Fifth harmonic and sag impact on PMSG wind turbines with a balancing new strategy for capacitor voltages

• Impact on wind turbines due to fifth harmonic and sag content.
• Converter topologies considered are two-level and three-level ones.
• Controllers are based on PI and fractional-order methods.
• New control strategy for the selection of output voltage vectors.
• Balancing voltages in the DC-link capacitors.

This paper deals with the computing simulation of the impact on permanent magnet synchronous generator wind turbines due to fifth harmonic content and grid voltage decrease. Power converter topologies considered in the simulations are the two-level and the three-level ones. The three-level converters are limited by unbalance voltages in the DC-link capacitors. In order to lessen this limitation, a new control strategy for the selection of the output voltage vectors is proposed. Controller strategies considered in the simulation are respectively based on proportional integral and fractional-order controllers. Finally, a comparison between the results of the simulations with the two controller strategies is presented in order to show the main advantage of the proposed strategy.