  This paper proposes a novel method to automatically enforce controls and
limits for Voltage Source Converter (VSC) based multi-terminal HVDC in the
Newton power flow iteration process. A general VSC MT-HVDC model with primary
PQ or PV control and secondary voltage control is formulated. Both the
dependent and independent variables are included in the propose formulation so
that the algebraic variables of the VSC MT-HVDC are adjusted simultaneously.
The proposed method also maintains the number of equations and the dimension of
the Jacobian matrix unchanged so that, when a limit is reached and a control is
released, the Jacobian needs no re-factorization. Simulations on the IEEE
14-bus and Polish 9241-bus systems are performed to demonstrate the
effectiveness of the method.
