# Basic usage and introduction to the Python package

This tutorial illustrates basic usage of the python package, gives pointer to some examples, and shows how to install everything on a Linux/MacOS/Windows system.

## Outline

- Induction motor example
- Some more examples
- Installation

## Induction motor example

To illustrate the functionality, a small induction motor example will be used where the model equations are borrowed from the paper Aguilera, F., et al. “*Current-sensor fault detection and isolation for induction-motor drives using a geometric approach*”, Control Engineering Practice 53 (2016): 35-46.

### Modelling

For reference, the equations are given below

There are also three measurement equations, where the two current sensors have modeled faults as

The modeling part is where the main differences between Python and Matlab versions are. This is due to that SymPy is used instead of the symbolic toolbox in Matlab. Therefore, let’s import the toolbox and sympy

```
import faultdiagnosistoolbox as fdt
import sympy as sym
```

Now, we define the model as a python dictionary with keys

`type`

- type of model, here we are definic a model using symbolic expressions`x`

- list of unknown variables in the model`f`

- list of fault variables`z`

- list of known variables`rels`

- list of model equations`parameters`

- list of parameters (optional) For the induction motor model, this corresponds to

```
model_def = {'type': 'Symbolic',
'x': ['i_a', 'i_b', 'lambda_a', 'lambda_b',
'w', 'di_a', 'di_b', 'dlambda_a',
'dlambda_b', 'dw', 'q_a', 'q_b', 'Tl'],
'f': ['f_a', 'f_b'],
'z': ['u_a', 'u_b', 'y1', 'y2', 'y3'],
'parameters': ['a', 'b', 'c', 'd', 'L_M',
'k', 'c_f', 'c_t']}
# Make symbolic objects of all variables/parameters before writing down equations.
sym.var(model_def['x'])
sym.var(model_def['f'])
sym.var(model_def['z'])
sym.var(model_def['parameters'])
model_def['rels'] = [
-q_a + w*lambda_a,
-q_b + w*lambda_b,
-di_a + -a*i_a + b*c*lambda_a + b*q_b+d*u_a,
-di_b + -a*i_b + b*c*lambda_b + b*q_a+d*u_b,
-dlambda_a + L_M*c*i_a - c*lambda_a-q_b,
-dlambda_b + L_M*c*i_b - c*lambda_b-q_a,
-dw + -k*c_f*w + k*c_t*(i_a*lambda_b - i_b*lambda_a) - k*Tl,
fdt.DiffConstraint('di_a','i_a'),
fdt.DiffConstraint('di_b','i_b'),
fdt.DiffConstraint('dlambda_a','lambda_a'),
fdt.DiffConstraint('dlambda_b','lambda_b'),
fdt.DiffConstraint('dw','w'),
-y1 + i_a + f_a,
-y2 + i_b + f_b,
-y3 + w]
```

Now, the `DiagnosisModel`

object can be created as

```
model = fdt.DiagnosisModel(model_def, name ='Induction motor')
```

and the API is very close to the Matlab version as described in the documentation.

### Model information, basic plotting, and MSO/MTES

As before, to display model information use the `Lint`

class method

```
model.Lint()
```

which gives

```
Model: Induction motor
Type:Symbolic, dynamic
Variables and equations
13 unknown variables
5 known variables
2 fault variables
15 equations, including 5 differential constraints
Degree of redundancy: 2
Degree of redundancy of MTES set: 1
Model validation finished with 0 errors and 0 warnings.
```

The degree of redundancy is 2 in the model since there are 3 output sensors and 1 unknown input to the system, the load torque `Tl`

. To plot the model structure, use the `PlotModel`

method as

```
# Plot model
model.PlotModel()
```

which gives the figure

Computing the set of MSO and MTES sets is done as below

```
# Find set of MSOS and MTES
msos = model.MSO()
mtes = model.MTES()
print(f"Found {len(msos)} MSO sets and {len(mtes)} MTES sets.")
# Check observability and low index for MSO sets
oi_mso = [model.IsObservable(m_i) for m_i in msos]
li_mso = [model.IsLowIndex(m_i) for m_i in msos]
print(f'Out of {len(msos)} MSO sets, {sum(oi_mso)} observable, {sum(li_mso)} low (structural) differential index')
# Check observability and low index for MTES sets
oi_mtes = [model.IsObservable(m_i) for m_i in mtes]
li_mtes = [model.IsLowIndex(m_i) for m_i in mtes]
print(f'Out of {len(mtes)} MTES sets, {sum(oi_mtes)} observable, {sum(li_mtes)} low (structural) differential index')
```

and the code outputs

```
Found 9 MSO sets and 2 MTES sets.
Out of 9 MSO sets, 9 observable, 4 low (structural) differential index
Out of 2 MTES sets, 2 observable, 2 low (structural) differential index
```

### Isolability analysis

To plot the isolability properties of the model under mixed casaliyu asssumption

```
# Isolability analysis
model.IsolabilityAnalysis(plot=True, causality='mixed')
```

and to examine in more detail, the Dulmage-Mendelsohn decomposition with a canonical form of the overdetermined subsystem is plotted by

```
model.PlotDM(fault=True, eqclass=True)
```

which gives the figure

For more details on the canonical decomposition of the overdetermined part, see Mattias Krysander, Jan Åslund, and Mattias Nyberg, “*An Efficient Algorithm for Finding Minimal Over-constrained Sub-systems
for Model-based Diagnosis*”.
IEEE Transactions on Systems, Man, and Cybernetics – Part A: Systems and Humans, 38(1), 2008.

### Code generation and residual generation

To wrap up this example, let us use one of the MTES sets and generate C++-code for a residual generator. First, let’s see which redundant equation that can be used for integral causality residual generation using the `MSOCausalitySweep`

class method

```
model.MSOCausalitySweep(mtes[0])
```

This outputs

```
['mixed', 'mixed', 'mixed', 'mixed', 'mixed', 'mixed', 'mixed', 'int', 'mixed', 'mixed', 'int', 'mixed']
```

and thus the 11:th element in the first MTES can be used. The 11:th element correspond to the second measurement equation

```
red_eq = mtes[0][10]
model.syme[red_eq]
Out[50]: Eq(f_b + i_b - y2, 0)
```

Now, get the rest of the equations to form the exactly determined set of equations and compute a mathing using the `Matching`

class method

```
M0 = [e for e in mtes[0] if e != red_eq]
Gamma = model.Matching(M0)
```

Now, all is set to generate the residual generator code using the `SeqResGen`

class method

```
model.SeqResGen(Gamma, red_eq, 'ResGen', batch=True, language='C')
```

which generate files `ResGen.cc`

and `ResGen_setup.py`

. Have a look at the `ResGen_core()`

function in the generated C++-file and you’ll se how things work. The generated code can now be compiled by executing

```
python ResGen_setup.py build_ext --inplace
```

in a terminal.

## More examples

In the distribution, there are a few more examples included. To find where `pip`

puts everything, run

```
fdt.__path__
```

and have a look in the `examples`

sub-folder.

## Installation

The package needs Python version 3.6 or newer, check which version you have installed with

```
python3 --version
```

Now, create a virtual environment, don’t install into the system wide python installation. You can do this as (only needed once) with

```
python3 -m venv env
```

and then activate the environment as

```
source ./env/bin/activate # Linux/MacOS
```

in MacOS/Linux or if you’re on a Windows machine

```
.\env\Scripts\activate # Windows
```

Always a good idea to upgrade the package manager `pip`

before continuing

```
pip install --upgrade pip
```

Then, install the toolbox

```
pip install faultdiagnosistoolbox
```

and that is that.

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