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 third is energy storage type, i.e., a super capacitance absorption device. When regenerative braking raises DC voltage, the device is working to absorb the energy and stores it into a super capacitor; when the locomotive is started to lower the DC voltage, the device works to discharge energy stored in the capacitor to DC traction grid, a way that can better use the braking energy and stabilize DC voltage.

Effect：CH1: Grid voltage waveform、CH2: Grid current waveform、CH3: Voltage waveform for the super capacitor、CH4: Charging and discharging current waveform for the super capacitor

Waveforms for a single charging and discharging cycle

Waveforms for repeated charging and discharging cycles

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.