Robust average current mode control of DC-DC PWM converters based on a three controller scheme

The purpose of this paper is to present a drastic improvement in the conventional ACC (average current mode control) of switching DC-DC power converters, consisting of the addition of an auxiliary controller in the control loop, besides the current and voltage regulators. The model-based auxiliary controller preserves the closed loop small-signal bandwidth (including loop gain crossover frequency and stability margins) of buck derived converters over a large range of variation of the power stage passive elements, the load and the line voltage. Moreover, this control scheme shows much better perturbation rejection properties (closed loop impedance and audiosusceptibility) than conventional ACC. From a control theory point of view, robust performance is achieved preserving stability. A 5 V-5 A, 50 kHz buck prototype operating from an input voltage ranging from 30 V to 15 V 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 (loop gain, closed loop audiosusceptibility and output impedance) 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 this paper in order to validate the concept