Modeling and controller design for series-connected output universal link converter

This paper conducts modeling and controller design for SEries-connected Output Universal Link(SEOUL) converter. The SEOUL converter was proposed to interface multiple distributed power sources to the grid with reduced number of reactive components. It employs high-frequency transformer instead of bulky line-frequency transformer as Solid State Transformers(SSTs). Besides, it does not use large DC-link capacitor at the input-side and reduce the size of the input filter. This is inherently possible due to its original operating characteristic. The H-bridges connected to the grid does not perform PWM operation to make the input phase current sinusoidal. Instead, their switches operate synchronized to the grid frequency and the input phase currents are synthesized sinusoidally by the high-frequency power transfer part of the SEOUL converter. This paper focuses on the power transfer of SEOUl converter and develops the analytic model of it. Based on the developed model, a DC-link voltage control strategy is proposed with the decoupling control method. The developed model and proposed control method was verified by experiments. The resultant input phase current is kept as sinusoidal at various operating conditions.