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an investigation of dual stator winding induction machines

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Lie derivative <strong>an</strong>d relative order degree are the two import<strong>an</strong>t definitions in this<br />

<strong>an</strong>alysis [8.1]. If ℜ → ℜ<br />

n<br />

h : is a scalar function while<br />

field in<br />

L f<br />

h<br />

293<br />

n n<br />

: ℜ → represents a vector<br />

f ℜ<br />

n<br />

ℜ , then the Lie derivative <strong>of</strong> h with respect to f is a vector field defined as,<br />

∂h<br />

= (8.24)<br />

∂x<br />

( x)<br />

f ( x)<br />

Then the Lie derivative h(<br />

x)<br />

L f is the directional derivative <strong>of</strong> h along the direction<br />

<strong>of</strong> the vector f . If <strong>an</strong> explicit relationship between the output <strong>an</strong>d input c<strong>an</strong> only be<br />

obtained after differentiating the output <strong>of</strong> the system r times, the system is said to have<br />

relative degree r. The mathematical definition is given as follows. If h(<br />

x)<br />

y = is a scalar<br />

output <strong>of</strong> a nonlinear system, the nonlinear system is said to have relative degree r in a<br />

−1<br />

region Ω if L L h(<br />

x)<br />

≠ 0<br />

r<br />

r−2<br />

g f while Lgh(<br />

x)<br />

= Lg<br />

L f h(<br />

x)<br />

= L = Lg<br />

L f h(<br />

x)<br />

= 0<br />

For example, the single input single output case is firstly considered here. If the<br />

output h(<br />

x)<br />

y&<br />

= L<br />

&y<br />

& = L<br />

&y&<br />

& = L<br />

y<br />

n<br />

M<br />

y = has a relative degree n, the expressions <strong>of</strong> all the derivatives are given as:<br />

f<br />

2<br />

f<br />

3<br />

f<br />

= L<br />

h<br />

h<br />

h<br />

n<br />

f<br />

( x)<br />

+ Lgh(<br />

x)<br />

⋅ u = L f h(<br />

x)<br />

2<br />

( x)<br />

+ Lg<br />

L f h(<br />

x)<br />

⋅ u = L f h(<br />

x)<br />

2<br />

3<br />

( x)<br />

+ L L h(<br />

x)<br />

⋅ u = L h(<br />

x)<br />

h<br />

g<br />

n−1<br />

( x)<br />

+ L L h(<br />

x)<br />

⋅ u<br />

g<br />

f<br />

f<br />

A new set <strong>of</strong> state variables is defined as:<br />

z&<br />

1<br />

z&<br />

z&<br />

z&<br />

2<br />

n<br />

= z<br />

n−1<br />

= z<br />

M<br />

2<br />

3<br />

= z<br />

= L<br />

n<br />

f<br />

n<br />

h<br />

n−1<br />

( x)<br />

+ L L h(<br />

x)<br />

⋅ u = a(<br />

x)<br />

+ b(<br />

x)<br />

⋅ u<br />

g<br />

f<br />

The matrix form <strong>of</strong> the new state variables is given as:<br />

f<br />

(8.25)<br />

(8.26)

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