## 1 Introduction
### Three-Phase Modular Rectifiers with Boost Converter  
The three-phase modular rectifiers with additional converter are usually composed of three single-phase modules, where each module controls its phase individually. In the numerous configurations that can be created, the single-phase rectifiers interact with each other, which eliminates the possibility of control by the involved boost converter [12; 13; 14]. This becomes a problem, since the purpose of the individual rectifiers is to control the current independently and to obtain a sinusoidal current with low THD and high PF in each phase. There are some three-phase modular rectifiers that were created with the ability to eliminate those current interactions. Here, some more relevant rectifiers are suggested by this paper.  
A simple way to solve the current interaction problem in a modular three-phase rectifier is analyzed in [15; 16]. In this work, the author was concerned with the avoiding the interaction between the phase input currents of the rectifier. For this, a transformer is implemented at the input of each single-phase rectifier. This isolation by transformers makes the interaction current stay in the secondary circuit of each rectifier and is not seen as effect in the primary circuit. The primary currents and the sensors to control them do not see any disturbance then. In this case, the PFC is working correctly but at the expense of transformers application. The problem with this solution is that the transformers are grid frequency type, and this, depending on the power of the rectifier, obliges them to be heavy, bulky, and expensive.  
In [17; 18; 19], to eliminate the current interaction, the author implemented yet another diode at the output of the negative pole of each boost converter. This diode is polarized inversely to the direction of the interaction current. An inductor at the negative terminal of the input of each boost converter do the rest of the job. The inductor of a classic boost converter in this case is split in two, one in the positive pole and one in the negative pole. The mitigation of the interaction occurs because the impedance of the inductor is high (due to the switching frequency) and therefore blocks the interaction current. Another method similar to this one but with a slight difference is presented in [20; 21]. In this method, the two inductors of the boost converter are replaced by a coil winding inductor coupled to increase the inductance effect by a factor 4, as it is calculated there. By this special double-windings inductor, the filtering effect better eliminates the possible interactions. The problem of this last solution [20; 21] is the increased danger of the possible saturation of the inductor, since it is a coupled inductor with concordant windings.  
Another possibility is also presented in [1], where the author replaces the inductor of the boost converter with a coupled inductor of discordant windings in each converter and implements a diode at the output of the negative pole of each converter. The coupled inductor implemented in addition to the boost inductor introduces impedance differences. The impedance in the direction of the interaction current is much higher than the impedance in the direction of the normal current; thus, the circuit functions as an additional filter for the interaction current. This solution [1] shows good results. One technology problem is the winding of the inductor core, since the coupled inductor must block the passage of the  
Figure 1: Three-phase hybrid rectifiers types [7; 8].  
interaction current and let the normal current pass. These inductors are not easy to find ready to be supplied and require a special attention.