A frequency-based LCL filter design and control considerations for three-phase converters for solid-state transformer applications

This paper presents a design methodology of a LCL filter for its application on the interconnection with the grid of a three-phase solid-state transformer, which is based on a three-stage configuration. The filter operates without damping resistors, and the design methodology proposed is based on the direct location of resonance frequencies, taking into consideration the effect of the grid impedance. The developed methodology can be applied to different power levels. In addition, control tuning considerations are proposed in order to avoid resonance points, evaluating the overall performance through the current total harmonic distortion in the point of common coupling. Furthermore, the used dq0 reference control frame achieves the objectives without the need to increase the number of sensors, neither the use of observers. The design methodology is validated by testing the operating system at 10 kW, 100 kW and 1 MW. For 1 MW, it is also implemented on a real-time simulator.