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Regenerative Braking Energy Inverter

Product Overview

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.
  
WindSun has developed three types of ground absorption devices. The first is energy feed 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. The second is energy consumption type, i.e. resistance-based absorption device. When regenerative braking raises DC voltage to the set value, the device is started and consumes so caused braking energy on resistor, thereby stabilizing the voltage of DC traction grid. 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. 

Application Field

As China’s economy grows fast, power grids in many regions sustain many problems, like huge peak-valley difference, low peak shaving capacity, large electricity consumption caused by power generation, transmission and distribution equipment, high demand pressure in summers and connection of large-scale renewable energy equipment that results in difficult in energy utilization. Large-scale energy storage device can solve “conflict of time difference between power generation and power consumption” and “direct impact of intermittent renewable power generation on the grid” to regulate electricity quality. For example, it can store “valley energy” into storage batteries and release it for production and operation in “peak period”, a way that can both reduce grid’s burden and lower operation cost. 

Main technical parameters

1. Common technical parameters
Rated power: 250kW~4000kW
Input voltage: DC1500V/750V
Permissible voltage range: DC1500V~2000V/DC700V~1000V
Working mode: intermittent
Voltages of assisted power supplies: The control, projection and signal circuits use 220VDC power supply; temperature, condensation heater and lighting circuits use 220VAC power supply. Required electric equipment work accurately and reliably when the respective power supply’s voltage changes within 80%~120% of the rated value.
Ambient temperature: -10~+45℃ and temperature change may not exceed ±5℃/h.
Relative humidity: ≤90%。
No condensation.
No conductive or explosive dust, no corrosive metal or insulation-damaging gas or steam exist in the working place.

Elevation: ≤1000m.
Mounting condition: Indoor
2. Technical parameters for energy feed type
Output voltage: AC1000V /AC400V three-phase three-wire system (connected to grids of different voltage levels via energy feed transformers)
Output frequency: automatically follow grid frequency
Total harmonics distortion of current: ≤4%
3. Technical parameters for energy consumption type
Control: PWM (duty ratio range 5%~95%)
Chopped wave module’s efficiency: ≧98%
Permissible resistance deviation: -5%~+7%
Maximum working temperature for the resistor: ≤300℃
Resistor cabinet’s cooling method: natural air cooling
Resistor material: Ni-Cir non-magnetic material with small PPM
Noise: ≤80dB (sound pressure level)
Resistor box: stainless steel body provides a strong and beautiful appearance; inside the box is a temperature sensor for over-temperature alarm and trip.
4. Technical parameter for energy storage type
See Part 3 for details. 

Applications

AC output end of the frequency modulation device in a storage type power station is connected to the onsite grid (output end of the micro-grid’s generator) to detect grid load’s power in a real time manner. In the event of abrupt load increase, energy is released from the super capacitor to support the load. In the event of abrupt load decrease, energy is charged into the super capacitor to suppress voltage spike. This device smooth electrical peaks for a local grid, greatly increasing the safety and reliability of temporary power station system for the local grid. Fast response, energy saving and environmental protection are what this device can provide. The following is its box diagram.


Product Characteristics

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.
It is multi-functional, including energy feed, PWM rectification and reactive power compensation.
  
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. 

Model and Specification

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.
It is multi-functional, including energy feed, PWM rectification and reactive power compensation.
  
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.
Models and Specifications
Product models and specifications are defined in Figure 1 with specific models listed in Table 1.


 
Note: WindSun reserves the right to upgrade and improve products without further notice. 

Main Technical Parameters

(1) Rated feed voltage for grid connection: AC380V-1000V
(2) Rated grid connection capacity: 2000 Kw
(3) Rated grid connection frequency: 50 Hz
(4) Over-load capacity: 120%: 1 minute; 150%: 3 seconds;
(5) Dynamic response time: <=50 ms;
(6) Super capacitor’s voltage range: 500-820V
(7) Power factor: >=0.98
Effect:
By working together with a generator unit, the device received tests in various complicated working conditions. Test results shows it has met user requirements in all aspects.

 
  
CH1 (yellow) is the load’s current waveform and CH2 (green) is the AC output current waveform of the energy storage double-direction converter. The load starts in time 1, which means an abrupt load power increase occurs. At time 2, the device detects such increase and starts to output energy. It is seen from the waveform that load current and device’s output current are opposite in phase, indicating that device is providing energy for the load. The period from time 1 to time 2 is about 13 ms, which is also the device’s response time. This means the detection is quite fast and accurate.
 
 
 
 
CH2 blue waveform in the above figure represents the output current of the compensated generator, CH3 pink waveforms the abrupt load change and CH4 green waveform the output current of the device. It can be seen from the compensation effect that step-like abrupt change of load, having been compensated by the frequency modulation device of storage type power station, appears to be a slow change from generator side, a means that greatly lowers the impact of load change on grid and increases the entire micro-grid’s safety. 
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