Fully Decou pled Controller Models for Voltage Source Converter based High Voltage DC Transmission

VSC-HVDC has two distinct advantages over its earlier generation thyristor based High
Voltage DC transmission. Synchronous voltage source is not required to commutate
against, for its operation and it does not suffer from commutation failures under adverse
conditions in interfacing ac system. These two properties make it amenable to wider
application areas. To make it adapt to operational conditions imposed on it in various
applications, its controller parameters need to be assessed and tuned through extensive
simulation studies. To facilitate this, two alternative controllers viz. a fully decoupled
controller model and also an instantaneous theory based fully decoupled hybrid controller
model are developed in the thesis. The decoupling is achieved by exploiting similarity
transformation in both the controllers. In the first controller model, the Park's currents
and voltages are directly obtained from the measured network variables and the reference
park's currents for the inner current loop are obtained from the instantaneous measured
power. In the second one, both the feedback as well as reference Park's currents for the
inner current loop are obtained from the Clarke's variables. An AC system interfacing
electronics based power transmission or distribution network experiences non-sinusoidal
voltage and current waveforms. Instantaneous power theory being suitable for steady as
well as transient states, is used for handling measured inputs. The performance of the
models is assessed through SIMULINK Power system Blockset aided simulations on a
VSC-HVDC link interfacing an ac system, having normal fault level, low fault level and
also witnessing a single line to ground fault on its rectifier transformer primary side.