Tese
Controle adaptativo de corrente aplicado a conversores estáticos conectados à rede elétrica
Fecha
2013-02-28Registro en:
MASSING, Jorge Rodrigo. Adaptive current control applied to grid-connected static converters. 2013. 199 f. Tese (Doutorado em Engenharia Elétrica) - Universidade Federal de Santa Maria, Santa Maria, 2013.
Autor
Massing, Jorge Rodrigo
Institución
Resumen
This thesis addresses the design of adaptive current controllers applied for voltagesource
grid-connected converters with LCL-filter. Due to the grid equivalent impedance
uncertainty and/or variation at the point of connection, the current controller of such
converters may become unstable or have a poor performance with fixed-gain controllers
because the grid impedance is part of the dynamic model. So, adaptive control techniques
are proposed to ensure stability and performance of current controllers for grid-connected
converter with LCL-filter even without knowledge of the grid equivalent impedance. Continuous
time adaptive control, from the theoretical point of view, is a well established
control technique. However, in this application, a discrete-time current controller is implemented.
There are some differences between discrete-time and continuous-time adaptive
controllers. When the controlled variable is the converter current, a model reference
adaptive state feedback is proposed. The adaptation algorithm, responsible to update
the gains in real-time, consists on a recursive least-squares (RLS) algorithm. When the
controlled variable is the grid current, a model reference adaptive state feedback is also
used. However, the RLS algorithm has some modifications to keep the controller robust
under unmodeled dynamics. The RLS algorithm is used because it has better parametric
convergence characteristics compared to other algorithms. The grid voltage disturbance is
rejected making some small modifications on the controller structure. Simulation results
are validated by experimental results in a 5,5kW three-phase grid-connected converter,
which shows good convergence and steady state stability of the adaptive controllers. Finally,
some comparisons with fixed gain current controllers are presented to show de
advantages and disadvantages of each controller.