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 CIARE-2012, IIT Mandi

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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 CIARE-2012, IIT Mandi

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BIOLOGICAL NEURAL NETWORK

Figure 1 Structure of biological neuron CIARE-2012, IIT Mandi

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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

CIARE-2012, IIT Mandi

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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. CIARE-2012, IIT Mandi

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The Artificial Neural Network

Figure 2 Structure of artificial neuron

Mathematically, the output expression of the N ⎡ network is given as Y = F ( S ) = F ∑ X K W K + b ⎤ CIARE-2012, IIT Mandi

⎢ ⎣ K =1

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ANNs – The basics

ANNs incorporate the two fundamental components of biological neural nets:

1. Neurones (nodes) 2. Synapses (weights)


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Properties of Artificial Neural Nets (ANNs)


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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


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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)


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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 CIARE-2012, IIT Mandi

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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 CIARE-2012, IIT Mandi

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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 CIARE-2012, IIT Mandi

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Neural Network Problems • • • •

Many Parameters to be set Overfitting long training times ...


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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.


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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). CIARE-2012, IIT Mandi

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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.


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Case-1 Problem Definition

The XOR problem requires one hidden layer & one output layer, since it’s NOT linearly separable.


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Design Phase


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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.


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Getting Started


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NN Network/ Data Manager


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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: CIARE-2012, IIT Mandi

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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 CIARE-2012, IIT Mandi

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Providing input


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Providing target data


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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:


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Defining XORNet network


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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


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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. CIARE-2012, IIT Mandi

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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.


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Training network


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Defining training parameters


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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. CIARE-2012, IIT Mandi

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Training process


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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


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


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


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Regression plot

Plots the linear regression of targets relative to outputs.


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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.


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XORNet Structure


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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).


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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. CIARE-2012, IIT Mandi

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Simulated result


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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 a time is considered47 CIARE-2012, at IIT Mandi

Data Collection

The input data is obtained from offline NewtonRaphson 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]. CIARE-2012, IIT Mandi

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Data Collection

The bus voltages V1, V2 and V3 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. CIARE-2012, IIT Mandi

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DATA COLLECTION


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DATA COLLECTION


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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.


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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.


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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.


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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. CIARE-2012, IIT Mandi

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TRAINING THE NETWORK

Table 1. MATLAB built-in transfer functions CIARE-2012, IIT Mandi

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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 • ..


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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. CIARE-2012, IIT Mandi

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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.


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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.


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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.


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FLOW CHART


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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 CIARE-2012, IIT Mandi

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OPENING nftool


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NETWORK FITTING TOOL

Network fitting tool appears as show below


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PROVIDING INPUT AND TARGET DATA

Clicking on next button provide option to give input and target data.


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VALIDATING AND TEST DATA

Here we define training, validating, and test data.


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DEFINING NETWORK SIZE

Here we set the number of neurons in the fitting network’s hidden layer.


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TRAIN NETWORK


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TRAINING PROCESS

By clicking on train button training process starts.


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PERFORMANCE PLOT


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TRAINING STATE PLOT


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REGRESSION PLOT


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EVALUATE NETWORK


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SAVE RESULTS


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SIMULINK DIAGRAM

Following are the simulink diagram of the network.


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Query

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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. CIARE-2012, IIT Mandi

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