How do dynamic brakes work

A chopper, on the other hand, only includes the regulatory circuit and switching device, with the resistors being separate components. This allows the resistors to be appropriately sized and mounted remotely, which can be important, since the resistors generate a significant amount of heat.

There are two types of control for dynamic braking: hysteresis control and PWM pulse-width modulation control. With hysteresis control, the control circuit keeps track of the DC bus voltage level and turns the transistor on when the voltage reaches a predetermined level, in order to avoid an overvoltage fault in the drive.

When current is flowing to the resistor, the energy is turned into heat, which causes the DC voltage to decrease. Where hysteresis control turns on the transistor and leaves it on until the voltage drops to a predetermined level, PWM control turns the resistor on and off according to the level of the DC bus voltage. Today, diesels use their tractive effort to help move a train up one side of a hill, and dynamic braking to ease it down the other side.

Indeed, in some spots like Cajon Pass in California, rules are in place to prevent a train from starting downgrade unless it has a specified number of units with functioning dynamic brakes. The only external evidence of dynamics is the presence of grilles covering the resistor grids.

These are found at the rear of the long hood under the radiator overhangs on General Electric units, and directly behind the cab just below the top of the long hood on newer General Motors products. Until the advent of the SD50 model in , the dynamic braking resistors of GM locomotives were located in the middle of the long hood directly above the diesel engine in a pronounced bulge or blister topped by one or two cooling fans on the roof.

Instead, the power was returned to the overhead distribution system With their motors functioning as generators, locomotives on downgrade trains could literally provide power to other trains going uphill. The electrical characteristics of modern, rectifier electric locomotives and multiple-unit cars do not permit the return of power to the distribution system. Such rolling stock is equipped for simple dynamic braking. A newer invention, electronically controlled pneumatic braking, may revolutionize train-handling in the decades to come.

Milwaukee Road passenger trains. Milwaukee Road history. Getting the most out of your overnight Amtrak trip. Union Pacific on Cajon Pass in the s. EMD at In some applications, one or multiple resistors are mounted remotely, where the heat they generate does not affect other electrical equipment.

There are two common control methods for dynamic braking — hysteresis control and pulse-width modulation PWM control. Pulse-width modulation control, on the other hand, switches the IGBT on-and-off continuously via a control algorithm and monitoring of the DC bus voltage, so torque ripple is greatly reduced. PWM control is primarily used when multiple drives are connected to a common DC bus, to avoid having one drive doing a disproportionate share of the dynamic braking work.

Regenerative braking takes the energy generated by the motor and feeds it back to the AC power source or to a common bus , where it can be used again.