Calculation of HVDC-converter harmonics in frequency domain with regard to asymmetries and comparison with time domain simulations

In order to study the effects of large HVDC power converters on the feeding AC networks, it is of importance to explain and to calculate harmonic phenomena which are a result of power converter operation. During commissioning of real HVDC power converters, it could be seen that harmonics resulting from asymmetry in the system voltages or from asymmetry in power converter operation led to significant difficulties concerning the system design. For this reason, not only the effects of characteristics but also the effects of noncharacteristic converter harmonics must be taken into account. The aim is to describe the steady state harmonic behavior of the converter. The harmonic spectra are not determined by time domain analysis but instead the solution is found by frequency domain calculations. This can result in reduced calculation time in comparison to conventional Fourier analysis of the time functions. The power converter is interpreted as an amplitude modulator with voltage and current converter functions which describe the coupling of the DC circuit and the AC network through the power converter. To verify the theory, comparisons of frequency domain with time domain calculations were carried out