## 4 Results and Discussions
The wind rotor torque reaches its maximum value at the end of zone II (at time \(t_{2}\approx\) 255 s), followed by a torque decrease into zone III for \(\approx\)5 s. At time \(t_{3}\approx\) 260 s, the electric generator enters the load (i.e., the wind system goes into phase 2), as the operating conditions of the DC electric machine as a generator are being met: \(\omega_{G}\geq b_{G}/a_{G}=76\) s\({}^{-1}\), Figure 4a. The generator torque increases rapidly up to the value \(T_{G}=\) 1.25 kNm (Figure 4c), with the decrease to zero of the angular acceleration (Figure 4b) and implicitly the entry of the system into steady-state (at time \(t_{4}\approx\) 280 s). In phase 3, the generator power stabilizes at \(P_{G}\approx-\)100 kW, the mechanical power extracted from the wind being \(P_{R}\) = 109.4 kW, Figure 4d; implicitly, the transmission efficiency has the value: \(\eta_{WT}=-P_{G}/P_{R}=-T_{G}\cdot\omega_{G}/(T_{R}\cdot\omega_{R})=0.9138\). The efficiency \(\eta_{WT}\) has a value close to the value \(\eta_{1}\) and is significantly higher than \(\eta_{2}\) (see Table 3); thus, the advantage of power branching in complex mechanisms compared to the serial connection of component mechanisms is also well emphasized. Figure 5 shows the distribution of torques and mechanical power on the inputs of planetary units I and II, as well as the influence of inertia on the WT dynamic behavior. In the first part of phase 1, a significant difference between the driving torque \(T_{R}\) and the resistant torque \(T_{H}\) is noted (Figures 2 and 5a). This fact is owing to the insignificant values of the torques \(T_{H1}\) and \(T_{H2}\), also caused by the reduced inertial resistances of the output shafts (the values of the moments of inertia \(J_{1}\) and \(J_{2}\) being much lower compared to \(J_{H}\): \(J_{H}\)\(\approx\) 2000\(J_{1}\)\(\approx\) 200\(J_{2}\), see Figure 2, Tables 2 and 3); this reduced inertial effect of the output shafts is also confirmed by their relatively reduced values of angular accelerations. As a result, the torque \(T_{R}\) is mostly used to overcome the inertial load of the input shaft \(H\). Once the generator enters the load, the \(T_{H1}\) torque increases much faster than \(T_{H2}\), becoming the major component of \(T_{H}\) in the steady state. Although the \(GR\) rotor and \(GS\) stator torques are equal in steady-state, the significant difference between \(T_{H1}\) and \(T_{H2}\) is explained by the large differences in the amplification ratios \(i_{a1}=15.8052\) and \(i_{a2}=-1.0837\) (see Table 3) corresponding to the two power branches. The power variation on the input shafts (Figure 5b) follows a similar evolution as the input torques (Figure 5a): most of the  
Figure 5: The dynamic response at the wind rotor side: (**a**) wind rotor vs. input torques; (**b**) wind rotor vs. input powers. wind rotor power (over 93%) is directed to the planetary unit I and, implicitly, to the \(GR\) rotor--the body with the highest rotation speed. Figure 6: The dynamic response at the generator side: (**a**) generator angular speeds; (**b**) generator angular accelerations; (**c**) generator rotor vs. output 1 torques; (**d**) generator rotor vs. output 1 powers; (**e**) generator stator vs. output 2 torques; (**f**) generator stator vs. output 2 powers; (**g**) mechanical powers. Figure 6 illustrates the WT dynamic behavior at the output side, characterized by the branched power transmission via the rotor \(GR\) and the stator \(GS\), respectively; the contribution of the mobile stator to the overall performance of the wind system is particularly highlighted. The output angular speeds and accelerations (Figure 6a,b) have a linear dependence on the independent motion of the wind rotor; according to the relations in Table 2, they follow the variation profile of the angular velocity \(\omega_{R}\) and acceleration \(\varepsilon_{R}\), respectively (Figure 4a,b), with values amplified with the ratios \(i_{a1}\), \(i_{a2}\), and \(i_{aG}\), respectively.