Page 199 - Hybrid-Renewable Energy Systems in Microgrids

Sensitivity and transient stability analysis of fixed speed wind generator 179

Figure 9.10 Variation of eigenvalue of the electrical mode with respect to the stator
resistance without SDBR.

a , a , a , a , a , and a are computed from the state matrix A and listed in
4,4
4,7
5,6
6,6
6,5
7,4
appendix.
From Fig. 9.13 it is clear that as the stator resistance is increasing, the electrical
mode is becoming more damped and moving further away from the imaginary axis.
Fig. 9.11 demonstrates the effect of SDBR on this specific mode, and it is evident that
the damping of that mode is much higher compared with the damping of the system
without SDBR.
Rotor Resistance: Varying the value of rotor resistance has significant impact in
electromechanical, mechanical, and monotonic modes. As long as rotor resistance is
increased, the stability of the system is increased. That means the system is becoming
more and more damped. The sensitivity of electromechanical mode with respect to
rotor resistance variation is presented by the following equation:

∂ λ ∂ λ ∂a ∂ λ ∂a
7 = 7 . 5,5 + 7 . 7,7 (9.36) ∂λ 7 ∂Rr=∂λ 7 ∂a5,5.∂a5,5∂Rr+∂
∂R r ∂a 5,5 ∂R r ∂a 7,7 ∂R r λ 7 ∂a7,7.∂a7,7∂Rr
As the contribution of SDBR is more significant in electrical modes rather than
electromechanical, mechanical, or monotonic modes, incorporation of SDBR has no
significant impact on the frequency oscillation or damping of these modes as shown in
Figs. 9.12–9.14. For sensitivity analysis of electromechanical, mechanical, and mono-
tonic mode, it has been observed that with the increment of rotor resistance, the damp-
ing of the system is improved and hence system stability margin is improved.

2.4.3 Transmission line parameters
Varying transmission line inductance while keeping all other parameters constant
has a significant impact on the eigenvalues displacement for the electro mechanical,
monotonic, and electrical modes.
The sensitivity of the electrical mode with respect to transmission line reactance
variation is presented by: