Page 255 - Modern Control of DC-Based Power Systems

CHAPTER SIX

Simulation

In this chapter the controllers presented in Chapter 1, Overview—
Voltage Stabilization of Constant Power Loads (CPLs), are evaluated. The
chapter is structured in such way that in Section 6.1 the results for a
cascaded system are presented. In Section 6.2 and its subsections the
shipboard power system is simulated for averaged and switched converter
representations. Section 6.3 summarizes this chapter.
The scope of these simulations lies solely in assessing the performance
of the stabilizing control action. Therefore, each generator is assumed as
an ideal voltage source that via a buck converter supplies the DC bus,
which operates under voltage control and in continuous conduction
mode (CCM). The electromechanical generation system is considered
too sluggish to react on the fast dynamics by the DC bus [9], thus it
appears during the fast DC bus transient as a constant. This assumption is
confirmed by the analysis performed in [10]; there, an examination with
a detailed generation model including speed governor and auto voltage
regulator versus a stiff voltage source was done. The conclusion was that
the maximum transient voltage error was 2% while applying a DC load
perturbation from 10% to 40%. Hereafter, the ideal voltage source was
used to reduce the study complexity and to focus purely on the control
for voltage stabilization. Hence, to evaluate the performance of the con-
troller, no limit on di=dt was imposed nor saturation on the current was
put in place, as those limits come from the physical realization, and as
technology evolves, this would skew the analysis from a pure performance
point.
For guaranteeing CCM the linear resistance was chosen in such way
that discontinuous conduction mode (DCM) is avoided [3]. This is
because in shipboard power systems the components are sized in a way
that they function at their highest efficiency in normal operating condi-
tions, and DCM would therefore show an irregular operation where low
load is requested and high losses occur. Due to the restrictions of the
Sliding Mode Control described in Section 5.8 we decided to omit it
from the simulation in this chapter.

Modern Control of DC-Based Power Systems. © 2018 Elsevier Ltd.
DOI: https://doi.org/10.1016/B978-0-12-813220-3.00006-5 All rights reserved. 219