DC link
The connected servomotors are supplied with energy from the DC link. It serves as an energy storage and first needs to be charged up after switching the device on, before it can supply the servomotors. The DC link is designed such that it can take up and store a certain degree of surplus energy from the motor (brake energy) and subsequently supply the motor again with this stored energy. If the upper limit of the energy storage is reached, the brake chopper feeds any further brake energy into the internal or external brake resistor, where it is converted into heat; it is then no longer available for the further operation of the motor. The voltage is taken and evaluated as the indicator for the current energy level of the DC link. As soon as the brake resistors have also reached their energy limit, the error ‘FD4C, DC link – overvoltage’ appears and the energy flow to and from the motor is interrupted, i.e. the motor makes uncontrolled movements.
In a drive system, the DC links of the individual devices are connected so that the energy level of all devices is the same, regardless of which motor the brake energy is currently being fed back from. In many cases these feedbacks do not happen at the same time, and without a DC link system, for example, a device would be at the limit and would already have to "destroy" energy in a brake resistor, even though other devices could still store energy in the DC link. In a DC link connection the energy could be stored, since the DC link of all linked devices would be loaded first, before the energy in the brake resistors would be converted to heat.