2 research outputs found
Generalized Voltage-based State-Space Modelling of Modular Multilevel Converters with Constant Equilibrium in Steady-State
This paper demonstrates that the sum and difference of the upper and lower
arm voltages are suitable variables for deriving a generalized state-space
model of an MMC which settles at a constant equilibrium in steady-state
operation, while including the internal voltage and current dynamics. The
presented modelling approach allows for separating the multiple frequency
components appearing within the MMC as a first step of the model derivation, to
avoid variables containing multiple frequency components in steady-state. On
this basis, it is shown that Park transformations at three different
frequencies (, and ) can be applied for deriving
a model formulation where all state-variables will settle at constant values in
steady-state, corresponding to an equilibrium point of the model. The resulting
model is accurately capturing the internal current and voltage dynamics of a
three-phase MMC, independently from how the control system is implemented. The
main advantage of this model formulation is that it can be linearised, allowing
for eigenvalue-based analysis of the MMC dynamics. Furthermore, the model can
be utilized for control system design by multi-variable methods requiring any
stable equilibrium to be defined by a fixed operating point. Time-domain
simulations in comparison to an established average model of the MMC, as well
as results from a detailed simulation model of an MMC with 400 sub-modules per
arm, are presented as verification of the validity and accuracy of the
developed model
On the modeling of MMC for use in large scale dynamic simulations
peer reviewedThis paper focuses on simplified models of the
Modular Multilevel Converter suitable for large-scale dynamic
studies, in particular simulations under the phasor approximation.
Compared to the existing literature, this paper does not a
priori adopt the modeling approach followed for the original twolevel
or three-level Voltage Source Converter. On the contrary,
a model is derived following a physical analysis that preserves
its average internal dynamic behavior. An equivalent control
structure is proposed and various alternatives are highlighted.
The proposed model with its controllers has been implemented
in a phasor simulation software and its response has been
validated against a detailed Electromagnetic Transient model.
Finally, an illustrative example is presented with the application
of the proposed model on a large grid consisting of AC areas
interconnected with a multi-terminal DC grid