  The operating conditions of the power system have become more complex and
changeable. This paper proposes a probabilistic load flow based on the cumulant
method (PLF-CM) for the voltage sourced converter high voltage direct current
(VSC-HVDC) hybrid system containing photovoltaic grid-connected systems.
Firstly, the corresponding control mode is set for the converter, including
droop control and master-slave control. The unified iterative method is used to
calculate the conventional AC/DC flow. Secondly, on the basis of the
probability model of load and photovoltaic output, based on the aforementioned
flow results, use correlation coefficient matrix of this paper will change the
relevant sample into independent sample, the cumulants of the load and
photovoltaic output are obtained; then, the probability density function (PDF)
and cumulative distribution function (CDF) of state variables are obtained by
using Gram-Charlie series expansion method. Finally, the mean value and
standard deviation of node voltage and line power are calculated on the
modified IEEE 34-bus and IEEE 57-bus transmission systems. The algorithm can
reflect the inherent uncertainty of new energy sources, and replace the complex
convolution operation, greatly improving the calculation speed and the
convergence.
