Controle adaptativo aplicado a conversores com filtro LCL com rejeição adaptativa de distúrbios e sob saturação da ação de controle

Abstract

The widespred use of static converters for different application purposes experienced a grown mainly since 80's, with a great increase of interest in recent years. It is possible to highlight their use in grid connected systems such as in power filters and distributed generation sources. The last contributed for the dissemination of microgrids and the advent of smartgrids. For grid connected applications, a filter is used to interface the converter with the grid in order to suppress the harmonic content due to the switching process of the converter. These filters may be purely inductive or of L type, or inductive-capacitive inductive or of LCL type. Due to its higher harmonic attenuation capacity, the LCL filter is preferably employed. However the LCL filter has some disadvantages quite evident. For example, it is a third-order filter, wich requires more complex control strategy not only to reject disturbances arisen from the grid, but also for stability and control purposes. To address such problems, several works in the literature consider different choices regarding the controlled quantity namely, the converter current or the grid current, and several control techniques such as deadbeat, hysteresis control, PI in synchronous reference frame, among others. This work discusses the use of the weighted average current of the LCL-filter as a control variable in order to alleviate the problem of control resulting from the use of this type of filter. It was used Model Reference Control in conjunction with an Adaptive Feedforward Cancellation scheme as a strategy to ensure stability and disturbance rejection for the system. It was also applied an approach to ensure the stability of the system facing situations of saturation of the control action using a Model Reference Adaptive Controller with an Adaptive Feedforward Cancellation scheme, designed to cope with the effect of saturation. Mathematical analysis and proofs of stability are presented with simulation and experimental results, that demonstrate the applicability of the proposal.