04-08-2012, 11:53 AM
Application of a Matrix Converter for the Power Control of a Variable-Speed Wind-Turbine Driving a Doubly-Fed Induction Generator
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Abstract
A grid-connected wind-power generation scheme
using a doubly-fed induction generator @FIG) in conjunction
with a direct AC-AC matrix converter is proposed. The
analysis employs a stator-flux vector-control algorithm and a
space vector modulated matrix converter to control the
generator rotor current. The system enables optimal speed
tracking for maximum energy capture from the wind and high
performance active and reactive power regulation. The paper
describes the operating principles of this power generation
scheme. The matrix converter-based rotor current control
scheme is highlighted. Simulation studies of the proposed
power generation system were carried out. Results obtained
are presented illustrating the good control performance of the
system.
INTRODUCTION
Wind power is widely recognized as a viable source of
renewable energy. In the UK the percentage of electrical
power generated by wind-driven turbines to the total power
generation increases steadily. Most wind turbines currently
operate at constant speeds through grid-connected
alternators or induction generators. The present system deals
with a variable-speed wind generation scheme. This has a
higher energy cap? .? capability than a constant speed
system and reduces mechanical stresses and audible noises.
Integration of the three-phase induction machine and power
electronic converter provides an effective means to achieve
variable-speed, constant-frequency (VSCF) wind-power
generation. A number of machine-converter configurations
have been proposed in the literature [1,2,3]. One of these,
considered most attractive by the authors, is that developed
by Pena et a1 [3], which employs a doubly-fed induction
generator (DFIG) interfaced to the power grid using a dclink
voltage-source converter, commonly known as a
Scherbius drive.
A MATRIX CONVERTER CONTROLLED DFIG
System ConJiguration
In the generation system, an AC-AC matrix converter may
be used to supply the variable-frequency voltages to the rotor
terminals of the induction machine. Fig. 3 shows schematics
of the matrix converter-DFIG configuration and its
simplified control scheme. The stator of the generator is
connected directly to the utility grid. A matrix converter is
inserted in the rotor circuit, giving direct AC-AC power
conversion between the rotor circuit and grid. The grid-side
connection is made via a three-phase LC filter to suppress
high-order harmonics. A matrix converter provides
bidirectional power-flow control thereby enabling the DFIG
to operate in either subsynchronous (or<ws) or supersynchronous
modes (w,>o,). In both modes the stator active
power is generated from the DFIG and delivered to the grid.
CONCLUSION
A variable-speed wind-power generator using a DFIG in
conjunction with a matrix converter is proposed. Stable
operation of the DFIG was achieved by means of stator-flux
oriented control technique. The operational principle of the
proposed wind-power generator and the validity of the
control scheme were illustrated by the steady-state and
transient responses of the power and currents associated with
the machine stator and rotor. Simulation results demonstrate
that the proposed wind-power generator is feasible and has
certain advantages.