EXAMPLE 10.1 Vector Control of Asynchronous Machine (PAGE. 305) Consider the variable-frequency VSC system of Figure 10.1. The machine is a 1.68 MW, wound-rotor, asynchronous machine whose rotor terminals are short

circuited. The machine parameters are given in Table 10.1 [53]. The VSC is a three-level NPC with a capacitive voltage divider (Fig. 6.18). The thirdharmonic injected PWM strategy with a switching frequency of fs = 1680 Hz is adopted for the VSC. The capacitance of each DC- side capacitor is 2 C = 19250_F. The voltages of the capacitors are equalized by the partial DC-side voltage balancer discussed in Section 6.7. The net DC-bus voltage is VDC = 3500 V. The on-state resistance of each switch cell is about 1.0 m_. Thus, the effective internal resistance of each phase of the VSC is approximately ron = 2 x 1.0 = 2 m_, which is considerably smaller than Rs and ignored in the control design process. If a time constant of 7/= 3.0 ms is desired TABLE 10.1 Asynchronous Machine Parameters: Example 10.1 Quantity Comment Nominal power Nominal voltage Nominal frequency R, R₂ L₂ L₂ 0₂ d, 0 Value 2250 hp (1.678 MW) 2300 V (line-to-line rms) 377 rad/s 29 ms2 22 m2 34.6 mH 35.2 mH 35.2 mH 0.0173 0.0173 0.0337 1.213 s 1.6 s 000 for the current controllers, one obtains kp = 13.6 and ki= 333 s-1 based on (10.36) and (10.37). The transfer function of the flux compensator is K(s) = 180(s + 0.625)/s, and_imr-refis set to 141 A, based on (10.46).