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1. DC-SIDE HARMONIC CURRENTS CALCULATION AND DC-LOOP RESONANCE
ANALYSIS FOR AN LCC–MMC HYBRID HVDC TRANSMISSION SYSTEM
ABSTRACT
For an LCC–MMC hybrid HVDC transmission system with reverse current blocking
diodes, this paper presents a method for dc-side harmonic current calculation and dc-loop
impedance calculation. First, in the calculation of dc-side harmonic currents, the line-
commutated converter at the rectifier side is replaced by the three-pulse harmonic voltage
sources; the modular multilevel converter is represented by an equivalent passive circuit based
on the linearization theory; an improved calculating method for the coupled line model is
introduced into calculating the admittance matrix of the dc transmission lines to improve the
computational efficiency; and then this paper describes the complete procedures of the proposed
method. Second, based on the dc-side equivalent models mentioned before and the nodal voltage
analysis method, this paper presents an analytical method for the calculation of dc-loop
impedance according to the definition of dc-loop impedance Finally, the PSCAD/EMTDC
simulation verifications have been carried out based on a 1500 MW/+500 kV MMC-HVDC
system, a 3000-MW/ 500-kV LCC–MMC hybrid HVDC system, and its dc network. The
simulation results and the analytical results coincide with each other, and the effectiveness of the
proposed methods is proved.