Performance Verification considering Single Wind Turbine

The variable wind speed is set to 8-18m/s as shown in Fig.4.17 (a). Rated wind speed is 12m/s and pitch angle remain zero until wind speed is equal or less than the rated speed.

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As pitch angle controller’s response is slow, it takes some time to operate. It increases the pitch to limit the output power and rotor speed according to wind speed variations. At t = 1s, a three line to ground fault is applied on the transmission line. The fault duration is 0.15s. As shown in Fig.4.17 (b), the grid voltage falls from 100% to 25 %. The transient behaviours of the grid real power and reactive power is shown in Fig.4.17 (d) and (e) respectively.

During this fault, the active power injection from the GSC to the grid is limited; however, the MSC injects power to the DC-link capacitor. So, the DC-link capacitor voltage increases to almost 1.5 times of its nominal value and is shown in Fig.4.17(f). The pitch angle is increased in the transient state. From Fig.4.17(f), it is found that the proposed coordinated control performs better compared to the conventional ESS control to regulate the DC-link voltage within the acceptable limit and the DC-link voltage fluctuations are reduced.

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(b)

(c)

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(e)

(f)

Fig.4.17. Simulation result for single symmetrical fault a) Variable wind speed b) Grid voltage c) Pitch angle d) Grid real power e) Grid reactive power f) DC link voltage

4.5.1.2. Repetitive Symmetrical Faults

This scenario describes the performance of proposed controller under the three grid faults. The first fault occurs at 1s for 0.15s duration. The second fault occurs at 1.2s for duration of 0.15s. Similarly, the third fault occurs at 1.4 s lasts for 1.55s. The grid voltage dip occurs and the voltage falls from 1p.u. to about 0.25 p.u as shown in Fig.4.18 (a). Rated wind speed is 12m/s and pitch angle remain zero until wind speed is equal or less than the rated speed. It increases to limit the output power and rotor speed according to wind speed variation. The pitch angle is increased in the transient state as shown in Fig.4.18

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(b). The transient behaviours of the grid real power and reactive power is shown in Fig.4.18 (c) and (d) respectively. During this fault, the active power injection from the GSC to the grid is limited; however, the MSC injects power to the DC link capacitor. So, the DC-link capacitor voltage increases to almost 1.5 times of its nominal value and is shown in Fig. 4.18(e). From Fig.4.18 (e), it is found that the proposed coordinated control performs better compared to the conventional ESS control to regulate the DC-link voltage within the acceptable limit and the DC-link voltage fluctuations are reduced.

(a)

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(c)

(d)

(e)

Fig.4.18. Simulation result for repetitive symmetrical fault a) Grid voltage b) Pitch angle c) Grid real power d) Grid reactive power e) DC link voltage

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4.5.1.3. Single Asymmetrical Fault

At t = 1s, a double line to ground fault is applied on the transmission line. Similarly, the fault duration is 0.15s. The grid voltage is reduced to 0.55p.u. as shown in Fig. 4.19(a). The pitch angle is increased in the transient state to reduce incoming power as shown in Fig.4.19(b). The transient behaviours of the grid real power, reactive power is shown in Fig.4.19(c) and (d) respectively. With limited active power injection to the grid during this fault, the voltage of the DC-link capacitor increases to 1.6 times from its nominal value and is shown in Fig. 4.19(e). Using the coordinated controller, effects of the grid fault are mitigated. It is found that the proposed coordinated control performs better compared to the conventional ESS control in DC-link voltage regulation reducing fluctuations and transients and the performances are shown in Fig. 4.19(e).

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(c)

(d)

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Fig.4.19. Simulation result for single asymmetrical fault a) Grid voltage b) Pitch angle c) Grid real power d) Grid reactive power e) DC link voltage

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4.5.1.4. Repetitive Asymmetrical Faults

This scenario describes the performance of proposed controller under the three asymmetrical grid faults. The first fault occurs at 1s for 0.15s duration. The second fault occurs at 1.2s for duration of 0.15s. Similarly, the third fault occurs at 1.4 s lasts for 1.55s. The grid voltage dip occurs and the voltage falls from 1p.u. to about 0.55 p.u as shown in Fig.4.20(a). Rated wind speed is 12m/s and pitch angle remain zero until wind speed is equal or less than the rated speed. It increases to limit the output power and rotor speed according to wind speed variation. The pitch angle is increased in the transient state as shown in Fig.4.20 (b). The transient behaviors of the grid real power, reactive power and generator speed is shown in Fig.4.20(c) and (d) respectively. During this fault, the active power injection from the GSC to the grid is limited; however, the MSC injects power to the DC link capacitor. So, the DC-link capacitor voltage increases to almost 1.5 times of its nominal value and is shown in Fig.4.20 (e). From Fig.4.20 (e), it is found that the proposed coordinated control performs better compared to the conventional ESS control to regulate the DC-link voltage within the acceptable limit and the DC-link voltage fluctuations are reduced.

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(b)

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Fig.4.20. Simulation result for repetitive asymmetrical fault a) Grid voltage b) Pitch angle c) Grid real power d) Grid reactive power e) DC link voltage