DC-AC variable-voltage and variable-frequency (VVVF) transmission is generally used in urban rail transit systems. Locomotives are braked electrically (regenerative braking), the main method, and mechanically, the supporting method. A locomotive is frequently started and braked due to short inter-station distance and therefore generates considerable braking energy. According to experience, a part (20%-80%, up to the locomotive density and inter-station distance) of the regenerative braking energy produced by a metro locomotive is absorbed and utilized by adjacent locomotives, the rest part is mainly consumed by absorption resistors of the locomotive by getting heat or by the absorption devices installed in the rail. Resistors are mainly used to absorb the regenerative braking energy generated by locomotives in Chinese urban rail transit systems, which wastes energy, increases the burdens of air-conditioning systems in stations and increases the cost of urban rail transit construction and operation, all of which can be solved if such regenerative energy can be reused.   
The first is energy recovery type to absorb and invert regenerative braking energy. This type inverts the part of regenerative braking energy that is not consumed by other locomotives or other equipment to an AC voltage whose frequency and phase are identical to the grid voltage by adjusting output current of inverter unit according to changes in DC bus voltage, and sends this inverted AC voltage to the grid, a way that can effectively recycles energy and stabilizes DC traction voltage.

FDBL series is absorbs and inverters regenerative braking energy generated in urban rail transit systems. It is designed to be highly reliable, easily operated and powerfully functional in order to absorb regenerative energy generated by locomotives. This series has the following characteristics: 

It can lower DC voltage fluctuation, improve voltage quality and stabilize system voltage. 

The inverter is designed with redundancies to provide high reliability.

Power circuit is designed with modules for easy maintenance and good interchangeability.

Completed protections against voltage imbalance, short circuit, over-current, over-heating and so on ensures high operation reliability.

AC phase sequence is not required to be considered when it is connected to the system, a way that eases the connection. 

Carefully designed circuit parameters ensures the inverter produces less heat and its compact structure requires a smaller area.

Small maintenance and low operation cost. 

Parallel installation is permitted for easy capacity extension.      

Host control ensures easy installation and commissioning.

Fiber optic cables are used to connect high voltage main circuit and the controller, ensuring the safety and reliability.

Completed failure monitoring circuit and failure data uploading function; high cost effectiveness.

Dimensions of  energy feedback Converters at Different Powers

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