The block Rotation_dq rotates u by an arbitrary angle theta into y according to
y = R_dq*uR_dq is the restriction of R_dq0 from dq0 to dq.
The matrix R_dq0 rotates dq0 variables around the o-axis in dq0-space with arbitrary angle theta.
It takes the form
[cos(theta), -sin(theta), 0]
R_dq0(theta) = [sin(theta), cos(theta), 0]
[ 0, 0, 1]
and has the real eigenvector
{0, 0, 1}
in the dq0 reference-frame.
Coefficient matrices of the form (symmetrical systems)
[x, 0, 0 ]
X = [0, x, 0 ]
[0, 0, xo]
are invariant under transformations R_dq0
The connection between R_dq0 and R_abc is the following
R_dq0 = P0*R_abc*P0'.with P0 the orthogonal transform 'Transforms.P0'.