Load Shedding A pply Neural Network and Power Sensitivity Theory
Published by :
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181
Vol. 7 Issue 04, April-2018
Load Shedding Apply Neural Network and
Power Sensitivity Theory
L.T. Nghia1, T.T. Giang1, Q.H. Anh1 P.T.T. Binh2
,
Bui.NguyenXuan. Vu1
1Faculty of Electrical and Electronics Engineering, HCMC University of Technology and Education
Hochiminh city, Vietnam
2Faculty of Electrical and Electronics Engineering, HCMC University of Technology
Hochiminh city, Vietnam
Abstract—This paper proposed the method load shedding on the
basis of the combination of Generalized Regression Neural
Network, power sensitivity theory and Phase Electrical Distance
theories to recover the frequency to allowable limit in the event loss
a generator occurring in the electric system. The phase electrical
distance calculation intended to calculate the distance between the
generator outage and the load to align the load buses in ascending.
The phase electrical distance sequence as compared to the fault
generator. From there, the loads on the buses which are near the
generator outage will be cut firstly, then the next loads until the
system return to stable. The effectiveness of the proposed method
are tested on the IEEE 39 Bus New England 10 Generators, which
demonstrated the effective the proposed method.
improve the frequency response and to reduce the risk of
unstable electric system.
This paper proposes the method of load shedding under pre-
designed load shedding rules based on phase electrical distance
method and power sensitivity theory. ANN neural networks are
used to identify and classify load shedding control strategies
based on the designed rules. The effectiveness of the proposed
method has been tested on the IEEE 39 Bus New England.
II.
MATERIALS AND METHODS.
A. Generalized regression neural network.
Keywords: Load Shedding, Phase Electrical Distance,
Power Sensitivity, Neural Network, Frequency Control.
I.
INTRODUCTION.
Load shedding is an effective method for restoring electrical
system frequencies by reducing the load to suit the power
supply. Most of the studies related to load shedding are based
on rate change of frequency and voltage of the power system.
H. Bevrani and et al [1] presented an overview of the key
issues in the use of frequency rate change (df/dt) in power
system emergency control schemes. The role of df/dt in
designing effective under frequency load shedding (UFLS) plan
was discussed. The impact of new variable renewable sources
(such as wind and solar units) on system frequency gradient is
analyzed, and the need for the revising of frequency
performance standards, re-tuning of automatic UFLS relays,
and use of ∆f/∆t rather than df/dt are emphasized.
Fig. 1. Generalized regression neural network.
GRNN (Generalized Regression Neural Network) is a
powerful tool in the application for identification problems.
GRNN is basically the same as fig. 1 including input layer,
radial function hidden layer and linear output layer. Neuron
network operation must include the spread parameter whose
optimum value is determined by the experimental error.
Urban Rudez and et al [2] studied a novel approach to
underfrequency load shedding is using the frequency second
derivative as a source of information for a forecast of the
frequency trajectory. A Newton method based approximation
and the interpolation of the frequency second derivative are
continuously performed in order to forecast the minimum
frequency value using a numerical integration.
F. Shokooh and et al [3] introduced the new technology of
intelligent load shedding application in a large industrial
facility.
Conventional methods of system load shedding often have
to wait until the frequency drops below the allowable threshold
to make the load shedding decision. However, due to the
complexity of the power system, it is imperative to treat it
promptly after a fault in order to minimize the damage, to
B. Phase electrical distance [4]
The definition of phase electrical distance between the two
nodes by using the elements of the matrix [dθ/dP] is the inverse
matrix from the power sensitivity matrix [dP/dθ], as follows:
DP(i,j)=(dθi/dPi)+(dθj/dPj)-(dθj/dPi)-(dθi/dPj)
(1)
The components [dθ/dP] are extracted from the Jacobian
matrix. There are two interpretations of the phase electrical
distance:
(2)
j
j
i
i
j
D (i, j) =
+
-
-
P
P
P
P
P
i
j
i
Write this distance in another way:
(3)
j
j
j
i
j
i
D (i, j) =
-
+
-
P
P
P
P
P
i
i
IJERTV7IS040393
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408
Published by :
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181
Vol. 7 Issue 04, April-2018
PowerWorld simulation software to shed for each generator in
trouble at different load levels. (including 41 load levels from
60% to 100%). Dismissed until the rotor angle, frequency and
voltage of the buses are within the allowable range of stopping,
so that for each case the incident will have the number of load
shedding corresponding to that case. The incident data collected
would correspond to a number of load shedding from the trained
neuron function.
Location of load shedding: Use phase electrical distance for
calculating distance between nodes. The load shedding position
will be based on the distances from the generator outage
(generator bus) to the remaining load buses to the load shedding
order, or in other words the priority of the nodes closer to the
generator will be first off, because these load nodes directly
affect the generator is the most trouble.
æ
ç
ö
÷
is phase difference between j and i caused by a
j
j
i
j
-
ç
ç
è
÷
÷
ø
P
P
active power injection in j.
æ
ç
ç
è
ö
is phase difference between i and j caused by a
j
÷
÷
ø
i
-
P
P
i
i
active power injection in i.
Then else:
(4)
j
j
j
i
i
j
D (i, j) =
-
+
-
P
P
P
P
P
i
i
æ
ç
ö
is variation in phase of j caused by a active power
÷
j
j
j
-
ç
ç
è
÷
÷
ø
P
P
i
The flowchart load shedding process is shown in Fig. 3 and
4.
transit from j to i.
æ
ç
ö
is variation in phase of i caused by a active power
÷
i
i
-
ç
ç
è
÷
÷
ø
P
P
i
j
transit from i to j.
Two nodes electrically very close will always have a very
small phase difference corresponding to the small distance D.
Therefore, in the event of a loss of generator, it should be cut
the load at the buses which near the generator in advance.
Fig. 3. Flowchart load shedding online
Fig. 2. The block diagram of the relationship between the generator j and
the loads
With:
D ( j,1) < D ( j,2) < D ( j,3)....< D ( j,n)
P
P
P
P
Prioritized load shedding: Load 1 à Load 2 à Load 3 à …
à Load n
III.
PROPOSED METHODS.
A. Set up load shedding program.
Load shedding are based on three main factors: the timing,
the amount of load to be shed and the location of load shedding
The timing: The system data is sent to the control center for
continuous measurement, when the system frequency is within
the allowable range of 59.7Hz<f<60.3Hz, the system frequency
is within the allowable value, whereas if the system frequency
is outside of the allowable range, the load shedding program
will start, the neuron function will be activated to identify the
generator with the fault and the load shedding sequence. The
time is calculated after the time of the incident is 300ms. This
interval includes time intervals: measurement of data
acquisition, data transfer, data processing, and load circuit
breaker operation. [5]
Fig. 4. Flowchart simulator sampling and neural network training
The amount of load to be shed: After obtaining the load
shedding sequence list for each generator failure, use the offline
Fig. 5. The process of developing a load shedding strategy
IJERTV7IS040393
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409
Published by :
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181
Vol. 7 Issue 04, April-2018
The process of developing a load shedding strategy,
including steps:
From: Dp(i,j) = (δθi/δPi) + (δθj/δPj) - (δθj/δPi) - (δθi/δPj), with
(δθi/δPi), (δθj/δPj), (δθj/δPi) and (δθi/δPj) are the corresponding
elements in row i colum j in matrix [J1].
The Jacobian matrix has the following general form:
Fig. 6. General Jacobian matrix
Step 1: Extract the Jacobian matrix J1
Step 2: Inverse J1
Fig. 8. Sampling process
Step 3: Apply phase electrical distance formula
Step 4: Building the relationship between the nodes containing
the generator and the nodes containing the load.
Step 5: Arranges the order of the load shedding with the
corresponding generator failure.
B. Application ANN to identify the failure.
Identification of failure in electrical systems is often
difficult due to its complexity. Traditional failure identification
methods are often unsuitable, which can cause problems not to
be resolved in time to endanger the system. Thus, the ANN
method with advantages of computational speed as well as
efficiency will best solve these difficult problems that other
traditional methods cannot solve.
Fig. 9. Neural network training model with inputs and outputs
IV.
TESTING ON THE IEEE 39 BUS NEW ENGLAND
First, need to build data sets for ANN learning. This
database is based on parameters at different load levels of the
system (rate change of generator power, load power, voltage at
buses, power variation on line, rate change of frequency at
buses). The database must meet the following requirements:
The database must fully display the status of the operation
and must show all the various failure scenarios.
The database created should ensure objectivity of the
parameters of the test power system.
The process of creating a database based on simulation
PowerWorld and is done through the following stages:
Fig. 10. The IEEE 39 bus New England
The proposed method is tested on The IEEE 39 bus New
England, using Powerworld software to collect samples and
Matlab software for neural network training.
Fig. 7. Simulation steps for input, output sampling
A. Calculate the phase electrical distance.
The phase electrical distance calculation is done in the
following steps:
Step 1: Take the Jacobian matrix J1 from Powerworld
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Published by :
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181
Vol. 7 Issue 04, April-2018
TABLE 2. Proposed load shedding strategy
Bus
Bus Bus
30 32
Bus
33
Bus
34
Bus
35
Bus
36
Bus
37
Bus
38
Bus
39
Order
1
Load Load Load Load Load Load Load Load Load
25 20 20 23 23 25 29 39
Load Load Load Load Load Load Load Load Load
16 16 21 21 28
Load Load Load Load Load Load Load Load Load
18 24 24 16 24 26 26
Load Load Load Load Load Load Load Load Load
15 15 24 16 18 27
Load Load Load Load Load Load Load Load Load
16 12 21 21 15 15 27 25
Load Load Load Load Load Load Load Load Load
26 15 18 18 18 18 18 18
Load Load Load Load Load Load Load Load Load
27 16 16 25
Load Load Load Load Load Load Load Load Load
15 18 23 23 15 16 16
Load Load Load Load Load Load Load Load Load
24 24 27 27 24 15 15
Load Load Load Load Load Load Load Load Load
25 27 27 26 26 24 27
Load Load Load Load Load Load Load Load Load
27 26 26 25 25 24
Load Load Load Load Load Load Load Load Load
21 21 25 25 21 21 26
Load Load Load Load Load Load Load Load Load
39 26 39 21
Load Load Load Load Load Load Load Load Load
23 23 20 20 23 12
Load Load Load Load Load Load Load Load Load
12 39 12 12 12 12 28 23 23
Load Load Load Load Load Load Load Load Load
28 20 39 39 39 39 29 39 20
Load Load Load Load Load Load Load Load Load
29 28 28 28 28 28 12 12 28
Load Load Load Load Load Load Load Load Load
20 29 29 29 29 29 20 20 29
4
2
3
3
7
3
8
8
7
4
4
3
3
5
4
6
Fig. 11. The Jacobian matrix
4
7
Step 2: Use the inv function of matlab to invert the matrix
Step 3: Apply phase electrical distance formula: Dp(j,i) =
3
3
3
3
3
J1.
8
4
4
9
Dp(i,j) = (δθi/δPi) + (δθj/δPj) - (δθj/δPi) - (δθi/δPj)
4
4
From the above formula, use the matlab software to set the
matrix related to the phase electrical distance between the nodes
in the network together, called the matrix Dp.
Step 4: From the relational parameters between the buses in
the system to the phase electrical distance, the relationship
between the nodes containing the generator and the nodes
containing the load is shown in Table 1.
10
11
12
13
14
15
16
17
18
8
8
7
7
4
8
8
8
8
7
7
8
7
7
7
TABLE 1. Table summarizes the relationship between the nodes containing
the generator and the nodes containing the load on phase electrical distance.
Bus 30 Bus 32 Bus 33 Bus 34 Bus 35 Bus 36 Bus 37 Bus 38 Bus 39
Bus 3 0.027 0.041 0.047 0.064 0.045 0.057 0.040 0.065 0.038
Bus 4 0.037 0.031 0.050 0.067 0.047 0.060 0.048 0.072 0.038
Bus 7 0.045 0.033 0.058 0.075 0.055 0.068 0.056 0.080 0.037
Bus 8 0.044 0.033 0.057 0.075 0.055 0.067 0.055 0.080 0.035
Bus 12 0.061 0.041 0.071 0.088 0.069 0.081 0.072 0.096 0.059
Bus 15 0.041 0.041 0.039 0.056 0.036 0.048 0.051 0.071 0.047
Bus 16 0.039 0.044 0.031 0.048 0.029 0.041 0.048 0.067 0.046
Bus 18 0.034 0.045 0.043 0.060 0.041 0.053 0.044 0.064 0.044
Bus 20 0.070 0.074 0.028 0.018 0.060 0.072 0.079 0.097 0.077
Bus 21 0.049 0.053 0.041 0.058 0.023 0.039 0.058 0.076 0.056
Bus 23 0.056 0.061 0.048 0.066 0.021 0.024 0.065 0.084 0.063
Bus 24 0.044 0.048 0.036 0.053 0.030 0.041 0.053 0.071 0.051
Bus 25 0.027 0.054 0.058 0.075 0.055 0.068 0.022 0.061 0.045
Bus 26 0.040 0.058 0.056 0.074 0.054 0.066 0.041 0.042 0.053
Bus 27 0.040 0.054 0.050 0.067 0.048 0.060 0.044 0.053 0.051
Bus 28 0.065 0.083 0.082 0.099 0.079 0.092 0.067 0.026 0.079
Bus 29 0.067 0.085 0.084 0.101 0.081 0.093 0.068 0.015 0.080
Bus 39 0.053 0.062 0.078 0.095 0.075 0.087 0.066 0.094 0.000
Explanation: According to the suggested strategy table
above, if there is a fault at generator 30, the load shedding order
will be Load 25 à Load 3 à Load 18 à ... until the system is
stabilized again. Similarly, for the remaining generators.
B. Test load shedding on the IEEE 39 bus New England
by Powerwold.
Process simulation sampling with the IEEE 10 generators 39
bus are made as follows:
Assuming the fault generator is 34, at load level 100%, the
frequency and deviation of the rotor angle become unstable.
Fig. 12. Diagram of rotor angle generator and frequency of bus at fault
generator 34 load level 100%
Step 5: Arranges the order of the load shedding with the
corresponding generators failure.
When the bus frequency and rotor angle exceeded the
allowable range, load shedding are made according to the
strategic proposed. In this case, just shed the Load 20, the rotor
frequency and angle have stabilized.
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Published by :
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ISSN: 2278-0181
Vol. 7 Issue 04, April-2018
V.
COMPARISON OF SUGGESTED METHOD WITH
OTHER METHODS.
A. Load shedding based on the AHP algorithm (Analytic
Hierarchy Process) [6]
AHP is the approach to making decisions. This method
presents balanced assessment options and criteria, and
integrates them into a final decision. AHP is particularly
suitable for cases involving analysis and quantification, make
decisions when there are multiple options depending on the
criteria with multiple interactions.
Fig. 13. Diagram of rotor angle generator and frequency of bus after shed
Load 20
Simulation proceeds from 60% to 100% load level at each
load level causing the outage generators from generator 30 to
39. After simulating and load shedding, the record is aggregated
into sample. The result of the number of samples after the
simulation of the case must load shedding when the generator
fault is 369 samples.
Table 3. The order of load shedding according to the AHP algorithm
Order
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Load
L39
L4
L8
L20
L7
L27
L29
L15
L16
L3
L24
L28
L21
L25
L23
L26
L18
L12
L31
load center
LC1
LC1
LC1
LC2
LC1
LC3
LC3
LC2
LC2
LC4
LC2
LC3
LC2
LC4
LC2
LC3
LC4
LC1
LC1
Wdi
0.37
0.22
0.22
0.3
Wkj
0.467
0.467
0.467
0.278
0.467
0.16
Wij
0.172543
0.104727
0.104727
0.08208
0.13
0.33
0.33
0.17
0.17
0.49
0.16
0.20
0.11
0.31
0.09
0.14
0.2
0.061118
0.053155
0.053155
0.048329
0.048329
0.047017
0.043056
0.031606
0.030445
0.029619
0.025351
0.022349
0.018659
0.011867
0.011867
C. Neural network training
This section introduces the generalized regression neural
network training model; the training process follows these
steps:
Step 1: Data collection, performs the collection via
simulation on the PowerWorld software to retrieve data for each
load level. Compile into a dataset, then split 85% of the sample
for training and 15% of the sample for testing.
Step 2: Create a network, implementing generalized
regression neural network training should provide only input
and output vector information along with spread constant, the
procedure as follows:
Create input_data is 85% of the samples (315 samples),
output_data, input_test is 15% of the samples (54 samples).
0.16
0.278
0.278
0.10
0.278
0.16
0.278
0.10
0.278
0.16
0.10
0.467
0.467
0.03
0.03
B. Load shedding based on under frequency load
shedding relays [7]
Load shedding based on under frequency load shedding
relays is the most commonly used method, which is still being
used in many parts of the world, including Vietnam. When the
grid frequency falls below the permitted threshold, the relay will
be load shedding, prevents the system frequency declines.
Without this load shedding control, the greatest possible
consequence is the blackout, ie, the widespread outage.
For example, the ERCOT load shedding program, has a load
shedding plan under frequency load shedding shown in Table 4.
Fig. 14. Neural network training structure
Step 3: Create a interface.
To facilitate training, monitoring, fault identification and
load shedding. The creation of an appropriate interface program
is necessary to enable the operator to easily monitor the
operation of the system. Combined with the idea of creating a
machine system that works on different power systems the
interface is created as follows:
Table 4. The ERCOT load shedding program
Frequency
59.3 Hz
58.9 Hz
58.5 Hz
Load
5% of total load
15% of total load
25% of total load
C. Simulate and compare methods with each other.
Fig. 15. The neural training system interface forecast load shedding in
case of generator failure
Fig. 16. Diagram of rotor angle and bus frequency after generator 34
outage according to the proposed load shedding method.
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Published by :
International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181
Vol. 7 Issue 04, April-2018
ACKNOWLEDGMENT
This research was supported by Ho Chi Minh City University
of Technology and Education under a research at the Power
System and Renewable Lab.
REFERENCES
[1]
[2]
H. Bevrani, Senior Member, IEEE, G. Ledwich, Senior
Member, IEEE, and J. J. Ford. "On the Use of df/dt in Power
System Emergency Control", 2009.
Urban Rudez, Rafael Mihalic, Faculty of Electrical
Engineering, University of Ljubljana, Trzaska 25, 1000
Ljubljana, Slovenia. "A novel approach to underfrequency
load shedding", 2011.
Fig. 17. Diagram of rotor angle and bus frequency after generator 34
outage according to the AHP method.
[3]
Farrokh Shokooh, J.J. Dai, Shervin Shokooh, Jacques Tastet,
Hugo Castro, Tanuj Khandelwal, & Gary Donner, IEEE
Industry Applications Magazine, "Intelligent load shedding,
case study of the application in a large industrial facility", 21
January 2011.
[4]
[5]
Lagonotte Patrick, Labroratoire d'Automaticque et
d'Informatique Industrielle, "The different electrical
distances"
Fig. 18. Diagram rotor angle and bus frequency after generator 34 outage
according to the under frequency load shedding relay method.
Tohid Shekari, Student Member, IEEE, Farrokh Aminifar,
Senior Member, IEEE, and Majid Sanaye-Pasand, Senior
Member, IEEE, "An Analytical Adaptive Load Shedding
Scheme Against Severe Combinational Disturbances", 2015
Nhan MaiNgoc, "Master Thesis: Study of load shedding
using neural network and AHP algorithm", Ho Chi Minh
City of University of Technology and Education, VietNam,
2017
Comparative results of the methods presented in Table 5.
[6]
Table 5. Comparative results of the methods
Frequency
recovery time
(s)
Frequency
stability
(Hz)
Amount of
load shedding
(MW)
Method
[7]
[8]
Ercot, "Under frequency Load Shedding, 2006
Proposed
AHP
45
60,030
60,157
60,89
628,000
738,852
1154,394
D. Kottick, “Neural Network for Predicting the Operation of
an Under Frequency Load Shedding System”, IEEE Trans.
on Power Systems, Vol.11, No. 3, pp. 1350-58, 1996.
55
UFLS relay
100
In the case of generators 34 outage with a load level of
100%, the proposed method has many advantages over the AHP
method and the low frequency method, as follows:
The amount of load shedding in at least 3 methods.
The rotor angle recovery time is almost the same, but the
frequency recovery time of the proposed method is earlier
(about 20 ÷ 25s). System stability sooner and increased
reliability in the supply.
It can be seen that the load shedding is based on phase
electrical distance are offset for both the remaining methods,
with fast recovery times, optimum capacity load shedding and
bus frequencies within the allowable range.
VI.
CONCLUSION.
The paper proposed the method load shedding on the basis
of the combination of Generalized Regression Neural Network,
power sensitivity theory and Phase Electrical Distance theories
to maintain a stable electrical system in the event loss a
generator occurring in the electric system. The effect of the
proposed method is to perform offline simulations on the IEEE
39 Bus New England test system. The results of the comparison
of the efficacy of the proposed method with the AHP method
and low frequency method revealed that: The proposed method
has a system frequency of recovery that is 18% faster than the
AHP method, 55% faster than the low frequency method; The
load shedding capacity was 15% less than the AHP method and
45.6% less than the under frequency load shedding relay
method.
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