Positive and negative sequence control for power converters under weak unbalanced networks

In the application field of AC/DC converters connected to utility networks, the DC-link voltage controller is generally too slow to compensate the second harmonic component caused by the unbalance of the phase voltages. Assuming the accurate description of the unbalance in the network voltages, namely by the accurate decomposition in the positive and negative sequence synchronous reference frame, the generated currents are also decoupled into two parts and separately controlled. For the proper cancellation of the oscillation in the power taken from the network, the unbalance in the voltages is taken into account in the calculation of the four current references. Results show that the DC-link voltage show no second harmonic component and is able to operate with weak networks under voltage unbalance.