Analyses of torque and speed variations Three
The coefficients K1, K2, & K3 and M1, M2, & M3 have amplitude and phase angle UNC1215 on (36), (37) and (38) that they affect the transforming parameter from rotor side to stator side according to (17). The frequency relations of stator and rotor components are determined by phase of K1, K2, & K3 and M1, M2, & M3 coefficients. The amplitude of K1, K2, & K3 and M1, M2, & M3 determines the amplitude of stator and rotor components like currents, voltages and impedances. Therefore, Fig. 3 is converted to three independent circuits as shown in Fig. 4 base on harmonic superposition principle. The circuit of (4-a) is the DFIG equivalent circuit in the main frequencies as shown in Fig. 1 that the stator and rotor circuits are coupled to each other with K1 and M1. Fig. 4b and c is produced because of two extra mechanical speed components (ωm0 + ωmr and ωm0 − ωmr) that Sx is slip calculated base on these frequencies. Eqs. (37), (A-1), (C-1), (C-2) and (38) must be considered for transforming the rotor components to stator side beside (13).