Limitations of PWM rectifier under unbalanced voltage supply

Voltage-unbalance conditions that can arise in the power network may affect operation of electric drives in a negative way. The cause of the unbalance may be a failure in the network or presence of an unbalanced load in the vicinity of the affected drive. Unsymmetrical system of voltages at the input of a voltage source inverter gives rise to the pulsations in the DC-link voltage when no suitable countermeasures are taken. This may result in significantly reduced power capabilities and, therefore, limited controllability of the drive as well as negative influence on the lifetime of the electric motor in the drive. The paper deals with methods to address this problem and with the constraints caused by the unbalanced voltage supply.