I. INTRODUCTION
The main objective of controlling a DC-DC converter is to
attain a regulated output voltage even under perturbations
which may arise due to change in load current as well as in
presence of disturbances one of the sources of which may be
due to change in input voltage. This is a classical problem of
robust control. Different robust control techniques have been
applied in literature [1]-[9] for voltage regulation of converters.
Both linear and nonlinear controllers have been used for
control of switching power converters [1]-[3]. -synthesis has
been employed in [4] to design a robust voltage controller for a
buck-boost converter to handle unstructured uncertainties.
Genetic algorithm based on Queen-bee optimization method
has been used in [5] to design a proportional-integralderivative (PID) controller for controlling boost converter. An
improved linear quadratic regulator (LQR) with state feedback
has been attempted in [6] for control of switching power
converters in discrete-time domain. [7]-[9] have applied
different linear and nonlinear control techniques to obtain
robust control of switching power converters. All these
techniques are one degree-of-freedom (1 DOF) in nature which
is based on conventional servomechanism as shown in Fig. 1 .
The 1 DOF control scheme suffers from the limitation that the
satisfactory response and loop performance may not be
simultaneously accomplished. The achievement of one
compromises the other.
In the present work, two degree-of-freedom (2 DOF) control
scheme as shown in Fig. 2 is employed to achieve the output
voltage regulation of boost converter. The aim of applying 2
DOF control is to have satisfactory robust stability, disturbance
rejection properties as well as to obtain desired output response
since this controller processes the reference and the feedb ack
signals differentially. Moreover, the design procedure of 2
DOF is simple compared to the design procedure involved in
control, -synthesis, genetic algorithm, LQR. Further, it
may be noted that the transfer function from the control input
to the output voltage for boost converter, always contains a
right half plane (RHP) zero, which is termed as non-minimum
phase zero. The presence of this RHP zero restricts the loop
goal performance, more specifically, gain margin and
bandwidth. The challenge of the present work is to achieve
satisfactory robustness even in presence of this non-minimum
phase zero with 2 DOF control, which has not yet been
employed as a robust control technique in literature. The 2
DOF control, employed here, is shown to achieve similar
results through both simulation and experiment, what the
robust controllers have achieved in literature [1]-[9].
The paper is organized as follows. Two degree-of-freedom (2
DOF) control scheme is discussed in Section II. The boost
converter considered in the present work is given in Section
III. The controller design and synthesis are presented in
Section IV. Results and discussion are in Section V.
Conclusions that have been drawn from the present work are
summarized in Section VI.