An Energy Conscious PV Generation and Energy Storage Based Converter for Metro DC Traction Grid

In recent years renewable energies are gradually being introduced to cope with issues accompanying with a rapid growth of the urban rail transit, such as tremendous energy consumption, serious carbon emission, limited capacity of the existing traction substations, etc. An energy conscious converter, combining a quasi-z source network based photovoltaic generation system and a high conversion ratio energy storage circuit, is proposed for the metro DC traction grid in this paper. The maximum power traction can be achieved through coordinated control between the LLC converter and quasi-z source network without additional conversion stages. The braking energy of trains can be recycled by the energy storage system besides absorbing the excessive solar energy. Adopting the presented modulation strategy in this paper, the gross voltage of batteries is no higher than one-fourth of the DC traction grid voltage. Therefore, fewer batteries need to be in series, which decreases the premature failure probability of the battery pack caused by the over- or under-charging of unbalanced individual cells.