AC/AC modular multilevel converters in wind energy applications: Design considerations

Modular multilevel topologies are possible candidates for medium-voltage wind turbines because of their scalability and possible redundancy. This paper concentrates on their design and investigates the influence of generator-to-grid voltage ratio, generator nominal frequency, module-capacitance minimising control approaches, third harmonic injection and fault ride-through capability requirement on the main design parameters (installed switching power, energy variation at module capacitors and efficiency). For different design scenarios, different topologies are concluded as being optimal.