Abstract
In wind energy applications, voltage source converters are employed to achieve energy conservation. Recently, multilevel converters have been showing promising advantages compared to the traditional 2-level converter scheme, due to the fact that they can overcome certain limitations during transient conditions. This paper investigates the transient performance of variable DFIG-based speed wind turbines taking into account different scheme configurations of the power converter system. The schemes investigated are a 2-level six step IGBT inverter, a parallel interleaved 2-level six step IGBT inverter, and a 3-level IGBT inverter. All schemes were compared during severe three-phase to ground fault at the terminal of the DFIG wind turbine using the conventional Phase Lock Loop (PLL) and a DC-chopper protection. A coordinated approach of improving the performance of all the converter schemes with series dynamic braking resistor (SDBR) was analyzed. Investigation of the best location for the SDBR in the DFIG architecture considering the best switching signal was also carried out. Furthermore, a new control strategy of PLL for the DFIG system was proposed in conjunction with the SDBR scheme for the converter systems. Simulations were carried out in Power System Computer Aided Design and Electromagnetic Transient Including DC (PSCAD/EMTDC). The results show that the proposed PLL and SDBR hybrid scheme in the various inverter topologies considered in the study can enhance the performance of the wind generator variables during severe three-phase to ground fault. This is because the proposed hybrid scheme could help to boost the capability of the current and recovery of the wind generator after post-fault scenarios. Also, the voltage source converter leg switched output voltage would be enhanced to maximum change in common mode voltage by the inverter schemes’ modulation of the space vector using the proposed strategy.
Highlights
The use of Insulated Gate Bipolar Transistors (IGBTs) has been increasing lately for high power applications among semiconductor devices
As the use of multilevel converters is becoming popular in wind energy conversion systems, because of their robustness during transient conditions, this paper aims to improve the performance of the six-step 2-level IGBT inverter by proposing a coordinated control of the inverter system with a new Phase Lock Loop (PLL) configuration together with a Series Dynamic Braking Resistor (SDBR)
Simulations were done based on the optimal switching signal (Figure 2) and placement (Figure1) of series dynamic braking resistor (SDBR) with a value 0.01 pu for a severe 3LG fault, which occurs at 0.1 s
Summary
The use of Insulated Gate Bipolar Transistors (IGBTs) has been increasing lately for high power applications among semiconductor devices. The Doubly Fed Induction Generator (DFIG) has one main merit of utilizing only 20–30% of the wind generator rating for the power converters linking the rotor side and the grid side (Xu and Cartwright, 2006; Okedu, 2020) This wind turbine technology has low power loss, cost effective power converters, four quadrants of power regulation for active and reactive power, and an improved mechanism for wind energy capture in comparison with the earlier technology of fixed speed induction generators (Djeriri et al, 2013). In wind energy generation applications, the multilevel converters are gaining popularity (Nabae et al, 1981; Stemmler and Geggenbach, 1993) This is because this type of converter topology for wind turbines has higher power ratings than the power converter structure, leading to less impact on the switches of the IGBTs. the low harmonic contents with improved voltage waveforms would be achieved considering this type of converter strategy
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