LCL Grid Filter Design of a Multimegawatt Medium-Voltage Converter for Offshore Wind Turbine Using SHEPWM Modulation

The switching frequency of medium-voltage high-power converters is limited to about 1 kHz due to semiconductor junction temperature constraint. The frequency band between the fundamental and carrier frequency is limited to a little more than one decade and the LCL filter design is usually a challenge to meet grid codes for grid-connected applications. Traditional designs focus on the optimization of the filter parameters and different damping circuits. However, this design is very influenced by the modulation technique and produced low-order harmonics. Widely used pulse width modulations (PWM), such as phase disposition PWM (PDPWM), produce low-order harmonics that constraint the design of the filter. Selective harmonic elimination PWM (SHEPWM) can eliminate theses low-order harmonics, enabling a more efficient design of the LCL filter. In this paper, the LCL grid filter of a multimegawatt medium-voltage neutral-point-clamped converter for a wind turbine is redesigned using the SHEPWM modulation. Experimental results demonstrate that the efficiency of the converter, filter, and overall efficiency are increased compared to that obtained with PDPWM.