Rectifier - Active
An IGBT converter is used to draw sinusoidal currents from the 480V supply to produce a constant DC bus of 750V at any engine speed.
Highlights
- The active rectifier can handle power flow in either direction. If the traction power demand exceeds the converter capacity, the voltage of the 750V bus falls towards 650V. The traction controllers automatically reduce the traction current when the voltage starts to fall.
- If the traction power exceeds the total power available on the 480V AC bus, the engine speeds begin to fall causing the frequency to reduce below 60Hz. The active rectifier control card limits the fall in frequency to 2Hz by reducing the forward power limit.
- If the power recovered from the traction motors during braking exceeds converter capacity, the 750V bus voltage starts to rise. The brake chopper conducts when the voltage reaches 800V. The duty cycle is adjusted to maintain the voltage at 800V.
- During braking, the converters are able to overdrive the engines to a speed higher than the governor setpoint. This allows the cranking losses of the engines to be used to absorb power from the bus in preference to the dynamic braking resistors. This has the benefit of eliminating emissions completely during braking and reducing the overall fuel consumption.
- If the power returned to the 480V AC bus exceeds the total demand of other loads, the current in the generator windings reverses in phase causing the generator to back-drive the diesel engine. If the torque exceeds the cranking losses of the engines, the engine speeds will start to increase causing the frequency of the bus to rise above 60Hz. The active rectifier control card limits the increase in frequency to 2Hz by reducing the reverse power limit.
Components used in this system
| Traction Drive: | 500HP DC Traction |
