Motion Control - ElmoMC

Shunt Regulator

Design consideration for a shunt regulator

Operation of the shunt regulator

A shunt regulator can be added to all the standard PS types. Shunt regulators are switching devices, that use dissipative elements (resistors) that are switched across the DC bus, whenever the voltage reaches a predetermined level (Vr).
The switching elements employed are MOSFETs.

The function of the shunt regulator is to regulate the voltage of the DC bus during the period of motor deceleration, whenever net energy outflows from the motor to the amplifier. The amplifier handles this reverse energy just as efficient as it provides energy to the motor. Most of the motor's energy is passed through the amplifier to the power supply, while the returning energy charges the filter capacitors above their normal voltage level, that was determined by the AC incoming voltage. When the capacitors charge-up reaches the predetermined voltage level (Vr), the shunt regulator begins its regulating action.

The bus is regulated to this range until regeneration ceases. Deciding if a regulator is required in a particular application, is best done empirically, using the actual system as a test-bed. On multi-axis systems, if the other axes always take power from the supply when a particular axis is regenerating, then the shunt regulator is probably not required. As a design aid, the following information is provided so that one may estimate if a regulator is required in a particular case. It can be shown that, neglecting friction and other secondary power loss mechanisms, the total energy returned to the power supply during a deceleration period is given by the equation:

Once this energy value has been calculated, the required capacitance needed to store the energy can be found from the expression:
In a power supply without a shunt regulator the value of the total capacitance (Cs) is fixed and the following inequality must exist.
If Cx is bigger than Cs then a shunt regulator must be used or additional capacitance should be added till the above inequality it met.