Limitation of adjustable-speed drive operation by unbalanced voltage supply

Operation of the drives may be negatively affected by non-standard conditions in the power network such as voltage unbalance, which may arise in three-phase power networks. The unbalance can be caused by a failure in the network or by unbalanced load in the vicinity of the affected drive. Unsymmetrical voltages at the input of a voltage source inverter cause pulsations in the DC-link voltage when not properly taken care of. This may result in reduced power capabilities of the drive. The paper deals with the methods to address this problem and with the limitations placed on the drive when operated from the unbalanced voltage supply.