# Optimized Multiport DC/DC Converter for Vehicle Drivetrains: Topology and Design Optimization
## 1 Introduction  
The recent technological developments in the fields of batteries, electric motors and power electronics interface (PEI) support electro-mobility transition. These advances introduce several possibilities, generating a broad variety of powertrain architectures as presented in [1]. Multiport converters (MPCs) are increasingly attracting research interest. By employing MPC, it is possible to diversify the energy sources so that power system availability can be increased in hybrid electric powertrain systems. MPCs can provide a unique solution to combine multiple energy sources (i.e., battery, supercapacitor, fuel Cell), which have different voltage-current (V-I) characteristics and energy density versus power density performances. Figure 1 illustrates the power distribution role of MPC in the Electric Variable Transmission (EVT)-based powertrain, which has been recognized as a promising and emerging technology for vehicles. A family of MPCs is classified as non-isolated and isolated topology. In an isolated topology, the sources are usually connected to a half bridge converter to achieve DC-AC conversion, which allows the use of a high frequency transformer for high voltage ratios. In addition, the transformer enables the galvanic isolation between the inputs and outputs. Furthermore, with a transformer, it is easier to connect several outputs at different voltage level by properly selecting the number of turns of the secondary winding. However, for high power applications, the transformer is a bulky component. Thus, in vehicular applications, non-isolated topologies are preferred. Non-isolated MPC can be divided into parallel ports topologies and shared components topologies. The advantage of a shared component topology is that less switches are needed and thus the price is expected to be lower; however some topologies as presented in [2] are unable to deliver energy simultaneously. Parallel ports instead inherently increase the system reliability as the ports can be driven either simultaneously or independently, relying on different active components [3]. The advantage of paralleling the ports in a single converter is the gain in flexibility on the energy management techniques, compared to shared component. In fact, the ports can be controlled separately. In addition, better packaging and thermal management can be achieved compared to standard DC/DC converters. Despite being lighter compared to isolated converters, weight and cost is the main drawback in confront of shared components MPCs. Therefore, the interleaving technique can be applied to reduce the global converter weight and cost. Several MPCs have been developed based on [3] as in [4; 5], proving a high efficient and compact solution for vehicle applications with a centralized control. Figure 2 shows a typical configuration of non-isolated bidirectional interleaved MPC in the vehicle powertrain. Figure 1: Multiport Converter integrated into the EVT-based powertrain. The design of MPC power electronics system requires multidisciplinary knowledge and a large number of design variables in different engineering fields (electrical, magnetic, thermal, mechanical). The ability and expertise of the designer may end up with a good, but not optimal design. It may require more effort for further iterations through hardware prototype testing to obtain better performance in term of efficiency and weight. Therefore, mathematical optimization techniques and computer-aided software have been developed to tackle the design problem. In the literature, optimization for the power converter design can be classified into two main techniques: the gradient-based techniques using the derivative information and the metaheuristic-based techniques using the stochastic search. Several gradient-based methods have been employed for the optimization problem of power converter. [PERSON] et al. [6] used the Nonlinear Programming (NP) based on Lagrangian functions to optimize a switched-capacitor converter. [PERSON] et al.