SST Medium Voltage Transformer with Bidirectional Power Transmission for Electric Railway Transport

Electric rail transport is positioned as environment-friendly technology that has good future prospects for development. The supply of electric rail transport from DC or AC power lines requires the use of specialized transformers that form the three-phase system in the lowvoltage circuit to power this load. Solid State Transformer (SST) are very attractive for use in power systems of electric locomotives. This paper examines a new architecture for the realization of SST transformers for their use in power systems of electric locomotives. The proposed SST transformer has the bidirectional high-frequency power transmission capability and at the same time ensures multiplication of phases in the low voltage circuit. The SST transformer is a single-phase / three-phase transformer, which can be supplied both from the high-voltage DC power network and from the AC network frequently used in electric rail transport. Changing the power supply type (of the current) does not lead to changes in the topology of the SST. The transformer is designed as an object made of identical functional modules. The ferromagnetic core is made of separate portions for each functional module. This simplifies the problem of ensuring the electrical stiffness of the transformer. The transistors of the module operate at variable switching frequency, have soft switching mode. Energy conversion takes place in a single step. This ensures that losses are diminished and transformer efficiency is increased in all load regimes. Mathematical simulations have confirmed that this transformer has a very low impact on the power supply, whether the power supply is DC or AC. Under-load operation of the SST transformer does not lead to pollution of the power supply network with higher current harmonics.