Sliding-Mode Control of DC-DC Switching Converters L. Martinez-Salamero, A. Cid-Pastor, A. El Aroudi, R. Giral, J. Calvente, and G. Ruiz-Magaz Departament d’Enginyeria Electrònica, Elèctrica i Automàtica, Universitat Rovira i Virgili (URV), Campus Sescelades, Avinguda Països Catalans 26, 43007 Tarragona, Spain, e-mail: luis.martinez@urv.cat Abstract: The sliding-mode control of DC-DC switching converters is presented in contrast to the traditional pulse width modulation approach. The method of the equivalent control is illustrated in the design of a cascade control for the voltage regulation of a non-minimum phase converter. The theoretical predictions are validated by means of PSIM simulations. Prospective applications of the method reported are also discussed. Keywords: switching dc-dc converters, power supplies, sliding-mode control, variable structure systems. 1. INTRODUCTION DC-DC switching converters are the keystones of the so- called power processing systems, which can be described in contrast to signal processing systems. While in the former case, the energy guarantees the transformation of input into output information, in the power processing systems the information is used to control the power flow from the input to output with the maximum efficiency. If we observe the elements employed in the analogue implementation of a signal processing system, we will find out that it is composed of resistors, capacitors, and semiconductor devices operating in linear region, the inductor being the element to be excluded in all designs. Performing the same observation in a power processing system would reveal that this one is made of inductors, capacitors and semiconductor devices operating in on-off zone, the resistor being the excluded elements in all configurations. The basic electronic features of a power processing system are: 1) voltage regulation 2) maximum power transfer 3) capability of association with other power processors 4) power signal generation from time-varying reference signal tracking. In this paper, we will focus on the voltage regulation function by reviewing the state of the art in power processing systems based on pulse width modulation (PWM) and by comparing these systems with those employing sliding-mode control. 2. PWM-BASED VOLTAGE REGULATION PWM-based voltage regulation is performed by means of the block diagram depicted in Fig. 1. The DC-DC switching converter constitutes the power stage and performs the transformation of the input energy under the form of unregulated voltage V g >0 into output energy under the form S D L PWM Controller v ramp (t) αV ref α V m T u(t) + - + V g v ctrl (t) C v C - R + v err Fig. 1. Block diagram of a DC-DC switching regulator. of regulated voltage v C . The regulation is obtained by processing the output voltage error v err =α(V ref –v C )= V r –αv C by means of a controller whose output v ctrl is the input of a PWM. When v ctrl equals the saw-tooth signal v ramp , the modulator establishes the ending instant for the subinterval of energy absorption in the switching converter. While v ctrl is still smaller than v ramp , the modulator output signal u(t) has a high level and the converter stores the input energy in the magnetic field of its inductors (T ON subinterval). When v ctrl equals v ramp , the signal u(t) takes its low value and the switching converter transfers the energy stored during the T ON subinterval to the output load (T OFF subinterval). It has to be pointed out that the modulator inputs v ctrl and v ramp are analogue while its output u(t) is a binary digital signal. Also, the sum of subinterval durations T ON and T OFF is T, which is a constant value given by the external signal v ramp (t). Both subintervals are usually expressed in terms of its relative duration with respect to the switching period T, namely, d=T ON /T, which is called the duty cycle, and d’=T OFF /T, which is complementary to d (d’=1–d). Signal v ctrl (t) has a slow variation in comparison with v ramp (t) to allow the modulation of the pulses duration. Regardless of the type of converter, the increase of the duty cycle implies a higher output voltage in absolute value. The periodic repetition of Preprints of the 18th IFAC World Congress Milano (Italy) August 28 - September 2, 2011 Copyright by the International Federation of Automatic Control (IFAC) 1910