Research on bi-directional four-port converter of solar electric vehicle

Existing electric vehicles are mainly powered by batteries, which have short driving miles, inconvenient charging, still a large proportion of charging electricity from fossil-fuel power plant, and still not solving the pollution problem from the source and other defects. Connecting solar power to electric vehicles to form a complex energy system can help solve these problems. A bi-directional four port converter consisting of one BOOST and three SEPIC/ZETA circuits is presented to control the composite energy system consisting of photovoltaic panels, battery and super capacitor. BOOST circuit enables maximum power tracking of the solar panels and delivers energy to the DC bus. The first bi-directional SEPIC/ZETA circuit enables the bi-directional flow of energy between the battery and the DC bus during discharge and charging. The second bi-directional SEPIC/ZETA circuit enables the bi-directional flow of energy between the super capacitor and the DC bus during discharge and charging. The third bi-directional SEPIC/ZETA circuit converts the DC bus voltage to a suitable load voltage or feeds the load braking energy back to the DC bus. The bi-directional four-port converter enables multiple modes of operation for complex energy systems, such as maximum power tracking of the photovoltaic panel, battery power to the load, high power density output from the super capacitor, return of braking energy from the load, power supply from the photovoltaic panel to the load, and charging of the photovoltaic panel to the battery and super capacitor, and so on. Simulations and experiments demonstrate that the proposed bi-directional four-port converter can manage multiple operating modes of the complex energy system well and ensure the stability of voltage and power during mode switching. It also proves that the addition of solar energy can effectively reduce the consumption of battery energy, thus improving the driving miles and battery life and contributing to the pure green operation of electric vehicles.