The Back-to-Back HVDC Modular Multilevel
Converter for Passive Networks – Simulation Model
Tony Endré Slettbakk – tony.slettbakk@gmail.com - CERN
PURPOSE OF THE MODEL
The model was developed through the work of the bachelor’s thesis [1] conducted at CERN
in 2018, as part of the technical student program together with the Norwegian University of
Science and Technology (NTNU). The thesis is titled “Development of a Power Quality
Conditioning System for Particle Accelerators”. The model is used to prove the feasibility of
the back-to-back HVDC converter for transient voltage dip mitigation, using the modular
multilevel topology. The voltage dips are mitigated using internal energy stored in the
submodule capacitors, together with extracting maximum allowed current from the grid. The
potential for such a system is large, as today’s particle accelerators experience issued with
transient voltage dips. Protection against this is of importance for future particle accelerators
of even larger dimensions.
DEVELOPMENT PROCESS
The model was developed in the MATLAB & SIMULINK environment, using the SimPower
electrical systems. The development process started from scratch, with only basic personal
experience in power electronics and simulation. Estimated time to gain knowledge of the
topology and control system is around 300 hours. Time spend on the simulation model in
building, refinement and validation is estimated to over 200 hours.
Basic knowledge of modular multilevel converters is based on the course presented in [2],
while more advanced knowledge was obtained from various international publications
presented in IEEE Explorer, and through technical brochures from Cigré, especially [3].
The modelling technique for this simulation is based on the example model of IREQ Quebec
[4], and other various examples from Mathworks inc, available online. The simulation model
was developed with its control system based on many separate publications and guidelines.
USER GUIDE
THE MODEL
The simulation model comes in two files. The first is a Matlab code ‘.m’-file, initializing most
of the parameters used for simulation, used for easy access for modifications. The other file
is the Simulink model ‘.slx’ file, containing the complete model. Before simulation can start,
the initialization file must be ran.
The model is the back-to-back HVDC modular multilevel converter supplying a passive
network with power. For the initial settings, the MMC rectifier and inverter is identical, and is
of 51 levels. Connection voltage is 66 kV. DC voltage is 135 kV at a steady state modulation
index of ~0.8. Rating of the converter is 220 MVA.
