3.4 AC–MTDC Load flow Analysis
Load flow study is an essential part of the planning and operation of a power system. It is also the first step before doing the dynamic simulation. The load flow analysis of combined AC–MTDC network is presented in the following sections. All AC side voltages and currents are expressed with respect to the common network reference frame 
–
and common base values.
3.4.1 AC Grid Load flow Model
The objective of the AC grid load flow is to determine the voltage magnitude and angle at each bus of the AC system. If the current injection at each bus of the AC system was known a priori, then (3.84) could be solved for the voltage phasors using the relation 
, which is linear in nature. Unfortunately, the current injection is not known beforehand and it is related to the the injected power and bus voltage at the 
th bus through the following load flow equation:
Depending on the constraints imposed by the nodes of the AC system, the problem becomes nonlinear ...
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