INPUT SOURCES FOR REGENERATION OR DYNAMIC SLOWDOWN
If the inverter is made to regenerate (i.e., to try to pump back the mechanical energy in the load to the ac supply), the source diode bridge cannot reverse its current flow. Thus, the absorbed energy will cause the dc bus voltage to increase. If this higher voltage is not absorbed, the source bridge, load inverter, and capacitor bank could get damaged.
Dynamic Braking
The simplest way to absorb the load energy that is regenerated is by using a resistor across the dc link (dynamic braking resistor). This is simply a large power-dissipating resistor that
is switched across the dc bus. The dynamic braking resistance chopper is controlled so that when the link voltage rises above a preset limit, the resistor is switched in until the voltage drops below the preset limit. Therefore, the regulator controls automatically the amount of braking applied.