LLC DC-DC Converter Performances Improvement for Bidirectional Electric Vehicle Charger Application

Abstract

Electric Vehicle (EV) bidirectional charger technology is growing in importance. It defines the fact of returning the electricity stored in the batteries of EV to Grid (V2G), to Home (V2H), to Load (V2L), or in one word V2X mode. The EV onboard charger is divided into two parts: AC-DC and DC-DC converters. The isolated bidirectional DC-DC LLC resonant converter is used to improve the charger efficiency within both battery power and voltage ranges. It is controlled by varying the switching frequency based on a small signal modeling approach using the gain transfer function inversion method. The dimensions of the DC-DC LLC converter directly affect the charger cost. Moreover, they cause an important control frequency saturation zone, especially in V2X mode, where the switching frequency is out of the feasibility zone. The new challenge in this paper is to design an optimization strategy to minimize the LLC converter cost and improve the control frequency feasibility zone, for a wide variation of battery voltage and converter power, in the charging (G2V) and discharging (V2X) modes simultaneously. For our best knowledge, this optimization problem, in the case of a bidirectional (G2V and V2X) charger, is not yet considered in the literature. An optimal design that considers the control stability equations in the optimization algorithm is elaborated. The obtained results show a significant converter cost decrease and important expansion of control frequency feasibility zones. A comparative study between initial and optimized values, in G2V and V2X modes, is generated according to the converter efficiency.

DESIGN AND APPLICATION OF AC/DC SWITCHING POWER SUPPLY WITH HALF BRIDGE DC/DC CONVERTER TOPOLOGY FOR BATTERY SYSTEMS of ELECTRICAL VEHICLE

“…Although, full-bridge and DAB based electrical vehicle battery charger are presented in [26], [27] for higher power, number of switch and voltage stress on the power switches are higher than presented study. [28] presents electrical vehicle charger based on LLC converter, but it does not present battery package structure as it is given presented study and have higher number of power switches increasing cost. However, presented study includes just DC-DC conversion, power factor correction is not a scope of the study.…”

Annotated Survey on the Research Progress within Vehicle-to-Grid Techniques Based on CiteSpace Statistical Result

“…From the distribution of major clusters along the timeline in Figure 5, it can be seen that energy storage and SOC have been long-term research topics in the V2G field. As shown in Figure 6, the keywords that exploded in recent years include scheduling, voltage control, DC-DC converter [88], load modeling [89], etc., which indicates that the theoretical validation of V2G has been basically perfected and that researchers have paid more attention to the technological challenges encountered in the implementation stage of V2G. It is mainly limited by the technology in terms of battery degradation as well as the communication and scheduling between the EV user side and the power grid side.…”

Review on Modeling and Control Strategies of DC–DC LLC Converters for Bidirectional Electric Vehicle Charger Applications

“…The isolated bidirectional DC-DC LLC resonant converter [15,16] is widely taken into account for control purposes in order to improve converter efficiency over a wide range of power and input/output voltages in industrial applications. On the other hand, because the resonant tank is not symmetric, there is a difference in the gain equation and the efficiency between the two operating modes (forward and reverse).…”

“…However, because these models are complex and nonlinear, design of the control is more difficult. Small signal modeling [15,17,24] consists of using harmonic approximation to obtain more simplified model. Small signal transfer functions can be derived that are more in accordance with the design of control strategies.…”