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Operation and Control of a Microgrid for Feeding Sensitive Loads
1
Operation and Control of a Microgrid
for feeding sensitive loads
Subcontract Number: AAD-0-30605-14
Principal Investigator:
Giri Venkataramanan
Robert Lasseter
NREL Technical Monitor:
Holly Thomas
Ben Kroposki
Electric Distribution Transformation Program
2004 Annual Program and Peer Review Meeting,
October 28-30, 2003, Coronado (San Diego), California 2
Problems and Needs of Sensitive
Loads Loads sensitive to power quality
disturbances Expensive process disruption Stringent demands on voltage
deviations Custom Power devices DVR,
UPS, etc. are expensive An integrated energy solution that
works in conjunction with the
electric grid is needed 3
Relevance of DR for Sensitive Loads Provide pull for technology
development Applications are more
sensitive to power quality
than capital cost Inverter embedded DR can
ensure high power quality Inverter and generation
control need advances 4
State of art control
& operational strategy Operate as a balanced three phase current
source in grid connected mode Operate as a balanced voltage source in off-
grid mode Discontinuity between two operating modes Parallel connected units operated in a master-
slave fashion with critical communication link Limited capability for premium power needs 5
Microgrids for Sensitive Loads Cluster of distributed resources Placed close to load locations Support grid to the extent capable Separate from grid upon deep disturbances Integrated heat harvest Minimize losses 6 Enable inverter embedded DR sources to meet
demands of sensitive loads Enable parallel clusters of DR sources to operate in
a stable manner without critical communication
Project Objectives 7
Technical objectives
Control strategy
1.
Real Power-Frequency Droop Characteristics
2.
Reactive Power-Voltage Droop Characteristics
3.
Address short term power quality issues in control
Operational strategy
1.
Ride through nominal amount of voltage sags and
frequency deviations in a benign manner
2.
Intentionally island and feed local critical loads upon
large deviation
3.
Reconnect upon system recovery seamlessly 8
Technical approach
Detailed analytical Modeling
Matlab, Mathcad, Mathematica
Detailed computer simulation
EMTP, Matlab-Simulink
Hardware verification
Laboratory scale microgrid
Multiple inverter platform 9
Analytical Modeling - microgrid
100ft
L
E
A
C
AC
AC
L
L
L
L
L
C
L
L
2
nd
Floor
1
st
Floor
2
nd
Floor 1
st
Floor
OFFICE 150kW
WAREHOUSE 100kW
BUSBAR
T1
T2
1.5MV
A
480V
13.8kV
BUSBARS
10 mi
1 mi.
aerial
1mi.
1
2MVA
120kV
13.8kV
Substation
(Ideal Source)
43
2
3
8
37
36
15
38
39
40
41
4
2
35
34
13
T3
480V
208V
0.3M
VA
14
11
32
12
33
Ceiling
L
DR 1
DR 2
L
L Lighting
C Computer
AC Airconditioner
Modeling of
facility 10
Analytical Modeling
-
microgrid
+
Inverter
Controller
Local
Feede
r
Gate
Signals
X
480 V
208 V
n
Inverter model
PQ spread for various
coupling parameters 11
Analytical Modeling - inverter
v
inv
*(t)
i
Lt
(t)
Voltage
regulator
i
Lf
*(t)
v
load
*(t)
v
Cf
(t)
Current
regulator
Space-vector
modulator
DR filter
interface
network
Command
voltage
modifier
i
Lf
(t)
Voltage
source
inverter
d
inv
(t)
v
cvm
(t)
V
dc
Modeling of internal control loops 12
Analytical Modeling
-
interconnection
P
M
1
P
L
1 1
P
L1-ref
P
M
2
P
L
2 2 2
P
L2-ref
P
tie 1
b
2
b
1
Modeling of
power control
loops 13
Computer simulations
Step response during grid
disconnection transient 14
Computer simulations
Voltage profile along an
unbalanced distribution
feeder
with conventional dg control
Voltage profile along an
unbalanced distribution
feeder
with unbalanced dg control 15
Laboratory scale microgrid
Grid
Interconnect
DG1
DG2
L
f2
L
t2
C
f2
L
t1
C
f1
L
f1
T
2
T
3
Tie-line
Interconnect
T
1
CB
2
CB
1
CB
3
*
CB
5
*
CB
6
*
SS
1
FD
1
B
1
B
2
B
3
Load12 (NSL)
Load1 (NSL)
Load2 (SL)
75 yard
cable
25 yard
cable
-Y
Y- Y- T
X
CN
1
R
1
CB
5
CN
3
*
CB
4
CN
2
*
CB
6
CN
4
*
DG3
L
f3
L
t3
C
f3
T
4
Y
B
4
CB
3 16
Laboratory scale microgrid
hardware details 17
Laboratory scale microgrid hardware
details 18
Laboratory scale microgrid
hardware results
Synchronization to grid
beat voltage
P and Q transients 19
Laboratory scale microgrid
hardware results
Synchronization to
grid
Voltage and current waveforms 20
Laboratory scale microgrid hardware
results
Disconnection from
grid
Voltage and current waveforms 21
Laboratory scale microgrid hardware
results
Step response of
power
Voltage and
current waveforms 22
Project Timeline
ID
Task Name
2002
2001
2004
2003
Q1
Q2
Q2
Q3
Q3
Q4
Q3
Q1
Q2
Q1
Q4
Q1
Q4
1
Development of power source emulator
2
Study of energy storage requirements
3
Demonstration of single inverter system
4
Development of DG control interface for inverter
5
Computer simulation for Tasks 1-4
6
Expansion of lab scale microgrid for utility interface and two
inverters
7
Development of second PSE and inverter
8
Demonstration of islanding and reconnection
9
Demonstration of two inverters power quality transients
10 Computer simulation for Tasks 6-9
11 Expansion of lab scale microgrid to accomodate third
inverter
12 Development of third PSE and inverter
13 Demonstration of 3 inverters with decentralized control
14 Demonstration of correction of common power quality
problems
15 Computer simulation for Tasks 11-15
Q2
Q3 23
Milestones
Sept 30, 2003 m-3.1.1
Complete expansion of laboratory scale microgrid. (Task 11) m-3.1.2
Complete fabrication of third power source emulator and inverter hardware. (Task 12) m-3.1.3
Develop computer simulation models for hardware design for Option year 2. (Task 16)
Oct 31, 2003 m-3.2.1
Complete demonstration of three inverter decentralized control operating on the
microgrid (Task 13 ) m-3.2.2
Develop updated computer simulation models for current hardware design. (Task 16)
Feb 28 2004 m-3.3.1
Complete demonstration correction of power quality problems on the microgrid. (Task 14) m-3.3.2
Develop updated computer simulation models for current hardware design.
(Task 16)
June 30, 2004 m-3.4.1
Complete demonstration of safe system operation under faulted conditions on
the microgrid. (Task 15)
m-3.4.2
Complete computer simulation models for Option Year 2 hardware design. (Task 16) 24
Deliverables
D-3.1
Monthly progress reports
15
th
of every month
D-3.2
Draft Project Technical Report
June. 31, 04
D-3.3
Final Project Technical Report
July. 30, 04
D-3.5
Annual Program Review Meeting
October 03
D-3.6
Microgrid expansion report (Task 11, 12)
Oct. 31, 03
D-3.7
3 inverters in a microgrid report (Task 13, 16)
Nov 30, 03
D-3.8 Power quality transient report (Task 14, 16)
Mar. 31, 04
D-3.9 Operation under faults report (Task 15, 16)
July 30, 04 25
Project budget
317
468
785
Total
100
149
248
Option Year 2 (31 Sep 2003 - 31Aug 2004 )
97
142
238
Option Year 1 (1 Apr 2002-31 Aug 2003)
120
177
297
Base Year (1 Dec 2000 30 Mar 2001)
Subcontractor ($K)
DOE/NREL ($K)
Total ($K) 26
Accomplishments 03
Hardware Microgrid with two inverters
Control strategy
Real Power-Frequency Droop Characteristics
Reactive Power-Voltage Droop Characteristics
Address short term power quality issues in control
Operational strategy
1.
Ride through nominal amount of voltage sags and
frequency deviations in a benign manner
2.
Intentionally island and feed local critical loads upon
large deviation
Reconnect upon system recovery seamlessly 27
Accomplishments 03
Simulation and Analysis
Control strategy
Real Power-Frequency Droop Characteristics
Reactive Power-Voltage Droop Characteristics
Address short term power quality issues in control
Operational strategy
Ride through nominal amount of voltage sags and
frequency deviations in a benign manner
Intentionally island and feed local critical loads upon
large deviation
Reconnect upon system recovery seamlessly 28
Accomplishments
Publications
B. Shi, M. Chandorkar, G. Venkataramanan, " Modeling & Design of a Flux
Regulator for Three Phase PWM Inverters with Constant Switching
Frequency", European Power Electronics Conference, Toulouse, 2003.
G. Venkataramanan, M. Illindala, Dynamic Phenomena in Wind Farms with a
Mix of Line Connected Induction Generators and Inverter Embedded
Generators, Caribbean Colloquium Electric Power Quality, June 2003
H. Zhang, M. Chandorkar, G. Venkataramanan, "Development of Static
Switchgear for Utility Interconnection in a Microgrid," Proceedings of the
IASTED Conference on Power and Energy Systems, Palm Springs,