Conversor CA-CC multinível de único estágio para aplicação em transformadores de estado sólido

Abstract

This work proposes the study and development of a single stage multi-level AC-DC converter for application in solid-state transformers. This type of application has been growing very much in the present time with the rise in the use of renewable energies, smart grids and systems that require reduction of weight and volume such as electric traction. The proposed converter is based on the dual active bridge (DAB) associated with the three state switching cell (3SSC). The converter has a structure that can be modularized and applied at high voltages and can operate both as rectifier or inverter. A qualitative analysis is performed where the analog and vector modulation technique is presented as well as the control strategy required for the converter. Subsequently, is performed a quantitative analysis of the converter power flow considering the real transformer voltage and current, the analysis of the input current ripple and the loss analysis considering two different switch models. The digital controllers are also dimensioned using the k factor method. Finally, the validation of the study is carried out through simulation and experimental results in a permanent and transient state. A great similarity between the developed models and the simulation and experimental values is obtained. The dimensioned control loops present dynamics with overshoot of less than 15 % and accommodation times of less than 200 ms. The bi-directionality of the structure is demonstrated with a power inversion test. The topology is capable of operating with unit power factor and low THD. In addition, the efficiency curve of the structure is shown which is capable of operating at a maximum of 87,5 % using IGBT switches. It is also demonstrated that this efficiency can be raised to 95,5 % with the use of better performance switches.