SIMES: A Simulator for Hybrid Electrical Energy Storage Systems Siyu Yue, Di Zhu, Yanzhi Wang, Younghyun Kim, Naehyuck Chang, and Massoud Pedram
Jan 05, 2016
SIMES: A Simulator forHybrid Electrical Energy Storage Systems
Siyu Yue, Di Zhu, Yanzhi Wang, Younghyun Kim,Naehyuck Chang, and Massoud Pedram
Background• Hybrid electrical energy storage (HEES) systemo Consists of several heterogeneous energy storage elements o Exploits the strengths (such as high cycle efficiency, high power density,
long cycle life, low cost, etc.) of each type of storage element and hide their weaknesses.
Control
DC/DC Converter
DC/AC Inverter
AC/DC Rectifier
DC/DC Converter
DC/DC Converter
DC/DC Converter
EES Bank #1 EES Bank #2
EES Bank #4
EES Bank #3AC Load
AC Source
CTI
Main Controller
Control
Status Status
• Some popular energy storage elements: Li-ion battery, lead-acid battery, Ni-Cd battery, supercapacitor, etc.
Background (cont’d)Applications of HEES systems:
Home application
Electric vehicle
Mobile device
Abstraction of HEES SystemsTop-level: We abstract a HEES system as a graph:
Source/load/bank/CTI => NodesConverters => Edges
Connection between a component (node) and a converter (edge) is abstracted as a port, which is simply a V-I curve.
Control
DC/DC Converter
DC/AC Inverter
AC/DC Rectifier
DC/DC Converter
DC/DC Converter
DC/DC Converter
EES Bank #1 EES Bank #2
EES Bank #4
EES Bank #3AC Load
AC Source
CTI
Main Controller
Control
Status Status
ConverterCport Vout
Iout
CportVin
IinIout=fc1(Vout,Vin,Iin,t)
V=fp(I,t)V=fp(I,t)
Modeling of HEES System ComponentsModeling of the energy storage banks:1. Open-circuit voltage as a function of state-of-charge2. Internal resistance as a function of state-of-charge3. Rate capacity effect4. Self-discharge effect5. State-of-health degradation (aging effect)
00.5110
11
12
13
14(1) OCV vs. SoC
SoC
OC
V(V
)
00.510
2
4
6
8(2) Internal Resistance vs. SoC
SoC
R(o
hm
)
ChargingDischarging
Fig 1. OCV and IR vs SoC curve of a lead-acid battery
0 1 2 3 4 520
40
60
80
100Discharge Efficiency vs. Discharge Current
Discharge Current(C)
Dis
cha
rge
Eff
icie
ncy
(%)
Measured ResultsCurve Fitting
Fig 2. Illustration of rate capacity effect
Modeling of HEES System Components Modeling of converters:
Reflects input/output voltage and current relations
Fig 3. Power conversion efficiency of a converter.
020
40
020
40
0.6
0.8
1
Vin (V)
(a) Efficiency at Iout
=0.6A
Vout
(V)
Effi
cien
cy
020
40
020
40
0.6
0.8
1
Vin (V)
(b) Efficiency at Iout
=1.6A
Vout
(V)E
ffici
ency
SIMES OverviewSIMES consists of three main modules:1. ParserParser parses the input XML file and
constructs the HEES system.2. SimulatorSimulator simulates the operation of the
HEES system.3. VisualizerVisualizer can help user create the input
XML file and visualize the output results.
Package Core
User
Visualizer(UI)
QT Libraries
DC/DC Converter
DC/AC Inverter
AC/DC Rectifier
DC/DC Converter
DC/DC Converter
DC/DC Converter
EES Bank #1 EES Bank #2
EES Bank #4
EES Bank #3AC Load
AC Source
CTI
Charge ManagerStatus Status
Control
ParserXML Parser
Simulator
Check Integrity
Adaptive Time-Step Simulation
Generate Output
CSourceBase CComponent
CBankBase
CPort
CLoadBase CConverterBase
CCTI
CController
CCTIPort
CSensor
Class Representation
Visualization of Results
SIMES
.xml Input
Output File
Implementation of SIMESSimulator runs adaptive time-step simulation.
At each time slot:•If it is a decision epoch, the main
controller sets the input or output current of each converter.
•Simulator calculates the current and voltage of each port.
•The maximum time-step which is acceptable for every component with regard to precision requirement is determined.
•Simulator simulates the operation of each component.
Check If Properly Set
Get Next Command
Cmd=Set/Get Property
Cmd=FinishCmd=Run Simulation till Time T
Current Time <T?
Set Load Current
MainController->Decision
Is Decision Epoch?
Converter->Solve
CTI->FindRegulatorCurrent
Determine min(TimeStep)
Yes
Component->Simulate
No
Yes
Simulator workflow
Sensor Output
Output File
Write To
Exit
No
Implementation of SIMESVisualizer is implemented using QT5.0 libraries.
Validation of SIMESWe compare SIMES’s simulation result with a HEES system prototype.
0 500 1000 150018
20
22
24
26(a) CTI Voltage
Vo
ltag
e (
V)
Time (s)0 500 1000 1500
22
23
24
25(b) Li-ion battery bank
CC
V (
V)
Time (s)0 500 1000 1500
-2
0
2
Cu
rre
nt (
A)
0 500 1000 150018
20
22
24
26(c) Lead-acid battery bank
CC
V (
V)
Time (s)0 500 1000 1500
-2
0
2
Cu
rre
nt (
A)
0 500 1000 15000
8
16
24
32
40(d) Supercapacitor bank
CC
V (
V)
Time (s)
0 500 1000 1500-5
0
5
Cu
rre
nt (
A)
Voltage(Measurement)
Voltage(Simulation)
Current
Fig 4. Simulation results vs. hardware measurement
Hardware Measurement Time
Simulator Runtime
30min 1.1s
Use Case Demonstration (1)•A single-family house equipped with a HEES system consisting of a Li-ion
battery and lead-acid battery.•This system draws energy from the grid when the electricity price is low and
supply energy to the grid when the price is high.•SIMES simulates the operation of such a system for one day and determine its
efficiency.
0 4 8 12 16 20 240
0.5
1
Sta
te o
f Cha
rge
Time (h)0 4 8 12 16 20 24
-5
0
5
Cur
rent
(A
)
Time (h)0 4 8 12 16 20 24
15
20
25
30
Vol
tage
(V
)
Time (h)
Li-ion
Lead-acid
Fig 5. SoC, current and voltage of both banks
Total energy drawn from the grid is 1575 Wh and supplied to the grid is 1266 Wh.Overall efficiency: 80.4%
Use Case Demonstration (2)•A mobile device with a HEES system consisting of a Li-ion battery and
supercapacitor.•An expert-based online management algorithm is implemented in the mobile
device which determines how to charge/discharge the supercapacitor to minimize the power loss in the system.
•SIMES simulates its operation and calculate the power consumption and power loss in the system. The baseline is using a Li-ion battery only as the power supply.
0 0.2 0.4 0.6
Power (W)
(a) Overall Power Consumption
Li-ion
Hybrid
Delivered power
0 0.02 0.04 0.06 0.08 0.1
Power (W)
(b) Power Loss
Li-ion
Hybrid
Power loss
Fig 6. Power consumption and power loss of the mobile device
Power consumption is reduced by 4% and power loss is reduced by 28%.
Q&A
Thank You!