This document discusses DG participation in distribution system volt/var control. It proposes an effective methodology for multi-objective variable power factor operation of DGs for distribution system volt/var control during normal and emergency situations. The document outlines electric distribution systems, distributed generation resources, volt/var control in distribution systems with DGs, and DG participation in volt/var control. It reviews literature on DG operating at constant and variable power factors for volt/var control.
2. DG participation in DS control
DG Operation for Distribution System Volt/Var
Control
N. Daratha
guided by
Prof. J.D. Sharma and Prof. B. Das
Department of Electrical Engineering
IIT Roorkee
PhD Seminar Course
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3. DG participation in DS control
Proposition
There is a need for an effective methodology of multi-objective
variable-power-factor distributed generation operation for
distribution system volt/var control during normal and emergency
situation.
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4. DG participation in DS control
Outline
Electric Distribution System
Distributed Generation
Volt/Var Control In Distribution System With DGs
DG Participation in Volt/Var Control
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5. DG participation in DS control
Electric Distribution System
Electric Power System
Distribution System
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6. DG participation in DS control
Electric Distribution System
Elements of Distribution Systems
Excluding DG, ....
All DS must have feeders and transformer with On-load Tap
Changer.
Most of them have shunt capacitors and/or shunt reactor
fewer of them have SVC (static Var compensator)
even fewer of them have D-STATCOM.
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7. DG participation in DS control
Electric Distribution System
We Want Many Objectives
A distribution system must
have good voltage regulation
be energy efficient
have wide stability margin
support transmission system reactive power need
of course, maximize overall profit.
However, achieving all of them at the same time is NOT possible.
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8. DG participation in DS control
Electric Distribution System
Feeders: Minimum Losses = Minimum Voltage Drop
Feeders bring electricity to consumers.
A feeder power loss is minimum when when load is pure
resistive.
A feeder voltage drop is minimum when load capacitive reactive
power equals feeders requirement.
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9. DG participation in DS control
Electric Distribution System
Control Devices in Distribution Systems
For effective, secure, and safe operation of DS, utility control:
Switches
Voltage regulators (OLTC, SC, SR)
Distributed Generators
Energy Storages
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10. DG participation in DS control
Distributed Generation
Distributed Generation (DG)
definition, altenative names
a distributed generation (DG) is a small generation connected to
distribution network
IEEE Standard Dictionary Terms :
Electric generation facilities connected to an Area EPS
(Electric Power System) through a PCC (Point of
Common Copling); a subset of DR (Distributed
Resources).
alternative names: embedded generation, dispersed generation
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11. DG participation in DS control
Distributed Generation
Distributed Generation (DG)
International Energy Agency’s Definition 1
Distributed generation is generating plant serving a customer
on-site or providing support to a distribution network, connected
to the grid at distribution-level voltages.
Dispersed generation is distributed generation plus wind power
and other generation, either connected to a distribution network
or completely independent of the grid.
1 Distributed Generation in Liberalised Electricity Markets, IEA, Paris, 2002
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12. DG participation in DS control
Distributed Generation
DG Classifications
DGs can be. . .
renewable (wind,PV,hydro) or non renewable (diesel)
dispatchable (diesel, micro/small hydro) or not-dispatchable
(wind, PV)
intermittent (PV, wind, ocean wave) or steady (diesel, hydro, fuel
cell)
grid-connected or isolated
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14. DG participation in DS control
Distributed Generation
DG Impacts on Voltage Regulation
Before Fault
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15. DG participation in DS control
Distributed Generation
DG Impacts on Voltage Regulation
After Fault
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16. DG participation in DS control
Distributed Generation
DG May Not Participate in Voltage Regulation
IEEE Standard 1547-2003:
4.1.1 Voltage regulation
The DR shall not actively regulate the voltage at the
PCC. The DR shall not cause the Area EPS service voltage
at other Local EPSs to go outside the requirements of ANSI
C84.1-1995, Range A.
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17. DG participation in DS control
Distributed Generation
Some DGs Reactive Power Capability
Interface that can control reactive power :
synchronous machine 3 (hydro,diesel)
voltage source converter (PV, DFIG4 , Ocean Energy)
(a) Synchronous Generator (b) Doubly-Fed Induction Generator
3 J.
Y. Jackson, “Interpretation and use of generator reactive capability diagrams”,
Industry and General Applications, IEEE Transactions on, vol. IGA-7, no. 6, pp. 729
–732, nov. 1971
4 S. Engelhardt, I. Erlich, C. Feltes, J. Kretschmann, and F. Shewarega, “Reactive
power capability of wind turbines based on doubly fed induction generators”, Energy
Conversion, IEEE Transactions on, vol. 26, no. 1, pp. 364 –372, march 2011
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18. DG participation in DS control
Distributed Generation
DGs Have Low Utilization Level
PV depends on solar irradiance.
Wind generator depends on wind speed.
Both solar irradiation and wind speed is highly intermittent
There is significant fraction of the time when DG works much
below rated power.
During those time, DGs can provide reactive power service.
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19. DG participation in DS control
Distributed Generation
Distributed Reactive Power Generation Control for
Voltage Rise Minimization in Distribution Network5
Prevent significant voltage rise because of DG presence.
2
∗ X X 2 2RPG
QG ≈ − − PG + 2
R2 + X 2 R2 + X 2 R + X2
Compared with constant power factor approach.
Effective reactive power control with two consequences:
increased stress on tap changers.
increased feeder losses.
Voltage become almost independent of DG real power
generation.
Voltage dependence on load is almost unchanged.
5 P.M.S. Carvalho, P.F. Correia, and L.A.F. Ferreira, “Distributed reactive power
generation control for voltage rise mitigation in distribution networks”, Power Systems,
IEEE Transactions on, vol. 23, no. 2, pp. 766 –772, may 2008
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20. DG participation in DS control
Distributed Generation
Voltage Become Almost Independent of DG Real
Power Generation
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21. DG participation in DS control
Distributed Generation
Voltage Dependence on Load is Almost Unchanged
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22. DG participation in DS control
Distributed Generation
Grid Interconnection of Renewable Energy Sources at
Distribution Level with Power Improvement Features 6
Some other functions that can be provided by DGs:
power transfer at unity power factor
local reactive power support
harmonic mitigation
load balancing
Those functions can be achieved simultaneously or individually
no additional hardware is needed
6 M. Singh, V. Khadkikar, A. Chandra, and R.K. Varma, “Grid interconnection of
renewable energy sources at the distribution level with power-quality improvement
features”, Power Delivery, IEEE Transactions on, vol. 26, no. 1, pp. 307 –315, jan. 2011
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23. DG participation in DS control
Distributed Generation
Observation I
DG can cause voltage rise on the feeder to which it is connected.
There is a method to mitigate the voltage rise
variable power factor operation
increased number of switching and losses.
Current grid code do not allowed DG to control its output voltage.
DGs is also potential to improve power quality.
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24. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Works in which DGs are in
constant power factor mode.
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25. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Optimal Distribution Voltage Control and coordination
with distributed generation 7
Minimize total losses and voltage deviation
Control OLTC, Shunt Capacitor (SC), Shun Reactor (SR), Step
Voltage Regulator (SVR), Static Voltage Controller (SVC)
Optimization methods : Genetic Agorithm
DGs = PVs with constant unity power factor.
Centralized control
7 T. Senjyu, Y. Miyazato, A. Yona, N. Urasaki, and T. Funabashi, “Optimal distribution
voltage control and coordination with distributed generation”, Power Delivery, IEEE
Transactions on, vol. 23, no. 2, pp. 1236 –1242, 2008
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26. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Optimal Distribution Voltage Control and coordination
with distributed generation
Objective: min w1 |Vn,ref − Vn | + w2 Loss
Contraints:
voltage limits
tap position limits (OLTC)
Optimization methods : Genetic Agorithm
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27. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Optimal Distribution Voltage Control and coordination
with distributed generation
SVC Model
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28. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Optimal Distribution Voltage Control and coordination
with distributed generation
SVR Model
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29. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Works in Which DGs are in CONSTANT power factor
mode 1
Alessandro Casavola, Giuseppe Franzè, Daniele Menniti, and
Nicola Sorrentino, “Voltage regulation in distribution networks in
the presence of distributed generation: A voltage set-point
reconfiguration approach”, Electric Power Systems Research,
vol. 81, no. 1, pp. 25 – 34, 2011 → OLTC only
Joon-Ho Choi and Jae-Chul Kim, “Advanced voltage regulation
method of power distribution systems interconnected with
dispersed storage and generation systems”, Power Delivery,
IEEE Transactions on, vol. 16, no. 2, pp. 329 –334, April 2001 →
OLTC only
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30. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Works in Which DGs are in CONSTANT power factor
mode 2
D. Viawan, F.A.; Karlsson, “Combined local and remote voltage
and reactive power control in the presence of induction machine
distributed generation”, IEEE Transactions on Power Systems,
vol. 22, no. 4, pp. 2003–2012, 2007, cited By (since 1996) 10 →
OLTC and SC
Miyoung Kim, R. Hara, and H. Kita, “Design of the optimal ultc
parameters in distribution system with distributed generations”,
Power Systems, IEEE Transactions on, vol. 24, no. 1, pp. 297
–305, feb. 2009 → OLTC only
all of them do not include SVC and D-STATCOM
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31. DG participation in DS control
Volt/Var Control In Distribution System With DGs
Observation II: Constant Power Factor Operation
Among paper considering DG constant power factor operation:
most include OLTC and DG
other also include SC
only one include SVR and SVC
none include D-STATCOM
single objective mathematical programming
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32. DG participation in DS control
DG Participation in Volt/Var Control
Works in which DGs are in
variable power factor mode
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33. DG participation in DS control
DG Participation in Volt/Var Control
Minimizing Reactive Power Support for Distributed
Generation8
Choosing power factor of DGs and setting of OLTC
Maximising DG reactive power generation
Reducing transmission system burden
Enhanced passive approach vs active approach
Uses DG and OLTC only
8 L. F. Ochoa, A. Keane, and G. P. Harrison, “Minimizing the reactive support for
distributed generation: Enhanced passive operation and smart distribution networks”,
Power Systems, IEEE Transactions on, vol. PP, no. 99, pp. 1, 2011
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34. DG participation in DS control
DG Participation in Volt/Var Control
Multiagent Dispatching Scheme for DGs for Voltage
Support on Distribution Feeders9
Each generator control its output based on local measurements.
Those measurements used to calculate sensitivity factors.
Coordination between DGs through a Control Net Protocol (CNP)
Reliable communication network
Uses DG and OLTC only
9 M.E. Baran and I.M. El-Markabi, “A multiagent-based dispatching scheme for
distributed generators for voltage support on distribution feeders”, Power Systems,
IEEE Transactions on, vol. 22, no. 1, pp. 52 –59, feb. 2007
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35. DG participation in DS control
DG Participation in Volt/Var Control
Options for Controls of Reactive Power by Distributed
PV Generators 10
Local control of PV generators
Local measurements were sufficient for voltage regulation
Support the idea of Baran and Markabi (2007)
Uses DG and OLTC only
10 K. Turitsyn, P. Sulc, S. Backhaus, and M. Chertkov, “Options for control of reactive
power by distributed photovoltaic generators”, Proceedings of the IEEE, vol. 99, no. 6,
pp. 1063 –1073, june 2011
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36. DG participation in DS control
DG Participation in Volt/Var Control
Voltage and Reactive Power Control in Systems with
Synchronous Machine-Based Distributed Generation11
Minimize total losses.
Include OLTC and SC.
DG regulate voltage at point of common connection.
If SC is enough, DG participation does not reduce losses
significantly.
Excess reactive power can support transmission system (Ochoa,
et. al. , 2011).
11 F.A. Viawan and D. Karlsson, “Voltage and reactive power control in systems with
synchronous machine-based distributed generation”, Power Delivery, IEEE
Transactions on, vol. 23, no. 2, pp. 1079 –1087, april 2008
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37. DG participation in DS control
DG Participation in Volt/Var Control
Short-Term Schedulling and Control of Active
Distribution Systems with High Penetration of
Renewable Energy Resources12
a day-ahead scheduler + intra-day (15 minutes) scheduler.
includes dispatchable and not-dispatchable DGs.
a day-ahead scheduler is a forecaster of generator and energy
storage.
intraday scheduler minimize generation deviation define by the
other scheduler.
12 A. Borghetti, M. Bosetti, S. Grillo, S. Massucco, C.A. Nucci, M. Paolone, and
F. Silvestro, “Short-term scheduling and control of active distribution systems with high
penetration of renewable resources”, Systems Journal, IEEE, vol. 4, no. 3, pp. 313
–322, sept. 2010
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39. DG participation in DS control
DG Participation in Volt/Var Control
The Day-Ahead Scheduler
objective is minimal energy cost
R N
min cj,r ∆tPjr
r =1 j=1
constraints:
Electrical Load balance
Storage units
Power and energy limits
Thermal load balance
inputs: load forecast, generation forecast, energy cost, limits of
generating units, initial status of storage units.
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40. DG participation in DS control
DG Participation in Volt/Var Control
The Intra-day Scheduler
Multiobjective:
min αSP + βPloss + γSV
∆x
minimal voltage deviation
minimal generation deviation
minimal network losses
Input: 15-minutes ahead forecast, state estimation results
output: control signal for OLTC, voltage regulators, DGs and
energy storages
controlled variable: active and reactive power generation and
OLTC tap position
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42. DG participation in DS control
DG Participation in Volt/Var Control
What are missing?
Further considerations are needed:
switching seguence?
transition cost?
security?
Optimum path?
Reachability?
Initial state Proposed
Optimum State
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43. DG participation in DS control
DG Participation in Volt/Var Control
Reducing Number of Switching:
1. Constraint Addition
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44. DG participation in DS control
DG Participation in Volt/Var Control
Importance of Switching Reduction
switching may initiate transients
device has limited total number of switchings
DG’s variable power factor mode increase OLTC’s switching
numbers
slow mechanical switch vs fast load change and intermitent
renewables
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45. DG participation in DS control
DG Participation in Volt/Var Control
Reactive Power and Voltage Control in Distribution
System with Limited Switching Operation 13
Objective : min energy losses
23
min E = f (x1 (t), x2 (t), x3 (t))
t=0
x1 discrete variables: OLTCs and Capacitors
x2 Q and V
x3 P and θ
13 M.B. Liu, C.A. Canizares, and W. Huang, “Reactive power and voltage control in
distribution systems with limited switching operations”, Power Systems, IEEE
Transactions on, vol. 24, no. 2, pp. 889 –899, may 2009
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46. DG participation in DS control
DG Participation in Volt/Var Control
Reactive Power and Voltage Control in Distribution
System with Limited Switching Operation
Constraints:
power flow equations
tap positions limits
capacity limits
additional constraints : Maximum Allowable daily switching
operation (MADSON)
23
h(x1 (0), x1 (1), ..., x1 (23)) = |x1(t+1) − x1(t) | ≤ Sx1 Cx1
t=0
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47. DG participation in DS control
DG Participation in Volt/Var Control
Reactive Power and Voltage Control in Distribution
System with Limited Switching Operation
Proposed optimization method:
discrete variables are treated as continous variables
inequality constraints are converted into equality constraints with
help from slack variables
x1(t) + su1(t) = x1(t)max
x1(t) − su1(t) = x1(t)min
x2(t) + su2(t) = x2(t)max
x2(t) − su2(t) = x2(t)min
h(x1(0) , x1(2) , ..., x1(23) ) = Sx1 Cx2
su1(t) , sl1(t) , su2(t) , sl1(t) ≥ 0
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48. DG participation in DS control
DG Participation in Volt/Var Control
Reactive Power and Voltage Control in Distribution
System with Limited Switching Operation
Proposed optimization method:
interior point method was used
KKT are derived and solved with Newton-Raphson method.
compared with Genetic Algorithm, BARON and DICOPT
test cases: Baran and Wu 69-buses system and chinese
14-buses system
the proposed method is faster than other methods.
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50. DG participation in DS control
DG Participation in Volt/Var Control
Alternative Approach:
Rule-based Control
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51. DG participation in DS control
DG Participation in Volt/Var Control
Reasons for Alternative Approach
Our problem is NP-hard MINLP unless some simplification is
assumed.
Distribution system is large
Slow voltage controller movement and changing load and
generation profile
minimum switching is favorable
some switching action are mutually exclusive
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52. DG participation in DS control
DG Participation in Volt/Var Control
Configurable, Hierarchical, Model-Based Control of
Electrical Distribution Circuits14
objective : close and better operating state; minimize change of
state
preference-based multi objectives and constraints:
voltage regulation
Capacity constraint
losses
priority is adjustable
control devices : SC, OLTC, SVR, DG
single step (SS) : SC, DG (on-min-on)
multi step (MS) : OLTC, DG (min - max discretized)
14 J. Hambrick and R. P. Broadwater, “Configurable, hierarchical, model-based
control of electrical distribution circuits”, Power Systems, IEEE Transactions on, vol.
PP, no. 99, pp. 1, 2010
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53. DG participation in DS control
DG Participation in Volt/Var Control
CHMC Main Loop
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54. DG participation in DS control
DG Participation in Volt/Var Control
CHMC Main Loop
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55. DG participation in DS control
DG Participation in Volt/Var Control
Selection of New State
If voltage deviation is smaller than before, accept this newer state.
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56. DG participation in DS control
DG Participation in Volt/Var Control
Selection of New State
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57. DG participation in DS control
DG Participation in Volt/Var Control
Selection of New State
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58. DG participation in DS control
DG Participation in Volt/Var Control
Ways to Reduce Number of Switching
Using previous methods, variable power factor DGs operation
increase number of switching. There are to ways to reduce the
number:
MADSON constraint
rule-based optimization
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59. DG participation in DS control
DG Participation in Volt/Var Control
Observation III: Variable Power Factor Operation
Among paper considering DG variable power factor operation:
most include only OLTC and DG (one include DG)
single-objective mathematical programming
increased number of switching is expected
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60. DG participation in DS control
DG Participation in Volt/Var Control
Observation IV: Possible Gaps for Future Research
What is not available in literature is volt/var control strategy/method
which:
include a rather complete types of (potential) voltage regulator
is multi-objective optimization plus higher information processing
In addition, optimum switching sequence needed to reach the
optimum state has not been well studied.
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61. DG participation in DS control
Summary
Summary
DGs reactive power capability is not fully utilised.
Grid codes require constant-power factor operation.
Most published research follow the grid codes.
Some works consider the variable-power factor (VPF) operation.
VPF operation increase number of switchings of voltage
regulators
two ways in limiting switching number: MADSON constraint and
a rule-based approach
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62. DG participation in DS control
Summary
Thank You Very Much
DG Operation for Distribution System Volt/Var
Control
N. Daratha
guided by
Prof. J.D. Sharma and Prof. B. Das
Department of Electrical Engineering
IIT Roorkee
PhD Seminar Course
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