Dual-Frequency Braking - Siemens SINAMICS PERFECT HARMONY GH180 Function Manual

8.9

Dual-Frequency Braking

8.9.1 Dual-Frequency Braking
VFD requirements for Braking Functionality
Many applications for VFDs require occasional negative torque for braking. Most static
converters used for VFDs are not capable of returning energy to the utility. Such applications
require additional circuits to regenerate the braking energy into the AC mains, or to dissipate the
braking energy in a resistor.
DC Injection Braking
One method of doing this that avoids additional power devices, is to use the existing circuits to
inject DC current into the motor windings. DC injection braking dissipates the braking energy in
the motor.
• DC injection braking is not effective unless the available current is several times rated,
especially for large motors.
• The estimation of motor speed is difficult during DC injection braking.
Dual-Frequency Braking (DFB)
Dual-frequency braking is another method to dissipate braking energy in the motor.
• DFB provides higher torque per ampere than DC injection braking.
• DFB permits continuous estimation of motor speed.
Like DC injection braking, DFB is implemented in software and requires no additional hardware
that can reduce the reliability of the drive.
Limitations of DFB
• When DFB is enabled, the motor flux is reduced above 50% speed to prevent overvoltage
trips.
• The drive must be maintained in the run state to produce the counter-rotating field for loss
production.
• DFB is not operable in V/Hz control mode.
DFB Operation
Enable DFB with parameter Enable braking (3360) or via SOP flag BrakingEnable_O.
DFB induces extra losses in the motor by applying a second set of three-phase voltage vectors to
the motor, in addition to the normal set of voltage vectors used for speed control. The motor uses
the extra losses to absorb the kinetic energy released during braking.
NXGPro+ Control Manual
Operating Manual, A5E50491925A
Advanced Operating Functions
8.9 Dual-Frequency Braking
243