4. EL ANÁLISIS EXPERIMENTAL DE LA CONDUCTA APLICADO A LA
4.3. Críticas a la educación tradicional y progresista
In this case, the PV solar farm is operated as a PV-STATCOM as soon as the fault is detected in the network. Two scenarios are investigated.
6.3.3.1 Scenario 1: PV solar farm located at induction motor
terminals
Fig. 6.6 depicts the IM response when the solar farm acts as a PV-STATCOM and is located at the IM terminal. The PV system DC link voltage is depicted in Fig. 6.6 (a), the real and reactive power from the PV solar farm are demonstrated in Fig. 6.6 (b), voltage at IM terminal is illustrated in Fig. 6.6 (c), IM speed is shown in Fig. 6.6 (d), and the real and reactive power at IM terminal are presented in Fig. 6.6 (e).
(i) Period I - During fault, t=5 seconds to t=5.15 seconds.
After the fault is initiated, the fault detector detects the fault and transforms the PV solar farm into a PV-STATCOM with a PCC voltage control mode of operation, as discussed earlier in section 6.2.3. As a result, the DC power generated by the PV modules reduces immediately to zero and the active power output of the PV inverter also gradually decreases to zero, as shown in Fig. 6.6 (b). The reactive power output of the PV- STATCOM provides voltage support during this period. The DC link voltage decreases gradually, as seen in Fig. 6.6 (a), due to this reactive power support. The IM terminal voltage also falls to a low value, as shown in Fig. 6.6 (c). The IM speed in Fig. 6.6 (d) and power in Fig. 6.6 (e) drop due to the fall of IM terminal voltage.
(ii) Period II - At post fault clearance, t= 5.15 seconds to t= 5.75 seconds.
The DC link voltage of the PV solar system shows a transient behavior (t=5.15 seconds to t= 5.5 seconds) as shown in Fig. 6.6 (a). Although, this transient behavior is due to the combined transient effect of real and reactive power of the inverter, the transient effect of real power is dominant, as observed in Fig. 6.6 (b). It is noted that there is no real power input at the inverter. Therefore, during this transient period when the active power flows
in the reverse direction, from PCC to inverter due to the switching action of the inverter, it increases the DC link voltage. When the active power flows towards the PCC from the inverter, it decreases the DC link voltage. The DC link voltage finally settles to its predefined value of 550Volts at t= 5.5 seconds when the real power transient has ended. On the other hand, the PCC voltage recovers much faster, as seen in Fig. 6.6 (c). During the period of t= 5.15 seconds to t= 5.3 seconds, the PCC voltage follows the transient behavior of the reactive power output of the PV-STATCOM inverter and settles to a predefined value of 1 pu at t= 5.3 seconds.
Figure 6.6 PV-STATCOM operation at the motor terminal.
(a)
(b)
(c)
(d)
During this period (t= 5.15 seconds to t= 5.75 seconds), the IM speed rises and settles to its pre-fault level at t= 7.5 seconds, as shown in Fig. 6.6 (d). The real and reactive power at the IM terminal shoot up with decreasing oscillation, as discussed earlier, and subsequently start decreasing, as shown in Fig. 6.6 (e). The increased power consumption by the IM during the transient period from t= 5.15 seconds to t= 5.75 seconds is due to the additional torque to bring back the IM to its pre-fault speed. The reactive power of the IM stabilizes at the pre-fault level, as seen in Fig. 6.6 (e), when the speed is settled at t= 5.75 seconds. It is noticed that after t= 5.3 seconds, the reactive power consumption by the IM in Fig. 6.6 (e) follows exactly the same behavior as the reactive power output of the PV-STATCOM inverter as shown in Fig. 6.6 (b). Therefore, it is obvious that the PV- STATCOM provides reactive power to meet the reactive power need of the IM until the speed of the IM stabilizes successfully. The PV-STATCOM reactive power then remains constant after t=5.75 seconds to maintain the PCC voltage constant.
6.3.3.2 Scenario 2: PV solar farm located far from motor terminal
To observe the effectiveness of this PV-STATCOM control on IM stability, the PV solar farm is located at a remote location: 19 km away from the IM terminals. Fig. 6.7 depicts the IM response for this scenario. The triggering signals of the fault detector are depicted in Fig. 6.7 (a), the real and reactive power from the PV solar farm are demonstrated in Fig. 6.7 (b), voltage at IM terminal is illustrated in Fig. 6.7 (c), IM speed is shown in Fig. 6.7 (d), and the real and reactive power at IM terminal are presented in Fig. 6.7 (e). It is evident that even when the PV system is connected 19 km away from the motor terminal, it prevents the IM instability through its PV-STATCOM operation. The behavior of different variables shown in Fig. 6.7 is very similar to those depicted in Fig 6.6. However, the IM speed recovery takes much longer than previously. This delay is attributed to the line impedances between the motor and the PV solar farm. It is noted that although there are two triggering signals generated by the fault detector from the monitoring of all three phase currents at different time instants, as shown in Fig. 6.7 (a), the first triggering signal which is based on the phase-b current signal, initiates the disconnection of PV modules and starts the PV-STATCOM operation, in this scenario.
Figure 6.7 PV-STATCOM operation when located 19 km far from motor terminal.