In this study new type wind power generating topology is considered which is composed of connecting PMSG with EDLC based IG in series can mitigate the problems of total power quality. All types of damping are discarded to obtain
worst case scenario. Symmetrical three line to ground fault (3LG) is considered as a network disturbance, which occurs at fault point F. the fault occurs at 5s, the circuit breaker of the faulted line is opened at 5.1s and 5.2s the circuit breakers are reclosed. In the simulation study it is assumed that the wind speed is stationary and equivalent to the rated speed of both fixed and variable speed WTGs. This is because it may be considered that wind speed does not change dramatically during the short interval of time of the simulation. Table 1 shows the case study of wind power system optimization model which divides 5 types A, B, C,D, and E respectively. Simulations have been carried out by using PSCAD/EMTDC.
A. Case 1. IG Only
Figure 5,6 and 7 show the simulation results of this case. These figures show the real power, reactive power and voltage outputs of an Induction generator. From the figures it is clear that when a fault occurs the output of the induction generator changes and returns to the normal condition after a long time. The grid code allows this time to be 3s as stated in the article. So, this system is not fulfilling the grid code requirement for low voltage ride through.
Real Power: The real power output of normal IG can be limited due to the rotor losses and the low power factor
Reactive Power: The reactive power output of normal IG can be affected by the load characteristics because the rotor cannot provide a constant voltage output.
Voltage Output: The voltage output of normal IG can also be affected by the load variations, which can result in voltage fluctuations.
B. Case 2. PMSG Only
Figure 8, 9 and 10 show the simulation results of this case. These figures show the real power, reactive power and voltage outputs of a permanent magnet synchronous generator. After fault this system returns to normal condition within a second. So, it fulfils the grid code requirement and will remain online after the fault, So PMSG can fulfil the necessary LVRT requirement of the system when connected with other wind turbine generators.
Real Power: The real power output of normal PMSG can be higher than normal IG because the permanent magnet provides a more constant voltage output.
Voltage Output: The voltage output of normal PMSG can also be more stable than normal IG because the permanent magnet provides a constant voltage output.
C. Case 3. IG with EDLC
Figure 11,12 and 13 show the simulation results of this case. These figures show the real power, reactive power and voltage outputs of a series connection. It uses the properties of EDLC as a manner to mitigate the fast fluctuations in a small capacity to enhance the LVRT capability of IGs.
Real Power: The real power output of IG with EDLC can be limited due to the excitation losses in the capacitor.
Reactive Power: The reactive power output of IG with EDLC can be affected by the load characteristics because the capacitor can not provide a constat voltage output.
Voltage Output: The voltage output of IG with EDLC can also be affected by the load variations, which can result in voltage fluctuations.
D. Case 4. PMSG and IG
Figure 13, 14 and 15 show the simulation results of this case. These figures show the real power, reactive power and voltage outputs of a series connection. It uses the properties of PMSG to enhance the LVRT capability of IGs. Which system is better can be commented on by comparing both systems?
Real power: IG with PMSG is a combination of two types of generators that can provide several advantages compared to other generator types. The real power output of IG with PMSG can be higher than other generator types because the PMSG provides a constant voltage output, which results in a more balanced distribution of real and reactive power
Reactive power: The reactive power output of IG with PMSG can be better than other generator types because the PMSG provides a more stable voltage output.
Voltage Output: The voltage output of IG with PMSG can also be more stable than other generator types because the PMSG provides a constant voltage output.
E. Comparison between IG, PMSG, IG with EDLC and IG with PMSG
Real Power: Real power is the actual power that is consumed or delivered to a load. From Fig. 16 we can say, the real power output of IG with PMSG is higher than other generator types because PMSG provides a constant voltage output, which results in a more balanced distribution of real and reactive power. This means that the generator can supply more real power to the load without exceeding its rated capacity.
Reactive Power: Reactive power is the power that is exchanged between the generator and the load to maintain the voltage level. From Fig. 17 we can say, IG with PMSG can provide better reactive power control than other generators because PMSG has a strong magnetic field that maintains the output voltage constant, irrespective of the load variations. This means that the generator can supply more reactive power to the load when required to maintain the voltage level.
Voltage Output: Voltage output is the magnitude of the voltage produced by the generator. From Fig. 18 we can say, IG with PMSG can provide a more stable voltage output than other generators because PMSG has a strong magnetic field that maintains the output voltage constant, irrespective of the load variations. This means that the generator can supply a more stable voltage output to the load even under varying wind speed.