Multiport bidirectional converters for off board charging stations of electric vehicles

In this paper, two multi-port bi-directional converters are proposed to be utilized as off-board Electric Vehicles (EVs) charging station. Both converters are designed to integrate renewable energy along with grid power. High gain, three ports, and four modes of operation are the main advantages of these converters. The first mode is Photovoltaic-to-Vehicle (PV2V), the second is Grid-to-Vehicle (G2V). In addition, both converters support Vehicle-to-Grid (V2G) mode (third mode) among with PV-to-Grid (PV2G) mode which is the fourth mode. Theoretical analysis and simulation are done in continuous current mode. Theoretical analysis and simulations show that both converters have the same gain in all four modes, however Boost-Boost-Buckboost (BBB) converter has higher efficiency and lower number of components than that of the Boost-Boost-SEPIC (BBS) converter. Theoretical Border Conduction Mode (BCM) and Discontinues Conduction Mode (DCM) is also conducted for BBB-MPB. A prototype is implemented for the BBB converter. The prototype is tested for all operating modes as the operating voltage is 56.5 V, the output voltage is measured to be 17.7 V in G2V, and PV2V, 158.3 V in V2G, and for the last mode PV2G the output is 102.83 V. The maximum efficiency is calculated to be 94.3%. Compared to latest converters, the proposed BBB converter has higher number of ports, higher number of operating modes and also higher efficiency. Small signal analysis and dynamic load response is studied for the proposed converter and show that the converter has a marginal stability. According to this analysis the converter needs a control algorithm to overcome the marginal stability.