Harmonic Instability at Sending End of the Exceedingly Weak HVDC System

As the development of high voltage direct current (HVDC) transmission, the problems of harmonic instability become more prevalent. Besides, harmonic instability in exceedingly weak HVDC systems is particularly serious. The modulation of the DC converter based on switching function is deduced. By considering the whole process of harmonic transferring at the AC and DC side through converters from the perspective of circuit, the generation conditions of harmonic instability are analyzed. Then an exceedingly weak HVDC system model is established and simulated in PSCAD/EMTDC software to verify the theoretical analysis. The study results provide theoretical basis and computational methods to solve the problems of harmonic instability in HVDC systems.