SECTION FOUR - COMPONENT DESCRIPTION AND SPECIFICATION 4.3
4.1.2.3. Shunt Regulator Circuit
Rapid motor deceleration or an overhauling load creates a situation in which energy is
regenerated back into the high voltage power supply. This regenerative energy will charge
the power supply bus capacitors. To prevent capacitor over voltage a shunt regulator
circuit senses when the bus voltage exceeds the regen cut-in voltage and via a regen
transistor, switches a regen resistor across the d-c bus, (in shunt), to dissipate the regen
energy. Hysteresis in the shunt regulator circuit keeps the regen circuit active until the bus
voltage is reduced below the regen cut-out voltage. The frequency at which the regen
circuit operates is dependent upon the magnitude of the regen energy. If the regen energy
exceeds the capacity of the regen circuit, a higher capacity regen resistor must be used.
The supply includes an internal regen resistor with 40 watt capacity. An optional external
regen resistor with higher capacity can be utilized, as explained in Section 2.4.
An electronic circuit breaker protects the regen circuit against external short circuits and
protects the regen resistor from exceeding its continuous rating. If the regen resistor
continuous rating is exceeded the electronic circuit breaker disables the shunt regulator
circuit. In this case, additional regen energy from the motor will cause the d-c bus voltage
to increase until an over voltage fault occurs. Under this condition, the regen circuit is
undersized for the application. Figure 4-3 provides energy vs. time curves for the
electronic circuit breaker. A regen fuse is provided to protect the regen resistor in case of
failure of the regen circuit electronics. A monitoring circuit provides a REGEN FUSE fault if
the regen fuse blows. The regen electronic circuit breaker prevents nuisance tripping of
the regen fuse.
