Drive Principles
In successive chapters extensive attention will be given to the modeling and control of rotating field machines. Rotating field machines can be conveniently modeled with the aid of a so-called ideal rotating transformer (IRTF). The initial part of this ch
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Drive Principles
In successive chapters extensive attention will be given to the modeling and control of rotating field machines. Rotating field machines can be conveniently modeled with the aid of a so-called ideal rotating transformer (IRTF). The initial part of this chapter explores the IRTF concept. It will be shown that torque production may be described mathematically by the cross product of a flux and current space vector. In the previous chapter, three-phase current control was introduced with the precise aim of being able to manipulate the current space vector. The reason for this approach is to develop a set of fundamental drive concepts which aim to, at an elementary level, control torque in drive systems based on rotating field machines such as synchronous or asynchronous machines. Application of the IRTF concept for brushed DC machines is also possible, though it is not widely used and will not be discussed in detail. Note that switched reluctance machines do not embrace the Lorentz force based concept, which implies that they do not follow the IRTF model and therefore they are treated separately in this book at a later stage.
4.1 ITF and IRTF Concepts The ideal transformer (ITF) and ideal rotating transformer (IRTF) concepts have been discussed extensively in the book Fundamentals of Electrical drives [5]. The IRTF was first used in [4]. The introduction of these concepts has proven to be effective for electrical machine modeling purposes. In this book, the ITF/IRTF concepts will be extended further. Hence, it is in the interest of readability to provide a brief review of these concepts prior to considering the machine models in this and following chapters. Symbolic ITF Model The symbolic ITF concept as shown in Fig. 4.1a represents a magnetically and electrically ideal transformer, i.e., without leakage inductances, copper or core © Springer Nature Switzerland AG 2020 R. W. De Doncker et al., Advanced Electrical Drives, Power Systems, https://doi.org/10.1007/978-3-030-48977-9_4
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4 Drive Principles
(a)
(b)
Fig. 4.1 Symbolic and generic space vector based ITF models. (a) Symbolic model. (b) Generic model
losses and with a primary (subscript 1) to secondary winding ratio of n1 : n2 . The ideal transformer requires no magnetizing current and can thus be regarded to have an infinite magnetizing inductance. The space vector equation set which corresponds with this model is of the form ψ 2 = i1 =
n2 n1
ψ 1
(4.1a)
n2 i2 . n1
(4.1b)
Flux- and Current-Based ITF Representation The flux/current equation set (4.1) forms the basis for the generic model given in Fig. 4.1b. Note that the generic model shown in Fig. 4.1b represents the so-called ITF-flux version, because the primary flux vector ψ 1 is designated as an input. The alternative so-called ITF-current version utilizes the primary current vector i1 as an input. The selection of a version depends on the nature of the machine model in which it is applied. It is emphasized that the ITF model is based on the use of flux lin
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