Page 26 - Modern Control of DC-Based Power Systems

Preface xxv

Stability of DC Microgrids is an interdisciplinary topic covering:
Power Electronics, Power Systems, and Control Engineering aspects.
Typically, Power Electronics and Control for Power Electronics books
deal with the control of a single converter, or at most they extend to the
cascaded systems, while leaving multisource and load systems not covered.
Power System books classically do not cover DC Power Systems at all.
Applications of Control Theory are often only shown at stand-alone con-
verter level, i.e., loaded by a simple resistive component and supplied by
an ideal voltage source, without looking at the system-level aspect.
Stabilizing Multiconverter Control is not covered at all.
In general, a Medium Voltage DC (MVDC) power system, indepen-
dently from the specific application, can be seen as an example of a power
electronic power system. A power electronic power system is an electrical
power network in which each device, generation, or load is connected to
the distribution system via a power converter. Such an idea started in the
United States in the framework of the so-called All Electric Ship research
program [2]. In the framework of the Electric Ship Research and
Development Consortium (ESRC) a notional integrated Power System
(IPS) was developed proposing DC as a way to increase flexibility in the
power management. The goal was to overcome a set of challenges such as:
• Reduction of weight on board: with the use of DC it becomes possi-
ble to imagine high speed generators based on lighter electrical
machines.
• Fast reconfiguration and flexible load dispatch to accommodate
dynamic load management.
This study and understanding of this new type of power system cre-
ated interesting new theoretical links between power system and control
theory. For the first time, the dynamics of a power system were fully
determined by feedback control loops instead of depending, at least partly,
on the dynamic of rotating machines. Stability of a power bus becomes a
control challenge related to the interaction of generator converters and
load converters.
More recently, these challenges have been also introduced in terrestrial
power systems with the goal to understand how DC could help increase
flexibility in the distribution system. Significant effort is currently per-
formed at RWTH Aachen in the framework of the Forschungscampus
(Research Campus) Flexible Electrical Network in a tight cooperation
between university and industry [3].