Inductor-Volume Comparison for 3Φ3W LCL Converter With Direct Digital Control and Different Filter-Inductance Drop-Rates

Magnetic powder cores have soft-saturation properties and high temperature stability compared with other materials, which are widely used in LCL filter design. Conventionally, when designing a filter for a 3Φ3W LCL converter controlled with
abc-to dq
frame transformation, a low drop-rate inductor is selected to stabilize the system and improve the current THD; however, it results in high inductor volume. With the proposed direct digital control (DDC) operating in nature frame, the filter is allowed to have a wide inductance drop-rate (75%) which can reduce core size significantly. The DDC is first addressed and the filter design is correspondingly presented. Comparison of filter volume, loss, and temperature rise for the converters with DDC and different drop-rates is presented, and it is the primary contribution. Simulated and experimental results from a 33 kW 3Φ3W LCL converter with different inductance drop-rates have been used to verify the analyses and discussions.