INTELLIGENT CONTROL FOR MICROGRID€¦ · DC Microgrid Protection Test. 14. LVDC fault test...
Transcript of INTELLIGENT CONTROL FOR MICROGRID€¦ · DC Microgrid Protection Test. 14. LVDC fault test...
INTELLIGENT CONTROL FOR MICROGRIDXianyong Feng, PhD, PECenter for ElectromechanicsThe University of Texas at Austin
Outline• Microgrid Overview
• MPC-based Microgrid Energy Management
• DC Microgrid Protection
• Summary
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Introduction
• Microgrid Definition: A group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. A microgrid can connect and disconnect from the grid to enable it to operate in both grid-connected or island-mode.
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PV system
ES system
~
Distributed Generator M
~
Microgrid
Communication link
Central controller
Local controller
Local controller
Local controller
Local controller
Distributed Generator 1
s1s2s3s4s5s6
s7
s8
s9
PCCUtility Grid
...
Controllable load 2
Critical load Controllable
load N
Controllable load 1
Local controller
Local controller
Local controller
Local controller
...
PCC controller
• Utility electricity price signal• Weather forecast
Introduction• MW dc microgrid at CEM in UT-Austin
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~ ~
~ ~
M ~D
480 V AC source 3-ph
AC breaker
480 V AC source 3-ph
AC breaker
490 kVA480 V/808 V transformer
DC disconnector
AC breaker
Diode rectifier 3.2 MVA
DC disconnector
DC cable
DC disconnector
DC disconnector
DC disconnector
DC disconnector
1 MVA motor drive
2 MVA motor
5 MW dynamometer
DC disconnector
1.2 MVA480 V/808 V transformer
1.2 MVA controlled rectifier
2 MW DC chopper
1.3 MW resistive load
1120 VDC
1120 VDC
Zone 1
Zone 2
DC bus 1
DC bus 2
Challenge and Opportunity
1. High Penetration DER• Accommodate high penetration
intermittent DERs2. Energy Efficiency
• Reduce operational cost• Reduce emission
3. Reliability and Resilience • Improve system stability• Reliable fault ride-through and
protection• Seamless mode transitions
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Time (sec)
Frequency (Hz)
60larger inertia
smaller inertia
LP∆ is the same
1f
2f
∑ =⋅
∆−= n
i i
L
HfP
dtfd
1
rated
2Total inertia
Stability and Resilience
PV generation (partial cloud day) Wind generation (daily curves)Renewable Intermittency
10 hrs.
Microgrid Control
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Tertiary control
Secondary control
Primary control
Information flow
Decision signals
Economic dispatchUnit commitmentOptimal power flowVoltage var controlTime frame: seconds to minutes
Real-time load managementSecondary load-frequency controlSecondary voltage control Automatic generation controlTime frame: 100s milliseconds
Droop control Protection control Time frame: milliseconds
MPC-based Microgrid EMSObjective and Approach
1. Objective• Enable economic and secure
steady-state operation• Seamless integration with local
controllers
2. Approach• Look-ahead operational planning:
Optimize DER schedule for the next 12-24 hours
• Online operation: Use ED/OPF to determine DER set-points
• Planned outage control
3. HIL Test• Test the EMS performance• Test the EMS and fast control
integration …
Mixed Integer Linear Programming (MILP)
problem
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1. Opal-RT simulator• Simulated a 13.8 kV
microgrid (step: 100 us)• Local controllers
communicate with Opal-RT simulators
2. Microgrid EMS• Improve the economics
and reliability• EMS is deployed on
central controllers• Dispatch signals are
transferred to local controllers through LAN
MPC-based Microgrid EMSHIL Test
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PXIe Real-Time/FPGA HIL System Opal-RT Simulator
High speed communication link
Opal-RT OP5600• eMEGAsim solver – 900 nodes at 50 µs• IEC61850 GOOSE and Sample Values• C37.118 interface• 32 Analog I/Os• 64 Digital I/Os
NI PXI HIL simulator• 2 eHSx64 solver – 144 switches at 250 ns• 48 Analog inputs• 100 Analog outputs• 364 Digital inputs• 48 Digital outputs
DC microgrid circuit in Opal-RTSimulated switching devices in NI PXI simulator
Potential Control, Protection and Monitoring Hardwares
Digital
/analo
g I/O
inter
face
MGCCTime Sensitive Network
NI cRIO controller
Novel dc microgrid EMS
...Local fault detection
and location
Stability control
...
MPC-based Microgrid EMSPreliminary Test Result
Low utility price
High utility price
Heuristic EMS
EMS optimization results for a day
Central EMS vs Heuristic Control
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1. DC microgrid• AC generator is interfaced with dc
grid through converter• Re-dispatch ac generators for
efficiency improvement
2. Hybrid approach• Use ESS to shift energy to operate
generator at the maximum efficiency point
• Develop comprehensive microgridEMS to improve the overall system efficiency
MPC-based Microgrid EMSImprovements
rotating speed [rad/s]
120 140 160 180 200 220 240 260 280
Torq
ue [N
-m]
300
400
500
600
700
800
900
0.1
0.15
0.2
0.25
0.3
Original operating point
Optimal operating point
125 kW contourRated power
time (hour)
0 5 10 15 20 25
spee
d (p
u)
0.5
0.6
0.7
0.8
0.9
Fuel efficiency map for a 250-kW fossil-fuel engine (unit in legend: kg/kWh)
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DC Microgrid Protection
AC fault current
DC fault current
=
L L
=~ =
DC Power Supply
...
...
Fault 1 Fault 2
Fault 3...
L L...
...
DC distribution system example
DC microgrid protection challenges1. No fault current zero-crossing2. Lower line impedance3. High di/dt4. Power electrics device can not tolerate
high fault current5. Fast capacitor discharge
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Fast DC Fault Localization Algorithm
Inductance-based dc fault location*1. Estimate fault inductance with local
measured v(t) and i(t)2. Use estimated L to locate fault
=
L L L
Zone 1 (20 m)
Zone 2 (65 m)
Zone 4 (1.5 m)
=~ =
DC Source
...
...
Fault 1 Fault 2
Fault 3...
L L L...
Zone 3 (10.2 m)...
...
Equivalent inductance
Distance
level 1 level 2 level 3
L1
L2
L3
Line inductance distribution
RF
LRi
v
+
-
Equivalent fault circuit
*X. Feng, et.al., “A novel fault location method for dc distribution protection,” IEEE Trans. Industrial Applications, vol. 53, no. 3, May-June, 2017.
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DC Protection Control PrototypeProtection strategy design
1. Online moving-window least square method2. Digital di/dt approximation3. Algorithm on embedded controller
ADC ADC
v (1) i (1)
PRUs read data sequentially and store
them in memory
Main program executes the fault detection and
location routine
Locate fault?
YSend tripping
Request new data once
finishing the previous cycle
N
v i Fault detection and location routine
Start
Go to next time intervalFault detected?
Yes
No
if k < M
No
Yes
k = 0
No
k = k + 1
Read in measurements v(k) and i(k)
=
)()(
)1()1(
)0()0(
kikdtdi
idtdi
idtdi
A
=
)(
)1()0(
kv
vv
B
+−+−
+−+−
=
)()(
)2()2(
)1()1(
kikdtdi
MkiMkdtdi
MkiMkdtdi
A
+−+−
=
)(
)2()1(
kv
MkvMkv
B
( ) BAAARR
L TT
F
1−=
+
if 0 < L < Lth
Yes
Send tripping signal
End
if t < Tmax
Yes
No
di/dt estimation
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DC Microgrid Protection Test
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LVDC fault test circuit
DC power supply
30 kW converter with FCL
Downstream circuit
NI sbRio control board
==
Line impedance 1
Load Source 2Source 1
Line impedance 2
Current sensor
Controller
DC Protection Test Results*: measured inductance value□: estimated inductance value
CASE #
1 2 3 4 5 6 7 8 9Es
timat
ed in
duct
ance
(uH
)0
10
20
30
40
50
CASE #
1 2 3 4 5 6 7 8 9
Estim
atio
n er
ror (
%)
-30
-20
-10
0
10
20
30
Case # RF (mΩ) L (µH)
1 33 12.5
2 33 24
3 33 42
4 50 12.5
5 50 24
6 50 42
7 100 12.5
8 100 24
9 100 42
Test Scenarios
*5 tests in each case
Test Circuit:• Single dc source • One line impedance
connecting source and load• Fault is on load side
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Summary1. The look-ahead EMS approach fully utilizes the most
recent load and renewable forecast to improve the predictive control accuracy
2. The decoupled DER schedule and real-time ED approach significantly reduces the computational complexity
3. DC prot. is enabling tech. for large-scale deployment of dc systems
4. Extra-fast fault location and restoration are keys for grid resilience
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Thanks for your attention
Contact information:Xianyong FengCenter for ElectromechanicsThe University of Texas at AustinEmail: [email protected]: 1-512-232-1623
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