Solution to the problem of low order harmonic resonance from HVDC converters

A severe form of the low-order harmonic resonance problem was identified in a HVDC/AC system. Solutions to the problem were sought by HVDC control means and were achieved by a proper design of the voltage-dependent current order limiter (VDCOL), the current regulator, and the timing pulse generator. Supplementary control loops were also introduced, resulting in a satisfactory performance as compared to that obtained with the use of an uncharacteristic harmonic filter on the AC side. Robustness of all the options has been demonstrated through recovery performance of the DC link in response to three-phase five-cycle faults on both rectifier and inverter commutating buses