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ee392n - Spring 2011 Stanford University
Intelligent Energy Systems 1
Lecture 3 Lecture 3 Intelligent Energy Systems:Intelligent Energy Systems:
Control and MonitoringControl and MonitoringBasicsBasics
Dimitry Gorinevsky
Seminar Course 392N ● Spring2011
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Traditional Grid
• Worlds Largest Machine!– 3300 utilities
– 15,000 generators, 14,000 TX substations
– 211,000 mi of HV lines (>230kV)
• A variety of interacting control systems
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22Intelligent Energy Systems
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Smart Energy Grid
3
Conventional Electric Grid
Generation
Transmission
Distribution
Load
Intelligent Energy Network
Load IPS
Source IPS
energy subnet
Intelligent Power Switch
Conventional Internetee392n - Spring 2011 Stanford University
Intelligent Energy Systems
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Business LogicBusiness Logic
Intelligent Energy Applications
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Intelligent Energy Systems 4
Database
Presentation LayerPresentation Layer
Computer
Tablet Smartphone
InternetCommunications
Energy Application
Application Logic(Intelligent Functions)
Application Logic(Intelligent Functions)
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Intelligent Energy Systems 5
Control Function
• Control function in a systems perspective
Physical system
Measurement System Sensors
Control Logic
Control Handles
Actuators
Plant
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Intelligent Energy Systems 6
Analysis of Control Function
• Control analysis perspective• Goal: verification of control logic
– Simulation of the closed-loop behavior
– Theoretical analysis
Control Logic
System Model
Control Handle Model
Measurement Model
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Key Control Methods
• Control Methods – Design patterns
– Analysis templates
• P (proportional) control• I (integral) control• Switching control• Optimization • Cascaded control design
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Intelligent Energy Systems 7
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Generation Frequency Control
• Example
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Intelligent Energy Systems 8
Controller
Turbine /Generator
sensor measurements
control command
Load
disturbance
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Generation Frequency Control• Simplified classic grid frequency control model
– Dynamics and Control of Electric Power Systems, G. Andersson, ETH Zurich, 2010
http://www.eeh.ee.ethz.ch/en/eeh/education/courses/viewcourse/227-0528-00l.html
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Intelligent Energy Systems 9
em PPI Swing equation:
dux
loade PP
dIP
uIP
x
e
m
/
/
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P-control• P (proportional) feedback control
• Closed –loop dynamics
• Steady state error
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Intelligent Energy Systems 10
dux xku P
dxkx p
)1(1
0tk
p
tk pp edk
exx
pss kdx /frequency droop
0 2 400.20.40.60.8
1
x(t)
Step response
frequency droop
x+0
u
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AGC Control Example
• AGC = Automated Generation Control• AGC frequency control
ee392n - Spring 2011 Stanford University
Intelligent Energy Systems 11Load
disturbance
AGCgeneration command
frequency measurement
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AGC Frequency Control• Frequency control model
– x is frequency error
– cl is frequency droop for load l
– u is the generation command
• Control logic
– I (integral) feedback control
• This is simplified analysis
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Intelligent Energy Systems 12
,lcugx
xku I
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ee392n - Spring 2011 Stanford University
Intelligent Energy Systems 13
P and I control• P control of an integrator
• I control of a gain system. The same feedback loop
dbux
xku P
g
-k I
cl
xxku I
,lcugx
-k p
bd
x
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Intelligent Energy Systems 14
outer loop
Cascade (Nested) Loops
• Inner loop has faster time scale than outer loop
• In the outer loop time scale, consider the inner loop as a gain system that follows its setpoint input
inner loop
-
inner loop setpoint
output Plant
Inner Loop Control
Outer Loop Control-
outer loop setpoint
(command)
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ee392n - Spring 2011 Stanford University
Intelligent Energy Systems 15
Switching (On-Off) Control
• State machine model – Hides the continuous-time dynamics – Continuous-time conditions for switching
• Simulation analysis– Stateflow by Mathworks
off on70x
71x
69x
passivecooling
furnaceheatingsetpoint
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Optimization-based Control
• Is used in many energy applications, e.g., EMS• Typically, LP or QP problem is solved
– Embedded logic: at each step get new data and compute new solution
ee392n - Spring 2011 Stanford University
Intelligent Energy Systems 16
Optimization Problem Formulation
Embedded Optimizer Solver
MeasuredData
ControlVariables
PlantSensors Actuators
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Cascade (Hierarchical) Control
• Hierarchical decomposition– Cascade loop design
– Time scale separation
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Intelligent Energy Systems 17
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Hierarchical Control Examples
• Frequency control – I (AGC) P (Generator)
• ADR – Automated Demand Response– Optimization Switching
• Energy flow control in EMS– Optimization PI
• Building control: – PI Switching
– Optimization
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Intelligent Energy Systems 18
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Power Generation Time Scales
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Intelligent Energy Systems 19
Power Supply Scheduling
• Power generation and distribution • Energy supply side
Time (s)1/10 10 10001 100http://www.eeh.ee.ethz.ch/en/eeh/education/courses/viewcourse/227-0528-00l.html
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Power Demand Time Scales
• Power consumption– DR, Homes, Buildings, Plants
• Demand side
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Intelligent Energy Systems 20
Demand Response
Home Thermostat
Building HVAC
Enterprise Demand Scheduling
Time (s)100 1,000 10,000
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Research Topics: Control
• Potential topics for the term paper.• Distribution system control and optimization
– Voltage and frequency stability
– Distributed control for Distributed Generation
– Distribution Management System: energy optimization, DR
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Intelligent Energy Systems 21
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Intelligent Energy Systems 22
Monitoring & Decision Support
Physical system
Monitoring & Decision
Support
Physical system
Measurement System Sensors
Data Presentation
• Open-loop functions- Data presentation to a user
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Intelligent Energy Systems 23
Monitoring Goals
• Situational awareness – Anomaly detection– State estimation
• Health management – Fault isolation– Condition based maintenances
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Intelligent Energy Systems 24
Condition Based Maintenance
• CBM+ Initiative
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Intelligent Energy Systems 25
SPC: Shewhart Control Chart• W.Shewhart, Bell Labs, 1924• Statistical Process Control (SPC) • UCL = mean + 3· • LCL = mean - 3·
Walter Shewhart (1891-1967)
sample3 6 9 1212 15
mean
qua
lity
varia
ble
Lower Control Limit
Upper Control Limit
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Intelligent Energy Systems 26
Multivariable SPC
• Two correlated univariate processes y1(t) and y2(t)
cov(y1,y2) = Q, Q-1= LTL
• Uncorrelated linear combinations
z(t) = L·[y(t)-]
• Declare fault (anomaly) if
22
12~ yQyz T
2
1
y
yy
2
1
21 cyQy T
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ee392n - Spring 2011 Stanford University
Intelligent Energy Systems 27
Multivariate SPC - Hotelling's T2
• Empirical parameter estimates
ytytyn
Q
XEtyn
Tn
t
T
n
t
cov))()()((1ˆ
)(1
ˆ
1
1
• Hotelling's T2 statistics is
• T2 can be trended as a univariate SPC variable
)(ˆ)( 12 tyQtyT T
Harold Hotelling(1895-1973)
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Advanced Monitoring Methods
• Estimation is dual to control– SPC is a counterpart of switching control
• Predictive estimation – forecasting, prognostics – Feedback update of estimates (P feedback EWMA)
• Cascaded design – Hierarchy of monitoring loops at different time scales
• Optimization-based methods – Optimal estimation
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Intelligent Energy Systems 28
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Research Topics: Monitoring
• Potential topics for the term paper.• Asset monitoring
– Transformers
• Electric power circuit state monitoring – Using phasor measurements
– Next chart
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Intelligent Energy Systems 29
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Optimization Problem
Measurements:• Currents • Voltages• Breakers, relays
State estimate • Fault isolationElectric
Power System
model
Electric Power Circuit Monitoring
vDfCxy
wBfAx
0
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30Intelligent Energy Systems
ACC, 2009
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End of Lecture 3
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Intelligent Energy Systems 31