Direct Power and Torque Control of AC/DC/AC Converter-Fed ...

1. Introduction
Control of the VSR can be considered as a dual problem with vector control of an
induction motor (see Fig.1. 4). The simples scalar control is based on current
regulation in three-phase system (AC waveforms) [15], [109].
Fig.1. 4. Classification of VSR control methods
Like for IM, vector control of VSR is a general control philosophy that can be
implemented in many different ways. The most popular method, known as voltage
oriented control – VOC [73], [83], [84], [85], [86], [87], [93], [97] gives high
dynamic and static performances via internal current control loops. In the VOC the
VSR equations are transformed in a line voltage vector oriented coordinate system.
In line voltage vector oriented coordinates there is a linear relationship between
current vector control components and power flow. To improve the robustness of
VOC scheme a virtual flux – VF concept was introduced by Duarte (see Malinowski
[93]). However, from the theoretical point of view, other types of mathematical
coordinate transformations can be defined to achieve decoupling and linearization of
the VSR equations. This has originated the methods known as nonlinear control.
Jung [56] and Lee [78] have been proposed a nonlinear transformation of VSR state
variables so that, in the new coordinates, the DC-link voltage and line current are
decoupled by feedback; this method is called also feedback linearization control –
FLC like for induction motor. Moreover, a passivity based control – PBC, as for IM,
was also investigated in respect to VSR [57], [65], [111].
In the mid of 1990s Manninen [95] and in the second part of 1990s, Nogouchi at
al. [105] have expanded the idea of DTC for VSR called direct power control – DPC
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