ABSTRACT of the Ph.D. Thesis: “Robust Model-Following Control of multilevel converters. 
Aplication to parallel active filters for harmonics correction in medium voltage grids.
PRESENTED BY: ALEJANDRO MUNDUATE TELLERÍA
CO-DIRECTORS: EMILIO FIGUERES AMORÓS and GABRIEL GARCERÁ SANFELÍU


In this Ph.D. Thesis two main novel contributions are presented. The first one is the proposal of a 
robust model following controller (RMF) to regulate the output currents and the DC-link voltage of 
an NPC (neutral point clamped) three-level converter, working as a parallel active filter (PAF) in 
medium voltage grids. The second important contribution of the thesis is the development of new 
small-signal models of the NPC-PAF three-level converter that allow to design with high precision 
both the current and the DC-link voltage linear controllers of the converter.  
On one hand, it has been developed a modelling methodology of three-phase converters in the 
synchronous dq0 reference frame. On the other hand, small and large signal models of the three-
level three-wire NPC PAF converter have been derived. The transfer functions for the lineal control 
of the converter have been obtained, having been derived the transfer functions for the control of 
the currents injected by the filter and of the DC-link voltage.   
It has been carried out a study of new alternatives for the control of the PAF currents and of the DC-
link voltage. After analyzing a conventional PI controller, a new robust RMF controller has been 
studied, applying both controllers to both the regulation of the current harmonics and to the control 
of the DC-link voltage. Furthermore, a "resonant controller" based on generalized integrators (PIS 
controller) has been also analyzed and applied to the control of currents injected by the converter. In 
all the cases a design methodology of the controllers' has been developed, both in continuous and in 
discrete time, having carried out a comparative analysis among the different proposed regulators, 
both of the current and of the voltage loop. It has been concluded that the best option for the current 
loop is the PIS controller, while the RMF controller is the best suited for the voltage loop.  
The theoretical study has been validated by means of simulation results with the software SABERTM.