Artificial Neural Networks

Artificial Neural Networks

Outline Introduction to Neural Network Introduction to Artificial Neural Network Properties of Artificial Neural Network Applications of Artificial Neural Network Demo Neural Network Tool Box Case-1 Designing XOR network Case-2 Power system security assessment 2

What are Neural Networks? Models of the brain and nervous system Highly parallel Process information much more like the brain than a serial computer Learning Very simple principles Very complex behaviours 3

BIOLOGICAL NEURAL NETWORK Figure 1 Structure of biological neuron 4

The Structure of Neurons A neuron has a cell body, a branching input structure (the dendrite) and a branching output structure (the axon) Axons connect to dendrites via synapses. Electro-chemical signals are propagated from the dendritic input, through the cell body, and down the axon to other neurons 5

The Structure of Neurons A neuron only fires if its input signal exceeds a certain amount (the threshold) in a short time period. Synapses vary in strength Good connections allowing a large signal Slight connections allow only a weak signal. Synapses can be either excitatory or inhibitory. 6

7 The Artificial Neural Network Figure 2 Structure of artificial neuron Mathematically, the output expression of the network is given as + = = = N K K K b W X F S F Y 1 ) (

ANNs The basics ANNs incorporate the two fundamental components of biological neural nets: 1. Neurones (nodes) 2. Synapses (weights) 8

Properties of Artificial Neural Nets (ANNs) 9

Properties of Artificial Neural Nets (ANNs) Many simple neuron-like threshold switching units Many weighted interconnections among units Highly parallel, distributed processing Learning by tuning the connection weights 10

Appropriate Problem Domains for Neural Network Learning Input is high-dimensional discrete or realvalued (e.g. raw sensor input) Output is discrete or real valued Output is a vector of values Form of target function is unknown Humans do not need to interpret the results (black box model) 11

Applications Ability to model linear and non-linear systems without the need to make assumptions implicitly. Applied in almost every field of science and engineering. Few of them are Function approaximation, or regression analysis, including time series and modelling. Classification, including pattern and sequence recognition, novelty detection and sequential decision making. Data processing, including filtering, clustering, blind signal separation and compression. Computational neuroscience and neurohydrodynamics Forecating and prediction Estimation and control 12

Applications in Electrical Load forecasting Short-term load forecasting Mid-term load forecasting Long-term load frecasting Fault diagnosis/ Fault location Economic dispatch Security Assessment Estimation of solar radiation, solar heating, etc. Wind speed prediction 13

Designing ANN models Designing ANN models follows a number of systemic procedures. In general, there are five basics steps: (1) collecting data, (2) preprocessing data (3) building the network (4) train, and (5) test performance of model as shown in Fig. Fig. 3. Basic flow for designing artificial neural network model 14

Neural Network Problems Many Parameters to be set Overfitting long training times... 15

INTRODUCTION TO NN TOOLBOX The Neural Network Toolbox is one of the commonly used, powerful, commercially available software tools for the development and design of neural networks. The software is user-friendly, permits flexibility and convenience in interfacing with other toolboxes in the same environment to develop a full application. 16

Features It supports a wide variety of feed-forward and recurrent networks, including perceptrons, radial basis networks, BP networks, learning vector quantization (LVQ) networks, self-organizing networks, Hopfield and Elman NWs, etc. It also supports the activation function types of bi-directional linear with hard limit (satlins) and without hard limit, threshold (hard limit), signum (symmetlic hard limit), sigmoidal (log-sigmoid), and hyperbolic tan (tan-sigmoid). 17

Features In addition, it supports unidirectional linear with hard limit (satlins) and without hard limit, radial basis and triangular basis, and competitive and soft max functions. A wide variety of training and learning algorithms are supported. 18

Case-1 Problem Definition The XOR problem requires one hidden layer & one output layer, since it s NOT linearly separable. 19

Design Phase 20

NN Toolbox NN toolbox can be open by entering command >>nntool It can also be open as shown below It will open NN Network/ Data Manager screen. 21

Getting Started 22

NN Network/ Data Manager 23

Design Let P denote the input and T denote the target/output. In Matlab as per the guidelines of implementation these are to be expressed in the form of matrices: P = [0 0 1 1; 0 1 0 1] T = [0 1 1 0] To use a network first design it, then train it before start simulation. We follow the steps in order to do the above: 24

Provide input and target data Step-1: First we have to enter P and T to the NN Network Manager. This is done by clicking New Data once. Step-2: Type P as the Name, and corresponding matrix as the Value, select Inputs under DataType, then confirm by clicking on Create. Step-3: Similarly, type in T as the Name, and corresponding matrix as the Value, select Targets, under DataType, then confirm. See a screen like following figures 25

Providing input 26

Providing target data 27

Create Network Step-4: Now we try to create a XORNet. For this click on New Network. See a screen like in the following figure. Now change all the parameters on the screen to the values as indicated on the following screen: 28

Defining XORNet network 29

Setting network parameters Make Sure the parameters are as follows: Network Type = Feedforword Backprop Train Function = TRAINLM Adaption Learning Function = LEARNGDM Performance Function = MSE Numbers of Layers = 2 30

Define network size Step-5: Select Layer 1, type in 2 for the number of neurons, & select TANSIG as Transfer Function. Select Layer 2, type in 1 for the number of neurons, & select TANSIG as Transfer Function. Step-6: Then, confirm by hitting the Create button, which concludes the XOR network implementation phase. 31

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Step-7: Now, highlight XORNet with DOUBLE click, then click on Train button. You will get the following screen indicated in figure. 33

Training network 34

Defining training parameters 35

Step-8: On Training Info, select P as Inputs, T as Targets. On Training Parameters, specify: epochs = 1000 Goal = 0.000000000000001 Max fail = 50 After, confirming all the parameters have been specified as indented, hit Train Network. 36

Training process 37

Various Plots Now we can get following plots Performance plot It should get a decaying plot (since you are trying to minimize the error). Training State Plot Regression Plot 38

Performance plot plots the training, validation, and test performances given the training record TR returned by the function train. 39

Training state plot plots the training state from a training record TR returned by train. 40

Regression plot Plots the linear regression of targets relative to outputs. 41

View weights and bias Step-8: Now to confirm the XORNet structure and values of various Weights and Bias of the trained network click on View on the Network/Data Manager window. NOTE: If for any reason, you don t get the figure as expected, click on Delete and recreate the XORNet as described above. Now, the XORNet has been trained successfully and is ready for simulation. 42

XORNet Structure 43

Network simulation With trained network, simulation is a way of testing on the network to see if it meets our expectation. Step-9: Now, create a new test data S (with a matrix [1; 0] representing a set of two inputs) on the NN Network Manager, follow the same procedure indicated before (like for input P). 44

Step-10: HighLight XORNet again with one click, then click on the Simulate button on the Network Manager. Select S as the Inputs, type in ORNet_outputsSim as Outputs, then hit the Simulate Network button and check the result of XORNet_outputSim on the NN Network Manager, by clicking View. This concludes the whole process of XOR network design, training & simulation. 45

Simulated result 46

Case-2 Problem Definition Power system security assessment determines safety status of a power system in three fold steps: system monitoring, contingency analysis and security control. load flow equations are required to identify the power flows and voltage levels throughout the transmission system The contingencies can be single element outage (N-1), multiple-element outage (N-2 or N-X) and sequential outage Here single only outage CIARE-2012, at IIT Mandi a time is considered 47

Data Collection The input data is obtained from offline Newton- Raphson load flow by using the MATLAB software. The data have matrix size [12X65]. In data collection, these input data are divided into three groups which are train data, validate data, and test data. The matrix size of train data is [12X32] while the matrix size of test data is [12X23]. 48

Data Collection The bus voltages V 1, V 2 and V 3 are not included in the train data and test data because they are generator buses. They will be controlled by the automatic voltage regulator (AVR) system. In train data, there are 10 train data in secure condition while 12 train data in insecure condition. For test data, there are 1 test data which is secure status while 10 test data are insecure status. 49

DATA COLLECTION 50

DATA COLLECTION 51

DATA PRE-PROCESSING After data collection, 3 data preprocessing procedures train the ANNs more efficiently. solve the problem of missing data, normalize data, and randomize data. The missing data are replaced by the average of neighboring values. 52

Normalization Normalization procedure before presenting the input data to the network is required since mixing variables with large magnitudes and small magnitudes will confuse the learning algorithm on the importance of each variable and may force it to finally reject the variable with the smaller magnitude. 53

Building the Network At this stage, the designer specifies the number of hidden layers, neurons in each layer, transfer function in each layer, training function, weight/bias learning function, and performance function. 54

TRAINING THE NETWORK During the training process, the weights are adjusted to make the actual outputs (predicated) close to the target (measured) outputs of the network. Fourteen types of training algorithms for developing the MLP network. MATLAB provides built-in transfer functions linear (purelin), Hyperbolic Tangent Sigmoid (tansig) and Logistic Sigmoid (logsig). The graphical illustration and mathematical form of such functions are shown in Table 1. 55

TRAINING THE NETWORK Table 1. MATLAB built-in transfer functions 56

Parameter setting Number of layers Number of neurons too many neurons, require more training time Learning rate from experience, value should be small ~0.1 Momentum term.. 57

TESTING THE NETWORK The next step is to test the performance of the developed model. At this stage unseen data are exposed to the model. In order to evaluate the performance of the developed ANN models quantitatively and verify whether there is any underlying trend in performance of ANN models, statistical analysis involving the coefficient of determination (R), the root mean square error (RMSE), and the mean bias error (MBE) are conducted. 58

RMSE RMSE provides information on the short term performance which is a measure of the variation of predicated values around the measured data. The lower the RMSE, the more accurate is the estimation. 59

MBE MBE is an indication of the average deviation of the predicted values from the corresponding measured data and can provide information on long term performance of the models; the lower MBE the better is the long term model prediction. 60

PROGRAMMING THE NEURAL NETWORK MODEL ANN implementation is a process that results in design of best ANN configuration. Percentages of classification accuracy and mean square error are used to represent the performance of ANN in terms of accuracy to predict the security level of IEEE 9 bus system. Steps of ANN implementation is shown in the following flow chart. 61

FLOW CHART 62

USING NN TOOLBOX First run the MATLAB file testandtrain.m. This file contains test data (input data) and target data. Name of input data is train Name of target data is target Network can be initialized from command prompt as >>nftool or by using following step 63

OPENING nftool 64

NETWORK FITTING TOOL Network fitting tool appears as show below 65

PROVIDING INPUT AND TARGET DATA Clicking on next button provide option to give input and target data. 66

VALIDATING AND TEST DATA Here we define training, validating, and test data. 67

DEFINING NETWORK SIZE Here we set the number of neurons in the fitting network s hidden layer. 68

TRAIN NETWORK 69

TRAINING PROCESS By clicking on train button training process starts. 70

PERFORMANCE PLOT 71

TRAINING STATE PLOT 72

REGRESSION PLOT 73

EVALUATE NETWORK 74

SAVE RESULTS 75

SIMULINK DIAGRAM Following are the simulink diagram of the network. 76

Query? 77

Epoch- During iterative training of a neural network, an Epoch is a single pass through the entire training set, followed by testing of the verification set. Generalization- how well will the network make predictions for cases that are not in the training set? Backpropagation- refers to the method for computing the gradient of the case-wise error function with respect to the weights for a feedforward network. Backprop- refers to a training method that uses backpropagation to compute the gradient. Backprop network- is a feedforward network trained by backpropagation. 78