Novel three-controller average current mode control of DC-DC PWM converters with improved robustness and dynamic response

This paper presents a novel average current mode control (ACC) strategy for the control of pulse width modulated (PWM) DC-DC converters, which represents a drastic improvement over conventional ACC. This new method consists of the addition of an auxiliary controller into the control loop, besides the current and voltage regulators. The model-based auxiliary controller can increase the closed loop small-signal bandwidth of Buck derived converters, preserving loop gain crossover frequency and stability margins over significant changes of the power stage passive elements values, the load and the line voltage. Moreover, this control scheme shows much better disturbance rejection properties, i.e., closed loop impedance and audiosusceptibility, than conventional ACC. From a control theory point of view, robust performance is achieved preserving stability. A Buck prototype has been experimentally tested with different LC output filters, line and load conditions, including discontinuous conduction mode. Measurements of the small signal frequency response of the converter have been carried out, showing the improvement achieved by the proposed control scheme. The empirical large signal response of the converter under load steps is also shown in order to validate the concept.