Installation manual

GEO Direct PWM Amplifiers – Preliminary Documentation

System Wiring 23

Ext. Shunt Connector Pin Out

Pin # Symbol Function

1 Ext regen+ Output

2 Ext regen- Output

Shunt Regulation

When the motor is used to slow the moving load, this is called regenerative deceleration. Under this

operation, the motor is acting as a generator consuming energy from the load while passing the energy

into the DC Bus storage capacitors. Left unchecked, the DC Bus voltage can raise high enough to damage

the drive. For this reason there are protection mechanisms built into the Geo Drive product such as shunt

regulation and over-voltage protection.

The shunt regulator monitors the DC Bus voltage. If this voltage rises above a present threshold (Regen

Turn On Voltage), the Geo Drive will turn on a power device intended to place the externally mounted

regen resistor across the bus to dump the excessive energy. The power device keeps the regen resistor

connected across the bus until the bus voltage is sensed to be below the Regen Turn Off voltage at which

time the power device removes the resistor connection.

Minimum Resistance Value

The regen resistor selection requires that the resistance value of the selected resistor will not allow more

current to flow through the Geo Drive’s power device than specified.

Maximum Resistance Value

The maximum resistor value that will be acceptable in an application is one that will not let the bus

voltage reach the drive’s stated over voltage specification during the deceleration ramp time. The

following equations defining energy transfer can be used to determine the maximum resistance value.

Energy Transfer Equations

Regen, or shunt, regulation analysis requires study of the energy transferred during the deceleration

profile. The basic philosophy can be described as follows:

• The load has stored energy in its rotating mass.

• The drive removes this energy by transferring it to the DC Bus.

• There are significant energy losses in the transfer, both electrical and mechanical.

• The DC Bus capacitors can store some energy.

• The remaining energy, if any, is transferred to the regen resistor.

Understanding this process in all its individual parts, it is possible to analyze the shunt regulator circuitry

in more detail.

Energy Stored in the Load

Energy stored in the moving mass is a function of inertia and velocity according to the equation:

j678.0