4)
(6,1
,3,4
)(1
,6,6
,2)
(2,3
,6,2
)(3
,2,6
,2)
(6,1
,6,2
)
120
CPU
Mem.
RF Amp.
Charg.
The lowest power loss
configuration
Experimental Results
21
Conclusion
Increase the transferring efficiency Minimize the total power loss in the DC-DC converters and charger Energy management algorithm will monitor the system status
Environmental status (energy harvesting) Status of charge in the system
Find the best array configuration to minimize the total power loss Our proposed technique will increase the reliability of the system
Without increasing the size of PV array or an energy storage Will reduce the disadvantages of the energy harvesting system
22
