5.3 Systems for Feeding into the Grid
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Fig. 5.7 Operation and control of a wind energy system. Sketch of data acquisition (left) and block diagram of operation management (right)
where U 1 , U 2 are the stator voltage and the rotor voltage vector referred to stator side, respectively. Note that in steady state the rotor quantities are of slip frequency (s · f1 ). When neglecting the stator resistance R1 in Fig. 5.8, which is permissible for most performance calculations not intending to render correctly the machine losses, currents and powers can be determined by a set of complex equations. Rotor and stator current are calculated: 1 U 2 −U 1 s U 1 k2 · e jϕ2 − s = ; where sk is the breakdown slip sk = R 2 /X σ Xσ sk + js Xσ sk + js U1 I 1 = I 0 − I 2 mit I 0 = (5.4) jX1 I2 =
Stator and rotor apparent powers are: S1 = 3U 1 · I ∗1 = P1 + j Q1
;
S2 = 3U 2 · I ∗2 = P2 + j Q2
(5.5)
where I ∗ denotes the conjugate complex of I. Note that a machine with three-phase windings both in stator and rotor is assumed, and U, I are per-phase values.
Fig. 5.8 L-model for asynchronous wound-rotor machines