## 2 Methodology
### Multiple Converter Configuration (C-MC)  
Figure 4 shows the diagram of the multiple converter configuration. The outputs of the two converters are the same as the direct current link voltage. A feature of the multiple converter configuration is its two bidirectional DC/DC power converters connected in parallel with the sources where the outputs of the two converters are the same as the direct current bus voltage. An advantage to this configuration is that the voltages of both the B pack and the UC bank can be kept below the  
Figure 1: Basic passive parallel configuration [7]. DC: direct current.  
Figure 3: Battery/ultracapacitor configuration [7].  
Figure 2: Ultracapacitor/battery configuration [7]. DC/DC: direct current to direct current.  
direct current bus voltage unlike the above-mentioned configurations. Additionally, the UC voltage can vary over a wide range.  
Regarding the study of vehicle powertrain configurations, there are few works focused on studying them in an analytical way and analyzing the influence of their configuration on HEV performance. The three configurations outlined above are described by [PERSON] and [PERSON] [16] and the differences among them and the advantages of using one with regards to the other, in terms of voltage manipulation in the B pack or the UC bank through the power converters, are presented considering how to accommodate the vehicle powertrain elements. In a study by [PERSON] [18], the C-UC/B and the C-B/UC are analyzed using an electric model, which provides information on the dynamic behavior of the voltages, currents, and state of charge of the B pack and the UC bank. This author analyzed the effect of the configurations (C-UC/B and C-B/UC) on the powertrain for different driving cycles. The results showed that the C-UC/B configuration performs better in an electric vehicle than the C-B/UC configuration. However, this work considered ideal efficiencies for the converters (that is, 100% efficiency, which implies that there are no voltage losses) and for each driving cycle it considered a certain pack size of Bs and UCs. In real applications the efficiencies of the converters are not 100% since there are losses associated with switching, conduction, and heat generation [19]. In the case of the dimensioning of the B pack and the UC bank, it is not realistic to have a sizing of the different energy sources for each type of terrain or driving cycle; in a real vehicle the driver drives randomly on different land types such as city, urban, semi-urban, etc. This work focuses on the analysis and evaluation of an HEV with a multiple converter configuration in the powertrain. Multiple converter configuration has not been examined analytically to investigate the performance of a hybrid electric vehicle. The following section describes vehicle characteristics (case study) in conjunction with the energy storage system and the Energy Management Strategy (EMS). An energy management strategy is one that allows B and UC operating restrictions to be met in order to operate both sources safely to meet the load demand [14; 17; 18; 20]. Energy management strategies are aimed at improving vehicle performance, taking care of battery life, and increasing autonomy. In this work the EMS is chosen from the literature since the purpose is to analyze C-MC topology in HEV performance.