Page 27 - Modern Control of DC-Based Power Systems

xxvi Preface

From an engineering point of view, this means a wider range of
degrees of freedom on how the dynamics of the system will be deter-
mined. This also means that the design of each converter encompasses
two different aspects: The local control of the correspondent generator or
load but also the interaction with the other converters in the same bus.
The book starts with an overview of the challenges and opportunities
offered by the application of DC Technology in ship power systems since
this was the sector that really drove the evolution of the application in the
first stage.
The second chapter presents the problem of the interaction of
generation-load converters in terms of the formulation of the Constant
Power Load (CPL) problem. This simple schema is a great way to intro-
duce the dynamic interaction issue in a very simple way. A stiff control of
the power demand as typically performed by power electronic driven load
introduced the idea of a negative impedance reaction able to reduce the
dumping capability of the network. The issue has been well known for a
long time for low power DC distribution systems (such as power supply)
but in the high power area it presents interesting aspects related to the
bandwidth of the different converters involved in the process. Given that
in MV the switching frequency of the converter is rather limited, the
interaction becomes definitely more complicated than in the low power
case. This analysis introduces the student to the problem of generator-
load interaction in a multiconverter system.
A deeper analysis of the dynamic interaction is then presented in
Chapter 4, Generation Side Control, where a full process of small-signal
model synthesis is derived. In this chapter the analysis and design of a single
converter is presented together with classical control solution. From the
analysis of the single converter system the significant transfer functions
describing the closed-loop behavior of the converter are derived and then
used to look at the cascading situation. The system analysis is complemented
with a review of the possible load representation. The chapter describes also
practical approaches to on-line system identification techniques that can be
used to extract the small-signal representation in a laboratory setting.
Chapter 5, Control Approaches for Parallel Source Converter
Systems, presents a complete review of classical and modern control
methods applied to the specific challenge. After reviewing basic stability
criteria, the state-based approach is reviewed presenting key concepts
such as controllability and observability together with pole placement
approaches.